No abstract
We are developing a set of dyed red, green, and blue color filter coatings for the fabrication of high resolution CCD and CMOS image sensor arrays. The resists contain photosensitive polymer binders and various curing agents, soluble organic dyes, and solvents. The new dyed photoresists are sensitive to i-line radiation, primarily at 365 nm, and are negative-working, requiring less than 500 mJ of exposure energy for patterning. The coatings are developed in standard Tetramethylammonium Hydroxide (TMAH) developers. Many dyes were examined in order to achieve the desired spectral properties as well as the meet the solvent solubility and thermal stability requirements. Computer modeling was utilized to determine the correct proportions of dye(s) in each resist, after which the modeling results were verified by actual formulation and testing. Thermal stability of the dyes was determined using isothermal. Thermogravimetric Analysis (TGA) at 200 o C for 30 minutes. The dyes were evaluated in both traditional (free radical) and novel polymer systems to see if adequate sensitivity, resolution, and feature quality could be obtained. The studies showed that traditional free radical-based photochemistries are marginal at best for high resolution (1-2 micron) applications. To overcome this limitation, a new polymer system having photodimerizable functional units and acid functional groups was developed to impart photosensitivity and developer solubility, respectively. This system, which does not use free radical-initiated photopolymerization as a mechanism for patterning, shows low exposure dose requirements and is capable of resolving features less than 2 micron in size.
Plasma trimming is a method widely used to achieve small feature sizes beyond the capability of photolithography. Plasma processes reduce the dimensions of photoresist, anti-reflective coating, hardmask, or device substrate patterns with varying degrees of anisotropy. The vertical trim rate is higher than or equal to the lateral trim rate. As a result, much of the line-edge roughness from the resist pattern remains. High aspect-ratio resist patterns are subject to necking and collapse during this process. However, by using a developer-soluble hardmask in place of traditional anti-reflective layers, it is possible to achieve controllable, anisotropic trim rates, as well as reduced roughness. Moreover, the process benefits from a very thin resist, or imaging layer, instead of relying on a thicker mask with a high aspect-ratio. The hardmask is patterned during a standard resist develop step, and the resist may be stripped prior to substrate etching due to the high etch resistance of the hardmask. Many other advantages have been discovered from this wet trimming process, including high resolution, extended depth of focus, controllable trim rate, and lower cost than traditional methods.
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