JP2016009695A - Semiconductor device manufacturing method and laser annealing apparatus - Google Patents

Abstract

In general, the present invention provides a technique for suppressing a temperature rise in a semiconductor substrate without adding a new heat insulation structure or the like when an annealing process is performed on the semiconductor substrate using laser light. It is the purpose. In the present invention, an annealing process is performed by irradiating a silicon carbide semiconductor substrate with a laser beam from one main surface side, and one of the silicon carbide semiconductor substrates is subjected to an annealing process. An inert gas is sprayed on the main surface side of silicon carbide semiconductor substrate 10 to cool it. [Selection] Figure 9

Description

  The present invention relates to a semiconductor device manufacturing method and a laser annealing apparatus.

  In power electronics equipment, insulated gate bipolar transistors (IGBT) and metal-oxide-semiconductor field- are used as means for switching between execution and stop of power supply for driving a load such as an electric motor. A switching element or a rectifying element such as an effect transistor (MOSFET) is used.

  Other switching elements or rectifying elements include a Schottky barrier diode (SBD), a pn diode, a bipolar junction transistor (BJT), a thyristor, and a gate turn off (GTO) thyristor.

  A semiconductor device formed of a silicon carbide (SiC) semiconductor has a higher voltage than a device formed of a silicon (Si) semiconductor and is excellent in a large current operation and a high temperature operation. Therefore, a semiconductor device formed of a silicon carbide semiconductor is expected as a next-generation power semiconductor device. Currently, in the field of silicon carbide semiconductor devices, development of low-resistance silicon carbide semiconductor devices is energetically aimed at realizing further reduction in loss.

  Of the silicon carbide semiconductor devices, when the carriers pass through the silicon carbide substrate in the vertical direction during operation, electrodes need to be provided on the back side of the silicon carbide semiconductor substrate. In this case, it is required to lower the contact resistance between the n-type silicon carbide (drain electrode) and the back electrode on the back side of the silicon carbide semiconductor substrate. In order to realize a low resistance contact, a metal silicide, which is a compound of metal and silicon (Si), is formed between a drain electrode formed of silicon carbide and a back electrode formed of metal. ing.

  In order to further reduce the resistance of a silicon carbide semiconductor device, a silicon carbide substrate is thinly processed to reduce element resistance. In a method for manufacturing a silicon carbide semiconductor device using a thin silicon carbide substrate, it is desirable that the number of processes for performing processing on the thin silicon carbide substrate be small. This is because the probability that a thin silicon carbide substrate will break in the processing step increases. Therefore, it is desirable to fabricate the element structure arranged on the surface of the silicon carbide semiconductor substrate, then thinly process the silicon carbide semiconductor substrate, and then form the back surface structure on the back surface of the silicon carbide semiconductor substrate.

  When forming the back surface structure, the ohmic electrode is formed by annealing only the back surface of the silicon carbide semiconductor substrate at a high temperature of about 1000 ° C. while maintaining the element structure on the surface of the silicon carbide semiconductor substrate at a low temperature. Need to form. One method for achieving this is laser annealing in which local heating is performed using a short pulse laser.

  A method for forming an ohmic electrode by laser annealing on a silicon carbide semiconductor substrate is disclosed in, for example, Patent Document 1 and Patent Document 2.

  In this method, first, the silicon carbide semiconductor substrate is thinly processed by polishing the back surface of the silicon carbide semiconductor substrate.

  Next, a nickel (Ni) film is deposited on the back surface of the silicon carbide semiconductor substrate, and then the nickel film is heated by irradiation with laser light. Thereby, a nickel silicide (NiSi) layer is formed at the interface between the nickel film and the silicon carbide semiconductor substrate. Since the nickel silicide layer is superior in ohmic characteristics to the silicon carbide semiconductor substrate, the nickel silicide layer becomes an ohmic electrode.

JP 2008-135611 A JP 2011-100948 A

  Usually, since the spot diameter of the laser beam is smaller than the area of the silicon carbide semiconductor substrate on which the ohmic electrode is formed, the ohmic electrode is formed by moving the laser beam relative to the silicon carbide semiconductor substrate for irradiation. Is done.

  When an ohmic electrode is formed by irradiating a silicon carbide semiconductor substrate with laser light, the metal film irradiated with the laser light and the silicon carbide semiconductor substrate are locally heated to 1000 ° C. or higher. Thereby, a part of the heat generated from the laser light irradiation part is released into the atmosphere, and the atmospheric temperature rises.

