JPH0472381B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of the Invention The present invention relates to a field effect semiconductor device, and particularly to a method for manufacturing a shot gate field effect transistor (SBFET) made of a gallium arsenide (GaAs) compound semiconductor.

(2) Technical background GaAs shot gate field effect transistors have excellent high frequency characteristics and can achieve high output.
Research and development is progressing and it is being put into practical use. In particular, various structures and manufacturing methods have been proposed to improve the performance (higher frequency, higher output, higher efficiency) and reliability of this field effect transistor. In order to improve performance, it is important to shorten the gate length and reduce parasitic resistances such as source-gate resistance (source series resistance R _s ) and gate resistance (R _g ).

(3) Prior art and problems A recessed structure in the gate electrode has been proposed as a method for improving the performance of GaAs shot gate field effect transistors. As shown in FIG. 1, the recess 4 is formed by selectively etching the active layer 3 on the buffer layer 2 that has been epitaxially and continuously grown on the GaAs substrate 1, and the recess depth is set just below the gate electrode 5. The active membrane thickness is set to an optimum value. Also, simply shortening the gate length will result in an increase in gate resistance R _g .
By increasing the thickness of the gate electrode, it is possible to reduce the gate resistance. In this case, the contact area between the gate electrode 5 and the active layer 3 decreases, and the height of the gate electrode 5 increases, making it easier for the gate electrode 5 to peel off during a cleaning process, for example. Generally, as shown in FIG. 1, a recess 4 is formed by etching using an electron beam exposure resist layer 6 as a mask using electron beam lithography suitable for microfabrication, and then a metal vapor deposition film 7 is formed on the entire surface. At this time, recess 4
A gate electrode 5 is formed thereon. Then, at the same time as removing the resist layer 6, the metal vapor deposited film 7 thereon is also removed (this is a so-called lift-off method). The recess 4 and the gate electrode 5 are formed in a self-aligned manner, and the resist layer only needs to be formed once, which is advantageous in terms of manufacturing process. However, since the positive resist is exposed to electron beam, the developed window (through hole) has a dovetail-like shape, and the recess width is larger than the gate electrode width (the first
figure). For this reason, the active layer 3 parts thinned by the recess 4 are on both sides of the gate electrode, and since the series resistance of the active layer is large in these parts, it is difficult to reduce the source-gate resistance (R _s ). do not have.

(4) Purpose of the Invention The purpose of the present invention is to prevent peeling of the gate electrode even if the gate length is shortened in a GaAs shot gate field effect transistor with a recessed structure, and to prevent separation of the source and drain in the active layer thinned by the recess. It is an object of the present invention to provide a method for manufacturing a semiconductor device of a GaAs shot gate field effect transistor which reduces the inter-resistance and operates with high performance at ultra-high frequencies.

(5) Structure of the Invention An object of the present invention is to sequentially stack an insulating film and a first mask layer on a semiconductor active layer, and to form an opening in a portion of the first mask layer corresponding to a region where a gate electrode is to be formed. forming an opening window in the insulating film by selectively removing the insulating film using the first mask layer as a mask, removing the first mask layer, and then forming a second mask layer. forming an opening in the second mask layer that is larger than the opening window and exposing the opening window, and further etching the semiconductor active layer to a predetermined depth using the insulating film as a mask; A method for manufacturing a semiconductor device, comprising the steps of: forming a recess in the opening, and depositing a metal serving as a gate electrode on the recess and the insulating film around the recess within the opening. achieved.

According to the manufacturing method of the present invention, the recess is formed by etching through the opening window provided in the insulating film, and the gate electrode is made of a conductor simultaneously formed on the insulating film on the recess through the opening window by vacuum evaporation or sputtering. It will be made up of layers.

(6) Embodiments of the invention The present invention will be described in detail below by way of embodiments of the invention with reference to the accompanying drawings.

As shown in FIG. 2, a semi-insulating GaAs substrate 11
A non-doped buffer layer 12 (thickness: 3 to 5 μm) is formed on top using a continuous vapor phase or liquid phase epitaxial growth method.
And active layer 13 (active layer, thickness: 0.1 to 0.5 μm)
form. Note that the impurity concentration of this active layer is 1
~3×10 ¹⁷ pieces/cm ³ . Then AuGe(Ge:
12 wt%) and Au are formed into a predetermined pattern by photoetching or lift-off to form a source electrode 14 and a drain electrode 15 on the active layer 3. These electrodes 14 and 15 are brought into ohmic contact by annealing at about 450°C.

