JP2637110B2 - Thin film formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a thin film forming method applied to the manufacture of semiconductors such as VLSI devices.

(Prior art) Conventionally used thin film forming methods can be roughly classified into a chemical vapor deposition method (Chemical Vapor Deposition: CVD method) and a physical vapor deposition method (Physical Vapor Deposition: PVD method).
are categorized. The CVD method is a method of forming a thin film on a substrate by using 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 forms 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, the aspect ratio (depth /
Techniques for depositing thin films in trenches with high width are becoming essential, but conventional plasma CVD methods (for example,
L. Vossen & W. Kern: Thin Film Process: Academic Press
1978), when an insulator is to be deposited in a deep groove formed in a silicon (Si) substrate, a large amount of the insulating species generated in the gas phase will be deposited on the corners of the groove. Therefore, the deposited species gradually become difficult to deposit at the bottom of the groove, and the inside of the groove is not completely filled with the insulator, and a cavity is generated,
There is a problem that the step coverage characteristics deteriorate. As a method for solving this problem, a technique called bias sputtering, which is one of PVD methods, is used (for example, T.Mo.
gami, Mmorimoto & Okabayashi: Extended abstracts 16th
conf.Solid State Devices & Materials.Kobe1984, P4
3). In this method, for example, a silicon oxide film is formed while applying physical sputtering to the substrate surface with argon (Ar) ions, so that no remarkable deposition of insulator occurs at the corners of the groove, and the substrate and the inside of the groove are not formed. The deposited film can be formed flat. However, since the deposited species in the gas phase enter the groove obliquely, it is still difficult to fill the groove if the aspect ratio is 1 or more. Furthermore, since a competitive reaction between the removal action of the deposited film and the deposition action by physical sputtering is used, the net deposition rate is not low and the productivity is extremely poor. Further, since the substrate is placed in the plasma, there is a problem that irradiation damage to the substrate cannot be avoided. As still another method, recently, an ECR bias sputtering method (for example, H.Oikawa: SEMITE
CNOLOGY SYM.1986 E3-1) This method has been proposed, and although the problem of the bias sputtering method described above is reduced, it is not an essential solution. In addition, for example,
TEOS pyrolysis method (eg RDRang, Y. Momose & Y. Nagakub)
o: Using IEDM.TECH.DIG.1982, P237), when a silicon oxide film is formed on a substrate such as silicon or in a groove formed in the substrate, excellent step coverage characteristics are exhibited due to large surface movement of the deposited species. Can be embedded. However, the oxide film embedded in the trench by this method was diluted, for example.
When the cleaning process is performed with an HF solution or the like, the removal rate of the oxide film in the central portion of the embedded oxide film is abnormally high, so that the flattening of the embedded film cannot be realized after all. It is considered that this is because the distortion between the oxide films grown from both sides of the groove wall remains near the center. As described above, it has been considered that embedding in a groove having a high aspect ratio is extremely difficult even by a method of forming a thin film in a conformable manner.

As a method for solving the problem that a thin film cannot be embedded in a groove having a high aspect ratio cc formed on a substrate by the above-described conventional method, the present inventors first formed a groove on a surface in a reaction vessel. While accommodating the treated substrate and introducing a reactive gas excited in at least a region different from the reaction vessel, exhausting the inside of the reaction vessel, and raising the temperature of the treated substrate to the reaction vessel A method of forming a thin film has been proposed in which the grooves on the surface of the substrate to be treated are filled with a thin film by cooling the gas to be introduced or the boiling point of the active species generated by the excitation below the boiling point (Japanese Patent Application No. 62-13838). issue).

According to this method, the groove formed in the substrate can be completely filled with the thin film, and further, the thin film can be formed on the substrate. However, when a silicon oxide film is deposited by this method, for example, a temperature lower than the boiling point of a reaction product by tetramethyl cytene (Si (CH ₃ ) ₄ : TMS) gas and oxygen atoms excited by microwave discharge is used.
When the substrate is cooled to about 40 ° C. and the temperature is rapidly returned to room temperature, or when an annealing process is performed to achieve the same density of the film, the problem that the formed film peels off from the substrate may occur. It was revealed.

(Problems to be Solved by the Present Invention) The present invention arises when the thin film is formed in the above-mentioned thin film forming method of the present inventors, when the temperature is rapidly returned to room temperature or an annealing step is added. An object of the present invention is to provide a method for forming a thin film that does not cause peeling of the thin film from a substrate.

