Method for manufacturing a semiconductor device

Abstract

A method of manufacturing a semiconductor device as an RC-IGBT, comprising: - forming two semiconductor elements (4) in spatially separated sub-regions of a first region (2) as an IGBT region of a semiconductor substrate (1); - forming a reflection layer (5) which covers the first region (2) and the semiconductor elements (4) and does not cover a second region (3) as a diode region of the semiconductor substrate (1); and - after forming the reflection layer (5), irradiating the first and second regions (2, 3) of the semiconductor substrate (1) with an electromagnetic wave (6), wherein: - the electromagnetic wave (6) is reflected by the reflection layer (5), - a plurality of holes (8) are formed in the reflection layer (5) to cause a part of the electromagnetic wave (6) to pass through the holes (8), - before the formation of the reflection layer (5), the first and second regions (2, 3) of the semiconductor substrate (1) are irradiated with charged particles in order to introduce crystal defects, - the crystal defects in the second region (3) of the semiconductor substrate (1) are compensated by irradiation with the electromagnetic wave (6), - the reflection layer (5) covers the spatially separated sub-regions of the first region (2) of the semiconductor substrate (1), - the second region (3) of the semiconductor substrate (1) not covered by the reflection layer (5) is formed between the partial regions of the first region (2) of the semiconductor substrate (1), - the reflection layer (5) continuously covers one of the partial regions of the first region (2) of the semiconductor substrate (1), so that crystal defects are left in this partial region of the first region (2) of the semiconductor substrate (1), and - the reflection layer (5) has the plurality of holes (8) in the other partial region of the first region (2) of the semiconductor substrate (1), so that some of the crystal defects in this other partial region of the first region (2) of the semiconductor substrate (1) are compensated.

