JP2021097138A - Semiconductor device and manufacturing method for the same - Google Patents

Abstract

To provide a semiconductor device in which the recovery loss can be reduced, and a manufacturing method for the same.SOLUTION: A first n-type buffer layer 2 is formed on a semiconductor substrate 1 in an active region. A second n-type buffer layer 3 is formed on the semiconductor substrate 1 in a termination region. An n-type drift layer 4 is formed on the first n-type buffer layer 2 and the second n-type buffer layer 3. A diode structure is formed on the n-type drift layer 4 in the active region. The first n-type buffer layer 2 has higher impurity concentration than the n-type drift layer 4. The second n-type buffer layer 3 has higher impurity concentration than the first n-type buffer layer 2.SELECTED DRAWING: Figure 1

Description

The present invention relates to a semiconductor device used for an inverter device or the like and a method for manufacturing the same.

A Schottky diode in which the structure of the active region is devised in order to prevent leakage current and reduce forward voltage has been proposed (see, for example, Patent Document 1). However, the terminal region outside the active region is not considered.

Japanese Unexamined Patent Publication No. 2000-58876

When a reverse voltage is applied to the diode during recovery of the inverter device, the depletion layer spreads in the bulk. The electron carriers existing around the depletion layer are discharged, a recovery current flows, and a recovery loss occurs. The depletion layer extends laterally from the active region to the channel stopper in the terminal region. However, the depletion region narrows at a certain angle from the p-type region on the outermost periphery of the active region. Since the distance that the electron moves becomes longer toward the end, the time for the carrier to be discharged becomes longer than that in the active region. Therefore, there is a problem that the recovery loss increases because the recovery current flows for a long time.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a semiconductor device capable of reducing recovery loss and a method for manufacturing the same.

The semiconductor device according to the present invention is formed on a semiconductor substrate, a first n-type buffer layer formed on the semiconductor substrate in an active region, and a terminal region outside the active region on the semiconductor substrate. A second n-type buffer layer, an n-type drift layer formed on the first n-type buffer layer and the second n-type buffer layer, and an n-type drift layer formed in the active region. The first n-type buffer layer has a higher impurity concentration than the n-type drift layer, and the second n-type buffer layer has a higher impurity concentration than the first n-type buffer layer. It is characterized by having.

In the present invention, a second n-type buffer layer having a higher impurity concentration than the first n-type buffer layer in the active region is formed in the terminal region. Therefore, in the terminal region, the distance between the depletion layer in the n-type drift layer and the second n-type buffer layer becomes narrow, and the carrier concentration gradient becomes gentle. This makes it easier for the carrier to come off during recovery, so recovery loss can be reduced.

It is sectional drawing which shows the semiconductor device which concerns on Embodiment 1. FIG. It is sectional drawing which shows the semiconductor device which concerns on Embodiment 2. FIG. It is sectional drawing which shows the semiconductor device which concerns on Embodiment 3. FIG. It is sectional drawing which shows the manufacturing method of the semiconductor device which concerns on Embodiment 4. FIG. It is sectional drawing which shows the manufacturing method of the semiconductor device which concerns on Embodiment 4. FIG. It is sectional drawing which shows the manufacturing method of the semiconductor device which concerns on Embodiment 5. It is sectional drawing which shows the manufacturing method of the semiconductor device which concerns on Embodiment 5. It is sectional drawing which shows the manufacturing method of the semiconductor device which concerns on Embodiment 6. It is sectional drawing which shows the manufacturing method of the semiconductor device which concerns on Embodiment 6. It is sectional drawing which shows the manufacturing method of the semiconductor device which concerns on Embodiment 6.

The semiconductor device and the manufacturing method thereof according to the embodiment will be described with reference to the drawings. The same or corresponding components may be designated by the same reference numerals and the description may be omitted.

Embodiment 1.
FIG. 1 is a cross-sectional view showing a semiconductor device according to the first embodiment. The semiconductor device has an active region and a terminal region outside the active region. The active region is a cell portion through which a current flows during operation of the semiconductor device. The terminal area has a guard ring structure. However, the terminal region is not limited to the guard ring structure, and may be a JTE structure or a RESURF structure. The JTE structure is a structure in which p-type layers are arranged at regular intervals so as to extend the depletion layer in the lateral direction. The RESURF structure is a structure in which an n-type drift layer is formed on a p-type layer and a depletion layer extends vertically to relax an electric field.

