TW201802929A - Method and apparatus for spin etching and manufacturing method of semiconductor wafer capable of improving in-plane thickness uniformity of a wafer - Google Patents

Abstract

Provided is a method and an apparatus for spin etching and manufacturing method of a semiconductor wafer which can improve in-plane uniformity of a back side of a semiconductor wafer, in which a distribution of cross section surfaces in the back side is distributed in a gull shape after the back side is ground, without using etching suppressant. The spin etching method includes: a step of grinding a back surface of a wafer by TAIKO grinding and preparing the wafer in a gull shape whose back surface is ground, in which a shape of a cross section surface in a recessed part of the back surface is distributed in a gull shape after the rear surface is ground; and a spin etching step of performing spin etching while swinging an etching liquid supplying nozzle by a predetermined swinging width in a diameter direction of the back surface, in which the etching liquid supply nozzle is swung between a center of the back surface of the wafer in the gull shape whose back surface is ground and a thick raised part in the gull shape after the back surface is ground so that the etching liquid supply nozzle is folded back at the thick raised part in the gull shape.

Description

Rotary etching method and device, and manufacturing method of semiconductor wafer

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

In the past, the thickness requirements of semiconductor wafers in the market (hereinafter also referred to simply as "wafers") were about 200 μm, but in recent years, the wafer thinness requirements in the market have gradually come to about 50 μm.

When the wafer is thinned, a back grind of the wafer is performed to thin the wafer. However, if a wafer with an 8-inch diameter (hereinafter referred to as an "8-inch wafer") is ground and thinned, the problem of wafer warpage or wafer strength may occur.

Therefore, in order to solve the problem of wafer warpage or wafer strength, a method called TAIKO grinding or a TAIKO process is known (see, for example, the following Patent Documents 1 and 2). In TAIKO grinding, as shown in FIG. 5, the outer peripheral end portion 100 of the wafer W is left for several mm, and only the crystal The center portion of the circle is thinned by mechanical grinding, thereby forming a wafer W having a back surface recessed portion 102 formed thereon. In TAIKO grinding, the outer peripheral end of the wafer is left without being ground, so it maintains mechanical strength and reduces problems such as wafer cracking and warping. That is, in TAIKO grinding, the back surface corresponding to the element region of the semiconductor wafer in which the element region and the peripheral region surrounding the element region are formed on the surface is ground and the back surface corresponding to the peripheral region is formed. A ring-shaped reinforcing portion is formed, and a back surface grinding of a back surface recessed portion is formed in an area of the back surface corresponding to the aforementioned element region. As shown in FIG. 5, the wafer W is formed with the back surface recessed portion 102.

In the wafer to which TAIKO grinding is applied as described above, the thickness of the back surface recessed portion 102 can be, for example, 100 μm or less. However, if the surface shape of the grinding surface of the wafer thinned to 100 μm or less is analyzed, as shown in FIG. 6, it can be seen that the surface shape is raised as the surface shape rises (thickness bulge as the center of the wafer moves further toward the outer periphery). 104), and it is formed into a shape with a flat cross section similar to a state in which a seagull spreads its wings (a so-called seagull shape). As described above, the wafer in the shape of a seagull means a wafer having a wall thickness ridge in a concentric circle in a part of the area around the center of the wafer. FIG. 7 shows a pattern of a wafer showing a seagull shape.

Wafer thinning has been progressing in recent years, and market demand for more uniformity of the in-plane uniformity of thinned wafers is increasing. In particular, in the manufacture of IGBT (Insulated Gate Bipolar Transistor), because the current flows in the thickness direction of the wafer, the in-plane uniformity of the wafer will affect the characteristics of the IGBT, so it is necessary to Make the thickness in the plane of the wafer uniform.

In addition, in order to support TSV (through-silicon via), the improvement of in-plane uniformity is indispensable.

On the other hand, after grinding the back surface of the wafer, CMP (Chemical Mechanical Polishing) is also used to planarize the wafer.

However, in the case of a power element system, in order to remove a damaged layer, a machining allowance of, for example, 15 μm is required, and therefore, CMP is not suitable.

