JP7135839B2 - Silicon carbide semiconductor device and manufacturing method thereof - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law November 1, 2017 At the 4th Lecture Meeting of the Advanced Power Semiconductor Subcommittee held at the Nagoya International Conference Center, "Formation of Ohmic Electrode of SiC Device by Laser Annealing -Ni- Formation of back electrode by P-plated film”

Application of Article 30, Paragraph 2 of the Patent Law Jun Kawai, Kazuhiko Sugiura, ``Formation of SiC device ohmic electrode by laser annealing - Formation of backside electrode by Ni-P plating film-'', 4th Lecture Meeting of Advanced Power Semiconductors Section Journal Proceedings, The Japan Society of Applied Physics Advanced Power Semiconductor Subcommittee, November 1, 2017, pp. 169-170

The present invention relates to a SiC semiconductor device capable of reducing the contact resistance of an ohmic electrode of a semiconductor element made of silicon carbide (hereinafter referred to as SiC), and a method of manufacturing the same.

When forming a semiconductor element such as a vertical power device using a SiC substrate, an ohmic electrode that reduces contact resistance when forming an electrode for connecting the device to an electric circuit or the like, especially a drain electrode on the back side of the substrate. It is desired to form

In addition, in order to reduce the on-resistance of the device, after forming various impurity layers and electrodes constituting the device on the front surface side of the SiC substrate, the back surface side of the SiC substrate is ground and thinned to reduce the substrate resistance. is considered to be reduced. In this case, after grinding the back side of the SiC substrate, it is necessary to form an ohmic electrode on the back side. However, when forming the ohmic electrode, various impurity layers and electrodes that make up the device are already formed on the surface side of the SiC substrate, so it is necessary not to give thermal damage to these. becomes. For example, as a technique for preventing thermal damage, a laser annealing technique capable of performing local heating is used.

Here, as a method of forming an ohmic electrode using laser annealing or the like, for example, there is a method of activating ion-implanted impurities by laser annealing. However, in addition to expensive ion implanters, the ion implantation process itself is expensive. Therefore, it is desirable to obtain an ohmic electrode without performing an ion implantation process.

Therefore, in Patent Document 1, a film of Ni (nickel) or the like is formed on SiC as an electrode material, and laser annealing is performed to form a silicide layer that is silicided by bonding with Si contained in SiC, thereby forming an ohmic contact. A method has been proposed to obtain

JP 2013-214657 A

However, problems have arisen such as that good ohmic characteristics cannot be obtained only by forming a silicide layer, and that the adhesion strength between SiC and electrodes is weakened.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a SiC semiconductor device capable of obtaining better ohmic characteristics and increasing the adhesion strength between SiC and an electrode, and a method of manufacturing the same.

In order to achieve the above object, the invention according to claim 1 provides a silicon carbide semiconductor substrate (1) having a front surface (1a) and a rear surface (1b), and at least one of the front surface side and the rear surface side of the silicon carbide semiconductor substrate. In the above, a SiC semiconductor device having an ohmic electrode (11) ohmically connected to silicon carbide, wherein the ohmic electrode is made of Ni containing 0.1 wt% or more and 15 wt% or less of impurity P, The ohmic electrode contains Ni silicide composed of NiSi, Ni ₅ P ₂ is contained in the Ni silicide, and the ohmic electrode has a crystallite diameter Xs measured with an X-ray diffractometer. is 30 nm or more .

Thus, the ohmic electrode in which NiSi is formed by including Ni ₅ P ₂ as Ni silicide has a low contact resistance and a high adhesion strength with SiC. As a result, it is possible to obtain a SiC semiconductor device in which better ohmic characteristics can be obtained and the adhesion strength between SiC and the electrode can be increased.

In the method of manufacturing a SiC semiconductor device according to claims 7 and 8 , Ni containing 0.1 wt % or more and 15 wt % or less of impurity P, which is an impurity, is used as an electrode material on silicon carbide to be ohmic-connected. Then, the metal thin film (110) is irradiated with a laser beam (50), and laser annealing is performed to react Ni with Si in silicon carbide to generate Ni silicide, thereby forming an ohmic electrode. including forming. In the method of manufacturing a SiC semiconductor device according to claim 7, when forming the metal thin film, the laser energy in the laser annealing is set to 8 W or more and the concentration of P is set to 5.5 wt % or less. In the method of manufacturing an SiC semiconductor device according to claim 8, when forming the metal thin film, the laser energy in laser annealing is set to 7 W or more and the concentration of P is set to 6.5 wt % or less.

