JPS6159674B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a bulk conduction type insulated gate field effect transistor using GaAs as a semiconductor.

A bulk conduction type insulated gate field effect transistor (hereinafter referred to as a bulk conduction type MOS FET) is a
As shown in the figure, a semiconductor layer 2 of one conductivity type is provided on a semi-insulating substrate 1, a source electrode 3 and a drain electrode 4 are provided on this semiconductor layer 2, and an insulating layer is provided on the semiconductor layer 2 between both electrodes. It has a structure in which a gate electrode 6 is formed through a film 5, and the current flowing through the semiconductor layer 2 between the source electrode 3 and the drain electrode 4 is controlled by the voltage applied to the gate electrode 6.
This bulk conduction type MOS FET has higher carrier mobility than the inverted type MOS FET, which is widely used in Si, etc., so it can operate at high speed, and even if the gate length is shortened, it can be used as an inverted type MOS FET. Short channel effects such as pulch-through do not occur. Furthermore, unlike shot-gate type FETs, gate current does not flow even when a positive voltage is applied to the gate electrode, so it has the advantage of allowing a large logic amplitude, making it an element suitable for high-speed operation. I can say that. And to enable higher-speed operation, it has a higher carrier mobility than Si.
Since the use of GaAs as a semiconductor material is advantageous in principle, research and development of such devices has been promoted in recent years.

By the way, in conventional methods for manufacturing GaAs bulk conduction type MOS FETs, the insulating film 5 is generally formed using a thermal oxidation method, an anodization method in an electrolytic solution, a plasma oxidation method, etc.
Methods of directly oxidizing a portion of GaAs, and methods of loading other insulating films on GaAs using CVD, vacuum evaporation, etc., have been adopted. However, GaAs bulk conduction type MOS manufactured by these conventional methods
The FET has a fatal drawback in that a large amount of interface states exist at the interface between the semiconductor layer 2 and the insulating film 5. Therefore, it is not possible to obtain a sufficient current change at low frequencies where the interface states respond, and the bulk conductivity type
The advantages of MOS FETs could not be fully demonstrated.

In other words, when configuring a logic element, each
Due to coupling problems with the next stage and the need to reduce power consumption, FETs must be of the so-called normally-off type, in which no current flows when no voltage is applied to the gate. It is required that a sufficient current change can be obtained with respect to the gate voltage. However, in a GaAs bulk conduction type MOS FET manufactured using a conventional manufacturing method, for example, a method in which the insulating film 5 is formed using a plasma oxidation method,
Its DC drain characteristics are, for example, as shown in FIG. 2, and because the interface state density is high, the change in drain current with respect to a positive gate voltage is small.

The present invention improves these conventional drawbacks, and its purpose is to provide a GaAs bulk conduction type MOS with excellent interface characteristics between a GaAs semiconductor layer and an insulating film.
The object of the present invention is to provide a method for manufacturing FETs. Examples will be described in detail below.

3 to 8 are process diagrams for explaining embodiments of the present invention, and in each figure, 7 is a GaAs
Semi-insulating substrate, 8 is GaAs layer, 9 is Al thin film, 10
11 is an anodic oxidation prevention film, 11 is an Al oxide film, 12 is a source electrode, 13 is a drain electrode, 14 is a gate electrode, and 15 is a gate region.

First, as shown in FIG. 3, a GaAs layer 8 having one conductivity type is formed on a GaAs semi-insulating substrate 7 by a liquid phase epitaxial method, etc., and after mesa etching both sides of the GaAs layer 8, a gate is formed. Only the region to be used is etched halfway through the GaAs layer 8. The reason for this structure is to lower the source resistance and to ensure that the entire region of the gate is included under the gate electrode.

Next, as shown in FIG. 4, on the entire surface of the GaAs layer 8, Al is vacuum-deposited to a thickness of, for example, 800 Å to form an Al thin film 9, and then on the Al thin film 9 at the position where the ohmic electrode is to be formed. Then, an anodic oxidation prevention film 10, which is a resist or an insulating thin film, is formed.

Next, this is anodized using an electrolyte solution, such as a mixture of tartaric acid, ethylene glycol, and water, thereby converting the Al thin film 9 into an Al oxide film 11, which is an insulator, as shown in FIG. However, the Al in the area where the ohmic electrode is to be formed is not oxidized because of the anodic oxidation prevention film 10, and there is an Al thin film 9 there.
remains.

