JPS61289670A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a stable threshold voltage by a method wherein working upon a semiconductor substrate and transfer of the semiconductor substrate between processes are carried out without exposing the main surface of the semiconductor substrate to the open air containing oxygen. CONSTITUTION:After donors are introduced into the surface layer of a semi- insulating GaAs substrate 1 to form an N-type layer 2, donors are implanted selectively to form an N<+> type source region 3 and an N<+> type drain region 4 by diffusion. The substrate is subjected to heat dissociation in a vacuum apparatus to remove a natural oxide film on the main surface of the substrate and an As beam is applied. Tungsten/aluminum is evaporated on the substrate 1 and a photoresist 11 is applied and Schottky gate electrode 5 is formed. Then, while the vacuum being maintained, the resist 11 is removed and a silicon oxide film is formed as a layer insulation film 6. After contact holes 7 are drilled in the layer insulation film 6, gold/germanium alloy films are evaporated to form a source electrode 8 and a drain electrode 9 which are brought into ohmic contact with the source region 3 and the drain region 4 respectively. With this constitution, a threshold voltage can be controlled at the stable and well reproducible value.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor device equipped with a Schottky barrier field effect transistor, and in particular improves the process of forming electrodes etc. after the impurity diffusion process to improve stability. The present invention relates to a method of manufacturing a semiconductor device that can obtain a threshold voltage of 100%.

[Technical background of the invention] Schottky barrier field effect transistor (MES)
A semiconductor device in which a FET (abbreviated as FET) is formed and a conventional manufacturing method thereof will be described with reference to FIG. Cr
An N-type layer 2 is formed by ion-implanting a donor into a semi-insulating GaAs substrate 1 doped with . Furthermore, selective ion implantation is performed to form N+ type [13 and 4]. Next, a metal film forming a Schottky barrier is bonded to this surface.

The gate electrode 5 is processed by lithography.

After forming a CVD SiO film as interlayer insulation II6, a contact hole 7 is opened, an AuGe alloy film is deposited, and annealed to form an ohmic contact between a source electrode 8 and a drain electrode 9. A metal film 10 for wiring such as aluminum is formed on this, and the MES F
Manufacture ET. As is well known in the MES FET, a Schottky barrier is formed between the gate electrode and the substrate surface, and the properties of this barrier 6 have a great influence on the characteristics of the MES FET.

[Problems of Background Art] As described above, the state of the interface between the gate electrode and the semiconductor substrate is a major factor that influences the characteristics of MES FETs. In conventional manufacturing methods, the interfacial stability is poor and many undesirable interfacial units are present. As a result, the first
The potential of the Schottky barrier takes values that are unstable and have poor reproducibility. Secondly, the depletion layer between the gate and the source and between the gate and the drain expands beyond the current limit, making it impossible to secure a sufficient current. Thirdly, variations in resistance value due to ohmic contact at the interface between the source electrode and the drain electrode and the substrate become large. As a result of the above, the threshold voltage has a large variation, making it impossible to form a circuit with good controllability, resulting in a decrease in performance and yield.

[Object of the Invention] An object of the present invention is to solve the above-mentioned problems in a MES FET and to provide a stable threshold II! ! It is an object of the present invention to provide a method for manufacturing a semiconductor device in which high pressure is obtained and there is little variation in ohmic contact resistance values of source and drain electrodes.

[Summary of the Invention I One of the main causes of the above problems in MES FETs is that a natural oxide film is formed on the substrate surface during the manufacturing process, and this oxide film is interposed at the interface between the gate electrode etc. and the substrate. We found that this is due to the formation of unspecified interfacial units. Therefore, the present invention is a manufacturing method that removes the natural oxide film on the substrate surface and prevents the formation of the natural oxide film in subsequent steps.

Note that the natural oxide film is an oxide film that is unintentionally formed when outside air containing oxygen comes into contact with the exposed portion of the surface of the semiconductor substrate during the manufacturing process.

That is, in manufacturing a semiconductor device in which a Schottky barrier field effect transistor is formed on one main surface of a semiconductor substrate, the present invention provides a method for manufacturing a semiconductor device in which a Schottky barrier field effect transistor is formed on one main surface of the semiconductor substrate. After removing the natural oxide film on the surface, until the entire main surface of the semiconductor substrate is covered with the gate electrode, interlayer insulating film, source electrode, and drain electrode, the main surface of the semiconductor substrate is removed. Processing (including preparatory work) on the semiconductor substrate without exposing the surface to outside air containing oxygen
and a method for manufacturing a semiconductor device, characterized in that the semiconductor substrate is transferred between processes.

Application of the present invention is particularly desirable when the semiconductor substrate is made of GaAs. Although there are various methods for removing the natural oxide film on the surface of a semiconductor substrate, it is preferable to heat the substrate in vacuum or to remove it by applying charged particles such as gas ions to the substrate surface.

[Embodiments of the invention] The following is an example of an ME using a GaAs board as an example of the present invention.
A method for manufacturing an S FET will be explained based on the drawings. Figure 2 shows a Schottky barrier field effect transistor (MES FET) on a semi-insulating GaAs semiconductor substrate.
) is a cross-sectional view of a transistor portion of a semiconductor device in which a semiconductor device is formed. The configuration of this MES FET is similar to that of conventional MES
Although it is similar to the FET and as described above, the manufacturing method is different.

