JPH1027778A - Surface treating device and nozzle provided thereto - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect the inner wall of a nozzle against damage to enhance the nozzle in long term stability, so as to enable a surface treating device to carry out a surface treatment such as etching for effectively forming a thin film of high performance or surface modification, by a method wherein the inner wall of the nozzle which jets out gas through its one end is formed of plasma-resistant material. SOLUTION: A Laval nozzle 3 is provided with an inlet through which material gas that is made to blow against the surface of a substrate 5 is fed and a gas inlet pipe 3a which decreases gradually in cross section up to a certain point with a distance from the inlet. A throat 3b which is smaller in cross section than any other part of the Laval nozzle 3 is joined to the gas inlet pipe 3a extending downwards, and a gas jet pipe 3c which increases gradually in cross section at a prescribed spreading angle and is provided with a jet nozzle through which plasma P is jetted out is joined to the other end of the throat 3b. The inner wall of the Laval nozzle S3 is surface-treated with plasma- resistant material. By this setup, processing such as thin film forming etching can be very efficiently carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment apparatus and a nozzle used for the same, and more particularly, to a nozzle of a surface treatment apparatus using plasma.

[0002]

2. Description of the Related Art In a state in which a gas is converted into a plasma by an induction plasma method, a DC plasma jet method, or the like, the gas is activated, and the reactivity is increased, and the plasma gas is jetted at a high speed toward the surface of a substrate to be processed. By
Techniques for performing a surface treatment such as thin film formation, etching or surface modification are already known, and are widely used for forming or etching a semiconductor thin film or surface modification treatment such as oxidation or nitridation.

In the case of forming a thin film using plasma, for example, a gas which has been converted into plasma and whose reactivity is increased is guided so as to reach a substrate to be processed at a supersonic speed in a short time. There is a need. This is for the following reasons. If the plasma gas cannot be guided to the substrate in a short time, the excited state (active state) cannot be maintained, and the adhesion between the substrate and the reaction product decreases, and This is because inconvenience such as peeling of an object may occur, or the film forming rate may be reduced, and the working efficiency may be reduced. Also, in the case of etching or surface modification, inconveniences such as a reduction in processing speed may occur.

[0004] Further, since the temperature of the plasma gas is extremely high, when the gas reaches the substrate to be processed, the temperature of the gas must be lowered to a temperature that the substrate can withstand. If the surface of the substrate to be processed is reached at a high temperature, not only the surface of the substrate to be processed is damaged, but also a film formation defect may occur. Further, it is also required to prevent impurities from being mixed into the plasma-formed reactive gas. This is because the contamination of the impurities causes deterioration of the film quality. Therefore, the present inventors have proposed a surface treatment apparatus having an improved structure which satisfies the above requirements and aims to improve the working efficiency, the film quality and the etching characteristics.

[0005] As shown in FIG. 1, a high-frequency induction coil is wound around a Laval nozzle (also called a divergent nozzle) 3. The Laval nozzle 3 has a gas introduction pipe 3a configured so that the cross-sectional area gradually decreases.
And a throat portion (throat portion) 3b connected to the gas introduction pipe 3a and configured to have the smallest cross-sectional area A1 (diameter d1) over the entire nozzle, and a predetermined spread angle connected to the throat portion 3b. The cross-sectional area is gradually expanded with θ,
And a gas injection pipe 3c configured to have a maximum sectional area A2 (diameter d2). Then, when the reactive gas is introduced from the gas introduction pipe 3a at the opening end of the gas introduction pipe 3a, the cross-sectional area in the gas introduction pipe 3a gradually decreases with the progress of the gas, and is stabilized at the throat portion. After
The reactive gas accelerated by adiabatic expansion in the gas injection pipe 3c and converted into plasma with a flow rate greater than the speed of sound is injected to the substrate 5 to be treated provided to face the nozzle outlet. It is.

Here, an induction coil 1 is wound around the outer periphery of the throat portion 3b so that a high-frequency current can be supplied to the induction coil 1. For this reason, when the induction coil 1 is energized, an induction electromagnetic field is formed in the throat 3b, and the energy of this field is increased in density to heat the gas passing through the throat 3b, thereby exciting the plasma. Then, the plasma-excited high-density gas is expanded and accelerated by the expansion of the nozzle diameter of the gas ejection pipe 3c on the downstream side, and is injected as a supersonic plasma jet P toward the substrate to be processed.

