Method for manufacturing semiconductor wafer and apparatus for manufacturing semiconductor wafer

Abstract

Provided is a method for manufacturing a semiconductor wafer that can be easily manufactured in a short time.　A method for manufacturing a semiconductor wafer 15 by irradiating a semiconductor ingot 10 from the surface toward the inside by a pulse laser beam 20, wherein, when the semiconductor ingot 10 is irradiated from the surface toward the inside by the pulse laser beam 20, a first semiconductor wafer processing step is performed by interposing a condensing means 21 to form a condensing point and moving the semiconductor ingot and the condensing point relative to each other to form a processing region that is parallel to the surface of the semiconductor ingot inside the semiconductor ingot, and then a second semiconductor wafer processing step of cutting along the processing region inside the semiconductor ingot using a wire saw is performed to obtain the semiconductor wafer, and a third semiconductor wafer processing step of polishing the surface of the semiconductor ingot is performed so that the surface of the semiconductor ingot that was cut out by the wire saw can be internally irradiated.

Description

Semiconductor wafer manufacturing method and semiconductor wafer manufacturing device

[0001] The present invention relates to a semiconductor wafer manufacturing method and semiconductor wafer manufacturing apparatus for manufacturing thin semiconductor wafers by slicing them from a semiconductor ingot.

[0002] Conventionally, when manufacturing semiconductor wafers such as silicon wafers, a cylindrical semiconductor ingot solidified from silicon melt in a crucible is cut into blocks of an appropriate length, the peripheral portions of which are ground to a target diameter, and the blocked semiconductor ingot is then sliced ​​into wafer shapes using a wire saw to manufacture the semiconductor wafers, although this is not shown in the drawings.

[0003] In recent years, silicon carbide (SiC) has been considered and developed as a next-generation semiconductor because of its excellent breakdown field strength, wide band gap, high hardness, and high thermal conductivity. However, because silicon carbide is harder than silicon, it is no longer possible to easily slice semiconductor ingots with a wire saw, and this inevitably leads to longer work times.

[0004] To solve these problems, Patent Document 1 describes a method in which a laser beam having a wavelength that is transparent to silicon carbide is irradiated from a focal point positioned inside a semiconductor ingot to form a modified layer and cracks on the surface to be cut, and the semiconductor ingot is pressed and rotated to apply torsional stress to separate the semiconductor wafers.

[0005] JP 2016-111143 A

[0006] In the semiconductor wafer manufacturing method described in Patent Document 1, the wafer is peeled off while extending cracks that have formed in the modified layer, thereby successfully shortening the time required for separation (cutting). However, on the other hand, uneven surfaces caused by the cracks remain on the surfaces of the semiconductor wafer and semiconductor ingot after separation, which causes a problem in that the process of polishing these uneven surfaces takes a long time.

[0007] This polishing process is generally divided into two stages: rough polishing and finish polishing. While this two-stage process does have the effect of shortening the time, it does not solve the problem of the long process time, as polishing hard materials such as silicon carbide requires a long time.

[0008] Another known method for manufacturing wafers from semiconductor ingots is to use a wire saw. However, because multiple wires are used to process a single ingot, although multiple wafers can be obtained at once, the processing time is long and it is less efficient than laser irradiation.

[0009] The present invention has been made in view of the above, and has as its object to provide a semiconductor wafer manufacturing method and manufacturing apparatus that can easily manufacture semiconductor wafers in a shorter time than conventional methods.

[0010] That is, the manufacturing method according to the present disclosure is a semiconductor wafer manufacturing method for manufacturing a semiconductor wafer by irradiating a semiconductor ingot from its surface to its interior with pulsed laser light, in which a first semiconductor wafer processing step is performed by using a focusing means to form a focusing point inside the semiconductor ingot when irradiating the semiconductor ingot from its surface to its interior, and relatively moving the semiconductor ingot and the focusing point to form a processing region inside the semiconductor ingot parallel to the surface of the semiconductor ingot, and then a second semiconductor wafer processing step is performed in which a wire saw peels the semiconductor ingot along the processing region inside the semiconductor ingot to obtain a semiconductor wafer, and a third semiconductor wafer processing step is performed in which the surface of the semiconductor ingot cut by the wire saw is polished so that the surface can be internally irradiated with pulsed laser light, thereby enabling the manufacturing of a new semiconductor wafer, and the first, second, and third semiconductor wafer processing steps to be performed continuously.

