JPS61202424A - Chemical vapor deposition equipment - Google Patents

Abstract

PURPOSE:To uniformize the vapor-deposition rate for the all parts of the object to be treated present on a heating jig plate by forming the inclined plane on the heating jig plate, which has such shape that the upper plane of a longitudinal cross section penetrating through the axis core of the heating jig plate is axial symmetry and the gradient becomes higher toward the periphery on the heating jig plate. CONSTITUTION:In a reaction chamber 22 for carrying out a chemical gas-phase reaction, a heating jig plate 18 of disc form is arranged horizontally, which is heated by high-frequency induction and on which an object to be treated is mounted. A nozzle 17 for supplying a material gas comprising a blow-off hole 17a from which the material gas is blown off radially on the upper surface of the treated object is stood vertically with the center of the jig plate 18 penetrated through. On the jig plate 18, the inclined plane 18b is formed, which has such a shape that the upper surface of a longitudinal cross section penetrating the axis core of the jig plate 18 is axial symmetry and the gradient becomes higher toward the periphery. Consequently the supplied gas flows in such a manner that the reaction becomes uniform from the central part of the jig plate 18 toward the peripheral edge part thereby uniformizing the vapor-deposition rate for the all parts of the treated object.

Description

[Detailed description of the invention] (Industrial application field) FIELD OF THE INVENTION The present invention relates to chemical vapor deposition apparatus.

(Prior art) Epitaxial growth, in which a thin film of the same single crystal is grown on a semiconductor substrate made of a single crystal such as silicon (Si), has recently been used in the field of semiconductors to achieve higher integration, higher performance, and higher reliability. This is an important process as it is promoted. Epitaxial growth is a vapor phase method.

Although many methods such as liquid phase method have been studied or put into practical use, gas phase method has recently become popular. Typical gas phase methods include a physical vapor deposition method in which a solid thin film is deposited by condensation from a gas phase to a solid phase interface, and a chemical vapor deposition method in which a solid thin film is deposited from a gas phase by a chemical reaction. A conventional chemical vapor deposition method and its apparatus will be explained below.

As an example of chemical vapor deposition, in the case of silicon epitaxial growth, gaseous 5iC1a (there are other cases where K5iHC13゜5iHzCb, SiH4, etc. are used)
but.

On a Si substrate heated to a high temperature (900-1200°C) K, it is reduced by carrier gas H2 as shown in the following formula,
A solid thin film of Si is grown on the substrate.

8iC1s<Ki) + ZHz (Ki) → Si (Hard) ↓ + 4H
CJ (qi) ↑ However, the above reaction formula is just a direct expression, and this reaction process involves side reactions that generate multiple reactive species. Also, this reaction system is in the gas phase.

Chemical reaction on the interface as well as mass transfer and heat transfer.

It is a complex system in which gas flows interact with each other.

Therefore, it is very difficult to provide uniform vapor deposition conditions over the entire reaction region in the vapor deposition apparatus, and it is difficult to provide an epitaxial layer with uniform thickness and quality on the same substrate or between substrates. Many studies are currently being conducted on equipment and operating conditions to obtain this.

On the other hand, as mentioned above, in the semiconductor field.

High integration and high reliability are rapidly progressing, and as a result, uniformity in the thickness and quality of the epitaxial layer will continue to be required more and more in the future.

Many types of chemical vapor deposition apparatuses for epitaxial growth have been put into practical use to date.

Among these, the most typical example is shown in FIG. This type is generally called a pan-cake type and is a type of high-frequency induction heating furnace.

A nozzle 12 and a nozzle holder 11 are fixed at the center of the device, and a cylindrical chuck 13 is attached to the outside.
Support tube 14. An adapter 15 is provided. A disk-shaped heating jig plate 16 whose upper and lower surfaces are parallel is installed on the adapter 15.

The upper surface of this heating jig plate 16 has a large number of counterbore portions 16a, and the substrate 3 to be processed is set in these.

Generally, the chuck 13 is connected to a rotational drive body, so that the heating jig plate 16 rotates at a low speed around an axis at the center of the apparatus.

