JP6573163B2 - Impurity introduction apparatus, impurity introduction method, and semiconductor device manufacturing method - Google Patents

Description

  The present invention relates to an impurity introduction device, an impurity introduction method, a method for manufacturing a semiconductor device using the impurity introduction method, and a semiconductor device. In particular, nitrogen (N) as an impurity element is applied to a solid material having a very small diffusion coefficient of the impurity element. It relates to the technology to be introduced.

A wide band gap semiconductor such as silicon carbide (SiC) has a large activation energy at the time of diffusion, so that a diffusion coefficient of the impurity element is small. When the semiconductor substrate is 4H silicon carbide (4H-SiC), ion implantation with a high dose of, for example, about 10 ¹⁵ / cm ² or more with respect to the (0001) plane ((000-1) plane) of 4H-SiC. In order to promote the activation of the impurity element, the semiconductor substrate is heated to about 300 to 800 ° C. in advance and heated, and after ion implantation, annealing at a high temperature of about 1600 to 1800 ° C. is performed. There is a need. However, even after such treatment, for example, N, which is an n-type dopant, hardly thermally diffuses in 4H—SiC crystals.

On the other hand, an n-type SiC substrate is immersed in a high-concentration aqueous ammonia solution (NH ₃ aq), and a laser light pulse is irradiated through the aqueous ammonia solution, thereby doping the SiC substrate with an n-type impurity. A method of forming a layer has been proposed (see Non-Patent Document 1). In the invention described in Non-Patent Document 1, a light pulse (KrF excimer laser, wavelength 248 nm) having an energy density of about 2.5 J / cm ² is used at an irradiation time of 55 ns using an aqueous ammonia solution having a concentration of 10% by weight. Irradiation is performed three times (three shots) to introduce N into the surface of the SiC substrate. However, in the case of the technique of Non-Patent Document 1, since the density of N that can substantially contact the SiC substrate is low, it is difficult to introduce N at a high thermodynamic equilibrium concentration in SiC, that is, higher than the solid solution concentration. There is a problem that.

“Nitrogen doping of 4H SiC by Laser Irradiation in Ammonia Solution” Yuki Inoue and 5 others, 74th JSAP Autumn Meeting, Proceedings (Autumn 2013) Doshisha University)

  The present invention has been made paying attention to the above-mentioned problem, and even if the diffusion coefficient of nitrogen is extremely small, for example, a solid material such as a wide band gap semiconductor, nitrogen is applied to the surface of the solid material. Impurity introducing apparatus capable of introducing at a high concentration exceeding the solid solution concentration (thermodynamic equilibrium concentration), impurity introducing method, semiconductor device manufacturing method and semiconductor device using this impurity introducing method Objective.

  In order to solve the above problems, an aspect of the impurity introduction apparatus according to the present invention includes a film forming apparatus that forms a nitride film on a surface of an object, a light source that emits a light pulse, and light applied to the nitride film. And a beam adjusting system for irradiating a pulse, and introducing the nitrogen in the nitride into the object.

  An aspect of the impurity introduction method according to the present invention includes a step of depositing a nitride film on a surface of an object and a step of irradiating the nitride film with a light pulse, and targets nitrogen in the nitride. The main point is to introduce it into a product.

  According to another aspect of the method for manufacturing a semiconductor device of the present invention, a step of preparing an intermediate product having a first n-type semiconductor region and a nitride film are deposited on the surface of the first n-type semiconductor region. A step of irradiating the nitride film with a light pulse, introducing nitrogen in the nitride into the first n-type semiconductor region at a concentration exceeding the thermodynamic equilibrium concentration, and forming the second n-type semiconductor region The present invention includes a step of forming and a step of forming an ohmic contact electrode film in contact with the second n-type semiconductor region.

  According to another aspect of the semiconductor device of the present invention, there is provided a first n-type semiconductor region and a first n-type semiconductor region which is provided in the first n-type semiconductor region and into which nitrogen is introduced at a concentration exceeding the thermodynamic equilibrium concentration. And an ohmic contact electrode film in contact with the second n-type semiconductor region.

  Therefore, according to the impurity introduction apparatus and the impurity introduction method according to the present invention, even if the solid material has a very small diffusion coefficient of nitrogen, nitrogen is introduced to the surface of the solid material at a high concentration exceeding the solid solution concentration of the solid material. can do. In addition, according to the method for manufacturing a semiconductor device according to the embodiment of the present invention, a semiconductor device including a contact structure with excellent ohmic characteristics can be manufactured. Further, the semiconductor device according to the embodiment of the present invention can have a contact structure with excellent ohmic characteristics.