[Configuration of the invention]

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention accommodates a substrate to be processed having a groove or a stepped portion on its surface in a reaction vessel, and includes a first substrate in the reaction vessel. While introducing the reactive gas and the second reactive gas, the first reactive gas is excited, the inside of the reaction vessel is evacuated to a predetermined pressure, and the temperature of the substrate to be processed is increased. By controlling the reaction intermediate product generated by the reaction of the excited first reactive gas and the second reactive gas to a boiling point at or below the pressure under the pressure, and liquefying the reaction intermediate product, A step of embedding a groove or a step in the surface of the substrate to be processed with a thin film; prior to embedding the groove or the step with a thin film, a thin film in which the groove or the step is preliminarily embedded in the surface of the groove or the step and the substrate. Provided is a method for forming a thin film, comprising a step of applying a thin film having good bonding with a processing substrate.

(Function) According to the present invention, by the action of the thin film previously applied to the surface of the groove or the step portion of the substrate to be processed, the bonding of the thin film embedding the groove or the step portion to which the thin film is applied and the substrate to be processed. The property becomes good. Further, after that, even if the substrate to be processed is annealed or the substrate to be processed is returned to normal temperature, the thin film embedded in the groove or the step becomes difficult to peel off from the substrate to be processed.

(Embodiment) Before describing an embodiment of a thin film forming method according to the present invention, first, an apparatus used in the embodiment method will be described. That is, FIG. 1 is a schematic configuration diagram of an apparatus used in the method of the embodiment of the present invention. This device has the following configuration.

Inside the reaction vessel (1), a substrate to be processed (3) having a groove or a step on its surface placed on a sample holder (2) is accommodated. ,
The active species of the first reactive gas X (6) and the second reactive gas (7) are introduced through the gas introduction pipes (4) and (5), respectively, and the exhaust gas is connected to the exhaust system. The pipe (8) is opened to be evacuated. Here, the first and second reactive gases are mass flow controllers (not shown).
To adjust the flow rate. The activation of the first reactive gas (6) is performed in a microwave discharge section (9) connected to the gas introduction pipe (4). here,
The gas introduction pipe (4) was made of quartz. Microwave power is supplied from a microwave power source (10) to the discharge unit (9) via a waveguide (11). Reactive gas X
The activation of (6) is performed by plasma in this embodiment, but may be performed by thermal excitation, light excitation, electron beam excitation, or the like. The pressure in the container (1) is controlled by a valve (not shown).
Is set by changing the conductance, and measured and controlled by a diaphragm gauge (not shown).

A cooling means (12) for cooling the substrate (3) is provided in the holder (2) of the substrate (3).
Is provided, and a heating means (13) may be further provided if necessary. Each of these means is provided with a substrate to be treated (3)
And a control system for setting the temperature at a constant value, that is, below the boiling point of the active species generated from the first reactive gas, the second reactive gas, or these reaction products. (Not shown).

Further, the heating means (13) may apply a heat treatment to the substrate (3) before cooling the substrate (3) to the boiling point or lower. In this case, the cooling means (12) is such as to carry nitrogen gas which has passed through liquid nitrogen to the holder (2) via a cooling pipe. Here, the control of the cooling means (12) was performed by adjusting the flow rate of the nitrogen gas with the needle dolbu provided in the cooling pipe.
Although a heater was used as the heating means (13),
The heating means is not limited to the one described above, and may be anything as long as the temperature can be set constant. The substrate to be processed is fixed to the sample stage so as to obtain good thermal contact with the sample holder.

Further, areas other than the substrate (3) to be processed of the reaction vessel (1) and the sample holder (2) for cooling the substrate to be processed are designed so as to maintain cleanliness in the reaction vessel (1). A structure in which a heater (14) for flowing an electric current is wound around the wall of the container (1) may be used.

Further, the thin film forming apparatus used in the present invention is provided with means for irradiating light such as electrons, ions, or laser light on the substrate to be processed, and has a structure in which the light irradiation means excites a reactive gas. It is also possible. According to the light excitation, influences such as damage to the substrate to be processed (3) can be reduced.

Although not shown, the substrate to be processed (3) is taken in and out of the reaction vessel (1) through a separate chamber provided adjacent to the reaction vessel (1). The active gas flows. As described above, by using a so-called load lock for the reaction vessel (1), the reproducibility of the process can be greatly improved.

Next, referring to the thin film forming apparatus shown in FIG.
The method for forming a thin film according to the present invention will be described with reference to the cross-sectional views in FIG.

In this embodiment, the substrate (3) to be processed is carried into the reaction vessel (1), and before the thin film is embedded in the groove or the step of the substrate (3), the surface of the groove or the step is formed in another chamber. The substrate (3) to be processed or the thin film having good bonding with the thin film is applied to the substrate (3), but the heating means (3) provided in the holder (3) in the reaction vessel (1) as described above. According to 13), a thin film may be formed in the groove or the step.

