JP2001007320A - Epitaxially grown compound semiconductor wafer and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress effects of a deep level which is formed of impurities and the like, which exist in the interface between a substrate and an epitaxial layer, and to obtain a semiconductor wafer having a buffer layer structure which has satisfactory reproducibility. SOLUTION: This wafer is an epitazially grown compound semiconductor wafer formed into a structure, where a buffer layer is formed on a GaAs substrate 2 and an active layer 1 is formed on the buffer layer. In this case, the buffer layer consists of an undoped AlGaAs layer 4 which is formed on the surface of the substrate, and an undoped GaAs layer 3 which is formed on this undoped AlGaAs layer, and the layer 4 is formed in such a way that the layer 4 is formed thinner than the layers 1 and 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxially grown compound semiconductor wafer and a field effect transistor (high electron mobility transistor (HEMT: HiMT) using the same.
gh Electron Mobility Transistor)
Called T. In particular, the present invention relates to an epitaxially grown compound semiconductor wafer in which the influence of impurities present at the interface between a semi-insulating semiconductor substrate and an epitaxial layer is suppressed, and a semiconductor device using the same.

[0002]

2. Description of the Related Art In a conventional general GaAs FET, a compound semiconductor active layer (hereinafter, referred to as an active layer) is formed on a semi-insulating GaAs substrate (hereinafter, referred to as a substrate), and electrodes are formed on the active layer. It was formed. But,
In a semiconductor wafer used for a GaAs FET having such a configuration, a defect or an impurity existing at the interface between the substrate and the active layer causes a decrease in electron mobility or compensation of carriers, resulting in a high-performance FET. The quality was not enough to obtain such a semiconductor device.

In order to prevent the influence of defects and impurities existing at the interface between the substrate and the active layer, a technique for forming a high-resistance buffer layer between the substrate and the active layer has been developed and is now widely used. . In a semiconductor wafer composed of a semi-insulating GaAs substrate / buffer layer / active layer, a structure using an undoped GaAs layer, an undoped AlGaAs layer, or an AlGaAs / GaAs superlattice as a high-resistance buffer layer has been proposed. Kaikai 54-12261
No., JP-A-58-107679). Further, in order to increase the resistance of the buffer layer, a method of doping oxygen into the buffer layer (JP-A-4-328822) has been proposed.

[0004]

However, in a semiconductor wafer using an undoped GaAs layer or an undoped AlGaAs layer as a high-resistance buffer layer, the buffer layer was statically high in resistance, but was operated as an FET. In this case, it is difficult to completely eliminate the influence of a deep level which is considered to be formed by impurities or the like existing at the interface between the substrate and the epitaxial layer. Further, in a semiconductor wafer using an AlGaAs / GaAs superlattice as the buffer layer, although the effect of reducing the influence of the interface between the substrate and the buffer layer can be seen, the quantum level formed in the superlattice is lower than that of the FET. There is a problem that the characteristics are affected, and the resistance of the buffer layer changes depending on the purity of the AlGaAs layer grown epitaxially.

The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to suppress the influence of deep levels formed by impurities and the like existing at the interface between a substrate and an epitaxial layer. Another object of the present invention is to provide a semiconductor wafer having a reproducible buffer layer structure.

[0006]

The summary of the invention disclosed in the present application is as follows.

That is, in an epitaxially grown compound semiconductor wafer (hereinafter abbreviated as a semiconductor wafer) in which a buffer layer is formed on a GaAs substrate and an active layer is formed thereon, the buffer layer is formed on the surface of the GaAs substrate. Undoped AlGaAs layer and undoped GaAs formed on the undoped AlGaAs layer
The undoped AlGaAs layer is made thinner than the active layer and the undoped GaAs layer. According to the structure of the buffer layer, it is possible to suppress the influence of the deep level formed by impurities and the like existing at the interface between the GaAs substrate and the epitaxial layer,
By making the undoped AlGaAs layer thin, Al
Variations in characteristics due to variations in the concentration of impurities such as oxygen in the GaAs layer can be reduced, so that a high-quality semiconductor wafer can be provided with good reproducibility.

Further, the thickness of the undoped AlGaAs layer constituting the buffer layer may be set to 20 nm or less, preferably 5 to 15 nm.

A semiconductor device using the above semiconductor wafer as a substrate and having electrodes formed on the surface of an active layer has excellent high frequency characteristics.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

This embodiment is an example in which the present invention is applied to a semiconductor wafer used for a GaAs FET. The semiconductor wafer of this embodiment was manufactured by performing epitaxial growth using MBE (molecular beam epitaxial growth).

