JP6743752B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method of manufacturing a semiconductor device, which locally irradiates an electromagnetic wave to heat a semiconductor substrate.

In the insulated gate bipolar transistor (IGBT), it is necessary to shorten the carrier lifetime in order to expedite the disappearance of the remaining minority carriers when the switch is turned off and to cope with a high frequency. As one of the methods of shortening the lifetime, a method of intentionally introducing crystal defects into a semiconductor substrate by irradiating charged particles such as electron beams, protons and helium is widely used. However, crystal defects are not required for the entire IGBT. For example, crystal defects are not locally introduced in the termination region where no current flows because crystal defects cause a reduction in breakdown voltage. Further, also in the RC-IGBT (reverse conduction IGBT) in which the IGBT and the diode are integrated on one chip to realize the miniaturization of the module, it is desired to shorten the lifetime in the IGBT region but not to shorten the diode region. Therefore, a technique for locally introducing crystal defects is required.

As a method for locally introducing crystal defects, there is a method in which a shield such as a resist is patterned on a semiconductor substrate and then irradiated so that charged particles are not irradiated to an unnecessary portion. However, when crystal defects are introduced from the surface of the semiconductor substrate to a depth of several tens to several hundreds μm, the resist thickness is also required to be several tens to several hundreds μm. Therefore, light cannot pass through the resist during exposure, and patterning is difficult. In addition, the amount of resist used is large and the cost increases.

On the other hand, a method has been proposed in which even if the semiconductor substrate is uniformly irradiated with charged particles, the semiconductor substrate is locally heated and crystal defects can be locally recovered. For example, a method has been proposed in which a focused laser beam is scanned at an intended location and only the periphery of the focusing point is heated without raising the temperature other than the focusing point (see, for example, Patent Document 1). Further, a method has been proposed in which a reflective film is formed in advance on a region where laser irradiation is not desired (for example, refer to Patent Document 2). As a result, the semiconductor substrate can be locally heated even if the laser is uniformly irradiated.

JP 62-259437 A JP, 2014-170959, A

However, only the method of locally heating the semiconductor substrate using the reflective film before forming the semiconductor element has been disclosed. In order to locally heat the semiconductor substrate after forming the semiconductor element including the wiring or the electrode, it has been necessary to adjust the irradiation range of electromagnetic waves such as laser as in the conventional case.

The present invention has been made in order to solve the above-mentioned problems, and the purpose thereof is a semiconductor capable of locally heating a semiconductor substrate without adjusting the irradiation range of electromagnetic waves even after forming a semiconductor element. A method for manufacturing a device is obtained.

A method of manufacturing a semiconductor device according to the present invention includes a step of forming a semiconductor element including a wiring or an electrode in a first region of a semiconductor substrate, and a step of covering the first region and the semiconductor element in a second region of the semiconductor substrate. The step of forming a reflective film that does not cover the area of 1) and the step of irradiating the first and second areas of the semiconductor substrate with an electromagnetic wave after forming the reflective film, the electromagnetic wave being reflected by the reflective film. The electromagnetic wave incident on the second region is absorbed by the semiconductor substrate, and the second region is locally heated .

In the present invention, the first and second regions of the semiconductor substrate are irradiated with electromagnetic waves after forming the reflective film that covers the first region and the semiconductor element and does not cover the second region. Thereby, even after the semiconductor element is formed, the semiconductor substrate can be locally heated without adjusting the irradiation range of the electromagnetic wave.

FIG. 7 is a cross-sectional view showing the method of manufacturing the semiconductor device according to the first embodiment of the present invention. FIG. 7 is a cross-sectional view showing the method of manufacturing the semiconductor device according to the second embodiment of the present invention. FIG. 9 is a cross-sectional view showing the method of manufacturing a semiconductor device according to the third embodiment of the present invention. FIG. 11 is a cross-sectional view showing the method of manufacturing the semiconductor device according to the fourth embodiment of the present invention. FIG. 13 is a cross-sectional view showing the method of manufacturing the semiconductor device according to the fifth embodiment of the present invention.

A method for manufacturing a semiconductor device according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repeated description may be omitted.

