JPH0480926A - Formation of oxide insulating film - Google Patents

Abstract

PURPOSE:To enable a high quality oxide insulating film to be formed by a method wherein a gaseous oxide in the ratio exceeding specific range to an inert gas is used for the sputtering process to form the title oxide insulating film. CONSTITUTION:A tantalum oxide film is formed on a silicon semiconductor and then an electrode is formed on the tantalum oxide film by electron beam evaporation process while the results of detected electrical characteristics are as shown in the figures. Within the figures, the slip from the ideal value of the flat band voltage in the less volume of Ar gas than oxidative gas i.e., not exceeding 25 minal % is reduced. A lower side electrode 2 is formed on a substrate 1 by sputtering process of Ar only in an island shape and then an insulating film 8 of tantalum oxide is formed on the electrode 2 next Al as an upper side electrode 4 is formed by Al evaporation process to complete a capacitor. In said procedures, since the breakdown strength is increased when the oxygen number during the film formation process is rapidly decreased at the voluminal % of Ar exceeding 25%, Ar is to be added at the voluminal % during the film formation process not exceeding 25% generally to oxygen of 100%, while in the ratio of specific dielectric constant to oxygen, the oxygen % is the, higher the better.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention is applicable to dielectric films of capacitors in semiconductor integrated circuits, interlayer insulating films, gate insulating films of insulated gate field effect transistors of active liquid crystal displays, etc. The present invention relates to a manufacturing method for forming an insulating film by sputtering.

"Prior Art" Active elements or semiconductor integrated circuits using insulating films fabricated by chemical vapor deposition or the like, or capacitors using dielectric films are attracting wide attention.

This insulating film (simply referred to as an insulating film or an insulating film because the dielectric film of the capacitor is also insulative) has conventionally been formed using a chemical vapor phase method, etc., so the maximum atmospheric temperature for its production is 450°C. It can be formed at a low temperature of °C, and inexpensive soda glass, borosilicate glass, etc. can be used as the substrate.

As other methods for producing an insulator at such low temperatures, a plasma CVD method and a sputtering method using 100% to 80% Ar atoms as a sputtering gas are known.

This is because there is a high probability that an inert gas such as Ar will knock out the target material (sputtering yield).

As a result of intensive studies on the characteristics of insulating films produced by sputtering, the inventors found that the lower formed surface, that is, the interface between the lower electrode active layer and the deposited insulating film, indicates the performance of the insulating film. It was found that the interface level of The metal component (Ta component) generates clusters (groups of grains with a grain size of 5 to 50 C).The flat band voltage, which reflects the number of fixed charges in the insulating film due to the clusters and damage to the O underlying surface, It was also seen that the decrease in dielectric strength or the proportion of Ar gas used during sputtering greatly depends on the drop in dielectric strength.

Furthermore, attempts have been made to fabricate a dielectric film for a capacitor using a photo-CVD method. No reaction damage with underlying semiconductor or electrode material, 2X10"eV-' cm-
Although an interface state density of about 2 has been obtained, the time required for film formation is long (the film formation rate is very slow), making it unsuitable for industrial applications. In addition, hydrogen was used, which induced the hot electron effect, so there were problems with long-term properties.

FObjects of the Invention The present invention is a method for solving the problems of the prior art, and consists of a metal oxide insulating film made of tantalum oxide, titanium oxide, barium titanate, lead titanate, etc. having good properties. The present invention provides a method of manufacturing without clusters, pinholes, etc., and without using hydrogen in a low-temperature process.

[Structure of the Invention] The structure of the present invention relates to a method for manufacturing a metal oxide film such as a dielectric material such as tantalum oxide or titanium oxide, or a ferroelectric material such as barium titanate.

In the present invention, such an insulating film is formed by a sputtering method.

The gas used for sputtering is an oxide gas, for example, an oxide gas containing 75% by volume or more of oxygen based on an inert gas such as argon, and more preferably an oxide gas that does not use any inert gas, especially a metal oxide or metal under conditions of only oxygen. This method is characterized by sputtering a target and producing an oxide insulating film by a layering method.

In sputtering, the sputtering gas is a gas that is part of the components of the deposited film, for example, in the case of tantalum oxide films, oxygen is 100% or 80 to 100% by volume.
Radio frequency (RF) sputtering is performed using a tantalum oxide target. Then, the oxidation reaction between the target material and oxygen, which is the sputtering gas, can be more completely carried out while the target material is in flight.