Next, as shown in FIG.
0.1 to 0.2 μm) is formed over the entire surface by sputtering, reduced pressure vapor deposition (CVD), or the like. At this time, the insulating film 16 is made of silicon dioxide (SiO ₂ ). A resist layer 17 of a first microphone layer is formed on this insulating film 16, and a dovetail-shaped opening (hole) 18 of a gate electrode pattern to be formed is formed by electron beam exposure. A commercially available positive resist for electron beam exposure is used for this resist layer 17, and the width of the hole 18 on the upper surface side is set to 0.2 to 0.5 μm, which corresponds to the width of the gate electrode (ie, gate length).

Next, using this resist layer 17 as a mask, the insulating film 16 made of silicon dioxide is selectively etched anisotropically by a dry etching method using CHF ₃ gas to open an opening window 19 (FIG. 4). The width of this opening window is 0.2 to 0.5 μm. Since this is a resist layer used when selectively etching only the insulating film, it can be formed thinly, and even if there is an opening in the form of a groove, its downward expansion is small, and the opening can be almost enlarged by anisotropic etching. The size of the opening in the resist layer is almost exactly the size of the opening window in the insulating film. Then, the resist layer 17 is removed.

As shown in FIG. 5, another resist layer 20 as a second mask layer is formed of the same positive resist as the resist layer 17, and holes 20 corresponding to the opening windows 19 are formed in the resist layer 20 by electron beam exposure. form. At this time, the width on the top side of this hole 21 is
Set to 0.5 to 1.0 μm. That is, an opening wider than the opening window 19 is formed.

Using the resist layer 20 and the insulating film 16 as a mask, the active layer 13 is etched with a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide to form a recess 22 (FIG. 6).
At this time, the depth of the recess 22 is set to a value determined from the set characteristics of the field effect transistor. The active layer 13 in the vicinity of the opening window 19 under the insulating film 16 is also etched as an undercut as shown in FIG.

Next, a metal (aluminum) constituting a gate electrode with shot barrier properties is deposited on the entire surface of the GaAs substrate 11 in a direction substantially perpendicular to it by vapor deposition or sputtering, thereby simultaneously forming a metal film 23 on the resist layer 20. Openings (holes) 21 in the resist layer 20
A gate electrode 24 is formed inside (FIG. 7).

By removing the resist layer 20, the metal film 23 thereon is also removed, as shown in FIG.
A GaAs shot gate field effect transistor is obtained. In this transistor, the gate electrode 24 extends into the recess (concavity) of the active layer 13 through an opening window 19 provided in the insulating film 16, and the gate length is defined by the window 19 (FIG. 6). ing. Furthermore, in forming the recess 22 (FIG. 6), the width of the recess 22 is defined by the opening window 19, so the gate electrode 24 fills almost the entire recess 22 (excluding the undercut portion). Therefore, since there is no active layer portion thinned by a recess, which is a problem in conventional field effect transistors, the source-gate resistance can be reduced accordingly. Further, since the gate electrode 24 is also placed on the insulating film 16, the adhesion area on the lower surface of the gate electrode 24 becomes large, making it difficult to peel off. Moreover, as is clear from FIG. 8, the volume of the gate electrode 24 can be made larger than in the conventional case, so that the gate resistance is reduced.

(7) Effects of the invention The GaAs shot gate field effect transistor manufactured according to the manufacturing method of the invention can be used particularly as a small signal (low noise) transistor,
The manufacturing method can also be applied to high mobility transistors having heterojunctions of the same conductivity type, such as HEMTs.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a semiconductor device showing a part of the manufacturing process of a conventional field effect semiconductor device, and FIGS. 2 to 8 show a method of manufacturing a field effect semiconductor device according to the present invention. FIG. 2 is a schematic cross-sectional view of a field-effect semiconductor device in a manufacturing process to be described. 1...GaAs substrate, 3...Active layer, 4...Recess (concave), 5...Gate electrode, 11...GaAs
Substrate, 13... Active layer, 14... Source electrode, 1
5...Drain electrode, 16...Insulating film, 17...
Resist layer, 18... Opening (hole), 19... Opening window, 20... Resist layer, 21... Opening, 23
...metal film, 24...gate electrode.

Claims (1)

[Claims] 1. An insulating film 16 and a first mask layer 17 are sequentially stacked on the semiconductor active layer 13, an opening 18 is formed in a portion of the first mask layer 17 corresponding to a region where a gate electrode is to be formed, and then the The insulating layer is selectively removed using the first mask layer 17 as a mask to form an opening window 19 in the insulating film 16, and a second mask layer 20 is laminated after removing the first mask layer. , an opening 2 in the second mask layer that is larger than the opening window 19 and exposes the opening window.
1 is formed, and then the semiconductor active layer 13 is etched and removed to a predetermined depth using the insulating film 16 as a mask to form a recess 22.
A method for manufacturing a semiconductor device, comprising the step of depositing metal to become a gate electrode 24 on the recess 22 and the insulating film 16 around the recess.