Si-Backside Protection Circuits Against Physical Security Attacks on Flip-Chip Devices
Takuji Miki, Makoto Nagata, Hiroki Sonoda, Noriyuki Miura, Takaaki Okidono, Yuuki Araga, Naoya Watanabe, H. Shimamoto, Katsuya Kikuchi
Abstract
This article presents a cryptographic key protection technique from physical security attacks through Si-backside of IC chip. Flip-chip packaging leads to a serious security hole that allows emerging backside physical security attacks. The proposed backside buried metal (BBM) structure forming a meander wire pattern on the Si-backside detects unexpected disconnection of the meander and warns the malicious attempts to expose a vulnerable Si substrate. Moreover, the BBM meander also shields key information of cryptographic circuit from both passive side-channel attacks and active laser fault injection as well. Unlike other conventional laminate-based protection, this backside monolithic approach does not require frontside wiring resources or additional packaging layers, resulting in only 0.0025% size-overhead. The BBM meander was formed on the backside of a 0.13-$\mu \text{m}$ CMOS cryptographic chip by wafer-level via-last BBM processing.