JPS6328075A - Schottky junction type viriable capacitance diode - Google Patents

Abstract

PURPOSE:To improve reliability with a planar structure and suppress the spread of a depletion layer along the surface to reduce 1/f noise by a method wherein a super-step type Schottky junction is formed in a boundary between a 1st region formed by selective diffusion of n-type impurity and a Schottky electrode. CONSTITUTION:A super-step type Schottky junction is formed in a boundary between 1st n-type region 3 and a Schottky electrode 4 and the spread of a depletion layer along the surface induced by the application of a reverse bias is blocked by annular 2nd region 8. As a result, the distance of a path through which a surface leakage current flows is limited to be short so that 1/f noise caused by the crystal defect in the surface can be suppressed within a small value. If the whole Schottky electrode 4 is within the 1st n-type region 3 which has a higher impurity concentration than an epitaxial layer 2, the spread of the detection layer is narrowed at the edge of the Schottky electrode 4, and an electric field is concentrated at that part so that dielectric strength is degraded. Therefore, the edge of the Schottky electrode 4 is extended onto the epitaxial layer 2 which has a low impurity concentration to widen the depletion layer a little and relieve the curvature of the depletion layer at the edge and the dielectric strength is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a varicap diode in which a hyperstep Schottky junction is formed at the interface between a compound semiconductor layer and an electrode.

BACKGROUND ART As a low-noise varicap diode for high frequency use, a Schottky junction type diode is used, which has a short reverse recovery time and a low forward rising voltage due to conduction by majority carriers. Furthermore, a compound semiconductor such as GaAs, which has high electron mobility, is used as the substrate material. The structure of Schottky junction type varicap diodes using such compound semiconductor base materials has mainly been mesa-shaped as shown in FIG.

This structure is made of n-type GaAs with a high impurity concentration (n0).
On the substrate 1, n-type GaAs with a low impurity concentration (n-) is formed.
An epitaxial layer 2 is formed by epitaxial growth, and an n-type impurity is diffused into the epitaxial layer 2 at a higher concentration to form an n-type impurity. A Schottky electrode 4 is formed, an insulating film 6 such as a silicon oxide film or a silicon nitride film is formed on a mesa portion 5 formed by mesa etching to a depth of 1 to 2 μm from the surface, and an ohmic electrode 7 is formed on the back surface of the GaAs substrate. This is the structure formed.

According to this structure, a hyperstep Schottky junction is formed at the interface between the n-region 3 and the Schottky electrode 4, and the voltage dependence of the capacitance can be increased. The extension can be limited by the mesa portion 5, and therefore the distance through which the surface leakage current that causes 1/f noise flows is shortened, and the 1/f noise can be reduced.

Problems to be Solved by the Invention In conventional mesa-shaped structures, the depth of the mesa etch is comparable to the thickness of the epitaxial layer. This thickness is usually 1~
Since the thickness is 2 μm, a large step is formed at the peripheral edge of the surface side, and it is difficult to completely cover this step, especially the etched portion, with an insulating film such as a silicon oxide film or a silicon nitride film. This posed a problem in terms of reliability.

For this reason, if a Brenna-type structure is used instead of a mesa structure, the difference at the surface disappears and the above problem disappears, but 1 the depletion layer spreads along the surface and the distance through which the surface leakage current flows becomes longer. /f There was an inconvenience that the noise became large.

An object of the present invention is to improve reliability by forming a Brenna-type structure, and to suppress the spread of the depletion layer along the surface to reduce 1/f noise.

Means for Solving the Problems The Schott-cow junction type varicap diode of the present invention has the following features:
A compound semiconductor substrate containing a high concentration of n-type impurities, an n-type epitaxial layer with a low impurity concentration formed on the same substrate, and a compound semiconductor substrate with a higher concentration of n-type impurities in the same epitaxial layer.
a first region formed by selectively diffusing type impurities; a ring-shaped second region surrounding the first region; A Schottky electrode formed on the surface of the compound semiconductor substrate, and an insulating film formed on the surface of the compound semiconductor substrate, and a hyperstep Schottky junction formed at the interface between the first region and the Schottky electrode. It is.

