JPH1074776A - Manufacture of field effect transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing field effect transistor by which the service life of a field effect transistor can be prolonged by relieving the characteristic variation of the transistor, such as the decrease of the current between the source and drain of the transistor, etc., without changing the gate metal of the transistor. SOLUTION: In a method for manufacturing a field effect transistor provided with source and drain electrodes 5 and 6 formed apart from each other on the surface of a gallium arsenide substrate l, a gate electrode 7 which controls the value of the current flowing through the current passage between the electrodes 5 and 6, and an insulating film 8 coating the surface, the characteristic variation of the transistor is relieved by giving a compressive or tensile stress to the semiconductor substrate l in the current passage by forming the insulating film 8 on the current passage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a Schottky junction field-effect transistor, and more particularly, when transistor characteristics fluctuate with long-term operation, the fluctuations are alleviated and the life of the transistor is extended. The present invention relates to a method for manufacturing a field effect transistor.

[0002]

2. Description of the Related Art In order to improve the reliability of a semiconductor device formed on a silicon substrate or a compound semiconductor substrate such as gallium arsenide, it is important to clarify a failure mechanism and take an effective countermeasure.

[0003] For example, a gallium arsenide MESFET (metal-semiconductor field effect transistor) will be described as an example.
FIG. 1 shows a cross-sectional shape of the MESFET. A channel region 2, a source region 3, and a drain region 4 are formed in a gallium arsenide substrate 1 by an ion implantation method. Next, the source region 3
And source electrode 5 in ohmic contact with drain region 4
A gallium arsenide substrate 1 on the gallium arsenide substrate 1 as a control electrode for controlling a current value flowing through the channel region 2 on the channel region 2 serving as a current path formed between the source region 3 and the drain region 4 and the drain region 6. The contacting gate electrode 7 is formed. In order to further protect the surface, the structure is covered with an insulating film 8 made of a nitride film formed by a plasma CVD method.

The insulating film 8 is formed, for example, at a substrate temperature of 200.
Monosilane, ammonia and argon diluted to 10% by volume with argon at 32 sccm and 51 sc, respectively.
cm, using a gas mixed at a rate of 110 sccm,
A high-frequency power of 1 Torr, 13.56 MHz, and 180 W was applied to form 1900 angstroms. This nitride film has almost no stress on the gallium arsenide substrate. The refractive index of this nitride film was 1.82.

In the MESFET having such a structure, the temperature of the channel layer rises during operation, the gate metal diffuses into the channel region, the actual channel area decreases, the pinch-off voltage decreases, and the source-drain current decreases. Fluctuates in the FET characteristics.

FIG. 3 shows an example of a change in FET characteristics. This shows the rate of change of the saturation current value (Idss) between the source and the drain when the gate voltage is 0 V measured at room temperature after leaving the MESFET at 300 ° C. in a nitrogen atmosphere for a predetermined time. As shown in the figure, when a case where a fluctuation exceeding 10% of the initial value occurs is regarded as a failure, the MES under this condition is considered.
The life of the FET was 5 hours. As the saturation current value between the source and drain decreases, FET characteristics such as pinch-off voltage and transconductance also change.

In order to prevent such fluctuations, a method using a heat-resistant gate metal has been proposed. However, materials capable of obtaining a high barrier height with respect to gallium arsenide are limited. There is a disadvantage that the manufacturing process becomes very complicated, such as formation.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and alleviates variations in FET characteristics such as a decrease in current between a source and a drain without changing a gate metal.
It is an object of the present invention to provide a method for manufacturing a field effect transistor having a long life.

[0009]

In order to achieve the above object, the present invention provides two ohmic electrodes formed on a surface of a semiconductor substrate at a distance from each other, a current path between the ohmic electrodes, and a current path between the ohmic electrodes. In a method for manufacturing a field-effect transistor including a control electrode that controls a value of a flowing current and an insulating film that covers the current path, an insulating film that generates a characteristic change to reduce a characteristic change during operation of the field-effect transistor, The present invention is characterized in that the current path is covered. In particular, the present invention is characterized in that the current path is covered with an insulating film for applying a stress to the semiconductor substrate to generate a current value variation that alleviates a variation in a current value flowing through the current path.

[0010]

Embodiments of the present invention will be described below. 1, a channel region 2, a source region 3, and a drain region 4 are formed in a gallium arsenide substrate 1 by ion implantation. Next, the channel region 2 is formed on the source electrode 5 and the drain electrode 6 in ohmic contact with the source region 3 and the drain region 4 and on the channel region 2 serving as a current path formed between the source region 3 and the drain region 4. A gate electrode 7 in Schottky contact with the gallium arsenide substrate 1 is formed as a control electrode for controlling a flowing current value. Further, the entire surface is covered with an insulating film 8 made of a nitride film formed by a plasma CVD method.

The insulating film 8 is made of monosilane, ammonia diluted to a volume ratio of 20% with nitrogen at a substrate temperature of 300.degree.
Nitrogen at 40 sccm, 9 sccm and 360 sc respectively
using a mixed gas at a pressure of 0.7 Torr
A high-frequency power of 13.56 MHz and 100 W was applied to form a film having a thickness of 2000 Å. This nitride film has a refractive index of 2.03, which is different from the properties of a conventional nitride film. Under such conditions, the insulating film 8 formed on the channel region 2 generates a tensile stress due to a difference in thermal expansion coefficient from that of gallium arsenide. Due to this stress, electric charges are generated in the gallium arsenide by a piezoelectric effect, and furthermore, the FET surface is exposed to plasma, thereby changing the FET characteristics.