  In order to stably form a low-resistance ohmic electrode, it is necessary to first irradiate the metal film with the first laser beam and then irradiate the metal film with the second laser beam. In that case, the second laser light irradiation is performed partially overlapping the position where the laser light was first irradiated. Therefore, the atmosphere around the metal film to which the second laser beam irradiation is performed is already warmed by the first laser beam irradiation. In addition, heat storage is also generated in the silicon carbide semiconductor substrate at the position where the second laser light irradiation is performed and the chuck stage that holds the silicon carbide semiconductor substrate.

  Due to these two factors, the temperature of the element structure on the surface of the silicon carbide semiconductor substrate gradually increases depending on the integrated irradiation time of the laser light. As a simple solution, it is conceivable to cool the silicon carbide semiconductor substrate held by a method such as water cooling of the chuck stage to suppress the temperature rise of the surface element structure, but the cooling measures significantly increase the cost. Because it is expected, it is not a desirable means.

  In the method of manufacturing a silicon carbide semiconductor device disclosed in Patent Document 1, when a silicon carbide semiconductor substrate is thinly processed to a thickness of, for example, about 150 μm or less, a silicon carbide semiconductor substrate is formed when a nickel silicide layer is formed by laser light irradiation. There is a concern that heat is conducted to the element structure on the surface of the element, and the temperature of the element structure rises to a level sufficient to thermally destroy the element structure.

  In the method for manufacturing a silicon carbide semiconductor device disclosed in Patent Document 2, a conductive heat insulating region is provided between the silicon carbide semiconductor substrate and the back electrode. And when the laser annealing process is performed on the back electrode by the heat insulating region, heat transfer to the surface side of the silicon carbide semiconductor substrate is suppressed, and thermal damage to the element structure is reduced. However, there is a problem that the addition of a new heat insulation region causes an increase in resistance and an increase in cost.

  The present invention has been made to solve the above-described problems. In general, when an annealing process is performed on a semiconductor substrate using a laser beam, the semiconductor is not added without adding a new heat insulating structure. It aims at providing the technique which suppresses the temperature rise in a board | substrate.

  In the method for manufacturing a semiconductor device according to one embodiment of the present invention, a semiconductor substrate is irradiated with laser light from one main surface side, whereby annealing treatment is performed. An inert gas is sprayed on one main surface side to cool the semiconductor substrate.

  A laser annealing apparatus according to one embodiment of the present invention includes a configuration for supplying the inert gas and a configuration for irradiating the semiconductor substrate with the laser light.

  According to the said aspect of this invention, the air | atmosphere in the location where a laser beam is irradiated flows with the inert gas sprayed on one main surface of a semiconductor substrate, and is maintained at fixed temperature. Therefore, the laser beam irradiation is performed in the atmosphere maintained at a constant temperature by an inert gas, and as a result, the annealing process can be stably performed.

  The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

It is sectional drawing which shows the manufacturing process of the manufacturing method of the semiconductor device regarding embodiment. It is sectional drawing which shows the manufacturing process of the manufacturing method of the semiconductor device regarding embodiment. It is sectional drawing which shows the manufacturing process of the manufacturing method of the semiconductor device regarding embodiment. It is sectional drawing which shows the manufacturing process of the manufacturing method of the semiconductor device regarding embodiment. It is sectional drawing which shows the manufacturing process of the manufacturing method of the semiconductor device regarding embodiment. It is sectional drawing which shows the manufacturing process of the manufacturing method of the semiconductor device regarding embodiment. It is a schematic diagram which shows the optical path of the laser beam in a laser annealing apparatus. It is a schematic diagram which illustrates the method of scanning a laser beam to the metal film formed in the back surface of a silicon carbide semiconductor substrate. It is a schematic diagram which illustrates the supply mechanism and discharge | emission mechanism of an inert gas at the time of scanning a laser beam in the metal film whole surface. It is a schematic diagram which shows the positional relationship of the silicon carbide semiconductor substrate irradiated with a laser beam, an inert gas supply mechanism, and an inert gas discharge mechanism. It is a schematic diagram which illustrates the other method of scanning a laser beam to the metal film formed in the back surface of a silicon carbide semiconductor substrate. It is a schematic diagram which illustrates the other method of scanning a laser beam to the metal film formed in the back surface of a silicon carbide semiconductor substrate. It is sectional drawing which shows the device structure after the laser annealing regarding embodiment. It is a schematic diagram which illustrates the other method of scanning a laser beam to the metal film formed in the back surface of a silicon carbide semiconductor substrate. It is a schematic diagram which illustrates the other method of scanning a laser beam to the metal film formed in the back surface of a silicon carbide semiconductor substrate. It is a schematic diagram which illustrates another form of the supply mechanism and discharge | emission mechanism of an inert gas at the time of scanning a laser beam in the metal film whole surface. It is a schematic diagram for demonstrating the structure of the inert gas supply mechanism regarding embodiment.