It is a block diagram including sectional drawing which illustrates typically the outline of the structure of the impurity introduction | transduction apparatus which concerns on embodiment of this invention. It is a block diagram which illustrates the outline of the structure of an arithmetic and control unit typically. It is a flowchart explaining the impurity introduction method which concerns on embodiment of this invention. It is process sectional drawing explaining the impurity introduction method which concerns on embodiment of this invention (the 1). It is process sectional drawing explaining the impurity introduction method which concerns on embodiment of this invention (the 2). It is process sectional drawing explaining the impurity introduction method which concerns on embodiment of this invention (the 3). It is process sectional drawing explaining the impurity introduction method which concerns on embodiment of this invention (the 4). It is process sectional drawing explaining the impurity introduction method which concerns on embodiment of this invention (the 5). 6 is a graph showing a profile of a step formed between an irradiation region and a non-irradiation region of a nitride film when an optical pulse is irradiated once in the impurity introduction method according to Example 1. FIG. 6 is a graph showing a profile of a step formed between an irradiation region and a non-irradiation region of a nitride film when an optical pulse is irradiated three times in the impurity introduction method according to Example 1. FIG. 6 is a graph showing a profile of a step formed between an irradiation region and a non-irradiation region of a nitride film when an optical pulse is irradiated ten times in the impurity introduction method according to Example 1. FIG. 6 is a graph showing a profile of a step formed on the upper surface of a nitrogen introduction region after removing a nitride film in the impurity introduction method according to Example 1. FIG. It is a graph which shows the profile obtained using SIMS about the nitrogen concentration and penetration depth of the nitrogen introduction area | region formed using the impurity introduction method which concerns on Example 1. FIG. 6 is a cross-sectional view illustrating a method for measuring current-voltage (IV) characteristics of a surface of a nitrogen introduction region formed using the impurity introduction method according to Example 1. FIG. It is a graph which shows the IV characteristic of the nitrogen introduction area | region formed using the impurity introduction | transduction method based on Example 1 for every frequency | count of irradiation. It is a graph which shows the resistance value of the nitrogen introduction area | region formed using the impurity introduction method which concerns on Example 1 for every frequency | count of irradiation. In the impurity introduction | transduction method based on Example 2, it is a graph which shows the profile of the level | step difference formed between the irradiation area | region of a nitride film, and the non-irradiation area | region at the time of irradiating a light pulse once. 6 is a graph showing a profile of a step formed between an irradiation region and a non-irradiation region of a nitride film when an optical pulse is irradiated twice in the impurity introduction method according to Example 2. FIG. FIG. 10 is a graph showing a profile of a step formed between an irradiation region and a non-irradiation region of a nitride film when an optical pulse is irradiated three times in the impurity introduction method according to Example 2. 6 is a graph showing a profile of a step formed between an irradiation region and a non-irradiation region of a nitride film when an optical pulse is irradiated five times in the impurity introduction method according to Example 2. FIG. 6 is a graph showing a profile of a step formed between an irradiation region and a non-irradiation region of a nitride film when an optical pulse is irradiated ten times in the impurity introduction method according to Example 2. FIG. It is a graph which shows the IV characteristic of the nitrogen introduction area | region formed using the impurity introduction method which concerns on Example 2 for every frequency | count of irradiation. It is a graph which shows the resistance value of the nitrogen introduction area | region formed using the impurity introduction | transduction method based on Example 2 for every irradiation frequency. It is typical process sectional drawing explaining the outline of the manufacturing method of the semiconductor device which concerns on embodiment of this invention (the 1). It is typical process sectional drawing explaining the outline of the manufacturing method of the semiconductor device which concerns on embodiment of this invention (the 2). It is typical process sectional drawing explaining the outline of the manufacturing method of the semiconductor device which concerns on embodiment of this invention (the 3). It is typical process sectional drawing explaining the outline of the manufacturing method of the semiconductor device which concerns on embodiment of this invention (the 4). FIG. 6 is a schematic process cross-sectional view for explaining the outline of the method for manufacturing a semiconductor device according to the embodiment of the present invention (No. 5).

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and it should be noted that the relationship between the thickness and the planar dimensions, the ratio of the thickness of each device and each member, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the directions of “left and right” and “up and down” in the following description are merely definitions for convenience of description, and do not limit the technical idea of the present invention. Thus, for example, if the paper is rotated 90 degrees, “left and right” and “up and down” are read interchangeably, and if the paper is rotated 180 degrees, “left” becomes “right” and “right” becomes “left”. Of course. In the present specification and the accompanying drawings, it means that electrons or holes are majority carriers in the region or layer bearing n or p, respectively. Further, + or − attached to n or p means a semiconductor region having a relatively high or low impurity concentration as compared with a semiconductor region not including + and −.

<Impurity introduction device>
An impurity introducing apparatus 1 according to an embodiment of the present invention includes a film forming apparatus 10 that forms a nitride film 4 on the surface of an object 2 made of a solid material, as shown on the left side in the block diagram of FIG. Prepare. Further, as shown on the right side in FIG. 1, the impurity introduction apparatus 1 includes a light source 34 that emits a light pulse, a beam adjustment system 33 that irradiates the nitride film 4 with the light pulse, and a light source control unit that controls the light source 34. 32. The light irradiation apparatus 20 having 32 is provided. Further, the impurity introduction apparatus 1 is capable of controlling film formation conditions such as the thickness of the nitride film 4 and light irradiation conditions such as the energy density of the laser light 6 and the relative light irradiation position of the light pulse with respect to the object 2. And a control device 30. The impurity introduction device 1 introduces N in the nitride contained in the nitride film 4 into the object 2.

The nitride film 4 is an N impurity introduction source for the object 2 and is a thin film containing a nitride, for example, silicon nitride (Si _x N _y , hereinafter simply referred to as “SiN”) or carbon nitride (C _x N). _y ) can be adopted. Hereinafter, a case where a SiN film is used will be described as an example.

The target object 2 will be described using an SiC substrate as an example, specifically, an n ⁺ type 4H—SiC substrate that is expected as a substrate material for a power semiconductor device. The object 2 has a thickness of about 10 μm at a concentration of about 1 × 10 ¹⁶ / cm ³ on a semiconductor substrate 21 having a (0001) plane ((000-1) plane) as illustrated in FIG. The n-type 4H—SiC epitaxial growth layer (hereinafter referred to as “epi layer”) 22 is provided. The object 2 illustrated in FIG. 1 is disposed toward the beam adjustment system 33 side with the surface on the epi layer 22 side as a surface (upper surface). Although not shown in the figure, a reference mark for alignment may be provided on the surface of the object 2.

The material of the object 2 is not limited to SiC, and the present invention can also be applied to other wide band gap semiconductors such as gallium oxide (Ga ₂ O ₃ ) and diamond. The object 2 is not limited to a wide band gap semiconductor as long as it is a solid material having a very small diffusion coefficient of N, but it is desirable that the object 2 be a solid material that can function as a donor-type impurity element.

  As the film forming apparatus 10, for example, a sputtering apparatus, an electron beam vapor deposition apparatus, a plasma CVD apparatus, or the like can be employed. As shown in FIG. 1, a film forming apparatus 10 according to an embodiment of the present invention includes a chamber 11 that can be evacuated, a lower electrode 12 that is provided in the chamber 11 and on which an object 2 is placed, and the lower electrode. 12 illustrates a case of a capacitively coupled plasma CVD apparatus including 12 and an upper electrode 13 provided to face each other in parallel in the vertical direction.

  The capacitively coupled plasma CVD apparatus further includes a high-frequency power source 15 connected between the lower electrode 12 and the upper electrode 13, and gas introduction for introducing a source gas for film formation into the chamber 11 connected to the chamber 11. The film forming apparatus 10 is provided with a valve 16 and a vacuum pump 17 connected to the chamber 11 and configured to be in a vacuum state in the chamber 11, such as a rotary pump, a turbo molecular pump, or a cryopump. A film thickness controller 31 that controls the film thickness of the nitride film 4 to be formed is connected to the high frequency power supply 15, the gas introduction valve 16, and the vacuum pump 17. Further, the film thickness control unit 31 can perform feedback control by monitoring a signal from a film thickness meter (not shown) provided in the film forming apparatus 10 in situ. The high frequency power supply 15, the gas introduction valve 16, and the vacuum pump 17 are connected to the arithmetic control device 30 via the film thickness control unit 31.