Description

BACKGROUND OF THE INVENTIONField of InterestThe present invention relates to a method for manufacturing a semiconductor device, in which the semiconductor substrate is irradiated with the electromagnetic wave and locally heated.BackgroundInsulated gate bipolar transistors (IGBTs) are needed to shorten a carrier lifetime to speed up elimination of remaining minority of carriers when a switch is off to be adaptable to high frequencies. A widely used method for shortening lives is a method in which crystal defects are intentionally introduced into a semiconductor substrate by irradiation with charged particles such as electron beams, protons or helium. However, crystal defects are not required for the entire IGBTs, and since crystal defects can induce weakening of withstand voltage, for example, in a non-excited influence region, and crystal defects are not locally introduced. Furthermore, in an RC-IGBT (reverse-conduction IGBT) in which an IBGT and a diode are integrated on a chip, in order to realize miniaturization of a module, it is desirable that lives in the IGBT region are shortened but not in the diode region. For this reason, there is a need for a technique that introduces crystal defects locally.As a method for locally introducing crystal defects, there is available a method in which charged particles are radiated after a shielding object such as a resist is formed on a semiconductor substrate so that charged particles are not radiated to locations where crystal defects are unnecessary. However, when crystal defects are introduced to a depth of several tens to several hundreds μm from the surface of the semiconductor substrate, the resist must also have a thickness of several tens to several hundreds μm. Therefore, light during exposure is difficult to pass through the resist, and patterning is difficult. The amount of the resist used is also large, which may result in an increase in cost.In contrast, a method is proposed that crystal defects can be compensated for by locally heating a semiconductor substrate even when charged particles are uniformly irradiated on the semiconductor substrate. For example, a method is proposed in which a condensed laser beam is used to scan an intended location to heat only around a condensed point without causing temperatures to increase at locations other than the condensed point (e.g., see Patent Literature 1). Further, a method of forming a reflective layer in advance at a region where it is desired to prevent irradiation with a laser beam is proposed (e.g., see Patent Literature 2). In this way, the semiconductor substrate can be locally heated even if a laser beam is irradiated uniformly.Patent Literature 1: JP 62-259437 APatent Literature 2: JP 2014-170 959 AThe publication DE 10 2005 021 302 A1 relates to a method for adjusting the charge carrier lifetime in a semiconductor body, which has two surfaces facing away from one another, in at least one region adjoining one of the surfaces of the semiconductor body. The following method steps are provided in this case: irradiating the semiconductor body with particles via one of the surfaces of the semiconductor body, such that defects are produced in the semiconductor body, and heating the at least one region of the semiconductor body by irradiating the surface of the semiconductor body 100, which is adjoined by this region, with laser light.The document DE 27 05 444 A1 discloses a method for locally limited heating of small regions of a solid body by irradiation with electromagnetic radiation, wherein the underlying solid body is irradiated in individual irradiation pulses through an irradiation mask.SummaryHowever, only methods for locally heating the semiconductor substrate using the reflective layer before a semiconductor element is formed have been disclosed. In order to locally heat the semiconductor substrate after the formation of the semiconductor element having wiring or electrodes, it is necessary to set an irradiation region with an electromagnetic wave such as a laser beam as in the conventional manner.The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a method of manufacturing a semiconductor device suitable for locally heating a semiconductor substrate without adjusting an irradiation range with an electromagnetic wave even after a semiconductor element is formed.This object is achieved by the features of claim 1.Solution of the ProblemA method for manufacturing a semiconductor device as an RC-IGBT according to the present invention includes: forming two semiconductor elements having a wiring or an electrode in spatially separated portions of a first region as an IGBT region of a semiconductor substrate; forming a reflection layer covering the first region and the semiconductor elements and not covering a second region as a diode region of the semiconductor substrate; and after forming the reflection layer, irradiating the first and second regions of the semiconductor substrate with an electromagnetic wave, the electromagnetic wave being reflected by the reflection layer. A plurality of holes are formed in the reflection layer to cause a part of the electromagnetic wave to pass through the holes. Before the formation of the reflective layer, irradiation of the first and second regions of the semiconductor substrate with charged particles is performed to introduce crystal defects, wherein the crystal defects in the second region of the semiconductor substrate are equalized again by the irradiation with the electromagnetic wave. The reflective layer covers the spatially separated partial regions of the first region of the semiconductor substrate. The second region of the semiconductor substrate not covered with the reflection layer is formed between the partial regions of the first region of the semiconductor substrate. The reflective layer continuously covers one of the partial regions of the first region of the semiconductor substrate, so that crystal defects are left in this partial region of the first region of the semiconductor substrate. The reflective layer has the plurality of holes in the other partial region of the first region of the semiconductor substrate, so that some of the crystal defects in this other partial region of the first region of the semiconductor substrate are equalized.Advantageous Effects of the InventionIn the present invention, the first and second regions of the semiconductor substrate are irradiated with the electromagnetic wave after the reflection layer covering the first region and the semiconductor element and not covering the second region is formed. Thereby, it is possible to locally heat the semiconductor substrate without adjusting the irradiation range with the electromagnetic wave even after the semiconductor element is formed.Brief Description of the DrawingsFurther details, features and advantages of the invention are evident from the following description of exemplary embodiments with reference to the drawings. The following shows:FIG. 1 is a cross-sectional view showing a method of manufacturing a semiconductor device according to a first example for explaining the background art of the present invention. FIG. 2 is a cross-sectional view showing a method of manufacturing a semiconductor device according to a second example for explaining the background art of the present invention. FIG. 3 is a cross-sectional view showing a method of manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view showing a method of manufacturing a semiconductor device according to another example for explaining the background art of the present invention. FIG. 5 is a cross-sectional view showing a method of manufacturing a semiconductor device according to another example for explaining the technical background of the present invention.DESCRIPTION OF EMBODIMENTSMethods of manufacturing a semiconductor device according to examples for explaining the background art and according to an embodiment of the present invention will be described with reference to the drawings. The same components are denoted by the same symbols, and the repeated description thereof may be omitted.First Example for Explaining Technical BackgroundFIG. 