JP2007335659A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cracking or warpage in a semiconductor wafer in steps of manufacturing a thin semiconductor device. <P>SOLUTION: An oxide film 13 as an etching resistance protective film is formed on front and rear surfaces of a wafer 11 having an element structure formed in its front side. The oxide film 13 formed on the rear surface of the wafer 11 is then removed while leaving a part of the wafer 11 corresponding to a predetermined width from its outer peripheral end. The rear surface of the wafer 11 is etched down to a predetermined depth and thereafter, the oxide films 13 are removed as left at the outer peripheral ends of the front and rear surfaces of the wafer 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a power semiconductor device whose characteristics are improved by thinning a semiconductor wafer.

  Conventionally, the thinning of a semiconductor wafer (hereinafter referred to as “wafer”) has become an indispensable technique for improving the characteristics of chip stacked packages and power semiconductor devices. When thinning a wafer, it is common to grind the wafer from the back surface (back grind) to obtain a desired thickness. However, if the back grinding is simply performed, the mechanical strength of the wafer is reduced and the wafer is easily broken. In addition, the wafer is likely to warp due to internal stress in the film such as a metal electrode formed on the surface of the wafer. For example, when a silicon wafer having a diameter of 6 inches is thinned to a thickness of 100 μm or less, the defect rate of the wafer due to cracking or warping increases rapidly.

  In order to reduce the defect rate of such a wafer, a support substrate system is known in which a support substrate is bonded to a wafer and a manufacturing process is advanced. In the support substrate method, the support substrate is bonded to the surface of the wafer before back grinding with an adhesive or the like, and the back grinding and the subsequent manufacturing process are performed on the wafer with the support substrate bonded thereto. According to this method, since the wafer is bonded to the support substrate, it is possible to reduce the cracking and warping of the wafer in the manufacturing process.

  As a method for thinning a wafer without using a support substrate, a method called a TAIKO process is known (for example, see Non-Patent Document 1 below). In the TAIKO process, the wafer is thinned by mechanically grinding only the central portion of the wafer, leaving a few mm on the outer periphery of the wafer. According to this method, the outer peripheral end portion of the wafer is not ground and remains in its original thickness, so that the mechanical strength is maintained and the cracking and warping of the wafer can be reduced.

  Also, after applying the resist on both sides of the wafer, the resist on the back side of the wafer is removed leaving the outer peripheral edge, and the remaining resist is used as a mask to etch the wafer with hydrofluoric acid, or both sides of the wafer. A method is known in which an oxide film is formed on the wafer, and the film on the back surface of the wafer is removed leaving the outer peripheral edge, and the wafer is thinned by etching with potassium hydroxide using the remaining oxide film as a mask (for example, (See Patent Document 1 below.) Also known is a method of thinning the wafer by masking the outer peripheral edge of the wafer with a seal packing provided in the etching pot and exposing the exposed surface of the wafer center to an etching solution (for example, the following) (See Patent Document 2).

JP 2004-253527 A Japanese Patent No. 3620528 Disco website, [online], [December 12, 2005 search], Internet <URL: http: // www. disco. co. jp / jp / news / product / 20051128. html>

  However, using the above-described support substrate method can reduce the cracking and warping of the wafer, but cannot perform high-temperature heat treatment that affects the properties of the support substrate and the adhesive, so the processing performed in the manufacturing process There is a problem that it is restricted. In addition, since a dedicated device is required for attaching and peeling the support substrate, there is a problem that the manufacturing cost of the semiconductor device increases.

  Further, the above-described TAIKO process requires a dedicated grinder, which increases the manufacturing cost of the semiconductor device. Further, since a step is formed by the element structure formed on the front surface of the wafer, there is a problem that when grinding is performed by a mechanical method, the wafer is broken by a force applied to the step. For example, in a power semiconductor device in which the front surface is protected by a polyimide film, since the step on the front surface is 5 μm or more, when the wafer is ground to a thickness of 100 μm or less, most of the wafers are broken.

  Further, in the method of Patent Document 1 described above, it is unclear how to leave the oxide film at the outer peripheral edge when removing the oxide film on the back surface of the wafer. Further, in the method of Patent Document 2 described above, since the etching pot is a single-wafer type, batch processing cannot be performed, and there is a problem that production efficiency is poor as compared with the dip method.

  The present invention provides a method for manufacturing a semiconductor device capable of reducing cracks and warpage in a manufacturing process including wafer thinning while suppressing production costs in order to eliminate the above-described problems caused by the prior art. With the goal.

