JP2000332265A - Diode and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain reduced depletion characteristic and soft recovery characteristic by forming a new semiconductor during an ordinary semiconductor manufacturing step. SOLUTION: A third N-type semiconductor layer 18 having a large diffusion coefficient is diffused on and near one surface of a first N-type semiconductor layer 2, which is highly doped with an impurity having a small diffusion coefficient. Then, a lightly-doped second N-type semiconductor layer 4 is epitaxially grown on such a surface of the layer 2, and the layer 18 having a large diffusion coefficient is embedded therein. A P-type semiconductor layer 8 is formed by thermally diffusing a P-type impurity over the surface of the layer 4, and a fourth N-type semiconductor layer 20 which is doped more heavily than the layer 4 is formed from the layer 18 having a large diffusion coefficient toward the layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a diode and a method for manufacturing the diode. In particular, the diode relates to a low-loss diode and a soft recovery diode.

[0002]

2. Description of the Related Art Conventionally, there is a diode having a structure as shown in FIG. 6, for example, a Schottky barrier diode for power. In FIG. 6, reference numeral 2 denotes a high concentration of impurities such as arsenic and antimony having a small diffusion coefficient (for example, 1).
An N-type semiconductor substrate (1st to 10th power atoms per cubic centimeter) and having a thickness of about 250 μm (first
N-type semiconductor layer). On this semiconductor substrate 2, a second N-type semiconductor layer 4 having a low concentration (for example, 10 15 atoms per cubic centimeter) and a thickness of about 5 μm is epitaxially grown. This second N-type semiconductor layer 4
P-type impurities such as boron are oxidized and driven from the surface of
A guard ring 8 of a P-type semiconductor layer is formed. Further, a silicon oxide film 10 covering a part of the P-type semiconductor layer 8 and the outer edge is formed. A Schottky barrier metal layer 12 is formed on the surface of the second N-type semiconductor layer 4 including the silicon oxide film 10 by vapor deposition or sputtering of molybdenum, tungsten, chromium, or the like. The anode electrode 14 and the cathode electrode 16 are formed on the surface of the Schottky barrier metal layer 12 and the other surface of the first N-type semiconductor layer 2 by vapor deposition, sputtering, plating, or the like.

Now, when a negative potential is applied to the anode electrode 14 and a positive potential is applied to the cathode electrode 16, the depletion layer is connected to the first N-type semiconductor layer 2 and the second N-type semiconductor layer 4 as shown by a broken line in FIG. From the joint J1 to the outside of the guard ring 8. When the potential applied to the anode electrode 14 and the cathode electrode 16 is increased, the lower A
The electric field concentrates more on the outer side B of the guard ring 8 and breaks down between the junction J1 and the outer side B of the guard ring 8.

[0004] Another diode is, for example, a diode having a structure as shown in FIG. In FIG. 7, 2 is
It is a semiconductor substrate (first N-type semiconductor layer) having a thickness of about 250 μm, containing a high concentration of impurities such as arsenic and antimony having a small diffusion coefficient (for example, 10 18 atoms per cubic centimeter). On this semiconductor substrate 2, a second N-type semiconductor layer having a low concentration (for example, 10 15 atoms per cubic centimeter) and a thickness of about 5 μm is epitaxially grown. Impurities such as boron are oxidized and driven from the surface of the second N-type semiconductor layer 4 to form a P-type semiconductor layer 6 and a P-type semiconductor layer guard ring 8 surrounding the P-type semiconductor layer 6. Furthermore, this P
Silicon oxide film 1 covering the outer edge from a part of die semiconductor layer 6
0 is formed. The anode electrode 14 and the cathode electrode 16 are formed on the surface of the P-type semiconductor layer 6 including the silicon oxide film 10 and the other surface of the first N-type semiconductor layer 2 by vapor deposition, sputtering, plating, or the like.

