JP3116415B2 - Semiconductor wafer and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates relates to a GaP epitaxial wafer, GaP epitaxial wafer and growth method thereof particularly epitaxially grown with different In _1-y Ga _y P crystal lattice constant through the GaP buffer layer on the GaP substrate It is related to.

[0002]

2. Description of the Related Art In recent years, there has been remarkable progress in the field of optoelectronics. In particular, light-emitting diodes (LEDs) and laser diodes (LDs) have been actively developed. For example, an epitaxial wafer in which GaAsP is epitaxially grown on a GaAs substrate has been developed. This is a high-brightness, high-emission light source, which has a direct transition-type crystal structure in the red to infrared color band by changing the mixed crystal ratio of arsenic (As) and gallium (Ga) in the Periodic Table Group V. Attention has been paid to the efficiency of the diode. Similarly, an epitaxial wafer in which InGaP is epitaxially grown on a GaP substrate for an orange to yellow band LED has been considered.

A problem with an epitaxial wafer having these constituent means is a decrease in crystallinity due to a mismatch in crystal lattice. For example, the lattice constant of GaP as a substrate is 5,450 5 ,, while the lattice constant of InP is 5,450 は.
At 8694 °, the lattice constant of the surface epitaxial layer In _0.3 Ga _0.7 P is 5,5758 °, and the lattice constant mismatch is as high as about 2.3%.

As described above, since the lattice constant of epitaxial growth and the lattice constant of the substrate are different, the crystallinity of the epitaxially grown crystal becomes worse as the distance increases, and the semiconductor device manufactured from such a wafer has poor electrical characteristics. An LED having high luminance and high luminous efficiency cannot be obtained.

FIG. 4 shows a substrate structure which has been conventionally employed when growing an In _1-x Ga _x P (x> 0.7) crystal having a lattice constant different from that of a GaP substrate. That is, according to the conventional concept, a composition gradient layer (or a lattice) that continuously changes the composition (ie, lattice constant) from In _1-x Ga _x P (x ≒ 0) having a composition close to the lattice constant on a GaP substrate. This is a method of providing a constant transition layer) to prevent crystallinity degradation due to lattice mismatch, and then growing a constant composition layer (or lattice constant layer) having a desired composition. This method is GaAs
A method has been put to practical use in the case of growing the _{GaAs 1-Z P Z (z} <0.4) on a substrate (see JP 51-8883).

[0006]

By the way, in the epitaxial wafer having the above substrate structure, an epitaxial wafer having a certain degree of crystallinity can be obtained, but the crystallinity is so good that it can be used for manufacturing a device. In addition, those having good surface morphology cannot be obtained.
The present invention solves this problem and improves the crystallinity of In.
_{A 1-y} Ga _y P / GaP epitaxial wafer is provided.

[0007]

The present invention focuses on the fact that surface morphology and crystallinity degradation are caused by a phenomenon at the interface between a GaP substrate and an InGaP crystal.
In order to alleviate the influence of the change in the material system on the substrate, a structure in which a GaP buffer layer is inserted as in the substrate structure shown in FIG. In the manufacturing method, the surface morphology and crystallinity are improved by optimizing the growth temperature of the buffer layer.

FIG. 1 shows the structure of an epitaxial wafer of the present invention. In the figure, reference numeral 1 denotes a GaP substrate which is usually obtained by a liquid-sealed Czochralski method (LEC method). 2 is a GaP buffer layer, which is preferably grown epitaxially by a vapor phase growth method. GaP buffer layer is G
This is for capturing crystal defects of the aP substrate and performing subsequent crystal growth in an almost ideal state. The thickness of the GaP buffer layer needs to be about 0.5 to 1 μm. If the thickness is smaller than this, the influence of the lattice constant of the substrate cannot be eliminated, and good crystals cannot be obtained in subsequent epitaxial growth. The effect does not change even if the thickness is too large. Reference numeral 3 denotes a composition gradient layer of In _1-x Ga _x P in which the mixed crystal ratio x changes. The mixed crystal ratio is x = 0
, And continuously changes to x = 0.3 close to the surface epitaxial growth layer to give a concentration gradient.

