JPH06172085A - Vapor-phase growth method - Google Patents

Abstract

PURPOSE:To form an epitaxial layer having high purity on a substrate by an organometallic vapor growth process by interrupting the supply of a raw material and exhausting the residual gas while passing a purge gas before starting the epitaxial growth of a semiconductor layer on a substrate. CONSTITUTION:The apparatus to be used for the process is provided with a gas-introducing pipe 18, a by-pass pipe 19 to discharge a gas by-passing a reaction pipe 2 and plural pipes 31-36 for the supply of raw material gases. Changeover valves V1-V8 are provided at the connection parts of the pipes 31-36 and the introducing pipe 18 and the by-pass pipe 19. Raw material gases are introduced into the reaction pipe 2 by operating the valves V1-V8 to effect the vapor-phase growth of a desired compound semiconductor layer on the substrate 4. Before starting the vapor-phase growth, the supply of the raw material is interrupted and the valves V1-V6 are alternately and repeatedly opened and closed while passing a purge gas through the pipes. The residual gas is exhausted even from a dead space between the branch point of the pipe and the valve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial growth technique, and more particularly to a technique suitable for use in epitaxially growing a high-purity compound semiconductor layer by MOCVD (metal organic chemical vapor deposition).

[0002]

2. Description of the Related Art VPE method (vapor phase epitaxial growth method) and M are used as epitaxial growth technology for compound semiconductors.
OCVD method and MBE method (molecular beam epitaxial method) are known. Among them, the MOCVD method has good film thickness controllability and is suitable for mass production, and is therefore used for epitaxial growth of compound semiconductor layers. The MOCVD method is a vapor phase growth method that uses an alkyl compound or a hydride as a source gas and utilizes a thermal decomposition reaction of these. For example III
In the growth of the group V compound semiconductor layer, as a group III raw material, I
An alkylated group II element (trimethyl indium, triethyl gallium, etc.) is used. These are a few at room temperature
A liquid or solid with a vapor pressure of several tens Torr,
It is contained in a carrier gas such as hydrogen and supplied to the reaction tube. On the other hand, the group V raw material may be supplied to the reaction tube as a hydride (gas at room temperature) of the group V element, or may be supplied to the reaction tube as an alkylated product (liquid).

FIG. 1 schematically shows an apparatus used for carrying out the MOCVD method. In this vapor phase growth apparatus,
The group III raw material is filled as an alkylated product (TMI, TEG, etc.) in stainless steel containers 11 and 12 called a bubbler, and the bubbler is filled with a carrier gas such as hydrogen by a purifier 13 and a mass flow controller 21 called a mass flow controller. , 22, and the group III raw material can be contained in this carrier gas and supplied to the mixer 1 called a manifold through the pipes 33, 34. Also, V
Group hydrides (PH ₃ , AsH ₃ ) are cylinders 15,
16 are filled with the mass flow controller 23,
The flow rate is adjusted by 24 and can be supplied to the manifold 1 through the pipes 35 and 36.

Switching valves V1 to V1 are provided in the manifold 1.
V8 is provided, and the raw material gas mixed at a desired ratio by switching these switching valves,
8 is introduced into the reaction tube 2 and flows down toward the substrate 4 placed on the barrel type susceptor 3, and is thermally decomposed on the substrate heated by the high frequency coil 5 to form an epitaxial layer on the substrate surface. Will be grown. A gas introduction pipe 18 and a bypass pipe 19 to the reaction pipe 2 are connected to the output side of the manifold 1, and by switching the switching valves V1 to V8 in the manifold 1, a desired raw material gas is supplied to the reaction pipe 2 It is configured so that it can be discarded as it is without being supplied to the inside or passing through the reaction tube 2. Further, the switching valves 41 to 45 are also provided in the middle of the pipes 31 to 38 heading to the manifold 1.
Are provided, and by controlling these, only the supply / cutoff of the source gas or the carrier gas (H ₂ ) or the purging gas (N ₂ ) can be made to flow. In FIG. 1, 6 is a filter, 7 is a pressure adjusting valve, 8 is a vacuum pump, 9 is a waste gas treatment device, 10 is a substrate rotation motor, and 1 is a substrate rotation motor.
Reference numeral 7 is a cylinder filled with a dopant gas.

[0005]

In the vapor phase growth apparatus having the above structure, the pipe 33 for guiding the source gas to the reaction tube 2 is provided.
When the temperature of ~ 36 is low, the raw material is deposited or adsorbed on the inner wall surface of the pipe, or when the residual raw material gas is swept with the purging gas, a part of the pipe in the manifold 1 becomes a dead space and the raw material gas remains. It may happen. That is, in FIG. 2, a part of the pipe in the manifold 1 is opened during growth, the valve V1 is opened and V2 is closed, and the raw material gas is flowed from the pipe 36 to the gas introduction pipe 18 through the branch pipe 51. At this time, the branch pipe 52 serves as a gas reservoir. The raw materials remaining in these pipes are gradually released at the time of subsequent growth, causing a problem that the growth film deviates from a desired composition ratio or the purity of the grown crystal decreases.

