JP2014146757A - Manufacturing method of silicon-carbide semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, in a silicon-carbide bipolar device, thermal annealing is not suitable as activation annealing after ion implantation since an entire wafer is to be heated but laser annealing is suitable, laser light cannot be absorbed since a higher temperature than silicon is required for activating silicon carbide and in addition a band gap is wide, a temperature is unlikely to rise, and when shortening a wavelength of laser light until it can be absorbed by silicon carbide, the temperature cannot rise as expected since an approach length of a laser is lacking, the temperature locally rises only on an irradiation surface or surface elements are desorbed by an ablation phenomenon.SOLUTION: As a method of activating an impurity element ion implanted to silicon carbide by laser annealing, a laser absorption film is formed on a surface of an ion implantation layer formed on a substrate and laser annealing is then performed, thereby performing activation using a laser of a long wavelength which cannot be absorbed by silicon carbide.

Description

The present invention relates to a method for manufacturing a silicon carbide semiconductor device by activating impurities at a high temperature.

  A silicon carbide power semiconductor device has a wide band gap and a high dielectric breakdown electric field, so that both high breakdown voltage and low on-resistance can be achieved. Furthermore, a bipolar device in which electrons and holes conduct via a pn junction has a large reduction effect in a high breakdown voltage region due to conductivity modulation.

  PN diodes and Insulated Gate Bipolar Transistors (IGBTs) are high breakdown voltage bipolar devices, and if ultrahigh breakdown voltage is realized using silicon carbide, it is expected to reduce power consumption of distribution systems such as smart grids.

  In the manufacturing process of the silicon carbide PN diode and IGBT, the n-type and p-type impurity regions are formed by epitaxial growth or ion implantation and subsequent activation annealing. In particular, when an impurity region is partially formed, ion implantation and activation annealing are widely used. In order to activate the impurity element ion-implanted by the activation annealing, a temperature of about 1600 ° C. or higher is required.

  The on-resistance of a bipolar device greatly depends on the lifetime of minority carriers in the drift layer, but it is known that the lifetime is significantly reduced by a thermal load of 1600 ° C. or higher. It will get worse. Therefore, the activation annealing requires a device for raising the temperature of only the ion implantation layer and protecting the drift layer from a high temperature.

  In addition, since annealing at 1600 ° C. or higher is a high temperature, it is necessary to complete the process before the formation of the oxide film and the electrode in the manufacturing process, which restricts the order of processes.

  From the above, in silicon carbide bipolar devices, thermal annealing is not suitable as activation annealing after ion implantation because the entire wafer is heated, and laser annealing is suitable.

In contrast, in the case of silicon IGBT, in order to reduce the resistance of the substrate, the substrate is removed by polishing after the surface structure process to expose the n-type drift layer on the back surface, and the p-type is thin by ion implantation and laser annealing. A method of forming a layer is possible.
This is because by optimizing the wavelength and output of the laser, only the vicinity of the back surface can be heated to suppress the temperature rise on the front surface side.

  Silicon carbide IGBTs require the same process to reduce on-resistance, but silicon carbide requires a higher temperature than silicon for activation, and can absorb laser light due to its wide band gap. However, the method has not been established since the temperature does not easily rise.

  As a countermeasure, it is conceivable to shorten the wavelength of the laser beam until silicon carbide can be absorbed. In this case, however, the laser penetration length is insufficient and only the irradiated surface temperature rises locally, or the surface element is ablated. The temperature cannot rise as expected due to problems such as desorption.

JP 2004-335815 A JP 2012-199271 A

  As described above, there is a problem of an impurity region activation method by laser annealing that is suitable as activation annealing after ion implantation in a silicon carbide bipolar device.