  The film forming apparatus 10 forms a film by causing the source gas introduced into the chamber 11 to adhere to the surface of the object 2 with a high frequency voltage applied by the high frequency power supply 15 between the lower electrode 12 and the upper electrode 13. The film forming apparatus 10 may be configured by an inductively coupled plasma CVD apparatus, a microwave plasma CVD apparatus, an electron cyclotron resonance (ECR) plasma CVD apparatus, or the like in addition to the capacitively coupled plasma CVD apparatus.

  The light irradiation device 20 includes a support base 24 that supports the object 2, and the object 2 is mounted via the support base 24 in an XY direction defined in a plane parallel to the main surface of the object 2. And an XY moving stage 23 that is freely moved. The light irradiation device 20 scans and irradiates the flat upper surface of the object 2 with the light pulse of the laser light 6 through the nitride film 4. The “photoexcitation effect” includes the effect of thermal energy.

  As shown in FIG. 1, the beam adjustment system 33 is provided integrally with a light source 34 that emits a light pulse having a large irradiation fluence (energy density) such as a laser beam 6, and the light pulse is constant on the surface of the object 2. Scan irradiation in the irradiation area of the dimension. The beam adjustment system 33 and the light source 34 are connected to a light source control unit 32 that controls the irradiation conditions of the irradiated laser light 6, and the light source control unit 32 is connected to the arithmetic control device 30.

As the light pulse having a large energy density, the laser light 6 having a wavelength capable of giving light energy to the lattice vibration of the impurity element and the object 2 so that sufficient reaction energy is generated through the nitride film 4. A pulse is preferred. For example, an excimer laser having an oscillation wavelength of 248 nm (KrF), 193 nm (ArF), 308 nm (XeCl), 351 nm (XeF), 266 nm (YAG fourth harmonic), 355 nm (YAG third harmonic), 532 nm A (YAG second harmonic) laser, 1.064 μm (YAG fundamental wave), 10.6 μm (carbonic acid (CO ₂ ) gas) laser, or the like can be used. Even if high-power continuous light such as a mercury (Hg) lamp or xenon (Xe) lamp is wavelength-selected by a spectroscope or a filter, a light pulse having a large energy density can be obtained. It is not something.

  Further, when the laser beam 6 having a wavelength in the ultraviolet region having an energy larger than the forbidden band width of the nitride film 4 and many semiconductor materials is irradiated like the excimer laser, the structure of the nitride film 4 is obtained. The vibrational energy of the element and the constituent element of the semiconductor material can be excited to excite surface reactions such as photocatalysis by the light energy in the ultraviolet region. For this reason, surface reactions including surface migration that excite the lattice vibration of the surface of the solid material to which the impurity element is introduced and move the impurity element to the introduction position such as the interstitial position or substitution position of the target solid material Etc. can be facilitated.

  However, since light having a shorter wavelength than that of an ArF (= 193 nm) laser or the like, that is, in the range of vacuum ultraviolet light is absorbed by oxygen molecules in the atmosphere and propagation is inhibited, laser doping in the atmosphere Is preferably a laser beam 6 having a wavelength of about 190 nm or more. Further, in order to sufficiently generate the reaction energy between the nitride film 4 and 4H—SiC, the laser beam 6 having a wavelength of about 380 nm or less, that is, a YAG third harmonic (= 355 nm) class or less is preferable.

  The beam adjustment system 33 is not shown in the figure, and a shaping device such as a variable slit for shaping the emitted laser light 6 into a predetermined shape, a condensing device such as a lens for condensing the laser light 6, Is provided. The shaped light pulse such as the laser beam 6 is irradiated toward the interface region between the upper surface of the object 2 and the nitride film 4. The shape of the laser beam 6 to be molded is preferably a rectangular shape (rectangular shape), but is not limited to a rectangular shape and may be other shapes.

  Although not shown, when the irradiation position of the light pulse on the object 2 is controlled, the beam adjustment system 33 is irradiated with an imaging device such as a CCD camera that images the reference mark of the object 2 and illumination light. An illumination light emitting device, a mirror that reflects and transmits illumination light, an alignment mechanism, and the like may be separately provided as necessary. When direct drawing (direct writing) described later is performed, a distance measuring system such as a laser interferometer may be further provided. Further, when sweeping the laser beam 6, the beam adjusting system 33 is provided with another optical system such as a reflection mirror or a prism that reflects the shaped laser beam 6 and guides it to the light collecting device, if necessary. Also good.

  The XY moving stage 23 supports the supporting base 24 horizontally from below and is connected to a moving stage driving device (not shown), and the moving stage driving device is controlled by the arithmetic control device 30, whereby the supporting base 24. The object 2 can be moved freely with respect to the irradiation position of the light pulse by freely moving each in the XY direction in the horizontal XY plane. For example, a region in which N is added by irradiating a range of a desired plane region with a direct drawing method by freely moving the relative position of the object 2 with respect to the irradiation position of the light pulse. Can be selectively patterned. Furthermore, by providing a Z moving stage for moving the supporting table 24 in the Z direction perpendicular to the XY direction between the supporting table 24 and the XY moving stage 23, in the Z direction in addition to the XY direction. Alternatively, the support 24 may be configured to be movable so that the focus and the like can be adjusted.

The arithmetic and control unit 30 includes an irradiation number calculating circuit 301 as shown in FIG. Further, as shown in FIG. 1, an input device 41 and a data storage device 42 are connected to the arithmetic control device 30, and the arithmetic control device 30 is configured to be able to access data stored in the data storage device 42. Has been. The data storage device 42 receives the thickness t _f of the nitride film 4, the energy density F of the light pulse, and the irradiation time (pulse width) τ of one pulse (one shot) via the input device 41.

