JPH04154124A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To simultaneously form a gate oxide film on an Si substrate and an oxide film on a nitride film by a method wherein the oxide film on the nitride film and the gate oxide film are formed, the Si substrate and the nitride film formed on it are exposed to an atmosphere which contains chlorine, oxygen and an inert gas and they are heated. CONSTITUTION:An element isolation film 2 is formed on an Si substrate 1; after that, a gate oxide film 3 is formed, by a thermal oxidation operation, in a region surrounded by it; and a floating gate 4 composed of polycrystalline Si is formed on the film 3. Then, the surface of the gate 4 is oxidized; a first oxide film 5 is formed; and as oxidation conditions at this time, dry oxygen which has been diluted with nitrogen or argon is used and an atmospheric temperature is set at 1000 deg.C. After that, a nitride film 6 is grown on the film 5 so as to be overlapped with end parts of the film 2 on both sides; and at this time, ammonia and silane are used as raw-material gases and a temperature is set at 720 deg.C. Then, the film 6 and the substrate 1 are oxidized simultaneously; and a second oxide film 8 is produced on the film 6 and a second gate oxide film 9 is produced on the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of simultaneously forming an oxide film on a nitride film and a gate oxide film.

The object of the present invention is to provide a method for forming a large ratio of the thickness of an oxide film on a nitride film to the thickness of a gate oxide film.

The Si substrate and the nitride film formed on the Si substrate are treated with chlorine or a compound containing chlorine, oxygen, and an inert gas.
A semiconductor device manufacturing method is employed in which a gate oxide film is formed on the Si substrate and an oxide film is simultaneously formed on the nitride film by exposing the semiconductor device to an atmosphere of 00° C. or higher.

Further, the compound containing chlorine is hydrogen chloride.

The ratio of the hydrogen chloride to the oxygen is 0.001 volume or more and 1 volume or less of hydrogen chloride per 1 volume of oxygen.

Further, the nitride film and the oxide film on the nitride film (which is part of the C interlayer insulating film between the J floating gate and the control gate) are formed by a method for manufacturing a semiconductor device.

[Industrial application field]

The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for simultaneously forming an oxide film on a nitride film and a gate oxide film.

With the recent demand for higher integration of semiconductor devices, there is a demand not only for devices to be smaller in the horizontal direction but also to be thinner in the vertical direction. However, since the power supply voltage is constant, the electrolytic strength applied to one interlayer insulating film increases, and therefore a thin insulating film of good quality is required.

[Conventional technology]

Conventionally, E P ROM (Erasable Pro
grammableRead-Only Memory
) was formed by oxidizing the polysilicon that is the floating gate, or because the polysilicon oxide film is affected by electric field concentration at the edge of the floating gate, the charges in the floating gate are removed from the edge of the floating gate. There was a problem with it falling out. Therefore, in order to avoid the influence of electric field concentration at the edge portion, a three-layer film of oxide film/nitride film/oxide film has been used as an interlayer insulating film.

Figure 3 shows a cross-sectional view of the EPROM, where I is a Si substrate, 2
3 is an element isolation film, and 3 is a first gate oxide film.

4 is a floating gate, and 5 is a first oxide film.

6 is a nitride film, 8 is a second oxide film, 9 is a second gate oxide film, 10 is a control gate, 11 is a gate electrode, 1
2 represents a source/train region, 13 represents an insulating film, and 14 represents a source/drain electrode.

The first oxide film 5, nitride film 6, and second oxide film 8 form an interlayer insulating film between the floating gate 4 and the control gate 1°. What is the thickness of each membrane?

For example, it is quadratic.

First oxide film: 5:100 Nitride film: 6:100 Second oxide film: 8:20 The second oxide film is formed by oxidizing the nitride film 6 in a water vapor atmosphere at about 900°C.