In addition, in Patent Document 3, as shown in FIG. 8-2 of Patent Document 3, the problem caused by wafer grinding is pointed out that the problem of uneven thickness in the wafer surface (so-called seagull shape occurs) Problem), a wafer processing method is proposed to solve the problems shown above. However, Patent Document 3 is not intended to improve in-plane uniformity by etching a seagull-shaped wafer.

On the other hand, when planarizing the grinding surface of a wafer having a cross-section seagull-shaped surface after grinding on the back surface as described above, conventionally, in order to pursue in-plane uniformity, etching has been performed so that the amount of etching becomes uniform. In the uniform etching shown above, the purpose is to maintain the in-plane shape change rate. Therefore, even if more machining allowance is added, the in-plane shape change rate will not change, and there will be a cross-section seagull shape in the plane. The problem is also maintained.

In addition, for example, Patent Document 4 also discloses a method of supplying an etching solution to a rotation center of a substrate, and moving a scanning arm to a region from a peripheral portion to a central portion of the substrate to swing the etching suppression solution to supply the And selective etching method. However, in the etching method using the etching suppression liquid as described above, since the etching liquid is mixed with the etching suppression liquid phase, the etching liquid cannot be recovered for reuse. In addition, Patent Document 4 is not intended to target a wafer obtained by TAIKO grinding.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2007-335659

[Patent Document 2] Japanese Patent 5613792

[Patent Document 3] Japanese Patent Laid-Open No. 2008-60470

[Patent Document 4] Japanese Patent Application Laid-Open No. 2003-318154

The present invention has been made in view of the problems of the conventional techniques described above, and aims to provide a uniform surface within the back surface of a semiconductor wafer in which the cross-sectional surface shape of the back surface after back grinding is distributed without using an etching suppression liquid. Rotary etching method and device with improved performance and manufacturing method of semiconductor wafer.

In order to solve the above problems, the rotary etching method of the present invention rotates a semiconductor wafer, and an etching solution is applied to the back surface of the semiconductor wafer. A rotary etching method in which an etching solution is dropped by supplying a nozzle includes performing a grinding process on a back surface corresponding to the element region of a semiconductor wafer in which an element region is formed on a surface and a peripheral region surrounding the element region. An annular reinforcing portion is formed on the back surface corresponding to the outer periphery surrounding area, and a back surface grinding of a back surface recessed portion is formed in the back surface area corresponding to the element area, and the cross-sectional surface shape distribution in the back surface recessed portion after the back surface grinding is prepared is a seagull shape A process of forming a seagull-shaped wafer after grinding the back surface; and a rotary etching process of performing rotary etching while swinging the etching solution supply nozzle in a predetermined swing width direction in the diameter direction of the rear surface; The shape of the wall thickness raised portion is folded back by swinging the etching solution supply nozzle between the center of the back surface of the seagull-shaped wafer after the back grinding and the seagull-shaped wall thickness raised portion.

Among them, in the aforementioned rotary etching process, it is more suitable to form a semiconductor wafer having a TTV indicating a flatness of 2.0 μm or less.

The wafer with a seagull shape after back grinding refers to a wafer in which the cross-sectional surface shape in the back concave portion after grinding is a seagull shape, and a wafer having a wall thickness raised portion in a region around the center of the wafer . That is, as shown in FIG. 6 and FIG. 7, it means that the crystal is formed into a shape having a flat cross-section similar to a state in which a seagull spreads wings once the surface shape is raised as it moves toward the outer periphery compared to the center of the wafer. circle. In the example shown in FIG. 6, the aforementioned seagull-shaped wall thickness bulges are in the range of 16 mm to 80 mm and -16 mm to -80 mm, and the apex of the wall thickness bulges are in positions of 48 mm and -48 mm.

Preferably, the etching solution supply nozzle is folded back at the apex of the seagull-shaped wall thickness raised portion, between the center of the back surface of the seagull-shaped wafer and the seagull-shaped wall thickness raised portion after the back grinding. The etching liquid supply nozzle is swinging.