The irradiation number calculation circuit 301 of the arithmetic and control unit 30 uses the film thickness t _f , energy density F, and one pulse irradiation time τ stored in the data storage device 42 to calculate the number n of light pulse irradiations based on empirical rules. calculate. The irradiation number calculation circuit 301 can be set so as to calculate the irradiation number n so that the nitride film 4 does not remain on the surface of the object 2 after the light pulse irradiation. It is also possible to set so that the number of times of light pulse irradiation n is calculated so that the nitride film 4 can remain on the surface of the object 2 at least by a thickness corresponding to one atomic layer after the light pulse irradiation. .

  When the nitride film 4 cannot remain on the surface of the object 2 after the light pulse irradiation for at least the thickness corresponding to one atomic layer, the degree of unevenness forming the surface defect in the nitrogen introduction region becomes severe, and the object 2 is processed in a later step. When an electrode is provided on the surface of the semiconductor device to manufacture a semiconductor device, the current value in the forward direction decreases and the leakage current increases during reverse bias, and sufficient characteristics cannot be provided.

Thickness _{t f} of the nitride film 4 is not less than about 10 nm, and is preferably set below about 1 [mu] m. If the thickness t _f is less than 10 nm, there is a case or if N is difficult to sufficiently introduce, in which the degree of unevenness of too thin to size the surface energy density F of the light pulse becomes severe. On the other hand, if it exceeds 1 μm, energy efficiency is deteriorated even if N can be introduced. The energy density F of the light pulses, 1.0 J / cm ² less than approximately, and is preferably set below about 6.0 J / cm ^2. When the energy density F is less than 1.0 J / cm ² , it is difficult to sufficiently introduce N. Moreover, when it exceeds 6.0 J / cm < ² >, energy efficiency will worsen and the grade of the unevenness | corrugation of the surface of a nitrogen introduction area | region will become intense.

  Further, the irradiation time τ of the light pulse can be appropriately set within a range of about 20 ns to 100 ns, and for example, about 50 ns is preferable. The number of times n of light pulses to be set can be selected as long as the nitride film 4 can remain at least as much as the thickness of one atomic layer. However, considering the mass productivity of the semiconductor device, 1 It is preferably within the range of not less than 100 times and not more than 100 times.

In this way, the surface n of the object 2 is determined by setting the number of times of light pulse irradiation n in consideration of the film thickness t _f of the nitride film 4, the energy density F of the laser light 6 and the irradiation time τ of one pulse. In addition, the degree of unevenness can be kept within an allowable range, for example, the desired IV characteristics can be achieved even if surface defects occur without excessively forming unevenness.

The data on the number of irradiations n calculated by the arithmetic control device 30 is input to the light source control unit 32 together with the data of the energy density F and the irradiation time τ input to the arithmetic control device 30. Further, the film thickness t _f data input to the arithmetic and control unit 30 is input to the film thickness control unit 31. Further, the arithmetic control device 30 may be configured to display data such as the film thickness t _f , the energy density F, the irradiation time τ, and the number of irradiations n by connecting a display device (not shown). Good.

The film thickness controller 31 includes the voltage of the high-frequency power supply 15 of the film forming apparatus 10, the gas introduction valve 16, and the vacuum pump so that the nitride film 4 is formed on the object 2 with the input film thickness t _f. 17 operations are controlled. The light source control unit 32 controls the operations of the beam adjustment system 33 and the light source 34 so that the scan irradiation of the light pulse is performed with the input energy density F, the irradiation time τ, and the calculated number of irradiations n.

<Impurity introduction method>
Next, the impurity introducing method according to the embodiment of the present invention uses the object 2 in which the n type epi layer 22 is formed on the upper surface side of the n ⁺ type semiconductor substrate 21 as shown in FIG. This will be described with reference to the flowchart of FIG. 3 and FIGS. Structure of the object 2 of Fig. 4 are exemplary, for example, a structure in which the epitaxial layer is formed of n-type on the upper surface of the p ⁺ -type semiconductor substrate to may be, p on the upper surface of the n ⁺ -type semiconductor substrate A structure with an epitaxial layer of the mold may be used. Alternatively, a bulk semiconductor substrate without an epi layer may be used.

  (A) First, in step S1 in FIG. 3, the surface of the epilayer 22 side of the prepared object 2 is arranged on the upper electrode 13 side as shown by a two-dot chain line inside the film forming apparatus 10 in FIG. It is placed and fixed on the lower electrode 12 toward the surface.

(B) Next, in step S 2, the nitride film thickness t _f , the energy density F of the light pulse, and the irradiation time τ are input via the input device 41 and stored in the data storage device 42. Step S2 may be performed before step S1.

(C) Next, in step S3, the arithmetic control device 30 of the impurity introduction device 1 reads the nitride film thickness t _f , the energy density F of the light pulse, and the irradiation time τ from the data storage device 42, and the number of irradiation times. n is calculated. Then, the calculated number of irradiations n, the energy density F of the light pulse, and the irradiation time τ are output to the light source controller 32 of the light irradiation device 20. And it outputs the film thickness _{t f} in the film thickness control portion 31 of the deposition apparatus 10.

(D) Next, the film thickness controller 31 of the film forming apparatus 10 controls the operations of the high-frequency power source 15, the gas introduction valve 16, and the vacuum pump 17 in step S4, as shown in FIG. the upper surface of the epitaxial layer 22 of the object 2, is formed to a thickness t _f of the thin film of the nitride film 4 of SiN film or the like is set.

  (E) Next, the object 2 on which the nitride film 4 is formed is taken out of the film forming apparatus 10 and transported to the light irradiation apparatus 20, and the upper surface of the nitride film 4 is directed to the beam adjustment system 33 side. Place on the support 24 and fix. The light irradiation device 20 is disposed in an air atmosphere at room temperature. In addition, the temperature of the target object 2 placed on the light irradiation device 20 can be appropriately set within a range of room temperature to about 600 ° C. Then, the beam adjustment system 33 is set so that the position of the reference mark corresponding to the first irradiation target position for doping the impurity layer N with respect to the epi layer 22 of the object 2 matches the optical axis of the laser beam 6. Move a predetermined amount in the X and Y directions.

  (F) Next, in step S5, the light source control unit 32 of the light irradiation apparatus 20 causes the beam adjustment system 33 so that the laser light 6 is irradiated with the input energy density F, irradiation time τ, and number of irradiations n. And the operation of the light source 34 is controlled. Then, as shown in FIG. 6, the light pulse of the laser beam 6 is irradiated on the upper surface of the epi layer 22 of the object 2 through the nitride film 4.