  In order to solve the above-described problems and achieve the object, a method of manufacturing a semiconductor device according to the invention of claim 1 includes an oxide film or a nitridation serving as an etching resistant protective film on the first main surface and the second main surface of a semiconductor wafer A forming step for forming a film, a covering step for covering the etching-resistant protective film with a photoresist, and a photoresist on the second main surface side of the semiconductor wafer from the outer peripheral end portion of the photoresist by photolithography. A resist removing step for removing the resist film while leaving a predetermined width, and a second main surface of the semiconductor wafer among the etching-resistant protective films, using the photoresist remaining at the outer peripheral end portion on the second main surface side of the semiconductor wafer as a mask. A first removing step of removing the etching-resistant protective film formed on the surface from the outer peripheral edge part leaving a predetermined width; and An etching process for etching the second main surface of the semiconductor wafer that has been removed and removed to a predetermined depth, and the anti-etching protection remaining on the outer peripheral ends of the first main surface and the second main surface of the semiconductor wafer after etching And a second removal step of removing the film.

  According to the first aspect of the present invention, the thickness of the semiconductor wafer is reduced by etching the semiconductor wafer leaving a predetermined width from the outer peripheral end portion. Thereby, the strength of the semiconductor wafer thinned by reducing the thickness can be maintained, and cracking and warping of the semiconductor wafer can be prevented. In addition, since a dedicated device is not required, a thin semiconductor device can be manufactured at low cost.

  According to a second aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the first aspect, wherein a semiconductor element or a part of the semiconductor element is fabricated on the first main surface of the semiconductor wafer in advance. To do.

  According to the second aspect of the present invention, the semiconductor wafer can be thinned while protecting the semiconductor element produced on the first main surface of the semiconductor wafer or a part thereof.

  According to a third aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the second aspect, wherein the etching-resistant protective film is formed by a heat treatment at 500 ° C. or lower.

  According to the third aspect of the present invention, it is possible to prevent the semiconductor element produced on the first main surface of the semiconductor wafer or a part thereof from being deteriorated by the heat treatment during the formation of the etching resistant protective film.

  According to a fourth aspect of the present invention, there is provided a semiconductor device manufacturing method according to any one of the first to third aspects, wherein the etching step is performed by immersing the entire semiconductor wafer in an etching solution. The second main surface is etched to a predetermined depth.

  According to the fourth aspect of the invention, since the entire semiconductor wafer is immersed in the etching solution for etching, the etching process can be efficiently performed by batch processing.

  According to a fifth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to any one of the first to fourth aspects, wherein the etching step is performed by using the alkaline solution as an etching solution to etch the second main wafer. The surface is etched to a predetermined depth.

  According to the invention of claim 5, anisotropic etching with an alkaline solution can be performed.

  According to a sixth aspect of the present invention, in the semiconductor device manufacturing method according to any one of the first to fifth aspects of the present invention, the first removal step may include the step of removing the etching-resistant protective film on the semiconductor wafer. It is characterized by being removed leaving a width of 1 mm to 20 mm from the outer peripheral end of the second main surface.

  According to the sixth aspect of the present invention, the central portion of the semiconductor wafer can be thinned while maintaining the mechanical strength of the semiconductor wafer.

  According to a seventh aspect of the present invention, there is provided a semiconductor device manufacturing method according to any one of the first to sixth aspects, wherein the outer peripheral end portion of the second main surface of the semiconductor wafer is the semiconductor wafer. The resist removing process is characterized in that the photoresist is removed leaving a predetermined width from a portion where the supporting claw and the semiconductor wafer are in contact with each other.

  According to the seventh aspect of the present invention, the etching-resistant protective film can be removed while avoiding the portion where the etching-resistant protective film is not formed on the back surface of the semiconductor wafer because it is in contact with the support claws. Strength can be maintained.

  According to the semiconductor device manufacturing method of the present invention, it is possible to reduce cracks and warpage in a manufacturing process including wafer thinning while suppressing production costs.

  Exemplary embodiments of a method for manufacturing a semiconductor device according to the present invention will be explained below in detail with reference to the accompanying drawings.

(Embodiment)
1 to 10 are diagrams illustrating a manufacturing process of the semiconductor device manufacturing method according to the embodiment. In the embodiment described below, a case where a field stop (FS) IGBT having a withstand voltage of 600 V is manufactured using a wafer having a diameter of 6 inches will be described as an example.

