JP2000243733A - Element isolation forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an element isolation in a semiconductor substrate, even though an etchback process is not provided. SOLUTION: This element isolation forming method consists of the steps, wherein a stopper film 1 is formed on the upper surface of a semiconductor substrate 2, the film 1 and the substrate 2 are patterned to form isolation grooves 3, then an insulating film having steps is formed on the film 1 and the grooves 3 and in a first process continued to the formation of the insulating film, the steps of the insulating film are flattened into a step lower than 0.2 μm using a first polishing agent and in a second process, and the insulating film on the film 1 is removed by using a second polishing agent on an etching agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for forming a device isolation capable of shortening a process in forming a trench device isolation.

[0002]

2. Description of the Related Art At present, ultra-large-scale integrated circuits tend to increase the packing density, and various microfabrication techniques have been studied and developed. Already, design rules are on the order of sub-half microns. One of the technologies that have been developed to satisfy such strict requirements for miniaturization is a CMP (Chemical Mechanical Polishing) technology. This technology completely flattens the layer to be exposed in the semiconductor device manufacturing process, reducing the burden of the exposure technology,
Since the yield can be stabilized, the technique is indispensable when performing, for example, flattening of an interlayer insulating film and trench isolation.

Conventionally, in a manufacturing process of a semiconductor device, a plasma CVD (Chemical Vapor Depth) is used.
fumed silica-based polishing agents are generally considered as CMP polishing agents for planarizing an inorganic insulating film layer such as a silicon oxide insulating film formed by a method such as oxidation, chemical vapor deposition, or low-pressure-CVD. It had been. Fumed silica-based abrasives are produced by subjecting silica particles to grain growth by a method such as thermal decomposition of tetrachlorosilicic acid and adjusting the pH. However, such a polishing agent does not have a sufficient polishing rate for the inorganic insulating film, and there is a technical problem of a low polishing rate for practical use.

In the generations before the design rule of 0.5 μm, LOCOS (local oxidation of silicon) was used for element isolation in an integrated circuit. After that, when the processing size is further reduced, a technique for narrowing the element isolation width is required, and trench isolation is being used. In the trench isolation, CMP is used to remove an extra insulating film formed on the substrate, and a stopper film is formed below the insulating film to prevent polishing of the silicon wafer. A silicon oxide film or the like is used as the insulating film. Silicon nitride or the like is used for the stopper film, and it is desirable that the polishing rate ratio between the silicon oxide film and the stopper film is large in order to stop polishing at the stopper film. on the other hand,
If the polishing rate ratio between the stopper film and the silicon oxide film is not large, it is necessary to finish polishing before the stopper film is completely removed. In this case, the polishing amount is adjusted by the polishing time.

Conventionally, silica-based abrasives have been used for CMP. The silica-based abrasive has a problem that the polishing rate is low and the flatness is poor. In general, since a projection having a large pattern is hard to be polished, if polishing is continued for a long time, polishing of a low portion proceeds excessively, and there is a problem that an insulating film in a trench isolation portion is removed. In order to solve this, conventionally, solutions such as removing a large pattern by etch back and forming a thin film having a low polishing rate such as silicon nitride on the surface thereof have been studied. All of these problems complicate the trench isolation formation process, leading to an increase in cost.

On the other hand, cerium oxide abrasives have been used as abrasives for glass surfaces such as photomasks and lenses. Cerium oxide particles have a lower hardness than silica particles and alumina particles and are therefore less likely to scratch the polished surface, and thus are useful for finish mirror polishing. However, since a cerium oxide abrasive for polishing a glass surface uses a dispersant containing a sodium salt, it cannot be directly used as an abrasive for semiconductors. Cerium oxide abrasives are often used at low concentrations of around 1%.
When the film pattern to be polished on the substrate becomes finer, the time during which the abrasive particles act on the pattern projections becomes shorter, and most of the abrasive particles escape from the projections to the concave portions of the pattern, and the polishing rate decreases. There was a problem. Such a phenomenon is not observed in the silica-based abrasive, but it is considered that the particle density is at least 10 times that of the cerium oxide-based abrasive and the supply of particles is sufficient.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming an element isolation on a semiconductor substrate without providing an etch-back step.

Another object of the present invention is to provide, in addition to the above-mentioned invention, a method for forming an element isolation in which a step of an insulating film can be reduced.

Another object of the present invention is to provide, in addition to the above-mentioned invention, a method for forming an element isolation which can further reduce the damage of an insulating film.

Another object of the present invention is to provide an element isolation forming method which further enhances the effect of preventing excessive polishing of an insulating film, in addition to the above-mentioned invention.

Another object of the present invention is to provide, in addition to the above-mentioned invention, a device isolation forming method capable of reducing the variation in the thickness of an insulating film.

[0012]

According to the present invention, a stopper film is formed on an upper surface of a semiconductor substrate, and the stopper film and the semiconductor substrate are patterned to form an isolation groove. Form an insulating film with a step, flatten the step of the insulating film to 0.2 μm or less using a first polishing agent in a subsequent first step, and apply a second polishing agent or an etching agent in a second step. The present invention relates to a device isolation forming method, wherein an insulating film on a stopper film is removed by using the method.

Further, the present invention comprises cerium oxide, water, a dispersant, and an anionic surfactant, and has a square pH A ₁ (5.5, 1.0 mPa · s) -B ₁ (5. 5,
2.5 mPa · s) −C ₁ (9.0, 2.5 mPa · s)
s) The present invention relates to a device isolation forming method using a polishing agent in a range surrounded by -D ₁ (8.5, 1.0 mPa · s) in the first step.

Further, according to the present invention, there is provided an element isolation forming method in which, in a second step, an insulating film on a stopper film is removed using a polishing agent having a polishing rate ratio (insulating film polishing rate / stopper film polishing rate) of 5 or more. About the method.

