JP4060405B2 - Manufacturing method of semiconductor wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor wafer such as silicon.
[0002]
[Prior art]
The trend toward higher integration of LSIs such as DRAMs widely used in main storage devices of workstations and personal computers has been steadily progressing, and now the practical use of 1 Gbit DRAMs is being considered. Along with this, the miniaturization of LSI design rules such as 0.18 μm is also progressing.
[0003]
As the design rule is further miniaturized, even a slight defect or contamination on the semiconductor wafer that has been allowed until now greatly affects the product yield. For this reason, the defect-free and non-contamination of the semiconductor wafer surface is required more than the present situation.
[0004]
As a means for giving an answer to this request, effective use of laser light in the semiconductor wafer process has been actively performed recently. For example, Japanese Patent Laid-Open No. 62-257731 discloses a method of irradiating a semiconductor wafer with an excimer laser, photodissolving a resist material applied on the semiconductor wafer, and further removing the resist material by vacuum suction. According to this method, contaminants such as residual particles of the resist material can be completely removed from the surface of the semiconductor wafer.
[0005]
Further, an extrinsic gettering method in which a laser beam is irradiated on the back side of the device generation surface of a semiconductor wafer to form a layer having a large damage is disclosed in, for example, Japanese Patent Laid-Open No. 58-37983. According to this method, it is well known that the layer having the above damage absorbs defects and metal atoms in the vicinity of the surface.
[0006]
[Problems to be solved by the invention]
As described above, in the semiconductor wafer process, defect-free near the wafer surface and non-contamination of the surface are required more than the current situation. By the way, as a process of contaminating a wafer in a process of manufacturing a general mirror-polished wafer, for example, a chemical polishing process or the like is raised. In the chemical polishing process, contaminants such as trace heavy metals remaining on the etching surface on the back surface of the device generation surface enter the mirror-polished device generation surface and cause contamination of the device generation surface. In order to avoid this problem, when manufacturing semiconductor wafers that require a high degree of surface cleanliness, the back side of the device generation surface, which originally does not need to be mirror-polished by the simultaneous double-sided mirror polishing method, At the same time, it is necessary to perform a mirror polishing process, which contributes to an increase in manufacturing cost.
[0007]
Although it is conceivable to use an epitaxial wafer as a substrate with very little contaminants and high surface cleanliness, the epitaxial wafer is more expensive and has a lower throughput compared to a general mirror-polished wafer. The manufacturing cost is about 1.4 to 1.7 times as high as that of a general mirror wafer, which is further expensive. The present invention has been made in view of the above problems, has a surface cleanliness equivalent to that of a double-sided mirror-polished wafer, and can be manufactured at a lower cost than a double-sided mirror-polished wafer. It is an object to provide a method for manufacturing a polished wafer.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, a semiconductor wafer manufacturing method of the present invention is a semiconductor wafer manufacturing method including a chemical polishing step, and after the chemical polishing step, the entire one main surface of the semiconductor wafer is mirror-polished. The method further comprises a step of laser ablating the entire other main surface of the semiconductor wafer, and a step of laser ablating the entire other main surface of the semiconductor wafer after the cleaning step of the semiconductor wafer . .
[0009]
By subjecting the entire other main surface to laser ablation, contaminants such as heavy metals existing on the other main surface can be evaporated and removed. Further, even after the cleaning process, the entire main surface of the other side is subjected to laser ablation, so that contaminants attached to the other main surface in the cleaning process can be removed. As a result, the contaminants do not enter one of the mirror-polished main surfaces, and a semiconductor wafer with a high surface cleanliness can be manufactured.
[0012]
The semiconductor wafer manufacturing method of the present invention is preferably a short pulse laser in which the wavelength of laser light used for laser ablation is in the range of 100 to 400 nm, and the emission time of one time is 500 ns or less. It is.
[0013]
By using the laser beam as described above, the laser beam is absorbed by the very surface portion of the semiconductor wafer, and the peripheral portion other than the processing region can be hardly damaged.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
A method for manufacturing a semiconductor wafer according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram of a semiconductor wafer manufacturing method according to an embodiment of the present invention. The semiconductor wafer shown in FIG. 1A is a silicon wafer 10 cut out from a silicon single crystal ingot and subjected to pretreatment such as beveling and lapping.
[0015]
Usually, the silicon wafer 10 is cut out from a silicon single crystal ingot by an automatic slicing machine having an inner peripheral blade in which diamond powder particles are electrodeposited along the inner periphery. In recent years, the silicon wafer 10 can be cut out while constantly injecting a slurry containing abrasive grains mainly composed of diamond powder into a special steel thin wire having a wire diameter of 0.25 to 0.35 mm. A machine that can be used can also be used.