When a positive potential is applied to the anode electrode 14 and a negative potential is applied to the cathode electrode 16 of the diode thus formed, a current IF flows through the diode in a forward direction as shown in FIG. When the current IF flows, a negative potential is applied to the anode electrode 14 and the cathode electrode 16
When a + potential is applied to the current, the current gradually decreases as shown in FIG. 8, and flows in the reverse direction transiently. After the reverse recovery current Irr having the maximum value flows, the current decreases to 0 with the decrease in the residual carrier.
Becomes

[0006]

In the former diode shown in FIG. 6, when the distance from the junction J1 to the lower portion A of the guard ring 8 is increased, the depletion layer can be expanded and the reverse breakdown voltage can be increased. As the second N-type semiconductor layer 4 becomes thicker, the ON voltage and the loss when a forward current flows through the diode increase.

In the latter diode shown in FIG.
Due to defects in the low-concentration second N-type semiconductor layer 4, the lifetime of the hole is shortened, and the reverse recovery time trr is shortened as shown in FIG. Therefore, the voltage VR applied to the anode electrode 14 and the cathode electrode 16 of the diode is connected to the diode in series and connected to the diode by the inductance of the wiring.
Is a voltage oscillated by a spike-like voltage higher than the voltage applied in a steady state. The effect of this spike voltage on other elements is large, and may destroy other elements.

[0008]

According to the first aspect of the present invention,
A first N-type semiconductor layer having a high concentration of an impurity having a low diffusion coefficient, and a third N-type semiconductor layer having an impurity having a high diffusion coefficient formed at a high concentration on one surface of the first N-type semiconductor layer and a portion near the first surface; A semiconductor layer; a second N-type semiconductor layer formed on one surface of the third N-type semiconductor layer and the first N-type semiconductor layer by epitaxial growth at a low concentration;
The guard ring of the P-type semiconductor layer formed by thermally diffusing P-type impurities from the surface of the second N-type semiconductor layer formed outside the N-type semiconductor layer, and the impurities of the third N-type semiconductor layer are formed by the second N-type semiconductor layer. A fourth N-type semiconductor layer formed by diffusing into the type semiconductor layer; an oxide film formed so as to cover an outer edge of the outer surface of the guard ring;
And a Schottky barrier metal layer formed on the surface of the N-type semiconductor layer.

That is, + is added to the Schottky barrier metal layer side.
When a negative potential is applied to the first N-type semiconductor layer side and a current flows, the voltage drop during this period is small because the impurity concentration of the fourth N-type semiconductor layer is high. Therefore, the voltage drop between the Schottky barrier metal layer and the first N-type semiconductor layer is small, the on-voltage of the diode is reduced, and the loss during mounting is reduced.

According to a second aspect of the present invention, there is provided a first N-type semiconductor layer in which an impurity having a small diffusion coefficient has a high concentration;
One or more fifth N-type semiconductor layers in which an impurity having a large diffusion coefficient is formed at a high concentration on one surface of the semiconductor layer and a part in the vicinity thereof, the fifth N-type semiconductor layer, and the first N-type semiconductor layer A second N-type semiconductor layer formed by epitaxial growth at a low concentration on one surface of the second N-type semiconductor layer; a surface formed on the inside of the fifth N-type semiconductor layer on the surface of the second N-type semiconductor layer; A first P-type semiconductor layer formed by thermally diffusing a P-type impurity from the surface to be formed;
And a guard ring of the semiconductor layer, and one or more sixth N-type semiconductor layers formed by diffusing impurities of the fifth N-type semiconductor layer into the second N-type semiconductor layer.

That is, when a current flows in the forward direction from the first P-type semiconductor layer to the first N-type semiconductor layer,
When a negative potential is applied to the n-type semiconductor layer and a positive potential is applied to the first n-type semiconductor layer, the depletion layer spreads from the lower part of the first p-type semiconductor layer to the sixth semiconductor layer side, and the depletion layer spreads to the highly concentrated sixth n-type semiconductor layer When it reaches, it spreads laterally. Then, the current reaches 0 at a high speed due to a defect in the second N-type semiconductor layer, further flows transiently in the opposite direction, and flows to the maximum reverse recovery current.
At this time, a hole remains between the junction between the first N-type semiconductor layer and the second N-type semiconductor layer and the depletion layer.
The reverse recovery current is gradually recovered to the type semiconductor layer side, and the diode has a soft recovery characteristic.