On the other hand, chamber base 4 and work coil cover 8.9
．． A spiral high-frequency induction work coil 7 is installed in an annular space surrounded by the IOK, and when a high-frequency current is passed through this work coil 7, an induced current is generated on the lower surface of the heating jig plate 16. 2 I have a fever. After that, K heat is transferred in the thickness direction (upward direction) of the heating jig plate 16 (thermal conduction),
Each substrate 3 placed on the heating jig plate is heated. At this time, in the reaction chamber 22 surrounded by the chamber 5 above the substrate,
Raw material gas 1 is supplied through nozzle holder 11 and nozzle 12 . The raw material gas flows over the substrate surface heated to a high temperature, and at this time, the raw material components cause a chemical reaction in a high temperature boundary layer formed along the substrate surface, forming an epitaxial layer. Note that various types of gas discharge from the nozzle have been devised and put into practical use in the past, but the current mainstream type is a two-way type.

That is, one is to provide an opening at the upper end of the nozzle.

Discharge gas in the direction of the ceiling (center) of chamber 5,
In the form of circular circulation within the chamber.

The other is a large number of discharge holes 12a arranged radially in the horizontal direction on the nozzle side wall.
are provided, and gas is discharged from these holes parallel to the substrate surface as shown by solid arrows.

FIG. 8 shows an example of the latter. After the gas circulates within the chamber as shown by the dashed line, it is discharged as exhaust gas 2. In the figure, 6 is a seal ring. However, in either case, the 5iC near the substrate surface and above the substrate surface
The Ganu body flow of 1l and H2 flows parallel to the substrate surface, and flows as much as possible along the substrate surface.

A uniform laminar boundary layer must be formed, and the only difference between the two is the gas flow direction of the disk-shaped heating jig plate, either toward the center or toward the outer circumference of the device.

(Problems to be Solved by the Invention) Here, we will discuss how the gas flow and the movement of the Si component, which is a reactant, generally affect the growth rate, which is directly related to the thickness of the epitaxial layer. state Assuming that the reaction temperature on the substrate surface is constant at all locations, the growth rate is mainly determined by the movement rate of reactants in the boundary layer formed near the substrate surface and the gas main flow flowing above the boundary layer. It is strongly influenced by two factors: the concentration of the reactants present. Generally, as both factors increase, the growth rate tends to increase. Among the above factors, the moving speed of the reactant is inversely proportional to the thickness of the boundary layer formed along the substrate surface, and the thickness of the boundary layer is measured from the origin where the boundary layer appears in the direction of gas flow. 1/2 of the distance
Proportional to the power. Therefore, in the direction of gas flow, the boundary layer becomes thicker and the moving speed of the reactants decreases. Further, the concentration of the reactant contained in the main gas flow gradually decreases in the gas flow direction due to reaction consumption on the substrate surface and the heating jig plate surface and diffusion into the surrounding gas.

Therefore, in principle, the growth rate must decrease in the direction of gas flow. This tendency has been confirmed empirically, and is an unavoidable problem in a vapor deposition apparatus having a conventional structure as shown in FIG.

The purpose of the present invention is to achieve a more uniform growth rate on all substrate surfaces by improving the above-mentioned gas flow, and to provide a chemical vapor deposition apparatus capable of obtaining a uniform thickness distribution of the epitaxial layer. Our goal is to provide the following.

(Means for solving the problem) The present invention horizontally arranges a disc-shaped heating jig plate on which a workpiece heated by high-frequency induction is placed in a reaction chamber in which a chemical vapor phase reaction is performed. In a chemical vapor deposition apparatus in which a nozzle for supplying raw material gas is vertically installed and has a discharge hole that penetrates the center of the heating jig plate and discharges raw material gas radially onto the upper surface of the object to be processed, the heating The present invention relates to a chemical vapor deposition apparatus in which a jig plate has an inclined surface whose upper surface in a vertical cross section passing through the narrow center of the jig plate is axially symmetrical and has a slope rising toward the outer circumference.

In order to make the growth rate of the epitaxial layer uniform in the direction of gas flow, the present invention uses gas flow.

In particular, we focused on the thickness of the boundary layer formed along the substrate surface of the processed object. Usually, a gas body is a viscous fluid, and when gas flows uniformly over a solid surface, the gas flow rate is O at the surface.
Tonashi 9 As the distance from the surface increases, the average flow velocity of the main body gas flow at a certain distance from the surface approaches exponentially. The region in which the gas flow velocity changes near the surface is called a boundary layer (strictly speaking, a velocity boundary layer). Generally, the flow within this boundary layer can be considered as a laminar flow state, and when dealing with heat transfer or mass transfer phenomena, the velocity of movement in this boundary layer is the most important factor. Namely.

