JPH0955480A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a film an the surface of a ground layer without providing a natural oxide film onto it. SOLUTION: An insulating film or a conductive film 3 is formed direct on a single-crystal silicon or a polycrystalline silicon 1 through such a method that a thermal treatment is carried out at least once at temperatures of 200 to 700 deg.C, and then the insulating film or the conductive film 33 is successively formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a natural oxide film (hereinafter, formed by intentional oxidation on a silicon-based substrate such as single crystal, polycrystal or amorphous silicon). Not a film that has been formed, but an oxide film that unintentionally inevitably grows while the wafer is being left standing or being transferred to or from a semiconductor manufacturing device is directly insulated without forming a "natural oxide film". The present invention relates to a method for manufacturing a semiconductor device capable of forming a film or a conductive film.

[0002]

2. Description of the Related Art In recent semiconductor devices, a natural oxide film having a thickness of 1 nm or less, which is inevitably formed on a wafer due to the miniaturization of elements, becomes a gate oxide film or a DRAM (Dynam).
icRandom Access Memory) has come to have a bad influence on the reliability of the capacitive insulating film.
This is because the film thickness ratio of the natural oxide film is relatively increased due to the thinning, and the influence of the poor quality natural oxide film cannot be ignored. In particular, in the capacitive insulating film of DRAM, it is difficult to form a thin film due to the natural oxide film. Also, when the contact size is reduced,
The natural oxide film also adversely affects contact resistance and the like.

In a conventional DRAM memory cell,
As shown in FIG. 3, a field oxide film 8 for element isolation is formed on a semiconductor substrate 7. Further, on the substrate 7, a memory transistor including a gate insulating film 11, a word line 9 made of polycrystalline silicon, and an N ⁺ diffusion layer 10 is formed. Then, on the interlayer insulating film 16, there is formed a capacitive element including a lower electrode 12 made of polycrystalline silicon, a capacitive insulating film 13, and an upper electrode 14 made of polycrystalline silicon. In addition, the interlayer insulating film 1
A bit line 15 made of polycrystalline silicon is formed in the inside 6.

As the capacitance insulating film 13, for example, S
An iN film and an oxide film SiO ₂ laminated film formed by oxidizing the upper part thereof are used.

[0005]

However, even if an attempt is made to remove hydrofluoric acid on the surface of the lower electrode 12 formed of polycrystalline silicon, a natural oxide film grows in the subsequent process, Therefore, the capacitive insulating film 13
Is inevitably a SiO ₂ / SiN / natural oxide film (SiO 2
There was a problem that it would be a three-layer laminated film of ₂ ).

FIG. 4 is an enlarged cross-sectional view showing a part of the capacitive element composed of the lower electrode 12, the capacitive insulating film 13 and the upper electrode 14. First, as shown in FIG. 4A, since the surface of the lower electrode 17 formed of polycrystalline silicon is covered with the natural oxide film 18, this is pre-washed with a hydrofluoric acid aqueous solution. As a result, the natural oxide film 18 on the surface of the lower electrode 17 is removed as shown in FIG.

However, various gases and the like are adsorbed on the surface of the lower electrode 17 in a molecular state or a monoatomic state during washing, drying, and waiting in the subsequent steps. For example, as shown in FIG.
Considering the case where water molecules H ₂ O are adsorbed on the surface of, the adsorption is bonded with a very weak bonding force and can be easily desorbed. However, when SiN is next deposited by the low pressure CVD method and loaded in a furnace at about 700 ° C.,
The water molecules adsorbed on the surface react with each other when exposed to high temperature, and an oxide film 19 is formed as shown in FIG. 4D. As a result, the SiN film 2 formed in this process
As shown in FIG. 4E, 0 is formed not on the lower electrode 17 but on the natural oxide film 19 on the lower electrode 17.

Finally, the SiN film 20 is oxidized (for example, 9
By performing pyrogenic oxidation at a temperature of 00 to 950 ° C., as shown in FIG.
Is formed. As described above, even if the pretreatment with hydrofluoric acid is performed by the conventional method, the substance in the high-temperature furnace may be heated by the substance containing water molecules or oxygen atoms adsorbed during the subsequent washing with water or during the standby until the next work. There is a problem that a natural oxide film of undesired quality and poor quality is grown on the semiconductor device due to oxidation during the time of loading to or after formation of a film after loading.