[0016]
The silicon wafer 10 cut out from the silicon single crystal ingot is subjected to chamfering (beveling) of the end face in order to prevent damage to the end face in the peripheral part in the subsequent process, and thereafter, both main surfaces are lapped. The The lapping process uses a double-sided wrap machine that rotates planetary gears. Normally, both main surfaces of each silicon wafer 10 are injected into a slurry of ^# 1200 alundum powder dissolved in oil or water while being injected into both main surfaces. Polish about 30-50 μm. As a result, both major surfaces have a lapped surface that is roughly polished (usually ^# 1200 alundum lapping surface).
[0017]
In the method of manufacturing a semiconductor wafer according to the present embodiment, first, both surfaces of a silicon wafer 10 having both surfaces wrapped (WS) are immersed in an HF / HNO ₃ acid solution and chemically polished (chemical etching). . Specifically, the silicon wafer 10 is mechanically moved up and down, left and right, and back and forth in an acid solution, and by applying ultrasonic waves to the silicon wafer 10, chemical polishing is performed efficiently and spatially uniformly. Is done. Here, in a product in which the flatness of the surface is particularly important, chemical polishing treatment may be performed using an alkaline solution instead of an acid solution. The surface of the silicon wafer 10 after chemical polishing is cut by about 20 to 30 μm, and both surfaces have an etched surface (ES) as shown in FIG.
[0018]
Thereafter, laser ablation processing is performed over the entire surface of the silicon wafer 10 that is not the device generation surface (hereinafter referred to as the back surface 12). As a result, the silicon wafer 10 is in the state shown in FIG. 1C where the back surface 12 has a laser ablation surface (LS) and the device generation surface (hereinafter referred to as the surface 14) has an etching surface (ES).
[0019]
Thereafter, the entire surface 14 is mirror-polished. In the mirror polishing process, a silicon wafer 10 is bonded to a surface plate using a paraffin-based thin film adhesive mixed with pine spider and the like, and a SiO ₂ sol or gel-like polishing solution is injected into the surface 14 of the silicon wafer 10. This is done using a mirror polishing machine driven by a carrier that performs planetary motion. The silicon wafer 10 is polished by laser ablation as shown in FIG. 1D by polishing the front surface 14 by about 10 to 20 μm while satisfying the specifications of the parallelism and thickness uniformity of the silicon wafer 10. The surface (LS) and the surface 14 are mirror surfaces (MS).
[0020]
The laser light used for the laser ablation process is desirably a short pulse laser having a wavelength in the range of 100 to 400 nm and a single emission time of 500 ns or less. Excimer lasers such as ArF laser, KrF laser, XeCl laser, and XeF laser have wavelengths of 193 nm, 248 nm, 308 nm, and 351 nm, respectively, and have pulse widths of several tens of ns. Therefore, they are used for laser ablation processing according to this embodiment. Ideal for. The Q-switched YAG harmonic laser also has a third harmonic wavelength and a fourth harmonic wavelength of 355 nm and 266 nm, respectively, and has a pulse width of several ns to several tens of ns. Can be used.
[0021]
The energy density of the laser beam to be irradiated is equal to or higher than the energy density necessary for ablating silicon, and is preferably an energy density that does not damage the deep portion of the silicon wafer 10, and is 3 to 20 J / cm ^2. The range of is preferable.
[0022]
Next, a method of irradiating the silicon wafer 10 with laser light in the laser ablation process will be described. Irradiation of the laser beam to the silicon wafer 10 is performed as shown in FIG. The laser light oscillated by the laser oscillator 16 is output-adjusted by the variable attenuator 18 and then shaped by the laser light shaping optical system 20. The laser beam shaped by the laser beam shaping optical system 20 is adjusted in the cross-sectional area of the light beam by the variable slit 22 and is folded vertically by the reflection mirror 24. The vertically folded laser light passes through the beam expander 26 and the linear beam shaping lens group 28 to become a linear laser beam having a linear cross section, and is placed on the moving stage 30 so that the back surface 12 faces up. The back surface 12 of the silicon wafer 10 is irradiated. Here, in order to perform laser ablation processing on the entire back surface 12 of the silicon wafer 10, the silicon wafer 10 may be irradiated with laser light while the moving stage 30 is sequentially moved.
