JPH0131291B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a compound semiconductor device, particularly a method for activating implanted atoms in an ion implantation layer formed from the surface of a compound semiconductor crystal substrate containing arsenic (As) to the inside of the substrate. The present invention relates to a heat treatment method.

In recent years, with the demand for ultra-high speed and ultra-high frequency semiconductor devices, gallium arsenide (GaAs), which has higher electron mobility than silicon (Si) semiconductor crystal, which has traditionally been used as a material for semiconductor devices, has been developed.
Semiconductor devices using compound semiconductors such as these have been attracting attention. In particular, remarkable progress has been made in GaAs shot barrier field effect transistors (GaAs MESFETs), which are high-frequency semiconductor devices using GaAs, and research and development aimed at integrated circuits (ICs) and large-scale integrated circuits (LSIs) are progressing steadily. ing. In the case of GaAs, which has many difficulties in diffusion technology, ion implantation, which is theoretically superior as a precision impurity doping method, requires particularly high controllability. It is expected that this will become the main technology for GaAsIC.

However, with regard to compound semiconductors such as GaAs, the phenomena that occur with ion implantation are much more complex than in single semiconductors such as Si, and the process of high-temperature heat treatment to activate the implanted atoms after ion implantation is A stable heat treatment method that prevents one of the constituent elements (for example, arsenic) from evaporating has not been established, and it has not yet achieved the status of a high-yield, reproducible manufacturing technology.

During heat treatment (hereinafter simply referred to as heat treatment) to activate the ion-implanted layer formed on the surface of a compound semiconductor containing As, for example, a GaAs crystal substrate.
To prevent arsenic from evaporating from the GaAs surface,
For example, Kasahara and Arai J.Electrochem.Soc.126No.11,
1997 (1979), hydrogen arsenide (arsine, AsH ₃ ) gas in an open tube at a molar partial pressure of 0.2 to
It is known that heat treatment at a temperature of about 750 to 900° C. in a hydrogen (H ₂ ) gas atmosphere containing about 10 Torr is effective.

However, the AsH ₃ gas used in this method is extremely toxic (tolerable concentration 0.05 ppm) and can be fatal to humans if accidentally inhaled, so extreme care must be taken when handling gas-filled containers and heat treatment equipment. is essential. In addition, in the event that AsH ₃ gas leaks from the container or heat treatment equipment, the current method is insufficient to instantly detect the leakage of a small amount of gas, which poses a problem in ensuring safety.

Furthermore, in this method, which uses AsH ₃ gas and H ₂ gas as an atmosphere, the atmosphere during heat treatment becomes strongly reducing due to the presence of a large amount of H ₂ gas, which exerts a reducing effect on the reaction container, etc., so that it may cause deterioration or deterioration of the container, etc. Arouse. Moreover, since _H2 gas is a very light gas,
There is a large density difference with AsH ₃ gas, which makes uniform mixing of H ₂ and AsH ₃ difficult, and under the above-mentioned temperature conditions, gas convection becomes intense and the atmosphere becomes non-uniform. This seems to be the cause, and in such conventional methods, the activation rate of the ion-implanted layer varies widely on the substrate surface, resulting in poor reproducibility for each heat treatment.

In addition, in the case of this method, in order to obtain a high activation rate of the ion-implanted atoms, as shown in FIG.
Substrate 13 (or other material including injection layer 11)
It is necessary to place the two GaAs substrates (not shown) in a heat treatment system so that the surface on which the injection layer 11 is formed is placed on the inside. However, in this case as well, the adhesion with the substrate 13 to be overlapped and the substrate 1
Since the activation rate is affected by the type of 3, etc., the activation rate is not uniform within the substrate surface, and the reproducibility for each heat treatment is not good.

This invention was made to eliminate the above-mentioned drawbacks regarding heat treatment performed after forming an ion-implanted layer on a compound semiconductor crystal substrate containing As, and uses less toxic trimethylarsine gas instead of extremely toxic AsH ₃ gas. (CH ₃ ) ₃ As] or triethylarsine [(C ₂ H ₅ ) ₃ As] gas. Both (CH ₃ ) ₃ As and (C ₂ H ₅ ) ₃ As decompose easily in the air and change to arsenite As ₂ O ₃ .nH ₂ O, which, like AsH ₃ , causes acute death by inhalation. Therefore, safety during heat treatment work is improved. Furthermore, by using a mixed gas with H ₂ gas whose main component is an inert gas from Group 8 of the periodic table in place of the conventional H ₂ gas, the implanted atoms can be activated uniformly and reproducibly at a high activation rate. It combines the advantages of

