JP3066654B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an improvement in a method of manufacturing a semiconductor device such as a heterojunction avalanche photodiode, which alleviates a change in composition to prevent a lattice constant from being mismatched and reduces lattice defects. MOVP that supplies gas containing elements A, B, C, and D to provide a method suitable for manufacturing a semiconductor device such as a heterojunction avalanche photodiode.
A first compound semiconductor layer composed of elements A, B, C, and D is formed by the method E, and then the source gas containing the elements A and B is gradually increased, and the source gas containing the elements C and D is gradually decreased. Forming a composition gradient layer in which the composition changes between the compound semiconductor composed of the elements A, B, C, and D and the compound semiconductor composed of the elements A and B according to the MOVPE method supplied. A heterojunction forming step of forming a second compound semiconductor layer composed of the elements A and B by a MOVPE method of supplying a source gas containing A and B, or
The first compound semiconductor layer which is a light absorption layer made of InGaAsP is formed by MOVPE method of supplying a source gas containing In, Ga, As, and P, and then the source gas containing In, P is gradually increased and A composition gradient layer whose composition changes between InGaAsP and InP is formed by the MOVPE method in which the source gas containing Ga and As is gradually reduced and supplied, and then the source gas containing In and P is supplied. A heterojunction forming step of forming a second compound semiconductor layer, which is a carrier multiplication layer made of InP, according to the MOVPE method is performed.

[Industrial applications]

The present invention relates to an improvement in a method of manufacturing a semiconductor device such as a heterojunction avalanche photodiode (APD).

In recent years, in an optical communication system, an APD using a heterojunction as a light-receiving element having a high-speed response is expected.

Since the APD has a carrier multiplication function inside the element, it is optimal as an element constituting a high-sensitivity receiver, and an ultra-high-speed APD to cope with a large capacity has been studied.

The 1-μm band APD with a small optical attenuation factor in an optical fiber has a semiconductor multilayer structure in which a light absorption layer made of InGaAs is lattice-matched to an InP substrate, and a carrier multiplication layer made of InP is formed on top of this. Has been realized.

APD with this structure has been conventionally used for liquid phase epitaxy (LPE
A heterojunction with good lattice matching and small dark current was obtained.

[Conventional technology]

However, recently, the APD has used the metal organic vapor phase epitaxy method (MOVPE method), which has good controllability, especially when growing a thin film, and has a high yield. It was found that a lattice defect was formed at the interface between the layer and the InP carrier multiplication layer, which caused a dark current and deteriorated the photoelectric conversion characteristics.

FIG. 3 is a diagram illustrating the composition of a conventional heterojunction APD manufactured by the MOVPE method.

As shown in this figure, the above-mentioned conventional APD is basically formed of In _x Ga _1-x As _1-y P _y, and has an InGaAs light absorbing layer, an InP carrier It has a structure in which a multiplication layer is formed.

In this APD, since the change in the composition of the boundary between the InGaAs light absorption layer and the InP carrier multiplication layer is sharp,
The occurrence of lattice defects cannot be avoided at that portion, and this becomes a deep level, causing an increase in dark current.

Therefore, it has been proposed to provide a composition gradient layer in the heterojunction region in order to alleviate the sharp change in the composition.

FIG. 4 is a diagram for explaining the composition of a heterojunction in which a gradient layer having a composition is provided in a conventionally proposed heterojunction region.

As shown in this figure, the above-mentioned conventionally proposed
An APD has a structure in which an InGaAs light absorbing layer, a composition gradient layer between InGaAs and InP, and an InP carrier multiplication layer are formed on an InP substrate.

[Problems to be solved by the invention]

However, it was found that when this APD was actually manufactured by the MOVPE method, a completely continuous composition gradient layer could not be formed between the InGaAs light absorption layer and the InP carrier multiplication layer.

The cause is that in the MOVPE method, the composition of the APD is performed by controlling the supply amount of the raw material gas containing the constituent elements, but when switching the valve of the mass flow controller that controls this supply amount from closed to open. This is because the supply amount of the raw material gas cannot be controlled linearly, and the raw material gas is supplied stepwise when switching to the open state, so that the composition changes sharply.

