JPH1079386A - Method of forming silicon dioxide film - Google Patents

Abstract

(57) [Problem] To form a silicon dioxide film while preventing generation of silicon clusters. SOLUTION: Under reduced pressure conditions of at least 40 Pa or more, the ratio of monosilane in the growth gas is 2.0% or less in molar ratio to the total amount of monosilane and nitrous oxide.
A silicon dioxide film is formed on the substrate 5 by chemical vapor deposition. Thus, a uniform film pressure distribution is realized while maintaining a practical growth rate, and a silicon dioxide film is formed while preventing generation of silicon clusters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to chemical vapor deposition (C).
VD) and a method of forming a silicon dioxide film on a substrate by VD).

[0002]

2. Description of the Related Art In a process of manufacturing a semiconductor device such as a MOS memory device (MOSRAM) or a static memory device (SRAM), a gate insulating film, a passivation film, and an interlayer are formed on a substrate such as a silicon wafer using silicon dioxide (SiO2). Forming an insulating film or the like has been performed.
Formation of a silicon dioxide film by a chemical vapor deposition method (CVD method) is performed by loading a wafer to be formed into a reaction furnace and supplying a growth gas to the reaction furnace.

[0003] The growth gas contains monosilane (SiH4) and nitrous oxide (N2O), and is typically formed at a temperature of about 700 ° C to about 850 ° C in a reactor.
A silicon dioxide film (SiO2 film) is formed on the wafer by H4 + 2N2O = SiO2 + 2H2O + 4N2. In the formation of the SiO2 film by such a conventional CVD method, the growth gas is based on the total amount of SiH4 and N2O.
Those containing iH4 in a molar ratio of 2.5% or more were used.

[0004]

However, in the formation of a SiO2 film by the conventional CVD method, a projection (silicon cluster) having a size of about several hundred angstroms is formed on the surface of the formed SiO2 film. There was a problem that it would. When the SiO2 film on which such a silicon cluster is formed is used, for example, as a gate insulating film of a semiconductor memory device, a predetermined gate withstand voltage cannot be obtained, and the reliability of the device is significantly reduced. For this reason,
The wafer on which the silicon cluster has been formed cannot be used for forming a semiconductor element, and the product yield has been significantly reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a method for forming a silicon dioxide film in which generation of silicon clusters is prevented.

[0006]

In order to achieve the above object, a method for forming a silicon dioxide film according to the present invention comprises the steps of: forming a silicon dioxide film on a substrate in a growth gas containing monosilane and nitrous oxide; In the method of forming by growing, the pressure is reduced to at least 40 Pa or more, and the ratio of monosilane in the growth gas is set to 2.0% or less in molar ratio with respect to the total amount of monosilane and nitrous oxide. I do.

In the formation of a SiO2 film by the CVD method, if the pressure condition is too low, the growth rate of the SiO2 film is considerably reduced, which is not practical. On the other hand, if the pressure is too high, the thickness distribution of the formed SiO2 film becomes uniform. Performance is reduced. If the molar ratio of SiH4 contained in the growth gas is too high, the concentration of SiH4 under the reduced pressure becomes higher than necessary, and silicon clusters are generated in the SiO2 film formed. Therefore, in the method of the present invention, a practical growth rate is realized by setting the pressure reduction condition to at least 40 Pa (Pascal) or more, and at the same time, the ratio of SiH4 in the growth gas is set to the sum of SiH4 and N2O. By setting the molar ratio to 2% or less with respect to the amount, the SiO2 film is formed while lowering the SiH4 concentration to suppress the absolute amount of SiH4 molecules in the growth gas and preventing the generation of silicon clusters.