An embodiment of the present invention will be described below with reference to the drawings. Figure 2 shows the result of this example method.
This figure shows an outline of a heat treatment system used to heat treat GaAs. Electric furnace 2 with wide constant temperature range
A quartz open tube 23 is placed inside the quartz tube 1, a support 22 made of quartz or the like is inserted therein, and the GaAs substrate 12 on which the ion-implanted layer 11 is formed is placed. In this way, 65 ml/min of H ₂ gas was maintained at 37° C. from the gas inlet 24 of the open quartz tube 23 to the bubbler 26 filled with (C ₂ H ₅ ) ₃ As 25.
35 ml of H ₂ gas from another inlet pipe 27.
Argon (Ar) gas is introduced at a rate of 900 ml/min and mixed with H ₂ gas that has passed through (C ₂ H ₅ ) ₃ As, and heat treatment is performed while flowing.

In this embodiment, the temperature of the electric furnace 21 was set at 850°C, but this temperature can be changed as appropriate depending on the type and amount of atoms to be implanted. The molar ratio of (C ₂ H ₅ ) ₃ As in the heat treatment atmosphere is bubbler 2.
6 temperature, i.e. (C ₂ H ₅ ) ₃ As vapor pressure and bubbler 2
It can be adjusted by the amount of H ₂ that passes through 6. The vapor pressure of As, which constitutes GaAs crystals, increases as the heat treatment temperature increases, so to prevent GaAs from decomposing during heat treatment, the molar ratio of (C ₂ H ₅ ) ₃ As in the atmosphere (in an open tube system) However, as the heat treatment temperature increases,
For heat treatment at about 900° C., the molar partial pressure of As (C ₂ H ₅ ) may be as high as 4×10 ⁻³ (corresponding to a partial pressure of about 3 Torr). In this example, the molar ratio of (C ₂ H ₅ ) ₃ As was set to 1.32 × 10 ^-3 , and the total flow rate of atmospheric gas was 1.
/min. H ₂ in the atmospheric gas is added to promote the decomposition of (C ₂ H ₅ ) ₃ As during heat treatment and to produce vapor of elemental As. When the amount of H ₂ in the atmosphere increases, the same disadvantages as those of the conventional example mentioned above occur, which is undesirable.

In the above embodiment, H 2 gas was passed through the (C ₂ H ₅ ) ₃ As bubbler 26, and H ₂ gas and Ar gas were introduced from another gas introduction pipe 27, but H ₂ gas was passed through the bubbler ₂₆ . Instead of gas, an inert gas such as Ar, which is the main component of the atmosphere, may be used. In that case, a predetermined amount of H ₂ gas may be introduced from the introduction pipe 27 shown in FIG. Bubbler 26 to further introduce (C ₂ H ₅ ) ₃ As
In this case, bubbling as shown in FIG. 2 is not an essential condition, and (C ₂ H ₅ ) ₃ As vapor may be supplied into the electric furnace 21 by various mechanisms.

As detailed above, in this example, a mixed gas containing inert Ar gas, (C ₂ H ₅ ) ₃ As, which is safer than AsH ₃ , and a predetermined amount of H ₂ gas is used as the atmospheric gas. , an ion implantation layer 11 is formed.
The surface of the GaAs substrate 12 is exposed to this atmospheric gas flow and subjected to heat treatment.

FIG. 3A shows the carrier concentration distribution in the depth direction (carrier profile) after the substrate is heat-treated by this method. The injection layer was formed by directly implanting Si ions into a Cr-doped semi-insulating GaAs substrate at a dose of 2×10 ¹² ions/cm ² at an acceleration energy of 250 keV, and the heat treatment time was 15 minutes. . Carrier profiles obtained when the same injection layer is heat treated by conventional methods are shown in FIGS. B shows a base 12 including the injection layer 11 and another GaAs base 13 as shown in FIG.
1 and 2 were superimposed and heat-treated, and C was heat-treated by exposing the base 12 including the injection layer 11 to an H ₂ gas atmosphere containing AsH ₃ .

As described above, according to the method of the present invention, the implantation efficiency of implanted ions can be improved by 30 to 50% compared to cases (b) and (c) using conventional methods. As can be seen from FIG. 3, among the conventional methods, the method of overlapping the substrates has higher injection efficiency than the method of exposing the substrate surface to the atmosphere. Hereinafter, when comparing the example of the method according to the present invention with the example of the conventional method, the example of the method of superposing the substrates will be applied to the conventional example.

