Scanner correction capabilities aware CMP lithography hotspot analysis

Abstract

CMP effects on manufacturability are becoming more prominent as we move towards advanced process nodes, 28nm and below. It is well known that dishing and erosion occur during CMP process, and they strongly depend on pattern density, line spacing and line width [1] . Excessive thickness or topography variations can lead to shrinkage of process windows, causing potential yield problems such as resist lifting or printability issues. When critical patterns fall into regions with extreme topography variations, they would be more sensitive to defects and could potentially become yield limiters or killers. Scanner tools compensate and correct topography variations by following the given profile [2] . However the scanner exposure window size is wider compared to local topography variations in design. This difference would generate new lithography focus sensitive weak points which may be missed. Experiments have been conducted as shown in Fig 1. Design under manufacturing has been subjected to scanner tool topography focus corrections. Despite of the corrections, Site B topography height has worsened while site A and C shown some improvements. As a result, additional improvements need to be done to meet manufacturability requirements.In this paper, we will present the work done in GLOBALFOUNDRIES´ 28nm process targeted on topography induced lithography focus shifts. We will share the results on best focus exhibiting strong correlation to the CMP topography for a reference set of lithography critical patterns. The paper would propose how this CMP topography information can be utilized to derive layout or design changes to minimize the topography impact on depth-of-focus or process optimization to meet these challenges. We will discuss following topics in this paper: 1) Correlation results between optimal focus selection and topography using same reference set of lithography critical patterns at high and low topography regions 2) Analysis of focus sensitive lithography weak points at high or low and high to low topography transition areas based on scanner topography correction 3) Design-for-Manufacturing (DFM) recommendations [3] on reducing total topography variations to minimize the topography impact on depth-of-focus