Effect: According to the structure of the present invention, an insulating film can be completely attached to the substrate surface without any step on the surface, and the spread of the depletion layer along the surface can be stopped by the ring-shaped second n-region. .

Embodiment FIG. 1 is a structural cross-sectional view of an embodiment of the Schottky junction type varicap diode of the present invention, in which the impurity concentration is I.
n-type G with high impurity concentration (n+) of X 10”/cnt
GaAs is epitaxially grown on an aAs substrate 1 to form an n-type epitaxial layer 2 with a low impurity concentration (n-) of 5 x 1015/cJ. Diffusion of selection,
A first n-region 3 with an impurity concentration of 1016 to 1017/c+j and a ring-shaped second n-region 8 surrounding it are formed simultaneously, and the edge extends beyond the first n-region 3 to form an epitaxial layer. 2, a single layer of platinum (Pt) or titanium (T) is applied to the surface.
i) A Schottky electrode 4 is formed using a biolayer film of platinum and gold (Au), and an insulating film consisting of two layers of a silicon oxide film formed by CVD and a silicon nitride film formed by plasma CVD is formed on the surface of the GaAs substrate 1. 6 is formed, GaAs
Gold/germanium alloy film (Au-Ge) on the back surface of the substrate 1
Ohmic electrode 7 with a gold film in contact with the film and this 5
It has a structure in which

According to this structure, the first n region 3 and the Schottky electrode 4
A super-stepped Schottky junction is formed at the interface with the ring-shaped second n-region 7, and the expansion of the depletion layer along the surface when a reverse bias is applied can be prevented.As a result, the surface leakage current Since the distance through which the particles flow is limited to a short distance, 1/f noise caused by surface bonding defects can be suppressed to a small level.

The reason why the edge of the Schottky electrode 4 extends beyond the first n-region 3 to a part of the epitaxial layer 2 is because the entire Schottky electrode 4 has an impurity concentration lower than that of the epitaxial layer 2. If it is within the high first n region 3,
Since the spread of the depletion layer at the edge of the Schottky electrode 4 becomes narrower, the electric field is concentrated there and the withstand voltage becomes lower. This is to widen the depletion layer a little, loosen the so-called curvature of the depletion layer, and increase the breakdown voltage.

Next, Fig. 2 shows a planar structure with a ring-shaped second
The carrier-to-noise ratio (C
/N) shows a comparison of noise.

As shown in the figure, by adding a ring in the n region, C
It is clearly seen that the /N and, therefore, the 1/f noise are improved.

Effects of the Invention According to the Schottky junction type varicap diode of the present invention, it has a planar structure, eliminates steps on the surface, completely covers the surface with an insulating film to improve reliability, and has an n-region ring around the Schottky electrode. By adding 1
The effect of suppressing /f noise to a low level is achieved.

[Brief explanation of the drawing]

Fig. 1 is a structural cross-sectional view showing an embodiment of the Schottky junction type varicap diode of the present invention, Fig. 2 is a comparison diagram of C/H between the conventional one with a planar structure and the one of the present invention, and Fig. 3
The figure is a structural cross-sectional view of a mesa structure of a conventional Schottky junction type varicap diode. DESCRIPTION OF SYMBOLS 1...GaAs substrate, 2...Epitaxial layer, 3...First n region, 4...
・Schottky electrode, 6... Insulating film, 7...
...Ohmic electrode, 8... Ring-shaped second n region.

Claims (1)

[Claims] A compound semiconductor substrate containing a high concentration of n-type impurities, an n-type epitaxial layer with a low impurity concentration formed on the same substrate, and a compound semiconductor substrate with a higher concentration of n-type impurities in the same epitaxial layer.
a first region formed by selectively diffusing shaped impurities; a ring-shaped second region surrounding the first region; and an edge extending beyond the first region to a part of the epitaxial layer. A Schottky electrode extended and formed on the surface, an insulating film formed on the surface of the compound semiconductor substrate, and a hyperstep Schottky junction formed at the interface between the first region and the Schottky electrode. Characteristic Schottky junction type varicap diode.