In this way, the ohmic electrode is formed by laser-annealing a material in which P, which is an impurity, is added to Ni forming silicide as the metal thin film. As a result, better ohmic characteristics can be obtained, and high adhesion strength can be achieved between the SiC and the electrode. Also, in the case of laser annealing, local annealing can be performed in a short period of time, so thermal damage to the device can be suppressed.

It should be noted that the reference numerals in parentheses attached to each component etc. indicate an example of the correspondence relationship between the component etc. and specific components etc. described in the embodiments described later.

1 is a cross-sectional view of a SiC semiconductor device according to a first embodiment; FIG. 2 is a cross-sectional view showing a step of forming a drain electrode in the SiC semiconductor device shown in FIG. 1; FIG. FIG. 10 is a diagram showing the results of examining the contact resistance when laser annealing is performed after forming an Ni layer and when laser annealing is performed after forming a Ni—P layer. FIG. 10 is a diagram showing results of examination of adhesion strength in the case of forming an Ni layer followed by laser annealing and in the case of forming a Ni—P layer followed by laser annealing. FIG. 4 is a diagram showing secondary ion mass spectrometry (hereinafter referred to as SIMS) results when the P concentration in the Ni—P layer is 0.6 wt %. FIG. 10 is a diagram showing SIMS results when the P concentration in the Ni—P layer is 3 wt %; FIG. 4 is a diagram showing the result of examining the structure of a silicide layer by Auger electron spectroscopy (hereinafter referred to as AES); FIG. 2 is a diagram showing the result of examining an electrode structure after sputtering a Ni layer with a P concentration of 3 wt % as an electrode material and then performing laser annealing using an X-diffraction apparatus (hereinafter referred to as XRD). FIG. 4 is a diagram showing the result of an XRD examination of an electrode structure after electroless plating of a Ni—P layer with a P concentration of 3 wt % as an electrode material and subsequent laser annealing. FIG. 4 is a diagram showing the result of an XRD examination of an electrode structure after electroless plating of a Ni—P layer with a P concentration of 11 wt % as an electrode material and subsequent laser annealing. FIG. 10 is a diagram showing the results of examining the contact resistance and the existence ratios of Ni ₅ P ₂ and NiSi when the phosphorus concentration is changed. It is a figure which shows the measurement result of adhesion strength. FIG. 3 is a diagram showing the relationship between the crystallite diameter Xs, which indicates the crystallinity of the main component, and the adhesion strength [N].

An embodiment of the present invention will be described below with reference to the drawings. In addition, in each of the following embodiments, portions that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
Hereinafter, embodiments of the present invention shown in the drawings will be described. First, the SiC semiconductor device according to this embodiment will be described with reference to FIG. In this embodiment, a SiC semiconductor device including a planar vertical power MOSFET as a SiC semiconductor element will be described. This SiC semiconductor device is suitable for application to, for example, an inverter.

A vertical power MOSFET is formed using an n ⁺ -type SiC substrate 1 . The n ⁺ -type SiC substrate 1 has a top surface as a main surface 1a and a bottom surface opposite to the main surface 1a as a back surface 1b, and is made of single crystal SiC. For example, as the n ⁺ -type SiC substrate 1, one having an impurity concentration of 1×10 ¹⁸ cm ⁻³ is used.

On the main surface 1a of the n ⁺ -type SiC substrate 1, there is an n ^- -type epitaxial layer (hereinafter referred to as an n ^- -type epilayer) 2 made of SiC having a lower dopant concentration than the n ⁺ -type SiC substrate 1. Laminated.

P ⁻ -type base regions 3a and 3b having a predetermined depth are formed apart from each other in a predetermined region in the surface layer portion of the n ⁻ -type epitaxial layer 2 . Further, deep base layers 30a, 30b having a partially thickened thickness are provided in the p ⁻ -type base regions 3a, 3b. The deep base layers 30a and 30b are formed in portions that do not overlap with n ⁺ -type source regions 4a and 4b, which will be described later. The thicker portions of the p ⁻ -type base regions 3a and 3b where the deep base layers 30a and 30b are formed have a higher impurity concentration than the thinner portions where the deep base layers 30a and 30b are not formed. It's getting darker. By forming such deep base layers 30a and 30b, the electric field intensity between the n ⁺ -type SiC substrate 1 and the deep base layers 30a and 30b can be increased, making it easier to cause avalanche breakdown at this position. be able to.

An n ⁺ -type source region 4a shallower than the p ⁻ -type base region 3a is formed in a predetermined region in the surface layer of the p ⁻ -type base region 3a. An n ⁺ -type source region 4b shallower than the p ⁻ -type base region 3b is formed in a predetermined region in the surface layer of the p ⁻ -type base region 3b.