In order for the reactants carried by the body gas flow to react on the substrate surface, the reactants diffuse toward the solid surface through this boundary layer, and heat moves from the solid surface toward the body gas flow. There must be. The smaller the thickness of this laminar boundary layer, the higher the mass transfer rate (or heat transfer rate), and the two are approximately inversely proportional.

Therefore, we will discuss how the thickness of the one-layer boundary layer is influenced by what factors. The thickness of the boundary layer is δ
, the viscosity coefficient of the gas is μ, the gas density is ρ2, the average flow velocity of the main gas flow is U, and the distance measured in the gas flow direction from the starting point where the boundary layer appears is X. Here, assuming that the surface of the substrate and the surface of the heating jig plate, which are exposed to the solid surface, are heated to a uniform temperature, the characteristics of the gas in the boundary layer, that is, μ and ρ, are assumed to be approximately constant in the direction of gas flow. be able to. Strictly speaking, this is because gas receives heat as it flows along a hot surface.

An increase in the temperature of the gas occurs in the direction of flow. However, the change in gas temperature within the boundary layer (temperature on the heated surface to main body gas temperature) is much larger, and when calculating the average temperature within this boundary layer, the temperature increase in the gas flow direction is almost ignored. As much as possible. At this time.

The boundary layer thickness δ is proportional to Nrosi τ.

Therefore, if the ratio (X/u) between the distance X and the average flow velocity U can be kept constant, the thickness δ of the boundary layer can be controlled to be almost constant along the gas flow.

Therefore, the average gas flow velocity U is expressed as a function of X.

Usually, a heating jig plate in a chemical vapor deposition apparatus is a circular plate with a constant thickness (outer radius b), and a hole of the same size (inner radius a) is provided in the center. A large number of substrates are arranged on this annular plane in the section from radius a to b. Further, the heating jig plate rotates the nozzle center axis at a constant speed (angular velocity ω), and furthermore, a number of holes are provided in the nozzle side wall radially in the horizontal direction. The raw material gas flows radially from the center of the heating jig plate toward the outer periphery at a flow rate Vr.
When the gas is discharged at It is expressed as the sum vector of " and the speed vector in the rotational direction, that is, the rotational speed Vθ of the heating jig plate. Furthermore, the rotational speed Vθ is a function of the distance X,
It is expressed as Vθ=(x−)−a)ω.

Therefore, the average flow velocity U of the two main gases is u=! It is an increasing function with respect to X. However, in general, the discharge speed Vr of the nozzle is greater than the rotational speed Vθ, and Vr tends to decrease slightly in the gas flow direction (centrifugal direction) due to the entrainment phenomenon of surrounding gas.

In reality, U can be considered almost constant with respect to X.

From the above, in the present invention, the upper surface of the heating jig plate has a gradient that rises in the direction of the gas discharged horizontally and radially from the discharge hole of the nozzle to the outer periphery of the heating jig plate (the gradient in which the gas flow rate increases). The gas flow rate is accumulated along the gas flow direction by forming an inclined surface having a shape of I did it like that. A plurality of discharge holes are provided in the nozzle side wall at equal intervals in the circumferential direction of the nozzle, and a large number of discharge holes are provided at narrow intervals in the axial direction of the nozzle at positions corresponding to the height of the inclined surface formed on the heating jig plate. By providing discharge holes in stages and shifting the positions of the discharge holes in each vertically adjacent stage in the circumferential direction, the concentration of the raw material gas to be discharged is increased and the gas flow is made uniform, and the interval between each discharge hole is It is preferable to reduce the strength of the nozzle of the tube body due to K.

In the above case, the flow velocity Vr in the centrifugal direction is Vr==CX(C:
proportionality constant), the average flow velocity U of the two main gases is u=J(
It can be expressed as 77. Therefore, from the above-mentioned relationship, the boundary layer thickness δ tends to decrease with respect to X.

However, in reality, each gas jet discharged from a nozzle expands in the flow direction and decelerates accordingly, so even if the surface of the heating jig plate has a slope, Vr does not necessarily
It is not necessarily proportional to (rather, Vr = cx':
It is more realistic to set n = O~1), therefore, the thickness of the boundary layer does not tend to decrease with respect to X. However, compared to a conventional device in which the gas flow from the nozzle and the heating jig plate surface are parallel, the increasing trend of the boundary layer thickness along the flow direction is much smaller and nearly constant.

