JPH06216209A - Inspection of epitaxial wafer - Google Patents

Abstract

PURPOSE:To provide an inspection method of an epitaxial wafer which enables improvement of yield of a semiconductor element manufacturing by checking a product of a sheet carrier concentration and mobility of a two-dimensional electron. CONSTITUTION:In an inspection process of an epitaxial wafer wherein a hetero junction is formed and a two-dimensional electronic layer is provided on a hetero junction interface, a sheet carrier concentration Ns and mobility mu of the two-dimensional electronic layer of the epitaxial wafer are measured, and a constant (a) of a=NsXmu is obtained by using the sheet carrier concentration and mobility. An epitaxial wafer is inspected by judging whether or not the epitaxial wafer is approved based on the constant (a).

Description

Detailed Description of the Invention

[0001]

The present invention relates to the formation of a heterojunction,
The present invention relates to a method for inspecting an epitaxial wafer having a two-dimensional electron layer at the heterojunction interface.

[0002]

2. Description of the Related Art Recently, a high electron mobility transistor (High Ele) using a junction of AlGaAs and GaAs is used.
ctron Mobility Transist
r; hereinafter abbreviated as HEMT), and the like, and the development and practical application of high-performance semiconductor devices by actively forming junctions of semiconductors having different band gaps. In addition, aiming at higher performance semiconductor devices, AlGaAs and InGaA
A strained-lattice HEMT using a junction with s and a HEMT in which InAlAs / InGaAs is grown on an InP substrate are also being developed.

In FIG. 3, InGaAs is used as a channel layer A
A cross-sectional view of a strained-lattice HEMT using 1 GaAs as an electron supply layer is shown. On the semi-insulating GaAs substrate 1, an undoped GaAs layer 2 as a buffer layer, an undoped InGaAs layer 3 as a channel layer, an undoped AlGaAs spacer layer 4, an n-type AlGaAs layer 5 doped with Si, which is an electron supply layer, and Si are doped. N-type GaAs layer 6
Sequentially, for example, molecular beam crystal growth method (Molecular
Beam Epitaxy method; hereinafter abbreviated as MBE method) and metalorganic vapor phase epitaxy method (Metal Organ)
ic Chemical Vapor Deposit
Ion method; hereinafter referred to as MOCVD method) for crystal growth. Ohmic electrodes 7 are provided in desired regions on the GaAs layer 6, and the GaAs layer 6 is etched between them to form a gate electrode 8 on the n-type AlGaAs layer 5.
Is provided.

FIG. 4 shows InG grown on an InP substrate.
A cross-sectional view of a HEMT in which aAs is a channel layer and InAlAs is an electron supply layer is shown. An undoped InAlAs layer 12 as a buffer layer on the semi-insulating InP substrate 11,
An undoped InGaAs layer 13, an undoped InAlAs spacer layer 14 as a channel layer, an n-type InAlAs layer 15 doped with, for example, Si which is an electron supply layer, an undoped InAlAs Schottky contact layer 19, Si
The n-type InGaAs layer 16 doped with
Crystal growth is performed using the BE method or the MOCVD method. InG
The ohmic electrode 17 is formed in a desired region on the aAs layer 16.
, The InGaAs layer 16 is etched between them, and the gate electrode 18 is provided on the n-type InAlAs layer 15.

[0005]

The characteristics of the HEMT shown in FIGS. 3 and 4 are the crystallinity of the crystal layer and AlGaAs /
InGaAs, InGaAs / GaAs, InAlAs
The interface steepness of a heterojunction such as / InGaAs or InAlAs / InP is strongly affected. For that purpose, it is important to first find out suitable crystal growth conditions for each crystal, and it is necessary to confirm that the epitaxial wafer can obtain desired HEMT characteristics according to the conditions.

As a method for examining the characteristics of the epitaxial wafer in HEMT, a method of measuring the sheet carrier concentration and mobility of two-dimensional electrons formed in the channel layers 3 and 13 is known. For example, it is known that when the doping concentration of Si in the electron supply layers 5 and 15 is increased, the sheet carrier concentration is increased, and when the spacer layers 4 and 14 are thick, the mobility is increased.