Further, n ⁻ -type layer 5a and n ⁺ -type layer 5b are formed on the surfaces of the n ⁻ -type epitaxial layer 2 and the p ⁻ -type base regions 3a and 3b between the n ⁺ -type source regions 4a and 4b ^. An n-type SiC layer 5 made of is extended. That is, the n-type SiC layer 5 is arranged so as to connect the source regions 4a, 4b and the n ⁻ -type epitaxial layer 2 in the surface portions of the p ⁻ -type base regions 3a, 3b. This n-type SiC layer 5 functions as a channel forming layer on the device surface during operation of the device. The n-type SiC layer 5 is hereinafter referred to as a surface channel layer.

The surface channel layer 5 is formed, for example, by ion-implanting n-type impurities into the surfaces of the n ⁻ -type epitaxial layer 2 and the p ⁻ -type base regions 3a and 3b. The dopant concentration of the n ⁻ -type layer 5a located above the p ⁻ -type base regions 3a and 3b in the surface channel layer 5 is lower than the dopant concentrations of the n ⁻ -type epitaxial layer 2 and the p ⁻ -type base regions 3a and 3b. It's becoming Also, the dopant concentration of the n ⁺ -type layer 5b formed on the surface of the n ⁻ -type epilayer 2 is higher than that of the n ⁻ -type epilayer 2 . Thereby, low on-resistance is achieved.

Concave portions 6a and 6b are formed in the surface portions of the p ⁻ type base regions 3a and 3b and the n ⁺ type source regions 4a and 4b. 30a, 30b are exposed.

A gate insulating film 7 made of a silicon oxide film or the like is formed on the upper surface of the surface channel layer 5 and the upper surfaces of the n ⁺ -type source regions 4a and 4b. Further, a gate electrode 8 is formed on the gate insulating film 7, and the gate electrode 8 is covered with an insulating film 9 made of a silicon oxide film or the like. In this way, a vertical power MOSFET, which will be a SiC semiconductor element, is formed on the n ⁺ -type SiC substrate 1 .

A source electrode 10 is formed on the surface 1a side of the n ^{+ -type} SiC substrate 1 so as to cover the insulating film 9 ^. It is connected.

A drain electrode 11 is formed on the back surface 1b side of the n ⁺ -type SiC substrate 1 . The drain electrode 11 is an ohmic electrode that is ohmic-connected to the back surface 1 b of the n ⁺ -type SiC substrate 1 . The drain electrode 11 is made of a material that forms at least one of metal reactants of silicide and carbide by reacting with SiC, and at least a part of the material is made of a metal containing impurities. The drain electrode 11 is formed by laser-annealing a Ni layer (hereinafter referred to as a Ni—P layer) into which P (phosphorus), which is an n-type impurity, is introduced. The P concentration in the Ni layer is set to a relatively low concentration range of 0.1 to 15 wt%. The drain electrode 11 contains metal Ni, Ni ₅ P ₂ , NiSi ₂ and NiSi, and contains at least Ni ₅ P ₂ and NiSi and has good crystallinity.

Metallic Ni is unreacted Ni that has not undergone silicidation or the like. NiSi ₂ is generally formed as Ni silicide, and is a material that is also produced when conventional Ni is used as an electrode material and laser annealing is performed. Ni ₅ P ₂ is produced by introducing P, which is an n-type impurity, as an impurity. Although the function of this Ni ₅ P ₂ is not clear, it is presumed that it functions as a catalyst for the production of NiSi. NiSi is a silicide that has a lower contact resistance with SiC _than NiSi2. This NiSi is produced by introducing an impurity into the electrode material and performing laser annealing.

Although Ni is used as the electrode material here, other electrode materials may be added to Ni. In that case, a structure in which a plurality of electrode materials containing Ni are laminated or mixed can be used. Moreover, when a plurality of electrode materials are used, it is sufficient that at least Ni among them contains P, and it is not necessary that all of the electrode materials contain P. For example, even when a Ni—P layer is used, it is possible to form a laminated structure in which a Mo (molybdenum) layer is formed on SiC and a Ni—P layer is formed thereon. As electrode materials other than Mo, materials such as Ti (titanium), Nb (niobium), Ta (tantalum), and W (tungsten) that react with SiC to form carbides can be applied.

The SiC semiconductor device having the vertical semiconductor element according to the present embodiment is configured by the structure as described above.

Next, a method for manufacturing the vertical power MOSFET shown in FIG. 1 will be described. However, since the basic manufacturing method of the vertical power MOSFET according to this embodiment is the same as the conventional method, the method of forming the drain electrode 11, which is different from the conventional method, will be mainly described.