Embodiment 1.
1A to 1D are cross-sectional views showing a method of manufacturing a semiconductor device according to a first embodiment of the present invention. First, the entire surface of the semiconductor substrate 1 including the first and second regions 2 and 3 is irradiated with charged particles such as an electron beam or an ion beam to introduce crystal defects. Next, the semiconductor element 4 including the wiring or the electrode is formed in the first region 2 of the semiconductor substrate 1. For example, the semiconductor element 4 includes an electrode whose outermost surface is covered with gold, and is an IGBT, a PN diode, a MOSFET, an SBD, or the like.

Next, the reflective film 5 that covers the first region 2 and the semiconductor element 4 of the semiconductor substrate 1 but does not cover the second region 3 of the semiconductor substrate 1 is formed. The reflection film 5 is made of a material having a higher reflectance for the electromagnetic wave 6 than the semiconductor substrate 1, and is, for example, an aluminum film.

Next, the entire surface of the semiconductor substrate 1 including the first and second regions 2 and 3 is irradiated with the electromagnetic wave 6. After that, the reflection film 5 is removed by etching or the like. The electromagnetic wave 6 is a lamp, a laser, a microwave or the like, for example, a laser having a wavelength of 808 nm. The electromagnetic wave 6 may be condensed by a lens to scan the semiconductor substrate 1, or the entire surface of the semiconductor substrate 1 may be irradiated with the electromagnetic wave 6.

The electromagnetic wave 6 incident on the second region 3 which is not covered with the reflective film 5 is absorbed by the semiconductor substrate 1, so that the second region 3 is locally heated. The irradiation of the electromagnetic wave 6 recovers the crystal defects in the second region 3. On the other hand, since the electromagnetic wave 6 is reflected by the reflective film 5, the electromagnetic wave 6 does not reach the semiconductor element 4 and the first region 2. Therefore, the first region 2 is not heated, and the crystal defects in the first region 2 are not recovered.

As described above, in the present embodiment, the first and second regions of the semiconductor substrate 1 are formed after forming the reflective film 5 that covers the first region 2 and the semiconductor element 4 but does not cover the second region 3. The entire surface including 2, 3 is irradiated with electromagnetic waves. Thereby, even after the semiconductor element 4 is formed, the semiconductor substrate 1 can be locally heated without adjusting the irradiation range of the electromagnetic wave. As a result, only the crystal defects in the second region 3 can be recovered, the crystal defects in the first region 2 can be left without being recovered, and the temperature rise of the wiring or electrode of the semiconductor element 4 can be prevented.

In the RC-IGBT, the IGBT region is desired to have a short lifetime, but the diode region is not desired to be short. Therefore, it is preferable that the first region 2 is an IGBT region and the second region 3 is a diode region.

Further, in the terminal region where current does not flow, crystal defects cause a decrease in withstand voltage, so it is not desirable to introduce crystal defects locally. Therefore, it is preferable that the first region 2 is the active region and the second region 3 is the termination region.

Embodiment 2.
FIG. 2 is a cross-sectional view showing the method of manufacturing a semiconductor device according to the second embodiment of the present invention. When the lower portion of the metal film 7 for electrodes or wirings coincides with a region which is not desired to be heated, a material having a reflectance of the electromagnetic wave 6 higher than that of the semiconductor substrate 1 is used as the material of the metal film 7. That is, the metal film 7 for electrodes or wiring is used as the reflective film. As a result, there is no need to separately form a reflective film, and there is no need to separately form and remove a reflective film, and the number of processing steps can be reduced. Other configurations and effects are similar to those of the first embodiment.

Embodiment 3.
FIG. 3 is a cross-sectional view showing the method of manufacturing a semiconductor device according to the third embodiment of the present invention. A plurality of minute holes 8 are formed in the reflective film 5 so that a part of the electromagnetic wave 6 is transmitted and the rest is reflected. This transmitted electromagnetic wave 6 is absorbed by the first region 2 of the semiconductor substrate 1, and the temperature rises. As a result, some of the crystal defects in the first region 2 are recovered. By changing the density of the holes 8, that is, the ratio of the area of the reflective film 5 to the area of the holes 8, the amount of transmission of the electromagnetic wave 6 changes, so that the amount of temperature rise can be controlled. Other configurations and effects are similar to those of the first or second embodiment.