The present invention also includes cerium oxide, water, a dispersant, and an anionic surfactant, and has a square pH A ₂ (5.5, 0.9 mPa · s) -B ₂ (5. 5,
3.0 mPa · s) -C ₂ (10.0, 3.0 mPa · s)
s) The present invention relates to a device isolation forming method using an abrasive in a range surrounded by -D ₂ (9.0, 0.9 mPa · s).

Further, the present invention relates to a method for controlling the viscosity η ₂ of the second abrasive.
And the ratio of the viscosity η ₁ of the first abrasive (η ₂ / η ₁ ) is 0.4 to 0.4
0.95.

Further, according to the present invention, there is provided an element for removing an insulating film on a stopper film using a polishing agent having a polishing rate ratio (silicon oxide film polishing rate / silicon nitride film polishing rate) of less than 5 in a second step. The present invention relates to a separation forming method.

The present invention also relates to a method for forming an element isolation using an etching agent in the second step.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, first, a stopper film is formed on the upper surface of a semiconductor substrate, and the stopper film and the semiconductor substrate are patterned to form an isolation groove. An insulating film having a step is formed on the separation groove. In the formation of the trench isolation, an insulating film is usually formed after forming a pad oxide film, forming a stopper film, forming a mask for stopper film patterning, and forming a trench by etching. Immediately after forming the insulating film, the depth is 0.4 to 1
There are steps over a wide range of dimensions of about μm and a width of 0.25 μm to 100 μm or more. In the present invention,
In the subsequent first step, the step of the insulating film is flattened to 0.2 μm or less using the first polishing agent, and in the second step, the insulating film on the stopper film is formed using the second polishing agent or the etching agent. Remove. The semiconductor substrate is preferably a Si substrate, the stopper film is preferably a silicon nitride film, and the insulating film is preferably a silicon oxide film.

FIG. 1 shows an example of a method for forming an element isolation according to the present invention. FIG. 1 shows a state in which a stopper (silicon nitride) film 1 is formed on the upper surface of a Si substrate 2 and a trench (isolation groove) 3 is formed by patterning the stopper film 1 and the Si substrate 2.
(1). Next, FIG. 1B shows a state in which a polishing target film 4 which is an insulating film having a step is formed on the stopper (silicon nitride) film 1 and the trench 3. After that, in the first step, the step is flattened to at least 0.2 μm or less to form the residual oxide film 5, and the state shown in FIG. The residual step is more preferably 0.1 μm or less in the first step because the final step can be reduced.

The first abrasive used in the first step is preferably an abrasive containing cerium oxide, water, a dispersant, and an anionic surfactant. By performing polishing using this abrasive, the anionic surfactant covers the surface of the insulating film on the substrate, and the action of the abrasive particles on the surface of the insulating film is inhibited, so that polishing does not proceed. However, when the polishing load is increased, the anionic surfactant covering the insulating surface is removed due to mechanical stress, so that the polishing proceeds. By adjusting the concentration of the anionic surfactant and the polishing load based on the polishing load dependency of the polishing rate caused by such an action, a convex portion having a large effective polishing load is selected according to the pattern shape of the insulating film. It is possible to realize the characteristic of polishing efficiently. As a result, the interlayer insulating film can be planarized with high efficiency and at a high level.

In order to realize global flattening with little pattern dependency, the anionic surfactant should be used within a range where the polishing rate of the concave portion of the pattern is sufficiently small as compared with the polishing rate of the convex portion. It is necessary to adjust the addition amount and the pH. The viscosity of the abrasive is 0.9-3.0 mPa ·
s, preferably 0.9 to 1.4 mPa
More preferably, it is within the range of s. As the viscosity of the polishing agent increases, the polishing rate of a wide convex portion having a width of 1 mm or more increases to a width of 1 mm.
There is a tendency that the pattern dependency of the film to be polished is increased, for example, the polishing rate is smaller than the polishing rate of the convex portion of not more than mm.

The viscosity of the abrasive in the present invention is calculated from the kinematic viscosity measured by an Ubbelohde viscometer and the specific gravity measured by a float type hydrometer while the abrasive is kept at 25 ° C.

When the polishing agent exceeds pH 5.5, the surface potential of a silicon oxide film usually used as an insulating film increases negatively. Further, in a region exceeding pH 5.5, an anionic surfactant such as ammonium polyacrylate is dissociated. By using an anionic surfactant as an additive as a surfactant, an appropriate load dependency can be obtained for the polishing rate due to the surface potential of the silicon oxide film and the electrical repulsion of the anionic surfactant. As the pH of the polishing agent is lower, the electric repulsion between the surface of the silicon oxide film and the anionic surfactant is weaker, and the load dependence of the polishing rate is seen at a smaller amount of the added anionic surfactant. Since the viscosity increases with the addition amount of the anionic surfactant, it is necessary to increase the viscosity in the range of 1.0 to 1.4 mPa · s to realize the flattening characteristics with little pattern dependence. The pH of the abrasive after the addition of the agent is preferably in the range of 5.5 to 10, and more preferably 5.5 to 9.
If the pH exceeds 10, the repulsion between the surface of the silicon oxide film and the anionic surfactant becomes large, and even if a large amount is added, the load dependency of the polishing rate tends not to be observed. As a result, since the pattern protrusions cannot be selectively polished, there is a tendency that the flattening characteristic for selectively polishing the protrusions cannot be realized. On the other hand, if the pH exceeds 9, a large amount of a surfactant is required to realize the load dependency of the polishing rate at which the protrusions can be selectively polished. This tends to make it impossible to realize global flatness with little pattern dependence. On the other hand, if the pH is less than 5.5, the cerium oxide particles tend to aggregate, so that the cerium oxide particles are not stable, and a sufficient polishing rate tends not to be obtained.

The pH of the abrasive in the present invention is measured at 25 ° C. with a pH meter (for example, HM-11 manufactured by Toa Denpa Co., Ltd.).

