JPS5932053B2 - 3↓-5 Method of impurity diffusion into compound semiconductors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for diffusing p-type diffusion impurities which is advantageous when manufacturing optical devices or electronic devices using a ■-V compound material containing In.

InP-InGaAsP double heterojunction lasers and light emitting diodes made from the same material are attracting attention in the field of optical communication technology, and other visible light materials such as InGaP, Inl$ as a Gunn effect element, and recently GaAs
Next to type materials, ■-V compound materials containing In as a group ■ element are attracting attention. In is made into a group element■
- Since the base material of the V compound material is InP,
X■) Process technology for i-materials is extremely important as a manufacturing technology for the various devices mentioned above. Regardless of the type of semiconductor material, one of the most important device manufacturing technologies is impurity diffusion technology, and it is no exaggeration to say that impurity diffusion technology is what promised today's development of integrated circuits using Si materials. . Furthermore, in double heterojunction lasers and light emitting diodes using GaAs-AlGaAs-based materials, the diffusion of the p-type impurity Zn is a strife semiconductor laser with a planar structure (for example, see Patent Application No. 51-6226 by the present inventor). ) is indispensable in the production of Also, p-type GaAs, p-type AlGaAs
Ohmic electrodes are primarily achieved by contacting highly Zn-diffused surfaces. ■InGaA
The bra/miner strife structure is essential for the realization of sP-based double heterojunction lasers, etc., and the diffusion depth of several μm is required, similar to the Zn diffusion in GaAs-AlGaAs-based double heterojunction lasers. A well-controlled impurity diffusion technique is required. Similar to GaAs, InP
Also, pulled or boat-grown crystals exhibit n-type unless doped with impurities, and these substrate materials can be of higher quality as n-type crystals than p-type.
In addition, n-type impurity diffusion is similar to that for GaAs.
However, it is difficult to increase the impurity concentration in the diffusion layer, and it is difficult to increase the impurity concentration in the diffusion layer.The diffusion technology that can control the diffusion depth of several μm for p-type impurities even for InP is the same as for Zn for GaAs. It is as important as the case. Conventionally, Zn, which is often used as a p-type impurity for GaAs, has been widely used as an impurity diffusion element for nP as well as for GaAs.

However, the diffusion rate of Zn into lnP is extremely fast; for example, when the inventors used Zn3p2 as a diffusion source during tube closure,
9.7×loIfE″3 n-type impurity concentration n
Diffusion experiments using p-crystal as a material to be diffused and heat treatment at 566° C. for 1 hour revealed that the depth of the p-n junction reached approximately 10 ftm, indicating an extremely fast diffusion rate. When creating a planar structure using an InP-InGaAsP double heterojunction laser, it is necessary to control the diffusion depth of several μm, and for a highly doped n-type layer for electrode formation, it is necessary to control the diffusion depth of 1 μm or less. What is needed is Ga
What about As-AlGaAs double-zero junction lasers? ) This can be easily inferred from the requirement for Zn diffusion. By the way, in the above-mentioned diffusion experiment by the present inventor, the diffusion depth d is proportional to the square root of the diffusion time t, so for example, a diffusion depth of 1 μm can be obtained even when using the Zn thermal diffusion method at an extremely low temperature of 5660 C. Considering the slow response speed and thermal phenomenon, it is difficult for Zn to achieve a diffusion depth of 1 μm with good reproducibility. A closed tube for heat diffusion, such as a closed tube with an internal volume of 5 m.
Even if a very small closed tube made from a 1-sized quartz tube is placed in a heat treatment furnace with an extremely large heat capacity, it will take about 3 minutes or more for the temperature of the closed tube to rise to a diffusion temperature of 566°C or higher. , Under these conditions, the thickness of several μm to InP
It is extremely difficult to achieve such a depth of Zn diffusion in a diffusion time of 10 minutes or less. Furthermore, the inventors have found that the flatness of the Zn diffusion front deteriorates due to the influence of dislocations, while the Cd diffusion provides a flat front with good reproducibility.

The object of the present invention is to provide a method for diffusing p-type impurity Cd into InP or a compound semiconductor material containing In, which can controllably obtain a p-type impurity diffusion layer of several micrometers and with good flatness of the diffusion front. be.

By using the method of diffusing the p-type impurity Cd of the present invention, it becomes extremely easy to manufacture various devices made of InP or a compound semiconductor material containing In. The gist of this invention is to use Cd as a p-type diffusion impurity in a compound containing In as a group element, and to set the upper limit of the phosphorus vapor pressure to C.
It is characterized by diffusing under the vapor pressure of phosphorus, which is in thermal equilibrium with dP2.

Hereinafter, embodiments of the present invention will be explained, and InP
An example will be shown in which a striped semiconductor laser is realized in a planar structure using a -1nGaAsP double hemijunction wafer.