By the way, if an attempt is made to form the second gate oxide film 9 of the peripheral transistor at the same time as the formation of the second oxide film in order to reduce the number of steps, a problem will arise. That is, the second layer is formed on the nitride film 6.
When the second gate oxide film 8 is formed to a thickness of about 200 nm, a second gate oxide film 9 is formed on the Si substrate 1 to a thickness of about 2000 nm. In this case, the gate oxide film is too thick to function as a peripheral transistor. Furthermore, if the oxidation conditions are set so that the thickness of the second gate oxide film 9 is 200 to 300, the thickness of the second oxide film 8 will be as thin as about 12, and the floating gate 4 will be A problem arises in that charge is lost.

[Problem to be solved by the invention]

Therefore, in the conventional method, the second oxide film 8 on the nitride film 6,
The second gate oxide film 9 on the Si substrate 1 cannot be formed at the same time, and the second oxide film 8 on the nitride film 6 and the second gate oxide film 9 on the Si substrate 1 are formed in separate steps. This made the process complicated.

In the present invention, the second oxide film 8 on the nitride film 6 and the second gate oxide film 9 on the Si substrate 1 are formed simultaneously.

It is an object of the present invention to provide a method for forming the second gate oxide film 9 to be thin enough to function, and to form the second oxide film 8 to be thick enough to prevent charges from leaking from the floating gate 4.

[Means to solve the problem]

The above problem can be solved by exposing the Si substrate 1 and the nitride film 6 formed on the Si substrate 1 to an atmosphere of 1000° C. or higher containing chlorine or a compound containing chlorine, oxygen, and an inert gas. This problem is solved by a method of manufacturing a semiconductor device in which a gate oxide film 9 is formed on the nitride film 6 and an oxide film 8 is formed on the nitride film 6 at the same time.

Further, the compound containing chlorine is hydrogen chloride.

The ratio of hydrogen chloride to oxygen is solved by a semiconductor device manufacturing method in which the ratio of hydrogen chloride to oxygen is 0.001 volume or more and 1 volume or less per 1 volume of oxygen.

Further, the nitride film 6 and the oxide film 8 on the nitride film 6 are
This problem is solved by a method of manufacturing a semiconductor device that is part of the interlayer insulating film between the floating gate 4 and the control gate 10.

[Effect]

When forming the gate oxide film 9 on the Si substrate 1 and the oxide film 8 on the nitride film 6 at the same time, using an atmosphere containing chlorine or a compound containing chlorine, oxygen, and an inert gas is easier than using a water vapor atmosphere. Also, the ratio of the thickness of oxide film 8 to the thickness of gate oxide film 9 can be increased. The oxide film 8 can be formed to be thick enough that no charge can escape from the floating gate 4 (and the gate oxide film 9 can be formed thin enough to function as a transistor).

Further, the ratio of the thickness of the oxide film 8 to the thickness of the gate oxide film 9 increases as the temperature of the atmosphere when forming the oxide film increases, and a large effect is produced at a temperature of 100° C. or higher. On the other hand, the growth rate of the oxide film increases as the temperature of the atmosphere increases, making it difficult to control the thickness of the grown film. Therefore, the oxidizing gas is diluted with an inert gas.

Increase the proportion of inert gas to suppress the growth rate.

Hydrogen chloride can be used as the chlorine-containing compound. The ratio of hydrogen chloride to oxygen is 0.001 volume or more and 1 volume or less of hydrogen chloride to 1 volume of oxygen, and 0.00
If it is less than 1 volume, there is no effect, and if it is more than 1 volume, the surface of the Si substrate 1 will be roughened.

In addition, in the method of the present invention, an oxide film 1 is formed on the nitride film which is a part of the interlayer insulating film between the floating gate 4 and the control gate 10 in a region where a transistor is to be formed.
The present invention can be very effectively applied to the process of simultaneously forming a gate oxide film on the substrate 1.

〔Example〕

FIGS. 2(a) to 2(f) are sectional views in the order of steps for forming an EPROM, and more specifically, sectional views in the order of steps for forming an ultraviolet erasable ROM. Below, referring to these figures,
An outline of the formation of an ultraviolet erasable EPROM will be explained.