The present invention was devised in view of such conventional problems, and a semiconductor capable of forming a film thereon without forming a natural oxide film on the surface of a base. An object is to provide a method for manufacturing a device.

[0010]

In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention is a method of directly insulating a silicon-based substrate such as single crystal silicon, polycrystalline silicon or amorphous silicon. In the method for manufacturing a semiconductor device in which a film or a conductive film is formed, when forming the insulating film or the conductive film, a step of performing heat treatment at least once at a low temperature of preferably 200 ° C. to 700 ° C. A step of continuously forming the insulating film or the conductive film.

Since a natural oxide film is inevitably formed on the surface of single crystal silicon or polycrystalline silicon, the natural oxide film on the silicon surface is removed by pretreating this with hydrofluoric acid. During the waiting time until the work is performed, various substances such as water molecules are adsorbed on the silicon surface in a molecular state or a monatomic state. For example,
When water molecule H ₂ O is adsorbed, TDS (Ther
mal Destruction mass Spec
According to the result of the roscopy), as shown in FIG. 2, the desorption peak of the water molecule (I in the figure) at 200 ° C. to 400 ° C.
) Is observed, and an OH group desorption peak (indicated by II in the figure) is observed at 400 ° C to 700 ° C. Therefore, it is understood that the adsorbed water molecule H ₂ O is desorbed at 200 ° C. to 400 ° C., while the OH group is desorbed at 400 ° C. to 700 ° C. Moreover, since this adsorption is bound by a very weak binding force, it can be easily desorbed.

Therefore, in the present invention, a step of performing a heat treatment at a temperature of 200 ° C. to 700 ° C. at least once is provided when forming an insulating film or a conductive film, and various heat treatment steps adsorbed on the silicon surface are performed. Since an insulating film or a conductive film is formed continuously after the removal of such a substance, a natural oxide film caused by a reaction of an adsorbed substance is not formed, and an insulating film or a conductive film is directly formed on the silicon surface. Can be formed.

The heat treatment in the present invention is performed at 300 ° C.
More preferably, it is carried out at a temperature of 500 ° C. This is because water molecules adsorbed on the silicon surface can be efficiently desorbed. The heat treatment in the present invention is more preferably performed at least once at a temperature of 300 ° C to 500 ° C, and more preferably once or more at a temperature of 500 ° C to 700 ° C. This is because the OH groups adsorbed on the silicon surface can be sufficiently desorbed.

The rate of temperature rise after the heat treatment at 300 ° C. to 500 ° C. in the present invention is more preferably 5 ° C./min or less. Is because OH groups are adsorbed to heating at high speeds by reacting with silicon prior to elimination results in forming an oxide film, the OH group H ₂ O by heating at a low speed
This is because it can be desorbed as.

[0015] The heat treatment in the present invention, a low pressure, preferably 10 ^- 3 Torr or less, more preferably 10 ^- 7To
It is performed under a pressure atmosphere of rr or less. This is because the substance containing oxygen adsorbed on the silicon surface can be desorbed efficiently only by making the atmosphere high vacuum.

The heat treatment in the present invention can be performed in an inert gas atmosphere having a water concentration of 10 ppb or less, preferably 50 ppt or less, in addition to the vacuum atmosphere. The inert gas is not particularly limited, but, for example, nitrogen gas or argon gas can be used.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the embodiment D of the present invention will be described.
A method of forming the capacitive insulating film of the RAM will be described in detail with reference to the drawings. Initially, the surface of the lower electrode 1 formed of polycrystalline silicon is covered with the natural oxide film 2 as shown in FIG. This natural oxide film is removed by pre-cleaning with a hydrofluoric acid aqueous solution. This state is shown in FIG. 1B, and most of the silicon dangling bonds on the lower electrode surface 1 are terminated with H groups, and some are terminated with F groups or OH groups.