[0023]
Further, as shown in FIG. 3, the length of the linear laser beam is expanded to the external dimension (diameter) of the silicon wafer 10 by the beam expander 26 and the linear laser beam shaping lens group 28, thereby moving the moving stage 30. The laser ablation process can be effectively performed on the entire back surface 12 of the silicon wafer 10 only by moving the laser beam in one direction perpendicular to the linear laser beam.
[0024]
Furthermore, as shown in FIG. 4, a transpiration removal device 32 for removing the transpiration generated by the ablation process may be provided in the vicinity of the upper portion of the portion irradiated with the laser light on the silicon wafer 10. The transpiration product remover 32 draws air from the suction port 34 using a vacuum pump, and makes the inside of the transpiration product removal device 32 have a negative pressure, thereby creating an air flow as shown in FIG. This air flow removes the transpiration from the upper part of the silicon wafer 10, and the cleanliness of the surface of the silicon wafer 10 can be kept at a higher level. Further, by adding a high-pressure electrostatic type (Cottrel type) dust collecting function to the transpiration product remover 32, it is possible to further enhance the effect of removing the transpiration product by the air flow.
[0025]
The silicon wafer 10 may be irradiated with laser light as shown in FIG. That is, instead of generating a linear laser beam having a linear cross section through the beam expander 26 and the linear beam shaping lens group 28, the condensing lens group 36 is used to condense the laser beam at one point, The entire back surface 12 of the silicon wafer 10 may be irradiated while moving the moving stage 30. In such a method, it is not necessary to use the beam expander 26, and the apparatus configuration is simplified.
[0026]
Further, the laser beam irradiation to the silicon wafer 10 may be performed as shown in FIG. That is, the laser beam shaped by the laser beam shaping optical system 20 and the sectional area of the light beam adjusted by the variable slit 22 is converted into a galvanometer mirror composed of a horizontal scan mirror 38 and a vertical scan mirror 40 and an F-Θ lens 42. In this method, the entire back surface 12 of the silicon wafer 10 placed on the fixed stage 44 with the back surface 12 facing upward is irradiated while scanning. When this method is used, the fixed stage 44 can be used in place of the moving stage 30, so that the apparatus can be miniaturized.
[0027]
Then, the effect | action and effect of the manufacturing method of the semiconductor wafer which concern on this embodiment are demonstrated. As in the semiconductor wafer manufacturing method according to the present embodiment, after the chemical polishing step, the entire back surface 12 of the silicon wafer 10 is subjected to laser ablation processing, so that contaminants such as heavy metals attached to the back surface 12 particularly during the chemical polishing step are removed. Can be evaporated, removed. Therefore, contamination of the surface 14 due to the contaminants entering the mirror-polished surface 14 in the subsequent process can be prevented.
[0028]
In particular, when the silicon wafer 10 is irradiated with pulsed laser light with an ultraviolet light such as an excimer laser and a pulse width of about several tens of ns, the laser light is absorbed only at the very surface portion of the silicon wafer 10 and does not reach the deep portion. In addition, an ultraviolet laser such as an excimer laser is different from an infrared laser with heat such as a YAG laser that oscillates at a wavelength of 1.06 μm and a CO ₂ laser that oscillates at a wavelength of 10.6 μm. It is possible to perform non-thermal processing in which the molecular bonds constituting the are cut with light.
[0029]
For example, when the silicon wafer 10 is irradiated with KrF excimer laser light having a wavelength of 248 nm, the energy density reaches several tens MW / cm ² on the surface portion of the silicon wafer 10 for a very short time. At the surface, the material evaporates with explosive momentum simultaneously with the laser light irradiation. However, since the pulse width is about several tens of ns and the laser light is absorbed only by the very surface portion of the silicon wafer 10, the processed portion does not spread except for the portion irradiated with the laser light, and almost no other than the processed portion. Does no damage.
[0030]
Further, by using a pulse laser, it is possible to control processing at a submicron level in the depth direction by controlling the irradiation energy density and the number of irradiation pulses.
[0031]
Further, since the laser ablation process is a non-contact and dry process, it is not necessary to use a solution that causes contamination, and it is easy to automate. Furthermore, since it is a physical process of laser light irradiation, any metal that can be removed is usable. Further, the back surface 12 of the silicon wafer 10 subjected to the laser ablation treatment can leave appropriate back surface damage in addition to the removal of the original contaminants by fine adjustment of the laser output. Therefore, the back surface 12 of the silicon wafer 10 has an optimum backside gettering effect required for the product, and an effect of absorbing defects and contaminants in the vicinity of or inside the surface of the silicon wafer 10 can also be expected. Furthermore, the stress applied to the surface portion of the silicon wafer 10 can be removed by the laser ablation process, and the warpage of the silicon wafer 10 can be prevented.