  First, the surface structure portion of the front surface semiconductor element and the aluminum electrode 12 of the wafer 11 are fabricated by the same process as in the prior art (FIG. 1). At this time, the wafer 11 is not thinned, and its thickness is, for example, 500 μm. The diameter of the wafer 11 is 6 inches (150 mm). Next, in order to remove an oxide film or the like generated on the back surface of the wafer 11, the back surface of the wafer 11 is mechanically ground to set the thickness of the wafer 11 to 350 μm, for example (FIG. 2).

  Subsequently, for example, a plasma CVD (Chemical Vapor Deposition) using TEOS (tetraethyl tetrasilicate) as a raw material is performed on both surfaces of the wafer 11 at a temperature of 350 ° C., for example, as an anti-etching protective film having a thickness of 1 μm, for example. (FIG. 3). The reason why the oxide film 13 is formed by such a method is that, since the aluminum electrode 12 is formed on the surface of the wafer 11, it is desirable to perform the treatment at 500 ° C. or less. In addition, as the anti-etching protective film, other oxide films or nitrogen films can be employed. Also in this case, what can be formed by processing at 500 ° C. or lower is desirable.

  Then, for example, a positive photoresist 14 is applied on both surfaces of the wafer 11 by a spin coater and then baked (FIG. 4). Subsequently, the back surface of the wafer 11 is exposed using a mask (not shown) that shields the outer peripheral edge of the back surface of the wafer 11 with a width of, for example, 5 mm. Alternatively, instead of using the positive photoresist 14, a negative photoresist is applied to both surfaces of the wafer 11 so that the entire front surface of the wafer 11 and the outer peripheral edge of the back surface are exposed to light with a width of, for example, 5 mm. A simple mask may be used to expose both sides of the wafer 11. Then, the resist 14 is developed to remove the resist 14 at the center of the back surface of the wafer 11 (FIG. 5).

  FIG. 6 shows a resist pattern on the back surface of the wafer 11. In FIG. 6, the back surface of the wafer 11 is on the upper side. On the back surface of the wafer 11, the resist 14 is removed leaving the outer peripheral edge of a width of, for example, 5 mm, and the oxide film 13 is exposed at the center. Here, the wafer support claw 20 of the semiconductor manufacturing apparatus is in contact with the outer peripheral edge of the back surface of the wafer 11. The oxide film 13 is not formed on the portion in contact with the wafer support claw 20. For this reason, there is a risk that the wafer 11 will be cracked or warped due to insufficient strength in a later process.

  Therefore, in the present embodiment, the resist pattern of the outer peripheral end portion of the wafer 11 that is in contact with the wafer support claw 20 is changed according to the shape of the wafer support claw 20. Specifically, the resist pattern is formed by escaping a portion where the wafer support claw 20 and the wafer 11 are in contact with each other. As a result, the oxide film 13 remains without being interrupted along the outer peripheral edge of the wafer 11 even after the oxide film 13 at the center of the back surface of the wafer 11 is removed in a process described later, thereby preventing a reduction in the strength of the wafer 11. be able to. If sufficient strength can be secured without considering the influence of the wafer support claw 20, the resist pattern where the wafer support claw 20 and the wafer 11 are in contact with each other need not be formed.

  Subsequently, the oxide film 13 at the center of the back surface of the wafer 11 is removed with an HF (hydrogen fluoride) solution diluted 1:10 (FIG. 7). Next, the resist 14 on both surfaces of the wafer 11 is stripped with a resist stripping solution (FIG. 8).

  Then, using the oxide film 13 remaining on the outer peripheral edge portions of the front surface and the back surface of the wafer 11 as a mask, etching is performed, for example, by a dip method to reduce the thickness of the back surface center portion of the wafer 11. Specifically, for example, the wafer 11 is immersed in a TMAH (tetramethylammonium hydroxide) solution at a temperature of 80 ° C. for about 6 hours to perform anisotropic etching, so that the thickness of the center of the back surface of the wafer 11 is, for example, 60 μm ( FIG. 9). In etching with an alkaline solution such as a TMAH solution, the selectivity between the oxide film and silicon is 500 or more. Therefore, if the thickness of the oxide film 13 is 1 μm, it can withstand silicon etching up to 500 μm.