  Hereinafter, embodiments will be described with reference to the accompanying drawings. Note that the drawings are schematically shown, and the mutual relationship between the sizes and positions of the images shown in the different drawings is not necessarily described accurately, and can be appropriately changed. Moreover, in the following description, the same code | symbol is attached | subjected and shown in the same component, and those names and functions are also the same. Therefore, the detailed description about them may be omitted.

  In the following description, terms that mean a specific position and direction such as “top”, “bottom”, “side”, “bottom”, “front” or “back” may be used. Is used for convenience in order to facilitate understanding of the contents of the embodiment, and is not related to the direction in which it is actually implemented.

<First Embodiment>
<Manufacturing method>
The details of the method for manufacturing the silicon carbide semiconductor device according to the present embodiment will be described with reference to FIGS. Here, a vertical Schottky barrier diode will be described as an example. In the following embodiments, a silicon carbide semiconductor device will be described. However, the present invention is not limited to this, and the present invention can also be applied to a semiconductor device using silicon, for example.

  1 to 6 are cross-sectional views showing the manufacturing steps of the silicon carbide semiconductor device according to this embodiment.

  In the step shown in FIG. 1, n type drift layer 12 is epitaxially grown on surface 11 (main surface) of n + type silicon carbide semiconductor substrate 10.

  In the step shown in FIG. 2, a mask made of an oxide film or the like is formed on the surface layer of the drift layer 12, and then an ion implantation mask is formed by photolithography etching. Note that the mask is not shown in FIG.

  Aluminum ions are selectively implanted from above the ion implantation mask to form an ion implantation region. Then, after removing the ion implantation mask, heat treatment is performed in an argon atmosphere in order to activate the implanted aluminum ions. By this heat treatment step, a plurality of p-type ion implantation regions 13 are formed.

  In the process shown in FIG. 3, a Schottky electrode 20 made of, for example, Ti is partially formed on the surface of the drift layer 12. Next, a wiring electrode 21 made of, for example, Al is formed on the surface of the Schottky electrode 20. Further, in order to improve the breakdown voltage, a protective film 30 made of polyimide, for example, is formed. Schottky electrode 20 is arranged so as to partially cover the surface of ion implantation region 13. The protective film 30 is formed so as to cover the end of the wiring electrode 21, the end of the Schottky electrode 20, and the surface of the ion implantation region 13. Thus, an element structure is formed on surface 11 of silicon carbide semiconductor substrate 10.

  In the process shown in FIG. 4, in order to realize low resistance, back surface 14 (main surface) that is the surface opposite to surface 11 of silicon carbide semiconductor substrate 10 is mechanically ground and polished, and silicon carbide semiconductor substrate is obtained. Decrease the thickness of 10. For example, the silicon carbide semiconductor substrate 10 is ground and polished until the thickness becomes about 150 μm.

  In the step shown in FIG. 5, metal film 40 is deposited on back surface 14 of thinned silicon carbide semiconductor substrate 10. As a material of the metal film 40, for example, Ni, Ti, Mo, W, or Ta can be assumed. The thickness of the metal film 40 can be set to 100 nm, for example.

  Next, an ohmic electrode forming process using the laser beam 50 is performed. Examples of the wavelength of the laser beam 50 to be irradiated include 355 nm and 532 nm. Further, the laser beam 50 to be irradiated is a spot laser beam that irradiates a range narrower than the entire surface of the back surface 14 of the silicon carbide semiconductor substrate 10. By irradiating the metal film 40 with the laser beam 50, The back surface 14 of the silicon semiconductor substrate 10 is reacted to form a silicide layer (annealing process).

  Here, an inert gas supply method and an exhaust method for suppressing a temperature rise on the surface 11, a laser beam energy setting method, a laser beam scanning method, and a combination thereof will be described.

<Configuration>
FIG. 7 is a schematic diagram showing an optical path of laser light in the laser annealing apparatus.