By using such a surface treatment apparatus, it is possible to improve the working efficiency, the film quality and the etching characteristics.

By the way, when the reactive gas is turned into plasma by the high frequency induction coil at the throat portion of the nozzle, the electric field becomes stronger near the inner wall of the nozzle, so that a high density gas plasma is generated and the plasma film forming apparatus is formed. Then, there is a problem that the thin film easily adheres to the inner wall of the nozzle. The deposited thin film increases in thickness with time, and when it reaches a certain thickness, peels off and mixes into the plasma gas to reach the surface of the substrate to be processed, thereby significantly deteriorating the film quality. Further, as shown in FIG. 4, the gas plasma having an etching action etches the inner wall material of the nozzle (throat portion 3b) and not only damages the nozzle, but also the substance etched on the inner wall of the nozzle becomes particles. It may adhere to the surface of the substrate to be processed and cause deterioration of device characteristics. In addition, the inner wall material of the nozzle may be consumed and the life of the nozzle may be shortened. In addition, when using not only such a film forming apparatus but also another surface processing apparatus such as an etching apparatus, the inner wall of the nozzle is often damaged, and the processing performance is often lowered. Thus, the same problem has occurred not only in film formation but also in etching and surface modification.

[0009]

As described above, in the conventional surface treatment apparatus using plasma, a thin film is deposited on the inner wall of the nozzle due to the reaction between the inner wall of the nozzle and the gas plasma excited by the reactive gas in the plasma generating section. Alternatively, problems such as etching of the inner wall of the nozzle are extremely serious.

The present invention has been made in view of the above-mentioned circumstances, and is configured to suppress a reaction between a gas plasma and a nozzle inner wall in a plasma generating unit, thereby protecting the nozzle inner wall and stably maintaining the nozzle for a long time. It is intended to perform high-performance and high-efficiency surface treatment such as thin film formation etching and surface modification.

[0011]

SUMMARY OF THE INVENTION Accordingly, a first feature of the present invention is that a nozzle configured to inject gas passing through the inside from one end and a reaction passage passing through a part of the flow path of the nozzle. A plasma generating unit for generating a gas plasma by exciting a reactive gas with a plasma, and performing a surface treatment on the substrate to be processed by injecting the gas plasma onto a substrate to be processed disposed in the vicinity of a nozzle of the nozzle. Wherein the inner wall of the nozzle is made of a plasma-resistant material.

A second feature of the present invention is that a gas introduction portion is configured to have a gradually decreasing cross-sectional area, and is connected to the gas introduction portion and configured to have a minimum cross-sectional area over the entire nozzle. A throat portion, and a gas injection portion connected to the throat portion, the cross-sectional area of which is gradually expanded at a predetermined spread angle, and configured to have a maximum cross-sectional area. A supersonic nozzle that forms a gas flow path that is adiabatically expanded and accelerates to be injected from the gas injection unit at a flow rate greater than the sonic velocity, and the supersonic nozzle that is wound around the throat part of the supersonic nozzle and A plasma generating means comprising a high-frequency induction coil for exciting a gas passing through the sonic nozzle and converting the gas into a plasma, and injecting gas plasma onto a surface of the substrate to be processed, Wherein the inner wall of the supersonic nozzle is made of a plasma-resistant material.

Preferably, the plasma-resistant material is aluminum oxide (Al ₂ O ₃ ), silicon nitride (Si
₃ N ₄ ), aluminum nitride (AlN), magnesium aluminate (MgAl ₂ O ₄ ), or diamond.

A third feature of the present invention is that a nozzle configured to inject a gas that has passed through the inside from one end and a reactive gas that passes through a part of a flow path of the nozzle to excite plasma. A plasma generating unit for generating gas plasma, wherein the surface processing apparatus forms a silicon thin film on the surface of the substrate to be processed by injecting the gas plasma to the substrate to be processed disposed near the nozzle of the nozzle. Wherein the inner wall of the nozzle is made of silicon.