Then, pure water cleaning is performed, and SiF-bonded F
The group is removed by hydrolysis, and as shown in FIG. 1 (c), a Si-OH bond is formed or H ^{+ in} pure water terminates with an H group or an OH group. Further, various gases and the like are adsorbed on the surface of the lower electrode 1 in a molecular state or a monoatomic state during drying and waiting for the work in the subsequent steps.

Here, for example, as shown in FIG.
Consider a case where water molecules H ₂ O are adsorbed on the surface of the lower electrode 1. Note that this adsorption is bonded with a very weak bonding force and can be easily desorbed. 2 shows the lower electrode 1
TDS of water molecules when water molecules are adsorbed on the surface of
It is an analysis result. According to this result, 200 ℃ ~ 400
A water molecule desorption peak (indicated by I in the figure) appears at 0 ° C, while an OH group desorption peak (I in the figure) occurs at 400 ° C to 700 ° C.
(Indicated by I) appears. That is, water molecules adsorbed on the surface of the lower electrode 1 are desorbed at 200 ° C to 400 ° C, and OH groups also adsorbed on the lower electrode 1 are 400 ° C to 700 ° C.
It will be desorbed at ℃.

Therefore, in the next SiN CVD step, the SiN CVD that has been heated to 400 ° C. to 500 ° C. in advance is performed.
The lower electrode 1 is loaded in the furnace. At this time, in order to prevent the entrainment of the atmosphere as much as possible, it is desirable to carry out the loading in the N ₂ flow. Further, as for the CVD furnace, the vertical furnace has a smaller amount of air entrainment than the horizontal furnace, and thus it is preferable to use the vertical furnace. The steps up to this point are the same as the CVD method using ordinary ramping.

Next, the inside of the furnace is evacuated while keeping the temperature at the time of loading. The vacuum degree in this case is at least 10
-High vacuum below ³ Torr is desirable, 10
-Ultra high vacuum of ⁷ Torr or less is more desirable. This is because most of the water molecules adsorbed on the surface of the lower electrode 1 are desorbed only by making the inside of the furnace vacuum. Further, by performing the heat treatment for a long time at that temperature, the adsorbed gas can be sufficiently desorbed as shown in FIG.

Then, the temperature is raised to the CVD temperature at a speed as low as possible while maintaining the above-mentioned degree of vacuum. At this time, the rate of temperature increase is preferably 5 ° C./minute or less. This is because when the temperature is rapidly raised, the adsorbed OH groups react with silicon to form an oxide film before being desorbed. By gradually raising the temperature, the OH groups are converted into H ₂ O. This is because it can be desorbed.

Next, the temperature rise is temporarily stopped at a temperature of 600 ° C. to 700 ° C., and heat treatment is performed again. As a result, FIG.
O adsorbed on the surface of the lower electrode 1 as shown in (f)
The H group can be removed more sufficiently. continue,
When the CVD process is performed at the CVD temperature of the SiN film, FIG.
As shown in (g), the SiN film 3 is formed on the lower electrode having less natural oxide film.

Next, the SiN film is oxidized to form the upper oxide film 4
To form This oxidation, for example, a temperature of 900 ° C. to 950
This can be done by pyrogenic oxidation at ° C.
As a result, as shown in FIG. 1 (h), SiO ₂ / Si
A two-layered N capacitive insulating film is formed.

Finally, when the upper electrode 5 made of polycrystalline silicon is formed, a capacitive element composed of the lower electrode 1, the capacitive insulating film and the upper electrode can be formed as shown in FIG. 1 (i). In the semiconductor device manufacturing process described above, it is possible to use a CVD device having a load lock chamber. In this case,
The steps shown in (e) to FIG. 1 (f) are as follows.

That is, first, the wafer having the lower electrode 1 formed thereon is loaded into the load lock chamber at room temperature. Next, the load lock chamber is evacuated to 400 ° C to 5 ° C.
Raise to a temperature between 00 ° C. The degree of vacuum and the heating rate at this time are the same as those in the above method.

