JPS6011801B2 - Thermal diffusion method of impurities into semiconductor materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impurity diffusion method that allows great control over the diffusion depth and diffusion layer concentration when impurities are thermally diffused into a semiconductor material.

Thermal axis diffusion is important in the semiconductor industry and is an important process that forms many manufacturing steps. In other words, currently, many p-n junctions in semiconductor devices and integrated circuits are made using an impurity diffusion process, and even though the diffusion process is the technology that made planar structures possible and promised the development of integrated circuits. It's no exaggeration. However, the thermal diffusion process always involves the risk of thermally deteriorating the semiconductor host crystal.

For example, when impurities are thermally diffused into Ca false, Gap, 1 rudder, etc., or into compound semiconductor materials such as GaAs, InGaP, etc. in the presence of impurity vapor, the atmosphere surrounding the material to be diffused is mixed with the base material. If the partial pressure of the base metal constituent elements necessary to maintain thermal equilibrium is not applied, some of the base metal constituent elements will leak out from the crystal surface from within the base metal crystal, causing so-called Ib chemical content in the base metal crystal. A large amount of theoretical defects, such as atomic vacancies, occur. However, in many cases, these elementary defects significantly reduce carrier mobility, lifetime, etc., which are the basic properties of semiconductor crystals, and devices manufactured with these stoichiometric defects occur. performance will be poor. For example, it is now clear that stoichiometric defects in GaP crystals are a significant factor that significantly reduces the efficiency of luminescence from the GaP crystal.

In addition, Ib-school theory defects are considered to be important factors governing the performance of various compound semiconductors.

In particular, many people are beginning to pay attention to this childish flaw as a serious factor that governs the reliability of devices made from compound semiconductors. The fact that stoichiometric defects are an important factor determining the properties of materials has recently begun to attract attention in the above-mentioned U-V compound semiconductors. A compound called CdS,
Research is progressing on low compounds such as Z-ships. GaA
s is an infrared light emitting diode due to the basic properties of the material, p-n
It is a material that is being used to create many practical devices such as junction injection lasers, Gunn diodes, field effect transistors, and photodetectors. However, since it is a compound semiconductor, it is extremely easy to introduce stoichiometric defects through careless heat treatment processes. Therefore, GaAs will be used as an example of the material for explaining the present invention. An extremely common and practically important representative example of a heat treatment process for GaAs is thermal diffusion of p-type impurity zinc.

Thermal diffusion of zinc is essential in the production of GaAs light emitting diodes and striped double heterojunction laser diodes called planar type. In view of the above points, in order to explain this invention in detail, G.
Take as an example the thermal diffusion of zinc into a sham. When thermally diffusing zinc into Ga, the atmosphere surrounding the base material GaAs must be made into a vapor that is in thermal equilibrium with the GaAs crystal, which is basically a system of Ga, As, and Zn. The elements constituting the base material, such as Ca and As, are scattered, and a region with stoichiometric defects is generated near the surface.

It is well known that when Zn is diffused into GaAs under a vapor pressure that is out of thermal equilibrium with GaAs as described above, even the surface condition of the GaAs is severely damaged and the flatness of the diffusion front becomes poor. A technique for Zn diffusion into Ga specimens with good reproducibility was achieved by using, for example, an alloy synthesized with a composition of 5% GaAs, 45% Zn, and 50% As as a Zn diffusion source. When this alloy is used as a Zn diffusion source, the alloy suddenly enters a thermal equilibrium with Ga, and Ga is supplied together with Zn into the atmosphere surrounding GaAs, which changes the surface state of Ga* and Ga$.
It is possible to prevent a large amount of stoichiometric defects from occurring in the Zn layer and to perform a well-controlled Zn diffusion. However, this Ga
The above-mentioned ternary diffusion source alloy consisting of , As, and Zn is synthesized in a sealed tube at high temperature (approximately 110 pi○) and under high pressure, which is dangerous and prevents contamination from the sealed tube material and crucible material. It is difficult to be a good diffusion source from the viewpoint of purity.

Further, when the above-mentioned alloy consisting of Ga, As and Zn is used as a diffusion source, the partial pressure of $ at the equilibrium vapor pressure during diffusion is high, and the Zn concentration in the diffusion layer becomes extremely high. Using this ternary alloy as a diffusion source, Zn was heated to G at 700°C.
When diffused into a melon, the Zn concentration on the GaAs surface is approximately 2.4 x 1 and -3.

