JP2737186B2 - Gallium arsenide compound semiconductor single crystal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gallium arsenide (GaAs) compound semiconductor single crystal, and more particularly to a GaAs compound semiconductor single crystal suitable for an integrated circuit substrate.

[Conventional technology]

Conventionally, this type of GaAs substrate for a GaAs integrated circuit has been manufactured using a liquid-sealed Czochralski (LEC) method or a horizontal Bridgman (H
It is manufactured by the B) method. Normally, the LEC method uses no added crystal, and the HB method uses a chromium added crystal.

[Problems to be solved by the invention]

In order for a GaAs crystal to be used as a substrate for an integrated circuit (IC), it must have a semi-insulating property with a specific resistance of 1.0 × 10 ¹⁷ Ω · cm or more and have a small or uniform number of crystal defects called dislocations. And that the characteristics between the field effect transistors (FETs) formed on the substrate in close proximity to each other do not affect each other, that is, the side gate (SG) effect It is required to be as small as possible.

However, when an integrated circuit is manufactured using the GaAs single crystal according to the above-described conventional technique, there is a drawback that the characteristics between the devices interact with each other and, in effect, do not operate as an IC.

[Means for solving the problem]

According to the present invention, in the crystal 7.0 × 10 ¹⁵ cm ^-3 or more 1.0 × 10
A GaAs compound semiconductor single crystal containing an enzyme element of ¹⁷ cm ⁻³ or less is obtained.

As a GaAs single crystal for integrated circuits, an undoped crystal is usually used, and its semi-insulating property is such that a donor-type deep level in a forbidden band called EL2 is a shallow acceptor level represented by carbon (C). It is made up of compensation. We investigated the causes of the side-gate effect between field-effect transistors fabricated on GaAs integrated circuits.
It was found that when heat-treated, the concentration of EL2 order decreased near the surface of the substrate, and as a result, the resistivity decreased on the very surface of the substrate.

The EL2 level is formed in the form of AS _Ga by occupying the Ga lattice position in the GaAs crystal with As atoms.Therefore, the decrease in the EL2 concentration at the extreme surface is caused by the high vapor pressure of As atoms during the heat treatment. Is generated by evaporation.

On the other hand, oxygen atoms in the GaAs crystal are EL2 (As _Ga ) in the forbidden band.
Contributes to the semi-insulating property of the GaAs substrate, and even if the GaAs substrate is annealed, its concentration including the pole surface does not redistribute in the crystal and is extremely stable thermally. Does not cause a reduction in the resistance of the very surface.

Although chromium-added GaAs single crystals for integrated circuits are also used, Cr in GaAs crystals is thermally unstable and redistributes during heat treatment, resulting in a lower surface resistance.

That is, the deep level formed by the oxygen element is EL
Since it has the same activation energy as the level referred to as 2 and is extremely thermally stable, the heat treatment does not lower the surface of the wafer pole.

Therefore, by using the substrate according to the present invention, a GaAs integrated circuit having extremely small side gate effect can be manufactured.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention.
₄ is a graph showing a relationship between a side gate breakdown voltage between FET elements manufactured on a crystal wafer to which oxygen is added in the form of ₂ O ₃ and an oxygen concentration in a crystal.

The GaAs crystal was produced as follows. 3100 g of Ga and As are charged in equimolar amounts into a 6-inch PBN crucible, and oxygen is further added to Ga ₂ O so that the oxygen concentration in the crystal changes within the range of 1.0 × 10 ¹⁵ to 1.0 × 10 ¹⁸ cm ^-3. Ga ₂ added in the form of ₃
An additional charge of As, which is equivalent to Ga in O ₃ , was added. This raw material was sealed with a liquid sealing agent B ₂ O ₃ , and crystals having different oxygen concentrations were produced by the LEC method. Similarly, an undoped single crystal to which oxygen was not added was prepared for comparison.

For each of these crystals, a wafer was cut out from a portion 20 mm from the top of the straight body to produce a field effect transistor, and the SG effect between adjacent elements was measured. The oxygen concentration in the crystal is determined by activation analysis, and the characteristic index used to determine the quality of the SG effect is the source voltage value of the nearest FET that reduces the drain current of any given FET in the integrated circuit by 10%. Was. As can be seen from the figure, the oxygen concentration in the crystal is 7.0 × 10
Good side gate resistance can be obtained in the range of ^{15 to} 1.0 × 10 ¹⁷ cm ⁻³ .

 Next, a second embodiment of the present invention will be described.

The procedure for preparing the crystal, the method for measuring the oxygen concentration, and the method for evaluating the SG effect are the same as those in the first embodiment, but in this embodiment, oxygen was added using As ₂ O ₃ during crystal growth. The result is exactly the same as the relationship shown in FIG. 1. In this example, good anti-side gade characteristics were obtained when the oxygen concentration in the crystal was in the range of 7.0 × 10 ^{15 to} 1.0 × 10 ¹⁷ cm ^−3. It was confirmed that it could be done.

〔The invention's effect〕

As described above, the use of the GaAs compound semiconductor single crystal according to the present invention can realize a GaAs integrated circuit and a large-scale integrated circuit having no or extremely little side gate effect,
There is an effect that the yield when these are manufactured on an industrial scale can be significantly improved.

[Brief description of the drawings]

 FIG. 1 is a graph showing the results of each embodiment of the present invention.

Claims (1)

(57) [Claims] An oxygen element forming a deep level having the same activation energy as an EL2 level in a crystal is 7.0 × 10 ¹⁵ cm ^−3.
A semi-insulating gallium arsenide compound semiconductor single crystal characterized by being free from intentional addition of impurities other than the above and containing 1.0 × 10 ¹⁷ cm ⁻³ or less.