[0011] The manufacturing apparatus according to the present disclosure is a semiconductor wafer manufacturing apparatus that manufactures semiconductor wafers by irradiating a semiconductor ingot from its surface to its interior with pulsed laser light, and includes a laser processing unit that, when irradiating the semiconductor ingot from its surface to its interior with pulsed laser light, uses focusing means to form a focusing point inside the semiconductor ingot and moves the semiconductor ingot and the focusing point relatively to form a processing region inside the semiconductor ingot parallel to the surface of the semiconductor ingot, a wire saw processing unit that uses a wire saw to peel along the processing region inside the semiconductor ingot to obtain a semiconductor wafer, and a polishing processing unit that polishes the surface of the semiconductor ingot so that the surface of the semiconductor ingot cut by the wire saw can be internally irradiated with pulsed laser light, and a transfer unit is provided to enable processing to be performed continuously by the three processing units: the laser processing unit, the wire saw processing unit, and the polishing processing unit.

[0012] The semiconductor wafers used in the manufacturing method and manufacturing apparatus are preferably silicon carbide. In the manufacturing method, the first, second, and third semiconductor wafer processing steps are preferably arranged on the same circumference so that they can be performed continuously. In the manufacturing apparatus, the processing units are preferably arranged on the same circumference. In the manufacturing method, a cleaning step for cleaning the ingot is preferably performed after the second semiconductor wafer processing step and / or the third semiconductor wafer processing step. In the manufacturing apparatus, a cleaning unit is preferably provided immediately after the laser processing unit and / or the polishing unit.

[0013] With this configuration, semiconductor wafers can be manufactured in a shorter time than with conventional manufacturing methods and manufacturing devices that use wire saws.

[0014] Furthermore, by forming a processing region inside the semiconductor ingot using pulsed laser light, it is possible to achieve thinner wires than before with a wire saw, thereby improving the production rate.

[0015] According to the present invention, it is possible to provide a semiconductor wafer manufacturing method and a semiconductor wafer manufacturing apparatus that can shorten the processing time when cutting a semiconductor ingot.

[0016] Fig. 1 is an explanatory diagram of a semiconductor wafer manufacturing apparatus. Fig. 2 is an explanatory diagram of a laser processing unit. Fig. 3 is a cross-sectional view of a semiconductor ingot showing a laser irradiation pattern in a first semiconductor wafer processing step. Fig. 4 is a cross-sectional view of a semiconductor ingot showing a modified example of the laser irradiation pattern in the first semiconductor wafer processing step. Fig. 5 is a partial cross-sectional view of a semiconductor ingot showing another modified example of the laser irradiation pattern in the first semiconductor wafer processing step.

[0017] Hereinafter, a manufacturing method and a manufacturing apparatus according to one aspect of the present disclosure will be described in detail with reference to the illustrated embodiments. Note that the drawings include schematic drawings and may not reflect actual dimensions or proportions.

[0018] FIG. 1 illustrates a semiconductor wafer manufacturing apparatus according to the present invention. The manufacturing apparatus includes a laser processing unit 40, a wire saw processing unit 50, and a polishing processing unit 60, all of which are arranged on the same circumference. A transfer unit 70 is also provided for transferring semiconductor ingots 10 on the same circumference. It is also preferable to provide an insertion / removal unit 80, a cleaning / drying unit 85, and a cleaning unit 90, all of which are arranged on the same circumference as the processing units. This provides a semiconductor wafer manufacturing method in which each manufacturing step is arranged on the same circumference and semiconductor ingots 10 are transferred while being rotated on the same circumference.

