High-accuracy alignment based on subspace decomposition

Amir Aalam Ghazanfarian; Xun Chen; Mark A. McCord; Roger Fabian W. Pease

doi:10.1117/12.310778

29 June 1998 High-accuracy alignment based on subspace decomposition

Amir Aalam Ghazanfarian, Xun Chen, Mark A. McCord, Roger Fabian W. Pease

Proceedings Volume 3334, Optical Microlithography XI; (1998) https://doi.org/10.1117/12.310778
Event: 23rd Annual International Symposium on Microlithography, 1998, Santa Clara, CA, United States

Abstract

One of the most crucial emerging challenges in Lithography is achieving rapid and accurate alignment under a wide variety of conditions brought about by different overlying films occluding the marks. The problem is exacerbated by planarizing processes such as Chemical Mechanical Polishing (CMP) and asymmetric processes such as metal deposition and photoresist coating. These processes give rise to displacement of the perceived position of the alignment mark. Thus, any effective algorithm must be based on the history of such displacements. A new approach based on subspace decomposition of the alignment signals is described. The method only applies to imaging and/or scanning based alignment signals. The main assumption is that the process-induced asymmetries are small enough such that only linear effects need to be considered. We first find the subspace of alignment signals using a set of alignment signals with pre-known positions. The positions of the new signals are measured based on the fact that, if shifted correctly, they will lie in the same subspace as the previous signals. Current alignment algorithms assume symmetric alignment signals. Since this method exploits the structure of the signals, it results in more accurate measurement of the position than the current algorithms. Simulation results show that the alignment error is about an order of magnitude smaller than that achieved with conventional Maximum Likelihood or phase-fitting approaches. The computational complexity also increases linearly with the dimension of the subspace and is linearly proportional to signal bandwidth.

Citation Download Citation

Amir Aalam Ghazanfarian, Xun Chen, Mark A. McCord, and Roger Fabian W. Pease "High-accuracy alignment based on subspace decomposition", Proc. SPIE 3334, Optical Microlithography XI, (29 June 1998); https://doi.org/10.1117/12.310778

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available