JPH11233796A - Manufacture of schottky diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the forward voltage VF of a Schottky diode without increasing the reverse current IR of the diode. SOLUTION: In a method for manufacturing Schottky diode, a first N-type epitaxial layer 2a is grown on the whole surface of a silicon substrate 1 including an N-type impurity layer 9 after the layer 9. is formed on the surface of the substrate 1. Simultaneously with the growth of the epitaxial layer 2a, an N<+> -type high-concentration area 3 is formed by causing the auto-doping of the impurity layer 9 to proceed. After the high-concentration area 3 is formed, a second N-type epitaxial layer 2b is formed on the whole surface of the first epitaxial layer 2a including the area 3. Then, after a guard ring layer 4 is formed, a Schottky metal 6 is formed on the surface of the second epitaxial layer 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a Schottky barrier diode capable of lowering forward voltage VF without increasing reverse current IR.

[0002]

2. Description of the Related Art FIG. 4 is a sectional view of a chip of a general Schottky barrier diode. An N-type epitaxial layer 2 is formed on an N ⁺⁺ -type silicon substrate 1, and a P-type guard ring layer 4 is provided annularly on the surface of the epitaxial layer 2. Oxide film 5 is formed annularly on epitaxial layer 2, and titanium 6, which is a Schottky metal, is formed in an opening (not shown) formed inside guard ring layer 4 so as to contact epitaxial layer 2. I have. In addition, 7 is an electrode made of nickel and 8 is an electrode made of aluminum.

A Schottky barrier diode is a diode having a rectifying effect by bringing a metal and a semiconductor into surface contact, and has advantages such as a higher switching speed and a lower forward voltage VF as compared with a PN junction diode. And the reverse current IR is generally large and the withstand voltage is low.

In recent years, in order to reduce power consumption, a Schottky barrier diode with a further reduced forward voltage VF has been demanded.

In order to lower the forward voltage VF of the Schottky barrier diode, for example, means such as selecting a metal material that reduces the barrier height ΦB at the Schottky metal-semiconductor interface, thinning of the epitaxial layer, or reduction of the epitaxial layer It can be performed by means such as increasing the impurity concentration to lower the resistance value of the epitaxial layer.

However, with the above-described means, while the forward voltage VF can be reduced, there is a disadvantage that the reverse current IR increases. For this reason,
There is a strong demand for the development of an ideal Schottky barrier diode that can reduce the forward voltage VF without increasing the reverse current IR.

As a Schottky barrier diode for realizing this, a configuration shown in FIG. 5 is proposed in Japanese Patent Application Laid-Open No. Hei 8-64845. Its structure is as shown in FIG. 5, N ⁺⁺
A high-concentration region 3 having an impurity concentration higher than the impurity concentration of the epitaxial layer 2 is embedded in an N-type epitaxial layer 2 formed on a silicon substrate 1 of a mold type. By providing the high-concentration region 3 having a low specific resistance, the series resistance is reduced just below the Schottky junction, and the forward voltage VF can be reduced. However,
Since the high-concentration region 3 does not reach the surface of the epitaxial layer 2, the specific resistance of the epitaxial layer near the Schottky junction and around the guard ring junction can be maintained at the initial value, and the reverse current IR increases. There is no. The high concentration region 3 is formed by ion-implanting impurities from the surface of the epitaxial layer 2.

[0008]

By the way, in order to form a high concentration region inside an epitaxial layer by ion implantation from the surface of the epitaxial layer, it is necessary to perform ion implantation with very large energy. However, when ions are implanted with high energy, damage is given to the vicinity of the surface of the epitaxial layer, and a non-single-crystal portion (crystal defect) occurs on the Schottky junction surface. For this reason, the Schottky junction is broken, and a leak current is generated from the Schottky junction, and the reverse current IR of the Schottky junction surface increases.

Further, "Electronic Materials, August 1985, P12
As described in “1 to 128 High-breakdown-voltage Schottky barrier diode”, recombination centers are generated in the epitaxial layer and at the interface between the epitaxial layer and the oxide film due to crystal defects formed on the surface of the epitaxial layer. May show a value higher than the theoretical value.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a method of manufacturing a Schottky barrier diode that can lower the forward voltage VF without increasing the reverse current IR. I do.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to deposit or apply an N-type impurity such as phosphorus almost at the center of the surface of an N ⁺⁺ type silicon substrate to form an N-type impurity layer. Forming an N-type first epitaxial layer on the entire surface of the silicon substrate including the N-type impurity layer; and, during the step, auto-doping the N-type impurity layer into the first epitaxial layer. By doing so, a step of forming an N ⁺ -type high concentration region in the first epitaxial layer and a step of forming an N-type second epitaxial layer over the entire surface of the first epitaxial layer including the high concentration region This is a method for manufacturing a Schottky barrier diode.

