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Method for TSV wafer strengthening during backend processing

IP.com Disclosure Number: IPCOM000240517D
Publication Date: 2015-Feb-05
Document File: 5 page(s) / 732K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to improve wafer level and die level fracture strength within the fabrication (FAB) processing.

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This is the abbreviated version, containing approximately 52% of the total text.

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Method for TSV wafer strengthening during backend processing

Semiconductor wafers that incorporate integrated circuits with Through Silicon Vias (TSVs) or what is also known as Through Wafer Vias (TWVs) are only 25% as strong mechanically as the same thickness wafer without incorporated TSVs. At a

finished wafer thickness of 150um or less, such wafers are extremely fragile and prone to suffering from mechanical damage during the module build process. Such mechanical damage can manifest via broken wafers, broken die, or cracked die. Currently, no solutions address this problem. Module builders typically invoke expensive and time-consuming "screens" to cull weak or fractured die prior to allowing such defects into electronic appliances. A method is needed to strengthen

the wafer during back end processing.

The novel contribution is a method to improve wafer level and die level fracture strength within the wafer fab and during assembly. The method removes some of the single crystal silicon substrate during the FAB back end processing to form trenches and then forms an alternate material in the trenches. The trenches form a crack stop to prevent propagation of cracks originating from the TSVs, thus increasing the fracture strength of the substrate.

The solution comprises at least two main ideas. A first is to form backside

"crackstop" trenches before the TSVs are formed. A second is to form backside

"crackstop" trenches after the TSVs are formed.

Idea #1: Backside "crackstop" trenches as a disposable layer ( removed during wafer thinning)

The first idea is to implement a structure that improves TSV wafer fracture strength during BEOL processing by etching backside trenches and filling these with a material that has a higher fracture strength compared to silicon (ie. a "ReDisk" metal, such as aluminum). The crackstop trenches are formed using lithography and reactive ion etching (RIE). The crackstop trenches are then filled with a material that has a higher fracture strength than silicon.

The key properties of the material that fills the crackstop trenches:

• Having a stress such that the finished wafer has no more than 3mm of bow
• Ability to withstand the highest temperature in BEOL processing


• Having sufficient thermal conductivity such that the circuits and devices of the die are not negatively affected

• Either a high or low Young's modulus - Low modulus ma...