Therefore, there is a method of purging the residual gas in the branch pipe 52 by closing the valve V1 and opening V2 and flowing the purging gas from the pipe 36 through the branch pipe 52 to the bypass pipe 19. At this time, the branch pipes 51, 53, and 54 become dead spaces, and the raw material gas remains. In the above case, it seems effective to open both valves V1 and V2 to purge the purging gas from the pipe 36 through the branch pipes 51 and 52. However, when the valves V1 and V2 are both opened, the residual gas in the bypass pipe 19 may flow back into the reaction pipe 2 through the gas introduction pipe 18 and contaminate the inside of the pipe. Therefore, opening both valves V1 and V2 must be avoided.

As a solution to the above problems, the inner surfaces of pipes and valves are smoothed to reduce the adsorption area to accelerate desorption, and to design and construct pipes to reduce dead space, and to develop pipes during growth. A method has been proposed in which the material is heated to a temperature of several tens of degrees Celsius higher than room temperature to prevent the precipitation and adsorption of the raw materials, and some effects have been achieved. However,
In particular, when it is attempted to grow an epitaxial layer having a low carrier concentration after growing an epitaxial layer having a high carrier concentration with one device, it is difficult to achieve high purification by the conventional method, and a sufficiently low carrier concentration is obtained. It became clear that there was a defect when the epitaxial layer was not obtained. The present invention has been made in view of the above problems, and an object thereof is to prevent adverse effects due to residual gas in a pipe when a compound semiconductor is epitaxially grown on a semiconductor substrate by a MOCVD method or the like. The object of the present invention is to provide a vapor phase epitaxial growth method capable of growing a high-purity epitaxial layer.

[0008]

In order to achieve the above object, the present invention has a gas introduction pipe for supplying a raw material gas into a reaction pipe, a bypass pipe for bypassing the reaction pipe and discarding the gas, and a gas. A plurality of pipes connected to a supply source and supplying a raw material gas to the gas introduction pipe and the bypass pipe,
A switching valve is provided at each of the connecting portions of the gas introduction pipe and the bypass pipe and the pipe, and these switching valves are appropriately switched to introduce the raw material gas into the reaction tube and to dispose on the substrate arranged in the reaction tube. In a vapor phase growth method using a vapor phase growth apparatus for growing a desired compound semiconductor layer, before the desired compound semiconductor layer is grown on the substrate, the supply of raw materials is interrupted and a gas for purging is supplied to the pipe. While flowing, the switching valve is alternately repeatedly opened and closed to exhaust the residual gas. Further, preferably, the pipe is heated when the residual gas is exhausted.

[0009]

According to the above means, even if there is a dead space between the branch point of the pipe and the switching valve, the residual gas in the pipe can be exhausted by repeatedly opening and closing the switching valve,
As a result, a high-purity epitaxial layer can be grown on the surface of the substrate in the reaction tube.

[0010]

【Example】

(Example 1) As an example, using the apparatus shown in FIG. 1, first, n-type InP having a carrier concentration of 4 × 10 ¹⁸ cm ⁻³ was used.
On a single crystal substrate 61, an n-type InP layer 62, an undoped InGaAsP layer 63, a P-type InP layer 64 and a P-type I are formed so as to have the epi structure for a semiconductor laser shown in FIG.
The nGaAsP layer was epitaxially grown by the MOCVD method. Next, after taking out the single crystal substrate 61 on which the epitaxial structure for the semiconductor laser is grown from the apparatus, the valves V7 and 43 are closed, and instead the valve 42 is opened and hydrogen gas is used as a purging gas to the manifold 1 through the pipe 35. The valves V3 and V4 in the manifold 1 were alternately closed and opened 100 times (total 100 minutes) at intervals of 30 seconds to clean the gas introduction pipe 18 and the bypass pipe 19. At the same time, the manifold 1 and the pipe 35 were heated to 70 ° C. After that, an n-type InP single crystal substrate 61 was newly loaded into the apparatus, and an undoped InP layer was epitaxially grown thereon by the MOCVD method. When the carrier concentration and the mobility of the obtained undoped InP layer were measured, the carrier concentration was 2 × 10 ¹⁴
The mobility was 2 × 10 ⁵ cm ² / V · s at cm ⁻³ , and it was found that the purity was extremely high.

(Comparative Example) The cleaning conditions were the same as those of the above example except that the purge gas (hydrogen) was flown through the pipe 35 and the valves V3 and V4 were opened and closed once for 30 seconds. . When the carrier concentration and the mobility of the obtained undoped InP layer were measured, the carrier concentration was 1
In × 10 ¹⁶ cm- ^3, the mobility is ^{2 × 10 4 cm 2 / V} · s, the purity was considerably lower.