A fourth feature of the present invention is that a nozzle configured to inject the gas that has passed through the inside from one end and a reactive gas that passes through a part of the flow path of the nozzle to excite plasma. A plasma generating unit that generates gas plasma, wherein the nozzle is configured to eject the gas plasma, wherein an inner wall of the nozzle is formed of a plasma-resistant material. .

In the apparatus of the present invention, strictly, an "insulated" state cannot be created, but the term "insulated" is used to mean a state in which the flow of heat is extremely reduced.

As described above, according to the present invention, since the inner wall of the nozzle is formed of the plasma-resistant material in the plasma generating section,
A thin film with good film quality can be formed without the inner wall of the nozzle being etched by plasma. In addition, it is possible to extend the life of the etching.

Here, the material constituting at least the inner wall of the plasma generating portion is a substance having high plasma resistance and hydrofluoric acid resistance, and having a high resistivity and a low dielectric loss tangent which are necessary conditions for generating plasma. It is desirable to use some aluminum oxide, silicon nitride, aluminum nitride, magnesium aluminate or diamond. The entire nozzle may be made of such a plasma-resistant material, or only the inner wall may be coated.
The region made of the plasma-resistant material may be only the plasma generating portion or the entire nozzle.

In the silicon thin film generating apparatus, the inner wall of the plasma generating section is made of silicon. Thereby, even if the inner wall is etched or mixed into the formed thin film, it can be formed without forming impurities.

Further, when the plasma is generated by a high-frequency induction coil wound around the outside of the nozzle, the generated circumferential electric field is small on the center axis of the nozzle and becomes large toward the end. The electric field becomes strong near the tube wall, and the reactive gas is more likely to be excited by plasma. However, according to the present invention, since the inner wall of the plasma generation unit is made of a plasma-resistant material, it is not etched, so that Is maintained. According to the present invention, the reactive gas to be sprayed on the surface of the substrate to be processed is turned into plasma, and becomes a highly reactive state (excited state, active state). And
According to the second aspect of the present invention, the gas which has been satisfactorily plasmatized without being etched by the plasma at the throat portion is adiabatically expanded by the supersonic nozzle and accelerated to have a flow velocity larger than the sonic velocity. At the same time, the plasma is efficiently formed, and the accelerated gas plasma is jetted toward the surface of the substrate to be processed. In this way, the gas plasma flow which has been turned into plasma and in a highly reactive state maintains high purity and reaches the target substrate to be ejected in a short time. Therefore, the film forming speed is increased, and the working efficiency is also improved. Furthermore, the temperature of the plasma gas is
Since the temperature of the substrate to be processed can be lowered to a level that the substrate can withstand by the adiabatic expansion, deterioration of the substrate to be processed can be prevented. The reactive gas can be efficiently turned into plasma, and the film quality is improved during film formation. In addition, a clean etching surface can be obtained during etching.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a plasma film forming apparatus according to an embodiment of the present invention.
As shown in FIG. 2, a high-frequency current of 13.56 MHz is applied to the induction coil 1 from the high-frequency power supply 2 to excite the raw material gas flowing through the aluminum oxide Laval nozzle 3 to generate gas plasma. To an n ⁺ -type single-crystal silicon substrate 5 installed in a vacuum chamber 4
At a supersonic speed to form a silicon thin film d. Here, the substrate as a substrate to be processed is configured to be able to be maintained at a desired temperature by a heater 6 provided on a substrate support table, and a temperature controller 9 detects a temperature of a heater power supply 7 while detecting a temperature by a thermocouple 8. The supply voltage to the heater is controlled.

In this Laval nozzle (also referred to as a divergent nozzle), as shown in an enlarged view of a main part in FIG. 2, the nozzle 3 is made of aluminum oxide, and the passing raw material gas is allowed to pass and adiabatically expanded without etching the inner wall. The nozzle is configured to be jetted from the nozzle outlet at a flow velocity u greater than the sonic velocity a under the conditions described later.