According to the Schottky barrier diode of the present invention, a high-concentration region having a small specific resistance is formed immediately below the Schottky junction surface so as to be in contact with the silicon substrate.
Can be lowered. Further, the high concentration region is covered with the second epitaxial layer, and the specific resistance of the epitaxial layer near the Schottky junction and around the guard ring junction can be maintained at the initial value, so that the reverse current IR does not increase. Absent.

Further, according to the present invention, at the same time as the formation of the first epitaxial layer, a high concentration region is formed by auto-doping the impurity layer formed on the silicon substrate. The concentration profile of the Schottky barrier diode obtained by this method is higher than that of the conventional method in which a high concentration region is formed by ion implantation from the surface of the epitaxial layer. The value becomes smaller, and the forward voltage VF can be made lower. On the other hand, since the second epitaxial layer is formed on the first epitaxial layer, the second
The main surface of the substrate including the epitaxial layer is maintained in a good state without crystal defects, and the reverse current IR does not increase.

Further, the impurity layer on the surface of the silicon substrate is
Then, auto-doping is performed until the surface reaches the surface of the epitaxial layer, and thereafter, a second epitaxial layer is formed to bury the high concentration region. Therefore, there is no need to set conditions for stopping the autodoping of the impurity layer in the middle of the epitaxial layer, and a high concentration region can be easily formed in the epitaxial layer. Further, it is easy to control the distance between the high concentration region and the surface of the second epitaxial layer.

[0015]

FIG. 1 is a sectional view of a chip of a Schottky barrier diode according to the present invention. An N-type first epitaxial layer 2a is formed on an N ^++- type silicon substrate 1, and an N ⁺ -type high-concentration region 3 is provided in the first epitaxial layer 2a. First including high concentration region 3
An N-type second epitaxial layer 2b is formed on the epitaxial layer 2a, and the high-concentration region 3 is formed so as not to be exposed on the Schottky junction surface. A P-type guard ring layer 4 is formed annularly from the surface of the second epitaxial layer 2b to the first epitaxial layer 2a.
An annular oxide film 5 is formed on the surface of second epitaxial layer 2b, and its opening (not shown) has a Schottky metal 6 made of titanium and a nickel 7, so as to be joined to second epitaxial layer 2b. An electrode made of aluminum 8 is formed.

In the present embodiment, the silicon substrate 1 has an impurity concentration of 3 to 4 × 10 ¹⁹ cm ⁻³ and a specific resistance of ³ mΩcm.
(Preferable range is 1 to 4 mΩcm), and the first and second epitaxial layers 2a and 2b have an impurity concentration of 5 × 10 ¹⁹ cm.
^{At −3} , the specific resistance was set to 2 Ωcm. The impurity concentration of the high-concentration region may be higher than the impurity concentration of the first epitaxial layer and a concentration range in which the second epitaxial layer 2b can be formed as a single crystal.
× 10 ¹⁹ cm ^-3 was set.

As described above, since the high-concentration region is formed in the first epitaxial layer, the series resistance immediately below the Schottky junction is reduced, so that the thickness of the epitaxial layer is reduced and the specific resistance of the entire epitaxial layer is reduced. And the forward voltage VF can be reduced. The high concentration region is covered with the second epitaxial layer, and the specific resistance of the epitaxial layer near the Schottky junction and around the guard ring junction is kept high, so that the reverse current IR does not increase.

Next, a method of manufacturing the Schottky barrier diode will be described with reference to FIGS.

First, an N ⁺⁺ type silicon substrate 1 doped with arsenic was prepared, and an oxide film 5 was formed leaving an opening (not shown) of 420 to 480 μm square at the center. After an N-type impurity, phosphorus, was deposited or applied to the opening, it was slightly diffused into the silicon substrate to form an impurity layer 9. This state is shown in FIG. Note that antimony or arsenic may be used as the N-type impurity.

Next, after removing the oxide film 5 on the surface of the silicon substrate 1, a first epitaxial layer 2 a was formed to a thickness of 4 μm on the entire surface of the silicon substrate 1. At this time, the impurity layer 9 is auto-doped from below at the same time as the formation of the first epitaxial layer 2a, so that the N ⁺ high concentration region 3 is formed. At this time, since the impurity layer 9 is auto-doped until it reaches the surface of the first epitaxial layer 2a, there is no need to set complicated conditions such as stopping in the middle of the epitaxial layer. This state is shown in FIG. The high concentration region 3 needs to have a surface concentration at which an epitaxial layer can be grown as a single crystal thereon, and is preferably 1 × 10 ¹⁹ cm ⁻³ or less.

