JPH0548080A - Schottky barrier diode - Google Patents

Abstract

PURPOSE:To improve efficiency of the effective area of a Schottky junction by making the recessed part of a projecting and recessed surface have a decomposition layer which was subjected to hydrogen plasma and forming a low-resistance semiconductor layer whose conductive type is identical with that of the original semiconductor substrate on a protruding part. CONSTITUTION:The surface of a semiconductor 3 is formed into a projecting and recessing shape, and on the bottom and the side part of the recessed part, a decomposition layer 5 which is formed after subjected to a hydrogen plasma is arranged and on the almost flat plane of the top part of a protruding part, a low-resistance semiconductor layer 4 is formed. Then, when a reverse direction voltage is applied, until the depletion layer which expands from the junction of a metal 1 with the decomposition layer 5 fills up the width (a) of the protruding part, the recombination current within the depletion layer expanding from the junction which is formed by the metal 1 and the low resistance semiconductor layer 4 occupies the most part of reverse direction current. By the pinch-off voltage filled with a depletion layer, the electric field affecting the Schottky barrier junction which is formed by the metal 1 and the semiconductor layer 4 is almost fixed. The recombination current within the decompletion layer which is formed by the metal 1 and the decomposition layer 5 becomes almost constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Schottky barrier diode structure having better rectifying characteristics and less loss than conventional ones.

[0002]

2. Description of the Related Art A Schottky barrier diode having a structure as shown in FIG. 1 which rectifies by utilizing a potential barrier generated by contact between a metal and a semiconductor (in the figure, 1 is a Schottky barrier forming metal, 2 is a surface protective film, 3 is a one conductivity type semiconductor substrate, 7 is a low resistance semiconductor layer such as an epitaxial layer having the same conductivity type as 3), which is faster than other diodes and has a low positive-direction rising voltage and low loss. It is often used for electric power. Particularly in recent years, the lowering of the driving voltage of the integrated circuit is increasing the necessity.

In order to realize a low-loss Schottky barrier diode, the forward voltage drop and the reverse current are smaller than those of the current one, and the diode loss, that is, the sum of the forward loss and the reverse loss is small. Realization of good characteristics is necessary. However, the forward voltage drop and the reverse current of the Schottky barrier diode are determined by the material (2) of the barrier metal forming the Schottky junction as shown in the qualitative relationship diagram shown in FIG. In general, the one having a small forward voltage drop has a large reverse leakage current, and the one having a small reverse leakage current has a large forward voltage drop. For example, when looking at the forward voltage drop of a conventionally known metal, as shown in FIG. 2, titanium (Ti), chromium (Cr), and molybdenum (Mo), which are most often used at present, become larger in order. It tends to increase the directional loss. Therefore, in a diode in which the loss is given by the sum of forward and reverse directions, it is unavoidable to select a material that achieves the lowest loss due to the balance of forward and reverse losses, and molybdenum (Mo) is most often used at present. Has been. However, in order to realize a Schottky barrier diode with a lower loss than the current one with the current structure, it is necessary to solve difficult problems such as the development of a new rectifying mechanism.

[0004]

DISCLOSURE OF THE INVENTION The present invention relates to the improvement of such a diode, which was found by the present inventors in a Schottky barrier diode in which the surface of a semiconductor substrate is formed in an uneven shape and a Schottky barrier metal is provided in the uneven portion. Utilizing this phenomenon (phenomenon in which φB changes when the semiconductor surface is exposed to plasma), the barrier height (φB) of the bottom and sides of the recess and the protrusion is changed to improve the efficiency of the effective area of the Schottky junction. The present invention provides a Schottky barrier diode having a lower loss than the conventional one, which is capable of changing the electrical characteristics according to the purpose.

[0005]

3 (a) and 3 (b) are a plan view and a sectional view showing an embodiment of the present invention, FIG. 4 is an operation explanatory view thereof, and A and B are Schottky barrier diode electrodes, and 1 is a Schottky barrier. Forming metal, 2 is a surface protective film, 3 is an N-type semiconductor substrate, 4
Is a low-resistance semiconductor layer of the same conductivity type formed in the semiconductor 3, 5 is an altered layer formed in the semiconductor 3 exposed to hydrogen plasma, and 6 is formed in the semiconductor 3.
This is a layer of opposite conductivity type, and is a region generally called a guard ring. (3) 7 is a low resistance semiconductor layer of the same conductivity type as the semiconductor 3, and 8 is an electrode metal. In addition, the surface of the semiconductor 3 is formed in an uneven shape, an altered layer 5 formed by exposure to hydrogen plasma is arranged on the bottom and side surfaces of the concave portion, and the low resistance semiconductor layer 4 is formed on a substantially flat surface above the convex portion. Are formed and arranged.