[0019] First, in the manufacturing method and manufacturing apparatus of the present invention, when irradiating pulsed laser light 20 from the surface toward the inside of semiconductor ingot 10, focusing means 21 is interposed to form a focusing point inside semiconductor ingot 10, and semiconductor ingot 10 and the focusing point are moved relatively to form a processing region (modified surface) inside semiconductor ingot 10 parallel to the surface of semiconductor ingot 10, thereby performing a first semiconductor wafer processing step.

[0020] 2 is an explanatory diagram of the laser processing unit 40. The first semiconductor wafer processing step can be performed in the laser processing unit 40 of FIG.

[0021] In the laser processing unit 40, a pulsed laser beam 20 is irradiated from a laser light source toward the semiconductor ingot 10. The energy and other characteristics of the pulsed laser beam 20 are adjusted by a laser control unit. The semiconductor ingot 10 is fixed on an ingot table 11, and the table control unit can control the ingot table 11 to move to any position in the horizontal direction (left-right direction in FIG. 2 ).

[0022] The pulse laser has specifications such as a wavelength of 1030 or 1064 nm, a repetition rate of 10 kHz or higher, energy of 1.0 to 20.0 μJ, and a pulse width of 500 fs to 10 ps. The focusing means 21 (lens specifications) has a focal length of 2 to 10 mm and a numerical aperture that is as high as possible (for example, a numerical aperture of 0.55 to 0.85), and the processing conditions for the pulse laser and focusing means 21 are a spot diameter of 10 to 50 μm. The above embodiment is an example of processing a silicon carbide wafer to a processing depth of 600 μm.

[0023] When irradiating the semiconductor ingot 10 with the pulsed laser beam 20, an arbitrary processing depth is determined in the depth direction from the Si-face side of the polished surface of the semiconductor ingot 10 according to the desired wafer thickness, and a plane parallel to the surface of the semiconductor ingot 10 at the determined processing depth becomes the planned cutting surface 35. The focal point is adjusted to be located on the planned cutting surface 35. For example, the focal point is positioned while either the pulsed laser beam 20 or the semiconductor ingot 10 is moved vertically as shown in FIG. 2 . Then, while maintaining the desired processing depth, the focal point is moved horizontally on the planned cutting surface 35 with either the pulsed laser beam 20 or the semiconductor ingot 10. In this manner, the internal processing of the semiconductor ingot 10 is continuously performed. These focal points are formed across the entire planned cutting surface 35, forming the modified surface 31, which is later cut by the wire saw processing unit 50.

[0024] Even if the semiconductor ingot 10 has an off-axis angle (for example, an off-axis angle of 4°), the cutting plane 35 can be made parallel to the surface of the semiconductor ingot 10. Since it is desirable to set laser irradiation conditions so as to minimize crack extension, the present invention does not actively utilize crack extension. These methods are advantageous for improving the product yield (reducing material loss) because they can reduce the adverse effects of cracks.

[0025] As described above, when irradiating the pulsed laser 20, either the pulsed laser 20 or the semiconductor ingot 10 is moved on a plane (left and right in the explanatory diagram of FIG. 2 ), and the relative movement may be such that the entire cutting surface 35 of the semiconductor ingot 10 is irradiated. Specifically, the movement may be linear, or may be curved and spiral. This allows for the surface shape of the semiconductor ingot 10 and the shape of the semiconductor wafer 15 to be either circular or rectangular.

[0026] FIG. 3 is a cross-sectional view of a semiconductor ingot 10 showing a laser irradiation pattern in the first semiconductor wafer processing step. Pulsed laser light 20 is irradiated onto the semiconductor ingot 10 to form a focal point within the semiconductor ingot 10. The focal point and the semiconductor ingot 10 are moved relative to each other to create a modified surface 31 on the intended cutting surface 35. FIG. 3 also shows the positions where modified portions 30 are created on the modified surface 31. The cylindrical semiconductor ingot 10 has a flat surface (orientation flat) at the bottom, which is used to indicate crystal orientation and for alignment. This modified surface 31 has modified portions 30 arranged at equal intervals in the vertical and horizontal directions in the figure. The pulsed laser light 20 is irradiated, for example, from the left end of the top row to the right, then down to the second row from the top when it reaches the right end, then from the right end of the second row to the left, then down to the third row when it reaches the left end, and then from the left end of the third row to the right. This process is repeated until irradiation is complete up to the bottom row. The above embodiment is merely an example of the irradiation order, and other irradiation orders may be adopted.