According to a third aspect of the present invention, there is provided a method for diffusing a high-concentration N-type impurity having a large diffusion coefficient into one surface of a first N-type semiconductor layer having a small diffusion coefficient and a high impurity concentration, and the vicinity thereof. A step of epitaxially growing a low-concentration second N-type semiconductor layer on one surface of the first N-type semiconductor layer and embedding a buried type seventh N-type semiconductor layer formed by the N-type impurity having a large diffusion coefficient;
A P-type impurity is thermally diffused on the surface of the second N-type semiconductor layer to form a P-type semiconductor layer, and a concentration higher than the concentration of the second N-type semiconductor layer from the buried N-type semiconductor layer to the second N-type semiconductor layer. In which the N-type semiconductor layer is formed by diffusion.

That is, an N-type semiconductor layer having a high concentration and a large diffusion coefficient is embedded between a first N-type semiconductor layer having a small diffusion coefficient and a second N-type semiconductor layer having a low concentration. Then, when the P-type semiconductor layer is thermally diffused to the surface of the second N-type semiconductor layer, the buried impurities of the seventh N-type semiconductor layer move to the first N-type semiconductor layer and have a high concentration in the second N-type semiconductor layer. 8th
An N-type semiconductor layer is formed. The high-concentration eighth N-type semiconductor layer inside reduces the voltage drop when a current flows in the forward direction. When a reverse voltage is applied, the depletion layer extending from the P-type semiconductor layer side spreads laterally in the eighth N-type semiconductor layer.

[0014]

FIG. 1 is a schematic sectional view showing an example of a first diode according to the present invention.
And FIG. 2 showing a forming process. Numeral 2 contains an impurity such as arsenic and antimony having a low diffusion coefficient at a high concentration (for example, 10 18 atoms per cubic centimeter) and has a thickness of about 250 μm.
N-type semiconductor layer). As shown in FIG. 2A, phosphorus having a large diffusion coefficient is ion-implanted or diffused from one surface of the N-type semiconductor substrate 2 at a high concentration (for example, 10 18 atoms per cubic centimeter) to form a surface and a surface. A third N-type semiconductor layer 18 is formed in the vicinity.

On the surface of the N-type semiconductor substrate 2 on which the third N-type semiconductor layer 18 is formed, low-density (for example, 10 15 atoms per cubic centimeter) epitaxial growth is performed to a thickness of about 5 μm, as shown in FIG. 2), the second N-type semiconductor layer 4 is formed. The heat during the epitaxial growth causes the growth of the second N-type semiconductor layer 4 and the third N-type semiconductor layer 18
Spread a little inside. On the surface of the second N-type semiconductor layer 4, a P-type impurity such as boron is diffused or ion-implanted from the surface formed outside the third N-type semiconductor layer 18, and then thermally diffused, as shown in FIG. As shown, a guard ring 8 of a P-type semiconductor layer is formed.

When forming the guard ring 8 of the P-type semiconductor layer,
The impurities of the third N-type semiconductor layer 18 diffuse into the second N-type semiconductor layer 4 by the heat of the thermal diffusion to form the fourth N-type semiconductor layer 20. The fourth N-type semiconductor layer 20 has a concentration one digit lower than the impurity concentration of the third N-type semiconductor layer 18, for example, a 10 17 atom per cubic centimeter. Note that the diffusion coefficient of the impurity in the first N-type semiconductor layer 2 is
Since the diffusion coefficient of the impurity in the third N-type semiconductor layer 18 is smaller than that of the impurity in the third N-type semiconductor layer 18, the diffusion coefficient of the impurity in the first semiconductor layer 2 does not diffuse into the second N-type semiconductor layer 4.