The pH and viscosity in the polishing agent of the present invention is rectangle _{A 1 (5.5,1.0mPa · s) -B} 1 (5.5,
2.5 mPa · s) −C ₁ (9.0, 2.5 mPa · s)
abrasives in the range surrounded by _{s) -D 1 (8.5,1.0mPa · s} ) is preferable from the viewpoint of reducing the step difference of the insulating film.

The amount of the anionic surfactant added depends on the concentration of the cerium oxide particles, the specific surface area and the pH of the abrasive. The addition amount is preferably about 1.5% to 10% by weight because the ratio of the polishing rate of the convex portions to the polishing rate of the concave portions becomes large.

In the first step of the present invention, the polishing table and the substrate are relatively moved while the substrate having the insulating film is pressed against the polishing cloth while the polishing agent is supplied onto the polishing cloth of the polishing table. In the polishing method for polishing the insulating film by the
The pressing pressure of the substrate having the insulating film against the polishing cloth is selectively polished with respect to the concave portions of the pattern according to the load-dependent characteristic of the polishing rate mainly determined by the amount of added surfactant and the pH. Must be set to a range. The pressure applied to the polishing cloth is preferably from 10 to 100 kPa, more preferably from 20 to 50 kPa. In order to satisfy the in-plane uniformity of the polishing rate and the flatness of the pattern, the polishing rate is more preferably 20 to 50 kPa. The pressing pressure on the polishing cloth is 100 kPa
If it is larger, polishing scratches are likely to occur, and 10 kPa
If it is less than 3, a sufficient polishing rate tends not to be obtained. When a pattern wafer is polished using a cerium oxide abrasive, the number of polishing scratches tends to be larger than when a blanket wafer without a pattern is polished. Thus, by reducing the step in the first step of the present invention, the occurrence of scratches can be reduced to a level equivalent to that of a blanket wafer. At this time, when the step is reduced in the first step, the thickness of the residual insulating film (residual oxide film 5) on the stopper film is 50 nm.
The above is preferable because the scratches generated in the first step can be removed in the second step.

Next, in a second step of the present invention, the insulating film (residual oxide film 5) on the stopper film 1 is removed by using a second polishing agent or an etching agent to form an element isolation portion 6, and FIG. 1 (4) is set.

The element isolation can be formed by removing the stopper film 1 by etching and setting the state shown in FIG. 1 (5).

In the second step of the present invention, a method of removing the insulating film on the stopper film using a second abrasive having a polishing rate ratio (insulating film polishing rate / stopper film polishing rate) of 5 or more is used. be able to. This is suitable when the polishing is stopped by the stopper film. When the polishing rate ratio is large, the polishing amount in the second step becomes insensitive to the polishing time, and the management becomes easy. In order to increase the polishing rate ratio, the second polishing agent contains cerium oxide, water, a dispersing agent, and an anionic surfactant, and has a pH and viscosity of square A ₂ (5.5, 0.9
mPa · s) −B ₂ (5.5, 3.0 mPa · s) −C ₂
(10.0, 3.0 mPa · s) -D ₂ (9.0, 0.
9 mPa · s).
In this case, the amount of the anionic surfactant added depends on the concentration of the cerium oxide particles, the specific surface area and the pH of the abrasive.
The addition amount is preferably 0.2 to 10% by weight because the polishing rate ratio becomes large. The second polishing agent is preferably different from the first polishing agent, and the amount of the anionic surfactant in the second polishing agent is preferably reduced. Also, the ratio (η ₂ ) of the viscosity η ₂ of the _second abrasive to the viscosity η ₁ of the first abrasive
/ Η ₁ ) is preferably in the range of 0.4 to 0.95.
The following effects are the causes of the increase in the polishing rate ratio (for example, the polishing rate of the silicon oxide film / the polishing rate of the silicon nitride film). In the range of pH 5.5 to 8.5, the surface potential of the silicon nitride film used for the stopper is positive to zero, whereas the surface potential of the silicon oxide film used for the insulating film is negative. Therefore, while the anionic surfactant adsorbs more to the silicon nitride film having less electric repulsion, the silicon oxide film has large electric repulsion and hardly causes adsorption. The anionic surfactant adsorbed in a large amount lowers the polishing rate because it inhibits the interaction between the film to be polished and the abrasive particles. The surface of the silicon nitride film is more likely to be covered with the anionic surfactant, and the polishing rate decreases with a small amount of the anionic surfactant added. As a result, the polishing rate ratio between the silicon oxide film and the silicon nitride film increases, and application to trench isolation becomes possible.
If the pH exceeds 8.5, the surface potential of the silicon nitride film becomes negative and the difference in surface potential with the silicon oxide film becomes small, so that the polishing rate ratio decreases. Especially pH 1
If it is 0.0 or more, the polishing rate ratio becomes smaller than that of the cerium oxide abrasive to which no anionic surfactant is added, and the effect of adding the surfactant tends to be lost.

Further, in the second step of the present invention, a method of removing the insulating film on the stopper film using a second polishing agent having a polishing rate ratio (insulating film polishing rate / stopper film polishing rate) of less than 5 Can also be used. Also in this case, the second abrasive is preferably different from the first abrasive used in the first step. Once the steps are flattened, if the insulating film and the stopper film are polished at approximately the same speed with a polishing agent having a reduced polishing rate ratio, the film thickness variation can be reduced. At this time, it is necessary to suppress the fluctuation of the polishing amount by controlling the polishing time.

As another method of removing the film to be polished in the second step of the present invention, an etching agent can be used. The etching method in this case can be used for both dry (dry) and wet (wet) methods. The etchant is not particularly limited as long as it can etch the insulating film, and fluorinated carbon gas (C ₃ F ₈ , C ₂ F ₆ , CF _{4 and} others), hydrofluoric acid, and the like can be used.

