JP3035994B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a compound semiconductor device for high frequency amplification provided with a MESFET.

[Conventional technology]

Generally, in this type of semiconductor device, after forming an active layer on a compound semiconductor substrate, a recess is formed in this active layer.
Further, a configuration is adopted in which a gate electrode is provided in this recess. In this case, in order to reduce the source resistance, the gate electrode often has a so-called offset structure that is biased toward the source.

Conventionally, in this type of semiconductor device manufacturing method, a recess is formed in a semiconductor substrate by a wet etching method using a mask formed on the semiconductor substrate, and then a gate metal such as aluminum is obliquely deposited using the same mask. Then, a method of offset forming the gate electrode in the recess is adopted. For example, IEICE ED, 88
-16.

Conventionally, in a method of manufacturing a semiconductor device of this type, a manufacturing method has been proposed in which a gate electrode is formed in an offset structure and the gate electrode has a mushroom structure to reduce the resistance of the gate electrode. For example, IEICE ED89-54.

This method is shown in FIGS. 3 (a) to 3 (e). First, as shown in FIG. 3A, ohmic electrodes as a source electrode 14 and a drain electrode 15 are formed on a semiconductor substrate 11 on which an active layer 12 is formed, and a silicon for forming an offset recess gate is formed in an intermediate portion thereof. Oxide film 13 is patterned to a required width.

Next, as shown in FIG. 3 (b), the entire surface is covered with a silicon nitride film 16, and a window 16a is opened in a part of the silicon nitride film 16 on the source electrode side.

Then, as shown in FIG. 3C, the silicon oxide film 13 is etched through the window 16a of the silicon nitride film 16. Subsequently, as shown in FIG. 3D, the window 16 of the silicon nitride film 16 is formed.
The semiconductor substrate 11 is etched through a to form a recess 17.

Then, a gate metal is formed on the entire surface as shown in FIG.
Gate electrode with a T-shaped (mushroom-shaped) cross-section by selective etching leaving the region containing 16a
18 can be formed in an offset structure.

[Problems to be solved by the invention]

In the conventional manufacturing method described above, the gate electrode cannot be formed in a mushroom structure in the former method, so that it is difficult to reduce the gate resistance and cannot be used in a semiconductor device that requires high-speed operation. There is a problem.

In the latter method, it is difficult to form the silicon oxide film 13 for forming the offset recess gate with good reproducibility, and it is difficult to form the recess with high accuracy.
Also, since the window 16a formed in the silicon nitride film 16 must be opened near the step on the source side, it becomes difficult to handle the photolithography technology used for this.
Unable to control window dimensions and position with high accuracy,
There is a problem that it is difficult to form the offset position of the gate electrode with high accuracy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a semiconductor device in which a recess can be formed with high precision and a low-resistance and high-precision offset gate electrode can be formed with high precision.

[Means for solving the problem]

The method of manufacturing a semiconductor device according to the present invention includes a step of forming an oxide film on a compound semiconductor substrate, a step of forming a photoresist film on the oxide film and opening a window in the photoresist film, Etching the oxide film through a film window to a wider state than the window;
Etching the semiconductor substrate through the window of the oxide film to form a recess wider than the window of the oxide film; and depositing metal from an oblique direction on the drain side with respect to the window of the photoresist film. Forming a gate electrode at a position on the source side of the recess.

In this case, the window of the photoresist film is composed of an upper window having a large width and a lower window having a small width provided at the bottom of the upper window, and a gate is formed on the bottom of the upper window including the lower window. A metal is deposited to form a gate electrode having a mushroom structure.

The upper window preferably has a tapered cross section, and the lower window preferably has an inverted tapered cross section.

[Action]

According to the method of the present invention, since a gate electrode is formed using a window in a photoresist film, a gate electrode having a mushroom structure biased toward the source side can be manufactured with high precision by opening the window with high precision. Becomes possible.

〔Example〕

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

1 (a) to 1 (d) are cross-sectional views showing a first embodiment of the present invention in the order of manufacturing steps.
An example applied to an SFET is shown.

First, as shown in FIG. 1A, an active layer 2 is formed on a GaAs substrate 1.
Is formed, an oxide film 3 is formed on the surface, and ohmic electrodes of a source electrode 4 and a drain electrode 5 are formed through windows (not shown) provided in required regions of the oxide film 3, respectively. Then, a photoresist film 6 is applied to the entire surface, and a window 7 is opened in the photoresist film 6.

At this time, the window 7 of the photoresist film 6 is formed so as to be constituted by an upper window 7a having a large width and a lower window 7b formed on the bottom surface of the upper window 7a having a small width. In this case, in the illustrated example, the upper window 7a has a tapered cross section,
Although the lower window 7b has a reverse tapered cross-sectional shape, these may be formed as windows of a vertical wall.