The Laval nozzle 3 is a medium-thin nozzle, and has a gas inlet (20 mmΦ) for supplying a raw material gas to be injected onto the surface of a wire as a substrate to be processed, and a cross-sectional area gradually decreases as the gas progresses. And the smallest cross-sectional area A1 (diameter d1: 10) of the entire nozzle.
mmΦ) and the cross-sectional area is gradually enlarged from the throat portion with a predetermined spread angle from the throat portion,
A gas injection pipe 3c from which a plasma flow P is injected from a gas injection port having a maximum sectional area A2 (diameter d2: 22 mmΦ). Outside the throat portion 3b, an induction coil 1 (coil diameter: 16 m) is provided as plasma generation means.
m, the number of coil turns: 5) is wound, and when a high-frequency current is applied to the induction coil 1, an induction electromagnetic field is formed in the throat portion 3b, and the gas passing through the throat portion 3b is plasma-excited. . Thus, the smallest cross-sectional area A
In the throat portion 3b having 1, a good plasma is formed.
Then, the plasma flow P is configured to be injected from the injection port of the Laval nozzle 3 toward the substrate.

This device is a supersonic nozzle under the conditions described below so that the reactive gas passing through the nozzle is adiabatically expanded and injected from the nozzle outlet at a flow velocity u greater than the sonic velocity a. A Laval nozzle (also called a divergent nozzle) 1 is configured. Laval nozzle 1
A gas inlet (50 mmΦ) for supplying a reactive gas (for example, a mixed gas of SiH ₄ and H ₂ ) to be injected onto the surface of the substrate 5 to be processed, A gas introduction pipe 3a configured to be small;
Minimum cross-sectional area A1 (diameter d1: 16 mmΦ) for the entire nozzle
And a gas injection pipe 3c into which a plasma flow P is injected from a gas injection port having a maximum cross-sectional area A2 (diameter d2: 40 mm.phi.) With a predetermined spread angle from the throat 3b. It is composed of An induction coil 1 (coil diameter: 16 mm, number of coil turns: 5) is wound around the throat portion 3b as plasma generation means. When a high-frequency current is applied to the induction coil 1, the throat portion 3b is turned on. An induced electromagnetic field is formed in 3b, and the gas passing through throat portion 3b is plasma-excited. Then, the plasma flow P is ejected from the ejection port of the Laval nozzle 3 toward the single crystal silicon substrate as the substrate 5 to be processed placed on the substrate support 4.

Next, the operation of the surface treatment apparatus will be described. First, a glass substrate as the substrate 5 to be processed is placed at the outlet of the gas ejection pipe 3c of the nozzle, and the substrate temperature is set to 400 °
And And the gas supply pipe 3a of the Laval nozzle 3
Is supplied with a reactive gas. Then, in the throat section 3b, a high-frequency current (500 W, 1
When 3.56 MHz flows, an induced electromagnetic field is generated in the tube, and the energy of this field heats and excites a high-density gas to generate plasma.

The high-density gas that has been turned into plasma is
The gas is expanded and accelerated due to the expansion of the nozzle by the gas jet pipe 3c on the downstream side, and is jetted from the gas jet as a supersonic plasma flow P. By guiding this plasma flow over the glass substrate 5 for 10 minutes, a polycrystalline silicon layer having a thickness of 1 μm is formed.

After the film forming process, neither etching on the inner wall of the throat portion 3b nor adhesion of a thin film was observed. Therefore, the film formation process could be repeatedly and efficiently performed many times.

In particular, the circumferential electric field generated by the high-frequency coil is small on the center axis of the nozzle and becomes large toward the end, so that more gas particles exist in the strong electric field region, and the reaction occurs on the tube wall. Although the activity of the reactive gas is increased, according to the present invention, since aluminum oxide having high plasma resistance is used, it is not etched by plasma.

The oxygen impurities in the polycrystalline silicon film thus formed were measured by SIMS. As a result, the oxygen concentration was 0.1% or less, which was below the detection limit, but was about 1% when quartz glass was used.

Next, the results of measurement of the plasma resistance, hydrofluoric acid resistance, resistivity and dielectric loss tangent of this aluminum oxide are shown in the following table.

[0032] Here, the plasma resistance was evaluated based on the film thickness etched when irradiated with Ar plasma for one hour.
The resistance to hydrofluoric acid was evaluated by the amount of corrosion per unit volume when immersed in a hydrofluoric acid solution for one day. From this result, it is found that aluminum oxide is about three times as large as quartz glass and about 10 ⁴ times as strong as hydrofluoric acid as compared with quartz glass. Further, it can be seen that the resistivity and the dielectric loss tangent have sufficient values.