The abrasive used in the first step or the second step in the present invention may be, for example, a composition comprising cerium oxide particles, a dispersant and water dispersed therein, and more preferably a biodegradable anion. It is obtained by adding a surfactant.

In general, cerium oxide is carbonate, nitrate,
It is obtained by oxidizing cerium compounds of sulfate and oxalate. A cerium oxide abrasive used for polishing a silicon oxide film formed by a TEOS-CVD method or the like can perform high-speed polishing as the primary particle diameter is larger and the crystal distortion is smaller, that is, the crystallinity is better. Polishing scratches tend to occur. Thus, the method for producing the cerium oxide particles used in the present invention is not limited, but the cerium oxide crystallite diameter is preferably 5 nm or more and 300 nm or less. In addition, since it is used for polishing a semiconductor chip, it is preferable that the content of each of the alkali metal and the halogen is suppressed to 10 ppm or less in the cerium oxide particles. As a method for producing cerium oxide particles, calcination or an oxidation method using hydrogen peroxide or the like can be used. The firing temperature is preferably from 350 ° C. to 900 ° C.

Since the cerium oxide particles produced by the above method are agglomerated, it is preferable to mechanically pulverize them. As the pulverization method, a dry pulverization method using a jet mill or the like or a wet pulverization method using a planetary bead mill or the like is preferable.

The concentration of the cerium oxide particles is not limited,
The range is preferably 0.5% by weight or more and 20% by weight or less from the viewpoint of easy handling of the dispersion. In addition, as a dispersant, since it is used for polishing semiconductor chips, sodium ions,
The content of each of alkali metal such as potassium ion and halogen is preferably suppressed to 10 ppm or less. For example, a polymer dispersant containing ammonium acrylate as a copolymer component is preferable. This polymer dispersant is also a water-soluble anionic surfactant. A polymer dispersant containing ammonium acrylate as a copolymerization component as a dispersant and a water-soluble anionic surfactant, a water-soluble nonionic surfactant, a water-soluble cationic surfactant, and a water-soluble amphoteric surfactant Two or more dispersants including at least one selected from agents may be used.

Examples of the water-soluble anionic surfactant include ammonium lauryl sulfate, polyoxyethylene alkyl ether triethanolamine sulfate, and a special polycarboxylic acid type polymer surfactant. Examples of the activator include polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene higher alcohol ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, and polyoxyalkylene alkyl. Ether, polyoxyethylene derivative, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostea Polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbite tetraoleate, polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate Rates, polyethylene glycol monooleate, polyoxyethylene alkylamine, polyoxyethylene hydrogenated castor oil, alkyl alkanolamides and the like, and as the water-soluble cationic surfactant,
For example, coconutamine acetate, stearylamine acetate and the like can be mentioned. Examples of the water-soluble amphoteric surfactant include lauryl betaine, stearyl betaine, lauryl dimethylamine oxide, 2-alkyl-N-carboxymethyl-N-hydroxyethyl. And imidazolinium betaine.

The amount of the dispersant added is determined based on the dispersibility of the particles in the slurry and the prevention of sedimentation.
The range is preferably from 0.01 part by weight to 2.0 parts by weight. The molecular weight of the dispersant is preferably from 100 to 50,000, more preferably from 1,000 to 10,000. When the molecular weight of the dispersant is less than 100, a sufficient polishing rate cannot be obtained when polishing the silicon oxide film or the silicon nitride film, and when the molecular weight of the dispersant exceeds 50,000, the viscosity becomes high. This is because the storage stability of the CMP abrasive drops.

As a method for dispersing the cerium oxide particles in water, a homogenizer, an ultrasonic disperser, a wet ball mill, or the like can be used in addition to the usual dispersion treatment using a stirrer.

The average particle size of the cerium oxide particles in the thus prepared CMP abrasive is 0.01 μm to 1.0 μm.
It is preferred that If the average particle size of the cerium oxide particles is less than 0.01 μm, the polishing rate is too low,
If the thickness exceeds 1.0 μm, the film to be polished tends to be easily damaged. In the present invention, the particle size of the particles in the abrasive is determined by a laser diffraction type particle size distribution meter (for example, Malver
n Instrument's Master Size
r).

As the anionic surfactant used in the first step of the present invention, acrylic acid or methacrylic acid copolymer and its ammonium salt or triethanolamine salt, polyvinyl alcohol, which do not contain metal ions, can be used. And other water-soluble organic polymers, such as ammonium lauryl sulfate, polyoxyethylene lauryl ether ammonium sulfate, and the like. In addition, a water-soluble nonionic surfactant, a water-soluble anionic surfactant, a water-soluble cationic surfactant, or the like may be used in combination. The molecular weight of the anionic surfactant is from 100 to 50.
000 is preferred, and 2,000 to 20,000 is more preferred. As a method for adding the surfactant, it is preferable to mix the surfactant with the cerium oxide slurry immediately before polishing. When a structure that mixes well in the slurry supply pipe of the polishing apparatus is provided, adjust the supply rates of the cerium oxide slurry and the surfactant aqueous solution individually and mix them to a predetermined concentration in the pipe. Is also possible. When stored for a long time after adding the surfactant, the particle size distribution of the cerium oxide abrasive may change, but the polishing rate and polishing characteristics such as scratches are not significantly affected. There is no limitation on the method of addition.