Subsequently, heat treatment is performed at a temperature of 400 ° C. to 500 ° C. to remove water molecules adsorbed on the surface of the lower electrode 1. After that, in a vacuum atmosphere, the wafer is loaded into a high temperature furnace of about 700 ° C. set to the CVD temperature of SiN. Here, the loading of the furnace into the furnace is performed at an extremely low speed so that the wafer is artificially elevated. The temperature rate can be reduced.

If the load lock chamber and the furnace are kept at the same temperature, the temperature can be controlled by the same method as described above. Note that the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the present invention.

For example, in the above-mentioned manufacturing method, the atmosphere in the furnace for degassing is a vacuum, but the purity is high, for example, the water concentration is at least 10 ppb or less, preferably 50 pp.
It is possible to desorb the adsorbed gas even if the heat treatment is performed in a flow of an inert gas such as nitrogen gas or argon gas of t or less.

Further, in the above-described embodiment, the DRAM
Although the present invention has been described with reference to the method for forming the capacitive element as described above, a stacked gate type NVM (Nonvol) having a gate insulating film of a transistor and a floating gate is described.
A thin film can be formed by a similar method when forming the first and second gate insulating films of the film memory).

The present invention is effective not only for forming a thin film of an insulating film but also for forming a conductive film on a contact or the like without forming a natural oxide film.

[0032]

As described above, according to the present invention, it is possible to prevent a natural oxide film from being formed between the single crystal silicon or the polycrystalline silicon and the insulating film or the conductive film, and the insulating film is formed. It is possible to reduce the film thickness, improve reliability, and prevent an increase in contact resistance in the contact.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a capacitive insulating film showing a method of manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a graph showing the results of analysis by TDS.

FIG. 3 is a sectional view of a memory cell of a stacked capacitor type DRAM formed by a conventional method.

FIG. 4 is a cross-sectional view showing a manufacturing process of a capacitive insulating film formed by a conventional method.

[Explanation of symbols]

1 ・ ・ Lower electrode made of polycrystalline silicon 2 ・ ・ Natural oxide film 3 ・ ・ SiN film 4 ・ ・ SiO ₂ (oxide film formed by oxidation of SiN) 5 ・ ・ Upper electrode made of polycrystalline silicon 6 ・ ・ Water Molecule 7 ... Semiconductor substrate 8 Field oxide film 9 Polycrystalline word line 10 N ⁺ diffusion layer 11 Gate insulating film 12 Polycrystalline silicon lower electrode 13 Capacitive insulation Membrane 14 ・ ・ Upper electrode made of polycrystalline silicon 15 ・ ・ Bit line made of polycrystalline silicon 16 ・ ・ Interlayer film 17 ・ ・ Lower electrode made of polycrystalline silicon 18 ・ ・ Natural oxide film 19 ・ ・ SiO ₂ (water molecules 20 .. SiN film 21 .. SiO ₂ (oxide film formed by oxidation of SiN) 22 .. Upper electrode made of polycrystalline silicon

Claims (7)

[Claims] 1. A method of manufacturing a semiconductor device in which an insulating film or a conductive film is directly formed on a silicon-based substrate, wherein the insulating film or the conductive film is formed at a predetermined low temperature at least once. A method of manufacturing a semiconductor device, comprising: a step of performing heat treatment; and a step of forming the insulating film or the conductive film following the step. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment is performed at a temperature of 200 ° C. to 700 ° C. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment is performed at a temperature of 300 ° C. to 500 ° C. 4. The manufacturing of a semiconductor device according to claim 1, wherein the heat treatment is performed at a temperature of 300 ° C. to 500 ° C. at least once, and further once or more at a temperature of 500 ° C. to 700 ° C. Method. 5. The method of manufacturing a semiconductor device according to claim 3, wherein the rate of temperature rise after the heat treatment at 300 ° C. to 500 ° C. is 5 ° C./min or less. Wherein said heat treatment, 10 ^- 3 Torr method of manufacturing a semiconductor device according to any one of claims 1 to 5, characterized in that at a pressure equal to or smaller than the atmosphere. 7. The heat treatment has a water concentration of 10 ppb.
The method for manufacturing a semiconductor device according to claim 1, wherein the method is performed in the following inert gas atmosphere.