The n-type buffer layer 2 is formed on the n + -type substrate 1 in the active region. The n + type buffer layer 3 is formed on the n + type substrate 1 in the terminal region. The n-type drift layer 4 is formed on the n-type buffer layer 2 and the n + -type buffer layer 3.

A p-type layer 5 is formed on the surface of the n-type drift layer 4 in the active region. A guard ring layer 6 is formed on the surface of the n-type drift layer 4 at the outer peripheral portion of the active region. The guard ring layer 6 has a p-type layer 6a and a p ⁺ type layer 6b formed on the surface of the p-type layer 6a. The outer end of the guard ring layer 6 is the boundary between the active region and the terminal region. An oxide film 7 is formed on the guard ring layer 6.

In the active region, the Schottky electrode 8 is Schottky bonded to the upper surface of the n-type drift layer 4 to form a diode structure. Here, in a Schottky diode without the p-type layer 5, when the current increases, the resistance simply increases and the VF increases, so that the chip is destroyed by the power of the current IF × the voltage VF. On the other hand, in the JBS structure in which the p-type layer 5 is formed, a current flows toward the PN structure and conductivity modulation occurs, so that the voltage VF is lowered in a large current region and the power can be reduced. Therefore, the chip is less likely to be destroyed when a large current such as an inrush current flows. Further, by providing the guard ring layer 6, the depletion layer extends outward and the electric field concentration is relaxed, so that the withstand capacity against high dv / dt can be increased.

A surface electrode 9 is formed on the Schottky electrode 8. The surface protective film 10 covers the outer peripheral portion of the surface electrode 9 and the oxide film 7. The back surface electrode 11 is formed on the lower surface of the n + type substrate 1. The material of the Schottky electrode 8 is Ti, the material of the front electrode 9 is AlSi, and the material of the back electrode 11 is Ti / Ni / Au.

The n-type buffer layer 2 has a higher impurity concentration than the n-type drift layer 4. The n + type buffer layer 3 has a higher impurity concentration than the n type buffer layer 2. The impurity concentrations of the n + type substrate 1 and the n + type buffer layer 3 are about the same.

When a reverse voltage is applied to the diode during recovery, the depletion layer 12 spreads in the bulk. The depletion layer 12 extends from the point where it hits the n + type buffer layer 3 in a loose arc in the terminal region. Let θ be the rough angle of the depletion layer 12 at this time. Let L be the lateral length of the termination region in which the n + type buffer layer 3 is provided. Let α be the thickness of the n + type buffer layer 3. Let g be the thickness of the n-type drift layer 4. If g'is defined as g'= L × θ, the relationship of g'+ α ≦ g holds.

As a method for manufacturing a semiconductor device according to the present embodiment, first, an n-type buffer layer 2 is formed on an n + -type substrate 1. Before epitaxially growing the n-type drift layer 4, an injection mask is used to selectively inject n-type impurities into the n-type buffer layer 2 in the terminal region. Next, impurities are diffused along with the epitaxial growth of the n− type drift layer 4 to form the n + type buffer layer 3. The concentration and depth of the n + type buffer layer 3 can be adjusted to desired values by performing a plurality of injections.

As described above, in the present embodiment, the n + type buffer layer 3 having a higher impurity concentration than the n-type buffer layer 2 in the active region is formed in the terminal region. Therefore, the distance between the depletion layer 12 and the n + type buffer layer 3 in the n− type drift layer 4 becomes narrow in the terminal region, and the carrier concentration gradient becomes gentle. This makes it easier for the carrier to come off during recovery, so recovery loss can be reduced.

Embodiment 2.
FIG. 2 is a cross-sectional view showing a semiconductor device according to the second embodiment. An n ++ type buffer layer 13 having a higher impurity concentration than the n + type buffer layer 3 is formed on the n + type substrate 1 in the terminal region at a distance from the active region than the n + type buffer layer 3. The impurity concentration of the n ++ type buffer layer 13 is higher than that of the n + type substrate 1. An n− type drift layer 4 is formed on the n ++ type buffer layer 13.

By arranging the high-concentration n ++ type buffer layer 13 in the portion far from the active region in this way, the carriers in the portion far from the active region can be more easily removed, so that the recovery loss can be reduced as compared with the first embodiment. Can be done. Other configurations and effects are the same as those in the first embodiment.

