JP3060258B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is ^applicable to 10 ¹⁹ cm ^-3 to 10 ²⁰ cm.
^{The present} invention relates to a method of manufacturing a semiconductor device comprising ^-3 epitaxial layers of GaAs doped with a high concentration of carbon, and more particularly to a method of reducing a strain in a GaAs layer caused by such a high concentration of carbon.

[0002]

2. Description of the Related Art Recently, GaAs doped with a high concentration of carbon has been developed.
(Hereinafter referred to as C: GaAs) is growing in interest.
In particular, carbon concentration ranges of the order of 1 × 10 ¹⁹ to 10 ²⁰ cm ^-3 have been noted. Specifically, the main purpose is to apply GaAs doped with such a high concentration of carbon to the base layer of a GaAs / AlGaAs heterojunction bipolar transistor (HBT). In other words, carbon becomes a p-type dopant for GaAs, but its diffusion coefficient is about three orders of magnitude lower than that of other p-type dopants such as zinc (Zn) and beryllium (Be). Even if doped, it is suitable for forming a thin and low-resistance base layer. In addition, Hall measurement and secondary ion mass spectrometry (SIMS)
The results show that carbon in C: GaAs is converted to As in the GaAs crystal.
And act as an acceptor, and its activation rate has been found to be 100% at all concentrations. That is, the concentration of electrically active carbon is equal to the concentration of carbon atoms.

[0003] Ga doped with a high concentration of carbon as described above
As epitaxial layer should be grown by gas source MBE (GSMBE) or metal organic chemical vapor deposition (MOCVD) using organic compound gas of group III element such as Ga, or molecular beam epitaxy (MBE) with graphite filament Can be. By these methods, C: GaAs containing a high concentration of carbon such as on the order of 10 ²¹ cm ⁻³ can be epitaxially grown.

[0004]

However, when the carbon concentration exceeds 1 × 10 ¹⁹ cm ⁻³ , the lattice constant of the GaAs epitaxial growth layer becomes smaller than the lattice constant of the GaAs crystal substrate in the <100> direction of 5.653 °. Is obtained. This indicates that the GaAs epitaxial layer has shrunk. According to the measurement result of this lattice constant, (1
00) The lattice mismatch between the substrate and the GaAs layer epitaxially grown on the GaAs surface, for example, with a carbon concentration of 1.3 × 10 ²⁰ cm ^-3 is Δa /
a = −1.8 × 10 ^-3 is reached. a is the lattice constant of the GaAs crystal in the <100> direction, and Δa is the difference in lattice constant between the GaAs crystal and the GaAs epitaxial layer. If such lattice irregularities exist, it is expected that the characteristics of the HBT having the GaAs layer as a base layer will deteriorate. Therefore, in order to improve the reliability of such a semiconductor device, it is desirable to minimize the distortion of the C: GaAs layer.

SUMMARY OF THE INVENTION The present invention relates to a highly carbon doped GaAs.
An object of the present invention is to solve the above-mentioned problem in the epitaxial growth layer.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to form a GaAs layer doped with carbon in a concentration range in which the lattice constant is smaller than that of a crystal substrate on one surface of the substrate, and then anneal the GaAs layer. In particular, in the step of epitaxially growing the GaAs layer, the substrate surface is irradiated with X-rays or electron beams, and the diffraction image of X-rays or electron beams Bragg reflected from the GaAs layer is reduced. Measuring the lattice constant of the GaAs layer from the above, and performing the annealing treatment on the crystal substrate based on the measurement result of the lattice constant, thereby alleviating the lattice mismatch between the GaAs layer and the crystal substrate. Is achieved by the method for manufacturing a semiconductor device according to the above.

[0007]

[Action] Carbon has an atomic radius of 0.77Å and arsenic (A
Smaller than the atomic radius of 1.20Å in s). Further, assuming that all of the doped carbon atoms replace As in GaAs, for example, at a carbon concentration of 2 × 10 ²⁰ cm ⁻³ , As
Will be occupied by carbon atoms. As a result, there is a high possibility that the GaAs growth layer shrinks and crystal distortion occurs with the non-doped GaAs crystal substrate. According to the present invention, the shrinkage of the GaAs layer doped with a high concentration of carbon as described above is reduced by annealing. In addition, by observing shrinkage of the GaAs layer and performing annealing in the step of epitaxial growth, a GaAs epitaxial growth layer with less distortion can be obtained.