[0027] 4 is a cross-sectional view of a semiconductor ingot 10 showing a modified laser irradiation pattern in the first semiconductor wafer processing step. The modified portions 30 are arranged concentrically on the cutting surface of the semiconductor ingot 10. The irradiation order may be from the center to the outside, or from the outside to the center. The modified portions 30 may also be arranged in a spiral rather than a concentric circle (not shown). A spiral arrangement allows for smoother relative movement of the focal point and the cutting surface 35 inside the semiconductor ingot 10.

[0028] FIG. 5 is a partial cross-sectional view of a semiconductor ingot 10 showing another modified example of the laser irradiation pattern in the first semiconductor wafer processing step. While FIGS. 3 and 4 illustrate the processing of a cylindrical semiconductor ingot 10, FIG. 5 is a partial cross-sectional view illustrating an irradiation pattern that can be applied to shapes other than cylindrical (e.g., rectangular parallelepiped). FIG. 5 shows the positions at which modified portions 30 are created on the modified surface 31. This modified surface 31 is not arranged so that the modified portions 30 are aligned in a straight line in the vertical direction, but are arranged with a stagger. The above embodiment is merely an example, and an optimal irradiation pattern, not shown, may be searched for and selected.

[0029] The proportion and arrangement of the modified portion 30 on the modified surface 31 affect the subsequent second semiconductor wafer processing step. For example, increasing the proportion of the modified portion 30 will lengthen the time for the first semiconductor wafer processing step, but will shorten the time for the second semiconductor wafer processing step. In other words, it is desirable to balance the time spent on each step in order to proceed with processing continuously.

[0030] After the semiconductor ingot 10 has been processed by the laser processing unit 40 (first semiconductor wafer processing step), it is transported to the right side (counterclockwise rotation direction) in the explanatory diagram of Figure 1, where the second semiconductor wafer processing step is carried out by the wire saw processing unit 50.

[0031] The wire saw processing unit 50 has at least one wire 51 for cutting the intended cutting surface 35 (modified surface 31) of the semiconductor ingot 10, and in the second semiconductor wafer processing step, the wire 51 is run to cut the semiconductor ingot 10, aiming at the modified surface 31 formed inside the semiconductor ingot 10. After cutting, the semiconductor wafer 15 is peeled off from the semiconductor ingot 10 and is held by suction on a wafer table 52. The wire saw processing unit 50 may also include a tensioner that applies a predetermined tension to the wire 51, a supply reel for supplying the wire 51, and a recovery reel for recovering the used wire 51.

[0032] The present invention offers a time-saving effect compared to conventional wire saw cutting. Irradiation with pulsed laser light modifies the material, turning it into an amorphous material. In the amorphous modified portion, the distances between atoms become irregular, weakening the bonding strength between atoms and creating cavities. These phenomena reduce the time it takes for the wire to pass through the modified surface and remove the material compared to conventional wire saw processing. Furthermore, because less force is required, the effect of reduced force can be used to shorten processing time by cutting faster, and the load on the wire is reduced, making it possible to make thinner wires.

[0033] Due to the lapping effect, the cut surface produced by the wire saw has smaller surface irregularities than other techniques (for example, the method described in Patent Document 1 in which the modified layer and cracks caused by internal irradiation are pressed while stress is applied by rotation to peel off the wafer), and the processing time for the next step, the polishing process, which is the third semiconductor wafer processing step, can be shortened.

