JP2801604B2 - Silicon oxide film forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for forming a silicon oxide film used for manufacturing a semiconductor such as an VLSI device.

(Prior Art) Thin film forming methods used in the manufacture of semiconductors such as VLSI devices are roughly classified into chemical vapor deposition (Chemical Vapor Deposition) methods.
Deposition: CVD) and physical vapor deposition (Physical Vapor
por Deposition (PVD). The CVD method is a method of forming a thin film on a substrate by utilizing a chemical reaction on the substrate surface or in a gas phase, and is mainly used for forming an insulating film such as a silicon oxide film or a silicon nitride film. The PVD method is a method of forming a thin film by causing deposited particles generated in a gas phase to collide with a substrate, and is mainly used for forming a metal film.

On the other hand, in recent VLSI devices, a technique of depositing a thin film in a trench having a high aspect ratio (depth / width) is becoming essential. However, for example, the conventional plasma CVD method (for example, JLV
ossen &W.Kern; Thin Film Process; Academic Press 1
978) and the like, as shown in FIG.
When, for example, a silicon oxide film 3 is buried in the groove 2 formed on the surface of the silicon substrate 1, the deposition species generated in the gas phase in the vicinity of the corner 4 of the silicon substrate 1 are largely deposited, and the deposition species gradually reach the bottom of the groove 2. It becomes difficult to enter, and a cavity is formed inside the groove 2 to deteriorate the step coverage characteristics.

As a method of improving the step covering shape, a technique called a bias sputtering method which is one of the PVD methods is known (for example, T. Mogami, Morimoto &Okabayasi; Extended).
abstracts 16th conf.Solid State Devices & Materia
ls.Kobe, 1984, p. 43). In this method, for example, a silicon oxide film is deposited by using a competitive reaction with the deposited species while physically sputtering the substrate surface with Ar ions. Therefore, unlike the case of the plasma CVD method,
Since the deposition does not occur near the corners of the silicon substrate but occurs only on the flat portion (substrate surface and groove bottom), the insulating film can be deposited in the groove. However, in this method, since the deposited species in the gas phase obliquely enter the groove, it is still difficult to fill the groove with an aspect ratio> 1. Further, since a competitive reaction between the removal of the deposition species by physical sputtering and the deposition is used, the effective deposition rate is low, and the productivity is extremely low. Furthermore, irradiation damage in plasma is inevitable.

Therefore, recently, the ECR bias sputtering method (for example, H. Oikaw
a; SEMITECHNOLOGY SYM.1986 E3-1) has been proposed. However, even though this method reduces the above-mentioned problem, it is not an essential solution.

In addition, for example, the pyrolysis method of TEOS (eg, RDRang,
Y.Momose &Y.Nagakubo; IEDM.TECH.DIG.1982, p.237)
When a silicon oxide film is formed by using, a large surface movement of the deposited species occurs. Therefore, as shown in FIG.
The silicon oxide film 3 deposited in the groove 2 formed on the surface of the silicon substrate 1 exhibits excellent step coverage characteristics. However, after the silicon oxide film 3 is buried in the groove 2 by this method, if the silicon oxide film 3 is washed, for example, with a diluted HF solution, as shown in FIG. ), The removal speed of the silicon oxide film 3 becomes abnormally high,
Eventually, burying flattening cannot be realized. This is caused by groove 3
It is considered that the strain between the silicon oxide films 3 grown from the side walls of the trench 3 remains near the center of the groove 3.

As described above, it has been considered that it is extremely difficult to embed an insulating film such as a silicon oxide film in a trench having a high aspect ratio even by a method of forming a thin film in a conformable manner.

In order to solve such a problem, tetramethylsilane (Si (CH ₃ ) ₄ ; TMS) gas is reacted with oxygen atoms excited by microwave discharge, and the substrate is cooled below the boiling point of the reaction product. Accordingly, a method of depositing a silicon oxide film in a groove having a high aspect ratio (liquid phase oxidation method) is known (for example, S. Noguchi et al .; SSDM S-II-13).
(1987) 451). According to this method, FIGS.
As shown in FIG. 3C, since the silicon oxide film 3 is deposited from the bottom of the groove 2 formed on the surface of the silicon substrate 1, the silicon oxide film 3 can be easily embedded in the groove 2 having a high aspect ratio. it can. However, in this method, the raw material gas is oxidized by the oxygen atoms activated by the microwave discharge, so that the deposition parameters such as the distance between the microwave discharge part and the sample wafer, the microwave discharge power and the microwave discharge pressure increase. However, there is a problem that the apparatus becomes complicated and the control of the deposition parameters becomes complicated.

