Wafer Back Grinding With Raised Pattern for Lower TTV
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Solution Overview
Problem
The existing methods for back grinding semiconductor wafers with bump electrodes result in increased Total Thickness Variation (TTV) due to height differences between the areas with and without bump electrodes, leading to potential cracking and separation issues.
Innovation Solution
A processing method involving the formation of a raised pattern on the areas without bump electrodes, adhering a front surface protection sheet that embeds the bump electrodes, and using a specific configuration of the protection sheet to reduce height differences, including a resin-based raised pattern with controlled shear storage modulus and loss tangent properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a front surface protection sheet is adhered on the workpiece having bump electrodes for back grinding, then the circuits on the front surface are protected, but the height difference between bump electrodes and circuit surface causes insufficient adhesion and workpiece damage
Solution Approach 1:
The protection sheet is designed with locally varying adhesive properties: the first region (over bump electrodes) has higher adhesive force to secure the protruding electrodes, while the second region (over circuit surface) has lower adhesive force to prevent damage to delicate circuits. This local differentiation of adhesive quality resolves the contradiction between protecting circuits and achieving uniform adhesion.
Solution Approach 2:
The adhesive force parameter of the protection sheet is changed across different regions. By controlling the adhesive force to be higher in the first region and lower in the second region, the sheet adapts to the height differences caused by bump electrodes while maintaining appropriate bonding strength in each area, thus resolving the adhesion uniformity issue.
2Ease of operation
If suction is applied to fix the workpiece on the grinding table, then the workpiece is held during grinding, but the height difference causes the outer circumference to warp and increases TTV
Solution Approach 1:
The protection sheet provides localized support: the first region with higher adhesive force supports the bump electrode areas that would otherwise be pulled down by suction, while the second region allows the outer circumference to maintain its natural position. This local differentiation prevents warping and reduces TTV while still enabling effective fixation.
Solution Approach 2:
The protection sheet is adhered beforehand to cushion and protect the workpiece surface from the harmful effects of suction. By having the sheet in place before suction is applied, it prevents the outer circumference from being pulled down and warping, thus compensating for the height difference issue before it can affect thickness uniformity.
3Ease of operation
If the outer circumference part is pulled down during suction, then fixation is achieved, but the workpiece warps after release and TTV increases
Solution Approach 1:
The protection sheet creates local quality differences in adhesion strength that prevent uniform pulling down of the workpiece. The first region with higher adhesive force anchors the bump electrode areas, while the second region with lower adhesive force allows the outer circumference to remain stable, preventing warping after suction release and maintaining thickness consistency.
Data Source
AI summary
A processing method of a workpiece capable of reducing Total Thickness Variation (TTV) of the workpiece includes adhering a front surface protection sheet on a front surface of a workpiece having the front surface and a back surface; grinding the back surface of the workpiece on which the front surface protection sheet is adhered; wherein the front surface of the workpiece has bump electrodes, a raised pattern has been formed along an outer circumference part on the front surface of the workpiece which is an area different from an area where the bump electrodes are formed when adhering the front surface protection sheet, the front surface protection sheet is adhered on the front surface of the workpiece so as to embed the bump electrodes, and a height Hb of each of the bump electrodes and a height H1 of the raised pattern satisfy Hb/8<H1<Hb/1.5.