Refer to FIG. 2(a) Si-based substrate - After an element isolation film 2 is formed by the LOCO3 method, a first gate oxide film 3 is formed on the Si substrate 1 by a thermal oxidation method. The thickness of the first gate oxide film 3 is 2, for example, 200.

Poly-Si that becomes a floating gate by vapor phase growth
For example, grow 2 to a thickness of 1000 and introduce phosphorus as an impurity. After diffusing phosphorus, the poly-Si is patterned to form floating gates 4.

See Figure 2(b) The surface of floating gate 4 is thermally oxidized.

A first oxide film (bottom poly-Si oxide film) 5 is formed. The oxidation conditions are as follows.

Oxidizing atmosphere: Dry oxygen diluted with nitrogen or argon Temperature: 1000°C Oxide film thickness: 100 people Next, the entire surface is coated with ammonia (NH3) and silane (S).
A nitride film 6 is grown by vapor phase growth using iH4) as a raw material gas.
grow. The growth temperature is 9, for example, 720° C., and the growth film thickness is 2, for example, 100.

Referring to FIG. 2(c), using the resist 7 as a mask, the nitride film 6 and first oxide film 3 in the two peripheral transistor regions are removed by etching.

The nitride film 6 is removed by dry etching, and the first oxide film 3 is removed by wet etching using a hydrofluoric acid solution.

After removing the resist 7 (see FIG. 2(d)), the nitride film 6 and the Si substrate 1 in the peripheral transistor area are simultaneously oxidized, and a second
A second gate oxide film 9 is formed on the Si substrate 1 in the transistor region around the oxide film 81.

For example, the oxidation conditions are 2. It is as follows.

Oxidation atmosphere: 2 volumes of oxygen 1 volume of anhydrous chloride 1 volume of nitrogen IO Atmosphere temperature: 1100°C Thickness of second oxide film 8, 25 people Thickness of second gate oxide film 9, 300 people Figure 2 (e ) Poly-Si is grown on the entire reference surface to a thickness of 3000 nm by vapor phase growth, and phosphorus is introduced as an impurity by vapor phase diffusion.

After that, pattern the poly-Si and 2. Second oxide film 8
Control gate 10 on top. A gate electrode 11 is formed on second gate oxide film 9.

As an impurity in the Si substrate 1 on both sides of the gate electrode 11.

For example, arsenic is introduced to form the source/druin region 12.

Referring to FIG. 2(f), an SiO□ film is grown as an insulating film 13 over the entire surface by vapor phase growth, and a source/drain electrode 14 is formed with openings in the source/train region 12.

In this way, an ultraviolet erasable ROM can be formed.

Note that when simultaneously forming the second oxide film 89 on the nitride film 6 and the second gate oxide film 9 on the Si substrate 1 in the peripheral transistor region, the second oxide film 8 is formed by changing the ambient temperature and time. The relationship between the thickness and the thickness of the second gate oxide film 9 was investigated in detail.

The results are shown in FIG. A conventional example is also shown for comparison.

The conditions for curves (a) to (d) are as follows.

(a) 1100°C 2 volumes of oxygen, 1 volume of anhydrous hydrogen chloride.

10 volumes of nitrogen (b) 1000°C (same as above) (c) 900°C (same as above) (d) 900°C steam (Conventional example) From Figure 1, anhydrous hydrogen chloride is added instead of conventional steam. It can be seen that by using oxygen of 10%, the ratio of the thickness of the first oxide film to the thickness of the second gate oxide film can be increased.

Furthermore, the ratio can be increased by increasing the ambient temperature, which is 1000°C.

The effect is great.

On the other hand, if the temperature of the atmosphere is high, the growth rate of the oxide film becomes large and difficult to control, so it is diluted with an inert gas such as nitrogen or argon.

Note that the ratio of hydrogen chloride to oxygen should be 0.001 volume or more and 1 volume or less of hydrogen chloride per 1 volume of oxygen. There is no effect if it is less than 0.001 volume, and if it is more than 1 volume, it is S.
The surface of the i-board 1 will be roughened.

