JP6076227B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device including a step of printing on a semiconductor wafer.

  Power devices, which are power semiconductor elements, are contactless switches that control large-capacity power. They are inverter circuits for home appliances such as air conditioners, refrigerators, and washing machines that are saving energy, and motor control for trains such as Shinkansen and subways. Has been applied. Furthermore, in recent years, from the viewpoint of protecting the global environment, the application fields such as inverter / converter control for hybrid cars that run in combination with electric motors and engines, and converters for solar and wind power generation have been expanded.

  Specific switching elements include an insulated gate bipolar transistor (IGBT: Insulated Gate Bipolar Transistor), a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and a diode. In some fields, compound semiconductors typified by silicon carbide (SiC) are also used as wafer materials, but silicon wafers are currently most used because of their ease of processing and low cost.

  Silicon wafers can be classified into various wafers according to the manufacturing method. Wafers used for power device applications are mainly epitaxial wafers, single crystal wafers, diffusion wafers, and the like. The epitaxial wafer is obtained by forming a high-resistance layer having a predetermined thickness on a low-resistance single crystal wafer by epitaxial growth. This epitaxial wafer is available in a relatively large diameter and is conventionally used for IGBTs and the like.

  The single crystal wafer is composed of a high resistance layer throughout and is used for devices such as IGBTs. When the device withstand voltage is 600 V or 1200 V, the final thickness of the single crystal wafer needs to be set to a few hundred tens of microns or less by the wafer process technology.

  The diffusion wafer is obtained by providing a low resistance layer by a diffusion layer on one side of a high resistance single crystal wafer, and handling is facilitated by a high resistance layer and a low resistance layer having a predetermined thickness necessary for the device. It is difficult to obtain a large-diameter product for this diffusion wafer, and it is used for diodes and some MOSFETs.

  Conventionally, epitaxial wafers have been mainly used as IGBT wafers, but single crystal wafers have recently started to be used due to advances in wafer process technology. For example, a recent trend is to achieve an improvement in electrical characteristics by finishing an element having a wafer thickness of about 120 μm in a 1200V withstand voltage product and a wafer thickness of about 60 μm in a 600V withstand voltage product. Furthermore, device manufacturing using single crystal wafers has become mainstream not only for IGBT but also for manufacturing diodes and other semiconductor elements, and it is considered that the specific gravity of single crystal wafers in power devices will increase in the future. It is done.

  In manufacturing a power device, a single crystal having a resistivity corresponding to the breakdown voltage of the device is required. For example, a 1200 V withstand voltage product requires a single crystal having a resistivity of about 60 Ω · cm, and a 600 V withstand voltage product requires a single crystal having a resistivity of about 30 Ω · cm. In an N-type silicon single crystal, it is necessary to dope an N-type impurity such as phosphorus accurately (within a range of ± 10%) according to the resistivity.

  The CZ (Czochralski) method is best known as a method for producing a silicon single crystal. This manufacturing method is a method in which polycrystalline silicon as a raw material and phosphorus as a dopant are placed in a quartz crucible, and a seed crystal is brought into contact with the surface of the heat-melted raw material to grow single crystal silicon. However, in this manufacturing method, the resistivity in the length direction of the single crystal ingot changes due to segregation of impurities, so it is difficult to make the variation in resistivity within a range of ± 10% in the entire length direction of the single crystal ingot. It is.

  FZ (Floating Zone) method, which is another silicon single crystal manufacturing method, heats and melts one end of rod-shaped polycrystalline silicon as a raw material with a ring-shaped high-frequency heating coil, and makes a seed crystal contact the molten portion from one end. In this method, a single crystal is obtained by moving a molten portion toward multiple ends. In this manufacturing method, phosphorus is doped by supplying a gas such as phosphine to the molten portion, so that a target resistivity can be obtained over the entire region in the length direction. However, this manufacturing method is characterized in that the variation in resistivity occurs in the in-plane direction of the wafer because the volume of the molten silicon melt is small and thermally unstable.