When a gate electrode is formed on a gallium arsenide substrate whose main surface has a (100) crystal plane and extends in the <110> direction, and a nitride film is formed on the channel region by a plasma CVD method, It is known that the value of the current flowing through is reduced. Further, the characteristics of the once reduced current value fluctuate in a direction to alleviate the current decrease with time. That is, by coating the insulating film, the characteristics change in a direction in which the value of the current flowing through the channel region increases with time.

On the other hand, as described above, the gate electrode of the FET diffuses into the channel region and changes its characteristics in the direction in which the value of the current flowing through the channel region decreases.

By combining such contradictory characteristic fluctuations, the fluctuation of the current flowing through the channel region can be reduced as a result, and the life of the FET can be extended. FIG. 1 is a diagram showing the characteristic fluctuation of the FET of the present invention. Here, the rate of change of the saturation current value (Idss) between the source and the drain at a gate voltage of 0 V measured at room temperature after being left for a predetermined time in a nitrogen atmosphere at 300 ° C. is shown in the same manner as described above. As shown in the figure, when a case where a fluctuation exceeding 10% of the initial value occurs is regarded as a failure, this ME
The lifetime of the SFET is 80 hours, which is 16 times that of the conventional FET.

The case where the fluctuation of the current value caused by the gate electrode fluctuates in the decreasing direction with the operation of the FET and the fluctuation of the current value fluctuates in the increasing direction due to the relaxation of the stress of the insulating film will be described. However, depending on the crystal plane of gallium arsenide forming the FET and the direction in which the gate electrode is formed, the fluctuation of the current value may increase in some cases. In that case,
What is necessary is just to comprise so that the fluctuation | variation of the current value resulting from the relaxation of the stress of an insulating film may become the decreasing direction.

In order to change the current value due to the relaxation of the stress of the insulating film in either the increasing direction or the decreasing direction, it is possible to control by changing the conditions for forming the insulating film. For example, a case of a nitride film formed by a plasma CVD method as an insulating film is taken as an example. At a substrate temperature of 300 ° C., a gas obtained by mixing monosilane, ammonia, and nitrogen diluted with nitrogen at a volume ratio of 20% at a ratio of 40 sccm, 9 sccm, and 360 sccm, respectively, was used at a pressure of 0.7 Torr and a pressure of 0.7 Torr.
A high-frequency power of 00 W was applied to form a 2000-Å-thick nitride film. Unlike the formation conditions described above,
The frequency of the applied high frequency power is 400 KHz. The generated nitride film generates a compressive stress on gallium arsenide, and the fluctuation of the current value caused by the relaxation of the stress is in a decreasing direction. As described above, the frequency to be applied is set to 1
When the frequency is changed to 3.56 MHz, the generated nitride film generates a tensile stress for gallium arsenide, and the fluctuation of the current value caused by the relaxation of the stress increases. Thus, the direction of the fluctuation can be arbitrarily controlled. Also,
By changing the film thickness to be formed, gas composition, generation temperature, etc.,
The time constant of the fluctuation can also be changed. These are FET
The optimum condition may be appropriately selected according to the time constant of the characteristic variation.

The insulating film is formed by a plasma CV
The method is not limited to the method D, and may be a thermal CVD method or a sputtering method. Further, the insulating film is not limited to a single layer, and two or three types of a nitride film, an oxide film, and a silicon nitride film may be selected to form a multilayer structure.

[0018]

As described above, according to the present invention, F
When the characteristics fluctuate with the operation of the ET, in order to alleviate the fluctuation, by applying a stress that causes a contradictory fluctuation to the semiconductor substrate, the fluctuation of the FET characteristics can be substantially reduced, The life of the FET was greatly extended. The stress applied to the semiconductor substrate can be realized by a simple method by using an insulating film forming process used in a normal semiconductor device manufacturing process.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a MESFET.

FIG. 2 is a graph showing a characteristic variation of the MESFET of the present invention.

FIG. 3 is a graph showing a characteristic variation of a conventional MESFET.

[Explanation of symbols]

 Reference Signs List 1 gallium arsenide substrate 2 channel region 3 source region 4 drain region 5 source electrode 6 drain region 7 gate electrode 8 insulating film

Claims (2)

[Claims] 1. A semiconductor device, comprising: a semiconductor substrate;
Two ohmic electrodes, a current path between the ohmic electrodes,
In a method for manufacturing a field effect transistor including a control electrode for controlling a current value flowing through the current path and an insulating film covering the current path, a characteristic variation that alleviates a characteristic variation during operation of the field effect transistor is generated. A method for manufacturing a field effect transistor, wherein the current path is covered with an insulating film. 2. The method for manufacturing a field effect transistor according to claim 1, wherein the insulating film for applying a stress to the semiconductor substrate to generate a current value variation that alleviates a variation in a current value during operation of the field effect transistor, A method for manufacturing a field effect transistor, comprising covering a path.