1 is a cross-sectional view showing a method of manufacturing a semiconductor device according to a first example for explaining the background art of the present invention. First, crystal defects are introduced by irradiating an entire surface including first and second regions 2 and 3 of a semiconductor substrate 1 with charged particles such as an electron beam or ion beam. Next, a semiconductor element 4 including wiring or electrodes is formed in the first region 2 of the semiconductor substrate 1. The semiconductor element 4 includes, for example, an electrode of which an outermost surface is covered with gold, and is an IGBT, a PN diode, a MOSFET, an SBD, or the like.Next, a reflection layer 5 is formed which covers the first region 2 of the semiconductor substrate 1 and the semiconductor element 4 but does not cover the second region 3 of the semiconductor substrate 1. The reflection layer 5 is made of a material such as an aluminum layer having a reflection coefficient of the electromagnetic wave 6 higher than that of the semiconductor substrate 1.Next, the entire surface including the first and second regions 2 and 3 of the semiconductor substrate 1 is irradiated with the electromagnetic wave 6. Thereafter, the reflective layer 5 is removed by etching or the like. The electromagnetic wave 6 is a lamp light, a laser beam, a microwave, or the like, and is, for example, a laser beam having a wavelength of 808 nm. The electromagnetic wave 6 may be condensed using a lens to scan the semiconductor substrate 1, or the electromagnetic wave 6 may be radiated to the entire semiconductor substrate 1.The electromagnetic wave 6 incident on the second region 3 not covered with the reflective layer 5 is absorbed by the semiconductor substrate 1, and thus the second region 3 is locally heated. Crystal defects in the second region 3 are compensated again by the irradiation with the electromagnetic wave 6. On the other hand, since the electromagnetic wave 6 is reflected by the reflection layer 5, the electromagnetic wave 6 does not reach the semiconductor element 4 or the first region 2. therefore, the first region 2 is not heated and crystal defects in the first region 2 are not equalized.As described above, according to the present example, the reflection layer 5 covering the first region 2 and the semiconductor element 4 but not covering the second region 3 is formed and then the entire surface including the first and second regions 2 and 3 of the semiconductor substrate 1 is irradiated with the electromagnetic wave. Thereby, it is possible to locally heat the semiconductor substrate 1 without adjusting the irradiation range with the electromagnetic wave even after the semiconductor element 4 is formed. As a result, it is possible to restore only crystal defects in the second region 3 and leave crystal defects in the first region 2 and prevent a temperature rise of the wiring or electrodes of the semiconductor element 4.In an RC-IGBT, it is desirable that the lifetime is shortened in the IGBT region but not in the diode region. Therefore, the first region 2 is preferably set as the IGBT region, and the second region 3 is preferably set as the diode region.In the non-excited terminal portion, crystal defects introduce degradation in withstand voltage, and thus crystal defects are preferably not locally introduced. Therefore, the first region 2 is preferably set as the active region, and the second region 3 is preferably set as the connection region.Second Example for Explaining Technical BackgroundFIG. 2 is a cross-sectional view showing a method of manufacturing a semiconductor device according to a second example for explaining the background art of the present invention. When a lower part of a metal layer 7 for electrodes or wiring coincides with the area to be non-heated, a material having a reflection coefficient of the electromagnetic wave 6 higher than that of the semiconductor substrate 1 is used as the material of the metal layer 7. That is, the metal layer 7 for electrodes or wiring is used as the reflection layer. This eliminates the need for separately forming a reflective layer, eliminates the need for separately forming and removing the reflective layer, and therefore can reduce the number of processing steps. The other configuration and effects are similar to those of the first example for explaining the technical background of the invention.Embodiment of the Present InventionFIG. 3 is a cross-sectional view showing a method of manufacturing a semiconductor device according to an embodiment of the present invention. A plurality of thin holes 8 are formed in the reflection layer 5 to cause a part of the electromagnetic wave 6 to pass through and the rest of the electromagnetic wave 6 to be reflected. The electromagnetic wave 6 passing through the holes 8 is absorbed by the first region 2 of the semiconductor substrate 1, and its temperature rises. In this way, some crystal defects of the first region 2 are compensated again. The amount of passage of the electromagnetic wave 6 is changed by changing the density of the holes 8, that is, the ratio of an area of the holes 8 to an area of the reflective layer 5, and thus it is possible to control and / or regulate the amount of temperature rise. The other structures and effects are similar to those of the first and second examples for explaining the technical background of the invention.Example for Explaining Technical BackgroundFIG. 4 is a cross-sectional view showing a method of manufacturing a semiconductor device according to another example for explaining the background art of the present invention. The electromagnetic wave is incident diagonally on a main surface of a semiconductor substrate. Therefore, an angle formed between a direction perpendicular to the main surface of the semiconductor substrate 1 and an incident direction of the electromagnetic wave 6 becomes larger than 0 degrees. This allows the electromagnetic wave to be incident directly below the reflection layer 5, making it possible to change a temperature distribution in a depth direction. The remaining structure and effects are similar to those of the above-described methods.Example for Explaining Technical BackgroundFIG. 5 is a cross-sectional view showing a method of manufacturing a semiconductor device according to another example for explaining the technical background of the present invention. The electromagnetic wave 6 is condensed into the semiconductor substrate 1. This allows the temperature inside the semiconductor substrate 1 to rise without the surface temperature of the semiconductor substrate 1 rising. This enables local heating not only in an in-plane direction of the semiconductor substrate 1, but also in a depth direction. The electromagnetic wave 6 is not condensed at the surface of the reflection layer 5, an energy density of the electromagnetic wave 6 condensed at the surface of the reflection layer 5 decreases, and it is possible to suppress a temperature rise of the reflection layer 5 and thereby suppress heat deformation and diffusion of the reflection layer 5. The other structure and effects are similar to those of the above-described methods.Note that the semiconductor substrate 1 is not limited to one made of silicon, but may be made of a wide band gap semiconductor having a wider band gap than silicon. Examples of the wide band gap semiconductor include silicon carbide, a nitride gallium based material, or diamond. The semiconductor device formed of a wide band gap semiconductor has high withstand voltage and high allowable current density, and therefore can be miniaturized. The use of this downsized semiconductor device also allows a semiconductor module including this semiconductor device to be downsized and highly integrated. In addition, since the semiconductor device has high heat resistance, it is possible to miniaturize cooling fins of its heat sink, accommodate an air cooling system instead of its water cooling system, and further miniaturize the semiconductor module. Furthermore, the semiconductor device has low energy loss and high efficiency, and thereby it is possible to provide a more efficient semiconductor module.In summary, a method of manufacturing a semiconductor device includes, among other things, forming a semiconductor element having a wiring or an electrode in a first region of a semiconductor substrate; forming a reflective layer covering the first region and the semiconductor element and not covering a second region of the semiconductor substrate; and, after forming the reflective layer, irradiating the first and second regions of the semiconductor substrate with an electromagnetic wave, the electromagnetic wave being reflected by the reflective layer.List of reference characters1 Semiconductor substrate 2 First region 3 Second region 4 Semiconductor element 5 Reflection layer 6 Electromagnetic wave 7 Metal layer 8 Hole

