JP6646510B2 - Spin etching method and semiconductor wafer manufacturing method - Google Patents

Description

  The present invention relates to a spin etching method and apparatus, and a method for manufacturing a semiconductor wafer.

  Conventionally, the demand for the thickness of a semiconductor wafer (hereinafter, also simply referred to as “wafer”) in the market has been about 200 μm, but in recent years, the demand for the thickness of the wafer in the market has been reduced to about 50 μm.

  When thinning a wafer, the wafer is thinned by back grinding. However, when a wafer having a diameter of, for example, 8 inches (hereinafter, referred to as an “8-inch wafer”) is thinned by back grinding, a problem of wafer warpage and a problem of wafer strength occur.

  Therefore, in order to solve the problem of wafer warpage and the problem of wafer strength, a method called TAIKO grinding or TAIKO process is known (for example, see Patent Documents 1 and 2 below). In the TAIKO grinding, as shown in FIG. 5, only the central portion of the wafer W is mechanically ground and thinned while leaving the outer peripheral end portion 100 of the wafer W of about several mm, so that the wafer W on which the back surface concave portion 102 is formed is formed. Becomes In the TAIKO grinding, the outer peripheral end of the wafer remains without being ground, so that the mechanical strength is maintained, and problems such as cracking and warping of the wafer are reduced. That is, in the TAIKO grinding, the device region and the outer peripheral surrounding region surrounding the device region are formed on the front surface, and the back surface corresponding to the device region of the semiconductor wafer is ground to form a ring on the rear surface corresponding to the outer peripheral surrounding region. By performing the back surface grinding so as to form the reinforcing portion and form the back surface concave portion in the region of the back surface corresponding to the device region, the wafer W having the back surface concave portion 102 is formed as shown in FIG. .

  In the wafer to which TAIKO grinding is applied as described above, the thickness of the back surface concave portion 102 can be set to, for example, 100 μm or less. However, when the surface shape of the ground surface of the wafer thinned to 100 μm or less is analyzed, as shown in FIG. 6, after the surface shape once rises toward the outer periphery from the center of the wafer (thick rising portion 104). It was found that the cross-section became a shape similar to a state where the gulls extended their wings (a so-called gull shape). As described above, the gull-shaped wafer means a wafer having a concentrically thick protruding portion in a partial region around the center of the wafer. FIG. 7 schematically shows a gull-shaped wafer.

  Wafers are becoming thinner in recent years, and there is an ever-increasing demand on the market to further improve the in-plane uniformity of thinned wafers. In particular, in the manufacture of an IGBT (Insulated Gate Bipolar Transistor), since current flows in the thickness direction of the wafer, the in-plane uniformity of the wafer affects the characteristics of the IGBT. It is necessary to make the inside thickness uniform.

  Further, in order to cope with TSV (through-silicon via) in the future, improvement of in-plane uniformity is indispensable.

  On the other hand, after grinding the back surface of the wafer, planarization is also performed using CMP (Chemical Mechanical Polishing).

  However, in the case of a power device system, a removal margin of, for example, 15 μm is required to remove a damaged layer, and therefore, CMP cannot be applied.

  Further, Patent Document 3 points out a problem (variation of a so-called seagull shape) in which the thickness in a wafer surface varies as shown in FIG. Therefore, a wafer processing method that solves such a problem is proposed. However, Patent Document 3 does not attempt to improve in-plane uniformity by etching a gull-shaped wafer.

  On the other hand, when flattening a ground surface of a wafer having a seagull cross-section after etching the back surface by etching as described above, conventionally, in order to pursue in-plane uniformity, etching is performed so that the etching amount is uniform. Had gone. Since such uniform etching aims at maintaining the in-plane shape change rate, the in-plane shape change rate does not change even if the etching allowance is increased, and the in-plane cross-section seagull shape is also maintained. There was a problem that would.

  Further, for example, in Patent Document 4, while supplying an etching liquid to the center of rotation of the substrate, a scan arm is moved to a region from the peripheral portion to the central portion of the substrate to swing and supply the etching suppressing liquid, A method for selective etching is also disclosed. However, in such an etching method using an etching suppressing liquid, the etching liquid is mixed with the etching suppressing liquid, so that the etching liquid cannot be collected and reused. Further, Patent Document 4 is not directed to a wafer obtained by TAIKO grinding.