[0008]

FIG. 1 is a schematic diagram of a gas source molecular beam epitaxy (GSMBE) apparatus used in the practice of the present invention, wherein a susceptor 2 installed inside a crystal growth chamber 1 is shown.
Thus, the substrate 3 made of GaAs crystal with the (100) plane exposed is supported. Crystal growth chamber 1 has ports 4A, 4B, 4
C,... Are provided. Ports 4A, 4B, 4C, ...
Are connected to the molecular beam sources 5A, 5B, 5C,... Which generate the molecular beam of the element or compound constituting the crystal or the impurity element or compound to be doped. For example, gallium (Ga) source gas trimethylgallium (TMG) is introduced through port 4A,
Arsine (AsH ₃ ), a source gas for arsenic (As), through 4C
Is introduced.

The crystal growth chamber 1 is evacuated by an exhaust device (not shown).
The inside is evacuated, the liquid nitrogen shroud 6 is cooled, and the TMG and AsH ₃ are introduced through the ports 4A and 4C while maintaining the substrate 3 at a predetermined temperature by the susceptor 2. By controlling the opening and closing of the shutters 7A, 7B, 7C, ... provided in front of the respective molecular beam sources 5A, 5B, 5C, ..., from the molecular beam sources 5A and 5C to the substrate 3. Then, TMG and AsH ₃ molecular beams are irradiated. As a result, a GaAs crystal is epitaxially grown on the substrate 3.

As described above, when TMG is used as a source gas, the organic group (CH ₃ -or the like) of TMG serves as a carbon source, so that it is not necessary to supply a source gas of carbon as a doping impurity. In this case, the amount of carbon incorporated into the GaAs crystal layer, the flow rate of AsH ₃ and a raw material gas of Group V element III
It varies with the ratio of the flow rate of TMG, which is the raw material gas for group elements.
This is shown in FIG. In the figure, the horizontal axis represents the flow rate ratio of the group V element source gas to the group III element source gas (V / III), and the vertical axis represents the hole concentration, that is, the carbon concentration and the hole movement in the GaAs epitaxial growth layer. Each degree is graduated.

As shown in FIG. 2, the carbon concentration decreases as the flow ratio V / III increases. Flow ratio V / II
Control of I is leave the flow rate of TMG constant, by performing by varying the flow rate of AsH _3, it is convenient because there is no need to readjust the other conditions. As can be seen from the figure, the mobility of holes hardly changes even if the carbon concentration changes.

As described above, the undoped GaAs crystal group
GaAs layers with different carbon concentrations (C) were epitaxially deposited on the (100) plane of the plate.
X-ray analysis results of three samples grown by xial
Is shown in FIG. The vertical axis is diffraction X-ray intensity, and the horizontal axis is arcsec.
Diffraction angle. As shown, each curve has
On the left side (low diffraction angle side), the diffraction peak of the (100) plane of the substrate is
Is appearing. Carbon concentration is C = 4.0 × 10¹⁹cm^-3In the sample
Is a small diffraction peak to the right of this peak (high diffraction angle side).
Is appearing. Furthermore, the carbon concentration is C = 1.3 x 10 ²⁰cm^-3
The smaller the diffraction peak, the higher the diffraction angle
It is shown to shift to the side.

If there is no difference in lattice constant between the epitaxially grown layer and the substrate, the diffraction peaks of all three samples should correspond. Therefore, FIG. 3 shows that the diffraction peak on the high diffraction side is due to the epitaxially grown layer, and that the lattice constant of the epitaxially grown layer decreases as the carbon concentration increases. That is, when the carbon concentration is as low as C = 6.3 × 10 ¹⁸ cm ⁻³ , no large shrinkage occurs in the crystal lattice of the C: GaAs growth layer. However, when the carbon concentration increases to about C = 4.0 × 10 ¹⁹ cm ^-3 , the lattice shrinkage becomes remarkable, and the carbon concentration becomes C = 1.3 ×
As it increases to 10 ²⁰ cm ^-3 , the shrinkage of the grid increases. As a result, it is presumed that a large strain is generated near the interface with the substrate.

