JP2001102305A - Manufacturing method of compound semiconductor eiptiaxial wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely remove Si impurity from a boundary face between the substrate of a compound semiconductor epitaxial wafer and an optiaxial layer, and to reduce leakage currents generated on the boundary face. SOLUTION: An organic V group compound is introduced immediately before an epitaxial layer 2 is grown on a semiconductor insulating GaAs substrate 1, so that Si impurity can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor epitaxial wafer and a method of manufacturing the same, and more particularly, to a semi-insulating G wafer.
The present invention relates to a method for manufacturing a compound semiconductor epitaxial wafer in which an epitaxial layer of a group III and group V compound is formed on an aAs substrate.

[0002]

2. Description of the Related Art For example, a high electron mobility type transistor (HEMT) can be formed by an epitaxial layer grown on a semi-insulating GaAs substrate.

This epitaxial layer is a compound of a group III and a group V and is formed by vapor phase epitaxial growth while heating a semi-insulating GaAs substrate in a reaction chamber.

An epitaxial wafer for HEMT is formed by sequentially epitaxially growing the following layers (1) to (4) on a semi-insulating GaAs substrate (see FIG. 1).

(1) As a buffer layer, an epitaxial layer having a multilayer structure of undoped GaAs with high resistance or undoped GaAs and undoped AlGaAs of 0.1 to 1 μm.

(2) As the spacer layer, undoped A
lGaAs is 2-3 nm.

(3) As an electron supply layer, n-type AlGa
As is 10 to 50 nm.

(4) As the ohmic contact layer, n
-Type GaAs 50-200 nm.

The buffer layer first grown and formed on the substrate forms a high-purity, high-resistance layer. Due to the presence of the buffer layer, the two-dimensional electron gas in the electron supply layer is adversely affected by the substrate. In addition, by controlling the thickness of the spacer layer on the order of several nm, high mobility can be obtained in the two-dimensional electron gas.

[0010]

In the compound semiconductor epitaxial wafer described above, a semi-insulating GaAs substrate and
There is a problem that a low-resistance conductive layer is interposed at the interface between the epitaxial layer grown on the substrate and the buffer layer in particular.

The reason that the low resistance layer is formed is that the semi-insulating G
Si (silicon) originally attached to the surface of the aAs substrate
This is because impurities are taken into the crystal during epitaxial crystal growth and become n-type carriers. If there is Si impurity acting as this n-type carrier,
The resistance at the interface between the substrate and the buffer layer drops, causing a leakage current in that buffer layer, thereby causing, for example, H
There is a problem that the characteristics of the EMT and the FET are deteriorated.

Therefore, conventionally, semi-insulating GaAs is used.
Prior to growing an epitaxial layer on a substrate, a cleaning treatment by sulfuric acid etching has been performed on the substrate surface in order to remove Si impurities on the surface of the s substrate.

However, the above-mentioned Si impurities cannot be completely removed only by cleaning treatment by sulfuric acid etching, and it is insufficient to solve the above-mentioned problem.

The problem to be solved by the present invention is to manufacture a compound semiconductor epitaxial wafer capable of reliably reducing the leakage current in the epitaxial layer and improving the performance of a high electron mobility type transistor such as a HEMT. It is to provide a method.

[0015]

The first means is to heat a semi-insulating GaAs substrate in a reaction chamber and to place a III-GaAs substrate on the substrate.
A method for producing a compound semiconductor epitaxial wafer, comprising introducing an organic group V compound into a reaction chamber immediately before growing a target epitaxial layer when a compound of group V and group V is grown by vapor phase epitaxial growth. It is.

According to the above means, the Si impurity concentration at the interface between the substrate and the epitaxial layer can be greatly reduced. This makes it possible to obtain a compound semiconductor epitaxial wafer in which the interface between the substrate and the epitaxial layer is formed with high purity and high resistance. In the epitaxial wafer manufactured as described above, since the leakage current in the epitaxial layer is reliably reduced, the performance of a high electron mobility type transistor such as, for example, HEMT can be improved.

[0017] The second means is the first means,
The introduction of the organic group V compound into the reaction chamber is performed by arsine (As
A method for producing a compound semiconductor epitaxial wafer, wherein H ₃ ) is performed without flowing into the reaction chamber.

According to the above-mentioned means, the removal can be performed without inhibiting the removal of the Si impurities by the introduction of the organic group V compound. Thereby, the Si impurity concentration at the interface between the substrate and the epitaxial layer can be reliably reduced.

A third means is the compound semiconductor epitaxial wafer according to the first or second means, wherein the substrate surface temperature is 350 to 900 ° C. when the organic group V compound is introduced into the reaction chamber. It is a manufacturing method of.

According to the above means, it is possible to effectively remove Si impurities from the substrate surface under a suitable temperature condition. Thereby, the Si impurity concentration at the interface between the substrate and the epitaxial layer can be reliably reduced.