[0034] Although some literature states that cutting using a wire saw device results in a large kerf loss, in the manufacturing method described in Patent Document 1, the semiconductor wafer is peeled off by connecting the modified layer caused by internal irradiation with pulsed laser light and the cracks extending from the modified layer, so that uneven surfaces caused by the cracks remain on the surfaces of the semiconductor wafer and semiconductor ingot, and the polishing process takes a long time. According to the present invention, the surfaces of the semiconductor wafer and semiconductor ingot are scraped off with a wire, which can eliminate the effect of laser irradiation on the ingot surface and reduce the burden of the polishing process.

[0035] After being processed by the wire saw processing unit 50, the semiconductor ingot 10 is transported to the cleaning unit 90 located on the upper right side (counterclockwise rotation direction) of the wire saw processing unit 50 in the explanatory diagram of FIG. 1, where cleaning is performed.

[0036] After cleaning, the semiconductor ingot 10 is transported to the upper left side (counterclockwise rotation direction) of the cleaning section 90 in the explanatory diagram of FIG. 1, where the third semiconductor wafer processing step is carried out by the polishing section 60.

[0037] The polishing section 60 is equipped with a grinding wheel 61 and a spindle for rotating the grinding wheel, and polishes the semiconductor ingot 10 by rotating both the semiconductor ingot 10 and the grinding wheel 61 while the grinding wheel 61 is in contact with the surface of the semiconductor ingot 10 after the semiconductor wafer 15 has been cut off. In this polishing, it is sufficient that the surface roughness of the semiconductor ingot 10 is adjusted to an extent that laser irradiation is possible. Note that a configuration may be adopted in which either the semiconductor ingot 10 or the grinding wheel 61 rotates, or a mechanism may be added that moves the semiconductor ingot 10 and the grinding wheel 61 relative to each other. This polishing may be performed in two stages, rough polishing and finish polishing, or both polishing stages may be arranged on the same circumference.

[0038] In the present invention, the second semiconductor wafer processing step reduces the surface irregularities of the semiconductor wafer 15 and the semiconductor ingot 10, thereby reducing the polishing allowance and reducing the burden of the polishing process. A smaller polishing allowance reduces material loss and increases the production yield. In other words, the fact that kerf loss increases when cutting using a wire saw refers to material loss during cutting, and should be compared based on a comprehensive evaluation that includes material loss due to subsequent polishing. Therefore, the present invention can improve the production yield compared to conventional wire saw cutting, and does not necessarily result in a worse production yield compared to manufacturing methods such as those in Patent Document 1.

[0039] After the semiconductor ingot 10 has been processed by the polishing section 60, it is transported to the cleaning and drying section 85 located to the left (counterclockwise rotation direction) of the polishing section 60 in the explanatory diagram of Figure 1, where it is cleaned and dried. After the cleaning and drying, the semiconductor ingot 10 is transported to the laser processing section 40 located below (counterclockwise rotation direction) the cleaning and drying section 85 in the explanatory diagram of Figure 1, where the first semiconductor wafer processing step is performed. Thereafter, the first to third semiconductor wafer processing steps are repeated.

[0040] In the above embodiment, the semiconductor ingot 10 is rotated around the same circumference while each processing step is performed, realizing continuous processing, and the insertion and removal of the semiconductor ingot 10 is also performed by the insertion / removal unit 80 arranged on the same circumference as each processing unit, and the transfer between each processing unit is performed by rotating the transfer unit 70. Arranging the units on the same circumference as in Figure 1 is advantageous for automation and time saving.

[0041] Furthermore, the process of polishing the cut surface of the semiconductor wafer 15 peeled off from the semiconductor ingot 10 after processing by the wire saw processing unit 50 may be arranged on the same circumference, or may be arranged outside the same circumference (not shown).