The seagull-shaped wafer after the back grinding is a wafer suitable for TAIKO grinding. More specifically, the back surface corresponding to the element region of the semiconductor wafer having the element region formed on the surface and the peripheral region surrounding the element region is ground, and a ring shape is formed on the back surface corresponding to the peripheral region. And a back grinding of the back recess formed in the back area corresponding to the aforementioned element area, so that the outer peripheral end portion of the wafer is left about several mm, and only the central portion of the wafer is mechanically ground and thinned. A wafer having a back recess.

The size of the aforementioned semiconductor wafer is not particularly limited, and it can be suitably applied to, for example, 6-inch, 8-inch, and 12-inch wafers. If the semiconductor wafer is an 8-inch wafer, the predetermined swing width is preferably ± 40 to ± 60 mm with the center of the diameter of the wafer as the base point. The meaning of the ± Xmm wide swing of the nozzle means that the center of the wafer swings + Xmm and -Xmm in the diameter direction.

Preferably, in the aforementioned rotary etching process, the surface shape distribution of the back surface of the seagull-shaped wafer after the back surface grinding before the etching is measured in advance, and at least the swing width is controlled corresponding to the surface shape distribution. The aforementioned surface shape distribution can be measured by measuring the thickness distribution with a thickness measuring device using a laser interference method, for example.

The rotary etching device of the present invention is the aforementioned rotary etching method. The rotary etching apparatus used includes: a rotary table which is rotatably provided with a wafer holding means thereon; and a swingable etching solution supply nozzle which supplies an etching solution on the upper surface of the rotary table.

The method for manufacturing a semiconductor wafer according to the present invention is a method for manufacturing a semiconductor wafer including an etching process performed by the aforementioned rotary etching method. By the method for manufacturing a semiconductor wafer of the present invention, a semiconductor wafer having a TTV showing a flatness of 2.0 μm or less can also be obtained. More specifically, a semiconductor wafer having a TTV of 2.0 μm or less and exceeding 0 μm can also be obtained.

TTV is an abbreviation of Total Thickness Variation, and represents a value in which the difference between the maximum value and the minimum value of the height in the wafer surface is measured in the thickness direction. The TTV system can be measured by, for example, a thickness measuring device using a laser interference method.

According to the present invention, there is provided a rotary etching method and device capable of improving the in-plane uniformity of the back surface of a semiconductor wafer whose cross-sectional surface shape is distributed into a seagull shape without the use of an etching suppression liquid on the back surface after grinding, and a semiconductor crystal. The remarkable effect of the manufacturing method of the circle.

10‧‧‧ Rotary Etching Device

12‧‧‧ rotating support

14‧‧‧Wafer holding means

16‧‧‧ rotating platform

18‧‧‧ Etching nozzle

20‧‧‧ gap

100‧‧‧ peripheral end

102‧‧‧Back recess

104‧‧‧Wall thickness bulge

D1‧‧‧Wide swing of etching solution supply nozzle

E‧‧‧etching solution

O‧‧‧Wafer Center

W‧‧‧ Wafer

FIG. 1 is a schematic perspective view showing a rotary etching apparatus used in the rotary etching method of the present invention.

Fig. 2 shows the back surface of a seagull-shaped wafer after grinding the back surface. A schematic side view of a state where an etching solution is dripped from the etching solution supply nozzle.

FIG. 3 is a plan view showing the measurement direction of TTV in the examples and comparative examples of the present invention.

FIG. 4 is a graph showing the shape of a machining allowance after the semiconductor wafer is etched using the rotary etching method of the present invention.

FIG. 5 is a schematic side view showing a semiconductor wafer after back grinding by TAIKO grinding.

FIG. 6 is a graph showing a cross-sectional surface shape distribution after back grinding by TAIKO grinding.

FIG. 7 is a schematic perspective view schematically showing a seagull shape in a back concave portion after back grinding by TAIKO grinding.

Fig. 8 is a graph showing the results of Example 1 of the present invention.

FIG. 9 is a graph showing the results of Example 2 of the present invention.

FIG. 10 is a graph showing the results of Example 3 of the present invention.