A fourth means is a method for manufacturing a compound semiconductor epitaxial wafer according to any one of the first to third means, wherein the organic group V compound is trimethylamine (TMAs).

According to the above means, the Si impurity concentration at the interface between the substrate and the epitaxial layer can be greatly reduced. This makes it possible to obtain a compound semiconductor epitaxial wafer in which the interface between the substrate and the epitaxial layer is formed with high purity and high resistance.

A fifth means is the method for producing a compound semiconductor epitaxial wafer according to any one of the first to third means, wherein the organic group V compound is tertiary butyl arsine (TBAs). .

According to the above-mentioned means, similarly to the above-mentioned fifth means, S at the interface between the above-mentioned substrate and the above-mentioned epitaxial layer is obtained.
The i impurity concentration can be significantly reduced. This makes it possible to obtain a compound semiconductor epitaxial wafer in which the interface between the substrate and the epitaxial layer is formed with high purity and high resistance.

A sixth means is the method for manufacturing a compound semiconductor epitaxial wafer according to any one of the first to third means, wherein the organic group V compound is trisdimethylaminoarsine (TDAAs). .

According to the above means, similarly to the fourth or fifth means, the Si impurity concentration at the interface between the substrate and the epitaxial layer can be significantly reduced. This makes it possible to obtain a compound semiconductor epitaxial wafer in which the interface between the substrate and the epitaxial layer is formed with high purity and high resistance.

[0027]

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

It should be noted that the same reference numerals indicate the same or corresponding parts between the drawings.

FIG. 1 schematically shows a cross-sectional structure of a compound semiconductor epitaxial wafer to which the technique of the present invention is applied.

The compound semiconductor epitaxial wafer shown in FIG. 1 is obtained by growing an epitaxial layer 2 on a semi-insulating GaAs substrate 1.

The epitaxial layer 2 is a compound of group III and group V, and has a buffer layer 21, a spacer layer 22, an electron supply layer 23, and an ohmic contact layer 24 sequentially formed.

The buffer layer 21 is made of a high-resistance undoped G
aAs or undoped GaAs and undoped AlG
a-As epitaxial layer having a multilayer structure of 0.1 to
It was formed with a thickness of 1 μm.

The spacer layer 22 is made of undoped AlGa
As is formed with a thickness of 2 to 3 nm.

The electron supply layer 23 is formed of n-type AlGaAs with a thickness of 10 to 50 nm.

The ohmic contact layer 24 is made of n-type G
aAs is formed in a thickness of 50 to 200 nm.

Each layer 21 to 2 in the epitaxial layer 2
4 is a semi-insulating GaAs substrate 1 in the reaction chamber.
Is formed by a vapor phase epitaxial growth method while heating.

Here, the interface 11 between the semi-insulating GaAs substrate 1 and the epitaxial layer 2 is formed by introducing an organic group V compound into the reaction chamber immediately before the growth of the epitaxial layer 2 (buffer layer 21). Si impurities have been removed. The method of removing Si impurities by the organic group V compound is known by the present inventors. According to this method, Si impurities on the substrate surface that cannot be completely removed by the cleaning treatment using sulfuric acid-based etching are also removed. It was confirmed that it could be almost completely removed.

Therefore, the above-described compound semiconductor epitaxial wafer is provided at the interface 11 between the substrate 1 and the buffer layer 21.
Is maintained at high purity and high resistance, whereby the leakage current in the buffer layer 21 is reduced, and the characteristics of, for example, HEMTs and FETs can be improved.

Next, a method for manufacturing the above-described compound semiconductor epitaxial wafer will be described.

First, an organic group V compound is introduced into the reaction chamber while the semi-insulating GaAs substrate 1 pre-cleaned by sulfuric acid etching is heated in the reaction chamber.

At this time, the introduction of the organic group V compound is as follows.
The reaction is performed without flowing arsine (AsH ₃ ) into the reaction chamber.
AsH ₃ is a substance (inorganic group V compound) that flows into the reaction chamber for epitaxial growth, but when the above organic group V compound is introduced, SiH formed by the organic group V compound is used.
In order to prevent the removal of impurities from being hindered, it is desirable that the organic V-group compound is not simultaneously introduced into the reaction chamber.

The surface temperature of the substrate 1 when introducing the organic group V compound into the reaction chamber is set at 350 to 900 ° C. The present inventors have confirmed that this temperature of 350 to 900 ° C. is most effective for removing Si impurities.

Examples of the organic group V compound include trimethylamine (TMAs) and tertiary butylarsine (TB
As) or trisdimethylaminoarsine (TDA
As) is used. These are each Si
The inventor has confirmed that it is effective in removing impurities, but does not prevent the use of organic Group V compounds other than those described above.

After the removal of the Si impurity by the introduction of the organic group V compound, the target epitaxial layer 2 is immediately grown. That is, Group III and Group V compounds are grown on the substrate 1 heated in the reaction chamber by vapor phase epitaxial growth.

