JPH0563003A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form a cavity (hollow region) within a recess in a field effect transistor having a recessed structure in order to eliminate a disadvantage that if the recess is filled with a passivation film, the capacitance between a gate and a drain increases, lowering a power gain. CONSTITUTION:A silicon oxide film 2 and a silicon nitride film 3 as a spacer are deposited on an n type active layer 1, these films are patterned with a photoresist 10, thereafter a recess 5 is opened by dry etching and wet etching (process A), the recess is formed and after formation of a gate (process B), a cavity 9 is formed within the recess 5 (process C). Thereby, power gain in the high frequency characteristic can be improved without increasing a capacitance value between the gate and drain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device according to a method of forming a gate portion of a field effect transistor having a recess structure.

[0002]

2. Description of the Related Art A conventional method for forming a gate portion of a recess structure type will be described with reference to FIG. FIG. 3 shows a conventional example
It is a sectional view of the toe part, which is manufactured by the following method. First, a silicon oxide film 2 serving as a spacer is deposited on the n-type active layer 1, and then a photoresist is applied, and a portion where a gate is to be formed is patterned by exposure and development. Next, the silicon oxide film 2 is etched using the photoresist as a mask to open the gate portion. At this time, the silicon oxide film 2 is also etched in the horizontal direction by wet etching or the like. This size has a wide recess width. If the recess width is small and the gate-source or drain-narrow becomes narrow, the gate breakdown voltage becomes low, and it cannot be used due to its characteristics.

After the recess width is determined by wet etching, the recess is formed by monitoring the current between the source and the drain. Next, the gate metal (Ti-A
l) is vapor-deposited and lift-off is performed with an organic solvent to form a Ti-Al gate 6 in the recess. After that, passivate
Silicon oxide film 7 and silicon nitride film 8
To form a gate portion of the recess structure type shown in FIG.

[0004]

In this conventional gate forming method, in the subsequent deposition of the passivation film by the silicon oxide film 7 or the silicon nitride film 8, the gate-drain or the recess in the recess is formed. The space between the sources is tightly filled with a passivation film. This has a drawback that it increases the gate-drain capacitance and lowers the gain which is a high frequency characteristic. Further, reducing the thickness of the passivation film in order to suppress the problem reduces the capacitance, but has a problem that the reliability of the device is reduced.

Therefore, the present invention provides a field effect transistor having a recess structure for solving the above-mentioned drawbacks and problems.
It is an object of the present invention to provide a method for manufacturing a semiconductor device according to a method for forming a gate portion, and more specifically, the semiconductor device capable of improving power gain in high frequency characteristics without increasing a gate-drain capacitance. It aims at providing the manufacturing method of.

[0006]

The present invention is characterized in that a hollow region is formed in the recess to provide a cavity, whereby high frequency characteristics can be achieved without increasing the gate-drain capacitance. The power gain in is improved.

That is, according to the present invention, a silicon oxide film serving as a gate lift-off spacer is deposited on the n-type active layer, and a silicon nitride film is deposited thereon to be thinner than the silicon oxide film. Patterning on the gate formation area by means of dry etching, the nitride film is removed by dry etching, then the nitride film is hardly etched by wet etching, and only the oxide film is removed up to the substrate. To form a void below the nitride film, then form a recess, deposit a gate metal, lift off with a resist to form a gate, and block the nitride film and the gate.
A method of manufacturing a semiconductor device is characterized in that a passivation film is deposited so that a recess is hollow.

The present invention will be described in detail below. In a field effect transistor having a recess structure, if the inside of the recess is filled with a passivation film, the gate-drain capacitance increases, leading to a decrease in power gain.The present invention solves this drawback. A cavity (hollow region) is formed in the recess. Then, it is usual to use only an oxide film as the recess spacer, but in the present invention, a nitride film whose etch rate is considerably slower than wet etching is further deposited on the oxide film, and the nitride film is formed in the recess. To create a roof, which creates a hollow area in the recess for subsequent passivation film deposition.
Since only a thin film is attached to the inside of the recess and the gap between the nitride film and the gate is closed, the hollow region can be maintained.