Ion implantation technology improves controllability of impurity doping,
Since this technology is attracting attention because it improves uniformity, it is important to ensure uniformity and reproducibility in heat treatment. The histogram shown in FIG. 4 compares the distribution of the implantation efficiency (activation rate) of implanted ions within the inner surface of the substrate between the method of the present invention and the conventional method. A is based on the method of this invention, and B is based on a conventional method. It can be seen that the method of the present invention has much better uniformity than the conventional method. Furthermore, as shown in FIG. 5, the reproducibility of the injection efficiency for each heat treatment is also superior in A according to the method of the present invention compared to B according to the conventional method. Note that the injection layer is the third
It was formed under the same conditions as in the figure.

In the heat treatment system shown in FIG. 2, the number of substrates installed is one for convenience, and this substrate is placed face down on a support stand 22. However _{, as} shown _{in FIG .}
Even if a plurality of sheets of 3 ₆ , 63 ₇ , 63 ₈ , and 63 ₉ are arranged vertically and subjected to heat treatment, the effects do not change at all as long as an equal temperature area is ensured. FIG. 7 shows a comparison of the injection efficiency among the substrates when the substrates were installed as shown in FIG. 6 and heat treated according to the method of the present invention. The numbers given to the base are the same as in FIG. 6. It can be seen that the variation between each substrate is very small.

In the above embodiments of the present invention, as a GaAs substrate,
This is explained using a Cr-doped semi-insulating substrate as an example.
Similar effects can be obtained when using other GaAs substrates, such as those grown epitaxially on a crystal substrate. Although (C ₂ H ₅ ) ₃ As was used in the above embodiment, (CH ₃ ) ₃ As may be used instead of (C ₂ H ₅ ) ₃ As. The temperature of the bubbler 26 and the amount of hydrogen passing through the bubbler 26 are
(CH ₃ ) ₃ Depending on the vapor pressure of As,
The molar ratio of (CH ₃ ) ₃ As was changed to (C ₂ H ₅ ) ₃ As in the above example.
A similar effect can be obtained by setting the molar ratio to be the same as that of .

As described above, according to the method of the present invention, compared to conventional methods, it is possible to more safely perform activation heat treatment which is stable, uniform, and has excellent reproducibility with high injection efficiency. In addition, there is no need to cover the substrate including the injection layer with a protective film or to overlap the substrates, simplifying the heat treatment process and making it easy to heat treat a large number of substrates at once. Furthermore, this method can be carried out without any problem even if there is an oxide film such as SiO ₂ or an insulating film such as nitride film such as SiN ₄ on a part or the entire surface of the compound semiconductor substrate including the injection layer. Since heat treatment is performed on a substrate that has been patterned into an iso-membrane material and selectively formed with an implanted layer, ion implantation is used in the production of field-effect transistors (FETs) and integrated circuits (ICs) using compound semiconductors. Effective when using technology.

[Brief explanation of drawings]

Figure 1 is a diagram illustrating a method of overlapping substrates in a conventional heat treatment method, Figure 2 is a schematic diagram of a heat treatment furnace used in an embodiment of the present invention, and Figure 3 is a diagram showing the carrier profile after annealing. Diagram comparing the conventional method and the method according to the present invention, No. 4
Figures A and B are injection efficiency distribution diagrams that similarly compare the uniformity within the substrate surface, Figure 5 is an injection efficiency distribution diagram that similarly compares the reproducibility for each heat treatment, and Figure 6 is another embodiment of the present invention. Figure 7 is a layout diagram of the substrate furnace according to Figure 6.
FIG. 3 is an injection efficiency distribution diagram of each substrate when the furnace arrangement shown in the figure is taken. In Figures 1, 2, and 6, 11... ion-implanted layer, 12,63 ₁ to 63 ₉ ... GaAs including the implanted layer
Base, 21... Electric furnace, 22... Base support, 2
3...quartz open tube, 25...triethylarsine (C ₂ H ₅ ) ₃ As, 26... bubbler, 27... gas introduction tube.

Claims (1)

[Claims] 1. A step of implanting ions from the surface of a compound semiconductor crystal substrate containing arsenic (As) as at least one constituent element and forming an ion-implanted layer inside the substrate; Ion implantation is performed in an atmosphere gas containing a mixture of an arsenic compound of either trimethylarsine [(CH ₃ ) ₃ As] or triethylarsine [(C ₂ H ₅ ) ₃ As] and hydrogen (H ₂ ) for Ar). 1. A method for manufacturing a compound semiconductor device, comprising the step of activating implanted atoms in an ion implanted layer by performing heat treatment while the layer surface is exposed.