[0042] When a semiconductor ingot is cut using a conventional wire saw device, multiple semiconductor wafers can be obtained at one time, but the cut wafers are temporarily stored in a container, and the container is brought in to coincide with the polishing process, the semiconductor wafers are removed from the container, and the semiconductor wafers are placed in a predetermined position for polishing. By arranging the process for polishing the cut surface of the semiconductor wafer 15 on the same circumference, the wire saw processing unit and the polishing processing unit are adjacent to each other, making continuous operation possible, and as a result, processing time can be shortened.

[0043] As described above, the present invention can provide a semiconductor wafer manufacturing method and manufacturing apparatus that can easily manufacture semiconductor wafers in a shorter time than conventional methods and can also improve the production yield.

[0044] Although the above description is based on the processing of a silicon carbide ingot, the present invention can also be applied to materials other than silicon carbide, such as gallium nitride (GaN), etc. Furthermore, the present invention is not limited to ingot cutting, and can also be applied to the extraction of thin wafers from thicker wafers.

[0045] REFERENCE SIGNS LIST 10 Semiconductor ingot 11 Ingot table 12 Table control unit 15 Semiconductor wafer 20 Pulsed laser light 21 Focusing means 22 Laser light source 23 Laser control unit 30 Modified portion 31 Modified surface 35 Planned cutting surface 40 Laser processing unit 50 Wire saw processing unit 51 Wire 52 Wafer table 60 Polishing processing unit 61 Grindstone 70 Transfer unit 80 Insertion / removal unit 85 Cleaning / drying unit 90 Cleaning unit

Claims

1. A method for manufacturing a semiconductor wafer by irradiating a semiconductor ingot from its surface to its interior, comprising the steps of: performing a first semiconductor wafer processing step in which, when irradiating the semiconductor ingot from its surface to its interior with pulsed laser light, a focusing means is interposed to form a focusing point inside the semiconductor ingot, and the semiconductor ingot and the focusing point are moved relatively to form a processing region inside the semiconductor ingot parallel to the surface of the semiconductor ingot; then performing a second semiconductor wafer processing step in which a wire saw peels the semiconductor ingot along the processing region inside the semiconductor ingot to obtain a semiconductor wafer; and performing a third semiconductor wafer processing step in which the surface of the semiconductor ingot cut by the wire saw is polished so that the surface of the semiconductor ingot can be internally irradiated with pulsed laser light.

2. The method for producing a semiconductor wafer according to claim 1, wherein the semiconductor wafer is made of silicon carbide.

3. A method for manufacturing semiconductor wafers according to claim 1, characterized in that the first, second and third semiconductor wafer processing steps are arranged on the same circumference so that they can be carried out continuously.

4. The method for producing a semiconductor wafer according to claim 3, further comprising a cleaning step of cleaning the ingot after the second semiconductor wafer processing step and / or the third semiconductor wafer processing step.

5. A semiconductor wafer manufacturing device for manufacturing semiconductor wafers by irradiating a semiconductor ingot from its surface to its interior, comprising: a laser processing unit that, when irradiating the semiconductor ingot from its surface to its interior with pulsed laser light, uses a focusing means to form a focusing point inside the semiconductor ingot and moves the semiconductor ingot and the focusing point relatively to form a processing area inside the semiconductor ingot parallel to the surface of the semiconductor ingot; a wire saw processing unit that uses a wire saw to peel along the processing area inside the semiconductor ingot to obtain a semiconductor wafer; and a polishing processing unit that polishes the surface of the semiconductor ingot so that the pulsed laser light can be irradiated inside the surface of the semiconductor ingot cut by the wire saw, and a transfer unit is provided to allow processing to be performed continuously by the three processing units, that is, the laser processing unit, the wire saw processing unit and the polishing processing unit.

6. The semiconductor wafer manufacturing apparatus according to claim 5, wherein the semiconductor wafer is made of silicon carbide.

7. The semiconductor wafer manufacturing apparatus according to claim 5, wherein said laser processing section, said wire saw processing section and said polishing processing section are arranged on the same circumference.

8. The semiconductor wafer manufacturing apparatus according to claim 7, further comprising a cleaning section provided immediately after said laser processing section and / or said polishing processing section.

Images