FIG. 11 is a graph showing the results of Example 4 of the present invention.

FIG. 12 is a graph showing the results of Example 5 of the present invention.

FIG. 13 is a graph showing the results of Example 6 of the present invention.

FIG. 14 is a graph showing the results of Comparative Example 1 of the present invention.

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

In FIG. 1, the rotary etching apparatus 10 is a rotary etching apparatus used in the rotary etching method of the present invention. The rotary etching device 10 is formed as Including: a rotating stage 16 provided to be rotatable by a rotating support 12 and having a wafer holding means 14 thereon; and a swingable etching solution supply nozzle 18 for supplying an etching solution E on the rotating stage 16 Make up.

The rotary etching method of the present invention is suitable for using the rotary etching device 10, but since the cross-sectional surface shape distribution in the back surface after the back grinding is seagull-shaped, the back-ground seagull-shaped wafer is the object of the rotary etching, so first prepare the back Seagull-shaped wafer W after grinding (preparation process of seagull-shaped wafer after back grinding).

Next, as shown in FIG. 2, the etching solution supply nozzle 18 is oscillated with a predetermined swing width in the diameter direction of the back surface. At this time, the etching solution supply nozzle 18 is folded back in the seagull-shaped wall thickness bulging portion 104 (refer to FIGS. 6 and 7), and the etching solution supply nozzle 18 is formed in a predetermined swing width in the diameter direction of the back surface. The web D1 is subjected to spin etching (rotary etching process). In particular, it is preferable to swing the etching solution supply nozzle so that the etching solution supply nozzle is folded back at the apex of the seagull-shaped wall-thickness raised portion 104. As a result, it becomes a wafer having improved TTV indicating flatness. In FIG. 2, the symbol O represents the center of the wafer.

The TTV is a value in which the difference between the maximum value and the minimum value of the height within the wafer surface is measured in the thickness direction. As shown in FIG. 3, the TTV system can be measured by a laser interference method using a thickness measuring device that measures the entire surface of the wafer in the thickness direction. The notch of the wafer W in FIG. 3 is a notch 20. In terms of the number of measurement points, it is more appropriate to express the difference between the maximum value and the minimum value of the height after 13 points are measured in the wafer surface.

In addition, if the aforementioned semiconductor wafer is an 8-inch wafer, the predetermined swing width is based on the center of the diameter of the wafer, and it is more suitable to be ± 40 to ± 60 mm. Among them, the swing speed of the etching solution supply nozzle 18 is preferably 10 to 50 mm / s.

The aforementioned rotary etching process is more suitable for measuring in advance the surface shape distribution of the back surface of the seagull-shaped wafer after the back surface grinding before etching, and at least the swing width is controlled corresponding to the surface shape distribution.

The control method includes, for example, increasing the swing width or adjusting the delay swing speed.

In addition, if the amount of etching increases, the wafer temperature becomes higher. Therefore, it is preferable to manage the temperature of the seagull-shaped semiconductor wafer W after the back grinding, and perform temperature management by means of wafer temperature sensing. The rotation speed of the seagull-shaped semiconductor wafer W after the back grinding is adjusted so that the temperature of the circle W does not exceed 24 ° C ± 1 ° C. In terms of wafer temperature sensing means, an infrared radiation thermometer is preferred. Regarding the aforementioned adjustment of the rotation speed, if the rotation is slowed down, the etching amount will increase (temperature rise), and if the rotation is accelerated, the etching amount will decrease (temperature drop), so the rotation speed is adjusted and the temperature Just manage it.

In the present invention, the etching is not performed so that the etching amount becomes uniform and the shape change rate is maintained, but the etching is performed locally to improve the in-plane uniformity of the seagull-shaped semiconductor wafer after the back grinding. By. That is, using the rotary etching method of the present invention to etch the seagull-shaped semiconductor wafer after the back grinding is performed, the machining allowance after etching is as shown in FIG. 4. The central portion of the wafer is hardly etched. The wall-thickness raised portion at the center of about 40 mm faces the outer periphery of the wafer, and the machining allowance for etching becomes larger.

