JPH02153072A - Method for depositing silicon oxide film - Google Patents

Abstract

PURPOSE:To deposit a silicon oxide film at a high deposition rate and a low film formation temp. by using specified starting material when a silicon oxide film is deposited by a chemical vapor growth method. CONSTITUTION:A silicon oxide film is deposited by a chemical vapor growth method with heteroalkoxysilane represented by a formula Si(OR)n-(OR')4-n (where R and R' are 1-3C different alkyl groups and n is 1, 2 or 3) as starting material. The silicon oxide film is deposited at a high rate, productivity is improved and process control is facilitated by a reduced film formation temp.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for depositing a silicon oxide film on a semiconductor device or the like by chemical vapor deposition.

Traditionally, silicon oxide films (SiO□) have been used to insulate between aluminum interconnects and aluminum layers in semiconductor device structures, and as capacitor dielectrics for charge retention in trench memory cells. It is used.

As is well known, D-RAM density has increased from 1 megabit to 4 megabits.
As the data size increases to megabits and even 16 megabits, device structures are increasingly becoming three-dimensional and finer. For example, with aluminum wiring.

With the progress of 2N or three-layer and three-dimensional technology, the line width and line spacing of aluminum interconnects in the -layer are becoming smaller and smaller, and three-dimensional memory cells, as typified by the trench structure, are becoming a reality. It's progressing.

Due to this current situation, the performance requirements for silicon oxide films are becoming higher, and improvements to conventional silicon oxide film forming methods are desired.

That is, conventionally, this Si film has been deposited by chemical vapor deposition (hereinafter abbreviated as CVD) using SiH and O2 or N and O as oxidizing agents.
In the current situation where the spacing between aluminum interconnections has become narrower as devices become more three-dimensional and miniaturized, such conventional methods have poor step coverage and are capable of depositing a film with a uniform thickness faithful to the underlying shape. Particularly in locations where the underlying surface is extremely uneven, such as aluminum wiring, and where a three-dimensional film is to be deposited, the deposited films stick together in localized areas, creating voids, which can act as traps for contamination. This has caused problems such as deterioration of film quality and, in turn, restrictions on device structure and performance.

In order to improve the poor step coverage of the method using SiH4 as a raw material, recently tetraethoxysilane (ethyl orthosilicate, Si(O
C*Hs)4) is beginning to be used.

How to use this tetraethoxysilane.

Using tetraethoxysilane and ○ as an oxidizing agent as raw materials
The so-called ozone method atmospheric pressure thermal CVD deposits a SiO□ film at a temperature of around 400°C under a pressure of OO to 760 Torr.
Alternatively, tetraethoxysilane and 02 as an oxidizing agent are used as raw materials under a pressure of 1 to 20 Torr.

S while applying high frequency plasma at a temperature of around 400℃.
A so-called plasma method low pressure CVD for depositing an iO2 film is known, and these methods have recently attracted attention as a technique that can deposit an SiO2 film with good step coverage despite the low temperature of around 400°C.

However, the above CVD using this tetraethoxysilane
The deposition rate is as low as 1000 to 2000 people/min for ozone atmospheric pressure thermal CVD and 2000 to 3000 people/min for plasma low pressure CVD at 400°C. 1~
When a film thickness of 2 or more tiles is required, a considerable amount of time is required for film formation, the range of application is limited, and productivity is poor.

Furthermore, although both of the above two CVD methods can form films at relatively low temperatures, a method that can form films at even lower temperatures is desired due to limitations in the device process and device materials. ing.

However, in the above two methods using tetraethoxysilane as a raw material, as shown in the comparative example described later, lowering the film forming temperature significantly reduces the deposition rate and reduces productivity, so lowering the film forming temperature is not possible. This was difficult in practice.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a method capable of depositing a silicon oxide film at a high deposition rate and at a lower temperature than conventional methods while maintaining good step coverage.

In order to achieve the above object, the inventors of the present invention have conducted intensive studies and found that tetraethoxysilane, which is conventionally used in a method for depositing silicon oxide films by chemical vapor deposition (CVD), has been developed. Instead, a heteroalkoxysilane represented by the following general formula (% formula %) (wherein R and R' are mutually different alkyl groups having 1 to 3 carbon atoms, and n is 1, 2 or 3) is used as a raw material. When used as a SiO2 film, it is possible to deposit a SiO2 film at high speed under the same film forming conditions as conventional tetraethoxysilane while maintaining the good step coverage that is an advantage of tetraethoxysilane, reducing the film forming time. We discovered that even if the film formation temperature is lowered, it is possible to maintain a sufficiently high deposition rate for practical use, unlike tetraethoxysilane, and it is possible to meet the demands for lowering the temperature of device processes. This is what we have come to do.