The gate portion forming means in the present invention will be described. First, a gate lift-off space is formed on the n-type active layer.
A silicon oxide film serving as a support is deposited. Next, a silicon nitride film is deposited on the oxide film to be thinner than the oxide film, and a photoresist is used to pattern the gate forming portion. After that, the nitride film is removed by dry etching, and then the oxide film is removed and side etching is performed by wet etching. At this time, since the nitride film is hardly etched by wet etching, the nitride film remains in the same pattern as the resist, but the oxide film can be arbitrarily determined to have the same size as the recess length. Then, a recess is formed, a gate metal is vapor-deposited, and a resist is lifted off to form a gate. After that, a passivation film is applied. At this time, since a nitride film roof is formed in the recess, the space between the gate and the gate is blocked and a cavity (hollow region) is formed in the recess.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail with reference to FIGS. (Embodiment 1) FIG. 1 shows a process (A) showing an embodiment of the present invention.
~ C) is a cross-sectional view of the gate portion in this order, in which the step A is
It is a process drawing on the way to forming a cavity in the recess,
A silicon oxide film 2 and a silicon nitride film 3 serving as a spacer are deposited on the n-type active layer 1 and patterned with a photoresist 10.
FIG. 6 is a diagram showing that the recess 5 is opened by dry etching and wet etching after the etching. Also, process B
FIG. 8 is a view after forming a recess and then forming a gate following step A, and step C is a cross-sectional view of the gate portion of the present invention in which a cavity 9 is formed in the recess 5. ..

To further explain these steps A to C, a silicon oxide film 2 of about 1500 angstrom is deposited on the n-type active layer 1 by LPCVD, and then a silicon nitride film 3 of 500 angstrom is formed by plasma CVD. Put on. Next, using the photolithography technique, the gate opening planned portion 4 is formed.
Then, the silicon nitride film 3 is first etched by dry etching, and then wet etching is performed by using 1: 6 buffered hydrofluoric acid to side etch only the silicon oxide film 3 (step A ).

After that, sulfuric acid: hydrogen peroxide: water = 1: 8: 60
Active layer 1 while monitoring current with 0 etchant
Is etched to form a recess 5 with a depth of about 1000 angstrom. After that, titanium (T
i) 500 angstrom and aluminum (Al) 3000 angstrom are vapor-deposited and lifted off with an organic solvent.
-Al gate 6 is formed (step B). Next, LPCVD oxide film (1000 angstrom) 7, plasma CVD nitride film (1800
(Angstrom + 2000 angstrom) 8 is deposited to form a cavity 9 in the recess 5 (step C).

(Embodiment 2) FIG. 2 is a sectional view of a mashroom type gate portion which is another embodiment of the present invention. This type of gate is of a mashroom type in order to reduce the gate resistance. Therefore, structurally, the space between the eaves and the gate electrode is filled with passivation. As a result, the capacity is increased more than in the first embodiment, which is disadvantageous to the power gain. In the case of this mashroom type, the gate forming means is the same as that of the first embodiment, and a double spacer of the oxide film 2 and the nitride film 3 is formed to form the mashroom gate 11. By forming a cavity 9 in the recess by the nitride film, it is possible to suppress an increase in capacitance and improve power gain.

[0014]

As described above, according to the present invention, a cavity is formed in the recess between the gate and the source or between the drains. Therefore, the thickness of the passivation film is increased. Regardless of this, there is an effect that the power gain in the high frequency characteristics can be improved without increasing the gate-drain capacitance.

[Brief description of drawings]

FIG. 1 is a sectional view of a gate portion in the order of steps showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a mashroom type gate according to another embodiment of the present invention.

FIG. 3 is a sectional view of a gate portion of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 n-type active layer 2 silicon oxide film 3 silicon nitride film 4 planned gate formation part 5 recess 6 Ti-Al gate 7 silicon oxide film 8 silicon nitride film 9 cavities 10 photoresist 11 mashroom gate

Claims (2)

[Claims] 1. A gate oxide film is deposited on the n-type active layer to serve as a gate lift-off spacer, and a silicon nitride film is deposited thereon to be thinner than the oxide film. After the patterning, the nitride film is removed by dry etching, then the nitride film is hardly etched by wet etching, and only the oxide film is removed up to the substrate. A void is formed in the hole, then a recess is formed and a gate metal is vapor-deposited.
A method for manufacturing a semiconductor device, characterized in that a gate is formed by performing lift-off with a resist, and a passivation film is deposited so that the nitride film and the gate are closed and the recess is hollow. .. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the gate is a mashroom type gate.