The method for manufacturing a semiconductor wafer according to the present invention is a method for manufacturing a semiconductor wafer including an etching process performed by the aforementioned rotary etching method. By the method for manufacturing a semiconductor wafer of the present invention, a semiconductor wafer having a TTV showing a flatness of 2.0 μm or less can also be obtained.

[Example]

Examples of the present invention are listed below for more specific description, but the present invention is not limited to those embodiments, and various modifications can be made without departing from the technical idea of the present invention.

(Example 1)

Prepare a wafer that has been back-grinded by 8-inch monocrystalline silicon wafers using TAIKO grinding. In the diameter direction shown in FIG. 3 (that is, the notch is measured from the right to the left), the thickness of the back surface of the wafer is measured at 13 points using a laser interference measurement method ( Thickness meter made by Hamamatsu Photonics Co., Ltd. (C11011-01) to measure thickness. Using the same apparatus as the rotary etching apparatus shown in FIG. 1, that is, MIMASU SPIN PROCESSOR manufactured by Sany Semiconductor Co., Ltd., using a mixed acid etching solution based on hydrofluoric acid and nitric acid, under the following etching conditions, The nozzle is swung, and the wafer is spin-etched.

<Etching conditions>

Etching solution temperature: 24 ° C, number of rotations: 900 rpm, etching solution flow rate: 3L / min, nozzle swing width: ± 50mm (return at the vertex of wall thickness bulge), nozzle swing speed: 30mm / sec

The meaning of the nozzle swing width of ± 50mm means that the center of the wafer swings + 50mm and -50mm in the diameter direction. The results are shown in Table 1 and FIG. 8. In the table, Time means the etching time and Rate means the etching rate.

(Example 2)

The spin etching was performed in the same manner as in Example 1 except that the etching conditions described below were performed.

<Etching conditions>

Etching solution temperature: 24 ° C, number of rotations: 900 rpm, etching solution flow rate: 3L / min, nozzle swing width: ± 50mm (return at the vertex of wall thickness bulge), nozzle swing speed: 60mm / sec 2 and Figure 9.

(Example 3)

Prepare a wafer that has been back-grinded by 8-inch monocrystalline silicon wafers using TAIKO grinding. In the diameter direction shown in FIG. 3 (that is, with the notch facing downward, The measurement was performed from right to left.) The thickness of the back surface of the wafer was measured at 13 o'clock using a thickness measurement device using a laser interference method (thickness meter made by Hamamatsu Photonics Co., Ltd., C11011-01). . Using the same apparatus as the rotary etching apparatus shown in FIG. 1, that is, MIMASU SPIN PROCESSOR manufactured by Sany Semiconductor Co., Ltd., using a mixed acid etching solution based on hydrofluoric acid and nitric acid, under the following etching conditions, The nozzle is swung, and the wafer is spin-etched.

<Etching conditions>

Etching solution temperature: 24 ° C, number of rotations: 500 rpm, etching solution flow rate: 3L / min, nozzle swing width: ± 40mm (return in the range of wall thickness bulge), nozzle swing speed: 60mm / sec

The results are shown in FIG. 10. The TTV before etching was 4.10 μm, while the TTV after etching was 4.63 μm. Therefore, the difference (improvement amount) of the TTV is -0.53 µm.

(Example 4)

The spin etching was performed in the same manner as in Example 3 except that the etching conditions described below were performed.

<Etching conditions>

Etching solution temperature: 24 ° C, number of rotations: 500 rpm, etching solution flow rate: 3L / min, nozzle swing width: ± 58mm (return in the range of wall thickness bulge), nozzle swing speed: 60mm / sec

The results are shown in FIG. 11. The TTV before etching was 3.90 μm, while the TTV after etching was 3.85 μm. Therefore, the difference (improvement amount) of the TTV is 0.05 μm.

(Example 5)

The spin etching was performed in the same manner as in Example 3 except that the etching conditions described below were performed.

