The trend toward narrower line widths in the manufacture of integrated circuits has put an increasing burden on contamination control in every aspect of semiconductor fabrication. For a deep sub micrometer device, metal contamination appearing on the device can cause fatal problems including increasing the leakage current at the p-n junction, decreasing the breakdown voltage of oxide. Many lithographic defects have been known and evaluated, however, the effects of metallic impurity (Zn) in solvent are seldom reported during lithography process. Solvents are component material for Photoresist and have been used for prewet, strippers, EBR, rinse and so on during photolithography process. Lithography plays a very important role because it is applied repeatedly onto the wafer surface during device manufacturing. Unfortunately, pattern lifting happened to well formation layer wafers that were reworked on a normal iline litho process after stripping the Photoresist with solvent (PGMEA). We also detected blocked pattern defect at 0.18 CMOS gate pattern coated with DUV resist applied solvent prewet step after BARC coating. From various investigations, we could know that pattern lifting and blocked defect were derived from solvent (PGMEA).
In this paper, we show mechanism of adhesion fails and blocked defect happened by metallic impurity Zn in solvent during solvent rework and prewet on organic BARC film. It shows that proper control of metallic impurities in thinner is an important item in FAB.
Critical Dimension of gate pattern in CMOS process is the most important parameter for transistor performance and Organic BARC is generally used for controlling gate CD by reducing the substrate reflectivity. After gate etch process, small poly-silicon block defects are formed and those are derived from BARC material. After S/W nitride deposition and etch process the defects become larger and formed block defects of Belly Button type. These “Belly Buttons” are blocking the active area of transistor, make the device characteristic worse and lead to yield loss. To reduce Belly Buttons, we have evaluated various BARC resist filtration methods including new filtration material and smaller size filter in 0.18~0.35 μm CMOS gate pattern process. It was possible to reduce Belly Buttons dramatically using optimized resist filtration method and we finally got the yield up.
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