Fourth Embodiment
FIG. 4 is a cross-sectional view showing the method of manufacturing a semiconductor device according to the fourth embodiment of the present invention. Electromagnetic waves are obliquely incident on the main surface of the semiconductor substrate. Therefore, the angle formed by the direction perpendicular to the main surface of the semiconductor substrate 1 and the incident direction of the electromagnetic wave 6 is larger than 0 degree. As a result, since the electromagnetic wave is also incident directly below the reflective film 5, the temperature distribution in the depth direction can be changed. Other configurations and effects are similar to those of the first to third embodiments.

Embodiment 5.
FIG. 5 is a cross-sectional view showing the method of manufacturing a semiconductor device according to the fifth embodiment of the present invention. The electromagnetic wave 6 is focused inside the semiconductor substrate 1. Thereby, the temperature inside the semiconductor substrate 1 can be raised without raising the temperature on the surface of the semiconductor substrate 1. Therefore, local heating is possible not only in the in-plane direction of the semiconductor substrate 1 but also in the depth direction. Further, the electromagnetic waves are not condensed on the surface of the reflective film 5, the energy density of the condensed electromagnetic waves 6 on the surface of the reflective film 5 is reduced, and the temperature rise of the reflective film 5 can be suppressed, so that the thermal deformation of the reflective film 5 is suppressed. And diffusion can be suppressed. Other configurations and effects are similar to those of the first to fourth embodiments.

The semiconductor substrate 1 is not limited to the one formed of silicon, and may be formed of a wide bandgap semiconductor having a bandgap larger than that of silicon. The wide band gap semiconductor is, for example, silicon carbide, gallium nitride-based material, or diamond. A semiconductor device formed of such a wide band gap semiconductor has high withstand voltage and high permissible current density, and thus can be downsized. By using this downsized semiconductor device, a semiconductor module incorporating this semiconductor device can also be downsized and highly integrated. Further, since the semiconductor device has high heat resistance, the heat radiation fins of the heat sink can be downsized, and the water cooling unit can be air-cooled, so that the semiconductor module can be further downsized. Moreover, since the power loss of the semiconductor device is low and the efficiency is high, the efficiency of the semiconductor module can be improved.

1 semiconductor substrate, 2 1st area|region, 3 2nd area|region, 4 semiconductor element, 5 reflective film, 6 electromagnetic wave, 7 metal film, 8 hole

Claims (9)

Forming a semiconductor element including wiring or electrodes in a first region of a semiconductor substrate;
Forming a reflective film that covers the first region and the semiconductor element and does not cover the second region of the semiconductor substrate;
Irradiating electromagnetic waves to the first and second regions of the semiconductor substrate after forming the reflective film,
The electromagnetic wave is reflected by the reflective film ,
The method of manufacturing a semiconductor device, wherein the electromagnetic wave incident on the second region is absorbed by the semiconductor substrate, and the second region is locally heated . The method further comprises the step of irradiating the first and second regions of the semiconductor substrate with charged particles to introduce crystal defects before forming the reflective film,
The method of manufacturing a semiconductor device according to claim 1, wherein the crystal defects in the second region are recovered by the irradiation of the electromagnetic wave. 3. The method of manufacturing a semiconductor device according to claim 2, wherein the first region is a diode region and the second region is an IGBT region. The method for manufacturing a semiconductor device according to claim 2, wherein the first region is an active region and the second region is a termination region. The method for manufacturing a semiconductor device according to claim 1, wherein a metal film for electrodes or wiring is used as the reflective film. The method for manufacturing a semiconductor device according to claim 1, wherein a plurality of holes are formed in the reflective film to allow a part of the electromagnetic wave to pass therethrough. 7. The method for manufacturing a semiconductor device according to claim 1, wherein the electromagnetic wave is incident on the main surface of the semiconductor substrate obliquely. The method of manufacturing a semiconductor device according to claim 1, wherein the electromagnetic waves are condensed inside the semiconductor substrate. 9. The method for manufacturing a semiconductor device according to claim 1, wherein the semiconductor substrate is formed of a wide band gap semiconductor.

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