In the irradiation region s of the nitride film 4 irradiated with the light pulse, N as a doping element is remarkably activated by the energy of the laser light 6, and the nitride film 4 is melted. At the interface 22, N is introduced into the epi layer 22 to a level exceeding the solid solution concentration. Also with the progress of laser doping reduces the thickness t _f of the nitride film 4. At this time, when the number of irradiations n is plural and the same irradiation region s is repeatedly irradiated with the light pulse, the nitride film 4 becomes thinner as the number of irradiations n increases. On the other hand, a melt flow region of SiN is generated around the irradiation region s.

  Then, after irradiation with the light pulse n times, as shown in FIG. 7, a nitrogen introduction region 2a is formed on the epilayer 22 corresponding to the irradiation region s. Further, a step is formed between the irradiation region s and the non-irradiation region of the nitride film 4. Further, a part of the SiN is raised and deposited by melt flow in a part of the region near the boundary between the irradiation region s and the non-irradiation region. In FIG. 7, a nitride is formed on the upper surface of the nitrogen-introduced region 2 a so that the formation of the unevenness that forms the surface defect of the object 2 is reduced by the processing of steps S 2 and S 3 performed in advance. The case where a part of the film 4 is deposited with a constant thickness and remains is illustrated.

(F) Next, when the nitride film 4 is an SiN film, it remains on the surface of the epi layer 22 using hot phosphoric acid (H ₃ PO ₄ ) or the like in step S6 as shown in FIG. The nitride film 4 is removed. Since the remaining nitride film 4 protected the upper surface of the nitrogen introduction region 2a, the nitrogen introduction region 2a is formed flat with the upper surface roughened. The impurity introduction method according to the embodiment of the present invention is constituted by the steps (a) to (f).

Next, Example 1 of the present invention will be described. In Example 1, the object 2 having the epi layer 22 as shown in FIG. 4 is prepared, and the nitride film 4SiNx is formed on the surface of the upper epi layer 22 of the semiconductor substrate 21 by using the film forming apparatus 10. As shown in FIG. 5, the film was formed with a thickness t _f = about 100 nm.

Next, as shown in FIGS. 6 and 7, the light pulse is applied to the nitride film 4 by the light irradiation device 20 provided in the atmosphere, and the irradiation time is about energy density F = 4.0 J / cm ^2. Irradiation was performed at τ = 50 ns, and N was doped into the epi layer 22. As the laser beam 6, a 248 nm (KrF) excimer laser was used, and the beam was shaped so that the irradiation region s had a planar pattern and a square shape of about 300 μm square. In the laser doping, the number of irradiations n was 1, 5, 3, 5 and 10 patterns, and patterning was performed in a total of 3 rows: a row, b row, and c row. FIG. 9 to FIG. 11 exemplarily show the profile of the level difference on the surface of the irradiation region s obtained in three patterns of n = 1, 3, and 10 among the five patterns.

  When the number of irradiations n = 1, as shown in the graph of FIG. 9, the maximum depth of the step was about 100 nm. When the number of irradiations n = 3, as shown in the graph of FIG. 10, the maximum depth of the step was about 150 nm to 200 nm. Further, when the number of irradiations n = 10, as shown in the graph of FIG. 11, the maximum depth of the step was about 200 nm to 250 nm. That is, it can be seen that the level difference increases as the number of irradiations n increases. 9 to 11, the position of “0” on the vertical axis corresponds to the height of the upper surface of the nitride film 4 formed before the light pulse irradiation.

  Next, as shown in FIG. 8, the nitride film 4 remaining on the upper surface of the epi layer 22 was removed. As shown in the graph of FIG. 12, in the case of four patterns of the number of irradiations n = 1, 2, 3, and 5, the height of the upper surface of the epi layer 22 in the irradiation region s is not substantially changed or accompanied by a slight bump. It was almost flat. On the other hand, when the number of irradiations n = 10, almost all of the nitride film 4 disappeared in the irradiation region s, and the upper part of the nitrogen introduction region 2a below the nitride film 4 was partially etched by 100 nm or more. When the number of irradiations is n = 10, it can be seen that significant irregularities were formed on the surface of the nitrogen introduction region 2a. In FIG. 12, the position of “0” on the vertical axis corresponds to the height of the upper surface of the epi layer 22, that is, the upper surface of the nitrogen introduction region 2a.

In the case of Example 1, as shown in the graph of FIG. 13, N greatly exceeds 1 × 10 ²⁰ cm ⁻³ or less, which is a solid solution concentration of 4H—SiC, on the outermost surface of the epi layer 22. × 10 ²¹ cm ⁻³ or more could be introduced. In addition, N could be introduced into the epitaxial layer 22 to a position near a depth of 50 nm. FIG. 13 shows a profile of the nitrogen concentration when the number of irradiations n = 10.

  Next, as shown in the cross-sectional view of FIG. 14, the two probe needles 58a and 58c were brought into contact with the surface of the nitrogen introduction region 2a at a distance from each other, and the electrical resistance was measured between the probe needles 58a and 58c. . The graph of FIG. 15 illustrates the IV characteristics obtained in the case of four patterns of n = 1, 3, 5, 10 among the nitrogen introduction regions 2a formed by changing the number of irradiations n to 5 patterns. Indicate. Also, the resistance values obtained in the case of 5 patterns when a voltage of 2 V is applied between the probe needles 58a and 58c are shown in the graph of FIG.

When the number of irradiations was n = 1, almost no current flowed even when the voltage was changed, as indicated by the broken line in FIG. In addition, as shown in FIG. 16, the three resistance values of the a column to the c column when a voltage of 2 V is applied are in the range of about 6 × 10 ^{8 to} 5 × 10 ¹⁰ Ω, which is a relatively high value. Indicated.

On the other hand, in the case of the number of irradiations n = 3, 5, and 10, as shown in FIG. 15, when the voltage was changed, an ohmic property in which a current proportional to the voltage flows was shown. In addition, as shown in FIG. 16, in the case of four patterns of irradiation times n = 2, 3, 5, and 10, each of the three resistance values when a voltage of 2 V is applied is 10 ³ Ω level. It was. 15 and 16, it can be seen that under the laser doping conditions of Example 1, the nitrogen introduction region 2a has effective IV characteristics when the number of irradiations n is 2 or more.

