JPH0226781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a field effect transistor using a compound semiconductor as a base material, and particularly relates to a GaAs MESFET.

(Prior Art) GaAs MESFET is known as the most typical field effect transistor using a compound semiconductor as a base material, and its basic configuration is shown in FIG.

In Figure 1, 1 is a semi-insulating GaAs substrate;
2 is an n ⁺ type source region, 3 is an n ⁺ type drain region, 4 is an n type active region, 5 is a source electrode, 6 is a drain electrode, and 7 is a gate electrode forming a Schottky junction. 2, 3, and 4 are usually formed using Si as an impurity.

Such a GaAs MESFET can be formed on the surface layer of a high-purity substrate, or by forming a high-purity epitaxial growth layer on a suitable substrate by a high-purity epitaxial growth method, and then It can also be formed inside.

In FETs fabricated on the above-mentioned substrate, the amount of residual impurities in the substrate is small, so the activation rate of the implanted donors is stable and the threshold voltage (hereinafter referred to as V _T ) of the FET is uniform. performance is improved to a level sufficient for the fabrication of integrated circuits. However, the following problems arise in this case.

This is because the band under the active region becomes less curved, causing the channel to apparently widen.
This means that the saturation characteristics of the FET become weaker, approaching the characteristics of a triode. Approaching triode characteristics is not desirable for normal GaAs logic circuit operation.

(Objective of the Invention) An object of the present invention is to form a field effect transistor having good saturation characteristics and uniform V _T on the surface of a substrate having at least a high purity surface layer as a starting material.

(Summary of the Invention) In order to achieve the above object, the present invention implants impurity ions before forming a field effect transistor so that acceptor impurities are present directly under the active region, thereby widening the channel. In order to improve the saturation characteristics by suppressing the
Alternatively, by using a shallow level acceptor impurity and a deep level donor impurity, an increase in substrate leakage current, which is a problem in ICs, is prevented, and the ion implantation of impurities is carefully controlled. The uniformity of V _T is maintained by

(Embodiments of the Invention) Examples will be described below with reference to FIG.

MOCVD on a commercially available GaAs substrate (not shown)
Thickness determined by growth method (organometallic chemical vapor deposition)
2.5 μm to 3 μm, total residual impurity concentration 10 ¹⁵ cm ^-3
A high purity epitaxial growth layer 1a of The implantation amount is 1×10 ¹² cm ^-2 , and the impurity layer 1 is a co-implanted layer of carbon and oxygen.
form b. In the impurity layer 1b, an n-type active region 4, an n ⁺ -type source region 2, and an n ⁺ -type drain region 3 are formed by implanting Si ions. The implantation energies of n-type and n ⁺ type are respectively
60KeV and 100KeV, and the injection amount is 3× each.
10 ¹² cm ^-2 , 2×10 ¹³ cm ^-2 and annealing at 800℃
It is 20min. Note that the dimensions of the gate electrode (made of W-Al alloy) are 1.7 μm×10 μm.

FIG. 2 is a diagram showing the static characteristics near the threshold voltage of an FET fabricated on a high-purity MOCVD substrate into which carbon and oxygen were implanted at 1×10 ¹² cm ⁻² each.

For comparison, Figure 3 shows an FET fabricated on a high-purity MOCVD substrate without implanting carbon or oxygen.
FIG. 2 is a diagram showing static characteristics near the threshold voltage of .

As is clear from the comparison between FIG. 2 and FIG. 3, the triode characteristics seen in FIG. 3 are not observed at all in FIG.

This can be considered to be because there are many ionized acceptors under the active region, which increases the bending of the band under the active region and reduces the current flowing under the active region.

As described above, it can be said that using a high purity substrate into which both shallow level acceptors and deep level donors are implanted is very effective in improving saturation characteristics. Also, since substrate leakage current will increase if only shallow level acceptors are used, the amount of deep level donors during co-implantation should be increased by increasing the amount of deep level donors when co-implanting, so that the part far enough away from the MESFET part will have high resistance. It is desirable that the amount be equal to or higher than that of .

In the above embodiment, the amount of carbon and oxygen implanted was 1
×10 ¹² cm ^-2 , but 0.5 × 10 ¹² cm ^-2 ~ 5 × 10 ¹² cm
Similar effects can be expected within the range of ^-2 .

In addition, the high purity epitaxial growth method is
The method is not limited to MOCVD, and may be MBE (molecular beam epitaxial growth), VPE (vapor phase epitaxial growth), or other methods.

In addition, in the above example, when forming an impurity layer by implanting impurity ions from the surface of a high-purity epitaxial growth layer of a compound semiconductor, an example was described in which a shallow level acceptor and a deep donor are co-implanted as impurities. However, a similar effect occurs with deep acceptor-only injection. Examples of deep level acceptors include vanadium and chromium.

(Effects of the Invention) As described above, the present invention suppresses the current flowing under the FET channel and solves the deterioration of saturation characteristics, which is a problem when using a high-purity substrate. It has the advantage of being able to be fabricated in bulk, and can be used in GaAs integrated circuits.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional structural diagram of one embodiment of the present invention, and FIG.
The figure shows the static characteristics near the threshold voltage of an FET without carbon and oxygen implanted, and Figure 2 shows the static characteristics near the threshold voltage of an FET with carbon and oxygen implanted. This is a diagram. 1... Semi-insulating GaAs substrate, 1a... High purity epitaxial growth layer, 1b... Impurity layer, 2...
...n ⁺ type source region, 3...n ⁺ type drain region,
4...n-type active layer region, 5...source electrode, 6
...Drain electrode, 7...Gate electrode.

Claims (1)

[Claims] 1. A compound semiconductor substrate with at least a high purity surface layer is prepared, impurity ions are implanted from the surface of the compound semiconductor substrate to form an impurity layer, and a source region and a drain region are formed in the impurity layer. ,
and a method for manufacturing a field effect transistor in which an active region is formed, wherein the impurity is a deep level acceptor;
Alternatively, a method for manufacturing a field effect transistor characterized in that there are two types: a shallow level acceptor and a deep level donor.