  The laser beam 50 emitted from the laser oscillator 60 is shaped into a predetermined laser beam spot profile by passing through an optical system 61 that shapes the spot of the laser beam 50. For example, a laser beam spot profile where there is a region where the energy density is constant near the center of the spot, or by extending the laser beam irradiation range in the vertical or horizontal direction, it can be shaped into a rectangular shape other than a circle. A laser beam spot profile is assumed.

  Thereafter, the optical path of the laser beam 50 is bent by the galvanometer mirror 62 so that the metal film 40 formed on the back surface 14 of the silicon carbide semiconductor substrate 10 is irradiated with the laser beam 50 that is a spot laser beam. In FIG. 7, the stage 63 on which the silicon carbide semiconductor substrate 10 is disposed is not moved, and the galvano mirror 62 is rotated to adjust the optical path of the laser light 50, and is formed on the back surface 14 of the silicon carbide semiconductor substrate 10. The entire surface of the metal film 40 is scanned.

<Action>
FIG. 8 is a schematic view illustrating a method of scanning the metal film 40 formed on the back surface 14 of the silicon carbide semiconductor substrate 10 with laser light.

  As an example of the order of scanning with laser light, first, the first line 100 on the metal film 40 is advanced along the traveling direction 1000 and reaches the end point position 101 of the first line 100, and then the second line. It moves to the starting point position 201 of 200. Then, the second line 200 is advanced along the traveling direction 2000. Thus, laser beam 50 is scanned over the entire back surface 14 of silicon carbide semiconductor substrate 10. As shown in FIG. 8, the traveling direction of the laser light in the second line 200 is opposite to the traveling direction of the laser light in the first line 100.

  FIG. 9 is a schematic view illustrating an inert gas supply mechanism and a discharge mechanism when laser light is scanned over the entire surface of the metal film 40.

  FIG. 10 is a schematic diagram showing a positional relationship among silicon carbide semiconductor substrate 10 irradiated with laser light, inert gas supply mechanism 400, and inert gas discharge mechanism 500. In FIGS. 9 and 10, an inert gas flow 300 is shown. Although not shown in FIG. 10, the laser light is emitted by the laser annealing apparatus provided with each configuration for irradiating the laser light 50 shown in FIG. 7 and the inert gas supply mechanism 400 and the inert gas discharge mechanism 500. 50 irradiation and supply of inert gas can be performed.

  The inert gas is supplied by an inert gas supply mechanism 400 arranged so as to surround the silicon carbide semiconductor substrate 10. Inert gas supply mechanism 400 is a ring-shaped mechanism having a diameter approximately 1.1 to 1.6 times that of silicon carbide semiconductor substrate 10, and is provided on the inner wall of inert gas supply mechanism 400. An inert gas is blown against the silicon carbide semiconductor substrate 10 through the active gas supply hole 401.

  At this time, the inert gas supply hole 401 is disposed at substantially the same height as the back surface 14 of the silicon carbide semiconductor substrate 10 to which the laser light is irradiated, and the inert gas is approximately in the back surface 14 of the silicon carbide semiconductor substrate 10. It is supplied horizontally and toward the center of the substrate. That is, the inert gas has a flow velocity component that goes inward in the radial direction of silicon carbide semiconductor substrate 10.

  Inert gas discharge mechanism 500 is a cylindrical mechanism disposed so as to cover the upper surface of back surface 14 of silicon carbide semiconductor substrate 10. Inert gas discharge mechanism 500 exhausts the inert gas supplied to back surface 14 of silicon carbide semiconductor substrate 10 in a direction away from back surface 14 by exhausting from the top of the cylindrical structure. That is, the inert gas is exhausted in a direction away from the back surface 14 of the silicon carbide semiconductor substrate 10.

  The flow rate of the inert gas is set so that the element structure formed on the surface 11 of the silicon carbide semiconductor substrate 10 does not exceed a predetermined temperature (for example, 300 ° C.). The flow rate of the inert gas can be 1 to 20 L / m (1000 to 20000 sccm). In the present embodiment, the total flow rate is 2.0 L / m (liter / minute = 2000 sccm). The temperature of the inert gas was set to 10 to 30 ° C., and the temperature at which the silicon carbide semiconductor substrate 10 could be cooled to 350 ° C. or less. Nitrogen, helium, argon or krypton can be used as the inert gas component. In this embodiment, nitrogen is used. The height of the cylinder is high enough to produce a vertical inert gas flow path inside the cylinder.

