JP2014022677A - Method of processing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent metal from being contaminated due to an etching liquid, when processing a wafer to make a copper post expose by wet-etching the rear face of the wafer.SOLUTION: When etching a rear face 1b of a wafer 1 by supplying the etching liquid, and making a copper post 2 having been embedded in the wafer 1 expose to and protrude from the rear face 1b, a method for processing the wafer includes using a liquid as an etching liquid L, which is composed at least of an alkali etching solution and an additive having an oxidation prevention function for copper or a copper alloy, specifically, a liquid containing benzotriazole of 0.5 wt.% or more in the alkali etching solution.

Description

  The present invention relates to a wafer processing method for etching a back surface side of a wafer such as a semiconductor wafer in which a copper post extending from a front surface to a predetermined depth is embedded to project the copper post to the back surface.

  When a silicon wafer on which a large number of devices are formed is subdivided for each device and the resulting semiconductor chips are stacked and placed in a semiconductor package, high integration is achieved by using a TSV (Through Silicon Via) wafer. In addition, efforts have been made to reduce the size and weight of mounted devices (see Patent Documents 1 and 2, etc.). A TSV wafer is provided with a large number of copper posts made of copper or a copper alloy as through electrodes. The copper post is embedded from the front surface of the wafer to a predetermined depth, and the back surface of the wafer is removed by etching so that the copper post protrudes from the back surface of the wafer. A semiconductor chip through which a copper post penetrates is manufactured by cutting and dividing along a boundary dividing line.

JP 2001-053218 A JP 2005-136187 A

  When processing the TSV wafer as described above, if the back surface is ground and polished and then the back surface is etched by wet etching, the ground and polished surface is in a very activated state in which no oxide film exists. . When etching is performed up to the copper post together with the silicon of the wafer, copper ions dissolved from the copper post enter the inside of the wafer and cause so-called metal contamination that is trapped between the crystal lattices of silicon. Copper ions entering between silicon crystal lattices cause problems such as malfunction of the device and increase in leakage current.

  The present invention has been made in view of the above circumstances, and a main problem thereof is to provide a wafer processing method that does not cause metal contamination when performing wet etching on the back surface of a wafer to expose a copper post. There is to do.

  The wafer processing method of the present invention is a wafer processing method in which a copper post extending from the front surface to a predetermined depth is embedded, and etching is performed by supplying an etching solution to the back surface of the wafer. It comprises an etching step that is exposed on the back surface and protrudes from the back surface of the wafer, wherein the etching solution is composed of at least an alkaline etching solution and an additive having an antioxidant function for copper or a copper alloy. And The copper post of this invention shall be comprised from copper or a copper alloy.

  According to the present invention, an anticorrosion film is formed on the exposed surface of the copper post exposed on the back surface by etching the back surface of the wafer with the etching solution. For this reason, the exposed copper post is not etched, and only the back surface of the wafer is etched. Therefore, there is no possibility of causing metal contamination due to dissolution of copper ions from the copper post.

  In the present invention, particularly when the wafer is made of silicon, it is effective that the alkaline etching solution is tetramethylammonium hydroxide (TMAH) and the additive is benzotriazole (BTA). It is. In this case, it is preferable that benzotriazole is contained in an amount of 0.5% by weight or more based on tetramethylammonium hydroxide. In this embodiment, a complex Cu-BTA is formed on the copper post exposed on the back surface of the wafer by etching, and this complex Cu-BTA acts as an anticorrosion film, thereby preventing the copper post from being etched.

  The present invention further includes a thinning step of grinding or polishing the back surface of the wafer to reduce it to a predetermined thickness before performing the etching step, wherein the copper post is disposed on the back surface of the wafer. The wafer is thinned to a thickness that is not exposed to the surface. According to this embodiment, the etching amount can be reduced and the amount of the etching solution used can be suppressed.

  According to the present invention, it is possible to provide a wafer processing method that does not cause metal contamination when performing wet etching on the back surface of a wafer to expose a copper post.

It is sectional drawing which shows typically the processing method of the wafer which concerns on one Embodiment of this invention. It is sectional drawing which shows the state in which the anticorrosion film which consists of complex Cu-BTA was formed in the exposed surface of a copper post by the etching of a wafer back surface. It is a perspective view which shows the supply apparatus of the etching liquid used with the processing method of one Embodiment. FIG. 4 is a side view showing a state in which gas is injected from the lower side of the wafer, which is a preferable mode when the wafer back surface is etched by the supply device shown in FIG. 3.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a wafer processing method according to an embodiment, and FIG. 1A shows a partial cross section of the wafer 1 before processing. This wafer 1 is the above-mentioned TSV wafer, and the silicon wafer 1 is made of copper or copper from the front surface 1a (in FIG. 1, the front surface 1a is the lower side and the back surface 1b is the upper side) to a predetermined depth. A plurality of copper posts 2 made of a copper alloy are embedded perpendicular to the thickness direction.

  One embodiment is a processing method in which the copper post 2 protrudes from the back surface 1b of the wafer 1 by removing the back surface 1b of the wafer 1 by etching, and the method will be described below according to the procedure.

  From the state shown in FIG. 1 (a), the back surface 1b of the wafer 1 is ground, and the ground surface is polished if necessary, and the copper post 2 is not exposed to the back surface 1b as shown in FIG. 1 (b). The wafer 1 is thinned to a thickness (thinning step). The back surface grinding of the wafer 1 can be performed using a well-known grinding apparatus (for example, JP 2007-175825 A, JP 2010-221378 A) for grinding a workpiece such as a semiconductor wafer.

