JPS5914905B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for manufacturing a Schottky gate field effect transistor (hereinafter referred to as MESFET).
The purpose of this invention is to automatically determine the pinch-off voltage value of the semiconductor substrate without knowing the initial thickness and impurity concentration of the semiconductor substrate.

Conventionally, in the case of compound semiconductor devices made of gallium arsenide or the like, thickness control is extremely important when epitaxially growing an n-type active layer as a semiconductor layer on a semi-insulating gallium arsenide substrate as a semiconductor substrate. For example, in a MESFET using a gallium arsenide substrate, in order to obtain a predetermined pinch off voltage, the thickness of the n-type active layer is kept within an accuracy of about ±0.02 μm for a thickness of 0.25 μm. There is a need.

Such precise thickness control is nearly impossible, even by making full use of chemical etching techniques, as well as epitaxial growth techniques that are commonly used in the past. As one method to solve this problem, an anodic oxidation method in an electrolyte has been developed.

This involves growing an oxide film with relatively high thickness accuracy by controlling current or voltage, and then removing this oxide film.
This method attempts to control the thickness of the active layer. However, even with this method, the thickness of the active layer that is initially formed must be formed uniformly and precisely over all regions, and it is necessary to form the active layer with uniform thickness over all such regions. It is not easy to form ■0. The present invention solves these problems, and uses the principle of light irradiation anodic oxidation that the present applicant generally proposed in Japanese Patent Application No. 75104/1983 to determine the initial thickness and concentration of the active layer. Pinch of the MESFET formed on the remaining active layer regardless of the
The purpose is to control the off-voltage to a predetermined value.

The details of the present invention will be described below based on embodiments and with reference to the drawings.

When an n-type 30 gallium arsenide layer formed on a semi-insulating gallium arsenide substrate is anodized, a depletion layer is formed in the n-type gallium arsenide layer by the junction between the oxide film and the n-type gallium arsenide.

The voltage VD generated across this depletion layer depends on the amount of irradiation light and the oxidation current. Now, if anodic oxidation is performed under light irradiation with a constant current and a constant amount of light, the oxidation will proceed until the edge of the depletion layer reaches the semi-insulating gallium arsenide substrate, and then the current will stop flowing and the oxidation will automatically stop. do. That is, remaining 11
The thickness of the gallium arsenide layer to be cooled is equal to the thickness of the depletion layer.

Therefore, at this time, the thickness of the remaining n-type gallium arsenide layer corresponds to VD. Thereafter, when this oxide film is removed to form a shot-off junction, the pitch-off voltage V in this case is given by the following equation. p=VD-Vbi However, Vbi is a constant determined by the contact potential of the formed shot key junction.

Therefore, by controlling VD, the pinch-off voltage V, of the MESFET can be controlled.

By the way, this VD can be arbitrarily changed depending on the oxidation current density and the amount of irradiation light. Now, - constant current density (j
FIG. 1 shows the relationship between the irradiation light amount φ and VD at 1 mA/Cd).

From the same figure, φ. It can be seen that if the above amount of light is irradiated, VD=0. However, since the thickness of the depletion layer is influenced by the carrier concentration of the n-type gallium arsenide layer,
This will also affect VD. By the way, the anodic oxidation voltage Vc is Vc(t
)::VD+d-T Since d has a constant relationship determined by the oxidation current density, the amount of irradiation light is φ.

From the difference between the oxidation voltage when the irradiation voltage is set above and the oxidation voltage when the irradiation light amount is lower than that, VD can be easily determined regardless of the concentration of the n-type gallium arsenide layer. This state is shown in FIG. In this way, when VD is at a predetermined value during anodization,
Light amount φ1 such that VDl, that is, Vp becomes a predetermined value
After the oxidation has stopped, the oxide film is removed, and this n-type active layer is used to form a MESFE.
By fabricating T, a MESFET with a constant pinch-off voltage can be obtained regardless of the initial active layer thickness and concentration.

Specific examples of the present invention will be described below.

As shown in FIG. 3, an ohmic electrode 32 is formed at the end of a gallium arsenide substrate 31 having an n-type epitaxial layer and connected to the positive electrode of a constant current power source 35. As shown in FIG. However, the ohmic electrode 32 is electrically insulated from the electrolyte 34. On the other hand, a platinum plate 33 is used as a cathode, and a current with a current density of 1 mA/d is passed between the two to perform anodic oxidation. The composition of the electrolytic solution used in this example was a mixed solution of 3 f tartaric acid, 100 d water, 200 r1 propylene glycol, and aqueous ammonia for hydrogen ion concentration control (PH 6.0). First, the gallium arsenide substrate 31 is irradiated with strong light 37 of 10,000 tX or more to perform anodic oxidation.

At this time, the anodic oxidation voltage Vc recorded on the chart recorder 36 increases linearly with time as shown at A in FIG. Next, the light intensity of the mixed light 37 is reduced, and the light intensity is adjusted so that the anodic oxidation voltage Vc becomes a straight line B, which is increased by the desired pinch-off voltage from the straight line A shown in FIG. Let's do it.

By detecting a sudden rise in the anodic oxidation voltage Vc on the chart recorder 36, stopping the oxidation, and removing the oxide film with dilute hydrochloric acid, a gallium arsenide epitaxial layer capable of manufacturing a MESFET having a desired pinch-off voltage is obtained. be able to.

Figure 5 shows the relationship between the set value VD during anodic oxidation and the pinch-off voltage of a MESFET manufactured using Cr/Pt/Au as a gate. Based on this relationship, the line A to B in Figure 4 is By controlling the change D in the anodic oxidation voltage Vc, a desired pinch-off voltage Vp can be obtained. As described above, the present invention is capable of anodizing a semiconductor layer formed on a semiconductor substrate using a constant DC current and light irradiation.
The pinch-off voltage of a field effect transistor to be formed later can be determined from the change in oxidation voltage, and a field effect transistor whose value is extremely uniform can be obtained.

Therefore, the present invention has extremely great industrial value, such as uniformity of performance and improvement of yield.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between irradiation light amount and depletion layer voltage, FIG. 2 is a diagram showing changes in anodic oxidation voltage over oxidation time, FIG. 3 is a diagram for explaining one embodiment of the present invention, and FIG. The figure shows the change in anodization voltage recorded on the chart recorder, and Figure 5 shows the set value of the depletion layer voltage according to the present invention and the measured value of the pinch-off voltage of the manufactured gallium arsenide shot gate field effect transistor. FIG. 31... Gallium arsenide substrate having an epitaxial layer, 32... Ohmic contact, 33
...Bakukin cathode, 34... Electrolyte, 35.
... Constant current power supply, 36 ... Chart recorder, 37 ... White light from tungsten lamp.

Claims (1)

[Claims] 1 Manufacturing a semiconductor device in which the semiconductor layer formed on a semiconductor substrate is oxidized by passing a predetermined current in an electrolytic solution and irradiating the semiconductor layer with light to leave the semiconductor layer with a desired thickness. In the method, the pinch-off voltage is determined by an increase in anodizing voltage when the amount of light irradiation is changed from an amount that does not form a depletion layer in the semiconductor layer to an amount that forms a predetermined depletion layer in the semiconductor layer. 1. A method for manufacturing a semiconductor device, the method comprising: determining .