JP2007-335659 Patent 5613792 JP 2008-60470 JP 2003-318154

  The present invention has been made in view of the above-described problems of the related art, and without using an etching suppression liquid, the cross-sectional surface shape distribution in the back surface after the back surface grinding is uniform within the back surface of the semiconductor wafer having a seagull shape. It is an object of the present invention to provide a spin etching method and apparatus with improved performance and a method for manufacturing a semiconductor wafer.

  In order to solve the above problem, a spin etching method of the present invention is a spin etching method in which a semiconductor wafer is rotated, and an etching solution is dropped from an etching solution supply nozzle on a back surface of the semiconductor wafer. A region and an outer peripheral surrounding region surrounding the device region are formed on the front surface of the semiconductor wafer, and the back surface corresponding to the device region is ground to form a ring-shaped reinforcing portion on the back surface corresponding to the outer peripheral surrounding region. A back surface grinding is performed so that a back surface concave portion is formed in a region of the back surface corresponding to the device region, and a cross-sectional surface shape distribution in the back surface concave portion after the back surface grinding is a seagull shape, a seagull shape wafer after the back surface grinding is prepared. And spinning while rotating the etching solution supply nozzle at a predetermined swing width in the diameter direction of the back surface. A spin etching step of performing etching, so that the etchant supply nozzle is folded back at the seagull-shaped thick rise portion, so that the back surface grinding after the back surface of the seagull-shaped wafer and the seagull-shaped thick rise. A spin etching method in which the etching liquid supply nozzle is swung between the first and second portions.

  In the spin etching step, it is preferable to use a semiconductor wafer having a flatness TTV of 2.0 μm or less.

  The gull-shaped wafer after the back surface grinding is a wafer having a gull-shaped cross-sectional surface shape distribution in the back surface concave portion after the back surface grinding, and has a thick raised portion in a partial region around the center of the wafer. Wafer. That is, as shown in FIGS. 6 and 7, the surface shape once rises toward the outer periphery than the center of the wafer, and then becomes flat, so that the cross section has a shape similar to a state in which seagulls have extended wings. Refers to a wafer that has become In the illustrated example of FIG. 6, the seagull-shaped thick rising portion is in a range of 16 mm to 80 mm and in a range of −16 mm to −80 mm, and the top of the thick rising portion is at a position of 48 mm and −48 mm. is there.

  The etching liquid supply nozzle is provided between the center of the back surface of the back-gulled gull-shaped wafer and the gull-shaped thick ridge so that the etching liquid supply nozzle is folded at the top of the gull-shaped thick ridge. Preferably, the nozzle is swung.

  The gull-shaped wafer after the back surface grinding is a wafer to which TAIKO grinding is applied. More specifically, a back surface corresponding to the device region of a semiconductor wafer having a device region and an outer peripheral region surrounding the device region formed on the surface is ground to form a ring-shaped reinforcement on the rear surface corresponding to the outer peripheral region. By performing the back surface grinding so as to form a portion and form a back surface concave portion in the region of the back surface corresponding to the device region, only the central portion of the wafer is mechanically ground while leaving the outer peripheral edge of the wafer about several mm. This is a wafer having a rear surface recess formed by thinning.

  The size of the semiconductor wafer is not particularly limited, but can be suitably applied to, for example, wafers having a diameter of 6 inches, 8 inches, or 12 inches. When the semiconductor wafer is an 8-inch wafer, it is preferable that the predetermined swing width is ± 40 to ± 60 mm from the center of the diameter of the wafer. The nozzle swing width ± X mm means that the nozzle swings + X mm and −X mm in the diameter direction from the center of the wafer.

  The spin etching step is to measure the surface shape distribution of the back surface of the gull-shaped wafer after the back surface grinding before etching, and to control at least the swing width according to the surface shape distribution. preferable. The surface shape distribution can be measured, for example, by measuring the thickness distribution with a thickness measuring device using a laser interference method.

  The spin etching apparatus according to the present invention is a spin etching apparatus used in the spin etching method, and includes a spin table rotatably provided and having a wafer holding means on an upper surface, and a swing table for supplying an etchant to the upper surface of the spin table. A movable etchant supply nozzle.

  A method of manufacturing a semiconductor wafer according to the present invention is a method of manufacturing a semiconductor wafer including an etching step by the spin etching method. According to the method of manufacturing a semiconductor wafer of the present invention, it is also possible to obtain a semiconductor wafer having a flatness of TTV of 2.0 μm or less. More specifically, it is also possible to obtain a semiconductor wafer having a TTV of 2.0 μm or less and exceeding 0 μm.