In order to further promote this, in addition to this, by simultaneously mixing 0.2 to 20% by volume of a gas containing a halogen element to the oxide gas, the alkali ions that are involuntarily introduced into the silicide oxide are removed. It also made it possible to neutralize the sum and unpaired bonds.

As the sputtering method used in the present invention, any method such as RF sputtering or DC sputtering can be used, but the sputtering target is an oxide with poor conductivity, such as T.
In the case of metal oxides such as A205, it is preferable to use a 13.56 MHz high frequency RF magnetron sputtering method in order to maintain stable discharge.

Oxide gases include oxygen (0□), ozone (03),
Examples include nitrous oxide (N20). In particular, when ozone or oxygen is used, there are no unnecessary atoms incorporated into the oxide insulating film, so the insulating film can be coated with a very good insulating film that does not contain any vinyl oxides, has little dielectric damage, and does not have large variations in dielectric strength. could be obtained on the formed surface.

Typical oxide insulating films include tantalum oxide and titanium oxide. In addition, barium titanate and lead titanate are the main ferroelectric oxides. For the halogen element to be added to these, nitrogen fluoride (NF, N2F,), hydrogen fluoride (HF), fluorine (F2), or fluorocarbon gas can be used as the fluoride gas.

NF3 is easy to use because it is easy to chemically decompose and easy to handle. As a chloride gas, carbon tetrachloride (CC1
4), chlorine (C12), hydrogen chloride (MCI), etc. can be used.

Further, the amount of nitrogen fluoride, for example, was 0.2 to 20% by volume relative to the oxide gas, for example, oxygen. These halogen elements are effective in neutralizing alkali ions such as sodium in oxide insulators and neutralizing unpaired bonds in metals through heat treatment, but if they are used in too large a quantity, the main components of the insulating film become gaseous. This is not good because it has the inherent possibility of Generally, a halogen element is mixed in the coating in an amount of 0.01 to 5 at % of the total number of elements.

The use of ozone as a gas for sputtering is either ozone or O
It was easily decomposed into radicals (the amount of O radicals generated per unit area was large, contributing to an improvement in the film formation rate).

The present invention will be explained in detail below using Examples.

"Example 1" A tantalum oxide film was formed on a silicon semiconductor by the method of the present invention, an aluminum electrode of 1 mm diameter was formed thereon by electron beam evaporation, and the electrical characteristics were investigated. The results are shown in FIG.

FIG. 2 shows the flat band voltage deviation (ΔVFB) characteristic in the C-■ characteristic when the MIS (aluminum metal-tantalum oxide insulating film-silicon semiconductor) structure is used.

Compared to 100% Ar gas, when the amount of Ar gas is less than the amount of oxidizing gas (oxygen in Figure 3) and is 25% by volume or less, the deviation of the flat band voltage from the ideal value is reduced. Recognize.

Perform BT (bias-temperature) treatment and apply a negative bias voltage of 2 x lo6 V/cm to the gate electrode side, 150
°C for 30 minutes, and a positive bias voltage was further applied under the same conditions. The difference between them, that is, the deviation in flat band voltage (ΔVFB), was also IOV. However, when this film was formed using 100% oxygen, the voltage was only 0.5V or less. Furthermore, when even a small amount of halogen element was added to this, the value further rapidly decreased to - several minutes.

From these facts, activated Ar atoms present in the reaction atmosphere during film formation by sputtering affect the film quality of the insulating film, and it is desirable to reduce the presence of Ar atoms as much as possible when forming a film by sputtering. It has been found.

The reason for this is that Ar ions interfere with the reaction between metal, which is one of the film components, and oxygen during sputtering.
A metal oxide with sufficient stoichiometry (the ratio of 05 to Ta2 is satisfied even at the micro level) is not formed. It is also conceivable that Ar ions or activated Ar atoms collide with the interface, causing damage or defects at the interface, and causing the generation of fixed charges.

"Example 2" FIG. 1 shows the manufacturing process of the insulating film of the present invention.

In this example, soda glass having a blocking layer, which is inexpensive as a substrate material, was used as the substrate (1).

A lower electrode (2) is formed in the form of an island on this substrate (1) by sputtering using only Ar to obtain the state shown in FIG. 1(A).

