JPH08330236A - Metal organic chemical vapor deposition - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a metal organic chemical vapor deposition method for forming an epitaxial layer containing a carbon-doped compound semiconductor having a flat and mirror-finished surface on a Group 3-5 compound semiconductor substrate. In the metal-organic chemical vapor deposition method of growing at least one carbon-doped group 3-5 compound semiconductor epitaxial crystal layer on a group 3-5 compound semiconductor substrate, the plane orientation of the substrate surface is changed from the <100> direction to It is tilted in the <110> direction at an angle larger than 0.1 ° and smaller than 1.0 °.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is for producing electronic devices such as FETs, HBTs and HEMTs, and light emitting devices such as LDs and LEDs.
The present invention relates to a metal organic chemical vapor deposition method for epitaxially growing a 3-5 group compound semiconductor crystal layer on a -5 group compound semiconductor substrate.

[0002]

2. Description of the Related Art GaAs and AlGaA are grown by metalorganic vapor phase epitaxy.
When manufacturing compound semiconductor crystal thin films such as s, InGaP, InP, InGaAs, etc., the crystal plane orientation of the compound semiconductor substrate is tilted 2 ° in the <110> direction from the <100> plane (commonly known as 2 ° off substrate). ) Is generally used. The reason is that when a thin film is grown on the <100> plane (commonly called just substrate) by metalorganic vapor phase epitaxy, dislocations (defects) in the substrate grow abnormally as nuclei, and the resulting epitaxial thin film has many defects. Is. Therefore, it is difficult to grow the mirror surface and the surface is often clouded.
On the other hand, when a 2 ° -off substrate is used, a monoatomic layer step (monolayer step) exists on the substrate, and growth (step flow growth) is performed using the step (kink) as a nucleus. In comparison, abnormal growth centered on dislocations in the substrate is suppressed, and mirror growth is possible.

In the growth mode of the ordinary metal-organic vapor phase epitaxy, TMGa and TMAl, which are group 3 raw materials, are sufficiently decomposed and the impurity concentration (carbon concentration) in the growing crystal is sufficiently lowered.
The growth temperature is raised to 600 ° C or higher and the supply ratio of the Group 5 and Group 3 raw materials (Group 5/3) is set to 10 or higher. In such a growth mode, by using the 2 ° -off substrate, the step flow growth is favorably performed, and the mirror surface growth becomes possible.

[0004]

When a C-doped compound semiconductor thin film is grown without using an intentional carbon C dopant (for example, CCl ₄ or CBr ₄ ), undecomposed carbon in the Group 3 raw material is removed. The method of incorporation into crystals is performed. In this case, the growth temperature and the supply amount ratio of the group 5 raw material and the group 3 raw material (group 5 /
Group 3) is lowered together, and a growth mode different from the growth mode of the usual metal-organic vapor phase epitaxy is used. For example, in the case of growing C-doped GaAs, the growth temperature is 480 to 600 ° C., 5
Supply ratio of Group 3 and Group 3 raw materials (Group 5/3 Group) is 0.5 to 2
To

However, in the growth mode different from the usual one, there is a problem that good step flow growth cannot be performed even if a 2 ° off substrate is used. That is, at this time, surface irregularities due to abnormal growth centered on dislocations of the substrate can be suppressed to some extent. However, during the growth under these conditions, or when the temperature inside the furnace is increased to make it a normal growth condition after this growth, or when annealing is performed at a high temperature after the growth, the steps of the monoatomic layer are gathered and several atomic layers to So-called step bunching, which is a step difference of a dozen atomic layers, occurs.

This situation will be schematically described with reference to FIG. FIG.
Puts a C-doped GaAs layer 2 on a 2 ° off GaAs substrate 1.
The structure sandwiched by the AlGaAs layers 3 is laminated to obtain a high magnification.
It is a figure which shows the image at the time of seeing with TEM (transmission electron microscope). C-doped GaAs with unusual growth mode
Layer 2 is grown, then AlGaAs layer 3 in normal growth mode
As a result, the (100) plane is emphasized on the C-doped GaAs layer 2 as shown in the figure. Although the irregularities on the surface are not defects on the crystal, the steepness of the interface is lost. As a result, for example, in the heterojunction bipolar transistor having the C-doped GaAs layer as a base, the n-value of the base current becomes large when performing the Gummel plot, which is one of the typical transistor characteristics. Occurred. Furthermore, due to this shape, the current gain may be reduced and the reliability may be reduced.

Incidentally, the phenomenon of this step bunching is
It has been confirmed that this will not happen if a just substrate is used. However, as described above, just substrate or <100>
When using a substrate within 0.1 degrees off, many surface defects called hillocks and pits appear on the surface, and there is a problem that the surface condition deteriorates. Therefore, an object of the present invention is to provide a metal organic chemical vapor deposition method for forming an epitaxial layer including a C-doped compound semiconductor layer having a flat and mirror-finished surface on a 3-5 group compound semiconductor substrate. To do.