The vertical power MOSFET according to this embodiment is manufactured through each manufacturing process shown in FIG.

First, as shown in FIG. 2A, an n ⁺ -type SiC substrate 1 having a thickness of 350 μm, for example, is prepared. The n ⁺ -type SiC substrate 1 is manufactured, for example, by slicing an SiC ingot doped with an n-type impurity and then polishing it. Then, although not shown, a device forming step is performed to form at least part of the components of the semiconductor element on the surface side of the n ⁺ -type SiC substrate 1 . That is, after the n ⁻ -type epitaxial layer 2 is epitaxially grown, ions are implanted using a mask (not shown) to form the p ⁻ -type base regions 3a and 3b and the deep base layers 30a and 30b, the n ⁺ -type source region 4a, The formation step of 4b and the formation step of the surface channel layer 5 are performed. Furthermore, by performing the formation process of the gate insulating film 7, the forming process of the gate electrode 8, the forming process of the insulating film 9, the forming process of the source electrode 10, and the like, each component of the vertical power MOSFET is formed as a device.

After that, although not shown, a portion of the n ⁺ -type SiC substrate 1 on the back surface 1b side is removed by grinding and polishing to thin the n ⁺ -type SiC substrate 1 . For example, after the back surface 1b side of the n ⁺ -type SiC substrate 1 is turned upside down and one surface on the opposite side is adhered to a glass substrate, CMP (Chemical Mechanical Polishing) or the like is performed, so that the back surface of the n ⁺ -type SiC substrate 1 is polished. Part of the 1b side is removed. Then, the step of forming the drain electrode 11 on the rear surface 1b of the thinned n ⁺ -type SiC substrate 1 is performed by performing the steps shown in FIGS.

Specifically, as a step shown in FIG. 2B, a metal thin film 110 containing impurities is formed on the rear surface 1b of the n ⁺ -type SiC substrate 1 after thinning. A Ni--P layer is used as the metal thin film 110, and the Ni--P layer is formed by subjecting the back surface 1b of the n ⁺ -type SiC substrate 1 to surface treatment for activation and then performing electroless plating. . The P concentration in the Ni—P layer is in a relatively low concentration range of 0.1 to 15 wt %, and the thickness is, for example, 50 to 300 nm.

Also, in order to form carbide between SiC and SiC, the Ni—P layer may be formed after the Mo layer is formed on the back surface 1b. When the Mo layer is formed, it is preferable that the molar ratio of Ni to Mo is greater than or equal to that of Mo, such as 1 to 2:1. Moreover, P may be included in the mixed metal of Ni and Mo, without being limited to the laminated structure of the Mo layer and the Ni—P layer.

Next, as a step shown in FIG. 2C, laser annealing is performed by irradiating the metal thin film 110 with a laser beam 50 . For example, while scanning using a solid-state laser such as an LD-pumped solid-state laser, the n ⁺ -type SiC substrate 1 on which the metal thin film 110 is formed is scanned on the XY plane, and the laser beam 50 is emitted to the n ⁺ -type SiC substrate 1. is irradiated to the rear surface 1b side. By performing local annealing such as laser annealing in this way, it is possible to form an ohmic junction with the drain electrode 11 by a low-temperature process capable of suppressing an increase in temperature in a region not irradiated with laser. Therefore, it is possible to suppress the influence on devices formed on the surface 1a side of the n ⁺ -type SiC substrate 1 . The low-temperature process referred to here is a temperature at which thermal damage to the device can be suppressed, specifically a temperature at which Al (aluminum), which is generally used as a wiring material for the device, does not melt during the process. It refers to processes at temperatures below °C.

At this time, for example, a solid-state laser having a fundamental wavelength of 1064 nm is used, and the laser light 50 is converted to a wavelength of 355 nm, which is the third harmonic, or 266 nm, which is the fourth harmonic, by a wavelength conversion adapter. These wavelengths can prevent the laser light 50 from transmitting through SiC. Also, the energy density of the laser light 50 is set to 1.4 J/cm ² or more, eg, 1.4 to 3.0 J/cm ² .

As a result, the metal element forming the metal thin film 110, here, Ni and Si contained in the n ⁺ -type SiC substrate 1 undergo a silicidation reaction to generate metal silicide. Further, when the metal thin film 110 contains a metal element such as Mo that can be carbided, the metal element reacts with C contained in the n ⁺ -type SiC substrate 1 to generate metal carbide. In the case of Mo, Mo carbide will be formed.