Next, as shown in FIG. 1 (b), the oxide film 3 is wet-etched through the window 7 of the photoresist film 6 to form a window 3a, and the GaAs substrate 1 is wet-etched through the window 3a. Recess 8 in active layer 2 of GaAs substrate 1
To form

Thereafter, as shown in FIG. 1C, aluminum 9 is deposited on the entire surface of the photoresist film 6 through the window 7. At this time, oblique deposition is performed so that aluminum 9 is deposited obliquely toward the source side. As a result, aluminum is vapor-deposited in the upper window 7 of the photoresist film 6 at a position shifted toward the source, and an aluminum gate electrode 9A is formed at a position shifted toward the source of the recess 8 through the lower window 7b.

Thereafter, as shown in FIG.
By removing the MESFET, a MESFET having a mushroom shape and having the gate electrode 9A formed at a position deviated toward the source in the recess 8 is formed.

Therefore, in this manufacturing method, the photoresist film 6
The recess 8 and the gate electrode 9A are formed in accordance with the window 7 formed in the step 7, and the size and position accuracy of the recess 8 and the gate electrode 9A are controlled by the size and position accuracy of the window 7. Since the window 7 can be opened with high precision by patterning on the flat surface of the photoresist film 6, the recess 8 and the gate electrode 9A can be formed with high precision.

It goes without saying that the gate resistance is reduced by the gate electrode 9A having a mushroom shape.

2 (a) to 2 (d) are sectional views showing a second embodiment of the present invention in the order of manufacturing steps. Here, the present invention is applied to HJFET
The same reference numerals are given to the same or equivalent parts as those in the first embodiment.

In this manufacturing method, as shown in FIG. 2 (a), n as an active layer on the GaAs substrate 1 ^- to form a AlGaAs layer 2A and the n ⁺ GaAs layer 2B,
Then, the recess 8 and the gate electrode 9A are formed in the steps shown in FIGS. 2 (b) to 2 (d). This step is exactly the same as in the first embodiment.

By this manufacturing method, a good mushroom gate can be formed, and an HJFET with reduced gate resistance can be formed.

[Effect of the Invention] As described above, the present invention provides a photoresist film
An upper window having a large width and a lower window having a small width provided at the bottom of the upper window are opened, and a gate metal is deposited on these windows from an oblique direction on the drain side to form a gate electrode. Therefore, since it is easy to open a window with high precision with respect to a flat photoresist film, a gate electrode with a low gate resistance biased toward the source side can be manufactured with high precision.

In the present invention, the window provided in the oxide film is formed to be wider than the window of the photoresist film, and the recess is formed to be wider than the window of the oxide film. On the other hand, the width of the recess can be made sufficiently large, and the gate electrode formed through the window of the photoresist film is not formed on the end or side of the recess, preventing the characteristics of the semiconductor device from deteriorating. I do.

[Brief description of the drawings]

1 (a) to 1 (d) are cross-sectional views showing a first embodiment of the present invention in the order of manufacturing steps, and FIGS. 2 (a) to 2 (d) are cross-sectional views showing a second embodiment of the present invention in the order of manufacturing steps. FIGS. 3A to 3E are cross-sectional views showing an example of a conventional manufacturing method in the order of steps. 1 ... GaAs substrate, 2 ... Active layer, 2A ... n ^- AlGaAs layer, 2B
... n ⁺ GaAs layer, 3 ... oxide film, 4 ... source electrode, 5 ...
... Drain electrode, 6 ... Photoresist film, 7 ... Window,
8 ... recess, 9 ... aluminum, 9A ... gate electrode, 11 ... semiconductor substrate, 12 ... active layer, 13 ... silicon oxide film, 14 ... source electrode, 15 ... drain electrode, 16 ...
... silicon nitride film, 17 ... recess, 18 ... gate electrode.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/338 H01L 21/28 H01L 29/812

Claims (1)

(57) [Claims] A step of forming an oxide film on a semiconductor substrate;
Forming a photoresist film on the oxide film and opening a window in the photoresist film; etching the oxide film through a window of the photoresist film to a wider state than the window; Etching a semiconductor substrate through a film window to form a recess wider than the oxide film window; and depositing a metal from an oblique direction on the drain side with respect to the photoresist film window to form the recess. Forming a gate electrode at a position on the source side, wherein the window of the photoresist film is larger than a top window having a tapered tapered cross section with a large width dimension, and a bottom provided at the bottom of the top window. A lower window having a small width dimension, and forming a gate electrode having a mushroom structure by depositing a gate metal on the bottom of the upper window including the lower window. The method of manufacturing a semiconductor device according to symptoms.