In the above embodiment, the case where the valve switching in the manifold 1 is performed 100 times has been described, but the number of valve switching is not limited to 100 and any number of times may be used. In that case, the higher the number of switching times, the higher the purity of the grown crystal. Assuming that the residual adsorbate in the dead space decreases to 1 / a (1 / a) by opening and closing the valve once, repeating this n times reduces the residual adsorbate to 1 / n of a. To do. Further, in the embodiment, hydrogen gas which is a carrier gas is used as the purging gas, but the purging gas is not limited thereto, and it does not damage the nitrogen gas or other pipes or valves and has no reactivity with the raw material gas. Any gas will do. Furthermore, the present invention can be used when an epitaxial layer is grown on a semiconductor substrate by a vapor phase growth method other than MOCVD.

[0013]

As described above, the present invention is connected to a gas introduction pipe for supplying a raw material gas into a reaction pipe, a bypass pipe for bypassing the reaction pipe and discarding the gas, and a gas supply source. A plurality of pipes for supplying a raw material gas to the gas introduction pipe and the bypass pipe are provided, and a switching valve is provided at a connection portion between the gas introduction pipe and the bypass pipe and the pipe, respectively. In a vapor phase growth method using a vapor phase growth apparatus for switching a source gas into a reaction tube and growing a desired compound semiconductor layer on a substrate arranged in the reaction tube, a desired compound semiconductor layer is formed on the substrate. Before the growth, the supply of the raw material was interrupted, and while the purge gas was allowed to flow through the pipe, the switching valve was alternately opened and closed repeatedly to exhaust the residual gas. Even if there is a dead space between the exchange valve and the switching valve, the residual gas in the pipe can be exhausted by repeatedly opening and closing the switching valve, whereby a high-purity epitaxial layer can be grown on the substrate surface in the reaction tube. The effect is that

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a suitable vapor phase growth apparatus to which the method of the present invention is applied.

FIG. 2 is an explanatory diagram showing a structure of a main part in a manifold.

FIG. 3 is a sectional view showing an example of an epi structure for a semiconductor laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Manifold 2 Reaction tube 3 Susceptor 4 Semiconductor substrate 5 High frequency coil 11,12 Bubbler (gas supply source) 15,16 Cylinder (gas supply source) 18 Gas introduction pipe 19 Bypass pipe 21-24 Mass flow controller 31-36 Piping V1-V8 Switching valve (valve)

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[Procedure amendment]

[Submission date] January 29, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

Example 1 As an example, using the apparatus shown in FIG. 1, first, n-type InP having a carrier concentration of 4 × 10 ¹⁸ cm ⁻³ was used.
On a single crystal substrate 61, an n-type InP layer 62, an undoped InGaAsP layer 63, a P-type InP layer 64 and a P-type I are formed so as to have the epi structure for a semiconductor laser shown in FIG.
The nGaAsP layer was epitaxially grown by the MOCVD method. Next, after taking out the single crystal substrate 61 on which the epi structure for the semiconductor laser is grown from the apparatus, the valves V7 and 43 are closed, and instead the valve 42 is opened and hydrogen gas is used as a purging gas to the manifold 1 through the pipe 35. The valves V3 and V4 in the manifold 1 were alternately closed and opened 100 times (total 100 minutes) at intervals of 30 seconds to clean the gas introduction pipe 18 and the bypass pipe 19. At the same time, the manifold 1 and the pipe 35 were heated to 70 ° C. After that, new abstinence
The limbal InP single crystal substrate 61 was loaded into the apparatus, and an undoped InP layer was epitaxially grown thereon by the MOCVD method. When the carrier concentration and the mobility of the obtained undoped InP layer were measured, the carrier concentration was 2 × 10 5.
^The mobility is ¹⁴ cm ⁻³ and the mobility is 1.5 × 10 ⁵ cm ² / V ·.
s and was found to be extremely high in purity.

Claims (2)

[Claims] 1. A gas introducing pipe for supplying a raw material gas into a reaction pipe, a bypass pipe for bypassing the reaction pipe and discarding the gas, and a raw material for the gas introducing pipe and the bypass pipe connected to a gas supply source. A plurality of pipes for supplying gas are provided, and a switching valve is provided at each of the connecting portions of the gas introduction pipe and the bypass pipe and the pipe, and the raw material gas is introduced into the reaction pipe by appropriately switching these switching valves. Then, in a vapor phase growth method using a vapor phase growth apparatus for growing a desired compound semiconductor layer on a substrate arranged in a reaction tube,
Before growing the desired compound semiconductor layer on the substrate,
A vapor phase epitaxial growth method characterized in that the supply of the raw material is interrupted and the purge gas is caused to flow through the pipe to alternately open and close the switching valve to exhaust the residual gas. 2. The vapor phase growth method according to claim 1, wherein the pipe is heated when the residual gas is exhausted.