  9 and 10, inert gas supply mechanism 400 and inert gas discharge mechanism 500 are arranged sufficiently close to each other in the height direction (the normal direction of back surface 14 of silicon carbide semiconductor substrate 10). Is desirable. 9 and 10, the inert gas supply mechanism 400 and the inert gas discharge mechanism 500 are arranged apart from each other. However, the inert gas supply mechanism 400 is inactive as a part of the inert gas discharge mechanism 500. It may be connected to the lower part of the gas discharge mechanism 500.

In the step shown in FIG. 6, the back electrode 42 is formed on the surface of the silicide layer 40a (ohmic electrode) formed in the step shown in FIG. Here, before forming the back electrode 42, an oxide film or the like formed on the surface of the silicide layer 40a (ohmic electrode) may be etched using Ar ⁺ ions or the like.

  In the present embodiment, the Schottky barrier diode is described as an example of the silicon carbide semiconductor element device, but the present invention can be similarly applied to other vertical power semiconductor elements such as MOSFETs. Further, in the present embodiment, the case where the laser beam 50 is irradiated to the position where the metal film 40 is formed is shown, but even if laser annealing is performed without using the metal film 40, the ambient temperature rises. It can be adopted as a method for suppressing the above.

<Effect>
Below, the effect by this embodiment is illustrated.

  According to the present embodiment, in the method for manufacturing a semiconductor device, the silicon carbide semiconductor substrate 10 is irradiated with the laser beam 50 from one main surface side, whereby annealing is performed. An inert gas is blown onto one main surface side of silicon semiconductor substrate 10 to cool silicon carbide semiconductor substrate 10.

  According to such a configuration, the atmosphere at the location where the laser beam 50 is irradiated flows by the inert gas blown onto one main surface of the silicon carbide semiconductor substrate 10 and is kept at a constant temperature. Therefore, the irradiation of the laser beam 50 is performed in the atmosphere maintained at a constant temperature by an inert gas, and as a result, the annealing process can be stably performed.

  In addition, since silicon carbide semiconductor substrate 10 is cooled, deformation of the resin film present on surface 11 of silicon carbide semiconductor substrate 10 is suppressed. For example, when the resin film is polyimide, it is deformed at 350 ° C. or higher. Therefore, the temperature and flow rate of the inert gas may be adjusted so that the temperature of the surface 11 of the silicon carbide semiconductor substrate 10 is 350 ° C. or lower.

  In addition, although structures other than these structures can be omitted as appropriate, the above-described effects can be produced even when any structure shown in this specification is appropriately added.

  In addition, according to the present embodiment, an element structure is formed on the surface 11 of the silicon carbide semiconductor substrate 10, and the metal film 40 is formed on the back surface 14 that is the surface opposite to the surface 11 of the silicon carbide semiconductor substrate 10. Then, annealing is performed by irradiating the metal film 40 with the laser beam 50. In the annealing process, the back surface 14 of the silicon carbide semiconductor substrate 10 is parallel to the back surface 14 of the silicon carbide semiconductor substrate 10. An inert gas having a flow velocity component is blown to cool silicon carbide semiconductor substrate 10.

  According to such a configuration, the air at the location where the metal film 40 is located flows by the inert gas blown to the back surface 14 of the silicon carbide semiconductor substrate 10 and is kept at a constant temperature. Therefore, the irradiation of the laser beam 50 is performed in the atmosphere maintained at a constant temperature by an inert gas, and as a result, an ohmic electrode having a low resistance can be stably formed.

  Further, according to the present embodiment, the inert gas has a flow velocity component that goes inward in the radial direction of silicon carbide semiconductor substrate 10 and is exhausted in a direction away from back surface 14 of silicon carbide semiconductor substrate 10.

  According to such a configuration, when the metal film 40 is irradiated with the laser light 50 for the second time and then the metal film 40 is irradiated with the laser light 50 for the second time, the metal film 40 is The air whose temperature has been raised by the first irradiation with the laser beam 50 at the position where it is located is quickly exhausted after the first irradiation with the laser beam 50. Therefore, the second irradiation with the laser beam 50 is performed in the atmosphere kept at a constant temperature by an inert gas, and as a result, an ohmic electrode having a low resistance can be stably formed.