Next, a second embodiment of the present invention will be described. Example 2 is a case where the nitride film 4 is a SiNx film as in Example 1, but the energy density F of the light pulse is 1.0 J /, which is about a quarter of that in Example 1. The laser doping condition was reduced to about cm ² and the other laser doping conditions were the same as in Example 1. Similarly to the case of Example 1, the number of times of irradiation n is set to 5 patterns of 1, 2, 3, 5, and 10 times, and a total of 3 rows, a row, b row, and c row in each pattern. Patterning was performed.

  When the number of irradiations is n = 1, as shown in the graph of FIG. 17, the maximum depth of the average step is about 20 to 30 nm. In the case of the laser doping conditions corresponding to Example 1 shown in FIG. The depth of the step was shortened to about 1/5 to 1/4. When the number of irradiations n = 2, the maximum depth of the step was about 30 to 70 nm as shown in the graph of FIG.

  When the number of irradiations n = 3, as shown in the graph of FIG. 19, the maximum depth of the step is about 70 nm, which is higher than that of the corresponding laser doping condition of Example 1 shown in FIG. The depth was reduced to about one-third to half. When the number of irradiations n = 5, as shown in the graph of FIG. 20, the maximum depth of the step was about 70 to 100 nm.

  Further, when the number of irradiations n = 10, as shown in the graph of FIG. 21, the depth is about 80 to 100 nm, and the depth of the step is larger than that of the corresponding laser doping condition of Example 1 shown in FIG. It shortened to about one-third to half.

  Similarly to the case of Example 1, among the nitrogen introduced regions 2a formed by changing the number of irradiations n to 5 patterns, IV obtained in the case of 4 patterns of n = 1, 3, 5, 10 were obtained. The characteristics are exemplarily shown in the graph of FIG. Further, the resistance values obtained in the case of five patterns by the method shown in FIG. 14 are shown in the graph of FIG.

In FIG. 22, the trajectory when the number of irradiations n = 1 exemplified by a broken line, the trajectory when the number of irradiations n = 3 exemplified by a one-dot chain line, and the number of irradiations n = 5 exemplified by a two-dot chain line. In each case, the trajectories are substantially overlapped on the same straight line. As shown in FIG. 22, in all cases of the number of irradiations n = 1, 3, and 5, almost no current flowed even when the voltage was changed. Further, as shown in FIG. 23, when the number of irradiations is n = 1, 2, 3, 5, the three resistance values of the a column to the c column when a voltage of 2 V is applied are approximately 1 × 10 ⁸ to 1 It was in the range of about × 10 ¹¹ Ω and showed a relatively high value.

On the other hand, when the number of irradiations n = 10, as shown in FIG. 22, when the voltage was changed, a large current flowed with ohmic characteristics. Further, as shown in FIG. 23, each of the three resistance values when a voltage of 2 V is applied is about 1 × 10 ² Ω, and four patterns of irradiation times n = 1, 2, 3, 5 It became much lower than. 22 and 23, when the energy density F of the light pulse is reduced, it can be understood that the nitrogen introduction region 2a can be controlled to have effective IV characteristics by increasing and adjusting the number of irradiations n. .

In addition to Example 1 and Example 2, the energy density F of the optical pulse is set to about 6.0 J / cm ^2, which is larger than those in Examples 1 and 2, and other laser doping conditions are set. It carried out like the case of Example 1 and Example 2. In this case, as in the case of Example 1 and Example 2, as the number of irradiations n increased, the step of the nitride film 4 increased and the etching depth when the nitrogen introduction region 2a was etched also increased.

According to the impurity introduction method according to the embodiment of the present invention, the light pulse of the light pulse is considered in consideration of the film thickness t _f of the nitride film 4, the energy density F of the light pulse, and the irradiation time τ at room temperature and atmospheric pressure. By irradiating the nitride film 4 with a light pulse after setting the number of irradiations n, introduction of N into the surface of the epilayer 22 of 4H—SiC is promoted. Therefore, the normal solid solution concentration (about 1 × 10 ²⁰ cm ⁻³ or less) of N, that is, the concentration of nitrogen on the surface of the epilayer 22 of 4H—SiC as the object 2 is 10 ²¹ cm ⁻³ level or higher is increased. It can be introduced up to a higher concentration level. Further, it is easy to introduce N up to a depth position of about 50 nm from the surface of the epi layer 22.

  Further, for example, in the case of a method of doping N by immersing a SiC semiconductor substrate in a high concentration aqueous ammonia solution and irradiating a laser light pulse through this aqueous ammonia solution, not only the target N atoms but also ammonia. There is a problem that oxygen (O) and hydrogen (H) contained in the aqueous solution enter the SiC crystal, and the crystallinity deteriorates. In this regard, according to the impurity introduction method according to the embodiment of the present invention, since a solid nitride film 4 is used instead of an aqueous ammonia solution, a large amount of O or H is a SiC crystal that causes deterioration of semiconductor characteristics. There is no entry inside. Moreover, it is possible to further suppress the entry of O and H by performing the irradiation atmosphere in a nitrogen atmosphere at atmospheric pressure. Further, in the impurity introduction method using SiC as an object as in the embodiment of the present invention, SiNx, which is a compound of Si and N, is used as a nitride, so that compatibility with SiC is good, and SiNx is ablated and SiNx is ablated. Even if it is deposited on the surface of 4H—SiC, the concern that it works as an unnecessary substance for the device can be reduced.

  Further, according to the impurity introduction method according to the embodiment of the present invention, since the state in which laser doping is performed is in the range of room temperature to 600 ° C., an extremely high temperature annealing of about 1600 to 1800 ° C. as in the prior art. There is no need to do. Therefore, N doping can be easily performed without applying stress deformation due to thermal history.

Conventionally, when an impurity element is provided as a solid phase introduction source on the 4H—SiC target 2 and laser doping is performed by irradiating the laser beam 6, it may be performed in a low pressure state of about 6.7 × 10 ⁻⁵ Pa. there were. According to the impurity introduction method according to the embodiment of the present invention, nitrogen can be introduced as an impurity element even under atmospheric pressure. Therefore, it is possible to eliminate the burden of equipment and work for setting the low pressure state, and to perform laser doping more easily and more quickly than before.