Embodiment 3.
FIG. 3 is a cross-sectional view showing the semiconductor device according to the third embodiment. The n + type layer 14 is formed below the n− type drift layer 4 in the terminal region and is connected to the n + type buffer layer 3. The n + type layer 14 has a higher impurity concentration than the n type buffer layer 2, and becomes thicker as the distance from the active region increases. As a result, the distance between the depletion layer 12 and the n + type layer 14 becomes narrower in the portion far from the active region, and carriers can easily escape, so that the recovery loss can be reduced as compared with the first embodiment. Other configurations and effects are the same as those in the first embodiment. The impurity concentrations of the n + type buffer layer 3 and the n + type layer 14 do not have to be the same.

Embodiment 4.
4 and 5 are cross-sectional views showing a method of manufacturing the semiconductor device according to the fourth embodiment. First, as shown in FIG. 4, the n-type impurity 15 is selectively injected into the upper surface of the n + -type substrate 1 with the first energy in the terminal region. At this time, in the active region, the n + type substrate 1 is covered with a mask pattern (not shown) such as a photoresist so that the impurity 15 is not injected.

Next, as shown in FIG. 5, the n-type buffer layer 2 and the n-type drift layer 4 are epitaxially grown on the n + type substrate 1 in both the active region and the terminal region. Impurities 15 are thermally diffused from the n + type substrate 1 to the n type buffer layer 2 with epitaxial growth to form a high concentration n + type buffer layer 3 in the terminal region. After that, the semiconductor device according to the first embodiment is manufactured by forming the p-type layer 5 and the like.

As described above, in the present embodiment, the high-concentration n + type buffer layer 3 is formed by injecting impurities. As a result, the manufacturing cost can be reduced as compared with the case where the n + type buffer layer 3 is formed by performing epitaxial growth a plurality of times.

Embodiment 5.
6 and 7 are cross-sectional views showing a method of manufacturing the semiconductor device according to the fifth embodiment. First, as in the first embodiment, the n-type impurity 15 is selectively injected into the upper surface of the n + type substrate 1 with the first energy in the terminal region. Next, as shown in FIG. 6, the n-type impurity 16 is selectively injected into the upper surface of the n + type substrate 1 with the second energy in the region of the terminal region separated from the active region. The first energy and the second energy may be the same or different.

Next, as shown in FIG. 7, the n-type buffer layer 2 and the n-type drift layer 4 are epitaxially grown on the n + type substrate 1 in both the active region and the terminal region. Impurities 15 are thermally diffused from the n + type substrate 1 to the n type buffer layer 2 with epitaxial growth to form a high concentration n + type buffer layer 3 in the terminal region. Further, along with epitaxial growth, impurities 15 and 16 are thermally diffused from the n + type substrate 1 to the n type buffer layer 2 to form an n ++ type buffer layer 13 having an impurity concentration higher than that of the n + type buffer layer 3 in the terminal region. Subsequent steps are the same as in the fourth embodiment. As a result, the semiconductor device according to the second embodiment is manufactured. By forming the n ++ type buffer layer 13 by injecting impurities, the manufacturing cost can be reduced as compared with the case where the n ++ type buffer layer 13 is formed by performing epitaxial growth a plurality of times.

Embodiment 6.
FIG. 8-10 is a cross-sectional view showing a method of manufacturing the semiconductor device according to the sixth embodiment. The steps up to the step of forming the n-type drift layer 4 are the same as those in the first embodiment. Next, as shown in FIG. 8, in the region of the terminal region separated from the active region, the n-type impurity 17 is added to the lower portion of the n-type drift layer 4 from the upper surface side of the n-type drift layer 4 as a third energy. Inject with. Next, as shown in FIG. 9, in a region of the terminal region further distant from the active region, an n-type impurity 18 is added to the lower portion of the n-type drift layer 4 from the upper surface side of the n-type drift layer 4. Inject with energy. Since the fourth energy is smaller than the third energy, the impurity 18 is injected into the n-type drift layer 4 from the upper surface to a portion shallower than the impurity 17. In this way, the n-type impurities 17 and 18 are injected stepwise from the upper surface side of the n-type drift layer 4 to the lower part of the n-type drift layer 4 in the terminal region.