Incidentally, as shown in the barrier height characteristic diagrams of FIGS. 5A and 5B, the low resistance layer 4 formed in the semiconductor 3 is shown.
Can change the barrier height φB under the condition of ion implantation and under the hydrogen plasma condition of the deteriorated layer 5 when forming the deteriorated layer.

The operation principle of the Schottky barrier diode having the structure of the present invention will be described below. This structure is, so to speak, represented by an equivalent circuit in which a Schottky barrier diode having a small barrier height and a Schottky barrier diode having a large barrier height are connected in parallel. Therefore, when a forward electric field in which the A electrode is positive and the B electrode is negative is applied, first, in the junction portion having the small barrier height, electrons are transferred from the semiconductor 4 having a low resistance to the metal before the junction having the large barrier height. Since it flows into 1, the JF-VF characteristic of the Schottky barrier diode with a small barrier height becomes dominant. Therefore, in the structure of the present invention, there is almost no difference in the forward characteristic as compared with the conventional structure Schottky barrier diode.

On the other hand, the reverse characteristic is such that when a negative voltage is applied to the A electrode and a positive voltage is applied to the B electrode, a depletion layer is formed on the semiconductor side from the metal / semiconductor junction and spreads with an increase in the reverse applied voltage. However, the wider the width of the depletion layer W is, the larger the Schottky barrier height φB is, and the larger the φB is, the smaller the recombination current in the depletion layer is. When a reverse voltage is applied, as shown in FIG. 4, until the depletion layer (a) expanding from the junction between the metal 1 and the altered layer 5 fills the width a of the convex portion, the metal 1 and the semiconductor layer having a low resistance are formed. The recombination current in the depletion layer extending from the junction formed by 4 accounts for most of the reverse current. (4) The width a of the convex portion is filled with the depletion layer extending from the junction between the metal 1 and the altered layer (b).
From the pinch-off voltage VP, the electric field E applied to the Schottky barrier junction formed by the metal 1 and the low resistance semiconductor layer 4 is almost fixed. Since the electric field E at the junction between the metal 1 and the low-resistance semiconductor layer 4 does not increase even if the reverse voltage thereafter becomes larger than VP, the recombination current JSBJ1 in the depletion layer formed by the metal 1 and the altered layer 5 is almost constant. It becomes a value. In other words,
While the leakage current across the junction having a small Schottky barrier height φB is small, it can be kept at a constant value and a small reverse current can be maintained even after the VP voltage. When a voltage is applied even after VP, the depletion layer extending from the junction formed by the metal 1 and the altered layer 5 extends until the voltage breakdown VB (c), but the recombination current JSBJ2 of the depletion layer formed by this junction is relatively small. It becomes the current value.

Next, an example of forming the altered layer 5 and the low resistance semiconductor layer 4 on a part of the N-type silicon epitaxial wafer will be described below. An epitaxial silicon layer 3 containing phosphorus as an impurity atom and having a specific resistance of 0.5 Ω · cm is deposited to 6 μm on a silicon substrate 7 having a specific resistance of 0.003 Ω · cm and a thickness of 400 μm doped with arsenic impurity atoms. A SiO2 film having a thickness of about 1 .mu.m is formed by a steam oxidation process, and a first photographic process is performed to remove the oxide film only on the guarding portion. Then, the window of the guard ring is opened with a hydrofluoric acid-based etching solution. Boron atom is about 1 × 10 by ion implantation
Implant 14 pieces / cm2 at 50 keV, 1100 ° C, 3
0 minutes, anodically diffused in O2 atmosphere, and guarded part P +
A diffusion of 3 μm (6) is formed.

Next, a second photographic process is performed to remove the oxide film on the entire surface of the guard ring. After that, a window is opened inside the guard ring with a hydrofluoric acid-based etching solution. About 6 × 10 12 antimony atoms / cm 2 25 ke
Implanted with V and annealed in an O2 atmosphere to form a low resistance layer N @ + diffusion 1 .mu.m. For the resistivity of the low resistance layer and the height of the barrier against metal, the low resistance layer is formed (5).
Conditions when performing, for example, the number of atoms (
Amount) and the temperature and time during diffusion. Also,
The area inside the guard ring was 0.01 cm 2. next,
A third photo is applied to form a photo pattern in which a 2 × 2 μm square oxide film pattern remains. RIE (Reactive Io
n Etching) apparatus is used to etch the oxide film and silicon by a known dry etching method. Thus, the uneven shape 9 having a = 2 μm, f = 3 μm, and h = 3 μm is formed.