<Method for Manufacturing Semiconductor Device>
Next, a method for manufacturing a semiconductor device according to the embodiment of the present invention will be described with reference to FIGS. 4 to 8 used in the impurity introduction method according to the embodiment of the present invention.
(G) First, as shown in the cross-sectional view of FIG. 24, an intermediate product 2 on which a semiconductor substrate 52 _SUB that will eventually become an n-type drift layer is formed as an object.

Inside the intermediate product 2 of the semiconductor substrate 52 _SUB Figure 24 upper surface in a plurality of p ^- type well region 53a, with 53b is selectively provided, the plurality of p ^- type Source regions 54a and 54b are provided in the respective well regions 53a and 53b. A gate electrode 56 is provided on the surface of the well regions 53a and 53b via a gate insulating film 55. An interlayer insulating film 57 is provided on the gate electrode 56, and a source electrode film 58 is provided on the interlayer insulating film 57 so as to short-circuit the well regions 53a, 53b and the source regions 54a, 54b. It has been. On the source electrode film 58, a passivation film 51 such as a silicon oxide film (SiO ₂ film) or a polyimide film is formed. That is, a MOS gate structure is formed on the surface of the intermediate product 2 shown in FIG.

(H) Then, using a method such as chemical mechanical polishing (CMP), the thickness adjustment is performed until the semiconductor substrate 52 _SUB has a desired thickness t _drift . As the desired thickness t _drift , for example, a thickness of about 10 μm to 60 μm can be selected. The remaining portion of the semiconductor substrate 52 _{SUB having} the desired thickness t _drift functions as the drift layer 52 of the semiconductor device. The drift layer 52 corresponds to the first n-type semiconductor region of the present invention.

(I) Next, as shown in the cross-sectional view of FIG. 25, the semiconductor device is turned upside down, and the drift layer on the side opposite to the MOS gate structure is placed inside the chamber 11 of the film forming apparatus 10 shown in FIG. It arrange | positions so that the back surface of 52 may become an upper surface. Then, in the same manner as shown in FIG. 5, the back surface of the drift layer 52 is deposited with a constant thickness t _f using a nitride film 4 a low-temperature film-forming technique such as plasma CVD.

  (J) Next, as shown in the cross-sectional view of FIG. 26, the back surface of the drift layer 52 is irradiated with the light pulse of the laser light 6 through the nitride film 4 in the same manner as shown in FIG. At this time, the entire back surface of the drift layer 52 is scanned and irradiated with the laser beam 6, and N is dissolved in the lower part of the drift layer 52 (represented as “upper part” in FIG. 26). Introduce at a high concentration exceeding the concentration. Scanning can be performed by moving the XY moving stage 23 as indicated by a bidirectional arrow in the XY moving stage 23 in FIG. 1 or by moving the beam adjustment system 33 side.

  At this time, when the energy density F of the light pulse to be irradiated is relatively large, as shown in FIGS. 15 and 16, it is excellent even if the number of times of irradiation n is suppressed to a small number such as 3 times or 5 times. A nitrogen introduction region having IV characteristics can be formed. By suppressing the number of irradiations n of the light pulses applied to the back surface of the drift layer 52, the manufacturing process of the semiconductor device can be shortened, and an increase in the etching amount of the surface of the nitrogen introduction region can be suppressed.

(K) Next, as shown in FIG. 8, the nitride film 4 remaining on the back surface of the drift layer 52 is removed, and as shown in the sectional view of FIG. Thus, an n ⁺⁺ type nitrogen introduction region doped with N to a level exceeding the solid solution concentration is formed as a drain region 52a on the entire surface opposite to the MOS gate structure. The drain region 52a corresponds to the second n-type semiconductor region of the present invention.

  (L) Next, as shown in the sectional view of FIG. 28, a drain electrode film 59 made of, for example, Ni is formed on the drain region 52a. The drain region 52a into which nitrogen is introduced at a high concentration and the drain electrode film 59 are in good ohmic contact as described with reference to FIGS. 13 to 23, and the second n-type semiconductor region has an ohmic contact structure. Is formed. The above-described steps (g) to (l) constitute the semiconductor device manufacturing method according to the embodiment of the present invention.

According to the method of manufacturing a semiconductor device according to the embodiment of the present invention, at room temperature, under atmospheric pressure, in consideration of the thickness t _f of the nitride film 4, the energy density F and the irradiation time of the light pulse τ light By irradiating the nitride film 4 with an optical pulse after setting the number of pulse irradiations n, the nitrogen concentration on the surface of the 4H—SiC semiconductor substrate is 10 ²¹ cm ⁻³ level or more, and the normal solid solution of N A semiconductor device 50 having a semiconductor region with low ohmic resistance and excellent contact properties can be manufactured by introducing a high concentration that greatly exceeds the solution concentration (1 × 10 ²⁰ cm ⁻³ or less).

Conventionally, the drain region provided on the back side of the semiconductor substrate is prepared, for example, by preparing a semiconductor substrate having a relatively large thickness in advance and forming a MOS gate structure or the like on the front side of the semiconductor substrate. Was thinned by CMP or the like. Then, since a process such as introducing n-type impurities and then performing high-temperature annealing is necessary, there has been a problem that the semiconductor substrate is warped or broken, such as cracks. However, according to the method for manufacturing a semiconductor device according to the embodiment of the present invention, since high-temperature annealing is not necessary, the semiconductor substrate on which the surface structure is formed is thinned to an extremely thin level of, for example, about t _drift = 10 μm to 60 μm. Even after that, it becomes possible to form the high concentration drain region 52a. Therefore, it is possible to reduce the manufacturing burden of the semiconductor device and improve the efficiency of the process, and to realize a semiconductor device with high speed operation and low loss.

(Other embodiments)
Although the present invention has been described with reference to the above disclosed embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, it should be understood that various alternative embodiments, examples, and operational techniques will become apparent to those skilled in the art. For example, in the method of manufacturing a semiconductor device according to the embodiment of the present invention, the number n of times of light pulse irradiation is determined using the thickness t _f of the nitride film 4, the energy density F of the light pulse, and the irradiation time τ as input data. Although the arithmetic processing unit 30 executes the arithmetic processing, the operator may determine the number of times n of the light pulse irradiation.