Figure 1 is a cross-sectional view of a quartz ampoule normally used for impurity diffusion by the sealed tube method. In the impurity diffusion method of the present invention, a quartz ampoule with an internal volume of 5 m1 is used. A compound containing In as the diffusion material 2 is prepared, and after evacuation, the quartz rod 3 is melted and sealed in an oxyhydrogen flame, and the entire quartz ampoule is placed in soil at a temperature within 1°C. Impurity diffusion was achieved by heat treatment in a furnace with a soaking length.

Figure 2 shows carrier concentration 9.7X10? -3 n-type 1nP
Zn was used as the impurity diffusion source 1 (Is the impurity diffusion source 1 prepared in the closed tube approximately 10η or more?) at diffusion temperatures of 566XC and 616C as the diffusion material.
3 is a graph showing the relationship between the obtained pn junction depth d and the square root of the diffusion time t (Hr) of Zn (broken line) and Cd (solid line) obtained using 3p2 and Cd3P2. Cd and Z at low temperature 566°C with slow diffusion rate
Depth d of p-n junction obtained per unit square root time of n
/X7t are 2.4μm/HrI and 9.6μ respectively
m/Hr survey shows that the value of d/Takumi for Cd is about 1A compared to Zn, and it is clear that Cd is more convenient for obtaining a much shallower diffusion layer than Zn. Znp2 and CdP2 are used as impurity diffusion source 1 for Zn and Cd, respectively.
When used for the diffusion of
The value of DA obtained for Zn and Cd is 6.5 at a diffusion temperature of 566, respectively.
μMArl is slower than 1.5μMArI, but still Z
The DA obtained with Cd is smaller than that of P-n, which is shallower than that of P-n.
It shows that it is much more advantageous to get a bond with a friend. Increasing the phosphorus pressure beyond that supplied by Znp2 or CdP2 significantly slows down the diffusion rate and requires raising the diffusion temperature, which also goes against the low-temperature processes needed to fabricate various devices. a? ). Furthermore, if Cd is finely dispersed under conditions where the phosphorus vapor pressure during diffusion is higher than the phosphorus vapor pressure given by Znp2 or CdP2, free phosphorus tends to adhere to the surface of the material to be diffused after diffusion, which is undesirable because the surface becomes dirty. On the other hand, if Cd is diffused under a phosphorus vapor pressure lower than the phosphorus vapor pressure supplied by Cd3P2, for example, I
The n-rubbed surface is not only undesirable because phosphorus escapes after diffusion, resulting in deterioration of the surface condition, but also the Cd concentration on the surface of the diffusion layer is decreased, which is not preferable. In addition, the diffusion temperature 5 shown earlier
If diffusion is performed at a diffusion temperature significantly lower than 66°C, the diffusion rate will decrease, but in the device manufacturing process, after the diffusion process, for example, heat treatment is performed during electrode formation, and this temperature is usually about 300°C to 40°C. Therefore, it is considered that the impurities diffused during such heat treatment will be diffused again, so it is not preferable to significantly lower the diffusion temperature. Furthermore, if the diffusion temperature is too low, the diffusion surface concentration will be low.
For example, a surface with a high impurity concentration suitable for electrode formation cannot be obtained. L. Therefore, the diffusion temperature is usually the crystal growth temperature (for example, InPJ<:), and the liquid phase epitaxial growth temperature of InGaAsP is about 65°C. ) and considerably higher than the temperature of electrode heat treatment, etc. From the above explanation, Cd is preferable to Zn as the diffusion impurity. It has been shown that by diffusing Cd under a phosphorus vapor pressure that is in thermal equilibrium with Cd3P2, it is possible to perform highly controllable diffusion to obtain a shallow p-type diffusion layer with no disturbance of the surface to be diffused. Next, in order to show that the Cd diffusion method of the present invention has excellent controllability and reproducibility in the device manufacturing process, InP-1nG using the Cd diffusion method of the present invention was
Let us show an example of a prototype Brenna stripe laser with an aAsP double heterojunction. FIG. 3 shows a cross section of a resonator of an InP-1nGaAsP planar stripe laser having the structure shown in the semiconductor laser device of Patent Application No. 51-6226 by the present inventor. The structure shown in FIG. 3 can be obtained as follows. First, n-type 1nP substrate 3
For example, n-type GaO. 25lnO. 75AsO
．． 55PO. 45 layer 32 is grown by liquid phase epitaxial LPE to a thickness of approximately 3 μm, and then this n-type GaO. 25lnO
．． 75ASO. 55PO. 45 Photo on the surface of layer 32
Using resist technology, a window is opened with approximately a predetermined stripe width, and a mixed solution of Br2 and CH3OH (volume ratio 5:10) is poured into this window.
00) etc. to create a groove 3 with a depth of approximately 1.5 μm.
Look for 3. After that, the photoresist is removed and groove 3 is opened again.
3. N-type GaO. 25lnO. 75ASO. 5
5 pO. On the 45 layer 32, an n-type 1nP layer 34 is grown to be flat even on the groove 33 and to a thickness of 0.4 μm in areas other than the groove 33, and then an n-type GaO layer with a thickness of about 0.3 μm is grown. 2
5InO. 75AsO. 55 pO. 45 layers 35, approximately 1●
5ゝ2◆0pm p-type 1nP layer 36, further 1.0~2
．． 0Pm (Dn type InP layer 37 is continuously grown by LPE).
Next, using SiO2, Si3N4, etc. as a selective diffusion mask, C
d is selectively diffused in stripes at a temperature of 566° C. using Cd3P2 as a diffusion source to obtain a Cd-diffused p-type inversion region 38. Diffusion time is 5×1 impurity concentration of n-type 1nP layer 37
In the case of 0 CTIL and 1 μm thick, n-type 1nP layer 37
To invert the stripe portion and diffusion portion 38 to p-type and create a planar structure, it is sufficient to perform the process for 30 minutes.Furthermore, in order to improve current concentration in the stripe portion, the p-type 1nP concentration is set to 101.
In the case where ρ is set, the p-type concentration in the stripe part diffusion part is NIn.
P37 and p-type 1nP36 Exceeds 10CTn up to 1.0Itm below the interface of each layer, p-type 1nP36 in the stripe part
As a result, the resistivity of the double hetero laser is lowered, and current concentration often occurs in the stripe area. The value current was found. A similar planar stripe structure was created using Zn.
566・C using 3p2 as a diffusion source (it is extremely difficult to obtain by DZn diffusion, because Zn has less DA than Cd).
The diffusion time is about 4 times as large, so the diffusion time is 1/16, or about 2 minutes, and even if Znp2 is used as a diffusion source, the diffusion time must be about 1/9, or about 3 minutes. Considering the heat capacity and heat conduction of the quartz amble, it is difficult to diffuse the quartz amble even at a constant temperature and it is extremely difficult to control the diffusion when heat treatment is performed for several minutes. An InP-1nGaAsP heterojunction laser can only be manufactured with good reproducibility by using the Cd diffusion process of the present invention. Cd has other advantages over Zn as a p-type impurity.