The manufacturing conditions were as follows.

Substrate temperature 350°C Reaction pressure 0.06 torrRf power (1
3,56MHz) 100W target
Metallic tantalum Gas used: Ar Film thickness: 2000 In addition, when forming the island shape, a metal mask was used in the embodiment, but a known photolithography technique may be used.

A tantalum oxide insulating film was formed thereon by the method of the present invention. The conditions are shown below.

Target Ta20599.99% Reaction gas 02100% by volume ~ 0% by volume Ar
O volume % ~ 100 volume % reaction pressure
0.05 torr Rf power 500 W Substrate temperature 100'C Distance between substrate targets 150 mm Next, AI was formed as the upper electrode (4) by electron beam evaporation to complete the capacitor.

When creating an insulating film in an atmosphere containing Ar gas at a ratio of 25% or less, the distance between the target and the substrate should be set to A.
By making the length longer than when fabricating with 0% R gas, it is possible to obtain an insulating film with almost the same quality as when fabricating with 0% Ar gas. Furthermore, the gate insulating film formed by mixing Ar gas at a ratio of 25% or less is irradiated with excimer laser light and subjected to flash annealing to activate the halogen elements such as fluorine incorporated into the film and remove the imperfections of silicon. It was also possible to neutralize the bonds and eliminate the cause of fixed charges in the membrane.

FIG. 3 shows the dielectric strength when the oxygen content is further increased. An Al electrode with a diameter of 1 mm was used, and the leakage current exceeded 1 μA.

Since there are variations depending on the sample, in the figure, X (mark in the center) and σ (dispersion sigma value) (upper and lower limits) are shown. This breakdown voltage suddenly decreases and becomes higher when the number of oxygen atoms in the film becomes 25% or more, and the σ value also becomes small. Therefore, the addition of argon is 25% by volume or less during film formation, generally 100%.
It would have been better to use 0.2 to 10% by volume of NF3 or the like to oxygen in addition to this.

The characteristics of the ratio of dielectric constant to oxygen under such conditions are shown in the fourth section.
As shown in the figure. As expected, as the amount of oxygen increases, the variation decreases, which is preferable.

Furthermore, all materials used for sputtering are preferably of high purity. For example, the sputtering target is 4N
Tantalum oxide, titanium oxide, barium titanate,
Lead titanate is most preferred.

However, even if metals such as tantalum and titanium are used, if the sputtering conditions are carefully selected, is it possible to obtain the same characteristics as shown in Figure 2 for the oxide film formation rate? I had to reduce it to about 1/4.

The oxygen content is preferably 100 to 90% by volume. Similarly, a gas of high purity (5N or higher) was used for the sputter link' to prevent impurities from entering the insulating film as much as possible.

"Example 3" FIG. 5 shows another embodiment of the invention.

The present invention was used to fabricate one cell of a DRAM (dynamic memory) of lTr/Cel l in this example. In the drawing, one gate type field effect transistor (20) is formed on a semiconductor substrate with a source or drain (8), a drain or source (9), a gate electrode (
7) and is configured as a gate insulating film (6).

Furthermore, one drain or source of this transistor (
9) includes a lower electrode (10) and a tantalum oxide dielectric (1).
1) A capacitor (21) consisting of an upper electrode (12) is provided in series. A buried insulating film (5) is left on the outer periphery of these. This structure shows the shape of a memory cell of a stacked DRAM. In this drawing, the dielectric film (11) of the capacitor was formed by coating the tantalum oxide target of the present invention by oxygen sputtering. This tantalum oxide has a dielectric constant of 27 and has excellent frequency characteristics up to high frequencies, so it
．． 8), a larger storage capacity can be obtained.

The gate insulating film of this insulated gate field effect transistor (20) is made of silicon oxide produced by thermal oxidation or by sputtering using 100% oxygen of silicon oxide. However, even if this protective film is made of tantalum oxide, the interface level with the silicon semiconductor is only 2X1010cm-2L,
It was good.

Further, the lower electrode (10) of this capacitor (21) was formed using a silicon semiconductor doped with phosphorus.

However, this electrode material may be metal tantalum, tungsten, titanium, molybdenum, or a silicide thereof.