Next, a normal RIE apparatus is used to perform plasma discharge in an H2 gas atmosphere. An altered layer 5 of silicon containing hydrogen is formed on the bottom and sides of the recess exposed to hydrogen plasma. Since the oxide film is still formed on the silicon surface above the convex portion, it is not exposed to hydrogen plasma. In addition, the film thickness of the altered layer, the properties, the barrier height against metal, etc. are the conditions for exposure to hydrogen plasma,
For example, it can be controlled by the pressure, the amount of input power, and the like. Next, the oxide film on the convex portion is removed with a hydrofluoric acid-based etching solution. In this way, the uneven surface having the low-resistance semiconductor layer 4 on the convex portion and the deteriorated layer 5 of silicon containing hydrogen was formed on the bottom and side portions of the concave portion.

After etching the convex oxide film, Al1 is vapor-deposited. In order to allow Al to sufficiently turn to the bottom side surface of the U-shaped Si, the deposition incident angle and the rotation and revolution angles of the wafer and the rotation speed were adjusted, but it is generally said that the step coverage is good. It can also be formed by using a sputtering method or a CVD method. Then, a Schottky barrier diode chip was completed in a usual process. Due to the above production process, the inner area of the guard ring is 0.01 cm2, A
l-Low resistance semiconductor Schottky area 7.48 x 10-3c
m2 Barrier height 0.6 eV, a = 2 μm Al-hydrogen-containing silicon altered layer Schottky region f = 3 μm
The barrier height of 0.85 eV was completed.

(6) FIGS. 6 (a) and 6 (b) are characteristic diagrams of the diode of the present invention in comparison with the conventional example, and FIG. 6 (a) is a forward characteristic diagram,
(B) is a reverse direction characteristic chart. In the figure, (a) is a conventional example, and the Mo Schottky barrier diode (barrier height 0.6 eV) which is most used at present is the example of the present invention. Indicates. That is, the forward characteristic (b) according to the embodiment of the present invention is V
F = 0.47volt (at 200Amp / cm2), and even though Al was used as the barrier metal, the forward characteristic close to that of the conventional structure (a) Mo Schottky barrier diode VF = 0.40volt was obtained. Was given.
On the other hand, in the reverse direction characteristic, in the present embodiment, as shown in the characteristic (B), IR = 0.5 at the point of breakdown voltage VB≈50volt.
A reverse leakage current (IR) of about 5 mA was obtained. In the conventional Mo Schottky barrier diode, IR = 1.0 mA
And could be reduced to about 1/2. Therefore, when applied to a rectifier circuit, the power loss could be reduced to about 3/5 as compared with the conventional structure Mo Schottky barrier diode.

[0014]

As is apparent from the above description, according to the present invention, a low loss Schottky barrier diode suitable for electric power can be provided. Further, according to the principle of the present invention,
By changing the barrier metal used, the conductivity type of the semiconductor, and the like, it is possible to provide a low loss Schottky barrier diode that has the desired characteristics and is very useful in industry.

[Brief description of drawings]

FIG. 1 is a structural diagram of a conventional Schottky barrier diode.

FIG. 2 is a rectification characteristic diagram of a conventional Schottky barrier diode.

FIG. 3 is a structural view showing an embodiment of the present invention, (a) is a plan view and (b) is a sectional view.

4 (7) is an operation explanatory diagram in FIG. 3. FIG.

FIG. 5 is a characteristic diagram of barrier height.

FIG. 6 is a characteristic diagram of an example of the present invention compared with a conventional example,
(A) is a forward characteristic chart, (b) is a reverse characteristic chart.

[Explanation of symbols]

 1 Schottky barrier forming metal 2 Surface protective film 3 Semiconductor substrate 4 Low-resistance semiconductor layer of the same conductivity type as 3 5 Deteriorated layer exposed to hydrogen plasma 6 3 Conductive guarding region 7 3 opposite conductivity type -Type low resistance semiconductor layer 8 Electrode metal 9 Concavo-convex shape A, B electrode

Claims (1)

[Claims] 1. A Schottky barrier diode in which the surface of a semiconductor substrate is formed in an uneven shape and a Schottky barrier metal is provided on the uneven surface, wherein the recesses on the uneven surface have an altered layer exposed to hydrogen plasma. A Schottky barrier diode characterized in that a low-resistance semiconductor layer of the same conductivity type is formed on the convex portion with respect to the original semiconductor substrate.