Wafer Rear Surface Grinding Method for Uniform Thickness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for grinding the rear surface of semiconductor wafers to form recessed portions are inefficient, leading to reduced yield and increased processing time due to difficulties in achieving uniform thickness and maintaining the original device formation area, especially with two-step grinding methods where finishing grinding often misses the outermost circumferential portions.
Innovation Solution
A two-step grinding method using an annular rotary grindstone with a larger grain size for rough grinding followed by a second grindstone with smaller grain size for finishing, ensuring the entire recessed portion is evenly machined, including the inner circumferential lateral surface and bottom surface, to maintain uniform thickness and prevent yield reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If finishing grinding is performed from the beginning with a high-mesh grindstone, then mechanical damage layer is suppressed and transverse rupture strength is maintained, but grinding performance deteriorates and processing time is prolonged
Solution Approach 1:
The grinding process is divided into two distinct stages: rough grinding using a low-mesh grindstone (#320-#600) to remove material efficiently, followed by finishing grinding using a high-mesh grindstone (#2000 or more) to achieve precise thickness and smooth surface. This segmentation allows each stage to optimize for its specific function, preventing the deterioration of grinding performance while maintaining strength.
Solution Approach 2:
Rough grinding is performed as a preliminary action before finishing grinding. The low-mesh grindstone pre-processes the wafer by removing the bulk material and forming the initial recessed portion, preparing the surface for the subsequent finishing grinding that ensures high precision and strength without the time penalty of using only high-mesh grindstone throughout.
2Force
If the outer circumferential side corner of the grindstone is removed or rounded, then grinding load is reduced, but the inner corner portion is ground in an R-shape and the outermost circumferential portion of the device formation area is not ground to target thickness
Solution Approach 1:
The grindstone is designed with non-uniform characteristics: the outer circumferential side corner is removed or rounded to reduce grinding load and prevent excessive material removal, while the inner corner portion maintains a sharp edge to ensure precise grinding of the recessed portion inner surface. This local differentiation of grindstone geometry allows simultaneous optimization of load distribution and grinding precision in different areas.
3Productivity
If a two-step grinding method is used with rough and finishing grinding, then processing time is reduced, but it is difficult to position the finishing grindstone at the inner circumferential lateral surface to conform to the shape and dimensions
Solution Approach 1:
The grindstone parameters are specifically optimized for the two-step process: the finishing grindstone has a grain size of #2000 or more and an outer diameter equal to or greater than the rough grindstone. These parameter changes enable the finishing grindstone to effectively position and conform to the inner circumferential lateral surface of the recessed portion, achieving precise thickness control despite the complexity of the two-step method.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach streamlines the rear surface grinding process, ensuring the device formation area remains intact and improving productivity by efficiently completing the grinding process without reducing the yield of semiconductor chips.
Implementation Method 1
an area of the rear surface corresponding to the device formation area is ground by an annular rotary type first grindstone or annularly arranged rotary type first grindstones to form a recessed portion
Implementation Method 2
a bottom surface of the recessed portion and an inner circumferential lateral surface which constitute an inner surface of the recessed portion are ground by a second grindstone which is an annular rotary type grindstone or annularly arranged rotary type grindstones
Data Source
AI summary
A recessed portion is formed in an area, of a rear surface of a wafer, corresponding to a device formation area is formed by a rough grinding wheel of a rough grinding unit and an annular protruding portion is concurrently formed around the recessed portion. The inner circumferential lateral surface of the recessed portion is next ground by a finishing grinding wheel of a finishing grinding unit and the bottom surface is subsequently ground.