Examples of the anionic surfactant used in the second step of the present invention include acrylic acid or methacrylic acid copolymers and their ammonium salts or triethanolamine salts, polyvinyl alcohols containing no metal ions. Water-soluble organic polymers such as, ammonium lauryl sulfate, polyoxyethylene lauryl ether ammonium sulfate, amino acid derivatives and the like can be used. In addition, a water-soluble nonionic surfactant, a water-soluble anionic surfactant, an alkylbenzenesulfonic acid and the like can be used, and a water-soluble cationic surfactant and the like may be used in combination. The molecular weight of the anionic surfactant is preferably from 100 to 50,000. As a method for adding the surfactant, it is preferable to mix the surfactant with the cerium oxide slurry immediately before polishing. When a structure that mixes well in the slurry supply pipe of the polishing apparatus is provided, adjust the supply rates of the cerium oxide slurry and the surfactant aqueous solution individually and mix them to a predetermined concentration in the pipe. Is also possible. When stored for a long time after adding a surfactant, the particle size distribution of the cerium oxide abrasive may change,
Since there is no noticeable effect on the polishing characteristics such as the polishing rate and polishing scratches, the method of adding the surfactant is not limited.

The preferable amount of the anionic surfactant in the first step or the second step includes the amount when the anionic surfactant is used as the dispersant.

As a method of forming the insulating film and the stopper film used in the element isolation forming method of the present invention, a low pressure CVD method,
A plasma CVD method is exemplified. Raw materials used in these CVD methods include monosilane: SiH as a Si source.
_4. Tetraethoxysilane: (TEOS) and the like. Oxygen: O ₂ , ozone: O _{3 and the} like are used as oxygen sources. Similarly, formation of a silicon nitride film by a low-pressure CVD method is performed by using dichlorosilane: SiH ₂ Cl ₂ or the like as a Si source and ammonia:
NH ₃ or the like is used.

In the present invention, a semiconductor substrate is used as a substrate, and trench element isolation can be formed in the semiconductor substrate. As a polishing device used for trench element isolation,
A general polishing apparatus having a surface plate on which a holder for holding a semiconductor substrate and a polishing cloth (pad) are attached (a motor or the like whose rotation speed can be changed) is attached can be used. As the polishing cloth, general nonwoven fabric, foamed polyurethane, porous fluororesin and the like can be used, and there is no particular limitation. Also,
The polishing cloth is preferably subjected to a groove processing for accumulating a CMP abrasive. The polishing conditions are not limited, but the rotation speed of the platen is preferably low, such as 200 rpm or less so that the semiconductor substrate does not jump out, and the pressure applied to the semiconductor substrate is preferably 100 kPa or less so that scratches are not generated after polishing. During polishing, an abrasive is continuously supplied to the polishing cloth by a pump or the like. Although the supply amount is not limited, it is preferable that the surface of the polishing cloth is always covered with the abrasive.

After the polishing is completed, the semiconductor substrate is preferably washed well in running water, and then dried using a spin drier or the like to remove water droplets adhering to the semiconductor substrate. After forming the flattened hull in this manner, wiring is formed on the insulating film layer, and an insulating film is formed again between the wirings and on the wiring, and then the above-mentioned CMP polishing agent is used. Polishing eliminates irregularities on the insulating film surface,
The surface is smooth over the entire surface of the semiconductor substrate. By repeating this process a predetermined number of times, a semiconductor having a desired number of layers is manufactured.

FIG. 2 shows a conventional element isolation forming method. FIG.
(1) and FIG. 2 (2) show the same steps as FIG. 1 (1) and FIG. 2 (2), and FIG. 2 (3) shows the state shown in FIG.
This is a state in which a part of the film-to-be-polished 4 in the convex portion is removed by etching back, and thereafter, the film-to-be-polished 4 in the convex portion is removed by the CPM to obtain the state shown in FIG. The film 1 is removed to obtain the element isolation shown in FIG. FIG.
From the state of (2) to the state of FIG. 2 (3), steps of resist application, exposure, and removal of the resist (uncured portion) are necessary, and there is a drawback that the steps become long.

[0049]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example (Preparation of Cerium Oxide Particles 1) Cerium carbonate hydrate 2k
g was placed in a platinum container and calcined at 700 ° C. for 2 hours in the air to obtain about 1 kg of a yellow-white powder. When this powder was subjected to phase identification by an X-ray diffraction method, it was confirmed that the powder was cerium oxide. The cerium oxide powder was mixed with deionized water so as to be 10% by weight, and pulverized at 1400 rpm for 120 minutes using a horizontal wet ultrafine particle dispersion pulverizer. The obtained polishing liquid was dried at 110 ° C. for 3 hours to obtain cerium oxide particles. The cerium oxide particles have a particle diameter of 5 nm to
It was found to be 60 nm, and the result of measurement of the specific surface area by the BET method was 39.5 m ² / g.

(Preparation 1 of Cerium Oxide Slurry) Cerium oxide particles 1 prepared in Preparation 1 of cerium oxide particles described above
An aqueous solution of ammonium polyacrylate having a molecular weight of 10,000 (the molecular weight is a weight average molecular weight in terms of standard polystyrene by gel permeation chromatography) obtained by copolymerizing 25 g of acrylic acid and methyl acrylate at a molar ratio of 3: 1. (40% by weight) 3 g and deionized water 2
372 g were mixed, and ultrasonic dispersion was performed while stirring. Dispersion was performed at an ultrasonic frequency of 40 kHz and a dispersion time of 10 minutes. The obtained slurry was filtered through a 2 micron filter, and further 2% by weight of cerium oxide slurry (A-1) was obtained by adding deionized water. The pH of the cerium oxide slurry (A-1) was 8.5. When the particle size distribution of the cerium oxide slurry (A-1) was examined with a laser diffraction type particle size distribution analyzer, the average particle size was 0.20 μm.
m was small. Further, 93.0% by weight of particles having a particle size of 1.0 μm or less was used.

(Preparation of Anionic Surfactant Solution 1) Ammonium polyacrylate having a molecular weight of 5000 (95 mol% of ammonium acrylate, 5 m of methyl acrylate)
ol%) 600 g of a 40% by weight aqueous solution and 180 deionized water
0 g was mixed to obtain an anionic surfactant solution (B-1). The pH of the anionic surfactant solution (B-1) is 7.0.
Met.