Second Embodiment
In the following, the same components as those described in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

<Action>
FIGS. 11 and 12 are schematic views illustrating another method of scanning the metal film 40 formed on the back surface 14 of the silicon carbide semiconductor substrate 10 with laser light. In the present embodiment, for the purpose of suppressing the temperature rise of the element structure on the surface 11 of the silicon carbide semiconductor substrate 10, scanning is performed so that the laser beam 50 is irradiated twice on the same location. Then, laser beam 50 is scanned over the entire back surface 14 of silicon carbide semiconductor substrate 10. FIG. 11 is a diagram regarding the first laser beam irradiation, and FIG. 12 is a diagram regarding the second laser beam irradiation. In the present embodiment, it is desirable that a metal that forms a carbon precipitate by a silicidation reaction with silicon carbide, such as Ni, is used for the metal film 40.

  As an example of the order of scanning with laser light, first, the first line 100 on the metal film 40 is advanced along the traveling direction 1000 and reaches the end point position 101 of the first line 100, and then the second line. It moves to the starting point position 201 of 200. Then, the second line 200 is advanced along the traveling direction 2000. As shown in FIG. 11, the traveling direction of the laser light in the second line 200 is opposite to the traveling direction of the laser light in the first line 100.

  As shown in FIG. 11, in the first irradiation, for example, if laser irradiation is performed with energy that Ni and the back surface 14 of the silicon carbide semiconductor substrate 10 react to form nickel silicide and carbon deposits, for example. Good. Since the silicidation reaction between Ni and silicon carbide occurs at about 500 ° C. or higher, it is sufficient to irradiate with low-energy laser light as compared with the case shown in the first embodiment. Alternatively, irradiation with a higher scanning speed is sufficient as compared with the case shown in the first embodiment. Irradiating laser light with low energy directly leads to longer life of the laser, leading to cost reduction. Irradiation at a high scanning speed leads to an improvement in throughput.

<Configuration>
FIG. 13 is a cross-sectional view showing the device structure after laser annealing.

  As shown in FIG. 13, the carbon precipitate generated by the first irradiation is generated as a graphite layer 40 b on the outermost surface of the back surface 14 of the silicon carbide semiconductor substrate 10. That is, when metal film 40 undergoes a silicidation reaction by laser irradiation, silicide layer 40a on back surface 14 of silicon carbide semiconductor substrate 10 and graphite layer 40b on the surface of silicide layer 40a are formed.

  As shown in FIG. 12, the second laser light irradiation is performed on the silicide layer 40a. For example, the line 600 is formed by the second laser light scanning. As a result, the second laser light irradiation is performed not only on the silicide layer 40a but also on the graphite layer 40b. Compared with the case where the metal film 40 is irradiated with the laser light, the laser light on the irradiation target is irradiated. The absorption rate of is extremely high. Moreover, since the graphite layer 40b has high thermal conductivity, the energy of the irradiated laser beam is efficiently diffused in the in-plane direction.

  Therefore, in the second irradiation in the present embodiment, it is sufficient to irradiate the laser beam with low energy as compared with the case of the first embodiment while suppressing the temperature rise of the element structure. Alternatively, irradiation with a higher scanning speed is sufficient as compared with the case shown in the first embodiment.

<Effect>
Below, the effect by this embodiment is illustrated.

  According to the present embodiment, the annealing treatment is performed on the metal film 40 with the laser beam 50 irradiating each portion of the back surface 14 of the silicon carbide semiconductor substrate 10 twice, while the back surface 14 of the silicon carbide semiconductor substrate 10 is irradiated. This is done by scanning over the entire surface.

  According to such a configuration, since the second laser beam irradiation is performed on the silicide layer 40a formed by the first laser beam irradiation, compared with the case where the laser beam irradiation is performed on the metal film 40. , The light absorption rate is significantly improved. Moreover, since the graphite layer 40b has high thermal conductivity, the energy of the irradiated laser beam is efficiently diffused in the in-plane direction. Therefore, it is sufficient to use low energy laser light for the second laser light irradiation. Alternatively, laser light irradiation with a high scanning speed is sufficient.

<Third Embodiment>
In the following, the same components as those described in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

<Action>
FIGS. 14 and 15 are schematic views illustrating another method of scanning the metal film 40 formed on the back surface 14 of the silicon carbide semiconductor substrate 10 with laser light. In the present embodiment, a scanning method when irradiating the laser beam 50 is devised for the purpose of suppressing the temperature rise of the element structure on the surface 11 of the silicon carbide semiconductor substrate 10. Specifically, the entire surface of the silicon carbide semiconductor substrate 10 is irradiated with laser light in a plurality of times. In the present embodiment, as an example, a method of irradiating the entire surface of the silicon carbide semiconductor substrate 10 in two steps will be described. FIG. 14 is a diagram regarding the first laser beam irradiation, and FIG. 15 is a diagram regarding the second laser beam irradiation.