  TTV is an abbreviation of Total Thickness Variation, and is a value indicating the difference between the maximum value and the minimum value of the height measured over the entire surface in the thickness direction in the wafer surface. TTV can be measured, for example, by a thickness measuring device using a laser interferometry.

  ADVANTAGE OF THE INVENTION According to this invention, the spin etching method and apparatus which improved the in-plane uniformity of the back surface of the semiconductor wafer in which the cross-sectional surface shape distribution in the back surface after a back surface grinding is a seagull shape without using an etching suppression liquid, and a semiconductor. There is a remarkable effect that a method for manufacturing a wafer can be provided.

FIG. 2 is a schematic perspective view showing a spin etching apparatus used in the spin etching method of the present invention. It is a side surface schematic diagram which shows the state which dripped the etching liquid from the etching liquid supply nozzle with respect to the back surface of the gull-shaped wafer after back surface grinding. It is a top view which shows the measurement direction of TTV of the Example of this invention, and a comparative example. 4 is a graph showing a margin shape obtained by etching a semiconductor wafer using the spin etching method of the present invention. It is a schematic side view which shows the semiconductor wafer after performing back surface grinding by TAIKO grinding. It is a graph which shows the cross-section surface shape distribution after performing back surface grinding by TAIKO grinding. FIG. 4 is a schematic perspective view schematically showing a seagull shape in a back surface concave portion after performing back surface grinding by TAIKO grinding. 4 is a graph showing the results of Example 1 of the present invention. 6 is a graph showing the results of Example 2 of the present invention. 9 is a graph showing the results of Example 3 of the present invention. 9 is a graph showing the results of Example 4 of the present invention. 9 is a graph showing the results of Example 5 of the present invention. 9 is a graph showing the results of Example 6 of the present invention. 5 is a graph showing the results of Comparative Example 1 of the present invention.

  One embodiment of the spin etching method of the present invention will be described with reference to the accompanying drawings.

  In FIG. 1, a spin etching apparatus 10 is a spin etching apparatus used in the spin etching method of the present invention. The spin etching apparatus 10 includes a spin table 16 rotatably mounted on a rotary support 12 and having a wafer holding unit 14 on an upper surface, and a swingable etchant supply for supplying an etchant E to the upper surface of the spin table 16 And a nozzle 18.

  In the spin etching method of the present invention, the spin etching apparatus 10 is preferably used, but the cross-sectional surface shape distribution in the back surface after the back surface grinding is a seagull shape, and the back-ground seagull shape wafer is a target of the spin etching. Therefore, a seagull-shaped wafer W after the back surface grinding is first prepared (a process for preparing a seagull-shaped wafer after back surface grinding).

  Then, as shown in FIG. 2, spin etching is performed while the etchant supply nozzle 18 is swung in a predetermined swing width in the diameter direction of the back surface. At this time, the etching liquid supply nozzle 18 is swung in a diametrical direction on the back surface so that the etching liquid supply nozzle 18 is folded back at the seagull-shaped thick rising portion 104 (see FIGS. 6 and 7). Spin etching is performed with the width D1 (spin etching step). In particular, it is preferable that the etching solution supply nozzle be swung so that the etching solution supply nozzle is turned back at the vertex of the seagull-shaped thick rising portion 104. As a result, a wafer having an improved TTV representing flatness is obtained. In FIG. 2, symbol O indicates the center of the wafer.

  TTV is a value indicating the difference between the maximum value and the minimum value of the height measured over the entire surface in the thickness direction within the wafer surface. As shown in FIG. 3, the TTV can be measured by a thickness measuring device that measures the entire surface of the wafer in the thickness direction using a laser interference method. The notch 20 in the wafer W in FIG. As the number of measurement points, for example, it is preferable to indicate the difference between the maximum value and the minimum value of the height measured at 13 points in the wafer surface.

  When the semiconductor wafer is an 8-inch wafer, the predetermined swing width is preferably ± 40 to ± 60 mm from the center of the diameter of the wafer. The swing speed of the etching liquid supply nozzle 18 is preferably 10 to 50 mm / s.

  The spin etching step is to measure the surface shape distribution of the back surface of the gull-shaped wafer after the back surface grinding before etching, and to control at least the swing width according to the surface shape distribution. More preferred.

  As a control method, for example, the swing width is increased or the swing speed is adjusted to be lower.