Claims

A method of manufacturing a semiconductor device as an RC-IGBT, comprising: - forming two semiconductor elements (4) in spatially separated portions of a first region (2) as an IGBT region of a semiconductor substrate (1); - forming a reflection layer (5) covering the first region (2) and the semiconductor elements (4) and not covering a second region (3) as a diode region of the semiconductor substrate (1); and - after forming the reflection layer (5), irradiating the first and second regions (2, 3) of the semiconductor substrate (1) with an electromagnetic wave (6), wherein: - the electromagnetic wave (6) is reflected from the reflection layer (5), - a plurality of holes (8) are formed in the reflection layer (5) to cause a part of the electromagnetic wave (6) to pass through the holes (8), - before the formation of the reflection layer (5), irradiation of the first and the second region (2, 3) of the semiconductor substrate (1) with charged particles is carried out in order to introduce crystal defects, - the crystal defects in the second region (3) of the semiconductor substrate (1) are compensated again by the irradiation with the electromagnetic wave (6), - the reflection layer (5) covers the spatially separated partial regions of the first region (2) of the semiconductor substrate (1), - the second region (3) of the semiconductor substrate (1) not covered with the reflection layer (5) is formed between the partial regions of the first region (2) of the semiconductor substrate (1), - the reflection layer (5) covers one of the partial regions of the first region (2) of the semiconductor substrate (1) continuously, such that crystal defects are left in this partial region of the first region (2) of the semiconductor substrate (1), and - the reflection layer (5) has the plurality of holes (8) in the other partial region of the first region (2) of the semiconductor substrate (1), so that some of the crystal defects in this other partial region of the first region (2) of the semiconductor substrate (1) are compensated for.The method for manufacturing a semiconductor device according to claim 1, wherein an electrode or a metal layer (7) for wiring is used as the reflection layer (5).The method for manufacturing a semiconductor device according to any one of the preceding claims, wherein the electromagnetic wave (6) is directed diagonally incident on a main surface of the semiconductor substrate (1).Method for producing a semiconductor device according to one of the preceding claims, wherein the electromagnetic radiation (6) is condensed into the semiconductor substrate (1).The method for manufacturing a semiconductor device according to any one of the preceding claims, wherein the semiconductor substrate (1) is formed of a wide band gap semiconductor.

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