In other words, Cd becomes an acceptor by substituting a group atom in a compound, but in a compound containing In, by using Cd, which has an atomic number adjacent to In, as an impurity, it does not impair the crystallinity of the material to be diffused. The reliability of an element having a Cd diffusion layer instead of Cd is high. Therefore, by using the Cd diffusion region obtained by the manufacturing method including the Cd diffusion method of the present invention in manufacturing various devices, the reliability of the devices can be significantly improved.

The above shows that Cd diffusion into InP is extremely convenient for manufacturing devices using compounds containing In.
Although the explanation was given by showing diffusion data, the diffusion rate of Cd is slower than that of Zn even for InGaAsP, and that
In compound semiconductors containing n, Cd in particular is an impurity with an atomic number adjacent to In and does not impair crystallinity.
d-diffusion ensures superior diffusion control and excellent crystallinity for In-containing -V compounds compared to Zn.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a very common quartz ampoule used for heat diffusion in a closed tube, which was used as a diffusion ampoule in an embodiment of the diffusion process which is a feature of the manufacturing method of the present invention.
Figure 2 shows the depth d (mix → n) of the p-n junction obtained by the accumulation of Cd and Zn. This is an example of the obtained InP-1nGaAsP double heterojunction planar stripe laser with a Cd diffusion region, and its Fabry-Pét resonator cross-section shows the cross-section structure. 1 is an impurity diffusion source, 2 is a material to be diffused, 3 is a quartz ampoule, 31 is an n-type 1D insulation plate, 32 is an n-type GaO. 25nO.
75AsO. 55 pO. 45 layers, 33 is a groove, 34 is an n-type 1nP layer, 35 is an n-type GaO. 25lnO. 75AsO
．． 55PO. 45 layer, 36 is a p-type 1nP layer, 37 is an n-type 1nP layer, and 38 is a striped current injection portion formed by Cd diffusion.

Claims (1)

[Claims] 1 In that is characterized in that Cd is diffused under a phosphorus vapor pressure within a range with the upper limit being the phosphorus vapor pressure in thermal equilibrium with CdP_2 and the lower limit being the phosphorus vapor pressure in thermal equilibrium with Cd_3P_2 at the impurity diffusion temperature. Contained as a group III element
A method for diffusing impurities into a III-V group compound semiconductor.