(Preparation of Anionic Surfactant Solution 3) 200 g of a 40% by weight aqueous solution of a polyammonium acrylate copolymer having a molecular weight of 5,000 (75 mol% ammonium acrylate, 25 mol% methyl acrylate) and 3,800 g of deionized water Mixed with an anionic surfactant solution (C
-1). P of anionic surfactant liquid (C-1)
H was 7.0.

(Formation of Element Isolation 1-Patterning of Substrate) A test pattern as shown in FIGS. 3 and 4 was formed on a silicon wafer having a diameter of 150 mm on a p-type Si substrate.
Pad oxide film (thermal oxide film) 10 nm (not shown), stopper film 15 made of silicon nitride (LP)
-CVD film) so as to have a thickness T1 of 100 nm, and was etched so that the element isolation portion depth T3 was 500 nm. The width X of the convex portion 11 was 0.35 to 100 μm, and the width Y of the element isolation portion was 1.5 times X. Further, a silicon oxide film having a thickness T2 of 800 nm was formed by a plasma CVD method.

(Formation of Element Separation 1-First Step) The above-mentioned (Formation of Element Separation) was carried out on a holder on which a suction pad for attaching a substrate was attached on a surface plate on which a polishing pad made of porous urethane resin was attached. 1) Patterning of the substrate), the patterned silicon wafer was set with the silicon oxide film face down, and a weight was placed so that the polishing load was 30 kPa. The above cerium oxide slurry (A-
1) (solid content: 2% by weight) and an anionic surfactant solution (B-1) were sent at a rate of 25 ml / min each, and the nozzle was adjusted just before the platen so as to become a one-part abrasive. While dropping, the platen was rotated at 40 rpm for 2 minutes to polish the insulating film. The pH of the dropped abrasive was 7.5, and the viscosity was 1.9 mPa · s. After polishing, the wafer was removed from the holder, washed well with running water, and further washed with an ultrasonic cleaner for 20 minutes. After washing, water droplets were removed with a spin drier, and dried with a dryer at 120 ° C. for 10 minutes. The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device. In addition, a step was measured using a stylus type step meter. The horizontal resolution of the step gauge used here is 10 μm
Therefore, with respect to a dense fine pattern of 10 μm or less, a step between a dense portion of the fine pattern and an element isolation portion with a width of 20 μm or more at the periphery was measured. Further, a scanning electron microscope photograph of the fracture surface of the wafer was taken, and the step of the fine pattern was evaluated.

(Formation of Element Separation 1-Second Step) The silicon wafer substrate with the pattern polished in the above (Formation of Element Separation 1-First Step) is replaced with an anionic surfactant (B
Polishing was carried out for 1 minute in the same manner as in (formation of element separation 1-first step) except that anionic surfactant (C-1) was used instead of -1). After the above polishing, the blanket wafer with the plasma CVD silicon oxide film and the blanket wafer with the low pressure CVD silicon nitride film were polished for 1 minute each. The pH of the dropped abrasive is 7.3 and the viscosity is 1.2 m
Pa · s. After polishing, the wafer is removed from the holder, washed well with running water, and further washed with an ultrasonic cleaner.
Washed for 0 minutes. After washing, water droplets were removed with a spin drier, and dried with a dryer at 120 ° C. for 10 minutes. The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device. In addition, the step of the patterned silicon wafer was measured using a stylus-type step meter. Since the horizontal resolution of the step meter used here was 10 μm, for a dense fine pattern of 10 μm or less, the step between the dense portion of the fine pattern and the element isolation portion with a width of 20 μm or more at the periphery was measured. Further, a scanning electron microscope photograph of the fracture surface of the wafer was taken, and the step of the fine pattern was evaluated. Further, no damage was observed on the surface of the insulating film by visual observation under a light source of a mercury lamp.

(Preparation of Cerium Oxide Particles 2) 2 kg of cerium carbonate hydrate was placed in a platinum container and calcined at 780 ° C. for 2 hours in the air to obtain about 1 kg of yellowish white powder. When this powder was subjected to phase identification by an X-ray diffraction method, it was confirmed that the powder was cerium oxide. Cerium oxide powder 1k
g was dry-ground using a jet mill. Observation with a transmission electron microscope showed that the cerium oxide particles had a particle size of 5 nm to 450 nm, and that the specific surface area measured by the BET method was 19 m ² / g.

(Preparation of cerium oxide slurry 2) (Cerium oxide slurry preparation 1) except that the cerium oxide particles prepared in Preparation 2 were used instead of the cerium oxide particles prepared in Preparation 1 of cerium oxide particles. Cerium oxide slurry (A-2) was prepared in the same manner as in (1). PH of this cerium oxide slurry (A-2)
Was 8.7. When the particle size distribution of the cerium oxide slurry (A-2) was examined with a laser diffraction type particle size distribution meter,
The average particle size was found to be as small as 0.21 μm. Further, 92.0% of the particles had a size of 1.0 μm or less.

(Preparation of Anionic Surfactant Solution 2) 240 g of a 40% by weight aqueous solution of a polyammonium acrylate copolymer having a molecular weight of 5,000 (100 mol% of ammonium acrylate, 0 mol% of methyl acrylate) and 2160 g of deionized water And an anionic surfactant solution (B)
-2). P of anionic surfactant solution (B-2)
H was 6.5.

(Formation of Element Isolation—Patterning of Substrate) A test pattern as shown in FIGS. 3 and 4 was formed on a silicon wafer having a diameter of 150 mm on a p-type Si substrate.
Pad oxide film (thermal oxide film) 10 nm (not shown), stopper film 15 made of silicon nitride (LP)
-CVD film) thickness T ₁ is then deposited to a 100 nm, was etched isolation region depth T ₃ so that 500 nm. The width X of the convex portion 11 was 0.35 to 100 μm, and the width Y of the element isolation portion was 1.5 times X. Further, a silicon oxide film having a thickness T ₂ of 800 nm was formed by a plasma CVD method.