(Problems to be Solved by the Invention) As described above, according to the conventional liquid phase oxidation method using microwave discharge, there is an advantage that a silicon oxide film can be deposited in a groove having a high aspect ratio. There is a problem that the deposition parameters related to the deposition increase and the deposition control becomes complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method capable of depositing a silicon oxide film in a groove having a high aspect ratio by a liquid phase oxidation method without using a microwave discharge, thereby controlling deposition parameters and simplifying an apparatus. It is in.

[Structure of the Invention] (Means and Action for Solving the Problems) According to a method for forming a silicon oxide film of the present invention, a substrate to be processed having a groove formed on a surface thereof is accommodated in a reaction vessel capable of being evacuated. Wherein SiH _a X _b (where X is at least one halogen atom selected from F, Cl, and Br, a = 0 to 4,
b = 0 to 4, a + b = 4) and a reactive gas containing oxygen capable of chemically reacting with the raw material gas are introduced, and the raw material gas and the reactive gas are reacted without exciting oxygen atoms. By setting the pressure in the reaction vessel and the temperature of the substrate to be processed under the condition that the gas or a reaction product of the gas becomes a liquid on the substrate to be processed, a silicon oxide film is formed in the groove on the surface of the substrate to be processed. Is embedded.

In the present invention, as the reactive gas containing oxygen capable of chemically reacting with the source gas, for example, H ₂ O, O ₂ , NO, NO ₂ ,
An organic compound gas containing CO, CO ₂ or at least silicon and oxygen can be used.

When the raw material gas and the reactive gas used in the method of the present invention and their reaction are exemplified, for example, SiC is used as the raw material gas.
When l ₄ and H ₂ O are used as a reactive gas, a hydrolysis reaction of SiCl ₄ + 2H ₂ O → SiO ₂ + 4HCl occurs. In addition, H _{2 is used} as a reactive gas.
When a siloxane compound having a functional group -OY is used instead of O, A condensation polymerization reaction occurs.

These reactions are intense chemical reactions, and the reactions occur without using the active species excited by the microwave discharge, so that the raw material gas, the reactive gas, or a reaction product of both becomes liquid on the substrate to be processed. If the pressure in the reaction vessel and the temperature of the substrate to be processed are set as the conditions, the silicon oxide thin film can be embedded in the groove on the surface of the substrate to be processed. Therefore, according to the method of the present invention, unlike the conventional liquid phase oxidation method using microwave discharge, control of deposition parameters when depositing a silicon oxide film in a groove having a high aspect ratio by the liquid oxidation method is performed. Can be easy.

In the present invention, the pressure in the reaction vessel and the temperature of the substrate to be treated cannot be unequivocally limited because the conditions for forming a liquid also vary depending on the type of the raw material gas, the reactive gas, or the reaction product of both. For example, for the above-mentioned reaction between SiCl ₄ and H ₂ O, when the pressure in the reaction vessel is about 2 Torr,
The temperature of the substrate to be processed may be 0 ° C. or lower, preferably −15 ° C. or lower. However, the temperature of the substrate to be processed for liquefying the raw material gas, the reaction gas, or the reaction product of both is determined by the pressure in the reaction vessel. , The temperature can be set higher.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic structural view of a reactor for carrying out the method of the present invention. In FIG. 1, a sample holder 12 is provided in a reaction vessel 11, and a heater 13 is provided in the sample holder 12, and a cooling pipe 14 is connected to the sample holder 12. The sample holder 12 is placed on the sample holder 12. It is possible to control the temperature of the sample 15 in the range of −100 ° C. to 600 ° C. In this device, a nitrogen gas cooled by liquid nitrogen is used as a cooling medium. The inside of the reaction vessel 11 is evacuated by a vacuum evacuation device 16, and the internal pressure can be adjusted by a conductance valve 17. A source gas and a reactive gas are introduced into the reaction vessel 11 from inlets 18 and 19, respectively, and supplied to the surface of the sample 15. Then, of the source gas, the reactive gas, and the reaction product of both, the residual gas not involved in the deposition is exhausted by the vacuum exhaust device 16.