Furthermore, this Zn concentration is 1.6×1 and 0−3 at 650°C, and 1.2×1 and 0−3 at 60°C, so even if the diffusion temperature is lowered, an extremely high surface concentration can be maintained. keep. In order to perform Zn diffusion with a Zn concentration of 1, 9-3 or lower, a system consisting of Zn and Ga is usually used as a diffusion source.

However, in closed-tube diffusion using a system consisting of Zn and Ga as a Zn diffusion source, not only is it necessary to have an extremely accurate weighing ratio commensurate with the volume inside the closed tube of Ga and Zn, but also
The melting point of the Zn alloy is as low as 30 qo or less, and the diffusion source is easily contaminated with oxygen in the air, making handling extremely inconvenient. Furthermore, the quartz material normally used for sealing tube materials is G
a It is easy to wet and react with metals at high temperatures, so contamination from the sealing tube material occurs during the heat treatment process. In addition, in diffusion using a diffusion source made of Ga and Zn, normally 80
A high temperature of 0°C or higher is required.

Therefore, it is difficult to perform Zn diffusion with good reproducibility in terms of post-diffusion surface condition, diffusion depth, diffusion concentration, etc. by diffusion using a diffusion source consisting of Ga and Zn. As a method, Zn-doped Si0
Two films were formed on a GaAs substrate, and Zn in SiQ was replaced with GaA.
There is also a method of diffusing to s.

However, the diffusion temperature needs to be high to about 900° C. or higher, and Ga diffuses into the Si02 film, causing stoichiometric defects to occur in the Ga film. Furthermore, there is a method of diffusing Zn from Zn vapor into Ga$ through a Si02 film, but
It is difficult to perform diffusion with good controllability because the 02 film thickness and the like are added to the parameters that determine the Zn diffusion depth and concentration. Furthermore, Zn diffusion in the barrier requires precise control of Zn vapor pressure on the Ga side substrate surface and precise control of Ca and pseudo vapor pressure on the Ga pseudo substrate to prevent thermal deterioration of the GaAs substrate. During Zn diffusion, Ga, As, and Zn vapors must be continuously flowed into the reaction tube and controlled.
Reproducible Zn diffusion is quite difficult.

In addition, this type of open tube method produces a large amount of Ga. Since As and Zn vapors are emitted, this method is not always preferred from the standpoint of preventing pollution. The purpose of this invention is to
It is an object of the present invention to provide a thermal axis diffusion method of impurities in a semiconductor material that does not cause stoichiometric defects except for the C point which the conventional method described above has.

However, if the thermal diffusion method of the present invention is employed, it is possible to very easily diffuse Zn into GaAs with a good surface condition after diffusion and with extremely good reproducibility in terms of diffusion depth and diffusion concentration.

Moreover, according to this diffusion method, the above-mentioned Ga5%, Zn45
%, Ga50%, at least at the diffusion temperature of 550°C to 700°C where the experiment was conducted, the diffusion rate is about three times faster and the surface concentration is about one order of magnitude lower. Zn can be diffused into the Ga side of three generations. The gist of the thermal diffusion method of this invention is that a thermal diffusion impurity element or a thermal diffusion impurity is placed on the same material as the thermal diffusion material as a diffusion source material placed in a position separate from the thermal diffusion material. It is characterized by using a compound containing an element or a multilayer or single-layer thin film containing at least a heat-diffusing element.

This method prevents thermal deterioration of the heat-diffusing material crystals,
Furthermore, diffusion with extremely high reproducibility in terms of diffusion depth and concentration can be achieved. Hereinafter, a method of thermally diffusing Zn into GaAs, which is an embodiment of the present invention, will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of a thermal diffusion source sample when the method of the present invention is applied to thermal diffusion of Zn into GaAs. 11 is G
12 is a Zn thin film layer formed by vapor deposition or the like.

