JP2813711B2 - (III)-(V) Method for diffusing zinc into compound semiconductor crystal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for diffusing zinc as a p-type impurity in a III-V compound semiconductor into a III-V compound semiconductor crystal containing phosphorus as a group V element.

[Conventional technology]

Impurity diffusion is an indispensable technique for manufacturing a semiconductor device, and it is important for an In _1-x Ga _x As _{1-y Py-} based compound semiconductor to diffuse zinc Zn as a p-type impurity in its crystal. In particular, when diffusing impurities to a depth of several μm or more from the surface, for example, when diffusing impurities to the operation layer of an optical element, it is difficult to apply ion implantation, and a thermal diffusion method is used. .

When impurity diffusion is used in the manufacture of a semiconductor device, generally, (1) no surface damage, (2) controllability of the diffusion depth at an appropriate diffusion time, (3) depth and concentration distribution of the diffusion layer (4) Controllability of concentration, (5) Flatness of diffusion front, (6) Controllability of lateral diffusion in selective mask diffusion. However, these requirements are almost unsatisfactory for III-V compound semiconductors. For example, see Toshiaki Ikoma, Yoshinari Matsumoto, Masatake Ogawa,
The latest compound semiconductor handbook, No. 1, pages 153 to 168, published by Science Forum Co., Ltd.

The reason why the above-mentioned requirements have not been solved is largely due to the properties inherent in III-V compound semiconductors. In particular, V with high vapor pressure
In a III-V compound semiconductor containing a group element, the group V element is thermally decomposed intensely in a temperature raising step, so that the crystal surface is damaged and a stoichiometric deviation occurs. Therefore, the above requirement (1) becomes a particularly serious problem. Thermal decomposition is particularly severe when the V element is phosphorus P. Further, indium In, gallium Ga, and aluminum Al, which are Group III elements, are low-melting metals, and tend to precipitate as a liquid phase on the crystal surface after the Group V elements are scattered by thermal decomposition.

When such surface damage occurs, it becomes a problem when discussing diffusion data such as the diffusion depth and the flatness of the diffusion front, and when it occurs in the device manufacturing process, the characteristics and reliability of the device are significantly impaired. .

In order to diffuse impurities in a soaking system while avoiding the occurrence of surface damage due to this thermal decomposition, generally, a diffusion source and a III-
V compound semiconductors need to form a quasi-thermal equilibrium system. Such conditions can be determined by a multi-phase diagram relating to the respective constituent elements of the compound semiconductor and the diffusion source. The simplest system composed of a compound semiconductor and an impurity can be described by a ternary phase diagram. However, these ternary phase diagrams are almost incomplete, and are only known for Zn diffusion into GaAs.

Regarding Zn diffusion into GaAs, a diffusion method with good controllability has been found using a phase diagram. This method is described, for example, by Panish, Journal of Electrochemistry Society, No. 113 (1966).
Year 86), p. 861 (MBPanish, J. Electrochem. Soc., 113 ,
p.861, 1966).

Since the knowledge of the ternary phase diagram is at this level, in the diffusion step in the manufacture of semiconductor elements other than GaAs, the diffusion conditions are often determined empirically.

As a diffusion method, a closed tube method is generally used. In the case of III-V compounds, it is difficult to control the gas pressure of the atmosphere and other conditions, and therefore, the open-tube method that is normally used for the production of Si devices is not generally used. In the closed tube method, a configuration of a gas phase and a solid phase in a tube is selected so that a liquid phase is not included in the system in a phase diagram, and impurities are diffused in a soaking system.

Cathay et al., Transactions of Material Society, AIME Vol. 242 (1968), p. 406 (H.
C. Casey et al., Tran. Met, Soc., AIME 242 , p. 406, 1968)
According to Ga, As and Zn, respectively, 5%, 50% and
Zn diffusion into GaAs was performed without surface damage using a diffusion source containing 45%. The uniformity and reproducibility at this time were good. In this method, the diffusion conditions are basically independent of the amount of diffusion source enclosed in the closed tube and are determined only by the temperature. Therefore, the controllability is excellent.

Yamamoto et al., Japanese Journal of Applied Physics, Vol. 19 (1980), No. 1, No. 12
Page 1 (Y. Yamamoto et al., Jpn J. Appl. Phys., Vol. 19, No.
1, p. 121, 1980) shows a Zn diffusion method using a combination of Zn ₃ As ₂ or ZnAs ₂ and GaAs or InGaAs. Ando et al., Japanese Journal of Applied Physics, Volume 20 (1981), Issue 3, L1
97 (H. Audou et al., Jpn J. Appl. Phys., Vol. 20, No. 3, L1
97, 1981) shows a Zn diffusion method using a combination of Zn ₃ P ₂ and InP. In these methods, the closed tube method is employed.