FIGS. 1(A) to 1(E) show the manufacturing process of the present invention in cross-sectional views of the device. Figure 1 (A> is GaAs
Gate electrode and source 1 on the main surface of the semiconductor substrate! This shows the state before forming the pole and drain electrodes. That is, C
Donors are introduced into the surface layer of the semi-insulating GaAs substrate 1 doped with ion implantation to form N-type Fm2, and then donors are further selectively implanted to form N4-type source regions 3 and drain regions 4. Next, as shown in the same figure (B), this substrate was 6
The natural oxide film on the main surface (front surface) of the substrate is removed by thermal dissociation at 50°C. In order to prevent the main surface of the wA substrate from becoming rough, an As beam is irradiated.

FIG. 1C shows a state in which a gate electrode 5 is formed on the substrate 1 after the natural oxide film removal process.

That is, following the process shown in FIG. 2B, tungsten aluminum is deposited on the substrate 1 while maintaining a vacuum, and then a photoresist 11 is applied and a Schottky gate electrode 5 is processed by well-known photolithography. do. Next, as shown in FIG. 4D, the resist 11 is removed while maintaining the vacuum, and a silicon oxide film is formed as an interlayer insulator 106 by CVD. Next, as shown in FIG. 6(E), a contact hole 7 is formed in the interlayer insulating film 6 by photolithography, and then a gold/germanium alloy film is deposited to form a source electrode 8 and a drain electrode 9, and a source electrode 8 and a drain electrode 9 are formed. 3
and the drain region 4, respectively.

In the present invention, the main surface of the semiconductor substrate is exposed to outside air containing oxygen between the natural oxide film removal step shown in FIG. 1(B) and the source electrode and drain electrode forming step shown in FIG. 1(E). The substrate must be processed or transferred without any problems. Therefore, the various manufacturing equipment used during this time are connected in the order of the process by an airtight tunnel with a transport mechanism, and the wafer processing chambers of the various VL manufacturing equipment are isolated from the outside air, and the loading, processing, and unloading operations of wafers are automated. , robotized. Further, the tunnel and the wafer processing chamber are kept in a vacuum except when introducing gases necessary for the process, or are filled with an inert gas such as nitrogen gas as desired.

Finally, as shown in FIG. 2, A1 is deposited and patterned to form a wiring metal layer 10.

In the above embodiment, a GaAs MESFET has been described, but the semiconductor substrate may be a silicon substrate or another compound semiconductor. Further, although dissociation by heating in vacuum was used to remove the natural oxide film on the main surface of the substrate, it is also possible to use sputtering in which charged particles such as ionized argon are applied to the main surface of the substrate. It is also possible to use silicide or pure metal such as platinum as the Schottky electrode.

[Effects of the Invention 1 200 MES FETs were manufactured using the manufacturing method of the present invention and 200 MES FETs were manufactured using the conventional manufacturing method, and the threshold voltage distributions thereof were measured. However, one element has a gate length of 1.5 μm and a width of 10 μm. FIG. 3 shows the threshold voltage distribution of the MES FET according to the method of the present invention, and FIG. 4 shows the distribution of the threshold voltage of the MES FET according to the conventional method.
This is the distribution of ET.

The threshold voltage of conventional MES FET is 140
1 V, whereas the MES of the present invention
The threshold voltage of FET is about 1/2 of that, 80 mV.
It is confirmed that the stability is within the range of .

As described above, according to the manufacturing method of the present invention, the interfaces where the main surface of the semiconductor substrate joins with each of the gate, source, and drain electrodes, as well as the natural As a result of suppressing the formation of an oxide film, the threshold voltage can be controlled to a stable and reproducible value, and the variation in ohmic contact resistance of the source and drain electrodes is also reduced, making it possible to improve the performance of high-performance semiconductor devices. It is now possible to manufacture at a high yield.

[Brief explanation of the drawing]

1(A) to E) are cross-sectional views showing the manufacturing process of an embodiment of the present invention, FIG. 2 is a cross-sectional view of a semiconductor according to the present invention and a conventional manufacturing method, and FIG. 3 is a cross-sectional view of a semiconductor according to the present invention. FIG. 4 is a threshold voltage distribution diagram of a semiconductor device manufactured by the conventional manufacturing method. 1... Semiconductor substrate (semi-insulating GaAsI board), 5...
- Gate electrode, 6... Interlayer insulating film, 8... Source electrode, 9... Drain electrode. Figure 3 Threshold voltage (mV)

Claims (1)

[Claims] 1. In manufacturing a semiconductor device in which a Schottky barrier field effect transistor is formed on one principal surface of a semiconductor substrate,
Before forming a gate electrode, a source electrode, and a drain electrode on the main surface of the semiconductor substrate, a natural oxide film on the main surface of the semiconductor substrate is removed, and from this natural oxide film removal step, a gate electrode formation step and an interlayer insulating film formation step are performed. Processing on the semiconductor substrate and transfer of the semiconductor substrate between the steps are performed without exposing the main surface of the semiconductor substrate to outside air containing oxygen until the process and the step of forming the source electrode and drain electrode are completed. A method for manufacturing a semiconductor device, characterized in that: 2 Claim 1 in which the semiconductor substrate is made of GaAs
A method for manufacturing a semiconductor device according to section 1. 3. The method of manufacturing a semiconductor device according to claims 1 and 2, wherein the semiconductor substrate is heated in a vacuum to remove a natural oxide film on the main surface of the substrate. 4. Claim 1, wherein the natural oxide film on the main surface of the semiconductor substrate is removed by bombarding the main surface of the semiconductor substrate with charged particles.
A method for manufacturing a semiconductor device according to items 1 and 2.