FIG. 1 is a sectional structural view of a semiconductor wafer according to this embodiment. The semiconductor wafer of this embodiment has a structure in which an undoped AlGaAs layer 4, an undoped GaAs layer 3, and an active layer 1 are sequentially stacked on a semi-insulating GaAs substrate 2. Buffer layer is undoped AlGaAs layer 4
And an undoped GaAs layer 3. The thickness of the semi-insulating GaAs substrate 2 is 600 μm, and undoped Al
The thickness of the GaAs layer 4 is 10 nm, the thickness of the undoped GaAs layer 3 is 600 nm, and the thickness of the active layer 1 is 300 nm.
It is. The carrier concentration of the active layer 1 is 1.5 × 10
¹⁷ cm- ³ .

In the semiconductor wafer of this embodiment, the buffer layer and the active layer having the above-described structure are connected to each other in order to examine the change in the leak current from the buffer layer with respect to the growth temperature.
Epitaxial growth was performed at growth temperatures of 0 ° C., 530 ° C., and 580 ° C., respectively. Further, a sample as shown in FIG. 4 was prepared to measure a leak current from the buffer layer. In the sample shown in FIG. 4, a circular electrode 10 having a diameter of 200 μm is formed on the active layer of each semiconductor wafer, and an electrode 20 is formed so as to surround the electrode 10 at a distance of 30 μm. The buffer layer is exposed by etching the active layer. For each sample, a current flowing when a voltage of 50 V was applied between the electrode 10 and the electrode 20 was measured, and this was defined as a leak current from the buffer layer.

FIG. 5 shows the result of measurement for each sample. In the case of the semiconductor wafer of the present embodiment, the leakage current from the buffer layer is less than 100 nA for the sample in which the buffer layer is grown at any temperature, and it can be said that the sample is stable regardless of the growth temperature.

Further, a source electrode, a drain electrode, and a gate electrode are formed on the active layer surface of the semiconductor wafer of this embodiment to manufacture an FET, and a noise figure (NF) and a gain (Gain) are obtained in order to examine a high frequency characteristic thereof. As a result, the noise figure was 0.52 dB and the gain was 11.1 dB.

In order to confirm the effect of the present embodiment, the present inventor manufactured a conventional semiconductor wafer and FET having a buffer structure and performed a comparative experiment.

Comparative Example 1 Comparative Example 1 is a semiconductor wafer in which a high resistance undoped GaAs layer, which is a conventional typical buffer structure, is used as a buffer layer, and the buffer layer and the active layer are formed by MBE in the same manner as in the above-described embodiment. It was formed by epitaxial growth by a method (molecular beam epitaxial growth method).

FIG. 2 is a sectional structural view of a semiconductor wafer of Comparative Example 1, which differs from this embodiment only in the configuration of the buffer layer. In Comparative Example 1, the undoped GaAs layer 5 was used as a buffer layer, and its thickness was 600 nm. Note that the thickness of the semi-insulating GaAs substrate 2, the thickness of the active layer 1, and the carrier concentration are the same as those of the semiconductor wafer of the present embodiment.

For Comparative Example 1, the leak current from the buffer layer was measured in the same manner as in this embodiment. FIG. 5 shows the measurement results of each sample. In the case of the semiconductor wafer of Comparative Example 1, the higher the growth temperature, the larger the leakage current from the buffer layer, and the magnitude of the leakage current was 10,000 nA or more.

A source electrode, a drain electrode, and a gate electrode were formed on the active layer surface of the semiconductor wafer of Comparative Example 1 to fabricate an FET, and a noise figure (NF) and a gain (Gain) were obtained in order to examine high-frequency characteristics. As a result, the noise figure was 0.64 dB and the gain was 10.8 dB.

Comparative Example 2 Comparative Example 2 is a semiconductor wafer using an AlGaAs / GaAs superlattice as a buffer layer, which is another typical buffer structure of the related art, and the buffer layer and the active layer are the same as in the above embodiment. It was formed by epitaxial growth by MBE (molecular beam epitaxial growth).

FIG. 3 is a sectional view of a semiconductor wafer of Comparative Example 2, which differs from this embodiment only in the structure of the buffer layer. In Comparative Example 2, the AlGaAs / GaAs superlattice layer 6 was used as a buffer layer, and its thickness was AlGaAs (15).
nm) / GaAs (5 nm) × 20 cycles for a total of 40
0 nm. The thickness of the semi-insulating GaAs substrate, the thickness of the active layer, and the carrier concentration are the same as those of the semiconductor wafer of the present embodiment.