  Subsequently, the wafer 11 is washed with water, and the oxide film 13 on both surfaces of the wafer 11 is completely removed with an HF solution diluted 1:10 (FIG. 10). Although the thickness of the central portion of the wafer 11 is, for example, 60 μm, silicon having a thickness of, for example, 350 μm remains at a width of, for example, 5 mm at the outer peripheral end portion of the wafer 11. Therefore, the mechanical strength of the entire wafer 11 can be sufficiently ensured. Further, the warpage of the wafer 11 can be suppressed to 500 μm or less.

  Further, since the wafer 11 is not warped during the etching with the TMAH solution, the oxide film 13 which is an etching protective film is not broken and the etching solution does not penetrate into the front surface side of the wafer 11, and the wafer 11. The front surface can be protected from the etching solution.

  As described above, according to the method for manufacturing a semiconductor device according to the embodiment, the semiconductor device is manufactured by thinning the wafer while leaving the thickness of the outer peripheral edge of the wafer without using a dedicated device. be able to. As a result, it is possible to produce a semiconductor device by reducing wafer cracking and warping at a lower cost than when a dedicated device is used, such as a support substrate method or a TAIKO process.

  Further, since the wafer is thinned by etching the back surface of the semiconductor wafer, no pressure is applied even if there is a step due to the element structure on the front surface of the wafer. Therefore, the wafer is not broken during the thinning. Moreover, since the wafer is thinned by etching by the dip method, the production efficiency can be improved as compared with the single wafer method.

  Further, since the heat treatment up to about 500 ° C. can be performed in the manufacturing process, the manufacturing process of the semiconductor device can be designed without restricting the contents of the processes other than the thinning process.

  As described above, the method for manufacturing a semiconductor device according to the present invention is useful for manufacturing a semiconductor device with a thin device thickness. In particular, a general-purpose inverter, AC servo, uninterruptible power supply (UPS), switching power supply, etc. It is suitable for manufacturing power semiconductor devices such as IGBTs used in industrial fields and consumer equipment fields such as microwave ovens, rice cookers or strobes.

It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment. It is a figure which shows the manufacturing process of the manufacturing method of the semiconductor device concerning embodiment.

Explanation of symbols

11 Wafer 12 Aluminum electrode 13 Oxide film 14 Resist 20 Wafer support nail

Claims (7)

Forming an oxide film or a nitride film serving as an etching-resistant protective film on the first main surface and the second main surface of the semiconductor wafer;
A coating step of coating the etching-resistant protective film with a photoresist;
A resist removing step of removing the photoresist on the second main surface side of the semiconductor wafer from the outer peripheral end portion by leaving a predetermined width out of the photoresist by photolithography;
Using the photoresist remaining on the outer peripheral edge of the second main surface side of the semiconductor wafer as a mask, the etching resistant protective film formed on the second main surface of the semiconductor wafer is the outer edge of the etching resistant protective film. A first removing step for removing a predetermined width from the first,
An etching step of etching the second main surface of the semiconductor wafer from which the etching-resistant protective film has been removed leaving an outer peripheral edge to a predetermined depth;
A second removal step of removing the etching-resistant protective film remaining on the outer peripheral ends of the first main surface and the second main surface of the semiconductor wafer after etching;
A method for manufacturing a semiconductor device, comprising:   2. The method of manufacturing a semiconductor device according to claim 1, wherein a semiconductor element or a part thereof is formed in advance on the first main surface of the semiconductor wafer.   The method of manufacturing a semiconductor device according to claim 2, wherein the etching-resistant protective film is formed by a heat treatment at 500 ° C. or less.   4. The semiconductor device according to claim 1, wherein the etching step includes immersing the entire semiconductor wafer in an etching solution to etch the second main surface of the semiconductor wafer to a predetermined depth. 5. Manufacturing method.   5. The method of manufacturing a semiconductor device according to claim 1, wherein in the etching step, the second main surface of the semiconductor wafer is etched to a predetermined depth using an alkaline solution as an etching solution.   The said 1st removal process removes the said etching-resistant protective film, leaving 1 mm-20 mm width from the outer peripheral edge part of the 2nd main surface of the said semiconductor wafer. The manufacturing method of the semiconductor device as described in one. The outer peripheral end of the second main surface of the semiconductor wafer is in contact with a support claw that supports the semiconductor wafer,
The semiconductor device manufacturing method according to claim 1, wherein the resist removing step removes the photoresist leaving a predetermined width from a portion where the support claw and the semiconductor wafer are in contact with each other. Method.

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