As an impurity doping method for solving the above problem, there is an NTD (Neutron Transmutation Doping) method. In this method, single crystal silicon that is not doped with impurities is placed in a nuclear reactor and irradiated with thermal neutrons. Thereby, the nuclear conversion reaction shown in the following formula (1) occurs, and phosphorus is doped in the silicon single crystal. In the formula (1), “ ³⁰ Si” and “ ³¹ Si” each represent an isotope of a silicon atom, “ ³¹ P” represents a phosphorus atom, “n” represents a thermal neutron, and β represents a beta ray. Show.
^{[30 Si + n] → 31} Si → [31 P + β] ··· (1)
However, the NTD method has a problem that radiation damage is generated in the single crystal while phosphorus can be uniformly doped in the single crystal. This radiation damage is formed as a pair of empty lattice points and ejected atoms when fast neutrons in the reactor collide with single crystal silicon and the atoms located at the lattice points are ejected. is there. Single crystal silicon in which radiation damage has occurred has a significant decrease in lifetime and an increase in resistivity, making it difficult to use as a semiconductor. Therefore, in order to measure the resistivity of the ingot after doping by the NTD method, a treatment for recovering radiation damage by annealing at a high temperature of several hundred degrees Celsius or higher is performed.

  This recovery heat treatment is most often performed (ingot annealing) in the state of a single crystal ingot after irradiation with neutrons (a state of a cylindrical lump). For example, in a small-diameter ingot having a diameter (φ) of 5 inches or less, heat treatment is performed at about 700 ° C. for several hours. However, as the diameter (φ) of the ingot increases to 6 inches or 8 inches, the volume and the heat capacity increase, making it difficult to perform the recovery heat treatment in the ingot state. Therefore, it is necessary to perform a recovery heat treatment in a wafer state with a small heat capacity.

  It is necessary to perform the recovery heat treatment in the wafer state by arranging the wafers one by one in the boat, and it is difficult to carry out all the wafers due to throughput problems. Therefore, the recovery heat treatment is performed only on the wafer used for the resistivity measurement, and the other wafers are shipped without being subjected to the recovery heat treatment. And the heat processing in the wafer process of a device manufacturing process is implemented also as the said recovery heat processing, and generation | occurrence | production of the malfunction on the characteristic by radiation damage can be suppressed in the manufactured device.

  However, in the process before the first heat treatment in the device manufacturing process, since the radiation damage is not recovered, there may be a problem due to the radiation damage. For example, in the printing process, which is the first step in the device manufacturing process, an identification symbol (letters, numbers, codes, etc.) for identifying and recognizing individual wafers is printed by irradiating the wafer with radiation damage remaining with a laser. The Here, when the wafer on which radiation damage remains is irradiated with a laser, a part of the laser output for melting and printing the wafer surface is used as energy for recovering the radiation damage. As a result, the wafer surface cannot be melted sufficiently, and it becomes difficult to print an identification symbol with good visibility.

  Also, a measure of raising the output in advance in consideration that a part of the laser output is used may be considered. However, if an output that exceeds the energy required to melt a certain area of the silicon surface is given, it will be inconvenient in the semiconductor wafer process, such as collapse of the printed shape, unevenness in the thickness direction, and dust generation due to bumping or scattering of the molten silicon. Will cause harmful effects.

  In addition, the degree of radiation damage remaining on the wafer depends on the target resistivity in the NTD method, the type of moderator introduced into the reactor (heavy water, light water), fast neutrons determined from the structure and state of the reactor It varies depending on the abundance ratio with thermal neutrons. For this reason, it is difficult to set the laser output according to individual wafers having different degrees of radiation damage.

On the other hand, for example, in Japanese Patent Laid-Open No. 2013-38268 (hereinafter referred to as Patent Document 1), a semiconductor substrate irradiated with a neutron beam is subjected to a heat treatment and then irradiated with a YVO ₄ laser to print an identification pattern. Has been proposed.