The present invention first provides the following method.
(1) A method for manufacturing a silicon carbide semiconductor device, the step of forming an impurity region by ion-implanting an impurity element on a silicon carbide substrate (S110), and a carbon film or a metal film on the ion-implanted surface, or A step (S120) of forming a laser absorbing film that can absorb a laser beam composed of a mixed film of the two over the entire surface, and irradiating the surface of the laser absorbing film with a laser beam to heat it to about 1600 degrees Celsius or more. And a step of activating the impurity region with heat from the absorption film (S130).

next,
(2) The manufacture of the silicon carbide semiconductor device according to (1), wherein the impurity ion implantation is performed on a back surface where an epitaxial growth layer is formed on a silicon carbide substrate and the substrate is removed and the epitaxial growth layer is exposed. Method,
and,
(3) The method for manufacturing a silicon carbide semiconductor device according to (2), wherein the ion implantation of the impurity element is an impurity having conductivity opposite to that of the epitaxial growth layer.

next,
(4) The method for manufacturing a silicon carbide semiconductor device according to any one of (1) to (3), wherein the impurity element is ion-implanted so that an n-type impurity and a p-type impurity are separated depending on a region. provide.

next,
(5) In the step of activating the impurity region, an ohmic electrode made of a silicide of metal and silicon carbide or carbide is formed at the same time as the activation, according to any one of (1) to (4) A method for manufacturing a silicon carbide semiconductor device is provided.

Also,
(6) The method of manufacturing a carbonized semiconductor device according to any one of (1) to (5), wherein a wavelength of the laser beam is 240 nm or more.

Finally,
(7) The method for manufacturing a carbide semiconductor device according to any one of (1) to (6), wherein the temperature on the opposite side of the substrate is 1000 ° C. or lower when the laser absorbing film is irradiated with the laser light. When,
(8) The method for manufacturing a carbide semiconductor device according to any one of (1) to (7), wherein the temperature on the opposite side of the substrate is 400 ° C. or lower when the laser absorbing film is irradiated with the laser light. I will provide a.

  According to the present invention, in the present invention, as a method of activating the impurity element ion-implanted into silicon carbide by laser annealing, laser annealing is performed after forming a laser absorption film on the surface of the ion-implanted layer formed on the substrate. This enabled activation using a laser with a long wavelength that silicon carbide cannot absorb.

  Note that Patent Document 1 discloses a method of forming a film on an irradiated surface when laser annealing silicon carbide. However, the purpose of this film is to prevent the transmission of laser light and to suppress the temperature rise under the film, and shows the opposite effect to the present invention.

  Further, in the present invention, by using a refractory metal for the laser absorption film, silicide is formed during laser annealing, and activation and ohmic contact formation can be performed in a single process.

  Patent Document 2 discloses a method in which a refractory metal is formed on silicon, a laser absorption film is formed thereon, and silicide of the refractory metal and silicon is formed by laser irradiation. However, the effect of the present invention is different in that the refractory metal itself functions as a laser absorption film, and is also performed simultaneously with the activation annealing of the ion implantation impurity into silicon carbide.

FIG. 1 is a process diagram showing the steps of the production method of the present invention. FIG. 2 is a diagram showing a conceptual diagram of the configuration of the semiconductor device in each step of the manufacturing method of the present invention. FIG. 3 is a process diagram showing the steps of the method of manufacturing the PN diode described in the first embodiment. FIG. 4 is a process diagram showing a back surface ion implantation activation process in the manufacturing method described in the second embodiment. FIG. 5 is a process diagram showing a back surface ion implantation activation process in the manufacturing method described in the third embodiment.

FIG. 1 is a main process diagram showing the main process of the manufacturing method of the present invention.
Specifically, in the method for manufacturing a silicon carbide semiconductor device, an impurity element is ion-implanted on a silicon carbide substrate to form an impurity region (S110), and a carbon film or a metal film on the ion-implanted surface, or A step (S120) of forming a laser absorbing film that can absorb a laser beam composed of a mixed film of the two over the entire surface, and irradiating the surface of the laser absorbing film with a laser beam to heat it to about 1600 degrees Celsius or more. And a step (S130) of activating the impurity region with heat from the absorption film. This represents a method for manufacturing a silicon carbide semiconductor device.
Each drawing ((2a), (2b), (2c)) in FIG. 2 is a conceptual diagram of the configuration of the semiconductor device in each step (S110 to S130) of the manufacturing method of the present invention, and FIG. It is a conceptual diagram of the semiconductor device manufactured by the manufacturing method of invention.