Next, a second epitaxial layer is formed on the entire surface of the first epitaxial layer 2a including the high concentration region 3 by 2 μm.
m, and the high concentration region 3 is embedded therein. This state is shown in FIG.

Next, boron as a P-type impurity was diffused from the surface of the second epitaxial layer 2b to form an annular guard ring layer 4. Thereafter, CVD and contact window etching were performed, and a Schottky metal 6, nickel 7, and aluminum 8 electrodes made of titanium were sequentially formed to complete a Schottky barrier diode. This state is shown in FIG.
(D).

FIG. 3A shows the concentration profile of the Schottky barrier diode of the present invention shown in FIG. 1. The second epitaxial layer 2b is formed thin on the surface, and the high concentration region 3 is 1, the same impurity concentration is maintained from the vicinity of the interface between the second epitaxial layers 2a and 2b to the silicon substrate 1. For this reason, the impurity concentration on the surface of the epitaxial layer can be reduced to ensure easy formation of the barrier, the specific resistance can be kept low, and the forward voltage can be sufficiently reduced. On the other hand, FIG.
FIG. 2 illustrates a concentration profile of a conventional Schottky barrier diode (illustrated in FIG. 5) in which high concentration regions 3 are formed by implanting ions into the epitaxial layer 2.
In the illustrated conventional example, the concentration decreases as approaching the silicon substrate 1 and the specific resistance of this portion increases, so that the forward voltage cannot be sufficiently reduced. However, in the present invention, the specific resistance is reduced and the forward voltage is reduced. The voltage can be lowered sufficiently.

In this embodiment, the case where the N-type silicon substrate is used has been described. However, the present invention is not limited to this, and the same effect can be obtained even when the P-type silicon substrate is used.

[0025]

As described above, according to the present invention, a high-concentration region can be formed without causing a defect on the surface of the epitaxial layer. Therefore, the forward current can be increased without increasing the reverse current IR of the Schottky barrier diode. Voltage VF can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a Schottky barrier diode of the present invention.

FIG. 2 is a diagram illustrating a method for manufacturing a Schottky barrier diode according to the present invention.

3A is a diagram showing a concentration profile of a Schottky barrier diode according to the present invention; FIG. 3B is a diagram showing a concentration profile of a conventional Schottky barrier diode;

FIG. 4 is a sectional view showing a conventional Schottky barrier diode.

FIG. 5 is a sectional view showing a Schottky barrier diode disclosed in Japanese Patent Application Laid-Open No. 8-64845.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 epitaxial layer 2a first epitaxial layer 2b second epitaxial layer 3 high concentration region 4 guard ring layer 5 oxide film 6 Schottky metal (titanium) 7 electrode (nickel) 8 electrode (aluminum) 9 impurity layer

Claims (4)

[Claims] A first step of forming an impurity layer having the same conductivity type as that of the semiconductor substrate in a predetermined region on the surface of the semiconductor substrate; and forming a first epitaxial layer on a main surface of the semiconductor substrate including the impurity layer. Forming the first epitaxial layer and, simultaneously with forming the first epitaxial layer, auto-doping impurities in the impurity layer into the first epitaxial layer, thereby forming the first epitaxial layer in the first epitaxial layer. A third step of forming a high-concentration region having a higher impurity concentration than that of the first epitaxial layer; and a fourth step of forming a second epitaxial layer on the first epitaxial layer including the high-concentration region. And a method for manufacturing a Schottky barrier diode. 2. The method for manufacturing a Schottky barrier diode according to claim 1, wherein in the third step, impurities in the impurity layer are auto-doped until the impurities reach the surface of the first epitaxial layer. 3. The method of claim 1, wherein the thickness of the second epitaxial layer is
2. The method for manufacturing a Schottky barrier diode according to claim 1, wherein the thickness is smaller than the thickness of the epitaxial layer. 4. A first step of forming an N-type impurity layer in a predetermined region on a surface of an N ^++- type silicon substrate; and forming an N-type first layer on a main surface of the silicon substrate including the N-type impurity layer. A second step of forming an epitaxial layer; and, simultaneously with forming the first epitaxial layer, auto-doping the N-type impurity layer into the first epitaxial layer. A third step of forming an N ⁺ -type high-concentration region; and a fourth step of forming an N-type second epitaxial layer on the first epitaxial layer including the high-concentration region. Manufacturing method of barrier diode.