Thus, the drain electrode 11 as shown in FIG. 2(d) is formed. After that, although not shown, Ti as a barrier metal, Ni as a eutectic material for soldering, Au (gold) as an oxidation protective agent, and the like can be laminated in this order as necessary. Then, a dicing tape is attached to the drain electrode 11 side, peeled off from the glass substrate, and then diced to divide into chips, thereby completing the SiC semiconductor device.

Here, when the drain electrode 11 is formed, as described above, the metal thin film 110 is made to contain impurities in at least one metal of silicide and carbide, and is laser-annealed to form the drain electrode 11. . For this reason, it has become possible to obtain better ohmic characteristics, and it has been possible to achieve a high adhesion strength between the SiC and the electrode. This will be described with reference to experimental results.

First, a Ni—P layer was formed as an electrode material by electroless plating and then laser annealed, and a Ni layer conventionally used as an electrode material was formed by sputtering and then laser annealed. was examined for contact resistance. Regarding the Ni--P layer, the cases where the P concentration was 0.6 wt % and 3 wt % were examined. For laser annealing, the duty ratio of laser light was adjusted so that the laser energy was 8W. FIG. 3 is a diagram showing the results.

As shown in this figure, when the Ni layer was used, the contact resistance was lowered in some cases, but the average of the results of multiple experiments was 0.41 mΩ·cm ² , and the variation was within ± It was 0.10 mΩ·cm ² . On the other hand, when the Ni—P layer is used and the P concentration is 0.6 wt %, the average of the results of multiple experiments is 0.33 mΩ·cm ² , and the variation is ±0.03 mΩ.・^cm2 . When the Ni—P layer was used and the P concentration was 3 wt %, the average of the results of multiple experiments was 0.30 mΩ·cm ² , and the variation was ±0.02 mΩ·cm ² . rice field.

From this experimental result, it can be confirmed that when the Ni--P layer is used and laser annealed, the contact resistance is small on average and its variation is small. From this, it can be seen that a low contact resistance can be stably obtained by performing laser annealing using the Ni—P layer.

Further, when the experiment was conducted under the same conditions as in FIG. 3, the adhesion strength between the electrode material and SiC was examined. The adhesion strength was examined by a tensile strength test in which the electrode material and SiC were pulled in opposite directions to examine the peeling state therebetween. FIG. 4 is a diagram showing the results.

As shown in this figure, when the Ni layer was used, the adhesion strength [N] was 332 [N] when the results of multiple experiments were averaged, and the variation was ±17 [N]. On the other hand, when the Ni-P layer is used and the P concentration is 0.6 wt%, the average of the results of multiple experiments is 1171 [N], and the variation is ±145 [N]. there were. When the Ni—P layer was used and the P concentration was 3 wt %, the average of the results of multiple experiments was 630 [N], and the variation was ±167 [N].

From this experimental result, when laser annealing was performed using the Ni—P layer, although the variation was large, the overall adhesion strength was high, and the adhesion strength was generally more than double that obtained when the Ni layer was used. It can be confirmed that From this, it can be seen that high adhesion strength can be stably obtained by performing laser annealing using the Ni—P layer.

We also investigated the mechanism by which such results are obtained. Specifically, the SiC surface was electrolessly plated with a Ni—P layer and then laser annealed, and the element concentration in the depth direction from the surface of the generated silicide layer to the SiC side was examined by SIMS. Here, too, the investigation was made for each of the cases where the P concentration in the Ni—P layer was 0.6 wt % and 3 wt %. Also, the P concentration in SiC was set to 3.0×10 16 cm ⁻³ so that changes in the P concentration could be easily confirmed. Figures 5 and 6 show those results.

As can be seen from FIGS. 5 and 6, in both cases, the depth profiles of Ni concentration and P concentration in the silicide layer were almost the same. This indicates that P is not segregated in the silicide layer, but diffusely present in the same manner as Ni. Moreover, the analysis by AES was also performed. FIG. 7 shows the results. This result also shows that both P and Ni are diffused and are not segregated. In addition, analysis by transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) was also performed, but in both cases P and Ni diffused together and no segregation was observed. .

Furthermore, in order to clarify the electrode structure, the electrode structure after laser annealing was examined by XRD for the case where the Ni layer was formed by sputtering and the case where the Ni—P layer was formed by electroless plating as the electrode material. . 8, 9A and 9B are diagrams showing the results.