<Etching conditions>

Etching solution temperature: 24 ° C, number of rotations: 500 rpm, etching solution flow rate: 3L / min, nozzle swing width: ± 70mm (return in the range of wall thickness bulge), nozzle swing speed: 60mm / sec

The results are shown in FIG. 12. The TTV before etching was 3.56 μm, while the TTV after etching was 4.41 μm. Therefore, the difference (amount of improvement) in TTV is -0.95 µm.

(Example 6)

The spin etching was performed in the same manner as in Example 3 except that the etching conditions described below were performed.

<Etching conditions>

Etching solution temperature: 24 ° C, number of rotations: 500 rpm, etching solution flow rate: 3L / min, nozzle swing width: ± 80mm (return in the range of wall thickness bulge), nozzle swing speed: 60mm / sec

The results are shown in FIG. 13. The TTV before etching was 3.95 μm, while the TTV after etching was 6.2 μm. Therefore, the difference (improvement) of TTV is -2.25 μm.

(Comparative example 1)

The spin etching was performed in the same manner as in Example 3, except that the nozzle was fixed to the center of the wafer without swinging, and the etching was performed under the following etching conditions.

<Etching conditions>

Etching solution temperature: 24 ° C, number of rotations: 500 rpm, etching solution flow rate: 3L / min, nozzle swing width: ± 0mm

The results are shown in FIG. 14. The TTV before etching was 3.74 μm, while the TTV after etching was 26.73 μm. Therefore, the difference (improvement amount) of TTV is -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 greatly improved compared with Comparative Example 1 of the conventional method. The use of an etching inhibitor is not required, and the cross-sectional surface shape distribution in the rear surface after the back surface grinding is not required. The in-plane uniformity of the back surface of the semiconductor wafer having a seagull shape is improved.

18‧‧‧ Etching nozzle

100‧‧‧ peripheral end

102‧‧‧Back recess

104‧‧‧Wall thickness bulge

D1‧‧‧Wide swing of etching solution supply nozzle

E‧‧‧etching solution

O‧‧‧Wafer Center

W‧‧‧ Wafer

Claims (6)

A rotary etching method is a rotary 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, and the method includes: performing an element region formed on a surface and surrounding the semiconductor wafer. The back surface corresponding to the device region of the semiconductor wafer in the peripheral region of the device region is ground, and a ring-shaped reinforcing portion is formed on the back surface corresponding to the peripheral region, and the region of the back surface corresponding to the device region is ground. A process of forming a back surface of the back surface recess to prepare a back surface ground seagull-shaped wafer with a cross-sectional surface shape distribution in the back surface recessed portion after the back surface grinding; and making the etching solution supply nozzle in the diameter direction of the back surface to A rotary etching process in which a predetermined swing is performed with a wide swing and a rotary etching is performed. The center of the back surface of the seagull-shaped wafer and the seagull shape are ground on the back surface so that the etching solution supply nozzle is folded back in the seagull-shaped wall thickness bulge. Between the raised portions of the Swing from the nozzle. For example, the rotary etching method according to item 1 of the patent application, wherein the center of the back surface of the seagull-shaped wafer and the seagull are ground on the back surface so that the etching solution supply nozzle is folded back at the apex of the seagull-shaped wall thickness ridge. The shape of the wall thickness raised portion is formed by swinging the etching solution supply nozzle. For example, if the aforementioned rotary etching method of the scope of patent application is applied, if the aforementioned semiconductor wafer is an 8-inch wafer, the predetermined swing width is ± 40 to ± 60 mm based on the center of the diameter of the aforementioned semiconductor wafer. For example, the rotary etching method of the first scope of the patent application, wherein the aforementioned rotary etching process determines in advance the surface shape distribution of the back surface of the seagull-shaped wafer after the back surface grinding before the etching, and at least controls the swing width corresponding to the surface shape distribution. . A rotary etching device is a rotary etching device used in the rotary etching method of item 1 of the scope of patent application, and includes: a rotary platform which is arranged to be rotatable and has a wafer holding means thereon; and The etching liquid supply nozzle is used to supply an etching liquid on the upper surface of the rotating platform. A method for manufacturing a semiconductor wafer includes an etching process performed by a rotary etching method such as the first item in the scope of patent application.