Expanding the lithography process window (PW) with CDC technology

Abstract

The continuous shrinking of the semiconductor device nodes requires tough specifications of CD uniformity which result in narrowing of the lithography process window. Finding methods for expanding the process window will enable to continue manufacturing at least one more generation using the existing litho equipment. The CDC technology has been described in detail in past studies beginning in 2006; however it has typically been studied from a mask shop perspective. In this paper we will demonstrate a way to improve the CD Uniformity (CDU) on a new mask, which has a CD uniformity problem that leads to shrinking of the lithography process window, by using the Carl Zeiss CD Control (CDC) Technology. The methodology used and the process window improvement verification we show are based purely on fab available techniques and do not require any input from the mask shop. A production memory product in PSC fab P1/2 showed reduced yield due to reduced process window in one line/space (L/S) layer. A close investigation in the fab showed wafer CD non-uniformity of 6.5nm Range and 3.95nm 3S in this layer due to a mask CDU problem. A CDC process to improve the CDU was applied by the Carl Zeiss CDC200 tool based on wafer CD data only. Post CDC treatment results show that CD Range was reduced to 3.8nm (42% improvement) and 3S was reduced to 1.94nm (51% improvement). Further assessment of the litho process window of this layer showed an increase of CD-DOF from 0.15um before (Pre) CDC to 0.30um after (Post) CDC and an exposure latitude increase from 14.1% Pre to 26.7% Post CDC. To summarize our findings, applying the CDC process to the problematic layers allowed to increase the PW in both DOF and exposure latitude by improving the CDU of the layer. This resulted in better yield of this product.