Thereafter, a silicon oxide film 10 covering a part of the P-type semiconductor layer 8 and the outer edge is formed, and the surface of the second N-type semiconductor layer 4 including this silicon oxide film is covered with molybdenum, tungsten, and chromium. The Schottky barrier metal layer 12 is formed by vapor deposition or sputtering of such a metal. After the formation of the Schottky barrier metal layer 12, the anode electrode 14 and the cathode electrode 16 are formed on the surface of the Shottky barrier metal layer 12 and the other surface of the first N-type semiconductor layer 2 by vapor deposition, sputtering, plating, or the like. I do.

Now, when a negative potential is applied to the anode electrode 14 and a positive potential is applied to the cathode electrode 16, the depletion layer is separated from the guard ring 8 by the first N-type semiconductor layer 2 and the second N-type, as shown by the broken line in FIG. It goes to the junction J1 with the semiconductor layer 4.
The inner depletion layer is formed between the fourth N-type semiconductor layer 20 and the second N-type semiconductor layer 20.
It extends along the junction J2 with the mold semiconductor layer 4. When the potential applied to the anode electrode 14 and the cathode electrode 16 is increased, the electric field concentrates on the outer side B of the guard ring 8 from the lower part A of the guard ring 8 as in the conventional case, and the junction J1 and the guard J Break down with the outside B of the ring 8.

On the other hand, when a positive potential is applied to the anode electrode 14 and a negative potential is applied to the cathode electrode 16 and a current flows from the anode electrode 14 to the cathode electrode 16, the fourth N-type semiconductor layer 20 and the third N-type semiconductor layer 18. First N-type semiconductor layer 2
, The voltage drop during this period is small. In addition, the thickness of the second N-type semiconductor layer 4 below the Schottky barrier metal layer 12 is reduced, the voltage drop is small, the on-voltage of the diode is reduced, and the mounting loss is reduced.

Next, an embodiment of a second diode according to the present invention will be described with reference to FIG. 3 showing a schematic sectional view, FIG. 4 showing a forming process, and FIG. 5 showing a characteristic diagram. As in the first diode, No. 2 contains a high concentration of impurities such as arsenic and ammonia having a small diffusion coefficient (for example, 10 18 atoms per cubic centimeter) and has a concentration of about 250 μm.
N-type semiconductor substrate (first N-type semiconductor layer) having a thickness of. From one surface of the N-type semiconductor substrate 2, FIG.
As shown in (a), a high concentration of phosphorus having a large diffusion coefficient (for example, 10 18 atoms per cubic centimeter)
Ion implantation or diffusion at the surface and near the surface to form a plurality of fifth
The N-type semiconductor layers 22a, 22b, 22c are formed.

As described above, the fifth N-type semiconductor layers 22a. 22
b. On the surface of the N-type semiconductor substrate 2 on which the substrate 22c is formed,
Low concentrations (eg 10 to 15 per cubic centimeter)
The second N-type semiconductor layer 4 is formed as shown in FIG. The heat during the epitaxial growth causes the growth of the second N-type semiconductor layer 4 and the fifth N-type semiconductor layer 22a,
Reference numerals 22b and 22c slightly diffuse into the second N-type semiconductor layer 4 to be semiconductor layers embedded between the first N-type semiconductor layer 2 and the second N-type semiconductor layer 4. On the surface of the second N-type semiconductor layer 4, the fifth N-type semiconductor layers 22a, 22b, 22c
A P-type impurity such as boron is diffused or ion-implanted from the inner surface and the outer surface to form a first P-type semiconductor layer as shown in FIG. 6 and a guard ring 8 of the second P-type semiconductor layer.

At the time of forming the first P-type semiconductor layer 6 and the guard ring 8 of the second P-type semiconductor layer, heat generated by thermal diffusion causes
The impurities of the fifth N-type semiconductor layers 22a, 22b, 22c are as follows:
The sixth N-type semiconductor layers 24a, 24b, 24c are formed outside the fifth N-type semiconductor layers 22a, 22b, 22c diffused and embedded in the second N-type semiconductor layer 4. The impurity concentration of the sixth N-type semiconductor layers 24a, 24b, 24c is
A concentration one order of magnitude lower than the impurity concentration of the N-type semiconductor layers 22a, 22b, 22c, for example, 10 per cubic centimeter.
Is the 17th power atom. Since the impurity of the first N-type semiconductor layer 2 has a small diffusion coefficient, it does not diffuse into the second N-type semiconductor layer 4.

