JPS63142639A - Formation of film - Google Patents

Abstract

PURPOSE:To form a film whose thickness is highly uniform and to form a thin film with good controllability by a method wherein the ambient temperature of a substrate is set at a value which is higher than the temperature for the formation of the film while a reaction gas is supplied after the ambient temperature has been lowered from the high temperature to the temperature value for the formation of the film. CONSTITUTION:Prior to an oxidation process, the temperature inside a heat- treatment furnace is set at a value which is higher than the temperature for the oxidation process. After the temperature inside the heat-treatment furnace has been lowered to the value for the oxidation process, the process is executed. If the oxidation process is executed for 5 min by supplying O2 at the rate of 9l/min, the thickness of a film in the central part of an Si substrate is almost uniform. The thickness of the film at the peripheral region of the Si substrate is thin. Accordingly, the uniformity of the film is good.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention supplies a reactive gas to the substrate while the ambient temperature of the substrate is at a predetermined temperature, and forms a film on the substrate by a reaction caused by the reactive gas. The present invention relates to a film forming method for forming a film.

[Summary of the invention]

In the film forming method as described above, the present invention makes it possible to form a film with highly uniform thickness by raising the environmental temperature of the substrate higher than the temperature during film formation prior to supplying the reaction gas. Furthermore, even thin films can be formed with good controllability.

[Conventional technology]

When manufacturing semiconductor devices, it is required to form relatively thin films. For example, when forming a field oxide film to separate elements of an integrated circuit device, Si
A SiO□ film of 100 Å or less is formed between the substrate and the Si3N4 film.

This Si0g film is formed by thermal oxidation, and thermal oxidation methods include a method in which the temperature of the heat treatment furnace is held constant, and a method in which the temperature is maintained during the insertion and removal of the substrate as shown in Figure 5. There has conventionally been a method called a ramping method in which the temperature of the heat treatment furnace is lowered than the temperature during oxidation to prevent entrainment oxidation.

Note that the arrows in Figure 5 indicate that thermal oxidation is performed by supplying oxidizers such as 0□ and Nz/Q into the heat treatment furnace only within this time range, and only N2, etc. is supplied to the heat treatment furnace during other time ranges. This indicates that thermal oxidation is not carried out by supplying the gas into the heat treatment furnace.

[Problem that the invention seeks to solve]

However, the uniformity of the thickness of a thermal oxide film generally decreases as the film thickness becomes thinner. In a method in which the temperature of the heat treatment furnace is held constant, uniformity of about ±5% can be obtained when the film thickness is 200 to 100 people, but when the film thickness is 100 Å
Uniformity decreases rapidly in the following cases.

Even if a ramping method is used, the uniformity of the film thickness is still low for extremely thin films. Figure 6 shows the case where thermal oxidation is performed for 3 minutes as shown in Figure 5 on a 5-inch diameter Si substrate. 81 on the diameter of the Si substrate after 6 minutes of thermal oxidation
The thickness of the thermal oxide film at each point of one interval is shown. As is clear from FIG. 6, the uniformity of the film thickness is very low.

Figure 7 shows the thickness of the thermal oxide film and the furnace temperature when Si substrates are placed at multiple positions in the axial direction in a cylindrical heat treatment furnace and thermal oxidation is performed for 6 minutes as shown in Figure 5. It shows the relationship with the internal position. The horizontal axis in FIG. 7 is the position measured from the back of the heat treatment furnace. The reaction gas is supplied from the back of the heat treatment furnace, and the Si substrate is inserted and discharged at a position before the heat treatment furnace.

The white circle in FIG. 7 indicates the film thickness at the center point 2 on the Si substrate shown in FIG. 7, and the vertical line indicates the range of the average value of the film thickness at points 1 to 5 ±3σ. . As is clear from FIG. 7, the uniformity of the film thickness is low overall and particularly at the ends of the heat treatment furnace.

On the other hand, even if the Si substrate is inserted into and discharged from a heat treatment furnace at 800 to 1000°C and no oxidizing agent is supplied, 25°C
~40 people and a thin thermal oxide film is formed.

In this case, although the uniformity of the film thickness is high, it is difficult to control the film thickness to a desired value. The film thickness is controlled by controlling the supply time of the oxidizing agent, but when the oxidizing agent is supplied, the uniformity of the film thickness decreases as described above.

The white circles in FIG. 4 indicate the relationship between the thickness of the thermal oxide film at the center of the Si substrate and the thermal oxidation time when thermal oxidation is performed as shown in FIG. As is clear from the white circles in FIG. 4, especially when the film thickness is thin, the film thickness does not match the theoretical formula that the film thickness is proportional to the 1/2 power of the thermal oxidation time. Therefore, this also shows that when the film thickness is small, the controllability of the film thickness is low.

According to the inventors of this application, the causes of the above problems are that the temperature of the Si substrate itself is not uniform, and that the initial natural oxide film is formed non-uniformly on the Si substrate. This is thought to be due to the substrate being contaminated. Such problems cannot be sufficiently improved even if the heat treatment time before oxidation is lengthened.