In the above embodiment, the entire nozzle is made of aluminum oxide. However, as a second embodiment of the present invention, a coating c of a silicon thin film may be applied to the inner wall of the nozzle 3 as shown in FIG. Good. When this apparatus is used for forming a silicon thin film, even if the coating C on the inner wall of the nozzle is temporarily etched and reaches the surface of the substrate to be processed, it becomes possible to form a thin film with high reliability without becoming an impurity. .

In the above embodiment, the nozzle is made of aluminum oxide. However, the present invention is not limited to this and can be changed as appropriate. In forming a thin film, a coating material containing a constituent element of the thin film to be formed may be used.

According to the theory of gas dynamics, for example, in the case of diatomic gas, the ratio P1 / P0 between the stagnation pressure P0 of the introduced reactive gas and the pressure P1 downstream of the injection port is about 0.52. Hereinafter, when the ratio (the divergent ratio) A2 / A1 of the cross-sectional area A1 of the throat portion to the cross-sectional area A2 of the injection port exceeds 1, the gas is adiabatically expanded and the injection flow velocity is supersonic, that is, the sound velocity a
The flow velocity u is larger than that.

If the divergence angle before and after the throat portion 3b is too large, separation of the boundary layer occurs on the wall surface. Therefore, the divergence angle needs to be set to an appropriate size, for example, about 15 °.

The high-density reactive gas heated and converted into plasma in the throat portion 3b is excited by the heat into a highly reactive state, that is, a state in which it reacts easily on the glass substrate. However, the temperature of this highly reactive gas is very high, and in some cases it can reach ten thousand degrees, so that if it is sprayed on a glass substrate, the glass substrate cannot withstand this temperature. There is.

However, since the Laval nozzle 3 is designed so that the reactive gas passing therethrough is adiabatically expanded as described above, the Laval nozzle 3 is rapidly cooled in the adiabatic expansion process and reaches the glass substrate surface before reaching the glass substrate surface. The temperature is appropriate to the extent that the substrate does not deteriorate. At this time, the temperature is set to the above-mentioned suehiro ratio A2 / A1 (in this example, 0.1 / 0.1).
4), an arbitrary temperature can be obtained depending on the design conditions of the nozzle 3.

Further, since the plasma flow P has a supersonic velocity, the time required to reach the substrate is extremely short, and the plasma-excited state does not return to the original state before reaching the substrate. . Thus, the temperature can be lowered to an appropriate temperature while maintaining the so-called excited state. Therefore, the film quality can be improved. Further, since the injection is completed in a short time, the film forming speed is increased, and the working efficiency is also improved. The above-described phenomenon is explained as follows by the theory of one-dimensional fluid dynamics. That is, the relationship between the fluid temperature and the flow velocity in the adiabatic flow of the complete gas is expressed by the following equation.

T0 = T + (1/2) · {(γ−1) / (γ · R)} · (u) ² (1) Alternatively, T0 / T = 1 + {(γ−1) / 2} · (M) ² ··· (2) where T0: total temperature of the flow (substantially equal to the temperature of the throat 3b, which is a heating unit) T: static temperature of the flow (so-called temperature) γ: specific heat ratio of gas R: Gas constant u: flow velocity M: Mach number.

The above equation (2) is obtained by rewriting the above equation (1) using Mach numbers (u / a, a: sound velocity).
Further, the Mach number M is uniquely determined as a function of the Suehiro ratio A2 / A1.

From the above equation (1), it can be seen that in the adiabatic expansion process, the value of the total temperature T0 is kept constant, so that the static temperature T decreases as the flow velocity u increases. That is,
The higher the flow rate, the more rapid the temperature drop.