[0008]

As a result of earnest studies to achieve the above object, the inventors have found that step bunching can be eliminated by changing the off angle of the substrate, and have reached the present invention. That is, the present invention provides a metal-organic vapor phase epitaxy method of growing at least one carbon-doped Group 3-5 compound semiconductor epitaxial crystal layer on a Group 3-5 compound semiconductor substrate, wherein the plane orientation of the substrate surface is <100. It is characterized in that it is inclined from the> direction in the <110> direction at an angle larger than 0.1 ° and smaller than 1.0 °. .

[0009]

The present invention is based on new experimental findings. That is, the size of the off-angle of the 3-5 group compound semiconductor substrate was changed, the 3-5 group compound semiconductor epitaxial crystal layer was grown, and the interface shape and surface state were examined in detail. As a result, when the off angle was <1 °, step bunching did not occur even in a growth mode different from the normal one. Also, when the off angle was> 0.1 °, mirror surface growth was obtained. From this fact, when growing a C-doped group III-V compound semiconductor epitaxial crystal layer, if the off-angle of the substrate is inclined at an angle larger than 0.1 ° and smaller than 1.0 °, a good surface condition is obtained. Epitaxial layers can be grown.

This phenomenon can be qualitatively understood as follows. That is, when the off angle is 1 ° or more, the step interval becomes relatively small, and the mean free path where the raw material can migrate on the substrate is larger than the step interval, so that step bunching occurs. Regarding the surface condition, step flow growth does not occur at an off angle of 0.1 ° or less, and abnormal growth occurs.

[0011]

EXAMPLES The present invention will be described in detail below based on examples. A GaAs: Si (n = 5x10 ¹⁸ cm ^-3 , thickness t = 500 nm) subcollector layer, GaAs: Si (n = 2x10 ¹⁶ cm ^-3 ,) on a GaAs <100> 0.4 ° off substrate. t = 500 nm) collector layer, GaAs: C (n = 4x10 ¹⁹ cm ^-3 , t = 70 nm) base layer, AlGaAs: Si (n = 5x10 ¹⁷ cm ^-3 , t = 200 nm) emitter layer , GaAs: Si (n = 5x10 ¹⁸ cm ^-3 , t = 100nm)
Was sequentially formed by metal organic chemical vapor deposition to prepare an epitaxial substrate for a heterojunction bipolar transistor. Growth temperature at this time and Group 5 raw material and 3
Table 1 shows the supply amount ratio (group 5/3 group) of the group raw materials.

[0012]

The top surface of the C-doped GaAs base layer (that is, the emitter-base interface) thus laminated was flat when observed by TEM, and the surface of the epitaxial substrate was in a good mirror state. A transistor element was produced using this epitaxial substrate, and the electrical characteristics were examined.
As a comparative example, metal organic chemical vapor deposition was carried out on a just substrate and a substrate at 2 ° off under the conditions of Table 1 as in the above-mentioned examples to prepare the same epitaxial substrate, and these epitaxial substrates were used. Then, a transistor element was produced and the electrical characteristics were examined.

Table 2 shows the surface state of the epitaxial substrate, the state of the emitter base (E / B) interface, and the electrical characteristics of the device in the above-mentioned Examples and Comparative Examples. The larger the current gain, the better the characteristics. Further, the idealization coefficient of the base current (IB) obtained from the voltage-current characteristics when the heterojunction bipolar transistor is operated, that is, the so-called Gummel plot n (IB) is shown. This value is 1
A value in the range of 2 can be taken, and a value closer to 1 indicates a state closer to the ideal. As can be seen from Table 2, when the present example and the comparative example are compared, the epitaxial substrate of the present example is good in both the surface state and the E / B interface state. In addition, the transistor element manufactured from the epitaxial substrate of the present example shows superior characteristics to the comparative example when the current gain and n (IB) are combined.

[0015]

In the above embodiment, the C-doped GaAs base layer grown on the GaAs substrate was used. However, the GaAs layer is not always required. For example, a C-doped AlGaAs layer grown on the GaAs substrate. Similar results were obtained for the InGaAs layer and the C-doped InGaAs layer on the InP substrate.

[0017]

As described above, according to the present invention, 3
In a metal organic chemical vapor deposition method for growing at least one carbon-doped Group 3-5 compound semiconductor epitaxial crystal layer on a Group-5 compound semiconductor substrate, the plane direction of the substrate surface is changed from <100> to <110>. To tilt at an angle greater than 0.1 ° and less than 1.0 °,
It has an excellent effect that the interface after growth is flat and a surface in a good mirror state can be obtained. Therefore, by using the epitaxial wafer grown in this way, a device having excellent electrical characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an epitaxial laminated substrate illustrating a problem of a conventional metal organic chemical vapor deposition method.

[Explanation of symbols]

 1 GaAs substrate 2 C-doped GaAs layer 3 AlGaAs layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Kojima 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A metal organic chemical vapor deposition method for growing at least one carbon-doped Group 3-5 compound semiconductor epitaxial crystal layer on a Group 3-5 compound semiconductor substrate,
The plane orientation of the substrate surface is changed from the <100> direction to the <110> direction.
An organometallic vapor phase epitaxy method characterized by inclining at an angle larger than 0.1 ° and smaller than 1.0 °.