[Means for solving problems]

The film forming method according to the present invention includes a step of increasing the environmental temperature of the substrate to a temperature higher than the temperature at the time of film formation, and supplying a reaction gas after lowering the environmental temperature from the high temperature to the temperature at the time of film formation. Each process has its own steps.

[Effect]

In the film forming method according to the present invention, the environmental temperature of the substrate is made higher than the temperature during film formation prior to supplying the reaction gas. For this reason, it is considered that the temperature of the substrate itself is highly uniform during film formation.

Further, even if the substrate is contaminated, this contamination is removed due to the above-mentioned high temperature, and it is considered that the influence of contamination of the substrate on film formation is small.

〔Example〕

Hereinafter, an embodiment of the present invention applied to the formation of an oxide film on a Si substrate will be described with reference to FIGS. 1 to 4.

FIG. 1 shows this embodiment. As is clear from FIG. 1, in this example, the temperature of the heat treatment furnace is set to 900°C, which is higher than the oxidation temperature of 850°C, prior to oxidation, and then the temperature of the heat treatment furnace is set to the oxidation temperature of 850°C. The structure is substantially the same as that of the previously described conventional example shown in FIG. 5, except that the oxidation is performed after the temperature has been lowered to a certain temperature.

FIG. 2 shows the results corresponding to FIG. 6 when thermal oxidation was carried out for 5 minutes by supplying 02 at a rate of 9ffi/min as shown in FIG. Comparing the values in FIG. 2 and the values marked by white circles in FIG. 6, the film thicknesses at the center of the Si4 plate are approximately equal. However, the film thickness at the periphery of the Si substrate is thinner in this embodiment.

Therefore, the uniformity of the film thickness is higher in this example.

FIG. 3 shows the results corresponding to FIG. 7 when thermal oxidation was performed as shown in FIG. 1 with a thermal oxidation time of 5 minutes and one cycle of about 90 minutes. In this example, the average value ±3σ range for all Si substrates was 39.07±4.30 people. As is clear from the comparison between FIG. 3 and FIG. 7, the uniformity of the film thickness is higher overall in this example.

The black circles in FIG. 4 indicate the results corresponding to the white circles in FIG. 4 when thermal oxidation was performed in which Ot was supplied at a rate of 91/min as shown in FIG. As is clear from the comparison between these black circles and white circles, in this example, even when the film thickness is thin, the film thickness is in good agreement with the theoretical equation that the film thickness is proportional to the 1/2 power of the thermal oxidation time. ing. Therefore, in this embodiment, the controllability of the film thickness is high even when the film thickness is small.

Further, the inventor of the present application conducted the following experiment in order to verify the above-mentioned consideration. That is, Experiment 1 and Experiment 2 were conducted on a St base substrate immediately after light etching the surface and a Si base substrate color on which an initial natural oxide film was formed to a thickness of 10 Å or more after being left for 1 day after light etching. The thickness of the thermal oxide film was obtained as shown in the table below.

In experiment 1, a Si substrate was inserted into a heat treatment furnace at 800°C.
The furnace temperature was raised to 1000℃, and Si was heated to 850℃.
The substrate was discharged from the heat treatment furnace. In Experiment 2, the furnace temperature was raised to 950° C., and the other conditions were the same as in Experiment 1.

Note that no oxidizing agent was supplied in either Experiments 1 and 2.

As is clear from the table of experimental results, the difference in film thickness, which existed by more than 10 Å before the heat treatment, almost disappeared after the heat treatment. From this result, it is considered that the initial native oxide film, that is, the contamination, was removed by evaporation in the high-temperature inert gas, and the clean surface of the Si substrate was exposed.

Note that although the above examples and experiments apply the present invention to the formation of a thermal oxide film on a Si substrate, the present invention
It can be applied to the formation of films on substrates other than i-substrates, and can also be applied to the formation of nitride films, epitaxial films, etc. by CVD or the like other than thermal oxidation.

〔Effect of the invention〕

In the film forming method according to the present invention, it is considered that the temperature of the substrate itself is highly uniform during film formation, and a film can also be formed that has a highly uniform thickness.

Further, it is thought that the influence of contamination of the substrate on film formation is small, and even thin films can be formed with good controllability.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the process of one embodiment of the present invention, FIG. 2 is a graph showing the relationship between the thickness of the thermal oxide film and the position on the substrate according to one embodiment, and FIG. FIG. 4 is a graph showing the relationship between the thickness of the oxide film and the position in the furnace. FIG. be. Figure 5 shows the process of a conventional example and is a graph corresponding to Figure 1, and Figure 6 shows the relationship between the thickness of the thermal oxide film and the position on the substrate in a conventional example, and Figure 2 The corresponding graph, FIG. 7, shows the relationship between the thickness of the thermal oxide film and the position in the furnace according to a conventional example, and is a graph corresponding to FIG. 3.

Claims (1)

[Claims] A film forming method in which a reactive gas is supplied to the substrate while the environmental temperature of the substrate is at a predetermined temperature, and a film is formed on the substrate by a reaction caused by the reactive gas, comprising: A film forming method comprising the steps of: raising the temperature to a temperature higher than the predetermined temperature; and supplying the supply after lowering the environmental temperature from the high temperature to the predetermined temperature.