  Next, as shown in FIG. 1 (c), an etching solution L is supplied to the back surface 1b of the wafer 1 until the copper post 2 is exposed to the back surface 1b and protrudes from the back surface 1b as shown in FIG. 1 (d). Then, wet etching is performed (etching step). The etching solution L is composed at least of an alkaline etching solution and an additive having an antioxidant function for copper or a copper alloy. Specifically, tetramethylammonium hydroxide (hereinafter, TMAH) is used as the alkaline etching solution, and benzotriazole (hereinafter, BTA) is used as the additive. The blending ratio between TMAH and BTA is preferably 0.5% by weight or more of BTA with respect to TMAH.

  Although the supply method of the etching liquid L to the back surface 1b of the wafer 1 is not specifically limited, For example, it can supply with the spin coat method using the supply apparatus 10 shown in FIG. The supply device 10 supports the wafer 1 horizontally and rotatably with a plurality of support plates 11, and rotates the wafer 1 by rotating the outer peripheral surface of the wafer 1 with a plurality of rollers 12 by frictional force. In this configuration, the etching solution L is supplied dropwise from the nozzle 20 to the center of the back surface 1 b of the wafer 1.

  In this case, three support plates 11 are arranged at equal intervals in the circumferential direction, and three rollers 12 are arranged one by one between the support plates 11. A convex portion 11a protruding upward is formed at the center of the support plate 11, and the wafer 1 is positioned at the etching solution supply position by the outer peripheral surface coming into contact with the side surface of the convex portion 11a. ing.

  Each roller 12 has a rotating shaft 13 extending downward, and a driving belt 14 is wound around the rotating shaft 13. A driving roller 16 that is rotationally driven by a driving motor 15 is installed in pressure contact with the outer peripheral surface of the driving belt 14. When the driving roller 16 is rotationally driven in the direction of arrow A, the driving belt 14 is driven in the B direction. The rotation of the drive belt 14 is transmitted from the rotary shaft 13 to the roller 12 so that the wafer 1 rotates in the direction of arrow C.

  The wafer 1 is set on the support plate 11 with the back surface 1 b facing upward, and the outer peripheral surface is set in contact with the peripheral surface of each roller 12, and rotates by rotating the drive motor 15. When this state is maintained and the etchant L is dropped from the nozzle 20 and supplied to the center of the back surface 1b of the wafer 1, the etchant spreads to the outer peripheral side by centrifugal force and is supplied to the entire back surface 1b.

  In addition, when the back surface 1b of the wafer 1 is wet-etched using the supply device 10, as shown in FIG. 4, the etching nozzle 30 is inactive to the etching reaction from the lower side (the front surface 1a side). It is preferable to spray the fluid G so that the etching solution L does not enter the surface 1a of the wafer 1 by the pressure of the fluid G because unnecessary portions such as the surface 1a and the side surfaces are not etched. As the fluid G, an inert gas such as nitrogen gas or pure water is used.

  According to the processing method of the present embodiment, an etchant containing 0.5% by weight or more of BTA with respect to TMAH is used as the etching solution on the back surface of the wafer. For this reason, even if the back surface 1b of the wafer 1 is etched to expose the copper post 2, the anticorrosive coating 3 made of complex Cu-BTA is formed on the exposed surface of the copper post 2 as shown in FIG. This anticorrosion coating 3 prevents the copper post 2 from being etched. For this reason, the exposed copper post 2 is not etched, and only the back surface 1b of the wafer 1 is etched. As a result, there is an effect that there is no possibility of causing metal contamination due to dissolution of copper ions from the copper post 2.

  Further, in the present embodiment, prior to the etching of the wafer back surface, the back surface 1b of the wafer 1 is ground to a thickness at which the copper post 2 is not exposed to the back surface 1b. For this reason, compared with the case where an etching amount is not ground, it becomes less and the advantage that the usage-amount of etching liquid can be suppressed can be acquired.

  In the present embodiment, it is described that the blending ratio of TMAH and BTA is preferably 0.5% by weight or more of BTA with respect to TMAH. In this regard, etching is performed using an etching solution in which the ratio of BTA to TMAH is changed to 0%, 0.3%, 0.5%, 0.8%, 1%, 3%, 5%. A test was conducted.

  As a result, it was confirmed that the copper post 2 was etched when the blending ratio of BTA was 0% and 0.3%. On the other hand, when BTA contained 0.5% or more, the result that the copper post 2 was hardly etched was obtained. Thereby, it was confirmed that it is preferable that 0.5% by weight or more of BTA is contained with respect to TMAH.

DESCRIPTION OF SYMBOLS 1 ... Wafer 1a ... Wafer surface 1b ... Wafer back surface 2 ... Copper post 3 ... Anticorrosion coating L ... Etching solution

Claims (4)

A method for processing a wafer in which a copper post extending from a surface to a predetermined depth is embedded,
Etching is performed by supplying an etchant to the back surface of the wafer, and exposing the copper post to the back surface of the wafer and protruding from the back surface of the wafer,
The method of processing a wafer, wherein the etching solution comprises at least an alkaline etching solution and an additive having an antioxidant function for copper or a copper alloy.   The wafer processing method according to claim 1, wherein the alkaline etching solution is tetramethylammonium hydroxide, and the additive is benzotriazole.   3. The wafer processing method according to claim 2, wherein the benzotriazole is contained in an amount of 0.5% by weight or more based on tetramethylammonium hydroxide. Before performing the etching step, further comprising a thinning step of grinding or polishing the back surface of the wafer to a predetermined thickness,
The wafer processing method according to claim 1, wherein in the thinning step, the wafer is thinned to a thickness at which the copper post is not exposed on the back surface of the wafer.

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