The crystallinity of the crystal layer is poor, or AlGaA
s / InGaAs, InGaAs / GaAs, InAl
If there is a "drip" at the interface of a heterojunction such as As / InGaAs or InAlAs / InP, or if there is an impurity at the interface between the substrates 1 and 11 and the crystal layer, the sheet carrier concentration and mobility of two-dimensional electrons will decrease. To do. in this way,
When an HEMT was experimentally manufactured using an epitaxial wafer having a problem of crystal quality, it was found that the characteristics of the HEMT, for example, the transfer conductance (gm) were deteriorated. Therefore, the crystallinity of the epitaxial wafer strongly affects the characteristic yield of the semiconductor, and the inspection of the epitaxial wafer becomes a very important problem.

Conventionally, after the growth of the epitaxial wafer, H
The sheet carrier concentration and the mobility of two-dimensional electrons were measured by the all measurement, and the acceptance / rejection of the epitaxial wafer was determined. Although it is possible to exclude those in which the sheet carrier concentration or mobility is remarkably reduced, for other epitaxial wafers, the device is manufactured such that the HEMT characteristics are not good even though the sheet carrier concentration is sufficient.
In many cases, the quality of the characteristics was unknown until the DC or RF characteristics were measured. Therefore, the yield of the semiconductor device is not stable, and the manufacturing cost is increased.

The inventor of the present invention prototyped HEMTs having different two-dimensional electron sheet carrier concentrations and mobilities, and examined the correspondence with DC and RF characteristics. As a result, the product Ns × μ of sheet carrier concentrations Ns and mobilities μ. It was found that there is a strong correlation between the and HEMT characteristics, and the present invention was devised.

According to the present invention, in a process of inspecting an epitaxial wafer having a heterojunction formed and having a two-dimensional electron layer at the heterojunction interface, the product of the sheet carrier concentration and the mobility of the two-dimensional electron is examined to obtain a semiconductor. An object of the present invention is to provide an epitaxial wafer inspection method capable of improving the yield of device manufacturing.

[0011]

According to a method of inspecting an epitaxial wafer according to the present invention, in the step of inspecting an epitaxial wafer in which a heterojunction is formed and a two-dimensional electron layer is formed at the heterojunction interface, The sheet carrier concentration Ns and the mobility μ of the three-dimensional electron layer are measured, and using the sheet carrier concentration and the mobility, a
= Ns × μ is obtained, and the acceptance / rejection of the epitaxial wafer is determined by this constant a.

Further, the epitaxial wafer is made of AlGaA.
Strained lattice HE with s / InGaAs / GaAs junction
In MT, the constant a obtained by measuring the room temperature is 8.
It is characterized in that 0 × 10 ¹⁵ V ⁻¹ s ⁻¹ or more is judged as a pass.

Further, the epitaxial wafer is InAl
HEM with As / InGaAs / InAlAs junction
At T, the constant a obtained by measuring the room temperature is 3.5.
It is characterized by determining that the result is × 10 ¹⁶ V ^-1 s ^-1 or more.

[0014]

By using the method for inspecting an epitaxial wafer in which a heterojunction is formed and a two-dimensional electron layer is formed at the heterojunction interface according to the present invention, the manufacturing cost of semiconductor devices can be reduced and the yield can be improved. it can.

[0015]

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

FIG. 1 shows InGaA whose sectional view is shown in FIG.
For the strained-lattice HEMT having an s-channel layer, the sheet carrier concentration Ns of two-dimensional electrons and the mobility μ of the epitaxial wafer at room temperature were measured, and the value of the constant a at a = Ns × μ and the transconductance gm of the HEMT were measured. It is the figure which showed the relationship of. As you can see from this figure,
The transconductance gm and the value of Ns × μ show a strong positive correlation, and when a is below 8.0 × 10 ¹⁵ V ⁻¹ s ⁻¹ , gm is ˜500 mS / mm to 300 to 400 mS.
/ Mm sharply decreases. Based on this result, a
The yield of the RF characteristics of the HEMT having the ^{value of} ≧ 8.0 × 10 ¹⁵ V ⁻¹ s ⁻¹ was significantly improved from the conventional yield of 45% when the inspection was not performed to 90%.