What is important here is to ensure that the Al thin film 9 is completely anodized but that the GaAs is not anodized too much.
The purpose is to reach the interface between the layer 8 and the Al thin film 9. In this way, an insulating film with the lowest interface state density can be obtained. However, according to experiments, after the oxidation of the Al thin film 9 is completed, some
It has been confirmed that even if the oxidation progresses to the GaAs layer 8, the interface state density is a sufficiently small value. Therefore, when using a constant current source, if the anode voltage at the end of anodic oxidation is in the range between the voltage at which oxidation of Al ends and a voltage approximately 1.1 times that voltage, the interface state density can be kept sufficiently low. It is something that can be done. Furthermore, Al and GaAs
Since the rate of anodic oxidation of Al is different, when the time change of the anode voltage is recorded on a recorder, the slope is different before and after the oxidation of Al is completed.Use this to perform anodization within the above range. You can also have them do this. Furthermore, since the surface reflectance of Al and GaAs is different, interference colors are not shown when the oxide layer is made of Al, but interference colors are shown when the layer is made of GaAs. Therefore,
The appearance of interference colors indicates that the oxidation of Al has ended, and it is also possible to optically detect the end of the oxidation of Al.

Next, as shown in FIG. 6, the anodic oxidation prevention film 10 is peeled off, and unoxidized Al in this region is selectively etched away using, for example, phosphoric acid.
Generally, Al oxides are extremely stable to chemicals, and it is not easy to process Al oxides by etching or the like after forming them. On the other hand, Al
can be easily removed using acid, so by employing the method according to the present invention, it becomes possible to selectively and extremely easily form an oxide film of Al in regions other than the source and drain.

Next, the element obtained in the above step is heat-treated at, for example, 400° C. for 30 minutes in an N ₂ atmosphere. The heat treatment temperature also varies depending on the heat treatment time, but for heat treatment for 30 minutes, the interface state density increases at a heat treatment temperature of less than 300℃, and for heat treatment at a temperature higher than 500℃, the voltage application At times, the insulating film becomes susceptible to dielectric breakdown. Therefore, the practically preferred range is approximately 300°C to 500°C.

Next, as shown in FIG. 7, an ohmic metal such as AuGeNi is deposited on the region where the unoxidized Al has been etched away to form a source electrode 12 and a drain electrode 13. Finally, as shown in FIG. 8, a gate electrode 14 made of, for example, Al is formed on the Al oxide film 11 in the gate region. here,
A narrow region 15 of the GaAs layer 8 serves as a gate region.

Figure 9 is a diagram showing an example of the DC drain characteristics of the GaAs bulk conduction type MOS FET manufactured as described above. As shown in the figure, the drain current is the same for both positive and negative polarity gate voltages. It can be seen that the interface characteristics of the GaAs bulk conduction type MOS FET according to the present invention are significantly superior to those of the conventional one.

In this way, in the method of this embodiment, Al is formed on the GaAs layer 8.
By depositing the thin film 9, forming an anodic oxidation prevention film such as a resist on the Al thin film 9 at the position where the ohmic electrode is to be formed, and then anodizing this,
The Al thin film 9 in areas other than the area where the ohmic electrode is to be formed is changed to the Al oxide film 11, and by controlling the Al thin film 9 to be anodized only, the interface state density is increased. It is possible to form a gate insulating film with a small thickness.

As explained above, according to the present invention, a high-quality Al oxide film with a low interface state density can be used as a source,
GaAs bulk conduction type MOS with excellent characteristics because it can be selectively formed in regions other than the drain
There is an advantage that FETs can be manufactured reliably. In addition, since the Al loaded on the main surface of the device is anodized except for the area where the ohmic electrode is to be formed, the gate insulating film is formed and other areas can be passivated at the same time. Therefore, it is very effective to apply the present invention to GaAs bulk conduction type MOS FETs or their integrated circuits. Note that when applied to an integrated circuit, it is effective to form an Al wiring pattern simultaneously with the formation of a gate insulating film by selectively anodizing Al to simplify the process.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a bulk conduction type MOS FET, Figure 2 is a diagram showing the DC drain characteristics of a GaAs bulk conduction type MOS FET manufactured using a conventional method.
Figures 3 to 8 are process diagrams for explaining examples of the present invention, and Figure 9 is a diagram showing the process of manufacturing according to the method of the present invention.
FIG. 2 is a diagram showing an example of DC drain characteristics of a GaAs bulk conduction type MOS FET. 7 is a GaAs semi-insulating substrate, 8 is a GaAs layer, and 9 is a GaAs semi-insulating substrate.
Al thin film, 10 is an anodic oxidation prevention film, 11 is Al oxide film, 12 is a source electrode, 13 is a drain electrode, 1
4 is a gate electrode, and 15 is a gate region.

Claims (1)

[Claims] 1 One conductivity type on GaAs semi-insulating substrate
A step of forming a GaAs layer and etching the gate region part of the GaAs layer halfway, a step of forming an Al thin film on the entire surface of the GaAs layer, and an anodizing prevention film on the Al thin film at the position where the ohmic electrode is to be formed. forming the Al thin film, and then anodizing the Al thin film to change the Al thin film other than the area where the ohmic electrode is to be formed into an Al oxide film;
A step of etching away the unoxidized Al thin film after peeling off the anodic oxidation prevention film, a heat treatment step after this step, and a step of forming an ohmic electrode in the region where the unoxidized Al thin film was etched away, and forming an ohmic electrode in the gate region portion. A method for manufacturing a semiconductor device, comprising the step of forming a gate electrode on the Al oxide film.