In this example, a tantalum oxide film (11) was formed on the lower electrode (lO) by the sputtering method of the present invention as shown in Example 1 or Example 2. Furthermore, an upper electrode (12) was formed on top of this using aluminum or a multilayer film of metal tantalum and aluminum to constitute a capacitor (21). The thickness of tantalum oxide was 300 to 3000. Typically, there are 500 to 1000 people, for example 1000 people. However, since silicon oxide and the like have a low dielectric constant, the thickness must be reduced to about 30 mm for a memory cell. However, since the tantalum oxide formed by the method of the present invention has a high dielectric constant, its thickness is, for example, 1000 mm.
I can do things with people. As a result, it has excellent insulation properties, and it has become possible to reduce the presence of pinholes.

Therefore, in FIG. 5, the channel length of the insulated gate field effect transistor is set to 0.1 to 1 μm, for example 0.5 μm.
In addition, the size of ITr/Ce1l is 20
One memory (1 bit) could be created in the μm port.

In addition, when forming this tantalum oxide, it is formed by a sputtering method that does not contain any hydrogen, and in addition, the upper and lower electrodes are also formed by a sputtering method that does not contain hydrogen, so the hydrogen in the film is removed during the subsequent heat treatment. Drift to the gate insulating film (
This also makes it possible to prevent hot carriers from becoming a trap center.

"Example 4" Figure 6 shows a pair of dynamic memory cells (2 pits)
It is configured and provided.

In the drawing, a semiconductor substrate (1), a buried insulating film (5), a drain or source (9) formed in a convex shape on the semiconductor surface, and a conductor electrode/lead (1) are shown on the semiconductor substrate (1).
9). A silicon oxide film (6) was formed on this side surface as a gate insulating film. A pair of gate electrodes (7), (7'') are formed by anisotropic etching, and a source or drain (8), (8°) is provided. Boron ion implantation is performed on the convex regions (9), (19) and the field insulating film (7') before forming the gate electrodes (7), (7').
5) and as a mask, lXl0"~5xlO"cm-
It was formed to a concentration of 3. and then the source or drain (8).

(8°) was prepared by ion implantation at a concentration of 1 x 101 g to 1 x 1021 cm-3. The capacitor (21) had a lower electrode (10), a tantalum oxide dielectric (11), and an upper electrode (12) formed in the same manner as in Example 3 according to Example 1.2.

I constitute two bits with a mouth size of 10-20μm
We were able to create Tr/Ce1l.

In addition, in order to avoid using hydrogen, which causes hot carrier trap centers to form in the gate insulating film,
Even with a channel length of μm, stable transistor characteristics could be obtained.

"Effects" All of these are based on experiments that show that a high-quality insulating film can be created by sputtering oxygen or oxide gas to reduce the amount of argon to zero or less than 25%, contrary to the conventionally known main gas, argon. Based on facts discovered in

By the method of the present invention, a thin film transistor with very good characteristics could be easily formed using only a low temperature process.

Furthermore, since the causes of hot carriers and fixed charges existing in the gate insulating film can be reduced, it has become possible to provide highly reliable transistors and capacitors with little change in characteristics during long-term use.

The shape of the capacitor or insulated gate transistor used in the present invention does not need to be staggered, but may be an inverted staggered or vertical channel transistor. Alternatively, it may be an insulated gate field effect transistor used as a part of a monolithic transistor (1c) using single crystal silicon rather than non-single crystal silicon for the transistor.

In addition, the capacitor may have a multi-layered structure instead of a single dielectric capacitor, and the electrodes may be arranged side by side instead of being sandwiched between the top and bottom.

[Brief explanation of the drawing]

FIG. 1 shows the manufacturing process of an embodiment of the present invention. FIG. 2, FIG. 3, and FIG. 4 show the relationship between the ratio of oxygen and Ar gas and the electrical characteristics during the fabrication of the insulating film. 5 and 6 show an embodiment of a semiconductor device which is a dynamic memory cell using the method of the present invention.

Claims (1)

[Scope of Claims] 1. A method for producing an oxide insulating film, which comprises forming a metal oxide insulating film by sputtering in an atmosphere in which an oxidizing gas is 75% by volume or more based on an inert gas. 2. Claim 1 states that an insulating film such as a dielectric film of a capacitor or a gate insulating film is formed by sputtering in an atmosphere containing 100% by volume of oxygen, which is an oxidizing gas. Features of oxide insulating film manufacturing method.