FIG. 3 is a process diagram showing the steps of a method for manufacturing a PN diode.
First, n-type low-concentration silicon carbide film 7 is formed on n-type silicon carbide substrate 1 by epitaxial growth.
Next, a p-type silicon carbide layer 8 to be the anode 9 is formed on the surface by epitaxial growth or ion implantation (FIG. 3a).
Next, a p-type region 10 serving as a termination structure is formed on the outer periphery of the p-type region by ion implantation (FIG. 3b). When the anode is formed on the entire surface of the wafer by epitaxial growth, a step of removing the p-type layer at the outer peripheral portion by dry etching is performed before the termination is formed.

Thereafter, a carbon film is formed on the surface as a laser absorbing film 3 by resist coating, chemical vapor deposition, sputtering, or the like (FIG. 3c), and the surface is irradiated with laser.
Thereafter, the carbon film is removed by oxygen plasma ashing and sacrificial oxidation. Then, the anode electrode 11 and the cathode electrode 12 are formed on the front and back surfaces to complete (FIG. 3d).

  By such a process, activation thermal annealing of the ion implantation impurity can heat only the periphery of the ion implantation layer on the surface without heating the entire substrate, so that the minority carrier lifetime of the drift layer is not deteriorated and the forward characteristic of the diode is improved. The resistance can be lowered, and the vicinity of the PN junction is heated to deteriorate the carrier lifetime, so that the recovery current during the on / off operation is small and a low switching loss is possible.

  FIG. 4 is a process diagram showing a back surface ion implantation activation process in the manufacturing method according to the present invention.

First, n-type low-concentration silicon carbide film 7 is formed on n-type silicon carbide substrate 1 by epitaxial growth.
For example, in the case of a planar gate type MOSFET, a p-type well region 13 is formed by ion implantation or epitaxial growth, or a combination thereof, and a source region 14 and a p-type contact region 15 are formed depending on the type of semiconductor device. The termination structure 10 is formed by ion implantation (FIG. 4a).

Thereafter, ion implantation impurities are activated by thermal annealing or laser annealing. Next, the substrate is removed from the back side by polishing to expose the epitaxial film, and n-type impurity 16 is ion-implanted into the surface (FIG. 4b).
In the case of an insulated gate bipolar transistor (IGBT), the implanted ions become the p-type impurity 17 and can be divided into an n-type and a p-type depending on the region to form a reverse conducting IGBT.

  After the back surface ion implantation, a laser absorption film 3 made of a carbon film, a metal film, or a mixed film thereof is applied to the surface (FIG. 4c) and formed by chemical vapor deposition, sputtering, etc., and the laser is applied to the surface. Irradiate. When the laser absorbing film contains a metal, simultaneously with activation, the metal and silicon carbide form a compound to form the ohmic electrode 18. Next, the carbon film is removed by oxygen plasma ashing or the like.

  Thereafter, a field oxide film 19, a gate oxide film 20, a gate electrode 21, an interlayer insulating film 22, a source electrode 23, and a wiring metal 24 are sequentially formed on the surface, and a back electrode 25 is formed (FIG. 4d).

  FIG. 5 is a process diagram showing another process of the back surface ion implantation activation in the manufacturing method according to the present invention.

First, n-type low-concentration silicon carbide film 7 is formed on n-type silicon carbide substrate 1 by epitaxial growth.
For example, in the case of a planar gate type MOSFET, a p-type well region 13 is formed by ion implantation or epitaxial growth, or a combination thereof, and a source region 14 and a p-type contact region 15 are formed depending on the type of semiconductor device. The termination structure 10 is formed by ion implantation (FIG. 5a).

  Thereafter, the ion implantation impurities are activated by thermal annealing or laser annealing.

  Thereafter, a field oxide film 19, a gate oxide film 20, a gate electrode 21, an interlayer insulating film 22, a source electrode 23, and a wiring metal 24 are sequentially formed on the surface (FIG. 5b).