The GaAs crystal wafer 11 (undoped single crystal Ga was used here) of the diffusion source sample shown in Fig. 1 was mirror polished with diamond paste, and then polished with Hiro S04 and 02
and 90°C in a solution where the volume ratio of string 0 is 3:1:1.
The material etched for 30 seconds was used. The thickness of Ga mother crystal wafer 11 is thus 300 to 400.
It was like a kite. Next, a Ga mother wafer 11 was placed in the vapor deposition layer, and Zn was vapor-deposited to a thickness of about one mountain surface. Thus, a diffusion source can be easily made with the structure shown in FIG. Next, as is very commonly done, the diffused G is placed in a closed cylindrical quartz ampoule.
a. The bamboo substrate and the diffusion source sample shown in FIG. 1 are sealed in vacuum. FIG. 2 is a side view of the quartz closed-tube ampoule made in this way, where 21 is the quartz ampoule, 22 is the diffusion source sample storage part of the quartz ampoule, 23 is the sealing part when the quartz ampoule is sealed in vacuum, and 24 is the quartz ampoule. Diffusion source sample, 25 is diffused G
An aAs substrate is shown. The internal volume of the stone hollyhock ampoule 21 in FIG. 2 is approximately 5 mm, and the area of the diffusion source subject 24 is 0.5 mm. At this time, the weight of the Zn layer 12 having the thickness of the IA rudder is about 340 muta. The quartz ampoule 21 manufactured in this way as shown in Fig. 2 was inserted into an electric furnace with a temperature uniformity of about 1°C in the direction of the ampoule length (approximately 80 mm).
When Zn is thermally diffused at 16°C, the diffusion depth xj is equal to the time t.
It increases in proportion to the square root of time t, and the square root of time t=t=
2.05 mountains per hour. This value is Ga
When using the aforementioned ternary alloy diffusion source consisting of 5% Zn, 45% Zn, and 50% As, the value at the same temperature 61 o is 0.7.
It is about 2.7 times larger than the 5 Buddhas. Further, even at a temperature of 566°C, a 0.9 ridge was obtained. This means that deep diffusion of Zn can be easily carried out at low temperatures. A similar diffusion rate can be obtained by preparing pure Zn metal instead of the diffusion source sample 24 in FIG. However, when pure Zn metal is used as a diffusion source, the surface condition of the CaAs substrate 25 to be diffused is severely damaged because Zn vapor reacts with the surface of the Ga pseudo substrate. As a method of preventing this change in surface condition, a method is usually used in which powdered GaAs is prepared in addition to pure Zn metal in the Zn diffusion source sample storage section 22. By putting powdered GaAs into a quartz ampoule, the GaAs surface area is much larger than the surface area of the diffused material.
By making the As surface on the diffusion source side, when the heat diffusion temperature rises, the vapor pressure of Ga is released from the powdered Ga powder, and the powdered GaA
Since the Z-term vapor pressure can be supplied to s from the molten Zn, changes in the surface of the GaAs to be diffused can be prevented. However, in order to prepare powdered Ga$, it must be crushed by rubbing the Ga in a mortar etc., which is very dangerous as it creates dust, and when preparing powdered Ga in a quartz ampoule. , Ga false powder may adhere to the walls of the quartz tube, etc., so extreme care must be taken when handling it. Also, powdered Ga
When the particle size of the As powder is increased, it is impossible to prevent the surface of the diffused Ga$ from being disturbed unless the number of powdered GaAs particles is increased. Furthermore, by pulverizing Ga pine, a decrease in purity will inevitably occur, and it is thought that the surface of powdered CaAs will adsorb a huge amount of air gas and the like. In addition, Z
Since n, false and Ga independently determine the atmospheric gas pressure, controllability of diffusion is not sufficient. According to this invention, when a Zn thin film layer formed in close contact with a Ga matrix is used as a diffusion source as shown in FIG. Correspondingly, Ga and the core melt, and the vapor pressure of Zn, Ga, and $ in the ampoule is mainly supplied from the Zn thin film layer in which the Ga bubbles are melted.

Since the decomposition pressure of the molten Zn solution of Ga and As is lower than that of Ga$, the equilibrium vapor pressure of Ga, false, and Zn in the ampoule is mostly supplied from the diffusion source sample 24, so that the GaAs substrate of the sample to be diffused is Z without damaging the surface of 25.
n diffusion is performed. Also, when the diffusion temperature is 600℃, lAm
The area of the diffusion source sample 24 with a Zn thin film layer of 0.15
Even when changing to ~1.0 ground, no change in the diffusion rate was observed.
Moreover, the surface condition of the diffused GaAs substrate 25 was also extremely good. Further, even if the substrate thickness of the diffusion source Ga layer 11 was less than 100 μm, there was no effect on the diffusion. Furthermore, even if the thickness of the Zn thin film 12 is changed from 0.2 to 3 cm, the total amount of Zn in an ampoule with an internal volume of 1 in 5 at 616°C is 56.
By setting the area of the diffusion source sample 24 to be 4 mm or more, no change in the diffusion rate and concentration was observed. The lower limit of the total amount of Zn in this diffusion source sample 24 is the ampoule internal volume 1
For each enemy, 14.7 yap or more is sufficient for 61 z 0. There is no upper limit. However, if there are more than 10 layers of Zn thin film, the melting of Ga and As into the Zn thin film will not proceed quickly, so Ga and As will not fully penetrate into the Zn, and Zn will rapidly enter the atmosphere. It protrudes and damages the surface of the sample being diffused. The lower limit of the total amount of Zn mentioned above is the diffusion temperature T (K
), and if the molar ratio of Zn in a solution consisting of Zn-Ga-As at that temperature is i, then Z must be placed in one ampoule V.
The lower limit nmin of the number of moles of n is determined by the following formula. iPV×
10-3 nmin=--11 RT R is the gas constant 0.0821・atom'deg・mo
It is l.