  FIG. 14 shows a state where the first irradiation is completed, which is in the middle of irradiation when laser beam 50 is irradiated to the entire surface of silicon carbide semiconductor substrate 10. As shown in FIG. 14, the first line 100 and the second line 200 formed by scanning the laser beam 50 are formed with a certain empty width. That is, laser beam 50 is scanned in a partial region of back surface 14 of silicon carbide semiconductor substrate 10. The air width is preferably about 40% to 60% of the spot diameter in the direction perpendicular to the scanning direction of the laser beam.

  By doing in this way, as for the position where the laser beam at the time of forming the 2nd line 200 is irradiated, temperature rise is suppressed compared with the case where it is shown in a 1st embodiment. That is, since the effect of heat storage on the entire silicon carbide semiconductor substrate 10 is mitigated, the temperature rise of the element structure on the surface 11 is suppressed.

  FIG. 15 shows the state of the second irradiation when irradiating the entire surface of silicon carbide semiconductor substrate 10 with laser beam 50. As shown in FIG. 15, in the second irradiation, the region 600 of the back surface 14 of the silicon carbide semiconductor substrate 10 that has not been irradiated by the first irradiation is irradiated, and a line 600 formed by the second laser beam is formed. Form. That is, scanning is performed in a region other than the partial region of back surface 14 of silicon carbide semiconductor substrate 10. The point that the effect of heat storage is alleviated is the same as in the first irradiation.

  In the example shown in FIG. 15, the partial regions where the first irradiation is performed are alternately arranged on the back surface 14 of the silicon carbide semiconductor substrate 10 with regions other than the partial regions where the second irradiation is performed. The

<Effect>
As described above, according to the laser light irradiation method in the present embodiment, it is possible to mitigate the effect of heat storage on the silicon carbide semiconductor substrate 10 and the chuck stage. In addition, since the same location is not irradiated multiple times as shown in the second embodiment, an increase in the temperature of the element structure can be suppressed without reducing the throughput. In the present embodiment, the method of irradiating the entire surface of silicon carbide semiconductor substrate 10 in two portions has been described, but the same effect can be obtained even more times.

<Fourth embodiment>
In the following, the same components as those described in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

  In the present embodiment, another embodiment will be described with respect to the laser light irradiation method shown in the first embodiment.

  The contact resistance value of the silicide layer (ohmic electrode) formed on the back surface 14 of the silicon carbide semiconductor substrate 10 is generally required to be about 1/100 of the resistance value of the entire device. In the vertical power semiconductor device, the higher the breakdown voltage, the thicker the drift layer, so that the drift resistance increases and the resistance value of the entire device increases. That is, the required contact resistance value varies depending on the breakdown voltage of the device. That is, an increase in contact resistance value is allowed as the device has a higher breakdown voltage. The contact resistance value is increased by irradiation with a high scanning speed or irradiation with low energy. Irradiation with a high scanning speed or irradiation with low energy directly leads to suppression of the temperature rise of the element structure, and also leads to cost reduction and throughput improvement.

<Fifth Embodiment>
In the following, the same components as those described in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

<Action>
FIG. 16 is a schematic view illustrating another form of the inert gas supply mechanism and discharge mechanism when the laser beam is scanned over the entire surface of the metal film 40. FIG. 17 is a schematic diagram for explaining the structure of the inert gas supply mechanism 500a. 16 and 17, an inert gas flow 300a is shown.

  As shown in FIG. 16, inert gas supply mechanism 500 a is a cylindrical mechanism that is arranged to cover the upper surface of back surface 14 of silicon carbide semiconductor substrate 10. The inert gas supply hole 501 is disposed on the inner wall of the inert gas supply mechanism 500a, and as shown in FIG. 17, the inert gas is supplied toward the center of the silicon carbide semiconductor substrate 10. The direction in which the hole is drilled is determined.

  Inert gas discharge mechanism 400a is a ring-shaped mechanism that is disposed so as to surround silicon carbide semiconductor substrate 10 and has a diameter that is approximately 1.1 to 1.6 times that of silicon carbide semiconductor substrate 10. The inert gas supplied by the active gas supply mechanism 500a is exhausted to the outside of the silicon carbide semiconductor substrate 10 through an inert gas discharge hole (not shown) formed in the inner wall of the inert gas discharge mechanism 400a. That is, the inert gas has a flow velocity component that goes outward in the radial direction of silicon carbide semiconductor substrate 10. Then, the inert gas is exhausted to the outside in the radial direction of silicon carbide semiconductor substrate 10.

