JPH0328061B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used for high frequency equipment in the GHz band.
It is related to the manufacturing method of MESFET, and in particular, it is necessary to prevent short circuits between electrodes due to the metal layer forming the source or drain extraction electrodes.
Involved in the manufacturing method of MESFET. The word MESFET used in this specification is
It is an abbreviation for Metal/Semiconductor field effect transistor and has the same meaning as shotgun barrier gate field effect transistor.

GaAsFET, a typical element of MESFET,
As shown in FIG. 3, an n-type active layer 31 is epitaxially grown on a semi-insulating GaAs substrate 30, and a shallow groove 32 is dug by selectively etching its surface. A gate electrode 33 is formed on the bottom as a channel region, and a source electrode 34 and a drain electrode 35 are formed on plateaus on both sides of the trench. Although a buffer layer may be formed between the semi-insulating GaAs substrate and the n-type active layer, it is omitted in FIG.

In an actual device, as shown in FIG. 4, the gate electrode 43 has a comb tooth axis pattern, and source electrodes and drain electrodes are alternately arranged with the tooth portions in between. The drain electrodes are connected to each other by lead electrodes 44 and 45.

The gate electrode is usually made of Al, and the source/drain electrodes are made of a stack of Au-Ge alloy and Au.

[Conventional technology]

The extraction electrode is formed in the following steps (see FIG. 2 below).

As the cross-sectional shape is shown in figure a, the semi-insulating
An n-type active layer 21 is epitaxially grown on a GaAs substrate 20, and a gate electrode 23, a source electrode 2
4. After forming the drain electrode 25, plasma
Deposit SIN _x 26 by CVD method and open windows on the source and drain electrodes.

Next, as shown in Figure b, a metal film 27 is formed by vapor deposition. This metal film is actually 3000Å from the bottom.
The film has a three-layer structure consisting of 1500Å of Ti, 1500Å of Pt, and 500Å of Au.

By patterning this, a source lead-out electrode 44 and a drain lead-out electrode 45 are formed as shown in FIG.

[Problem that the invention seeks to solve]

When an extraction electrode is formed in the above process, a residual portion is generated in the metal film as shown as 29 in FIG. 2c. This means that a gate electrode with a height of, for example, 7,000 Å is formed in a trench with a depth of 2,000 Å, and source and drain electrodes are formed on the plateau on both sides, with a distance of about 1 μm from the gate electrode. As a result, deep depressions occur in the SiN _x layer, which occurs because the metal film cannot be completely etched during patterning.

If this remaining portion of the metal film is generated along the gate electrode, there is usually a point where the gate electrode and the source lead-out electrode intersect, as shown in FIG. 4, so that the two will be short-circuited at that point.

The present invention provides a method for forming an extraction electrode in which such a short circuit does not occur.

[Means for solving problems]

In the present invention, before the metal film deposition step, the region including the deep depressions is covered with a photoresist layer to fill the depressions, and then the metal film is deposited by means such as vapor deposition to eliminate unnecessary By removing the photoresist, the occurrence of the residual portion is eliminated.

[Effect]

As described above, since the depressions are filled with photoresist and the metal film is deposited, there are no parts that cannot be etched completely, and complete patterning is achieved. Further, since the metal film is formed by vapor deposition, the temperature rise on the substrate surface is slight, and no inconvenience due to decomposition of the photoresist occurs.

In addition to photoresist, it is possible to use a resin such as polyimide, in which case it is possible to produce a similar effect by patterning the polyimide.

〔Example〕

FIG. 1 is a sectional view showing an embodiment of the process of the present invention (see FIG. 1 below).

Figure a shows a gate electrode 1 formed on a substrate 11 in a normal process.
3. The source/drain electrodes 14 and 15 and the SiN _x layer 16 are formed, and a window is opened in the SiN _x layer using the photoresist 16 as a mask.

In this embodiment, a metal film 17 is deposited, leaving the photoresist layer as shown in Figure b. Next, the metal film is patterned to form extraction electrodes 44 and 45. The photoresist layer is removed with a resist stripping solution, and a MESFET with no remaining metal film is formed as shown in Figure c.

In the above embodiment, the photoresist for opening the window was used, but the photoresist may be removed once and then reapplied mainly to the recessed area around the gate electrode.

As mentioned above, it is possible to use a resin such as polyimide in addition to the photoresist, and the embodiments when using the resin are almost the same as those when using the photoresist.

〔Effect of the invention〕

According to the process of the present invention, when forming the extraction electrode of the source/drain electrode, no metal film remains in the vicinity of the gate electrode, and no short circuit between the source/drain and the gate occurs.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the steps of an embodiment of the present invention;
FIG. 2 is a sectional view showing a conventional process, and FIGS. 3 and 4 are a sectional view and a plan view showing the electrode structure of a MESFET. In the figure, 10, 20, and 30 are semi-insulating
GaAs substrate, 11, 21, 31 are n-type active layers,
13, 23, 33, 43 are gate electrodes, 14, 2
4, 34 are source electrodes, 15, 25, 35 are drain electrodes, 16, 26 are SiN _x layers, 17, 27 are metal coatings, 18 is photoresist, 29 is a remaining portion of the metal coating, 32 is a shallow groove, 44 45 is a source lead electrode, 45 is a drain lead electrode, and 46 is a gate bonding pad.

Claims (1)

[Claims] 1. A step of forming a groove on the surface of a semiconductor substrate, forming a gate electrode in the groove, and forming a source electrode and a drain electrode with the gate electrode sandwiched therebetween; the gate electrode and the source electrode; a step of covering the drain electrode with an insulating material layer; a step of depositing a resin layer on the resin layer so as to fill the recesses formed on the surface of the insulating material layer; and a step of covering the insulating material layer and the resin layer. selectively opening a window to expose the surfaces of the source and drain electrodes; depositing a metal film on the semiconductor substrate covered with the resin layer or the insulating material layer; and patterning the metal film. A method for manufacturing a MESFET, comprising the steps of: forming source and drain extraction electrodes, and then removing the resin layer.