Next, an embodiment in which a silicon oxide film is actually deposited using this apparatus will be described.

Example 1 In this example, silicon tetrachloride (SiC
l _4), it was used water (H ₂ O) as a reactive gas. Reaction vessel 1
Accommodating the silicon substrate in which the groove of the aspect ratio of 5 is formed in the 1, 12 sccm flow rate of SiCl _4, the partial pressure ratio of SiCl ₄ and H ₂ O a _{(SiCl 4 / H 2 O)} 1/2, the reaction vessel The deposition rate and shape of the silicon oxide film when the pressure in 11 was set to 2 Torr and the substrate temperature was changed were examined. FIG. 2 shows the relationship between the substrate temperature, the deposition rate, and the deposition shape.

As shown in FIG. 2, the temperature of the silicon substrate 1 is zero.
At a temperature of not less than ° C., the silicon oxide film 3 was deposited in an overhanging state on the upper part of the groove 2, and a cavity was formed in the groove 2. On the other hand, when the temperature of the silicon substrate 1 is set to -15 ° C. or lower, the silicon oxide film 3 is formed from the bottom of the groove 2, the groove having an aspect ratio of 5 can be easily buried, and the surface is completely flattened. .

The reaction mechanism between the source gas and the reactive gas in this embodiment will be considered. Here, the phase diagram of H ₂ O is shown in FIG.
FIG. 4 shows a phase diagram of SiCl ₄ . Under the above conditions, the partial pressure of H ₂ O is about 1.3 Torr, and the partial pressure of SiCl ₄ is about 0.7 Torr.
It is. However, from FIGS. 3 and 4, it is considered that neither H ₂ O nor SiCl ₄ becomes liquid on the substrate at −15 ° C. Therefore, these gases are SiCl ₄ + H ₂ O → SiCl ₃ (OH) + HCl SiCl ₄ + 2H ₂ O → SiCl ₂ (OH) ₂ + 2HCl SiCl ₄ + 3H ₂ O → SiCl (OH) ₃ + 3HCl SiCl ₄ + 4H ₂ O → Si By the reaction of (OH) ₄ + 4HCl, reaction intermediates of SiCl ₃ (OH), SiCl ₂ (OH), SiCl (OH) ₃ , and Si (OH) ₄ are generated, and these reaction intermediates are liquefied to produce grooves. And then further into SiCl ₃ (OH) + H ₂ O → SiO ₂ + 3HCl SiCl ₂ (OH) ₂ + H ₂ O → SiO ₂ + 2HCl + H ₂ O SiCl (OH) ₃ + H ₂ O → SiO ₂ + HCl + 2H ₂ O Si (OH) ₄ + H ₂ O → SiO ₂ + 3H ₂ O It is considered that hydrolysis occurs and a silicon oxide film is formed.

Inspection of the infrared absorption spectrum of this deposited film revealed that it was a silicon oxide film having Si—O, Si—OH and OH bonds immediately after deposition. But,
By performing annealing at a low temperature of 300 ° C, Si-O
Each bond of H and OH disappeared, and a complete silicon oxide film was obtained.

In the above, the case where SiCl ₄ is used as a source gas and H ₂ O is used as a reactive gas has been described, but SiF ₄ and H ₂ O,
With each combination of SiBr ₄ and H ₂ O, the same deposition shape and film quality as described above can be obtained.

Example 2 In this example, silicon tetrachloride (SiC
l ₄ ), tetramethoxysilane (Si (OC
H _{3) 4)} was used. A silicon substrate on which a groove having an aspect ratio of 5 was formed was placed in a reaction vessel 11, and the flow rate of SiCl ₄ was set to 12 s.
ccm, the partial pressure ratio between SiCl ₄ and Si (OCH ₃ ) ₄ (SiCl ₄ / Si (OC
H ₃ ) ₄ ) was set to 1, the pressure in the reaction vessel 11 was set to 2 Torr,
The deposition rate and deposition shape of the silicon oxide film when the substrate temperature was changed were examined. FIG. 5 shows the relationship between the substrate temperature and the deposition rate.