As shown in FIG. 8, NiSi ₂ is mainly produced when the Ni layer is used. NiSi ₂ is a silicide that has a relatively high contact resistance with SiC. In contrast, as shown in FIGS. 9A and 9B, when the Ni—P layer is used, metal Ni, Ni ₅ P ₂ and NiSi are produced in addition to NiSi ₂ . Metal Ni is a highly crystalline metal. NiSi is a silicide that has a _lower contact resistance with SiC than NiSi2.

From this result, it can be seen that by including P in Ni, highly crystalline metallic Ni is produced, Ni ₅ P ₂ is produced, and NiSi is produced instead of NiSi ₂ . Further, the crystallite diameter Xs of the silicide layer was examined by XRD, and it was confirmed that a large value was obtained as the crystallite diameter Xs, and the crystallinity was also good. Specifically, as shown in FIG. 9B, even when the P concentration was 11 wt%, the crystallite diameter Xs was a large value of 18 nm, but as shown in FIG. 9A, when the P concentration was 3 wt% , the crystallite diameter Xs was 38 nm and a large value exceeding 30 nm. From this, it can be said that a high crystallite size Xs can be obtained by including P in Ni, and a higher crystallite size Xs can be obtained by setting the P concentration to 3 wt % or less.

Moreover, when the contact resistance and the existence ratio of Ni ₅ P ₂ and NiSi were examined by changing the P concentration, the results shown in FIG. 10 were obtained. The abundance ratios of Ni ₅ P ₂ and NiSi were obtained from XRD peak area ratios to NiSi ₂ . As shown in FIG. 10, as the P concentration increased, the contact resistance decreased, while the metal Ni decreased and the Ni ₅ P ₂ and NiSi increased.

Thus, the results show that P and Ni _{diffuse together} as shown in FIGS. The result is that there is From this result, it can be _{concluded that the formation of Ni 5 P 2 acts as a catalyst to form NiSi, and that Ni 5 P 2 acts as a} nucleus for crystal growth. It is presumed that this is the mechanism by which the crystallinity is improved.

Moreover, as can be seen from the results of FIG. 10, the higher the P concentration is, the more the contact resistance is lowered, but the higher the P concentration is, the more the metallic Ni is reduced. Although the crystallinity of NiSi is good, the crystallinity is inevitably lowered due to the reduction of metallic Ni. Therefore, it is preferable to limit the P concentration to a certain level.

However, there is a correlation between the P concentration and the state of the reaction product formed by the reaction of Ni and P. If the P concentration is high, furnace annealing that heats the entire wafer like a general heating furnace or lamp annealing is performed. Even Ni ₅ P ₂ is produced. However, it was confirmed that Ni ₅ P ₂ is not generated unless laser annealing is performed when the P concentration is relatively low such as 15 wt % or less.

That is, when the P concentration is 15 wt % or less, when furnace annealing is performed, the reaction product of Ni and P becomes Ni ₃ P, not Ni ₅ P ₂ . On the other hand, when laser annealing was performed, the reaction product of Ni and P was Ni ₅ P ₂ . Although this mechanism is not clear, it is presumed that when laser annealing is performed, annealing is locally performed at a high temperature of 1000° C. or higher in a short period of time. Actually, the electrode structure was analyzed by performing _both laser _annealing and furnace _annealing using a heating furnace. was not generated.

Furthermore, the relationship between the electrode structure and the P concentration and adhesion strength was investigated in more detail. Again, experiments were conducted under the same conditions as in FIG. 3, and adhesion strength was measured under the same conditions as in FIG. Then, the adhesion strength was measured. In addition, to examine the tendency of change in adhesion strength with respect to laser energy, when the P concentration is 3 wt % and 7 wt %, the adhesion strength is different when the laser energy is 7 W and 8 W, respectively. I made a measurement. FIG. 11 shows the results.

As shown in this figure, when the P concentration was changed to 3 wt %, 7 wt %, 9 wt %, and 11 wt %, the lower the P concentration, the higher the adhesion strength. When an approximate curve passing through the adhesion strength at each P concentration was drawn for the case where the laser energy was 8 W, it was confirmed that the adhesion strength increased exponentially as the P concentration decreased. From this approximation curve, when the laser energy is 8 W, the P concentration at which the adhesion strength becomes 500 [N] or more is 5.5 wt % or less. In addition, when the laser energy is 7 W, the same tendency is observed as when the laser energy is 8 W. Therefore, when an approximate curve passing through the median value of the adhesion strength at each P concentration is drawn, the adhesion strength is 500 [N] from the approximate curve. The P concentration that becomes above becomes 6.5 wt % or less. Here, the laser energy used was 7 W or 8 W, but when the laser energy used is less than or equal to the used laser energy, when the P concentration is the same, a higher adhesion strength is obtained than when the laser energy is 7 W or 8 W. be able to. Therefore, if the laser energy is 7 W or less, the P concentration is 6.5 wt % or less, and if the laser energy is 8 W or less, the P concentration is 5.5 wt % or less, and an adhesion strength of 500 [N] or more can be obtained. can be done. At 7 W or less, the energy density becomes 1.4 J/cm ² or less and the silicidation reaction does not sufficiently occur, so it is preferable to set the laser energy to 7 W or more.