Next, as shown in FIG. 10, impurities 17 and 18 are activated to connect to the n + type buffer layer 3, have a higher impurity concentration than the n-type buffer layer 2, and become thicker as the distance from the active region increases. The n + type layer 14 is formed. Subsequent steps are the same as in the fourth embodiment. As a result, the semiconductor device according to the third embodiment is manufactured. By forming the n + type layer 14 by injecting impurities, the manufacturing cost can be reduced as compared with the case where the n + type layer 14 is formed by performing epitaxial growth a plurality of times.

Although the case where the present invention is applied to a Schottky barrier diode made of silicon carbide has been described as Embodiment 1-6, the present invention is not limited to this, and the present invention can also be applied to a diode made of silicon. However, assuming that the withstand voltage is the same as that of silicon carbide, the thickness of the drift layer is about 10 times thicker in the case of silicon, so injection and diffusion are repeated many times in order to form the n + type layer 14 of the sixth embodiment. Will have to be implemented.

Further, since the silicon carbide semiconductor device has high withstand voltage resistance and allowable current density, it can be miniaturized. By using this miniaturized silicon carbide semiconductor device, the semiconductor module incorporating this silicon carbide semiconductor device can also be miniaturized and highly integrated. Further, since the silicon carbide semiconductor device has high heat resistance, the heat radiation fins of the heat sink can be miniaturized, and the water-cooled portion can be air-cooled, so that the semiconductor module can be further miniaturized. Further, since the power loss of the silicon carbide semiconductor device is low and the efficiency is high, the efficiency of the semiconductor module can be improved.

1 n + type substrate (semiconductor substrate), 2 n type buffer layer (first n type buffer layer), 3 n + type buffer layer (second n type buffer layer), 4 n-type drift layer (n type drift layer) ), 13 n ++ type buffer layer (third n type buffer layer), 14 n + type layer (n type layer), 15-18 impurities

Claims (7)

With a semiconductor substrate
A first n-type buffer layer formed on the semiconductor substrate in the active region,
A second n-type buffer layer formed on the semiconductor substrate in the terminal region outside the active region, and
The first n-type buffer layer, the n-type drift layer formed on the second n-type buffer layer, and the n-type drift layer.
It has a diode structure formed in the n-type drift layer in the active region, and has a diode structure.
The first n-type buffer layer has a higher impurity concentration than the n-type drift layer.
A semiconductor device characterized in that the second n-type buffer layer has a higher impurity concentration than the first n-type buffer layer. A third n-type buffer layer formed on the semiconductor substrate in the terminal region away from the active region of the second n-type buffer layer and having a higher impurity concentration than the second n-type buffer layer. The semiconductor device according to claim 1, further comprising. It is formed in the lower part of the n-type drift layer in the terminal region, is connected to the second n-type buffer layer, has a higher impurity concentration than the first n-type buffer layer, and becomes thicker as the distance from the active region increases. The semiconductor device according to claim 1, further comprising an n-type layer that becomes thicker. The semiconductor device according to any one of claims 1 to 3, wherein the semiconductor device is a silicon carbide semiconductor device. A step of injecting an n-type first impurity into the upper surface of the semiconductor substrate in the terminal region outside the active region, and
A first n-type buffer layer and an n-type drift layer are epitaxially grown on the semiconductor substrate in both the active region and the termination region, and the first impurity is removed from the semiconductor substrate from the semiconductor substrate along with the epitaxial growth. A step of thermally diffusing the type buffer layer to form a second n-type buffer layer in the terminal region, and
A step of forming a diode structure in the n-type drift layer in the active region is provided.
The first n-type buffer layer has a higher impurity concentration than the n-type drift layer.
A method for manufacturing a semiconductor device, wherein the second n-type buffer layer has a higher impurity concentration than the first n-type buffer layer. A step of injecting an n-type second impurity into the upper surface of the semiconductor substrate in a region of the termination region separated from the active region,
Along with the epitaxial growth, the first impurity and the second impurity are thermally diffused from the semiconductor substrate to the first n-type buffer layer to provide the terminal region with a higher impurity concentration than the second n-type buffer layer. The method for manufacturing a semiconductor device according to claim 5, further comprising a step of forming a third n-type buffer layer having a structure. A step of injecting an n-type second impurity stepwise from the upper surface side of the n-type drift layer to the lower part of the n-type drift layer in the terminal region.
The n-type that activates the second impurity and is connected to the second n-type buffer layer, has a higher impurity concentration than the first n-type buffer layer, and becomes thicker as the distance from the active region increases. The method for manufacturing a semiconductor device according to claim 5, further comprising a step of forming a layer.

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