  Furthermore, since the temperature of the wafer increases when the amount of etching increases, the temperature of the back-ground seagull-shaped semiconductor wafer W is temperature-controlled by the wafer temperature detecting means, and the temperature of the back-ground seagull-shaped semiconductor wafer W is 24 ° C. ± 1. It is preferable to adjust the rotation speed of the gull-shaped semiconductor wafer W after the back surface grinding so as not to exceed ° C. As the wafer temperature detecting means, an infrared radiation thermometer is preferable. As for the adjustment of the rotation speed, the rotation speed is adjusted in consideration of the fact that if the rotation is slowed, the etching amount increases (temperature rises), and if the rotation is increased, the etching amount decreases (temperature falls), What is necessary is just to manage temperature.

  In the present invention, the etching is performed so that the etching amount becomes uniform and the purpose is not to maintain the shape change rate, as in the related art. The inner uniformity is improved. That is, when the seagull-shaped semiconductor wafer is etched after the back surface is ground using the spin etching method of the present invention, the etching allowance is as shown in FIG. The etching allowance is increased from the thick ridge at a position about 40 mm away from the center toward the outer periphery of the wafer.

  A method of manufacturing a semiconductor wafer according to the present invention is a method of manufacturing a semiconductor wafer including an etching step by the spin etching method. According to the method of manufacturing a semiconductor wafer of the present invention, it is also possible to obtain a semiconductor wafer having a flatness of TTV of 2.0 μm or less.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples, and various modifications can be made without departing from the technical idea of the present invention. Of course.

(Example 1)
An 8-inch silicon single crystal wafer was prepared by grinding its back surface by TAIKO grinding. In the diameter direction shown in FIG. 3 (that is, measured from right to left with the notch down), a 13-point thickness measuring apparatus using laser interferometry (manufactured by Hamamatsu Photonics Co., Ltd.) on the back surface of the wafer. Was measured using a thickness gauge C11011-01). Using a MIMASU SPIN PROCESSOR manufactured by Mimasu Semiconductor Industry Co., Ltd., which is the same apparatus as the spin etching apparatus shown in FIG. 1, using a mixed acid etching solution based on hydrofluoric acid and nitric acid under the following etching conditions: Then, the wafer was subjected to spin etching by swinging the nozzle.
<Etching conditions>
Etching solution temperature: 24 ° C., number of rotations: 900 rpm, etching solution flow rate: 3 L / min, nozzle swing width: ± 50 mm (turning back at the top of the thick rising portion), nozzle swing speed: 30 mm / sec
The meaning of ± 50 mm of the nozzle swing width means that the nozzle swings +50 mm and −50 mm in the diameter direction from the center of the wafer. The results are shown in Table 1 and FIG. In the table, Time means the etching time, and Rate means the etching rate.

(Example 2)
Spin etching was performed in the same manner as in Example 1 except that the following etching conditions were used.
<Etching conditions>
Etching solution temperature: 24 ° C., number of rotations: 900 rpm, etching solution flow rate: 3 L / min, nozzle swing width: ± 50 mm (turning back at the top of the thick ridge), nozzle swing speed: 60 mm / sec
The results are shown in Table 2 and FIG.

(Example 3)
An 8-inch silicon single crystal wafer was prepared by back-grinding the wafer by TAIKO grinding. In the diameter direction shown in FIG. 3 (that is, measured from right to left with the notch down), a 13-point thickness measuring apparatus (manufactured by Hamamatsu Photonics Co., Ltd.) using the laser interferometer on the back surface of the wafer. Was measured using a thickness meter C11011-01). Using a MIMASU SPIN PROCESSOR manufactured by Mimasu Semiconductor Industry Co., Ltd., which is the same apparatus as the spin etching apparatus shown in FIG. 1, using a mixed acid etchant based on hydrofluoric acid and nitric acid under the following etching conditions: Then, by spinning the nozzle, spin etching was performed on the wafer.
<Etching conditions>
Etching solution temperature: 24 ° C., number of revolutions: 500 rpm, flow rate of etching solution: 3 L / min, nozzle swing width: ± 40 mm (returning in the range of the thick rising portion), nozzle swing speed: 60 mm / sec
The results are shown in FIG. The TTV before etching was 4.10 μm, whereas the TTV after etching was 4.63 μm. Therefore, the difference (improvement amount) in TTV was -0.53 [mu] m.

(Example 4)
Spin etching was performed in the same manner as in Example 3 except that the following etching conditions were used.
<Etching conditions>
Etching solution temperature: 24 ° C., number of rotations: 500 rpm, etching solution flow rate: 3 L / min, nozzle swing width: ± 58 mm (returning within the range of thick ridge), nozzle swing speed: 60 mm / sec
The results are shown in FIG. The TTV before etching was 3.90 μm, while the TTV after etching was 3.85 μm. Therefore, the difference (improvement amount) in TTV was 0.05 μm.