That is, it is effective to change the mixed crystal ratio x of the composition gradient layer 2 from x = 0 to x = 0.3 and gradually change the lattice constant in this range. The thickness of the composition gradient layer 2 needs to be 1 to 3 μm. Thus, the G
If the difference in lattice constant between the substrate 1 and the surface epitaxial growth layer 3 is compensated by combining the aP buffer layer 4 and the composition gradient layer 2, the crystallinity of the surface epitaxial growth layer 3 is significantly improved, and the effect of the present invention is improved. Be demonstrated. In the figure, reference numeral 3 denotes an In _1-y Ga _y P epitaxial growth layer having a constant composition on the surface. y has a constant value selected in the range of 0.25 to 0.35 according to the required emission wavelength. This constant composition layer 3
Must have a thickness of 2 to 5 .mu.m.

Next, a method for manufacturing a semiconductor wafer according to the present invention will be described. Since the lattice constant is determined by the composition of the crystal, a vapor phase growth method in which the composition of the crystal to be epitaxially grown is constantly changed is advantageous for changing the lattice constant. In particular, an epitaxially grown crystal having good crystallinity can be easily obtained by changing the reaction gas mixture ratio by MOCVD. For example, In _1-x Ga _x P
The crystals to be epitaxially grown, for example, trimethyl indium as an In source _{(TMIn: In (CH 3)} 3), trimethyl gallium as a Ga source _{(TMGa: Ga (CH 3)} 3), using a phosphine (PH ₃₎ is used as a P source I do. To grow the GaP buffer layer 4 uses TMGa and PH _3. To grow the In _1-x Ga _x P composition change layer 2, first, TMGa and PH ₃ are used, and the composition is controlled by gradually decreasing TMGa and increasing TMIn. In order to grow the In _1-y Ga _y P composition constant layer 3, TMIn and TMGa may be mixed so as to have a target composition and grown while maintaining a constant flow rate.

What is important in the present invention is the growth temperature of the GaP buffer layer. The growth temperature of the GaP buffer layer is usually 570 to 900
C., which has been found to have a significant effect on the morphology of the surface of the subsequent final In _1-y Ga _y P epitaxial layer. As a result of the experiment, it was found that a remarkable effect was exhibited when the growth temperature was 650 ° C or higher. Therefore, in the present invention, the vapor growth temperature of the GaP buffer layer was set to 650 ° C. or higher. The optimum temperature is 650-720 ° C.

The growth temperature of In _1-x Ga _x P occurs at 600 to 750 ° C. The growth temperature of InGaP is not particularly hindered in the temperature range in which it is usually used, but the surface morphology is usually improved when grown at a temperature lower by about 50 ° C. than the GaP buffer layer.
As other growth conditions, known means generally used can be used.

[0013]

[Function] By growing a GaP buffer layer on a GaP substrate at a high temperature, the effect of the difference in lattice constant between the substrate and the epitaxially grown crystal is reduced, and side reactions at the interface between the substrate and the epitaxial layer are suppressed. is there. Furthermore this
A composition change layer of In _1-x Ga _x P is provided on the GaP buffer layer,
This is to eliminate the adverse effect of the lattice constant mismatch. As a result, the crystallinity of the subsequently grown film is improved, and the surface morphology is significantly improved.

[0014]

EXAMPLE An S-doped GaP was used as a substrate, and (10
On the 0) plane, GaP and InGaP layers were epitaxially grown by MO-CVD. Trimethyl gallium (TMGa: Ga (CH ₃ ) ₃ ) and trimethyl indium (TMIn: In (CH ₃ ) ₃ ) were used as the group III organic metal, and phosphine (PH ₃ ) was used as the group V hydride. . High-purity hydrogen was used as a carrier gas.