  Next, the substrate is removed by polishing from the back side to expose the epitaxial film, and n-type impurity 16 is ion-implanted into the surface. In the case of an insulated gate bipolar transistor (IGBT), the implanted ions become the p-type impurity 17 and can be divided into an n-type and a p-type depending on the region to form a reverse conducting IGBT.

  After the back surface ion implantation, a laser absorption film 3 made of a carbon film, a metal film, or a mixed film thereof is applied to the surface (FIG. 5c), formed by chemical vapor deposition, sputtering, etc., and a laser is applied to the surface Irradiate. When the laser absorbing film contains a metal, simultaneously with activation, the metal and silicon carbide form a compound to form the ohmic electrode 18.

  Next, the carbon film is removed by oxygen plasma ashing or the like, and the back electrode 25 is formed and completed (FIG. 5d).

  The ratio of the absorption by the laser absorption film and the absorption by silicon carbide can be changed depending on the wavelength of the laser used for laser annealing, and the temperature rise on the surface side can be controlled. However, if the wavelength is 240 nm or less, the absorption on the surface of the absorption film is excessive and the absorption film itself sublimes, and the temperature cannot be increased.

  If the laser wavelength and output are optimized and the surface temperature is set to 1000 ° C. or less, it can be carried out after the gate oxide film is formed on the surface side. If the surface side temperature is set to 400 ° C. or less, the surface side is set. It can be implemented after the metal wiring is formed.

  If the back surface can be activated after the surface structure such as the gate oxide film or metal wiring is completed, the substrate can be removed in the final stage process, and there is a risk that the thinned wafer will be damaged by proceeding with the process. Can be reduced.

  In the above-described embodiment, the MOSFET and the IGBT are shown, but the present invention can be applied to all vertical semiconductor devices such as a PN diode, a Schottky diode, and a bipolar junction transistor.

DESCRIPTION OF SYMBOLS 1 Silicon carbide substrate 2 Ion implantation 3 Laser absorption film 4 Impurity region 5 Laser light 6 Active region 7 Low concentration n-type silicon carbide layer 8 p-type silicon carbide layer 9 Anode 10 Termination structure 11 Anode electrode 12 Cathode electrode 13 P-type well region 14 source region 15 p-type contact region 16 n-type impurity region 17 p-type impurity region 18 ohmic electrode 19 field oxide film 20 gate oxide film 21 gate electrode 22 interlayer insulating film 23 source electrode 24 wiring metal 25 back electrode

Claims (8)

A method for manufacturing a silicon carbide semiconductor device, comprising:
Forming an impurity region by ion-implanting an impurity element on the silicon carbide substrate;
Forming a laser absorption film over the entire surface of the ion-implanted surface that can absorb a laser beam composed of a carbon film or a metal film, or a mixture of both;
Irradiating the surface of the laser absorption film with laser light to heat it to about 1600 degrees Celsius or higher, and activating the impurity region with heat from the heated laser absorption film;
A method for manufacturing a silicon carbide semiconductor device, comprising:   2. The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein the impurity ion implantation is performed on a back surface where an epitaxial growth layer is formed on a silicon carbide substrate and the substrate is removed to expose the epitaxial growth layer.   The method for manufacturing a silicon carbide semiconductor device according to claim 2, wherein the ion implantation of the impurity element is an impurity having conductivity opposite to that of the epitaxial growth layer.   4. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the impurity element is ion-implanted so that an n-type impurity and a p-type impurity are separated depending on a region. 5. In the step of activating the impurity region,
5. The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein an ohmic electrode made of a silicide of metal and silicon carbide or carbide is formed simultaneously with the activation.   The method for manufacturing a carbonized semiconductor device according to claim 1, wherein a wavelength of the laser light is 240 nm or more.   7. The method for manufacturing a carbide semiconductor device according to claim 1, wherein when the laser absorption film is irradiated with the laser light, the temperature on the opposite side of the substrate is 1000 ° C. or lower.   8. The method for manufacturing a carbide semiconductor device according to claim 1, wherein when the laser absorption film is irradiated with the laser light, the temperature on the opposite side of the substrate is 400 ° C. or lower.

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