Therefore, an object of the present invention is to provide a semiconductor device having a heterojunction in which a change in composition is reduced and lattice defects in the region are reduced, in particular, an APD having a small dark current.

[Means for solving the problem]

The method for manufacturing a semiconductor device according to the present invention comprises the steps of:
A first compound semiconductor layer composed of elements A, B, C, and D is formed by a MOVPE method in which a raw material containing C and D supplies a gas, and then a raw material gas containing the elements A and B is gradually increased and The composition changes between the compound semiconductor consisting of the elements A, B, C, and D and the compound semiconductor consisting of the elements A and B by the MOVPE method in which the raw material gas containing the elements C and D is gradually reduced and supplied. A heterojunction forming step of forming a composition gradient layer to be formed and then forming a second compound semiconductor layer composed of the elements A and B by a MOVPE method in which a source gas containing the elements A and B is supplied. Or In, Ga, As,
Forming a first compound semiconductor layer which is a light absorption layer made of InGaAsP by a MOVPE method of supplying a source gas containing P;
Then, the source gas containing In and P is gradually increased, and the source gas containing Ga and As is gradually reduced and supplied.
MOVPE that forms a composition gradient layer in which the composition changes with gradient between InP and InP, and then supplies a source gas containing In and P
A heterojunction forming step of forming a second compound semiconductor layer, which is a carrier multiplication layer made of InP, depending on the method.

In the method of manufacturing a semiconductor device according to the present invention, a source gas containing the elements A, B, C, and D is supplied, and the MOVP
Forming a first compound semiconductor layer composed of elements A, B, C, and D by the method E, gradually increasing the source gas containing the elements A and B, and gradually decreasing the supply of the source gas containing the elements C and D; And the elements A, B, C, D and the elements A, B
To form a heterojunction having a step of forming a composition gradient layer between the above and a step of supplying a source gas containing the elements A and B and forming a second compound semiconductor layer composed of the elements A and B by MOVPE. The process was adopted.

It is to be noted that an avalanche photodiode is manufactured in which A is In, C is Ga, D is As, B is P, and the first compound semiconductor layer is a light absorption layer and the second compound semiconductor layer is a carrier multiplication layer. Can be.

[Action]

2 (a) to 2 (c) are explanatory diagrams of an APD by the conventional MOVPE method.

FIG. 2 (c) shows the control of the source gas flow rate by the MOVPE method.

This figure shows the process of shifting from the light absorbing layer to the composition gradient layer. The process of forming the InGaAs light absorbing layer is performed by using a valve of a mass flow controller for controlling the supply amount of PH ₃ as a source gas containing P. Then, the valve is closed and narrowed down to 0, and this valve is opened when moving to the process of forming the composition gradient layer. By this opening, the supply amount of the raw material gas increases linearly from 0 as shown by the broken line. Rather, as shown by the solid line, in the case of a full-scale 1000 cc mass flow controller, the flow rate reaches 50 cc / min in a stepwise manner, and then increases linearly with the opening angle of the valve.

FIG. 2 (b) is a diagram showing a state of a change in the composition y of P in the vicinity of the light absorbing layer and the composition gradient layer formed by the supply of the source gas.

As shown in this figure, the composition y of P does not increase linearly from 0 as shown by the broken line from the light absorbing layer, but increases stepwise as shown by the broken line. To increase.

Therefore, a mismatch in lattice constant occurs in this portion, and the characteristics of the heterojunction are impaired.

FIG. 2 (a) is a diagram illustrating the composition of the entire APD having the heterojunction described with reference to FIG. 2 (b).

As shown in this figure, basically In _x Ga _1-x As
_1-y is formed from P _y, on an InP substrate, InGaAs light absorbing layer, the composition gradient layer between the InGaAs and InP, have been structured from InP carrier multiplication layer, the starting point of the composition gradient layer There is a step in the composition.

The step in the composition causes a mismatch in the lattice constant, and the lattice defect generated thereby becomes a deep level, increasing the dark current.

The present invention has been made by considering the mechanism in which the lattice defects occur, when forming a light-absorbing layer, by supplying a minimum flow PH ₃ gas which can be narrowed linearly with mass flow controller InGaAsP When the formation of the composition gradient layer is started, the step of the composition is eliminated by using the control of the supply amount range in which the mass flow controller can linearly control.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

1 (a) to 1 (c) are explanatory diagrams of an APD by the MOVPE method according to an embodiment of the present invention.