(Formation of Element Separation 2-First Step) The above-mentioned (Formation of Element Separation) was carried out on a holder on which a suction pad for attaching a substrate was attached on a surface plate on which a polishing pad made of porous urethane resin was attached. The patterned silicon wafer prepared in (2—Patterning of Substrate) was set with the silicon oxide film surface down, and a weight was placed so that the polishing load was 30 kPa. The above cerium oxide slurry (A-
2) (Solid content: 2% by weight) and anionic surfactant solution (B-2) are each sent at a rate of 25 ml / min, and the nozzle is adjusted so as to become a one-part abrasive immediately before the platen. While dropping, the platen was rotated at 40 rpm for 2 minutes to polish the insulating film. The pH of the dropped abrasive was 7.0, and the viscosity was 1.4 mPa · s. After polishing, the wafer was removed from the holder, washed well with running water, and further washed with an ultrasonic cleaner for 20 minutes. After washing, water droplets were removed with a spin drier, and dried with a dryer at 120 ° C. for 10 minutes. The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device. In addition, a step was measured using a stylus type step meter. The horizontal resolution of the step gauge used here is 10 μm
Therefore, for a dense fine pattern of 10 μm or less, a step between a dense portion of the fine pattern and an element isolation portion with a width of 20 μm or more around the dense portion was measured. Further, a scanning electron microscope photograph of the fracture surface of the wafer was taken, and the step of the fine pattern was evaluated.

(Formation of Element Isolation—Second Step) The silicon wafer with the pattern polished in the above (Formation of Element Isolation—First Step) is replaced with an anionic surfactant (B-
Except for using an anionic surfactant (C-1) in place of 2), the same procedure as in (Formation of element separation 1-first step) was repeated except that 1).
Polished for minutes. After the above polishing, the blanket wafer with the plasma CVD silicon oxide film and the blanket wafer with the low pressure CVD silicon nitride film were polished for 1 minute each. After the above polishing, the blanket wafer with the plasma CVD silicon oxide film and the blanket wafer with the low pressure CVD silicon nitride film were polished for 1 minute each. The pH of the dropped abrasive was 7.3, and the viscosity was 1.2 mPa · s. After polishing, the wafer was removed from the holder, washed well with running water, and further washed with an ultrasonic cleaner for 20 minutes. After washing, water droplets were removed with a spin dryer,
It dried for 10 minutes with the dryer of ° C. The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device. In addition, the step of the patterned silicon wafer was measured using a stylus-type step meter. Since the horizontal resolution of the step meter used here was 10 μm, for a dense fine pattern of 10 μm or less, the step between the dense portion of the fine pattern and the element isolation portion with a width of 20 μm or more at the periphery was measured. Further, a scanning electron microscope photograph of the fracture surface of the wafer was taken, and the step of the fine pattern was evaluated. Further, no damage was observed on the surface of the insulating film by visual observation under a light source of a mercury lamp.

(Formation of Element Separation 3-Patterning of Substrate) A wafer with a pattern was produced in exactly the same manner as in Formation 1 of Element Separation.

(Formation of Element Isolation 3-First Step) The first step was performed in exactly the same manner as in the formation 1 of element isolation.

(Formation of Element Isolation 3-Second Step) The silicon wafer with the pattern polished in the above-mentioned (Formation of Element Isolation 3-First Step) is replaced with an anionic surfactant (B-
Polishing was carried out for 1 minute in the same manner as in (formation of element separation 1-first step) except that deionized water was used instead of 1). After the above polishing, the blanket wafer with the plasma CVD silicon oxide film and the blanket wafer with the low pressure CVD silicon nitride film were polished for 1 minute each. The pH of the dropped abrasive was 8.3, and the viscosity was 0.9 mPa · s. After polishing, the wafer was removed from the holder, washed well with running water, and further washed with an ultrasonic cleaner for 20 minutes. After washing, water droplets were removed with a spin drier, and dried with a dryer at 120 ° C. for 10 minutes. The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device. In addition, the step of the patterned silicon wafer was measured using a stylus-type step meter. The horizontal resolution of the step gauge used here is 1
Because of 0 μm, for a dense fine pattern of 10 μm or less, a width of 20 μm between a dense portion of the fine pattern and a peripheral portion thereof.
The level difference from the element separation part of m or more was measured. Further, a scanning electron microscope photograph of the fracture surface of the wafer was taken, and the step of the fine pattern was evaluated. Further, no damage was observed on the surface of the insulating film by visual observation under a light source of a mercury lamp.

(Formation of Element Isolation 4-Second Step) The patterned silicon wafer polished in the above (Formation of Element Isolation 3-First Step) is placed in a 2% aqueous solution of hydrofluoric acid.
The remaining silicon oxide film was etched by immersion for 0 minutes. After the etching, the wafer was removed from the holder, washed well with running water, and further washed with an ultrasonic cleaner for 20 minutes.
After washing, water droplets were removed with a spin drier, and dried with a dryer at 120 ° C. for 10 minutes. The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device. In addition, the step of the patterned silicon wafer was measured using a stylus-type step meter. Since the horizontal resolution of the step meter used here is 10 μm, the width of the dense portion of the fine pattern and its peripheral portion is 2 for a dense fine pattern of 10 μm or less.
The level difference from the element separation part of 0 μm or more was measured. further,
Scanning electron micrographs of the fracture surface of the wafer were taken, and the steps of the fine pattern were evaluated. Further, no damage was observed on the surface of the insulating film by visual observation under a light source of a mercury lamp.

