JPH02268445A - Manufacture of field effect transistor - Google Patents

Abstract

PURPOSE:To reduce the series resistance by forming a shallow temporary recess, an insulating film, and ohmic electrodes, performing side etching, and etching a semiconductor base substance with the insulating film used as a mask to form a recess. CONSTITUTION:A photoresist film 3 is formed on a GaAs substrate 1, on which an active layer 2 is formed, and a window 3a is made. A shallower temporary recess 4 than a purposed recess is formed by wet etching through the window 3a. An oxide film 5 is formed, windows are made in ohmic electrode parts, and source and drain ohmic electrodes 6 are formed. A photoresist film 7 is applied, a window 7a is made, and then the film 5 is etched with the film 7 used as a mask. The substrate 1 is etched with the films 7 and 5 used as masks to form a recess 8. Gate metal 9 is adhered and the film 7 is removed to complete an FET. Thereby widening of the upper end of the recess is suppressed and the series resistance decreases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a ME'S field effect transistor having a recessed structure.

[Conventional technology]

Conventionally, as shown in FIG. 3, a method for manufacturing a field effect transistor of this type has been carried out using a Ga film with an active layer 2 formed thereon.
An insulating film 5 is selectively formed on an As substrate 1, and each of the source and drain ohmic electrodes 6 is formed using this insulating film 5. Further, the insulating film 5 is opened at the gate position, and the GaAs 1 plate 1 is etched using the photoresist film 7 selectively formed thereon as a mask to form a recess (concave portion) 8A.
A gate electrode 9 is formed on the bottom surface of the recess 8A by a lift-off method using this photoresist film 7.

[Problems to be Solved by the Invention] In the conventional manufacturing method described above, when opening the insulating film 5 when forming a recess, it is necessary to side-etch the insulating film 5 to some extent in order to prevent problems such as a decrease in breakdown voltage. is being carried out. For this reason, when the recess becomes deep,
The width increases at the top of the recess.

Therefore, in order to reduce the series resistance in MESFET, the ohmink electrode 6 and gate electrode 9 on the source side are
If the distance between the recess 8A and the ohmic electrode 6 is designed to be small, the recess 8A may interfere with the ohmic electrode 6 on the source side.

For this reason, conventionally it is necessary to design the distance between the ohmic electrode and the gate electrode to some extent, which is an obstacle to lowering the resistance of the MESFET.

An object of the present invention is to provide a method for manufacturing a MESFET that can reduce series resistance and obtain sufficient breakdown voltage.

[Means to solve the problem]

In the MESFET manufacturing method of the present invention, a temporary recess shallower than the original recess is first selectively formed in the semiconductor substrate, an insulating film is formed, an ohmic electrode is formed, and this insulating film is temporarily recessed. This process includes the steps of performing side etching on the recess, and using this insulating film as a mask, etching the semiconductor substrate to a predetermined depth to form the original recess.

[Effect]

With this manufacturing method, the amount of side etching when forming the original recess from the temporary recess is extremely small. The resistance is reduced.At the same time, the distance between the gate and the recess edge can be determined by the position of the temporary recess, making it possible to arbitrarily control the gate breakdown voltage.

(Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of a MESFET manufactured by the method of the present invention, and the manufacturing method is shown in the order of steps in FIGS. 2(a) to (C').

First, as shown in FIG. 2(a), G
A photoresist film 3 is formed on the aAs substrate 1 and patterned to form a window 3a. and,
A temporary recess 4 is formed by wet etching the GaAs substrate 1 through this window 3a. At this time, the temporary recess 4 is formed to be shallower (for example, 1500 depths) than the original recess depth (2000 depths).

Next, as shown in FIG. 2(b), an oxide film 5 is formed on the entire surface by CVD or the like, and a window is formed at the ohmic electrode portion. Then, ohmic metal is deposited on this oxide film 5 and selectively removed to form source and drain ohmic electrodes 6. Subsequently, a photoresist film 7 is applied to the entire surface, and a window 7a is opened above the temporary recess 4 at the location where the gate electrode is to be formed. Then, using this photoresist film 7 as a mask, the oxide film 5 is etched using, for example, buffered hydrofluoric acid.

At this time, the oxide film 5 is side-etched toward the outside of the window 7a of the photoresist film 7.

Next, as shown in FIG. 2(C), the photoresist film 7
Then, using the oxide film 5 as a mask, the GaAs substrate 1 is etched to form a recess 8 of the original depth. At this time, since the amount of etching of the recess 8 is small, the amount of side etching on the lower side of the oxide film 5 is extremely small.

Then, by depositing the gate metal 9 on the entire surface and then removing the photoresist film 7, as shown in FIG.
A gate electrode 9 is formed on the bottom surface of the recess 8 by a so-called lift-off method.
is formed to complete the MESFET.

Therefore, in this manufacturing method, after first forming the temporary recess 4, the ohmic electrode 6 is placed outside the temporary recess 4.
, and then the original recess 8 is formed by very slight side etching, so even if the distance between the recess 8 and the ohmic electrode 6 is reduced, the recess 8 and the ohmic electrode 6 do not interfere with each other. M.E.
SFET can be formed. As a result, the ohmic electrode 6
It becomes possible to design the distance between the recess 8 and the recess 8, and a MESFET with reduced series resistance on the source side can be constructed.

Furthermore, since there is extremely little side etching when forming the original recess 8 from the state of the temporary recess 4, the recess gate end can be determined by the bottom surface position of the temporary recess 4, and the gate withstand voltage can be controlled arbitrarily. . Therefore, it is possible to easily increase the gate breakdown voltage.

[Effects of the Invention] As explained above, the present invention first selectively forms a shallow temporary recess, then forms an ohmic electrode, and then uses the insulating film formed on the temporary recess as a mask to perform the original process. Since the recess is formed by etching, the amount of side etching is reduced when forming the actual recess from the temporary recess, suppressing the upper end of the recess from spreading laterally, and reducing the distance between the gate electrode and the ohmic electrode. MESFETs with reduced series resistance can be manufactured.

In addition, by suppressing the side etching, the end of the original recess can be made to approximately coincide with the end of the temporary recess, which allows the distance between the gate and the recess end to be determined by the position of the temporary recess, and the gate withstand voltage can be adjusted arbitrarily. MESF controlled by
There is also the effect that ET can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a MESFET manufactured by the method of the present invention,
2(a) to 2(C) are cross-sectional views showing the manufacturing method of the MESFET shown in FIG. 1 in the order of steps, and FIG. 3 is a cross-sectional view showing a part of the steps of the conventional manufacturing method. DESCRIPTION OF SYMBOLS 1... GaAs substrate, 2... Active layer, 3... Photoresist film, 4... Temporary recess, 5... Oxide film, 6
... Ohmic electrode, 7... Photoresist film, 8
, 8A... Recess, 9... Gate electrode. Funeral map Figure 2 Figure 3

Claims (1)

[Claims] 1. A step of selectively forming a temporary recess shallower than the original recess in the semiconductor substrate on which the active layer has been formed, and forming an insulating film on the entire surface and using this insulating film to form an ohmic electrode on the outside of the temporary recess. a step of forming a photoresist film on the insulating film and opening a window in the photoresist film at a location where the gate electrode is to be formed; and a step of side etching the insulating film through the window of the photoresist film. Then, using this insulating film as a mask, the semiconductor substrate is etched to a predetermined depth to form the original recess, and a gate electrode is deposited on the entire surface, and a lift-off method using the photoresist film is used to etch the semiconductor substrate to a predetermined depth. A method for manufacturing a field effect transistor, comprising the step of selectively forming a gate electrode on the bottom of the recess.