A silicon oxide film 10 is formed so as to cover the outer edge from a part of the first P-type semiconductor layer 6. The surface of the P-type semiconductor layer 6 including this silicon oxide film 10 and the surface of the first N-type semiconductor layer 2 are formed. An anode electrode 14 and a cathode electrode 16 are formed on another surface by depositing aluminum, sputtering, plating, or the like.

A positive potential is applied to the anode electrode 14 of the second diode thus formed, and the cathode electrode 1
When a negative potential is applied to 6, the holes from the first P-type semiconductor layer 6, the second N-type semiconductor layer 4, the sixth N-type semiconductor layer 24a,
24b, 24c, fifth N-type semiconductor layer 22a, 22b, 2
2c, toward the first N-type semiconductor layer 2, and toward the cathode electrode 16. The first N-type semiconductor layer 2 and the second N-type semiconductor layer 4
Electrons from the (fifth N-type semiconductor layers 22a, 22b, 22c, sixth N-type semiconductor layers 24a, 24b, 24c, and second N-type semiconductor layer 4) travel to the anode electrode 14. As a result, a current IF flows as shown in FIG.

When a negative potential is applied to the anode electrode 14 and a positive potential is applied to the cathode electrode 16 in this state, the first
A depletion layer extends from the junction between the P-type semiconductor layer 6 and the guard ring 8 and the second N-type semiconductor layer 4 to the cathode electrode 16 side, and the highly-concentrated sixth N-type semiconductor layers 24a, 24b, 24
When it reaches c, it spreads out in the horizontal direction as shown in FIG. At this time, the current reaches 0 at a high speed due to the defect of the second N-type semiconductor layer 4, and further transiently flows in the opposite direction.
As shown in the figure, the maximum reverse recovery current Irr flows.

However, each of the sixth N-type semiconductor layers is located between a portion indicated by hatching in FIG. 3, that is, a junction J1 between the first N-type semiconductor layer 2 and the second N-type semiconductor layer 4 and a depletion layer indicated by a broken line. 2
A hole remains in a portion between 4a, 24b and 24c, and the hole is gradually removed from the cathode electrode 16 via the first N-type semiconductor layer 2. Therefore, the current flowing through this diode gradually recovers as shown in FIG.
This diode will have soft recovery characteristics.

Therefore, when a diode having such a soft recovery characteristic is used as a diode connected in parallel to the control element of the inverter circuit, the current becomes 0 at high speed and further soft recovery is performed. As described above, even if the wiring inductance or the like has a large vibration does not occur.

In the second diode, a plurality of fifth N-type semiconductor layers 6 are provided. One fifth N-type semiconductor layer smaller than the surface of the first P-type semiconductor layer 6 is provided below the first P-type semiconductor layer. It may be provided.

[0029]

According to the diode of the first aspect, the thickness of the second N-type semiconductor layer 4 at a portion where the current flows at a low concentration is thin, and the ON voltage when the current flows is reduced. And the loss at the time of mounting can be suppressed low.

In the diode according to the present invention, when a voltage is applied in a reverse direction from a state in which a current flows in a forward direction, a junction between the first N-type semiconductor layer and the second N-type semiconductor layer is reduced.
Holes between the depletion layer are gradually removed, and the diode has a soft recovery characteristic. Therefore, when the diode is used as a diode connected in parallel to the control element of the inverter circuit, the current becomes 0 at high speed, and the current is further soft-recovered. Further, unlike the related art, the spike voltage does not affect other elements, and the other elements are not destroyed.