FIG. 1 (c) shows the control of the source gas supply amount by the MOVPE method according to the embodiment of the present invention.

As shown in this figure, when the light absorbing layer is formed, it can be linearly narrowed down by a mass flow controller in advance.
InG light absorption layer by supplying a minimum flow PH ₃ gas of about 50cc
When forming with an aAsP layer and starting formation of a composition gradient layer,
By increasing the flow rate of the PH ₃ gas by using the control of the linear controllable supply amount range of the mass flow controller, which eliminates the step of composition was present in the prior art.

FIG. 1 (b) is a diagram showing a state of a change in the composition y of P in the vicinity of the light absorbing layer and the composition gradient layer formed by supplying the source gas according to the embodiment of the present invention.

As shown in this figure, since the PH ₃ gas is supplied at 50 cc / min when forming the light absorbing layer, P is contained in the light absorbing layer in a molar fraction of about 2 to 3%.

The light-absorbing layer moves linearly without a large step from the composition gradient layer to the composition gradient layer, and the composition of the heterojunction does not change sharply in this portion, and therefore, no lattice defect occurs. There is no loss.

FIG. 1 (a) is an explanatory diagram of the overall composition of an APD according to an embodiment of the present invention having the heterojunction described with reference to FIG. 1 (b).

As shown in this figure, the whole is basically In _x Ga _1-x As _1-y P _y
And an InGaAsP light absorbing layer on the InP substrate.
It is composed of a composition gradient layer between InGaAsP and InP and an InP carrier multiplication layer without any step.

The above example is based on In _x Ga _1-x As _1-y P _y
PD, but the present invention is not limited to the above composition,
The present invention can be generally applied to a semiconductor device using a compound semiconductor material and having a problem of lattice matching of a heterojunction.

In this case, In of the embodiment is A, Ga is C, As is D, and P is B.
And can be generalized and expressed.

〔The invention's effect〕

As described above, in the semiconductor device according to the present invention, it is possible to prevent the occurrence of lattice mismatch between heterojunctions, thereby reducing the occurrence of lattice defects and improving the characteristics of the heterojunction. In the APD according to the present invention, defects near the interface between the light absorption layer and the carrier doubling layer can be reduced, and as a result, dark current can be reduced, which contributes widely in the semiconductor technology field. But big.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) to 1 (c) are explanatory diagrams of an APD by the MOVPE method of an embodiment of the present invention, and FIGS. 2 (a) to 2 (c) are conventional MOVs.
FIG. 3 is an explanatory view of an APD by a PE method, FIG. 3 is an explanatory view of a composition of a conventional heterojunction APD manufactured by a MOVPE method, and FIG. It is composition explanatory drawing of joining.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 31/10-31/119 H01L 21/205

Claims (2)

(57) [Claims] 1. A first gas comprising elements A, B, C, and D formed by a MOVPE method for supplying a source gas containing the elements A, B, C, and D.
Then, the source gas containing the elements A and B is gradually increased, and the source gas containing the elements C and D is gradually reduced and supplied from the elements A, B, C and D by the MOVPE method. A composition gradient layer in which the composition changes with a gradient between the compound semiconductor and the compound semiconductor composed of the elements A and B is formed, and then the element A is supplied by the MOVPE method in which a source gas containing the elements A and B is supplied. And a heterojunction forming step of forming a second compound semiconductor layer composed of B and B. 2. A source gas containing In, Ga, As, and P is supplied.
Forming a first compound semiconductor layer, which is a light absorbing layer made of InGaAsP, by MOVPE, and then gradually increasing the source gas containing In and P and gradually decreasing the source gas containing Ga and As to supply MOVPE InGaAsP depending on the method
Forming a composition gradient layer in which the composition changes in a gradient manner between InP and InP, and then a second compound which is a carrier multiplication layer made of InP by MOVPE method of supplying a source gas containing In and P. A method for manufacturing a semiconductor device, comprising a step of forming a heterojunction for forming a semiconductor layer.