<Effect>
According to the present embodiment, the inert gas is uniformly supplied to the entire surface of the silicon carbide semiconductor substrate 10 to suppress the temperature rise of the element structure and to form a more uniform ohmic contact in the surface.

<Modification>
In each of the above embodiments, the material, material, dimension, shape, relative arrangement relationship, or implementation condition of each component may be described, but these are examples in all aspects, and The invention is not limited to that described. Thus, countless variations not illustrated are envisaged within the scope of the present invention. For example, a case where an arbitrary component is deformed, added or omitted, and at least one component in at least one embodiment is extracted and combined with a component in another embodiment are included. .

  In addition, as long as no contradiction occurs, “one or more” components described as being provided with “one” in each of the above embodiments may be provided. Furthermore, a constituent element constituting the invention is a conceptual unit, and includes a case where one constituent element includes a plurality of structures and a case where one constituent element corresponds to a part of the structure.

  Also, the description herein is referred to for all purposes of the present invention, and none is admitted to be prior art.

  DESCRIPTION OF SYMBOLS 10 Silicon carbide semiconductor substrate, 11 surface, 12 drift layer, 13 ion implantation area | region, 14 back surface, 20 Schottky electrode, 21 wiring electrode, 30 protective film, 40 metal film, 40a silicide layer, 40b graphite layer, 42 back surface electrode, 50 laser beam, 60 laser oscillator, 61 optical system, 62 galvanometer mirror, 63 stage, 100 first line, 101 end point position, 200 second line, 201 start point position, 400, 500a inert gas supply mechanism, 400a, 500 Active gas discharge mechanism, 401,501 Inert gas supply hole, 600 lines, 1000, 2000 direction of travel.

Claims (11)

An annealing process is performed by irradiating the semiconductor substrate with laser light from one main surface side.
In the annealing process, an inert gas is sprayed on the one main surface side of the semiconductor substrate, and the semiconductor substrate is cooled.
A method for manufacturing a semiconductor device. On the surface of the semiconductor substrate, an element structure is formed,
On the back surface, which is the surface opposite to the surface of the semiconductor substrate, a metal film is formed,
Annealing treatment is performed by irradiating the metal film with laser light,
During the annealing treatment, the inert gas having a flow velocity component in a direction parallel to the back surface of the semiconductor substrate is sprayed on the back surface of the semiconductor substrate, and the semiconductor substrate is cooled.
A method for manufacturing a semiconductor device according to claim 1. Before the metal film is formed, the back surface of the semiconductor substrate is ground.
A method for manufacturing a semiconductor device according to claim 2. The annealing treatment is performed by scanning the metal film with a spot laser beam that irradiates a narrower range than the entire back surface of the semiconductor substrate over the entire back surface of the semiconductor substrate.
A method for manufacturing a semiconductor device according to claim 2. In the annealing treatment, the spot laser beam is scanned over the entire back surface of the semiconductor substrate while irradiating each portion of the back surface of the semiconductor substrate twice with respect to the metal film. Made,
A method for manufacturing a semiconductor device according to claim 4. In the annealing treatment, the spot laser beam is scanned in the partial region on the back surface of the semiconductor substrate and then scanned in a region other than the partial region on the back surface of the semiconductor substrate. Made by
A method for manufacturing a semiconductor device according to claim 4. The partial regions are alternately arranged with regions other than the partial regions on the back surface of the semiconductor substrate.
A method for manufacturing a semiconductor device according to claim 6. The inert gas has the flow velocity component toward the inside in the radial direction of the semiconductor substrate, and is exhausted in a direction away from the back surface of the semiconductor substrate.
The method for manufacturing a semiconductor device according to claim 2. The inert gas has the flow velocity component toward the outside in the radial direction of the semiconductor substrate, and is exhausted to the outside in the radial direction of the semiconductor substrate.
The method for manufacturing a semiconductor device according to claim 2. The semiconductor substrate is made of silicon carbide.
The method for manufacturing a semiconductor device according to claim 1. A configuration for supplying the inert gas according to claim 8 or 9,
A structure for irradiating the semiconductor substrate with the laser light,
Laser annealing equipment.

Images