JP3017509B2 - Compound semiconductor wafer and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a compound semiconductor wafer, and more particularly to a wafer suitable for forming a Schottky electrode.

[Conventional technology]

2. Description of the Related Art In recent years, a Schottky gate field effect transistor (FET) has attracted attention as an element for an integrated circuit that can operate at high speed. The general structure of a conventional Schottky gate field-effect transistor is that an n-type active layer having a uniform thickness is formed on the surface of a semi-insulating semiconductor substrate such as GaAs by epitaxial growth or ion implantation. A source electrode, a drain electrode and a Schottky gate electrode are formed by depositing a metal on the substrate.
6168, JP-A-58-147160).

In the prior art, the surface of a compound semiconductor substrate (hereinafter referred to as a wafer) is chemically etched or
After the plasma etching, an electrode metal is adhered to the wafer surface by a vacuum deposition method, a sputtering method, or the like. Next, the electrode metal is generally processed into a predetermined shape by photolithography to form a Schottky electrode.

[Problems to be solved by the invention]

Schottky electrode formed on the most important point is that the large Schottky barrier height [Phi _B. To form a large electrode [Phi _B is cleaned semiconductor surface, the choice of metal (electrode material) is important. In the conventional electrode forming techniques, there is a semiconductor material such as InP that can form a large electrode [Phi _B is difficult due to the influence of semiconductor surface level.

The present invention focuses on that the state of the semiconductor surface affects the [Phi _B, the oxygen ion implantation step into a conventional electrode forming step, by adding a surface modifying step such as an oxygen plasma treatment process, the surface state The purpose is to change it to form a good Schottky electrode.

[Means for solving the problem]

The barrier height Φ _B of the Schottky electrode greatly changes depending on the cleanliness of the semiconductor surface and the thickness and quality of the surface oxide film.
The present invention has found that Φ _B increases by increasing the oxygen concentration at a certain depth from the semiconductor surface. That is, by setting the oxygen ion concentration to 1 × 10 ¹⁸ atoms · cm ⁻³ or more in a shallow region of 0.1 μm or less from the surface, the barrier height Φ _B of the Schottky electrode is increased and a good Schottky electrode can be formed. I understood. Usually, the oxygen concentration is 10
¹⁸ higher than the atoms · cm ^-3, but after removal by etching or the like of these adsorbed oxygen to form a good electrode, the oxygen concentration is 10 ¹⁶ atoms · cm ^-3 or less, the [Phi _B 0.4
It is about eV. In the present invention, the oxygen concentration in the Schottky electrode formation region after removing the adsorbed oxygen is increased to 10 ¹⁸ atoms · cm ⁻³ or more. The results [Phi _B becomes more 0.6 eV, it is possible to form a good Schottky electrode.

In order to increase the oxygen concentration of the substrate, a method of performing treatment by an ion implantation method can be used.

In a method of forming a Schottky electrode including an oxygen ion implantation step, first, a semiconductor surface is cleaned by a generally practiced method. For example, after performing pretreatment such as polishing, chemical etching, or sputtering with ions, oxygen ions are implanted into the semiconductor by a commonly used ion implantation apparatus to perform surface modification. The implantation energy increases the oxygen concentration near the surface and reduces the damage caused by semiconductor implantation to 50 keV.
The following low energy is desirable. The implantation dose of oxygen ions is preferably in the range of 1 × 10 ¹² to 1 × 10 ¹⁴ cm ⁻² . 1
× In 10 ¹² cm ^-2 or less, the surface modification effect is not observed an increase in insufficient [Phi _B, 1 in × 10 ¹⁴ cm ^-2 or higher, the injection damages the cause degradation and a decrease in device performance [Phi _B Good Schottky bonding cannot be obtained.

After modifying the surface by ion implantation, a suitable metal thin film is deposited on the semiconductor surface by vacuum evaporation or the like,
Form a Schottky junction. Thereafter, the metal is processed into a desired shape by a commonly used photolithography technique to form a Schottky electrode.

[Action]

It is considered that the above-mentioned surface modification step increases the surface oxygen concentration and changes the bonding state of the semiconductor. It is estimated that this coupling state causes a change in the surface state or the band gap of the semiconductor, and the Schottky barrier height Φ _B increases.

〔Example〕

Example 1 In the related art, a method of forming an Au Schottky electrode on an InP single crystal substrate, which is considered to be difficult to obtain a good Schottky junction, will be described later.

After the mirror polished surface (100) of undoped InP substrate (N-type), the substrate to Br ₂ -CH ₃ OH (Br ₂ concentration = 1%) an etchant was immersed for 1 minute at room temperature. After etching, the surface was washed with ultrapure water and dried to clean the surface.

Next, an electrode pattern was formed on the wafer surface by a photoresist (positive type) using a normal photolithography technique.

In order to prevent the channeling effect, the tilt angle of the patterned wafer is set to 7 degrees in the axial direction with respect to the ion beam, and the angle between the <0> direction and the tilt axis is set to 30 degrees in the rotational direction. It was set in the injection device.

The ion implantation conditions were as follows: oxygen monovalent ions (mass number = 32)
The wafer was implanted with an energy of 10 keV and a dose of 1 × 10 ¹³ cm ⁻² . After the ion implantation, gold was vapor-deposited on the wafer surface by a resistance heating type vacuum vapor deposition method for about 2000 mm to form a Schottky junction. Thereafter, the photoresist was removed and the electrode pattern was formed by a normal lift-off method. FIG. 1A shows the result of measuring the oxygen concentration of this wafer by SIMS.

In FIG. 1, up to 0.01 μm from the surface depends on adsorbed oxygen, but a high concentration of oxygen due to ion implantation is observed at a peak of 0.03 μm.

FIG. 2 (a) shows the forward current-voltage characteristics of the Schottky electrode obtained by the above method. FIG. 2B also shows, for comparison, the characteristics of a conventional electrode in which the ion implantation step was omitted. Also, from these measurement results, the Schottky barrier height and the ideality factor (n
Table 1 summarizes the results of determining the values. The ideal factor is IV
This is a value obtained by calculation from the characteristic curve. Oxygen ion implantation increases the Schottky barrier height by about 0.3 eV,
A good Schottky electrode could be formed also in the nP crystal.

[Effects] According to the present invention, the electrical characteristics of the Schottky electrode are improved, and the performance of a device using the Schottky electrode is improved,
It is possible to form an unprecedented Schottky electrode, and it can be applied to a new device such as an InP MESFET for ultrahigh frequency power.

[Brief description of the drawings]

FIG. 1 is a diagram showing the oxygen concentration in the depth direction of the wafer, and FIG. 2 is a diagram showing a forward current-voltage curve.

Claims (1)

(57) [Claims] After cleaning the surface of a semiconductor substrate, oxygen ions are implanted at a dose of 1 × 10 ¹² cm ⁻² to 1 × 10 ¹⁴ cm ⁻² , a metal thin film is deposited on the surface, and A method for manufacturing a compound semiconductor wafer, comprising forming a Schottky electrode by processing a metal thin film into a desired shape.