The reason why the deposition rate of heteroalkoxysilane according to the method of the present invention is higher than that of tetraethoxysilane is not necessarily clear, but unlike tetraethoxysilane, the alkoxy groups of heteroalkoxysilane are not all the same;
It is inferred that this is because the uneven distribution of electron density occurs due to the molecular structure, and chemical bonding sites where breakage and decomposition are likely to occur occur, contributing to the high deposition rate and low film forming temperature.

The present invention will be explained in more detail below.

The method of the present invention uses the following general formula % formula % as a silicon oxide film forming raw material. ) is used.

Here, the alkyl group having 1 to 3 carbon atoms is a methyl group (Me
), ethyl group (Et) + n or i-propyl group (Pr
), Therefore, the heteroalkoxysilane of the present invention has two or more of methoxy, ethoxy, n- or i-propoxy groups in one molecule. It should be noted that groups of butoxy or higher cannot be used in production because the boiling point of the silane containing skeletons becomes high.

Among the heteroalkoxysilanes according to the present invention, for example, S
L(OMe)3(OEt) (boiling point 130°C).

S i (OMe)z (OE t)z (boiling point 142℃
)t Si(OMe)(OEt)s (boiling point 155℃L
Si(OMe), (OPr) (boiling point 138°C).

S L (OMe), (OP r), (boiling point 154℃
) etc., these boiling points are higher than those of conventional tetraethoxysilane (
It has a boiling point of 168°C) and is easy to use in production.

In other words, since tetraethoxysilane is a low vapor pressure and high boiling point substance as a CVD raw material, it tends to condense in the piping or the reactor when heating the evaporator and inserting the carrier gas into the reactor. In order to accurately control the flow rate, it was a burden on the equipment, such as heating all the pipes along the way to prevent condensation, and special measures needed for control parts such as mass flow controllers in the middle of the pipe, but Tetra By using the above-mentioned heteroalkoxysilane having a boiling point lower than that of ethoxysilane, the burden on these devices can be reduced.

The heteroalkoxysilane according to the present invention can be obtained by a known method, for example, the following transesterification reaction method 5l(OR)4 + (4-n) R'○H-+5i(
OR)n(OR'), -n+(4-n)ROI (or the following disproportionation method nSi(OR)4+(1-n)SL(OR')4-+5
i(OR)rl(OR'),.

After the reaction, it can be purified to the purity required for CVD by operations such as distillation.

In this case, the heteroalkoxysilane gradually undergoes the following redisproportionation reaction 5i(OR)n at a high temperature of 100°C or higher.
(OR'), n # 5i (OR), +5i (OR')
4 is formed, homoalkoxysilane (5i(ORχi5
In order to return to i(OR')4), it is preferable to perform distillation, etc. at a temperature lower than 100°C.

Furthermore, if substances with different boiling points coexist in the CVD evaporator, the composition evaporated from the evaporator will change moment by moment, affecting the film forming conditions. Therefore, the purity of heteroalkoxysilane must be 95% or higher. It is preferable that there be.

When performing CVD using the heteroalkoxysilane according to the present invention, it can be vaporized from an evaporator or the like by a known method and sent to a reactor. in this case.

For example, conventional tetraethoxysilane is generally evaporated at a temperature in the evaporator of 60 to 80°C (vapor pressure of tetraethoxysilane at 60°C is 13 ma + Hg, 80°C
The temperature range of the heteroalkoxysilane according to the present invention, in which the vapor pressure of 36 °C Hg) corresponds to the vapor pressure of tetraethoxysilane in this temperature range, is, for example, Si(OMe), (OEt) 28 to 47 °C SL (
OMe)z(OEt)2 36~57℃S xco M
e) (OE t)z 47~68℃SL(OMe
), (OPr) 34-55℃Si(OMe),
(OPr), 44-67℃Si(OMe)(OP
r), 60-80''C, and therefore can be selected from this temperature range.

When the heteroalkoxysilane according to the present invention is used as a raw material, normal conditions can be used for film formation in a CVD reactor.
This can be carried out under the same conditions as when conventional tetraethoxysilane is used.