Regarding the generation of silicon clusters in the formation of a SiO 2 film by the CVD method, silicon clusters tend to be less likely to occur when the pressure condition is high, and silicon clusters tend to be less likely to occur when the SiH 4 concentration is low. The relationship between the pressure condition and the SiH4 concentration is correlated to some extent, and in practice, when these two conditions are combined, the SiO2 can be generated without generating silicon clusters.
It is possible to form two films.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming a silicon dioxide film according to the present invention will be described with reference to examples. First, an apparatus for performing the method for forming a silicon dioxide film according to the present invention will be described with reference to FIG. The apparatus includes a cylindrical heater 1 and a heater 1.
An external reaction tube 2 accommodated inside the internal reaction tube, an internal reaction tube 3 accommodated inside the external reaction tube 2, and a boat 4 for holding a wafer 5 to be film-formed in the internal reaction tube 3 are provided. .
The upper end of the outer reaction tube 2 is closed to define a reaction chamber containing the inner reaction tube 3, and the inner reaction tube 3 is open at the upper end and communicates with the reaction chamber. This reaction chamber is a heater 1
The SiO2 film is formed on the wafer 5 housed in the reaction chamber at a predetermined temperature of 700 to 850 ° C.

A gas introduction pipe 6 is connected to the lower end of the internal reaction tube 3, and a growth gas supply source (not shown) is connected to the gas introduction pipe 6 so that the growth chamber containing SiH 4 and N 2 O in the reaction chamber. It is designed to supply gas. An exhaust pipe 7 connected to an exhaust device (not shown) is provided at the lower end of the external reaction pipe 2.
Are connected to each other, and the gas in the reaction chamber is exhausted from the exhaust pipe 7. Therefore, the growth gas introduced from the gas introduction pipe 6 flows through the internal reaction tube 3 containing the wafer 5, generates SiO 2 at a predetermined heating temperature, and forms an SiO 2 film on the wafer 5. Here, the pressure in the reaction chamber can be reduced to 40 Pa or more by adjusting the gas supply amount from the gas introduction pipe 6 and the exhaust amount from the exhaust pipe 7.

The step of forming a SiO 2 film using SiH 4 and N 2 O is generally performed at a temperature in the range of 700 ° C. to 850 ° C., and a temperature gradient from the lower part to the upper part of the heater 1 within the above-mentioned temperature range. The temperature of the lower portion of the heater 1 is set lower than that of the upper portion. The reason for providing the temperature gradient in this manner is that the reaction gas concentration is higher at the lower part of the heater 1, that is, at the lower side of the reaction chamber, and the reaction gas is consumed upward and the gas concentration becomes lower. This is to make the film thickness from the upper part to the lower part equal.

In the above apparatus, the pressure in the reaction chamber is set at 4
0 Pa, 80 Pa, and 160 Pa, and the ratio of SiH4 contained in the growth gas to the total amount of SiH4 and N2O is set to the following five molar ratios and gas flow rates.
The thickness 3 is applied to the entire surface of the silicon wafer 5 having a diameter of 8 inches.
A SiO2 film of 00 Å was formed. That is, (1) the molar ratio is 1/30 (that is, about 3.4
%), Gas flow rate is 35 SCCM for SiH4 and 10 for N2O.
50 SCCM, (2) 1/40 by mole ratio (ie,
2.5%), gas flow rate is 27 SCCM for SiH4, N2O
1050 SCCM, (3) 1/50 by mole ratio (ie, 2.0%), and SiH4 by gas flow rate of 21 SCCM, N
2O is 1050 SCCM, (4) 1/60 (ie, about 1.7%) by mole ratio, and SiH4 is 18 SCC by gas flow rate.
M, N2O is 1050 SCCM, (5) 1/7 in molar ratio
0 (ie, about 1.4%), with a gas flow rate of 15
SCCM and N2O were set to 5 types of 1050 SCCM.
The SiO2 film formed by this experiment was subjected to S
Tables 1 to 3 show the results of the EM observation.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

Table 1 shows a pressure of 40 Pa, and Table 2 shows a pressure of 80 Pa.
Pa, Table 3 shows the observation results of the SiO2 film formed at 160 Pa, and in each table, the presence of silicon clusters was observed corresponding to the molar ratio of SiH4 contained in the growth gas. In this case, the mark is marked with a circle, and when the presence of a silicon cluster is not observed, the mark is marked with an X. The uniformity of the film thickness is determined in the circumferential direction in the wafer,
The film thickness is measured at a plurality of points at equal intervals in the meridian direction, and a deviation is obtained. The film formation rate is obtained by dividing the average film thickness of the upper, middle, and lower wafers in the wafer processing region by the deposition time. Further, according to the refractive index, the crystalline state (film quality) of the film formation can be determined.