However, in the closed tube method, the degree of freedom in selecting the concentration of the diffusion layer is poor, and it is difficult to perform low concentration diffusion. For this reason, the surface Zn concentration obtained by the closed tube method becomes 10 ²⁰ cm ⁻³ or more, and the concentration becomes as high as about 10 ¹⁹ cm ⁻³ even near the diffusion front. Such a high concentration cannot be used, for example, as a pn junction of a light emitting diode.

In addition, the jig used in the closed tube and the inside of the closed tube is made of high-purity quartz, and in order to use it for the diffusion process, perform sufficient cleaning, heating, high vacuum evacuation, and other processing to avoid contamination with necessary impurities There is a need. For this reason, there is a disadvantage that it takes time to prepare for the diffusion step. In addition, the inside of the closed tube is welded and sealed with a high vacuum, and after the diffusion, the closed tube is broken and opened.
There was a drawback that it became disposable.

As a method for solving such a drawback, an open tube method can be considered. In order to perform zinc diffusion into a compound semiconductor crystal by the open-tube method, the compound semiconductor liquid crystal is placed in a reaction tube, and a gas of an organic zinc compound is introduced into the reaction tube and thermally decomposed to generate Zn vapor. The Zn is diffused into the compound crystal. By using the open tube method, the diffusion depth can be controlled by the time of flowing the gas of the organic zinc compound and the heating temperature, and the diffusion concentration can be controlled by the molar flow rate of the organic zinc compound and the heating temperature. Further, the open tube method is easy to carry out since the diffusion step can be prepared simply by putting the compound semiconductor crystal into the reaction tube, and can be carried out with the same apparatus as the epitaxial step.

[Problems to be solved by the invention]

However, when attempting to diffuse zinc into a III-V compound semiconductor crystal containing phosphorus as a group V element by an open tube method, phosphorus evaporates from the compound semiconductor crystal at a temperature for thermally decomposing an organic zinc compound serving as a diffusion source. Then, the crystal surface is damaged. Therefore, phosphorus is contained as a group V element.
The use of the open tube method for zinc diffusion into III-V compound semiconductor crystals has not been generally performed until now.

The problem to be solved by the present invention is to provide a method of performing zinc diffusion by an open-tube method on a III-V compound semiconductor crystal containing phosphorus as a group V element while minimizing damage occurring on the crystal surface. It is.

[Means for solving the problem]

The measures taken by the present invention include the use of phosphorus as a group V element II
A compound semiconductor crystal of a group I element and a group V element is heated in a reaction tube, a gas of an organic zinc compound is introduced into the reaction tube, and the organic zinc compound is thermally decomposed to diffuse zinc into the semiconductor crystal. In the method of diffusing zinc into a III-V compound semiconductor crystal, the temperature of the semiconductor crystal is 20
When the temperature exceeds about 0 ° C, flow gas containing PH ₃ into the reaction tube,
_{When the} semiconductor crystal is further heated while flowing a gas containing ₃ to reach a predetermined temperature, a gas of an organic zinc compound is introduced into the reaction tube in addition to the gas containing PH ₃ to thermally decompose the organic zinc compound. After stopping the introduction of the gas of the organozinc compound into the reaction tube and terminating the thermal decomposition,
To keep the gas containing PH ₃ flowing into the reaction tube until the temperature of the semiconductor crystal drops to about 200 ° C. again.

The pressure of PH ₃ is set to be equal to or higher than the vapor pressure of phosphorus.

When the III-V compound semiconductor crystal contains phosphorus and arsenic, for example, in the case of an AlGaAsP system, it is preferable to use both PH ₃ and AsH ₃ .

As the organic zinc compound, diethyl zinc (DEZ) or dimethyl zinc (DMZ) is used.

(Operation)

To prevent damage to the crystal surface by phosphorus scattering of III-V compound semiconductor crystal containing phosphorus as a group V element, introducing a gas containing PH ₃ into the reaction tube. The thermal decomposition of PH ₃ starts at around 200 ° C., and at a higher temperature, phosphorus can be supplied to the compound semiconductor crystal. On the other hand, the evaporation of phosphorus from the crystal becomes intense at 400 ° C. or higher, but occurs even at a lower temperature, and the longer the standing time, the greater the amount of phosphorus evaporation. Therefore, PH ₃ is introduced from about 200 ° C., and PH ₃ is kept flowing during zinc diffusion at a higher temperature and thereafter until the compound semiconductor crystal reaches about 200 ° C.
Thereby, damage due to thermal decomposition of the crystal surface can be minimized.