For example, in ozone atmospheric pressure CVD, the deposition substrate temperature is 250
~450℃, reactor pressure 100~760Torr, O3
The concentration can be 1000-20000 ppm, 03/heteroalkoxysilane (flow rate ratio) ~0.3-3,
In plasma method low pressure CVD, the deposition substrate temperature is 250 to 450.
“C1 reactor pressure 1-20 Torr.

02/heteroalkoxysilane (flow rate ratio) = 10-3
0, a high frequency frequency of 13 MHz, a high frequency power density of 0.1 to 3 W/cd, and a high frequency power density of 0.1 to 3 W/cd.

1. Lesson UυHhinder The method of the present invention uses heteroalkoxysilane instead of Tej-raethoxysilane, which has been conventionally used as a raw material, in a method for depositing silicon oxide films on semiconductor devices, etc. by chemical vapor deposition. By using
It is possible to deposit silicon oxide films at high speed even under the same deposition conditions as conventional methods, improving productivity by shortening deposition time and expanding the range of applications, and it is also possible to lower the deposition temperature than before. Since this is possible, it is possible to lower the temperature of the device process, and it is expected that the selection range of materials for devices and the like will be expanded and process control will be facilitated.

EXAMPLES Hereinafter, the present invention will be specifically explained by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1] S i (OMe) z (OE t) z (dimethoxyjethoxysilane) was put into an evaporator as a raw material, and the liquid temperature was set at 42°C (the vapor pressure of dimethoxyjethoxysilane at 42°C was 18 oalg). ) and N2 as carrier gas.
was passed through the evaporator at a flow rate of 3 Nfl/min, and N2 containing dimethoxyjethoxysilane was supplied to the gas disperser in the reactor.

At the same time, 0□ was flowed through the ozonizer at a flow rate of 7.5 NQ/win, and 02, which had a concentration of 03 of 9500 ppm in the ozonizer, was supplied to the gas disperser in the reactor, and the N2 containing the dimethoxyjethoxysilane and the gas Mixed in a disperser and fed to the reactor at a pressure of 760 Torr.

The temperature of the silicon wafer placed on the susceptor in the reactor was set to 4.
00°C, and deposited Sin on the silicon wafer.

A film was deposited. The deposition rate at this time was 3500 people/win based on the measurement results of the film thickness after deposition.

In addition, a Sio film was deposited in the same manner as above except that the temperature of the silicon wafer was 300°C.

The deposition rate at that time was 3000 people/win.

[Example 2] A silicon wafer patterned with aluminum wiring having a width of 0.7 mm and a height of 1-1 and a wiring spacing of 1.3-1 was used, and the temperature of the silicon wafer in one reactor was set to 400°C. Sin under the same conditions as 1.

A film was deposited.

When the deposition state was observed using a scanning electron microscope after a deposition time of 1 minute and 3 minutes, it was found that the deposition thickness was uniform and no voids were formed between the interconnects, demonstrating the good step coverage and void-free nature of the method of the present invention. The groove embedding property was confirmed.

[Comparative example]

5L (OEt), (tetraethoxysilane) as raw material
SiO was deposited on a silicon wafer in the same manner as in Example 1, except that it was placed in an evaporator and the liquid temperature was kept at 65°C.
2 was deposited. In addition, 65℃ of tetraethoxysilane
The vapor pressure at 18 oal (g) is the same as the vapor pressure at 42 °C of dimethoxyjethoxysilane in Example 1,
Therefore, the feed rate of raw material Si is the same as in Example 1.

The deposition rate of S io is as follows when the temperature of the silicon wafer is 40
1500 people/min at 0℃, 700 people/min at 300℃
It was a win/win.

Comparing Example 1 and Comparative Example, the supply rate of raw material Si is the same, but the deposition rate of Comparative Example is 1/2 to 1/2 of that of Example 1.
The deposition rate of the comparative example is significantly lower, especially when the silicon wafer temperature is 300°C.1 The deposition rate of the method of the present invention is good, and it is practical even at lower temperatures than the conventional method. It could be confirmed.

Applicant: Shin-Etsu Chemical Co., Ltd. Agent: Patent Attorney Takashi Kojima

Claims (1)

[Claims] 1. In a method of depositing a silicon oxide film by chemical vapor deposition, the following general formula Si(OR)_n(
OR')_4_-_n (However, in the formula, R and R' are mutually different alkyl groups having 1 to 3 carbon atoms, and n is 1, 2 or 3.) A method for depositing a silicon oxide film.