In this way, by creating a certain slope on one surface of the heating jig plate (the surface on which the substrate is placed), the thickness of the boundary layer can be controlled to be approximately constant along the gas flow direction. If the thickness of the boundary layer is constant, the mass transfer rate and heat transfer rate take constant values regardless of location. 9 If the concentration of the raw material components in the main gas is considered to change almost in the direction of gas flow, the growth rate of the epitaxial layer can be determined by linearly changing the slope of the heating jig plate. A constant and uniform film thickness distribution can be obtained regardless of the thickness of the film.

On the other hand, when the concentration of raw material components changes in the gas flow direction (normally, the concentration decreases in the flow direction due to the relationship between raw material consumption by two reactions), the surface of the heating jig plate cannot be However, if a higher-order curved (eg, quadratic) slope is applied, the boundary layer thickness tends to decrease along the flow direction. In this case, since the mass transfer rate increases in the flow direction, it is possible to compensate for the decreasing tendency of the raw material component concentration.

Since the growth rate of the epitaxial layer is considered to be proportional to the product of the mass transfer rate and the concentration, the growth rate can be kept constant in the flow direction by balancing the increasing tendency of the mass transfer rate and the decreasing tendency of the boundary layer thickness. can do.

In addition, the above-mentioned high-order curved slope is actually approximated by an arc-shaped slope or a broken-line slope whose angle increases stepwise in the flow direction, and the surface of the heating jig plate is processed. Good too.

However, there are cases where the raw material component concentration does not decrease uniformly in the gas flow direction. For example, the jet from the nozzle passes through the outermost periphery of the heating jig plate and finally collides with the side wall of the chamber of a chemical vapor deposition apparatus, after which some of the gas flows onto the heating jig plate again. do.

If this phenomenon is significant, the concentration will be locally high on the outer peripheral side of the heating jig plate. In such cases.

An effective means is to reduce the upward slope on the outer circumferential side or to make the outer circumferential side horizontal.

The material of the heating jig plate in the present invention is easily heated by high-frequency induction, has high thermal conductivity for uniform temperature, and has sufficient heat resistance against two reaction sources.

Any material may be used as long as it is not corroded by reactive gases such as H, HCI, silane, and carrier gas, and graphite material is preferred, although there is no particular limitation. Furthermore, in epitaxial growth, it is common to strictly control the impurity concentration inside the chemical vapor deposition apparatus. Graphite material has the disadvantage of easily adsorbing impurity gases due to its large number of small pores, so graphite heating jig plates are made of SiC on the entire surface.

It is preferable to form a vapor-deposited film having airtightness such as S i3 N4. The material of the nozzle is not limited as long as it has airtightness, heat resistance, and corrosion resistance, but quartz is preferable.

(Example) Regarding the above-mentioned present invention, Sections 1 to 7 showing Examples of the present invention are as follows.
This will be explained in detail using figures.

First, FIG. 1 is a vertical sectional view showing the internal structure of a two-reactor reactor, in which a heating jig plate 18 made of SiC-coated artificial graphite and a nozzle 17 made of quartz according to the present invention are installed.

The nozzle 17 has a large number of stones arranged at narrow intervals in the axial direction on the side wall at a position corresponding to the height of the inclined surface 18b, so that the jet of gas 1 uniformly contacts the entire area of the inclined surface 18b of the heating jig plate 18. Discharge holes 17a in stages were provided, and the positions of the discharge holes in each vertically adjacent stage were shifted in the circumferential direction, and a plurality of discharge holes were provided at equal intervals in the circumferential direction.

The heating jig plate 18 has an inclined surface 18b as shown in FIG.
has a linear slope, and this inclined surface 18b is provided with a number of counterbore portions 18a on which the substrate 3 is placed. Also, Fig. 2.

FIG. 3 is a top view of the heating jig plate 18, both of which show the inclined surface 1.
8b and an example of how to arrange the counterbore portion 18a.

FIG. 2 shows an example in which the inclined surface 18b is constituted by a conical surface coaxial with the core of the heating jig plate itself, and a large number of counterbore portions 18a are arranged on this conical surface in the circumferential direction.

FIG. 3 shows an example in which the inclined surface 18b is composed of a polygonal pyramidal surface (coaxial with the jig plate), and the same number of counterbore portions 18a are arranged on each surface (plane).

Furthermore, FIGS. 5 to 7 are longitudinal cross-sectional views showing examples of heating jig plates having slopes other than one straight line.

