A Method to Fabricate Embedded Security Chips at BEOL by Directed Self-Assembly
Publication Date: 2016-Apr-12
The IP.com Prior Art Database
Disclosed is a method to fabricate random and unique embedded security chips at the back-end-of-line (BEOL) of semiconductor manufacturing processes by Directed Self-Assembly. Such a security chip can be used for authentication purposes.
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A Method to Fabricate Embedded Security Chips at BEOL by Directed Self -
A hardware-level security chip is critical for a variety of applications, such as Internet-of-Things (IoT). Conventional processes generate and assign a unique key to each user for later authentication process; however, this approach is susceptible to theft or key cloning.
The novel contribution is a Physical Unclonable Function (PUF). This is an improved authentication concept that utilizes a unique circuit, instead of a unique key, and generates a unique output (response) for each input (challenge). If the number of input/output (or challenge/response) pairs is close to infinite, then the PUF system can be used as a system with a unique and disposable key, thereby removing the concern for theft or cloning.
The authentication procedure of a PUF system follows:
1. Generate several challenge/response pairs and store the pairs in a database
when the PUF is first fabricated and under a secure environment
2. When the PUF is deployed in the field and used for authentication, the security system:
A. Searches the database
B. Picks a random challenge/response pair
C. Sends the challenge to the PUF chip
D. Verifies the response
3. Delete the challenge/response pair from the database after use, rendering any theft or clone of this challenge/response pair ineffective
4. Implement a replenish process under a secure environment (i.e., after the verification process is successful) when the stored challenge/response pairs in the database become depleted
A PUF was realized by utilizing the intrinsic random circuit delay from the semiconductor manufacturing process. However, circuit delay is known to vary with the environment (e.g. temperature) and has a certain level of uncertainty/noise. As a result, authentication with such a system is never exact and needs to tolerate quite a few incorrect bits, which means the probability of false positive and false negative exists.
This approach utilizes the controllable random defects in a Directed Self-Assembly (DSA) hole shrink process, as illustrated in Fig. 1, to create a unique array with a certain number of missing holes at random locations, as illustrated in Fig. 2.
Figure 1: DSA hole shrink process flow