By forming the buffer layer 21, the spacer layer 22, the electron supply layer 23, and the ohmic contact layer 24 in this order by this epitaxial growth, a compound semiconductor epitaxial wafer for HEMT having a sectional structure as shown in FIG. Can be formed.

[0046]

Embodiments of the present invention will be described below.

FIG. 2 shows a sectional structure of a wafer formed for evaluating a compound semiconductor epitaxial wafer according to the present invention.

This wafer is obtained by sequentially forming a high-resistance buffer layer 21 and an active layer 231 as an epitaxial layer 2 on a 2 ° OFF (100) plane semi-insulating GaAs substrate 1 by vapor phase epitaxial growth. is there. The high resistance buffer layer 21 is made of 50% undoped GaAs.
The active layer 231 is made of n-type GaAs of 100 nm thick.
It was formed with a thickness of nm. These two layers 21, 231
Can have a simple FET structure.

In forming the above epitaxial wafer,
Immediately before the epitaxial layer 2 was grown, an organic group V compound was introduced. At this time, the flow rate of the organic group V compound was 100 cc / min, and the time was 1 minute.

The epitaxial wafer into which the organic group V compound was introduced as described above was prepared for each type of the organic compound material (TMAs, TBAs, TDAAs). For comparison, a wafer on which the epitaxial layer 2 was grown without introducing an organic group V compound was also prepared under the same substrate and the same growth conditions.

Hereinafter, measurement results of the characteristics and quality of each wafer will be described.

Table 1 shows the epitaxial layer 2 of the wafer.
3 shows a pinch-off voltage of the FET structure formed in FIG. The pinch-off voltage is an index indicating high purity and steepness of the buffer layer 21. As is clear from Table 1, it is clear that the introduction of the organic group V compound is superior in the steepness of the buffer layer, and that good device characteristics are obtained.

[0053]

[Table 1]

Further, the interface 11 between the epitaxial layer 2 having the FET structure and the substrate 1 was subjected to two-dimensional ion mass spectrometry to identify residual elements. Table 2 shows the results. As apparent from Table 2, when the Si concentration at the interface 11 between the GaAs substrate 1 and the epitaxial layer 2 is compared, the Si concentration in the case where the organic group V compound is introduced is clearly reduced, and the high-quality buffer layer is obtained. It can be seen that 21 is formed.

[0055]

[Table 2]

As can be seen from the above results, in the compound semiconductor epitaxial wafer according to the present invention, the Si impurity concentration at the interface between the substrate and the buffer layer is significantly reduced, whereby the leakage current in the epitaxial layer is reliably reduced, and It was confirmed that the performance of the transistor formed of the layer was improved.

[0057]

According to the present invention, in a compound semiconductor epitaxial wafer having a semi-insulating GaAs substrate on which an epitaxial layer of a group III and group V compound is formed, Si impurities at the interface between the substrate and the epitaxial layer are reduced. , Organic V performed immediately before the growth of the epitaxial layer
By being surely removed by the introduction of the group III compound, the effect that the leak current in the epitaxial layer can be surely reduced and the performance of a high electron mobility type transistor such as HEMT can be improved can be obtained. Can be

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a compound semiconductor epitaxial wafer for HEMT to which the technique of the present invention is applied.

FIG. 2 is a view showing a sectional structure of a compound semiconductor epitaxial wafer for a simple FET to which the technique of the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 semi-insulating GaAs substrate 2 epitaxial layer 11 interface between substrate and epitaxial layer 21 buffer layer 22 spacer layer 23 electron supply layer 24 ohmic contact layer 231 active layer

Claims (6)

[Claims] When a semi-insulating GaAs substrate is heated in a reaction chamber and a group III and group V compound is grown on the substrate by a vapor phase epitaxial growth method, immediately before a target epitaxial layer is grown, A method for producing a compound semiconductor epitaxial wafer, comprising introducing an organic group V compound into a reaction chamber. 2. The method according to claim 1, wherein the introduction of the organic group V compound into the reaction chamber is performed without flowing arsine (AsH ₃ ) into the reaction chamber. 3. The method for producing a compound semiconductor epitaxial wafer according to claim 1, wherein the substrate surface temperature when introducing the organic group V compound into the reaction chamber is 350 to 900 ° C. 4. The method according to claim 1, wherein the organic group V compound is trimethylamine (TM).
4. The method for producing a compound semiconductor epitaxial wafer according to claim 1, wherein the method is As). 5. The organic group V compound is tertiary butyl arsine (TBAs).
The method for producing a compound semiconductor epitaxial wafer according to any one of the above. 6. The method according to claim 1, wherein the organic group V compound is trisdimethylaminoarsine (TDAAs).
4. The method for producing a compound semiconductor epitaxial wafer according to any one of items 1 to 3.