JP 2013-38268 A

  In the method proposed in Patent Document 1, an identification pattern with good visibility can be printed by performing heat treatment before printing the identification pattern. However, in this method, since the heat treatment process for recovering the damage introduced by the NTD method is performed separately from the printing process, there is a problem in that the efficiency of the entire device manufacturing process is lowered.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a semiconductor device capable of printing an identification symbol with good visibility on a semiconductor wafer while suppressing a decrease in manufacturing efficiency. Is to provide.

  A method of manufacturing a semiconductor device according to the present invention includes a step of preparing a semiconductor wafer in which radiation damage remains, and a heating member while heating a region in which radiation damage remains on one main surface of the semiconductor wafer by a heating member. Irradiating the region with laser light from a different laser light source and printing on the semiconductor wafer.

  According to the method for manufacturing a semiconductor device according to the present invention, it is possible to print an identification symbol with good visibility on a semiconductor wafer while suppressing a decrease in manufacturing efficiency.

3 is a flowchart schematically showing a method for manufacturing a semiconductor device according to an embodiment of the present invention. It is a schematic plan view which shows a silicon single crystal wafer. FIG. 3 is a schematic sectional view taken along a line segment A-A ′ in FIG. 2. FIG. 6 is another schematic cross-sectional view taken along line A-A ′ in FIG. 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
First, Embodiment 1 which is one embodiment of the present invention will be described. In the method for manufacturing a semiconductor device according to the present embodiment, for example, a semiconductor device such as an IGBT, MOSFET, or diode is manufactured. Referring to FIG. 1, in the method of manufacturing a semiconductor device according to the present embodiment, a semiconductor wafer preparation step is first performed as a step (S10).

  In this step (S10), first, an ingot (not shown) made of single crystal silicon is produced by CZ method, FZ method or the like. Next, doping of an impurity element is performed on the ingot produced by the NTD (Neutron Transform Doping) method.

In this NTD method, first, an ingot made of single crystal silicon is placed in a nuclear reactor. Then, the single crystal silicon is irradiated with thermal neutrons generated by fast neutrons losing energy by the moderator in the nuclear reactor. As a result, ³⁰ Si present in the single crystal silicon becomes ³¹ Si by neutron irradiation, and thereafter beta (β) decays and is converted to ³¹ P, which is a stable isotope element. By this nuclear conversion reaction, the impurity element phosphorus is uniformly doped in the single crystal silicon.

  In this step (S10), fast neutrons in the nuclear reactor collide with single crystal silicon, and silicon atoms are ejected from lattice points. As a result, radiation damage consisting of pairs of empty lattice points and ejected silicon atoms is formed in the single crystal silicon.

  Next, the ingot made of single crystal silicon, which has been doped with phosphorus, is cut into a predetermined thickness. Thereby, a plurality of silicon single crystal wafers 1 (semiconductor wafers) shown in FIG. 2 are obtained. The silicon single crystal wafer 1 has a disk shape and has a notch portion 2 with a part of the end portion notched.

  The silicon single crystal wafer 1 still has radiation damage formed during phosphorus doping by the NTD method. This radiation damage can be recovered by an annealing process (ingot annealing) in an ingot state before cutting, but this annealing process is not performed in the present embodiment. Therefore, a silicon single crystal wafer 1 with radiation damage remaining is prepared.

  Next, a printing step is performed as a step (S20). In this step (S20), with reference to FIG. 2 and FIG. 3, identification symbols (characters, numbers, codes, etc.) are printed on the silicon single crystal wafer 1 prepared in the step (S10). This identification symbol is for identifying and recognizing the individual silicon single crystal wafer 1 in a later step. FIG. 3 schematically shows a cross section of the silicon single crystal wafer 1 taken along line A-A ′ in FIG. 2.

  Referring to FIG. 2, first, a laser printing area 3, which is an area where an identification symbol is to be printed, is set on one main surface 1 a of silicon single crystal wafer 1. The laser printing area 3 is set not in the central area where the device of the silicon single crystal wafer 1 is to be formed but in the area on the end side. The laser printing area 3 may have a rectangular shape or other shape. Further, since radiation damage remains on the entire silicon single crystal wafer 1, radiation damage also remains on the laser printing region 3.