The organic zinc compound mixed with PH ₃ is a Zn vapor generated by thermal decomposition, which is diffused into a compound semiconductor crystal. The diffusion depth is controlled by the time of flowing the gas of the organozinc compound and the heating temperature. The diffusion concentration is controlled by the molar flow rate of the organozinc compound and the heating temperature.
Since the diffusion source is a gas, there is no steep gradient of the diffusion concentration unlike the case of using a solid diffusion source, and the uniformity of the diffusion concentration is high, and the diffusion depth and the reproducibility of the diffusion concentration are excellent. I have.

〔Example〕

 FIG. 1 shows the configuration of a diffusion device embodying the present invention.

The reaction tube 1 has an on-off valve 2-1 and a flow meter 3-1.
Arsine AsH ₃ is introduced via the
And dimethyl zinc is introduced via a flow meter 3-2, nitrogen N ₂ is introduced via an on-off valve 2-3 and a flow meter 3-3, and an on-off valve 2-4 and a flow meter 3-4 are introduced.
Hydrogen H ₂ via the introduction of, phosphine PH ₃ is introduced via the opening and closing valve 2-5 and the flow meter 3-5.
Nitrogen introduced from opening / closing valves 2-3 and 2-4, respectively
N ₂ and hydrogen H ₂ are for dilution.

The exhaust gas from the reaction tube 1 is sent to the abatement apparatus via the exhaust pump 4 when the pressure inside the reaction tube 1 is reduced, and via the valve 5 when the pressure inside the reaction tube 1 is reduced to normal pressure. .

A susceptor 6 is disposed in the reaction tube 1, and a III-V compound semiconductor crystal substrate 7 is mounted on the susceptor 6. As the susceptor 6, for example, a carbon graphite plate whose surface is covered with SiC is used. The crystal substrate 7
The gas introduced into the reaction tube 1 is arranged so as to flow uniformly on its surface in a laminar flow state. About this arrangement, Yoshifumi Mori, edited by Sasumi Cold Water and Yoshifumi Mori, published by Science Forum Inc. on June 15, 1986, "Epitaxial Growth Technology Data Collection, Vol. 1, MBE and MOCVD, Vol. 1,
MOCVD ", pages 33-36.

A high frequency coil 8 is arranged around the reaction tube 1. The high-frequency coil 8 heats the susceptor 6 by high-frequency heating, thereby controlling the temperature of the crystal substrate 7.

Here, an InP substrate is used as the crystal substrate 7 and Zn
Will be described as an example.

FIG. 2 shows the relationship between the temperature of the crystal substrate 7 and the flow rates of PH ₃ and dimethyl zinc.

First, the InP substrate placed on the susceptor 6 is heated by high frequency heating as shown in FIG. In order to prevent the substrate surface from being damaged by thermal decomposition during the heating, PH ₃ is started to flow when the substrate temperature reaches about 200 ° C. After the substrate is in a uniform temperature state at the diffusion set temperature T, dimethyl zinc is flowed to start diffusion. Dimethyl zinc is thermally decomposed on the substrate and becomes a diffusion source of Zn.

For this reaction, see Fillardson, Beer Editing,
Lazegi, "Semiconductors and Semimetals, Lightwave Communications Technologies," Vol. 22, Part A, 1985, pp. 299-375.
Page, Academic Press (M. Razeghi, “Semicond
uctors and Semimetals, Lightwave Communications Tec
hnology ", Vol.22, Part A, Edit.by RKWillardson and
A. Beer, pp. 299-375, 1985, Academic Press Inc.).

Stopping the flow of dimethylzinc after diffusion time t _2, the temperature is reduced by stopping the heating at the same time. When the temperature of the substrate drops to about 200 ° C. at which no surface damage occurs, the flow of PH ₃ is stopped.

The diffusion concentration and the diffusion depth of Zn are controlled by the substrate temperature, the concentration of dimethyl zinc, and its flow rate.

FIG. 3 shows an example of measuring the carrier concentration after Zn diffusion. This figure shows the diffusion time of each undoped InP substrate at 500 ° C.
For the sample in which Zn was diffused for 60 minutes and 30 minutes, the carrier concentration N of the p-type phase was measured in the depth direction x from the surface. This measurement is based on Bio-Rad Semiconductor Measurement Systems (BIO-RAD Semiconductor
It was measured by Polaron Profiler (available in Japan from Japan Bio-Rad Laboratories).

The flow rate of the gas introduced into the reaction tube 1 for preparing this sample was such that the total flow rate of H ₂ and N ₂ was 4.8 / sec at a flow rate ratio of 1: 1.
PH ₃ diluted to a concentration of 20% with H ₂ 0.17 / sec, density 150 He
Dimethyl zinc diluted to 0 ppm was 0.1 / sec. The surface of the substrate was not damaged and the mirror surface was maintained.

In this measurement example, it has been difficult in the conventional closed tube method 10 ¹⁸
It shows that control can be performed at cm ^-3 or less.