The saturated vapor pressure of pure Zn was determined by metallurgical thermochemistry (Pergamo) by Au Kubaszewski et al.
nPrees) 4th edition was used as a reference. Also, Zn, Ga,
The molar ratio of Zn in a solution consisting of M. B. Panis
h: J. Elect “Hem, SoS, 113
861 (1966) as reference. The diffusion method of this invention uses the region of the Ga-core-Zn ternary phase diagram where Zn is abundant. Furthermore, if the total amount of Zn in the ampoule shown in the above example is made smaller than nm, it is possible to achieve even lower concentration Zn diffusion.

In this case, the total amount of Zn in the ampoule must be determined, but the Zn amount must be determined accurately from the film thickness instead of weighing, and the surface of the diffused Ga crystal can be maintained well after diffusion. has a big advantage. Diffusion with good controllability similar to that of the above embodiment can also be obtained by the following method.

For example, in Zn diffusion, a thin film is deposited on a GaAs substrate by sputtering using ZnAS2 or Z~As2 as a target, and this is used as a diffusion source. Thin films deposited by sputtering often have a large deviation in stoichiometric ratio, as in the case of Znx trillion, but such thin films can also undergo thermal equilibrium diffusion similar to the above embodiment. The basis for thermal equilibrium diffusion can be easily read from the phase diagram in the reference literature on page 15, line 7 to line 8 of this specification, and
Details are on the day. C. Casey and M. B. Punish
Tra ship by et al. Met. S ratio.

There is an explanation of AME 242 406 (19 spots). As is clear from these two references, Example Z of the present invention
If a structure in which an n thin film is attached to GaAs is heated, Ga pseudo is melted in the Zn thin film, and a large solution with a Zn composition in which Ga and pseudo are dissolved is formed, and this solution is composed of three As solid phases and a GaAs solid phase. This shows that it is possible to coexist with the phase. Therefore, even if the diffusion source thin film is ZLAsy, and the stoichiometric ratio of this diffusion source thin film Znxmatsuy is different, by heating it melts the Ga pseudo solid phase and mixes the Z~As2 solid phase and the Ga pseudo solid phase in appropriate amounts. As a result, the composition of the solution having a large Zn composition is automatically adjusted to be determined by the diffusion temperature. Also Zn
If xAsy is applied by sputtering or the like, the difference in vapor pressure naturally tends to cause x>y, and the state y>>x is almost never obtained.

That is, it can be handled in the same way as the Zn thin film alone. Furthermore, in order to prevent oxidation of Zn, even if Au is further deposited on the thin film 12 of the diffusion source sample 24 by evaporation to an extent of 0.3 mm, Zn diffusion will be performed in the same way regardless of the presence or absence of Au. It will be done. This is because the vapor pressure of Au is sufficiently lower than that of Zn, and the Au is well absorbed into the diffusion source GaAs, so that it does not affect the atmospheric gas in the diffusion ampoule. This invention has been explained above with respect to the case of Zn diffusion into GaAs.
It is clear that the present invention can be applied to any compound semiconductor sample to be diffused and to any diffusion impurity.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the present invention.
FIG. 2 is a cross-sectional view of a diffusion source sample used when thermally diffusing
FIG. 2 is a cross-sectional view of a quartz ampoule showing the structure of a closed tube ampoule used for heat diffusion. 1 1 is a GaAs wafer, 12 is a Zn layer formed by vapor deposition, etc., 21 is a quartz ampoule, 22 is a diffusion source sample storage section, 23 is a quartz ampoule enclosing section, 24 is a diffusion source sample, 25
is a diffused GaAs substrate. ＊'Picture roof Z diagram

Claims (1)

[Claims] 1 In a method of thermally diffusing impurities into a compound semiconductor material in a closed system, a heat source formed by evaporation etc. on the same base material as the material to be diffused is used as an impurity diffusion source placed separately from the material to be diffused. A compound of a diffusion impurity element or a thermal diffusion impurity element and at least one element constituting the base material,
Alternatively, a method for thermally diffusing impurities into a semiconductor material, which is characterized by using a multilayer or single-layer thin film containing at least a thermally diffusive element.