Therefore, when the P concentration is relatively low, high adhesion strength can be obtained. When the P concentration is 6.5 wt % or less, the adhesion strength becomes as high as 500 [N] or more.

Moreover, when the interface between SiC and the Ni silicide layer was examined by taking a cross-sectional TEM image, it was confirmed that graphite was formed at the interface. Graphite was confirmed for each of the cases where the P concentration was changed.

When Ni silicide is formed by heating after a Ni film is formed on a SiC substrate, graphite is formed from carbon remaining due to the use of Si in silicidation. It is known that this graphite lowers the adhesion strength of the electrode and causes peeling. For this reason, a method of removing graphite by etching has been proposed, but this method can only remove the graphite formed on the electrode surface, and cannot remove the graphite between the electrode and SiC, so that the desired adhesion strength can be obtained. I can't.

However, in the case of the structure of this embodiment, low resistance and high adhesion strength are obtained as described above even if graphite is generated. Therefore, a SiC semiconductor device with low resistance and high adhesion strength can be obtained without removing graphite.

FIG. 12 shows the results of the measurement results and the relationship between the crystallite diameter Xs, which indicates the crystallinity of the main component, and the adhesion strength [N] when the Ni layer is sputtered. As a result, when the P concentration of the Ni—P layer was 3 wt %, the crystallite diameter Xs exceeded 30 nm and a high adhesion strength of 500 [N] or more was obtained.

Therefore, by forming the drain electrode 11 by laser annealing while using the Ni—P layer as the electrode material, as in the present embodiment, it is possible to obtain better ohmic characteristics, and the gap between SiC and the electrode can be improved. High adhesion strength can be achieved.

As described above, the drain electrode 11 is formed by laser-annealing the metal thin film 110 by using a material in which P is added as an impurity to Ni forming a silicide. As a result, better ohmic characteristics can be obtained, and high adhesion strength can be achieved between the SiC and the electrode. Also, in the case of laser annealing, local annealing can be performed in a short period of time, so thermal damage to the device can be suppressed.

Further, when silicide is formed by laser annealing while performing ion implantation, a contact resistance of about 0.2 mΩcm ² is obtained, but even when the drain electrode 11 is formed as in this embodiment, the contact resistance is about 0.3 mΩcm ² . Contact resistance is obtained. Therefore, the desired contact characteristics can be obtained without performing an impurity ion implantation process, so that the cost of performing an ion implantation process can be reduced.

(Other embodiments)
The present invention is not limited to the above-described embodiments, and can be appropriately modified within the scope of the claims.

(1) For example, in the first embodiment, the ohmic electrode on the back side of the device in which each component is formed on the front side of the SiC substrate was described as an example. However, the structure described in the first embodiment is not applicable only to the back side of the device in which each component is formed on the front side of the SiC substrate. can be applied to any part. For example, it can be applied to the case of forming an ohmic electrode on the surface side of the SiC substrate. Even in that case, if the ohmic electrode is formed after forming each component of the device, local heating is possible by using laser annealing, and the device is heated. It is possible to suppress the influence. Further, in the above embodiments, the case of using Ni as the electrode metal or the case of using Mo in addition to Ni has been described, but Ti or the like can also be added to these. For example, after forming a film of Ti or the like on the surface of SiC, a Ni--P layer may be formed, or a Mo layer and a Ni--P layer may be formed in order and laser annealed.

(2) In addition, in the first embodiment, the use of a solid-state laser was described as an example of laser annealing, but the present invention is not limited to solid-state lasers, and excimer lasers, for example, can also be used. When an excimer laser is used, it is preferable to set the energy density to 1.4 J/cm ² or more while using, for example, a wavelength of 248 nm or 308 nm.

(3) In addition, in the above embodiment, the case of forming the Ni—P layer by electroless plating was explained, but when the Ni—P layer is formed by plating, not only the back side of the SiC substrate but also the front side of the SiC substrate can be formed at the same time. Therefore, for example, when forming a vertical power MOSFET as a SiC semiconductor element as in the above embodiment, when forming a Ni—P layer as the metal thin film 110 for forming the drain electrode 11, the source electrode 10 is A Ni--P layer can be formed at the same time. By doing so, it is possible to simplify the electrode forming process.