Specifically, in this embodiment, a silicon substrate (20) was used as the substrate to be processed (3) as shown in FIG. 2 (9). A thin film (23) was applied to the surface of the groove (21) having an aspect ratio of 1 or more and formed on the substrate (20) and the substrate (22). Here, the formed thin film (23) is a silicon oxide film.
A known thin film forming method such as a VD method, a wet processing method, or a thermal oxidation method may be used.

Thereafter, the substrate (3) to be processed was placed in the reaction vessel (1) of the thin film forming apparatus shown in FIG. 1 in order to completely fill the groove of the substrate to be processed on which the thin film was applied.

In this embodiment, oxygen (C ₂ ) gas is used as the first reactive gas, and tetramethylsilane (Si (CH ₃ ) ₄ : TMS) is used as the second reactive gas. First, an O ₂ gas (6), which is a first reactive gas, is introduced from a gas introduction pipe (4),
Oxygen radical (O) by 2.45GHz microwave discharge
Is generated, and this oxygen radical is transported to the reaction vessel (1). On the other hand, since TMS is not discharged, it is introduced into the reaction vessel (1). The total pressure in the reaction vessel (1) was set at 2 Torr. The sample holder (2) contains stainless steel pulp (1
2) is embedded and cooled N ₂ through liquid nitrogen
By flowing a gas to lower the temperature of the substrate (3) to be processed to -25 ° C., the groove (21) of the substrate (20) is formed as shown in FIG.
It was completely embedded with the thin film (23).

The temperature of −25 ° C. at which the substrate (20) was cooled was lower than the boiling point (about −20 ° C.) of hexamethyldisiloxane, which is a reaction product of tetramethylsilane. 23) The gas molecules, active species, etc. are liquefied in the groove (21) by lowering the boiling point of the introduced gas, active species generated by excitation or the reaction product of the introduced gas, which contributes to the formation of the gas. Any temperature may be used as long as it is a temperature at which it adheres.
In other words, this means that the gas molecules, active species, etc.
This is because, when it adheres to (0), a thin film is formed to fill the groove while reacting with the reactive gas in the reaction vessel.

Then, even if annealing is performed to increase the density of the thin film or is rapidly returned to room temperature, the transition region at the interface between the substrate (20) and the thin film (23) is firmly formed. ) Was not observed at all. As a comparative example, FIG. 3 is a cross-sectional view in which the groove (2) is buried with the thin film (23a) by the method as described above without forming the thin film (22) in advance as in this embodiment, and then annealing is performed. Shown in As can be seen from this figure, a gap (24) is formed between the substrate (20) and the thin film (23a) after annealing.

Further, it was found from experiments that the deposition rate of the thin film (23) greatly depends on the cooling temperature of the substrate (20), the type of gas introduced, and the flow ratio.

For example, tetramethylsilane (TM
In the case of S) gas and oxygen (O ₂ ) gas, the flow ratio of O ₂ / TMS is 4
Practical embedding was possible from the vicinity, and the maximum deposition rate was 5000Å / min at a flow rate ratio of 20. Here, the substrate temperature was −40 ° C., and the flow rate of TMS was 7 SCCM.

Next, the flow ratios of TMS gas and O ₂ gas were set to 7 SCCM and 56
When SCCM is used, a practical thin film can be formed from a substrate temperature of about -20 ° C, and a deposition rate of about -40 ° C is the maximum.
It was found to be 3000 A / min.

The silicon oxide film (22) is formed by wet treatment in a mixed solution of hydrogen peroxide and sulfuric acid, or deposited using TMS and oxygen excited by microwave discharge at a substrate temperature of 300 ° C. After that, the substrate (2
By setting the temperature of 0) to −25 ° C. or lower, the same effect was obtained even when the grooves having a high aspect ratio were buried. In the latter case, the composition of the silicon oxide film formed thinly on the silicon substrate and the silicon oxide film deposited at a low temperature on this film are further the same, so that the transition region at the interface is formed more firmly. Even if the temperature of the substrate (20) is continuously changed and cooled to -25 ° C or less, the transition region is formed because the interface between the substrate (20) and the silicon oxide film (22) is formed at a high temperature. Since the process is firmly formed and then the process shifts to a process of continuously embedding a groove having a high aspect ratio with the thin film (23), there is no other interface, which is effective.