With respect to Comparative Example 2, the leakage current from the buffer layer was measured in the same manner as in this embodiment. However, only two growth temperatures of 430 ° C. and 530 ° C. were used. FIG. 5 shows the measurement results of each sample. In the case of the semiconductor wafer of Comparative Example 2, the leakage current from the buffer layer was 10,000 nA or more for the sample grown at 430 ° C. Leak current decreased to less than 100 nA.

A source electrode, a drain electrode, and a gate electrode were formed on the active layer surface of the semiconductor wafer of Comparative Example 2 to fabricate an FET, and a noise figure (NF) and a gain (Gain) were obtained in order to examine the high-frequency characteristics. As a result, the noise figure was 0.55 dB and the gain was 11.1 dB.

From the above, the leakage current from the buffer layer was smaller in the semiconductor wafer of the present embodiment than in the comparative examples 1 and 2.
It can be said that it is smaller than that of No. 2 and stable regardless of the growth temperature. Table 1 shows the results of evaluating the high-frequency characteristics by using a noise figure (NF) and a gain (Gain). When compared with the noise figure (NF), this embodiment is the lowest, and is not affected by the interface. It can be seen that the characteristics have been improved. Thus, according to the semiconductor wafer of the present embodiment, it is possible to suppress the influence of the deep level formed by the impurities and the like existing at the interface between the GaAs substrate and the epitaxial layer. An excellent high quality semiconductor device can be produced.

[0026]

[Table 1]

Although the present embodiment has described the semiconductor wafer used for the FET, the present invention is not limited to this. For example, by forming an electron supply layer made of n-type AlGaAs or the like on the surface of the active layer of the semiconductor wafer of the above embodiment, the semiconductor wafer used for HEMT can be obtained.

It is clear that the same effects as those of the present invention can be obtained even if a thin AlGaAs layer is present in the undoped GaAs buffer layer, and it goes without saying that such a structure is also included in the scope of the present invention. No.

[0029]

The invention disclosed in the present application is based on GaAs.
In an epitaxially grown compound semiconductor wafer having a buffer layer formed on an s substrate and an active layer formed thereon, the buffer layer comprises an undoped AlGaAs layer formed on the surface of the GaAs substrate and the undoped AlGa layer.
And an undoped GaAs layer formed on the As layer. The undoped AlGaAs layer is thinner than the active layer and the undoped GaAs layer.
The influence of the deep level formed by impurities and the like existing at the interface between the aAs substrate and the epitaxial layer can be suppressed, and by making the undoped AlGaAs layer thin,
Since fluctuations in characteristics due to fluctuations in the concentration of impurities such as oxygen in the AlGaAs layer can be reduced, a high-quality semiconductor wafer can be provided, and a high-performance semiconductor device can be manufactured by using this semiconductor wafer.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor wafer of the present embodiment.

FIG. 2 is a cross-sectional view of a semiconductor wafer of Comparative Example 1.

FIG. 3 is a cross-sectional view of a semiconductor wafer of Comparative Example 2.

FIG. 4 is a schematic configuration diagram of a sample used when measuring a leak current from a buffer layer.

FIG. 5 is a graph showing a result of measuring a leak current from a buffer layer for a semiconductor wafer on which a buffer layer and an active layer are grown at each temperature.

[Explanation of symbols]

 Reference Signs List 1 active layer 2 semi-insulating GaAs substrate 3 undoped GaAs buffer layer 4 undoped AlGaAs buffer layer 5 high-resistance GaAs buffer layer 6 GaAs / AlGaAs superlattice buffer layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 29/201 F-term (Reference) 5F052 DA05 DB06 GC04 JA10 5F102 FA01 GB01 GC01 GD01 GJ05 GK05 GK06 GK08 HC01 5F103 AA04 DD03 DD05 HH03 LL09 RR06

Claims (3)

[Claims] 1. An epitaxially grown compound semiconductor wafer having a buffer layer formed on a GaAs substrate and an active layer formed thereon, wherein the buffer layer is formed of G
an undoped AlGaAs layer formed on the surface of an aAs substrate and an undoped GaAs layer formed on the undoped AlGaAs layer;
An epitaxially grown compound semiconductor wafer, wherein the layer is thinner than the active layer and the undoped GaAs layer. 2. An undoped A constituting said buffer layer
The thickness of the lGaAs layer is 20 nm or less, preferably 5 to 1 nm.
2. The epitaxially grown compound semiconductor wafer according to claim 1, wherein the thickness is 5 nm. 3. A semiconductor device comprising the epitaxially grown compound semiconductor wafer according to claim 1 or 2 as a substrate and electrodes formed on the surface of the epitaxially grown layer.