(4) In addition, in the above-described first embodiment, the SiC semiconductor device including a vertical power MOSFET as a semiconductor element was described as an example, but this is also a mere example, and other semiconductor elements such as diodes and IGBTs can be used. may be provided. That is, any SiC semiconductor device may be used as long as it is provided with an ohmic electrode for a semiconductor element formed on a SiC semiconductor substrate.

REFERENCE SIGNS LIST 1 n ⁺ type SiC substrate 1b back surface 10 source electrode 11 drain electrode 50 laser light 110 metal thin film

Claims (11)

A silicon carbide semiconductor substrate (1) having a front surface (1a) and a rear surface (1b), and an ohmic electrode (11) ohmic-connected to silicon carbide on at least one of the front surface side and the rear surface side of the silicon carbide semiconductor substrate. ), a silicon carbide semiconductor device having
The ohmic electrode is made of Ni containing 0.1 wt % or more and 15 wt % or less of impurity P as an electrode material, and contains Ni silicide composed of NiSi. Ni ₅ P ₂ is included ,
The silicon carbide semiconductor device , wherein the ohmic electrode has a crystallite diameter Xs of 30 nm or more as measured by an X-ray diffraction device. A silicon carbide semiconductor substrate (1) having a front surface (1a) and a rear surface (1b), and an ohmic electrode (11) ohmic-connected to silicon carbide on at least one of the front surface side and the rear surface side of the silicon carbide semiconductor substrate. ), a silicon carbide semiconductor device having
The ohmic electrode is made of Ni containing 0.1 wt % or more and 15 wt % or less of impurity P as an electrode material, and contains Ni silicide composed of NiSi. Ni ₅ P. ₂ contains
The silicon carbide semiconductor device, wherein the ohmic electrode has a crystallite diameter Xs of 18 nm or more as measured by an X-ray diffraction device. 3. The silicon carbide semiconductor device according to claim 1, wherein said ohmic electrode contains unreacted metal Ni. 4. The silicon carbide semiconductor device according to claim 1 , wherein said ohmic electrode contains Mo. 5. The silicon carbide semiconductor device according to claim 4 , wherein said ohmic electrode contains Mo carbide. 6. The silicon carbide semiconductor device according to claim 1, wherein said ohmic electrode contains Ti. A silicon carbide semiconductor substrate (1) having a front surface (1a) and a rear surface (1b), and an ohmic electrode (11) ohmic-connected to silicon carbide on at least one of the front surface side and the rear surface side of the silicon carbide semiconductor substrate. A method for manufacturing a silicon carbide semiconductor device that forms
forming a metal thin film (110) using Ni containing 0.1 wt % or more and 15 wt % or less of impurity P as an electrode material on the silicon carbide to be ohmic-connected;
forming the ohmic electrode by irradiating the metal thin film with a laser beam (50) and performing laser annealing for reacting the Ni with Si in the silicon carbide to generate Ni silicide ;
A method for manufacturing a silicon carbide semiconductor device , wherein in forming the metal thin film, the laser energy in the laser annealing is set to 8 W or more and the P concentration is set to 5.5 wt % or less . A silicon carbide semiconductor substrate (1) having a front surface (1a) and a rear surface (1b), and an ohmic electrode (11) ohmic-connected to silicon carbide on at least one of the front surface side and the rear surface side of the silicon carbide semiconductor substrate. A method for manufacturing a silicon carbide semiconductor device that forms
forming a metal thin film (110) using Ni containing 0.1 wt % or more and 15 wt % or less of impurity P as an electrode material on the silicon carbide to be ohmic-connected;
forming the ohmic electrode by irradiating the metal thin film with a laser beam (50) and performing laser annealing for reacting the Ni with Si in the silicon carbide to generate Ni silicide;
The method for manufacturing a silicon carbide semiconductor device, wherein in forming the metal thin film, the laser energy in the laser annealing is 7 W or more and the concentration of P is 6.5 wt % or less. 9. The silicon carbide according to claim ₇ , wherein in forming the ohmic electrode, _Ni5P2 is produced as a reaction product of the P and the Ni and NiSi is produced as the Ni silicide by the laser annealing. A method of manufacturing a semiconductor device. 10. The method of manufacturing a silicon carbide semiconductor device according to claim 7 , wherein forming the metal thin film includes forming Ni containing P as the metal thin film on the rear surface side by plating. 11. The method of manufacturing a silicon carbide semiconductor device according to claim 7, wherein forming the metal thin film sets the P concentration to 3 wt % or less.

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