As the first reactive gas used in the present invention, a gas containing at least oxygen, nitrogen, hydrogen, or a halogen element can be used, and argon (Ar), helium (He) is used as the first reactive gas. An inert gas such as the above may be mixed.

Further, according to the present invention, as a second reactive gas, a gas containing at least one element from Group 2 to Group 6 of the periodic table is used, and an oxide of the element is formed on the substrate to be treated. A nitride, a hydride, a simple substance of the element, or a compound of the element can be formed.

Further, as the second reactive gas, an organic compound of metal or semiconductor, a halogen compound, a carborne compound, or a mixed gas containing at least carbon and hydrogen can be used.

Furthermore, a gas obtained by mixing the first reactive gas and the second reactive gas may be used as the first reactive gas.

As described above, the present invention can be applied to a case where a desired thin film is formed and embedded by changing the type of gas introduced into a groove formed in a substrate to be processed.

Needless to say, the present invention can be applied not only to a groove having a high aspect ratio but also to a substrate to be processed having a stepped portion.

In addition, the present invention may be appropriately changed without departing from the gist of the present invention.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, the coupling | bonding of the to-be-processed base | substrate which has a groove | channel or a step part on the surface and the thin film which fills the said groove | channel or a step part can be made favorable.

[Brief description of the drawings]

FIG. 1 is a schematic view of a thin film forming apparatus applied to a method according to an embodiment of the present invention, FIG. 2 is a process sectional view for explaining the present invention, and FIG. 3 is a comparison of effects with the present invention. FIG. DESCRIPTION OF SYMBOLS 1 ... Reaction container, 2 ... Holder, 3 ... Substrate to be processed, 4.5 ... Gas introduction pipe, 12 ... Cooling means, 13 ... Heating means, 20 ... Substrate, 21 ... Groove, 22 ... Preformed thin film, 23, 23a ... Thin film.

Claims (8)

(57) [Claims] 1. A substrate to be processed having a groove or a step on its surface is housed in a reaction vessel, and a first reactive gas and a second reactive gas are introduced into the reaction vessel and the first and second reactive gases are introduced into the reaction vessel. Is excited to evacuate the reaction vessel to a predetermined pressure, and the temperature of the substrate to be treated is increased by the reaction between the excited first reactive gas and the second reactive gas. Controlling the reaction intermediate product generated by the reaction intermediate product to a boiling point or lower under the pressure, and liquefying the reaction intermediate product, thereby embedding a groove or a step portion on the surface of the substrate to be processed with a thin film, Prior to embedding the groove or the step portion with a thin film, a step of applying a thin film in which the groove or the step portion is buried in advance and a thin film having good bonding properties with the substrate to be processed on the surface of the groove or the step portion. Thin film forming method according to symptoms. 2. A thin film formed in advance on a surface of a groove or a step portion of a substrate to be processed and a thin film embedded in the groove or the step portion on which the thin film is formed are films of the same material. The method for forming a thin film according to claim 1. 3. The method according to claim 1, wherein the thin film previously formed on the surface of the groove or the step portion of the substrate to be processed is formed by a thermal CVD method, a photo CVD method, a wet processing method or a thermal oxidation method. 2. The method for forming a thin film according to claim 1. 4. The method according to claim 1, wherein the substrate to be processed is a silicon substrate, and the thin film formed in advance on the surface of the groove or the step portion and the thin film buried thereafter are silicon oxide films. 3. The method for forming a thin film according to claim 2. 5. A silicon oxide film previously formed on a surface of a groove or a step portion of the substrate to be processed is formed by a wet processing method in which the substrate to be processed is immersed in a mixed solution of hydrogen peroxide and sulfuric acid. 5. The method for forming a thin film according to claim 4, wherein: 6. The substrate to be processed in order to previously form a thin film for embedding the groove or the step and a thin film having good bonding with the substrate to be processed on the surface of the groove or the step on the substrate to be processed. Is temporarily maintained at a temperature higher than the boiling point under the pressure of the reaction intermediate product generated by the reaction between the excited first reactive gas and the second reactive gas. The method for forming a thin film according to claim 1. 7. A temperature of the substrate to be processed is set to a temperature higher than a boiling point of the reaction intermediate product generated by the reaction between the excited first reactive gas and the second reactive gas under the pressure. Holding the substrate once, forming the thin film on the surface of the groove or the step portion of the substrate to be processed, and continuously embedding the groove or the step portion on the surface of the substrate to be processed with the thin film, 7. The method for forming a thin film according to claim 1, wherein 8. The method according to claim 1, wherein a heat treatment is performed after the step of embedding the groove or the step portion of the substrate to be processed with a thin film.