FIG. 5 shows an example of a nine jig plate in which an inclined surface 19b having a higher-order curved slope is provided depending on the degree of change in the raw material component concentration in the flow direction of the gas 1.

Furthermore, both FIGS. 6 and 7 are examples of jig plates that approximate the slope of the complex award certificate shown in FIG. 5 with a simpler shape that is easier to process. That is, FIG. 6 shows a heating jig plate 20. with an inclined surface 20b having a slope approximated by a circular arc. FIG. 7 shows a heating jig plate 21 composed of inclined surfaces 21b, 21C, and 21d having a polygonal slope whose angle increases stepwise in the gas flow direction. In the figure, 19a, 20a, 21a
is the counterbore section.

(Experimental example) Discharge hole and outer diameter of quartz nozzle in the above example 30
The slope of the pitch coke-based artificial graphite heating jig plate of the five cabinets is configured as shown in Table 1, and the heating jig rod is configured as shown in Figures 4, 5, 6, and 7. counterbore portion 18a,
19a, 20a, and 21a were provided on the outer circumferential side and five on the inner circumferential side, for a total of 10 pieces, and a silicon semiconductor substrate was placed on each counterbore, and placed in the chamber of the chemical vapor deposition apparatus shown in FIG. Raw material gas 8iC14 was pumped together with carrier gas H2, and epitaxial growth was performed by heating the substrate surface by passing an electric current through the work coil so that the temperature of the substrate surface reached 1200°C.

As a comparative example, an epitaxial growth experiment was conducted using a chemical vapor deposition apparatus shown in FIG. Table 1 shows the film thickness distribution of the epitaxial layer grown on the substrate.

It can be seen from Table 1 that the variation in film thickness in the above experimental example is reduced to 1/2 or less within the same substrate and to 1/3 or less between substrates and is made uniform compared to that of the comparative example.

(Effects of the Invention) According to the present invention, since the supplied gas flows from the center of the heating jig plate toward the outer peripheral edge so that the reaction is uniform, the gas that is placed on the heating jig plate is The rate of vapor deposition on the object to be processed is made uniform over all parts, and the object to be processed can have a uniform vapor-deposited film thickness.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a chemical vapor deposition apparatus according to an embodiment of the present invention, FIGS. 2 and 3 are top views showing a heating jig plate in an embodiment of the present invention, and FIGS. The figure is a longitudinal sectional view of a heating jig plate according to an embodiment of the present invention, and FIG. 8 is a longitudinal sectional view showing the structure of a conventional chemical vapor deposition apparatus. Explanation of symbols 1... Raw material gas 2... Exhaust gas 3... Substrate 4... Chamber pace 5... Chamber 6... Seal ring 7... Work coil 8... Work coil cover 9 ...Work coil cover 10...Work coil cover 11...Nozzle holder 12...Nozzle 13...
・Chuck 14... Support tube 15... Adapter 16... Heating jig plate 17... Nozzle
18... Heating jig plate 19... Heating jig plate
20...Heating jig plate 21...Heating jig plate 2
2...Reaction chamber 1st port'42nd figure Kaya 3

Claims (5)

[Claims] 1. A disk-shaped heating jig plate on which the object to be processed is placed and heated by high-frequency induction is horizontally arranged in a reaction chamber in which a chemical vapor phase reaction is carried out, and the object to be processed is inserted through the center of the heating jig plate. In a chemical vapor deposition apparatus in which a nozzle for supplying raw material gas is vertically installed and has a discharge hole for discharging raw material gas radially onto the upper surface of an object, the upper surface of the heating jig plate in a longitudinal section passing through its axis is A chemical vapor deposition device that forms an inclined surface that is axially symmetrical and has a slope that rises toward the outer circumference. 2. 2. The chemical vapor deposition apparatus according to claim 1, wherein the inclined surface of the upper surface of the heating jig plate is an inclined surface having a high-order curved cross section. 3. 2. The chemical vapor deposition apparatus according to claim 1, wherein the inclined surface of the upper surface of the heating jig plate is an inclined surface having an arcuate cross section. 4. 2. The chemical vapor deposition apparatus according to claim 1, wherein the inclined surface of the upper surface of the heating jig plate is an inclined surface having a broken line shape in cross section. 5. The chemical vapor deposition apparatus according to any one of claims 1 to 4, wherein the discharge hole of the nozzle is a discharge hole provided in the side wall of the nozzle at a position corresponding to the height of the inclined surface of the upper surface of the heating jig plate. .