[0032]
In the method for manufacturing a semiconductor wafer according to the present embodiment, the back surface 12 of the silicon wafer 10 is laser ablated and then the surface 14 of the silicon wafer 10 is mirror-polished. In this case, it is more effective to laser ablate the back surface 12 of the silicon wafer 10 after the surface 14 of the silicon wafer 10 is mirror-polished.
[0033]
Furthermore, in the method for manufacturing a semiconductor wafer according to the present embodiment, laser ablation processing is performed after the chemical polishing step. However, in addition to the chemical polishing step, the method is similarly effective when performed after each cleaning step. . That is, the contaminants attached to the back surface 12 of the silicon wafer 10 are removed by the laser ablation process in the cleaning process, thereby preventing the contaminants from entering the surface 14.
[0034]
In the method for manufacturing a semiconductor wafer according to the present embodiment, the silicon wafer 10 is used, but a wafer made of a III-V group compound semiconductor crystal such as a germanium wafer or GaAs may be used. Even when these wafers are manufactured, the same effects as those of the above-described embodiment can be obtained by the laser ablation process.
[0035]
【The invention's effect】
As in the semiconductor wafer manufacturing method of the present invention, by performing laser ablation on the back surface of the semiconductor wafer after the chemical polishing step, the contaminants such as heavy metals adhering to the back surface in the chemical polishing step are removed by evaporation, and in the subsequent step. It is possible to prevent contaminants from entering the mirror-polished surface. Similarly, by performing laser ablation processing on the back surface of the semiconductor wafer after the cleaning step, it is possible to prevent contaminants attached to the back surface from flowing around the surface in the cleaning step.
[0036]
In addition, by finely adjusting the output of the laser beam applied to the semiconductor wafer, it becomes possible to remove transpiration of contaminants such as heavy metals without impairing the flatness of the surface of the semiconductor wafer before the laser beam irradiation. Therefore, it is possible to manufacture a semiconductor wafer having a surface cleanliness equivalent to that of a double-sided mirror-polished wafer at a lower cost.
[0037]
Further, by performing laser ablation processing using an ultraviolet pulse laser, it is possible to provide a high-quality wafer without damaging portions other than the processed portion.
[0038]
Moreover, it is possible to leave a desired backside damage on the back surface of the semiconductor wafer according to the quality specifications required for the product.
[Brief description of the drawings]
FIG. 1 is a process diagram of a semiconductor wafer manufacturing method according to an embodiment of the present invention.
FIG. 2 is a diagram showing a laser beam irradiation method in a semiconductor wafer manufacturing method according to an embodiment of the present invention.
FIG. 3 is a diagram showing a laser beam irradiation method in a method for manufacturing a semiconductor wafer according to an embodiment of the present invention.
FIG. 4 is a diagram showing a laser beam irradiation method in a method for manufacturing a semiconductor wafer according to an embodiment of the present invention.
FIG. 5 is a diagram showing a laser beam irradiation method in a method for manufacturing a semiconductor wafer according to an embodiment of the present invention.
FIG. 6 is a diagram showing a laser beam irradiation method in the semiconductor wafer manufacturing method according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Silicon wafer, 12 ... Back surface, 14 ... Front surface, 16 ... Laser oscillator, 18 ... Variable attenuator, 20 ... Laser beam shaping optical system, 22 ... Variable slit, 24 ... Reflection mirror, 26 ... Beam expander, 28 ... Line Laser beam shaping lens group, 30 ... moving stage, 32 ... transpiration remover, 34 ... suction port, 36 ... condensing lens group, 38 ... horizontal scan mirror, 40 ... vertical scan mirror, 42 ... F-Θ lens, 44 ... fixed stage, WS ... wrapped surface, ES ... etched surface, LS ... laser ablation surface, MS ... mirror surface

Claims (2)

In a method for manufacturing a semiconductor wafer including a chemical polishing step,
After the chemical polishing step,
While mirror-polishing the entire one main surface of the semiconductor wafer,
Laser ablating the entire other main surface of the semiconductor wafer ;
After the cleaning process of the semiconductor wafer,
A step of laser ablating the entire other main surface of the semiconductor wafer;
A method for producing a semiconductor wafer, comprising: The laser beam used for the laser ablation process is
The wavelength is in the range of 100-400 nm,
2. The method of manufacturing a semiconductor wafer according to claim 1 , wherein the light emitting time is a short pulse laser having a light emission time of 500 ns or less.

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