FIG. 2 shows InAl used as a channel layer of InGaAs grown on an InP substrate whose sectional view is shown in FIG.
For a HEMT having an electron supply layer of As, the sheet carrier concentration Ns of two-dimensional electrons and the mobility μ of the epitaxial wafer at room temperature were measured, and the value of the constant a at a = Ns × μ and the transconductance gm of the HEMT were measured. It is the figure which showed the relationship. It can be seen that there is a strong positive correlation between the transconductance gm and the value of Ns × μ, as in the case of the strained grating HEMT having the InGaAs channel layer of FIG. In this example, the value of a is 3.5 × 10 ¹⁶ V ⁻¹ s ⁻¹
Above, a high gm of ˜800 mS / mm or more was obtained, and the value of a was 3.5 × 10 ¹⁶ V ⁻¹ s ⁻¹ or more.
The yield of the RF characteristics of the EMT is significantly improved from the conventional yield of 35% when the inspection is not performed to 95%.

In the embodiment, AlGaAs / InGa is used.
HEMT and InA having a heterojunction of As / GaAs
Although the case of HEMT of 1As / InGaAs / InAlAs has been described, a value of a = Ns × μ is used as a method for inspecting an epitaxial wafer even in a semiconductor device using an epitaxial wafer having a quantum well layer by a heterojunction such as InGaP / GaAs. The same effect can be obtained by using as a pass / fail criterion.

[0019]

As described above, according to the present invention, in the inspection process of an epitaxial wafer having a heterojunction and having a two-dimensional electron layer at the interface of the heterojunction, a sheet carrier of the two-dimensional electron of the wafer is inspected. By using the inspection method in which the concentration and the mobility are measured and the inspection reference value is set to the value of the product of both, the manufacturing cost of the semiconductor device can be reduced and the yield can be improved.

[Brief description of drawings]

FIG. 1 is a first HEMT constant a and g according to the present invention.
The diagram which shows the correlation with m.

FIG. 2 is a second HEMT constant a and g according to the present invention.
The diagram which shows the correlation with m.

FIG. 3 is a strained lattice HE having an InGaAs channel layer.
Sectional drawing of MT.

FIG. 4 is a cross-sectional view of a HEMT in which InGaAs grown on an InP substrate is used as a channel layer and InAlAs is used as an electron supply layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semi-insulating GaAs substrate 2 ... Undoped GaAs layer 3 ... InGaAs channel layer 4 ... Undoped AlGaAs spacer layer 5 ... Si-doped AlGaAs layer 6 ... Si-doped GaAs layer 7 ... Ohmic electrode 8 ... Gate electrode 11 ... Semi-insulating InP substrate 12 ... Undoped InAlAs layer 13 ... InGaAs channel layer 14 ... Undoped InAlAs spacer layer 15 ... Si-doped InAlAs layer 16 ... Si-doped InGaAs layer 17 ... Ohmic electrode 18 ... Gate electrode 19 ... Undoped InAlAs Schottky contact layer

Claims (3)

[Claims] 1. A sheet carrier concentration Ns and a mobility μ of the two-dimensional electron layer of the epitaxial wafer are measured in a step of inspecting an epitaxial wafer having a two-dimensional electron layer formed at a heterojunction interface. , A = Ns × μ using the sheet carrier concentration and the mobility
The method for inspecting an epitaxial wafer is characterized in that the pass / fail of the epitaxial wafer is determined based on the constant a. 2. The epitaxial wafer is AlGaAs /
Strained lattice HEMT with InGaAs / GaAs junction
In, the constant a obtained by measuring the room temperature is 8.0 ×
The method for inspecting an epitaxial wafer according to claim 1, wherein a ^{value of} 10 ¹⁵ V ^-1 s ^-1 or more is determined to be acceptable. 3. The epitaxial wafer is InAlAs /
In a HEMT including an InGaAs / InAlAs junction, the constant a obtained at room temperature is 3.5 × 10 5.
^The method for inspecting an epitaxial wafer according to claim 1, wherein a ^{value of 16} V ^-1 s ^-1 or more is determined to be acceptable.