Comparative Example (Formation of Element Separation 5) An example (Formation 1 of Element Separation 1) was carried out on a holder on which a suction pad for attaching a substrate was stuck on a surface plate on which a polishing pad made of porous urethane resin was stuck. A silicon wafer with a pattern similar to that produced in (Patterning of Substrate) was set with the silicon oxide film surface down, and a weight was applied so that the polishing load was 30 kPa.
A commercially available silica abrasive (SiO ₂ particle concentration 12.5
(% By weight) was fed at a rate of 50 ml / min while the platen was rotated at 40 rpm for 8 minutes to polish the insulating film. After the above polishing, the blanket wafer with the plasma CVD silicon oxide film and the blanket wafer with the low pressure CVD silicon nitride film were polished for 1 minute each. The pH of the dropped commercial silica abrasive is 10.3 and the viscosity is 8 mP
a · s. After polishing, the wafer is removed from the holder, washed well with running water, and then further cleaned with an ultrasonic cleaner.
Washed for minutes. After washing, water droplets were removed with a spin drier, and dried with a dryer at 120 ° C. for 10 minutes. The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device. From the film thickness measurement, it was confirmed that no insulating film remained on the stopper film having a width of 20 μm. In addition, a step was measured using a stylus type step meter. Since the horizontal resolution of the step meter used here was 10 μm, for a dense fine pattern of 10 μm or less, the step between the dense portion of the fine pattern and the element isolation portion with a width of 20 μm or more at the periphery was measured.
Further, a scanning electron microscope photograph of the fracture surface of the wafer was taken, and the step of the fine pattern was evaluated. Further, no damage was observed on the surface of the insulating film by visual observation under a light source of a mercury lamp.

Table 1 shows the measurement results (unit: nm) of the film thickness and the step when the element isolation forming method according to the present invention is applied and according to the comparative example.

[0069]

[Table 1] As shown in Table 1, in the element isolation forming method according to the present invention, the final step is as small as 50 nm or less, and the variation in the stopper film thickness is also small. Since it is desirable that the final step is small and the stopper film thickness variation is small in the trench element isolation, the present invention is preferable for forming the element isolation. In the comparative example, the result of forming an element isolation structure by ordinary single-step polishing using a silica abrasive widely used in CMP was shown. In the comparative example, the variation in the stopper film thickness is larger than the result according to the present invention, and the step size largely depends on the pattern size.

[0070]

According to the present invention, a semiconductor device isolation can be formed by a simple process without providing an etch-back process.

Further, according to the present invention, scratches on the insulating film can be reduced, and variations in the thickness of the insulating film can be reduced.

[Brief description of the drawings]

FIG. 1 shows a device isolation forming method according to the present invention.

FIG. 2 shows a conventional element isolation forming method.

FIG. 3 shows a plan view of a test pattern.

FIG. 4 shows a cross-sectional view of a test pattern.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Stopper (silicon nitride) film 2 Si substrate 3 Trench 4 Polished film 5 Residual oxide film 6 Element separation part 7 Etch back part 11 Convex part 12 Concave 13 Element separation part 14 Silicon oxide film 15 Stopper (silicon nitride) film 16 Si substrate T ₁ of silicon nitride film thickness (1000 Å) T ₂ silicon oxide film thickness (8000 Å) T ₃ element isolation portion depth (5000 Å) X convex width (0.35~100μm) Y isolation portion width (1.5X)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshihiko Akahori 4-3-1-1, Higashicho, Hitachi City, Ibaraki Prefecture Inside the Ibaraki Research Laboratory, Hitachi Chemical Co., Ltd. (72) Inventor Hiroto Otsuki 4-1-1, Higashicho, Hitachi City, Ibaraki Prefecture Inside the Yamazaki Plant of Hitachi Chemical Co., Ltd. F term (reference) 5F032 AA35 AA44 AA77 DA03 DA04 DA24 DA33 DA78

Claims (9)

[Claims] A stopper film formed on an upper surface of the semiconductor substrate;
The stopper film and the semiconductor substrate are patterned to form a separation groove, then an insulating film having a step is formed on the stopper film and the separation groove, and then a first polishing agent is used in a first step. Flatten the step of the insulating film to 0.2 μm or less,
An element isolation forming method, comprising removing an insulating film on a stopper film using a second polishing agent or an etching agent in a second step. 2. The method according to claim 1, wherein the step is flattened to 0.1 μm or less in the first step. 3. The method according to claim 1, wherein the thickness of the insulating film on the stopper film is set to 50 nm or more in the first step. 4. A composition containing cerium oxide, water, a dispersant, an anionic surfactant and having a square A ₁ (5.
5,1.0 mPa · s) −B ₁ (5.5, 2.5 mPa
_{· S) -C 1 (9.0,2.5mPa ·} s) -D 1 (8.
4. The element isolation forming method according to claim 1, wherein the first abrasive in a range surrounded by 5,1.0 mPa · s) is used in the first step. 5. The insulating film on the stopper film is removed by using a polishing agent having a polishing rate ratio (insulating film polishing rate / stopper film polishing rate) of 5 or more in the second step. The element isolation forming method according to the above. 6. A composition comprising cerium oxide, water, a dispersant, an anionic surfactant and having a pH and viscosity of square A ₂ (5.
5,0.9 mPa · s) −B ₂ (5.5, 3.0 mPa)
_{· S) -C 2 (10.0,3.0mPa ·} s) -D
6. The element isolation forming method according to claim 5, wherein the second abrasive in a range surrounded by ₂ (9.0, 0.9 mPa · s) is used. 7. The method according to claim ₁ , wherein the ratio (η ₂ / η ₁ ) of the viscosity η ₂ of the _second abrasive to the viscosity η ₁ of the first abrasive is 0.4 to 0.95. The element isolation forming method according to the above. 8. The method according to claim 1, wherein in the second step, the insulating film on the stopper film is removed using a second polishing agent having a polishing rate ratio (insulating film polishing rate / stopper film polishing rate) of less than 5. 4. The method for forming an element isolation according to any one of 4. 9. The method according to claim 1, wherein an etching agent is used in the second step.