As shown in FIG. 5, the temperature of the silicon substrate 1 is −40 ° C.
In the above case, the silicon oxide film 3 was deposited in an overhanging state on the upper part of the trench 2, and a cavity was formed in the trench 2. On the other hand, when the temperature of the silicon substrate 1 is set to -50 ° C. or lower, the silicon oxide film 3 is formed from the bottom of the groove 2, the groove 2 having an aspect ratio of 5 can be easily buried, and the surface is completely flattened. .

The reaction mechanism between the source gas and the reactive gas in this embodiment will be considered. Under the conditions described above, SiCl ₄ and Si (O
The partial pressure of CH ₃ ) ₄ is about 1 Torr. According to FIG.
It is considered that SiCl ₄ becomes liquid on the silicon substrate 1. Therefore, it is considered that SiCl ₄ liquefies and flows into the groove, and the silicon oxide film 3 is formed by a polycondensation reaction of SiCl ₄ + Si (OCH ₃ ) ₄ → 2SiO ₂ + 4CH ₃ Cl.

When the infrared absorption spectrum of this deposited film was examined, immediately after deposition, each bond of Si—O, Si—OH, and OH was present, but each bond of Si—C, C—O, etc. was not found. It was found that the film was a silicon oxide film containing no carbon. However, by performing annealing at a low temperature of 300 ° C, Si
The bonds of -OH and OH disappeared, and a complete silicon oxide film was obtained.

Further, SiCl ₄ as a raw material gas in the above has described the case of using the Si (OCH _{3) 4} as the reactive gas, SiCl ₄ and _{Si (OC 2 H 5) 4} , SiF 4 and Si (OCH _{3) 4} , SiF ₄ and Si (OC ₂ H ₅ ) ₄ can provide the same deposition shape and film quality as described above.

[Effects of the Invention] As described above in detail, according to the method of the present invention, the control of deposition parameters when depositing a silicon oxide film in a groove having a high aspect ratio by a liquid oxidation method is simplified, and its industrial value is increased. Is big.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a reaction apparatus used in an embodiment of the present invention, and FIG. 2 shows a relationship between a temperature of a silicon substrate and a deposition rate and a deposition shape of a silicon oxide film in the embodiment 1 of the present invention. FIG. 3 is a phase diagram of H ₂ O, FIG. 4 is a phase diagram of SiCl ₄ , FIG. 5 is a graph showing a temperature of a silicon substrate, a deposition rate and a deposition shape of a silicon oxide film in Example 2 of the present invention. FIG. 6 shows a conventional plasma
FIGS. 7 (a) and (b) are cross-sectional views of a silicon substrate showing problems of the conventional TEOS pyrolysis method, showing the problems of the CVD method, and FIGS. 8 (a) to (b). (c) is a sectional view of a silicon substrate showing a conventional liquid phase oxidation method. DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Groove, 3 ... Silicon oxide film, 11 ... Reaction vessel, 12 ... Sample holder, 13 ... Heater, 14 ... Cooling tube, 15 ... Sample, 16 ... Vacuum Exhaust system,
17… Conductance valve, 18, 19 …… Inlet.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H01L 21/316 H01L 21/31

Claims (2)

(57) [Claims] 1. A substrate to be processed having a groove formed in a surface thereof is accommodated in a reaction vessel capable of being evacuated, and SiH _{a Xb} (where X is at least one member selected from F, Cl, and Br) is contained in the reaction vessel. A source gas represented by a halogen atom, a = 0 to 4, b = 0 to 4, a + b = 4) and a reactive gas containing oxygen capable of chemically reacting with the source gas are introduced, and the oxygen atom is excited. Without setting the pressure in the reaction vessel and the temperature of the substrate to be processed under the condition that the raw material gas, the reactive gas, or the reaction product of both becomes liquid on the substrate to be processed, A method for forming a silicon oxide film, comprising: burying a silicon oxide film in a groove on a surface of a base. 2. The reactive gas is H ₂ O, O ₂ , NO, NO ₂ , CO, CO ₂
2. The method according to claim 1, wherein the gas is an organic mixed gas containing at least silicon and oxygen.