Referring to FIG. 3, next, laser light source 4 is arranged in the main surface 1a side area (above laser printing area 3), and heater 5 (heating member) is on the other side opposite to main surface 1a. It arrange | positions at the main surface 1b side. The laser light source 4 and the heater 5 are arranged so as to overlap with the laser printing region 3 in plan view. The heater 5 is disposed in contact with the main surface 1b. Then, while the laser printing area 3 is heated by the heater 5, the laser light source 4 irradiates the laser printing area 3 with laser light (arrow in FIG. 3). As a result, the single crystal silicon constituting the laser printing region 3 is melted by irradiation with laser light while being heated by the heater 5, and the melted portion is printed on the main surface 1a of the silicon single crystal wafer 1 as an identification symbol.

  The silicon single crystal wafer 1 on which the identification symbol is printed is obtained by the steps (S10) and (S20). Thereafter, formation of an impurity region, formation of an oxide film, formation of an electrode, and the like are performed to manufacture a semiconductor device such as an IGBT, a MOSFET, or a diode.

  Next, after describing the characteristics of the method of manufacturing the semiconductor device according to the present embodiment, the operation and effect will be described. In the method of manufacturing a semiconductor device according to the present embodiment, a step of preparing a silicon single crystal wafer 1 (semiconductor wafer) in which radiation damage remains, and radiation damage on one main surface 1a of the silicon single crystal wafer 1 remain. The laser printing area 3 is heated by the heater 5 (heating member), and the laser light source 4 different from the heater 5 is irradiated with laser light to the laser printing area 3 to print on the silicon single crystal wafer 1. .

  In the method for manufacturing a semiconductor device according to the present embodiment, first, a silicon single crystal wafer 1 into which radiation damage has been introduced by the NTD method in step (S10) is prepared. In step (S20), the laser printing region 3 where the radiation damage remains is irradiated with laser while being heated by the heater 5, whereby an identification symbol is printed on the main surface 1a. Therefore, it is possible to print the identification symbol by melting silicon by laser irradiation while recovering radiation damage by heating the heater 5. Thereby, a part of laser output is used for recovery from radiation damage, and it is possible to suppress a decrease in energy for melting silicon. As a result, it is possible to print an identification symbol with good visibility on the silicon single crystal wafer 1 where radiation damage remains. Further, unlike the case where printing is performed after the silicon single crystal wafer 1 is heat-treated, a decrease in manufacturing efficiency can be suppressed by printing while heating. Therefore, according to the method for manufacturing a semiconductor device according to the present embodiment, it is possible to print an identification symbol with good visibility on the silicon single crystal wafer 1 while suppressing a decrease in manufacturing efficiency.

  In the semiconductor device manufacturing method, in the printing step (S20), the laser printing region 3 is heated by the heater 5 arranged on the main surface 1b opposite to the main surface 1a, and is arranged on the main surface 1a side. Alternatively, the laser light may be emitted from the laser light source 4 to the laser printing region 3. By arranging the laser light source 4 and the heater 5 in the above-described arrangement, it becomes easy to perform laser irradiation while heating the laser printing region 3.

  In the semiconductor device manufacturing method, the heater 5 may be disposed in contact with the main surface 1b (FIG. 3). Thereby, the laser printing region 3 can be efficiently heated by the heater 5.

  In the semiconductor device manufacturing method, the heating member may be the heater 5 disposed in contact with the main surface 1b, but is not limited thereto. For example, the heating member may be a lamp arranged with a space between the silicon single crystal wafer 1. By adopting the non-contact heating method in this way, it is possible to suppress the introduction of dirt and scratches on the main surface 1b of the silicon single crystal wafer 1.

