Abstract
The color filter required for manufacturing a CMOS image sensor was redeveloped to optimize its optical uniformity. An in-depth study of the three-dimensional (3D) coating process and how it gives rise to various radial-shaped striation patterns was conducted. These radial-shaped striation patterns were systematically investigated with reference to two types of patterns: the orthogonal type found only at the orthogonal edges of the wafer and the diagonal type found mostly at the corner of each quadrant. The formation of the orthogonal pattern was based on the wide standing wave created by the incident force of the spreading color photoresist (PR) and the reflective force from the bump pads acting as coating barriers. The diagonal pattern was found to be generated by the turbulent wakes created behind the bump pads by the drag force, which interfered with the coating flow. An in-depth study using Ansys CFX software and an in-line inspection tool revealed that lowering the viscosity of the color PR material is a key factor for improving the phenomenon whereby the 3D striation patterns of the orthogonal and diagonal types are formed. Based on this finding, it was possible to drastically reduce the formation of the 3D striation patterns by decreasing the viscosity of the material comprising each color PR. This study provides not only an empirical and theoretical understanding of the 3D color PR coating mechanism, but also guidelines for future color filter processes.
Highlights
Since the advent of the mobile era, the CMOS image sensor (CIS) market has grown drastically owing to the strong demand for high-quality images captured by portable device cameras [1], [2]
The pigment-type coating process in CIS manufacturing is performed on the bump pads and the surface groove by the preceding integration, making it more difficult to ensure that the optical properties are uniform
The 3D radial-shaped striation patterns were categorized into two types: the orthogonal type, found only at the orthogonal edges of the wafer, and the diagonal type, which is mainly found at each quadrant edge
Summary
Since the advent of the mobile era, the CMOS image sensor (CIS) market has grown drastically owing to the strong demand for high-quality images captured by portable device cameras [1], [2]. Photographs and videos captured by smartphone cameras are frequently affected by noise in the form of faint patterns (e.g., discoloring and staining) inherent in the manufacturing process of CIS devices [3], [4]. Considering these technical challenges, a color filter (CF) is a key component for obtaining spectral color information from light, maintaining optical uniformity, and suppressing optical noise in CISs [5].
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