From the above table, regarding the generation of silicon clusters in the formed SiO 2 film, if the pressure conditions are high, silicon clusters are less likely to be generated, and SiH 4
It can be seen that the smaller the molar ratio, the lower the tendency for silicon clusters to occur. The reason why the silicon cluster hardly occurs when the pressure condition becomes high is that C
In the formation of the SiO2 film by the VD method, when the pressure is high, the moving speed of the SiH4 molecules and the N2O molecules in the growth gas is slowed, and the decomposition of N2O is performed smoothly, thereby suppressing the generation of silicon clusters. It is thought that. Also, the reason that the silicon cluster is less likely to be generated when the molar ratio of SiH4 is small is that the SiH4 concentration in the growth gas is reduced and the absolute amount of SiH4 molecules is reduced, so that the probability that Si atoms are aggregated is reduced. It is thought to be down.

As is clear from the above table, when the pressure reduction condition is 40 Pa, if the molar ratio of SiH4 is 1/50 or less, no silicon cluster is generated in the SiO2 film. The ratio is 1/4
When the value was set to 0 or less, no silicon cluster was generated in the SiO2 film, and no silicon cluster was generated in the SiO2 film under the reduced pressure condition of 160 Pa even when the molar ratio of SiH4 was 1/30. Therefore, the pressure reduction condition is 40 Pa to 1
60 Pa, and the ratio of SiH4 in the growth gas was SiH4 and N
1/50 in molar ratio to the total amount with 2O (ie,
2.0%) or less, by combining these two conditions, it is practically possible to form a SiO2 film without generating silicon clusters.

From a practical point of view, if the pressure is 40 Pa or less, the film forming speed becomes slow, and the film forming time is greatly required.
Along with the increase in the amount of expensive reactive gas used, a serious drawback is a decrease in throughput due to a reduction in the processing capability of the apparatus, and furthermore, a delay in subsequent steps, which is not suitable for the semiconductor device manufacturing process. Therefore, at a condition of 40 Pa or more and a molar ratio of 2.0 or less, in consideration of a practical film forming rate and film thickness uniformity, and further taking into account that a large change in the refractive index does not occur as shown in FIG. The pressure and the molar ratio may be appropriately selected.

[0020]

As described above, according to the method for forming silicon dioxide according to the present invention, the generation of silicon clusters can be prevented by setting the conditions of reduced pressure and the concentration of monosilane in the growth gas. A film can be formed. And the pressure reduction condition is at least 40 Pa or more,
Since the molar ratio of monosilane in the growth gas is 2.0% or less with respect to the total amount of monosilane and nitrous oxide, a silicon dioxide film having extremely high uniformity in film pressure distribution can be formed into silicon clusters. , And can be formed at a practical growth rate. Therefore, according to the method for forming silicon dioxide according to the present invention, since silicon clusters can be prevented from being formed in the formed silicon dioxide film, a semiconductor element having excellent performance such as dielectric strength can be manufactured. Also has the effect.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an apparatus for performing a method according to the present invention.

FIG. 2 is a graph showing the relationship between the concentration of monosilane and the quality of a silicon dioxide film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 2 External reaction tube 3 Internal reaction tube 4 Boat 5 Wafer 6 Gas introduction tube 7 Exhaust tube

Claims (1)

[Claims] 1. A method for forming a silicon dioxide film on a substrate by chemical vapor deposition in a growth gas containing monosilane and nitrous oxide, wherein the pressure of the growth gas is at least 40 Pa or more, and the ratio of monosilane in the growth gas is Wherein the molar ratio is 2.0% or less with respect to the total amount of monosilane and nitrous oxide.