According to the third aspect of the present invention, the first N-type semiconductor layer and the second N-type semiconductor layer are formed by heat for diffusion for forming the P-type semiconductor layer.
A new high-concentration N-type semiconductor layer is formed by diffusing the high-concentration N-type semiconductor layer embedded between the high-concentration semiconductor layers into the second N-type semiconductor layer, and the new high-concentration N-type semiconductor layer is formed.
It can be formed without adding a special device for forming the mold semiconductor layer, and the process is further simplified.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of the invention described in claim 1;

FIG. 2 is a schematic sectional view in a step of forming the diode of FIG. 1;

FIG. 3 is a schematic sectional view showing an embodiment of the invention described in claim 2;

FIG. 4 is a schematic cross-sectional view in a step of forming the diode of FIG. 3;

5 is an output characteristic diagram of the diode of FIG.

FIG. 6 is a schematic sectional view of a conventional diode.

FIG. 7 is a schematic sectional view of another conventional diode.

FIG. 8 is an output characteristic diagram of the diode of FIG. 7;

[Explanation of symbols]

 2 (first) N-type semiconductor layer 4 (second) N-type semiconductor layer 6 (first) P-type semiconductor layer 8 guard ring 10 silicon oxide film 12 Schottky barrier metal layer 14 anode electrode 16 cathode electrode 18 (third) N-type semiconductor layer 20 (fourth) N-type semiconductor layer 22a, 22b, 22c (fifth) N-type semiconductor layer 24a, 24b, 24c (sixth) N-type semiconductor layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M104 BB13 BB16 BB18 CC03 FF13 FF31 FF35 GG03 HH20

Claims (3)

[Claims] An impurity having a high diffusion coefficient is formed at a high concentration on a first N-type semiconductor layer having an impurity having a low diffusion coefficient at a high concentration, and at one surface of the first N-type semiconductor layer and at a part thereof. A third N-type semiconductor layer, a second N-type semiconductor layer formed on one surface of the third N-type semiconductor layer and the first N-type semiconductor layer by low-density epitaxial growth, and a third N-type semiconductor layer. The guard ring of the P-type semiconductor layer formed by thermally diffusing P-type impurities from the surface of the second N-type semiconductor layer formed further outside, and the impurities of the third N-type semiconductor layer are added to the second N-type semiconductor layer. A fourth N-type semiconductor layer formed by diffusion, an oxide film formed to cover an outer edge of the outer surface of the guard ring, and a Schottky formed on the surface of the second N-type semiconductor layer including the oxide film. Barrier metal layer and A diode. 2. An impurity having a high diffusion coefficient is formed at a high concentration on a first N-type semiconductor layer having an impurity having a low diffusion coefficient at a high concentration, and at one surface of the first semiconductor layer and a part thereof. One or more fifth N-type semiconductor layers;
A second N-type semiconductor layer formed by epitaxial growth at a low concentration on one surface of the N-type semiconductor layer and the first N-type semiconductor layer; and a second N-type semiconductor layer on the surface of the second N-type semiconductor layer. A first P-type semiconductor layer formed by diffusing a P-type impurity from the surface formed and the surface formed outside; a guard ring of the second P-type semiconductor layer; A diode including one or more sixth N-type semiconductor layers formed by thermally diffusing impurities into the second N-type semiconductor layer. 3. A step of diffusing a high-concentration N-type impurity having a large diffusion coefficient into one surface of the first N-type semiconductor layer having a low diffusion coefficient and having a high impurity concentration, and the vicinity thereof, A low-concentration second N-type semiconductor layer is epitaxially grown on one surface of the semiconductor substrate, and a buried type 7N semiconductor layer formed by the N-type impurity having a large diffusion coefficient is formed.
Embedding a p-type semiconductor layer, thermally diffusing a p-type impurity into the surface of the second n-type semiconductor layer to form a p-type semiconductor layer, and removing the second n-type semiconductor layer from the embedded n-type semiconductor layer.
A method for manufacturing a diode, comprising a step of diffusing an N-type semiconductor layer having a concentration higher than that of a second N-type semiconductor layer into an N-type semiconductor layer.