(Example 5)
Spin etching was performed in the same manner as in Example 3 except that the following etching conditions were used.
<Etching conditions>
Etching solution temperature: 24 ° C., number of revolutions: 500 rpm, flow rate of etching solution: 3 L / min, nozzle swing width: ± 70 mm (returning in the range of the thick rising portion), nozzle swing speed: 60 mm / sec
The result is shown in FIG. The TTV before etching was 3.56 μm, while the TTV after etching was 4.41 μm. Therefore, the difference (improvement amount) in TTV was -0.95 [mu] m.

(Example 6)
Spin etching was performed in the same manner as in Example 3 except that the following etching conditions were used.
<Etching conditions>
Etching solution temperature: 24 ° C., number of rotations: 500 rpm, etching solution flow rate: 3 L / min, nozzle swing width: ± 80 mm (returning in the range of the thick rising portion), nozzle swing speed: 60 mm / sec
FIG. 13 shows the results. The TTV before the etching was 3.95 μm, whereas the TTV after the etching was 6.2 μm. Therefore, the difference (improvement amount) in TTV was -2.25 [mu] m.

(Comparative Example 1)
Spin etching was performed in the same manner as in Example 3 except that the nozzle was fixed at the center of the wafer and was etched under the following etching conditions without swinging.
<Etching conditions>
Etching solution temperature: 24 ° C., rotation speed: 500 rpm, etching solution flow rate: 3 L / min, nozzle swing width: ± 0 mm
FIG. 14 shows the results. The TTV before etching was 3.74 μm, while the TTV after etching was 26.73 μm. Therefore, the difference in TTV (improvement amount) was −22.99 μm.

  As can be seen from Examples 1 to 6 and Comparative Example 1, according to the present invention, the value of TTV is significantly improved as compared with Comparative Example 1 of the conventional method, and the back surface is used without using an etching suppressing liquid. It can be seen that the in-plane uniformity of the back surface of the semiconductor wafer having a seagull-shaped cross-sectional surface shape distribution in the back surface after grinding is improved.

  10: Spin etching apparatus, 12: Rotary support, 14: Wafer holding means, 16: Spin table, 18: Etching liquid supply nozzle, 20: Notch, 100: Outer edge, 102: Concave recess, 104: Thick emboss Ascending portion, D1: swing width of the etching solution supply nozzle, E: etching solution, O: wafer center, W: wafer.

Claims (5)

A spin etching method comprising rotating an semiconductor wafer and dripping an etchant from an etchant supply nozzle on a back surface of the semiconductor wafer,
A back surface corresponding to the device region of the semiconductor wafer having a device region and an outer peripheral region surrounding the device region formed on the surface is ground to form a ring-shaped reinforcement on the rear surface corresponding to the outer peripheral region. A back surface grinding is performed so as to form a back surface concave portion in the region of the back surface corresponding to the device region, and the cross-sectional surface shape distribution in the back surface concave portion after the back surface grinding is a seagull shape, the back surface ground seagull shape wafer. The step of preparing,
A spin etching step of performing spin etching while oscillating the etchant supply nozzle at a predetermined oscillation width in the diameter direction of the back surface,
The etchant supply nozzle is provided between the center of the rear surface of the back-ground grinded gull-shaped wafer and the seagull-shaped thick ridge so that the etchant supply nozzle is folded back at the gull-shaped thick ridge. A spin-etching method that makes it swing.   The etching liquid supply nozzle is provided between the center of the back surface of the back-gulled gull-shaped wafer and the gull-shaped thick ridge so that the etching liquid supply nozzle is folded at the top of the gull-shaped thick ridge. 2. The spin etching method according to claim 1, wherein the nozzle is swung.   3. The spin etching method according to claim 1, wherein when the semiconductor wafer is an 8-inch wafer, the predetermined swing width is ± 40 to ± 60 mm from a center of the diameter of the semiconductor wafer.   The spin etching step, measuring the surface shape distribution of the back surface of the back-gull-shaped seagull-shaped wafer before etching before etching, according to the surface shape distribution, at least the swing width was controlled, Item 4. The spin etching method according to any one of Items 1 to 3.   A method for manufacturing a semiconductor wafer, comprising an etching step by the spin etching method according to claim 1.

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