Note that chlorine gas may be used instead of hydrogen chloride.

Figure 4 shows the leakage characteristics of the second oxide film using the film thickness of the second oxide film as a parameter.
The relationship between the electric field strength applied to the three-layer oxide film and the current density of the current flowing therein is shown.

If the thickness of the second oxide film is 12 people, leakage is a major problem, but if it is about the same as 22 people, it is practically a problem.

Further, FIG. 5 shows the relationship between the thickness of the second oxide film and the charge loss from the floating gate 4, and is shown based on the case where the thickness of the second oxide film is 30 people. The charge loss can be evaluated, for example, from the change over time in the threshold voltage V l h of the transistor.

If the thickness of the second oxide film is greater than 30, the charge loss will not necessarily be zero, and there will be no practical problem. On the other hand, if the thickness of the second oxide film is too small, charge loss becomes large and becomes a problem.

In the method of the present invention, an oxide film 2 is formed on a Si substrate 1 in a region where a peripheral transistor is to be formed on a nitride film which is a part of an insulating film between the floating gate 4 and a control gate 10.
When applied to the manufacturing process of, for example, an ultraviolet erase type EPROM in which a gate oxide film is simultaneously formed on top of the film, it is extremely effective, and has the effect of reducing the number of steps and facilitating manufacturing.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to simultaneously form the oxide film on the nitride film constituting the interlayer insulating film and the gate oxide film of the peripheral transistor. When applied, it has the effect of reducing man-hours and facilitating manufacturing, and also reduces charge loss from the floating gate, contributing to improved reliability.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the thickness of the second gate oxide film and the thickness of the second oxide film. FIGS. 2(a) to 2(f) are sectional views showing steps of forming an EPROM. FIG. 3 is a cross-sectional view of the EPROM. Figure 4 shows the leakage characteristics of the second oxide film. FIG. 5 is a diagram showing the relationship between the thickness of the second oxide film and charge loss. Figure here. 1 is a Si substrate. 2 is an element isolation film. 3 is a gate oxide film, which is a first gate oxide film. 4 is a floating gate. 5 is an oxide film, which is a first oxide film. 6 is a nitride film. 7, resist 8 is an oxide film, which is a second oxide film. 9 is a gate oxide film, which is a second gate oxide film. 10 is a control gate. 11 is a gate electrode. 12 is a source/drain region. 13 is an insulating film. 14 shows the relationship between the film thickness of the second oxide film of the source/drain electrodes and the film thickness of the second oxide film. Cross-sectional view of OM Figure 5 (b) Figure 2 (active 1) (e) (f) Step-by-step cross-sectional view of EPROM formation Figure 2 ('f 2) tw strength E (MV/cm) 2nd Reef of the liquefied membrane special・1 note ￥14 Figure Koshibu (A) The second liquefied membrane of the glue thickness and the opening of the electric charge top arrow Figure 5

Claims (1)

[Scope of Claims] [1] The Si substrate (1) and the nitride film (6) formed on the Si substrate (1) are heated to a temperature of 1000° C. or higher containing chlorine or a compound containing chlorine, oxygen, and an inert gas. A gate oxide film (9) is formed on the Si substrate (1) by exposing it to an atmosphere of
and simultaneously form an oxide film (8) on the nitride film (6).
1. A method of manufacturing a semiconductor device, comprising: forming a semiconductor device. [2] The chlorine-containing compound is hydrogen chloride, and the ratio of the hydrogen chloride to the oxygen is 0.001 volume or more and 1 volume or less of hydrogen chloride per 1 volume of oxygen. 1. The method for manufacturing a semiconductor device according to 1. [3] The nitride film (6) and the oxide film (8) on the nitride film (6) are part of an interlayer insulating film between the floating gate (4) and the control gate (10). 2. The method of manufacturing a semiconductor device according to claim 1.