Development of a New Wafer Thinning Solution, the "UltraPoligrind" Wheel
DISCO Corporation has developed the UltraPoligrind wheel as a new stress relief processing solution to be applied after rough grinding and fine grinding, in the silicon wafer thinning process. An UltraPoligrind wheel will be on display at SEMICON Japan 2007 in December.
Photograph: UltraPoligrind
Development Background
The memory device, typically NAND flash memory and DRAM, are become thinner to meet the demands of SiP (System in Package). Also, the demand for thinning is increasing for other logic and RF devices. In response to this, DISCO has already proposed various solutions to support wafer thinning. However, thinning needs have recently grown due to a further increase in package density, and now there are many devices that are starting to appear that target a final grinding thickness of less than 50 µm.
The established backgrinder process leaves distortions, called a fractured layer, because silicon wafer grinding is a process that uses a destructive action. This can lead to wafer breaking and cracking during die mounted after dicing. To eliminate this destructive layer, stress relief processes, such as dry polishing or CMP (chemical mechanical polishing), are increasingly being used to maintain die strength.
However, because a sufficient gettering effect(#1) cannot be secured when thin grinding to less than 50 µm, a new problem
from heavy-metal contamination is starting to occur in traditional stress relief methods(#2).
The UltraPoligrind has been developed as a new solution for stress relief processing to maintain die strength while securing sufficient gettering effect for wafer thinning to less than 50 µm.
#1
The Gettering effect is a mechanism that forms crystal defects or distortions (=gettering sites) inside the silicon wafer (bulk or backside) and then capture the impurities in these gettering sites.
#2
Device destruction due to heavy-metal contamination, which occurs with the inability to secure the gettering effect, is different depending on the device material and other conditions.
UltraPoligrind Features
[Maintains die strength]
Realizes equivalent die strength to traditional stress relief processes. The minimum die strength is used as the yardstick because it greatly influences product yield. (Refer to the die strength using the ball measurement graph below)
Die strength using the ball measurement graph
[Gettering effect]
Maintains an appropriate amount of gettering effect with ultra fine grit grinding.
[Equivalent productivity]
Maintains productivity equivalent to traditional stress relief.
DISCO's Wafer Thinning SolutionDISCO is successfully responding to the needs of various devices and processes by providing a
wide range of solutions for wafer thinning. These include stress relief using "dry polishing," which DISCO
has been proposing for some time, and “plasma etching, "fine grit grinding using the Poligrind, and ultra-fine
grit grinding using the newly developed UltraPoligrind.
Schedule
December 2007
On display at SEMICON Japan 2007
April - June 2008
Commencement of test cuts
Note: DISCO recommends conducting a test cut before adopting the UltraPoligrind wheel.
Contact: Aya Osumi
Marketing Communications Team,
Marketing Communications Department,
Corporate Strategy Division
DISCO Corporation
E-Mail:
Phone: 81-3-4590-1090