The GaAs layer having a high carbon concentration as described above is
A GaAs crystal substrate grown by Xial, for example, containing As
<100> direction when annealed at 900 ℃ in atmosphere
FIG. 4 shows an example of the change in the contraction of the lattice at the time of FIG. The figure is charcoal
Elemental concentration is C = 1.3 × 10²⁰cm^-3In the case of C: GaAs layer, the horizontal axis
Is the annealing time (sec), and the vertical axis is the lattice irregularity Δa / a.
Figure 4 shows the change in shrinkage of the represented lattice. As shown
The shrinkage of the C: GaAs layer as-grown is -1.8 × 10^-3In
Annealing at 900 ° C for 2700 seconds (45 minutes)
−1.15 × 10^-3To decrease. That is, the carbon in FIG.
Concentration C = 1.3 x 10 ²⁰cm^-3C: GaAs layer on high diffraction side
Small peaks appearYoGradually lower
Shift to the diffraction side. In other words, low carbon concentration C: GaAs layer
It approaches the X-ray diffraction spectrum. Therefore, the base
Means that the strain near the interface with the plate has decreased
are doing.

In the above-described annealing at 900 ° C., there is a possibility that As may be volatilized from the surface of the GaAs crystal layer to change the composition. To prevent this, before annealing, cover at least the surface of the GaAs growth layer with a thin film of, for example, aluminum nitride (AlN) or silicon nitride (Si ₃ N ₄ ), or cover the GaAs crystal plate Keep it. Alternatively, a method of annealing the GaAs crystal substrate 3 by heating the GaAs crystal substrate 3 with the susceptor 2 while flowing AsH ₃ in the GSMBE apparatus as shown in FIG. 1 is also effective.

Further, in the crystal growth chamber 1 of the GSMBE apparatus shown in FIG. 1, for example, reflection high energy electron diffraction (RHEED)
Means is provided, and the lattice irregularity Δ
By controlling the annealing time according to the value of a / a,
C: G while reducing lattice mismatch in the growth process of GaAs layer
It is also possible to grow an aAs layer. For this purpose, for example, an electron gun 8A is installed at the port 8, and a diffracted electron beam by the GaAs growth layer on the substrate 3 is detected by the electrode 9A installed at the port 9. In this case, it goes without saying that the substrate 3 is cooled to about room temperature during the period of measuring the lattice constant, and the substrate 3 is heated to a predetermined temperature by flowing AsH ₃ during the annealing.

[0017]

According to the present invention, a high-concentration carbon-doped GaAs
Distortion due to lattice mismatch between the layer and the substrate can be reduced, which has the effect of promoting the practical use of HBTs with a high-concentration carbon-doped GaAs layer as a base layer and contributing to the improvement of reliability.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a GSMBE apparatus used for implementing the present invention.

FIG. 2 is an explanatory diagram of an example of a method for controlling a carbon concentration in a GaAs growth layer.

FIG. 3 is an X-ray diffraction diagram showing a change in lattice constant of a GaAs growth layer depending on carbon concentration.

FIG. 4 is a diagram showing an example of a reduction in lattice mismatch of a C: GaAs growth layer by annealing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crystal growth room 2 Susceptor 3 Substrate 4A, 4B, 4C, 4D, 8, 9 Port 5A, 5B, 5C, 5D Molecular beam source 6 Liquid nitrogen shroud 7A, 7B, 7C, 7D Shutter

Continuation of the front page (51) Int.Cl. ⁷ identification code FI H01L 21/66 H01L 21/66 N 29/205 29/205 (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/324 H01L 21/203 H01L 21/205

Claims (2)

(57) [Claims] 1. A step of epitaxially growing a GaAs layer doped with carbon in a concentration range in which a lattice constant is smaller than that of a crystal substrate on one surface of the crystal substrate, and irradiating the substrate surface with X-rays or electron beams. The Ga on the substrate
Measuring a lattice constant of the GaAs layer from a diffraction image of the X-ray or electron beam reflected from the As layer; and performing an annealing process on the crystal substrate based on the measured lattice constant; A method of alleviating lattice irregularity between a GaAs layer and the crystal substrate. 2. The method according to claim 1, wherein the concentration range is 1 × 10 ¹⁹ cm ⁻³ or more.