  In the method for manufacturing a semiconductor device according to the embodiment of the present invention, the MOSFET is described as an example. However, the semiconductor device is not limited to the MOSFET. The present invention can be applied to n-type semiconductor regions of various semiconductor devices (semiconductor elements) such as IGBT, SIT, GTO, and SI thyristor as well as including a diode. As described above, the present invention includes various embodiments and the like not described above, and the technical scope of the present invention is defined only by the invention specifying matters according to the appropriate claims from the above description. Is.

1 Impurity introduction device 2 Object (intermediate product)
2a Nitrogen introduction region 4 Nitride film 6 Laser beam 10 Film formation device 20 Light irradiation device 21 Semiconductor substrate 22 Epitaxial growth layer 23 XY movement stage 30 Arithmetic control device 31 Film thickness control unit 32 Light source control unit 33 Beam adjustment system 34 Light source 50 Semiconductor device 52 Drift layer (first n-type semiconductor region)
52a Drain region (second n-type semiconductor region)
53a, 53b Well regions 54a, 54b Source region 55 Gate insulating film 56 Gate electrode 57 Interlayer insulating film 58 Source electrode film 59 Drain electrode film (ohmic contact electrode film)
F energy density n number of irradiations t _f film thickness τ irradiation time

Claims (19)

Depositing a nitride film on a surface of an object made of a solid material in which nitrogen functions as a donor-type impurity element ;
Irradiating the nitride film with a light pulse so as to reduce the thickness of the nitride film, and introducing nitrogen in the nitride into the object ;
Including
Irradiating the light pulse comprises:
In consideration of the film thickness of the nitride film, the energy density of the light pulse, and the irradiation time per time of the light pulse, the nitride film has at least one atom on the surface of the object after the light pulse irradiation. Determining the number of times the light pulse is irradiated so as to remain for a considerable film thickness;
Irradiating the nitride film with the light pulse at the energy density, the irradiation time and the number of irradiations;
Impurity introduction method characterized by including . The impurity introduction method according to claim 1 , wherein the nitride film is a silicon nitride film. 3. The impurity introduction method according to claim 1, wherein the nitride film has a thickness of 10 nm to 1 μm. The energy density, impurity introduction method according to any one of claims 1 to 3, characterized in that 1.0 J / cm ² or more 6.0 J / cm ² or less. The impurity introduction method according to claim 1, wherein a wavelength of the light pulse is 190 nm or more and 380 nm or less. The impurity introduction method according to any one of claims 1 to 5, wherein the irradiation of the light pulse is performed at an irradiation frequency of 1 to 10 times per irradiation region. The nitrogen is introduced into the range of a desired plane region by the scan irradiation in which the light pulse is irradiated while moving the object relative to the irradiation position of the light pulse in the XY plane. 7. The impurity introducing method according to claim 1, wherein the planar pattern is directly drawn. The impurity introducing method according to any one of claims 1 to 7 , wherein the step of irradiating the light pulse is performed by setting the temperature of the object to a room temperature to 600 ° C. A film forming apparatus for forming a nitride film on a surface of an object made of a solid material in which nitrogen functions as a donor-type impurity element ;
A light source that emits light pulses;
A beam adjustment system for irradiating the nitride film with the light pulse so as to reduce the thickness of the nitride film;
In consideration of the film thickness of the nitride film, the energy density of the light pulse, and the irradiation time per time of the light pulse, the nitride film has at least one atom on the surface of the object after the light pulse irradiation. The number of irradiation times of the light pulse is determined so as to remain for a considerable film thickness, and the beam adjustment system irradiates the nitride film with the energy density, the irradiation time, and the number of irradiation times. A light source control unit for controlling the light source;
An impurity introducing apparatus characterized in that nitrogen in nitride is introduced into the object. The impurity introduction apparatus according to claim 9 , further comprising an arithmetic control device that executes arithmetic processing for determining the number of times of irradiation using the film thickness, the energy density, and the irradiation time as input data. The impurity introduction apparatus according to claim 9 or 10 , wherein the film forming apparatus forms a silicon nitride film as the nitride film. The light source control section, an impurity introduction apparatus according to any one of claims 9 to 11, wherein the controller controls the energy density below 1.0 J / cm ² or more 6.0 J / cm ^2. The impurity introduction apparatus according to claim 9, wherein the light source emits the optical pulse having a wavelength of 190 nm or more and 380 nm or less. The impurity according to any one of claims 9 to 13, wherein the light source control unit performs control so that the light pulse is emitted at an irradiation frequency of 1 to 10 times per irradiation region. Introduction device. An XY moving stage for mounting the object and moving the object in an XY plane;
The beam adjustment system irradiates the nitride film on the surface of the object moved by the XY movement stage with the light pulse, so that the nitrogen is applied to a range of a desired plane region. The impurity introduction apparatus according to claim 9, wherein the introduced planar pattern is directly drawn. Providing an intermediate product having a first n-type semiconductor region in which nitrogen functions as a donor-type impurity element ;
Depositing a nitride film on the surface of the first n-type semiconductor region;
The nitride film is irradiated with a light pulse so as to reduce the thickness of the nitride film, and nitrogen in the nitride is introduced into the first n-type semiconductor region at a concentration exceeding the thermodynamic equilibrium concentration. Forming a second n-type semiconductor region;
Forming an ohmic contact electrode film in contact with the second n-type semiconductor region;
Only including,
The step of forming the second n-type semiconductor region includes:
Considering the film thickness of the nitride film, the energy density of the light pulse, and the irradiation time per time of the light pulse, the nitride is formed on the surface of the first n-type semiconductor region after the light pulse irradiation. Determining the number of times of irradiation of the light pulse so that the film remains for a film thickness corresponding to at least one atom;
Irradiating the nitride film with the light pulse at the energy density, the irradiation time and the number of irradiations;
A method for manufacturing a semiconductor device, comprising: The step of forming the second n-type semiconductor region is performed by scan irradiation performed while moving the plane position of the first n-type semiconductor region relative to the irradiation position of the light pulse in the XY plane. The method of manufacturing a semiconductor device according to claim 16 , wherein a planar pattern of the second semiconductor region is directly drawn.   The impurity introducing method according to claim 1, further comprising a step of removing the nitride film after the step of irradiating the light pulse.   The method of manufacturing a semiconductor device according to claim 16, further comprising a step of removing the nitride film after the step of forming the second n-type semiconductor region.

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