(Embodiment 2)
Next, Embodiment 2 which is another embodiment of the present invention will be described. The manufacturing method of the semiconductor device according to the present embodiment is basically performed in the same manner as the manufacturing method of the semiconductor device according to the first embodiment and has the same effects. However, the semiconductor device manufacturing method according to the present embodiment is different from the semiconductor device manufacturing method according to the first embodiment in the printing process.

  Referring to FIG. 4, in the present embodiment, both laser light source 4 and lamp 6 (heating member) are arranged in a region on main surface 1a side (above laser printing region 3). The laser light source 4 and the lamp 6 are arranged so as to overlap with the laser printing region 3 in plan view. The lamp 6 is disposed at a distance from the silicon single crystal wafer 1, and is disposed at a position farther from the silicon single crystal wafer 1 than the laser light source 4 (above the laser light source 4). Then, while the laser printing area 3 is heated by the lamp 6, the laser light source 4 irradiates the laser printing area 3 with laser light (arrow in FIG. 4). Thereby, the single crystal silicon constituting the laser printing region 3 is melted by the irradiation of the laser beam while being heated by the lamp 6, and the melted portion is printed on the main surface 1 a of the silicon single crystal wafer 1 as an identification symbol. Even if the main body (laser oscillating unit) of the laser light source 4 is arranged at another place and a part of the optical system for guiding the laser beam to the laser printing region 3 is arranged between the lamp 6 and the main surface 1a. Good.

  As described above, in the printing process of the manufacturing method of the semiconductor device according to the present embodiment, the laser printing area 3 is heated by the lamp 6 (heating member) arranged on the main surface 1a side, and the main surface 1a side is heated. Laser light is irradiated to the laser printing region 3 from the arranged laser light source 4. The lamp 6 is disposed with a space between the silicon single crystal wafer 1 (semiconductor wafer). Even when the laser light source 4 and the lamp 6 are arranged as described above, as in the case of the first embodiment, it is possible to print an identification symbol with good visibility on the silicon single crystal wafer 1 while suppressing a decrease in manufacturing efficiency. it can.

  In the method for manufacturing the semiconductor device according to the present embodiment, the heating member may be the lamp 6 but is not limited thereto. For example, the heating member may be another laser light source that generates laser light having a larger spot diameter than the laser light generated by the laser light source 4. As a result, similarly to the lamp 6, the laser printing area 3 can be easily heated.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The method for manufacturing a semiconductor device of the present invention can be applied particularly advantageously in a method for manufacturing a semiconductor device including a step of printing on a semiconductor wafer.

  DESCRIPTION OF SYMBOLS 1 Silicon single crystal wafer, 1a, 1b main surface, 2 notch part, 3 laser printing area | region, 4 laser light source, 5 heater, 6 lamps.

Claims (7)

Preparing a semiconductor wafer with radiation damage remaining;
By heating only a part of the semiconductor wafer with a heating member, the printing region included in the region where the radiation damage remains on one main surface of the semiconductor wafer is heated from a laser light source different from the heating member. A method of manufacturing a semiconductor device, comprising: irradiating a printing region with a laser beam and printing on the semiconductor wafer. Wherein the portion of the semiconductor wafer, said the one main surface is a part of the other main surface on the opposite side,
The laser light source is Ru is disposed on the main surface side of said one method of manufacturing a semiconductor device according to claim 1.   The method of manufacturing a semiconductor device according to claim 2, wherein the heating member is disposed in contact with the other main surface.   The method of manufacturing a semiconductor device according to claim 2, wherein the heating member is disposed with a space between the heating member and the semiconductor wafer. The portion of the semiconductor wafer is part of the one main surface,
The laser light source is Ru is disposed on the main surface side of said one method of manufacturing a semiconductor device according to claim 1.   The method of manufacturing a semiconductor device according to claim 5, wherein the heating member is disposed with a space between the heating member and the semiconductor wafer.   The method of manufacturing a semiconductor device according to claim 6, wherein the heating member is another laser light source that generates laser light having a spot diameter larger than that of the laser light generated by the laser light source.

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