A GaP substrate was set on a susceptor in a reaction vessel, the pressure was maintained at 100 Torr, and the substrate was heated while flowing hydrogen gas. When the substrate temperature reaches 400 ° C, P
H ₃ was introduced at a rate of 475 cc / min to prevent the volatilization of P. Further, when the substrate temperature reaches 690 ° C., the temperature is maintained for 5 minutes, and then TMGa is introduced at a rate of 12.8 cc / min for 20 minutes,
A 0.8 μm thick GaP buffer layer was formed. Next, the temperature of the substrate was lowered to 610 ° C. and maintained for 5 minutes. Then, introduction of TMIn was started, and the amount was increased to 137 cc / min over 30 minutes.
TMGa is reduced to 8.8 cc / min, and the mixed crystal ratio x is from x = 1.0 to x
An In _1-x Ga _x P epitaxial layer continuously changing to 0.70 was grown to a thickness of 2.0 μm. TMGa and TMIn
In _0.3 Ga where the mixed crystal ratio y is 0.3
_{A 0.7} P epitaxial layer was grown to a thickness of 3.6 μm over 60 minutes. As a method for evaluating the obtained epitaxial wafer, the density of protrusions (hillocks) on the surface of the grown film was measured for the surface morphology, and the half width of the rocking curve by the X-ray two-crystal method was measured and calculated for the crystallinity. These results are shown in FIGS. As shown in FIG.
The hillock density decreased as the growth temperature of the P buffer layer increased, and could be suppressed to 40 cm ^-2 at 690 ° C.

Also, as can be seen from FIG. 3, when the composition of the grown film is substantially constant at In _0.3 Ga _0.7 P,
It can be seen that as the growth temperature of the aP buffer layer increases, the half-width of the X-ray rocking curve decreases and the crystallinity improves. At 690 ° C., the time was 220 seconds, which means that crystallinity enabling device fabrication was obtained despite a lattice mismatch of 1.4%.

[0017]

According to the present invention, In _1-y Ga _y P having a lattice constant different from that of a GaP substrate (0.65 ≦ y ≦
0.75) The epitaxial growth layer can be obtained as a thin film having good surface morphology and having sufficiently good crystals for device fabrication. In addition, this method is a vapor phase growth method applicable to other material systems (for example, GaAsP / GaAs, GaAsP / GaP, InGaAs / GaAs) in crystal growth in a system having a lattice mismatch.

[Brief description of the drawings]

FIG. 1 is a diagram showing an InGaP / GaP wafer structure according to the present invention.

FIG. 2 is a diagram showing a relationship between hillock density and GaP buffer layer growth temperature.

FIG. 3 is a graph showing the relationship between crystallinity and GaP buffer layer growth temperature.

FIG. 4 is a diagram showing a conventional InGaP / GaP wafer structure.

[Explanation of symbols]

Reference Signs List 1 GaP substrate 2 In _1-x Ga _x P composition gradient layer 3 In _1-y Ga _y P composition constant layer 4 GaP buffer layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-48-34082 (JP, A) JP-A-60-210598 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/20 H01L 21/205

Claims (1)

(57) [Claims] 1. A semiconductor device having a lattice constant different from its lattice constant on a GaP substrate.
In _1-y Ga y P layer having a child constants (where, 0.65 ≦
(y ≦ 0.75) for the vapor phase growth.
Epitaxy of GaP crystal on GaP substrate at temperature of ~ 720 ° C
And then growing the GaP crystal epitaxially.
At a temperature lower than the growth temperature, the mixed crystal ratio x changes
In _1-x Ga _x P layer (provided that 0.70 ≦ x ≦ 1.0
0) and an In _1-y Ga _y P layer having a constant composition.
Semiconductor way characterized by epitaxial growth
C Manufacturing method.