From the above equation (2), the temperature ratio T0 / T
Increases in proportion to the square of the Mach number M. For example, in the case of a diatomic gas (γ = 1.4), the Mach number M = 5
At this time, the temperature ratio T0 / T = 6. That is, by adiabatically expanding and accelerating the reactive plasma heated to a high temperature to a high Mach number using the Laval nozzle 1, the plasma temperature T can be lowered to a temperature suitable for the surface treatment of the substrate S to be treated. At this time, since the plasma particles are accelerated at an extremely high speed (for example, T =
1500 (K), γ = 1.4, R = 500 (J / kg
K), M = 5, u = 5123 (m / s)), the time required to reach the target substrate 5 is very short, and the plasma is applied at a low temperature while almost maintaining the initial active state. The processing substrate can be reached.

In the above-described embodiment, an example of forming a polycrystalline silicon thin film has been described. Similarly, if a mixed gas of CH ₄ and H ₂ is used, a graphite thin film, or NH ₄ gas and B ₂ When H ₆ gas or the like is used as the reactive gas, c-BN can be formed.

Depending on the type of the reactive gas, various surface treatments such as etching, oxidation and nitriding can be performed.

In the embodiment, the gas is plasma-excited by the high-frequency induction coil 1, but it may be excited by using another electrodeless plasma device such as ECR plasma or helicon plasma.

[0047]

As described above, according to the present invention, it is possible to suppress the reaction between the reactive gas and the inner wall of the nozzle in the plasma generating section, and perform a high-speed and high-reliability surface treatment repeatedly over a long period of time. It becomes possible.

[Brief description of the drawings]

FIG. 1 shows a surface treatment apparatus.

FIG. 2 is a sectional view of a main part of the surface treatment apparatus according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a main part of a surface treatment apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a cross section of a nozzle after a thin film forming process using a conventional apparatus.

[Explanation of symbols]

 1 Induction coil 2 High frequency power supply 3 Laval nozzle 3a Gas introduction pipe 3b Throat section 3c Gas injection pipe 4 Chamber 5 Substrate to be processed P Plasma flow (high-speed plasma jet) 8 Thermocouple 9 Temperature controller

Claims (5)

[Claims] 1. A nozzle configured to inject a gas that has passed through the inside from one end, and a plasma generation that generates a gas plasma by exciting a reactive gas passing through a part of a flow path of the nozzle by plasma. A surface treatment apparatus for performing a surface treatment on the substrate to be processed by injecting the gas plasma onto the substrate to be disposed disposed near the nozzle of the nozzle, wherein an inner wall of the nozzle is A surface treatment apparatus comprising a plasma material. 2. A gas inlet configured to have a gradually decreasing cross-sectional area, a throat connected to the gas inlet and configured to have a minimum cross-sectional area over the entire nozzle,
A gas injection portion connected to the throat portion, the cross-sectional area of which is gradually expanded at a predetermined spread angle, and configured to have a maximum cross-sectional area, and the gas passing through the nozzle is adiabatically expanded. A supersonic nozzle that constitutes a gas flow path that accelerates so as to be injected at a flow velocity greater than the sonic velocity from the gas injection unit, and the inside of the supersonic nozzle that is wound around the throat part of the supersonic nozzle. A plasma generating means comprising a high-frequency induction coil for exciting a passing gas to generate plasma, and performing a surface treatment of the substrate to be processed by injecting gas plasma onto a surface of the substrate to be processed In the apparatus, an inner wall of the supersonic nozzle is made of a plasma-resistant material. 3. The surface treatment apparatus according to claim 2, wherein the plasma-resistant material includes one of aluminum oxide, silicon nitride, aluminum nitride, magnesium aluminate, and diamond. 4. A nozzle configured to inject a gas passing through the inside from one end, and a plasma generation for generating a gas plasma by exciting a reactive gas passing through a part of a flow path of the nozzle by plasma. A surface treatment apparatus comprising a portion, and forming a silicon thin film on the surface of the substrate to be processed by injecting the gas plasma to the substrate to be processed disposed in the vicinity of the nozzle of the nozzle, wherein the inner wall of the nozzle is And a surface treatment apparatus comprising silicon. 5. A nozzle configured to inject a gas that has passed through the inside from one end, and plasma generation for generating a gas plasma by plasma-exciting a reactive gas passing through a part of a flow path of the nozzle. A nozzle configured to eject the gas plasma, wherein an inner wall of the nozzle is made of a plasma-resistant material.