FIG. 4 shows the relationship between the diffusion depth and the diffusion time obtained from the measurement example of FIG. The diffusion depth increases in proportion to the square root of the diffusion time t (t 2 in FIG. ₂ ), indicating that this is a Zn diffusion phenomenon in the InP crystal in a normal closed tube method or the like.

When diffusing into a mixed crystal substrate containing As and P, both PH ₃ and AsH ₃ are introduced into the reaction tube 1. Diethyl zinc can be used instead of dimethyl zinc,
It is also possible to use a mixture of the two.

 FIG. 5 shows another example of the diffusion device.

In this apparatus, dimethylzinc or diethylzinc is put in a container whose temperature is controlled in a thermostat 10, and is supplied to the reaction tube 1 by bubbling.

That is, instead of the on-off valve 2-2 and the flow system 3-2 for dimethyl zinc in the apparatus shown in FIG.
It comprises a closing valve 2-6 and 2-7 and the flow meter 3-6,3-7 for H ₂ or N for _2.

The H ₂ or N _{2 that} has passed through the opening / closing valve 2-6 and the flow meter 3-6 bubbling dimethyl zinc or diethyl zinc contained in a container temperature-controlled in the thermostat 10, and the reaction tube through the valve 11. Introduced in 1. Open / close valve 2-7
And H ₂ or N ₂ passed through the flow meter 3-7 is introduced directly into the reaction tube 1.

In this apparatus, since the bubbling is performed at a controlled temperature, the concentration of dimethylzinc or diethylzinc can be controlled with high precision.

In the diffusion device shown in FIG. 1 or the diffusion device shown in FIG. 5, a mass flow controller can be used instead of the flow meters 3-1 to 3-7.

Figure 6 is the relationship between temperature and PH ₃ and dimethylzinc crystal substrate 7 illustrates another example the second FIG.

In the example shown in FIG. 2, the supply of Zn was stopped and the temperature was lowered at the same time. As a result, a Zn distribution in which the carrier concentration rapidly changes in the depth direction at the diffusion front was obtained. In the example of FIG. 6 contrast, by keeping for a certain time t ₃ at high temperatures T _D after stopping the supply of Zn, it is possible to gradually change the distribution in the depth direction of the carrier concentration.

〔The invention's effect〕

According to the present invention, III-V containing phosphorus as a group V element
When diffusing zinc compound semiconductor crystal by open tube method, by introducing PH ₃ from about 200 ° C., PH ₃ to between zinc diffusion at higher temperatures, and then the semiconductor crystal is about 200 ° C. By continuing the flow, damage to the crystal surface due to the scattering of phosphorus can be minimized. Therefore, it becomes practically possible to utilize the open-tube method for zinc diffusion into the III-V compound semiconductor crystal containing phosphorus.

The present invention has a high practical value particularly in the production of an optical element in which the operation layer is formed at a depth of several μm or more from the surface.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a diffusion device embodying the present invention. FIG. 2 is a diagram showing the relationship between the temperature of the crystal substrate and the flow rates of PH ₃ and dimethyl zinc. FIG. 3 is a diagram showing a measurement example of a carrier concentration after Zn diffusion. FIG. 4 is a diagram showing a relationship between diffusion depth and diffusion time. FIG. 5 is a diagram showing another example of the diffusion device. Figure 6 is a diagram showing the relation between flow temperature and PH ₃ and dimethylzinc crystal substrate. 1 .... reaction tube, 2-1 to 2-7 ... open / close valve, 3-1
3-7: Flow meter, 4: Exhaust pump, 5, 11: Valve, 6: Susceptor, 7: Crystal substrate, 8: High frequency coil, 10: Constant temperature bath.

Claims (1)

(57) [Claims] 1. A group III element containing phosphorus as a group V element and V
III-V compound semiconductor in which a compound semiconductor crystal with a group III element is heated in a reaction tube, a gas of an organic zinc compound is introduced into the reaction tube, and the organic zinc compound is thermally decomposed to diffuse zinc into the semiconductor crystal. In the method of diffusing zinc into a crystal, when the temperature of the semiconductor crystal exceeds about 200 ° C., a gas containing PH ₃ is flowed into the reaction tube, and the semiconductor crystal is further heated while flowing a gas containing PH ₃ to determine the temperature in advance. When the temperature reached, the gas of the organic zinc compound in addition to the gas containing PH ₃ was introduced into the reaction tube to thermally decompose the organic zinc compound, and the introduction of the gas of the organic zinc compound into the reaction tube was started. after completion of the thermal decomposition is stopped, the up to a temperature of the semiconductor crystal is reduced again to about 200 ° C., III-V compound semi a gas containing PH _3, characterized in that continuing to flow into the reaction tube A method for diffusing zinc into conductor crystals.