Development of new photoresist stripping agent

Abstract

Optical lithography is one of the most extensively used technologies in the fabrication of a printed circuit board (PCB) or a semiconductor device. In recent years, as the demand for smaller sized electronic appliances increases and the cost of the stripping agents keeps escalating, higher standard and requirement on existing photoresist stripping technology is demanded for the semiconductor industry. In conventional techniques, photoresists can be removed by simple hydroxides based stripping agents. Proprietary stripping agents which are predominantly based on amine chemistry have attracted much attention because of their proven ability to make the photoresist film particulate into small features thus to show faster and improved stripping efficiency. However, the photoresist stripping ability of known stripping agents is insufficient to tackle the newly developed fine process and short time treatment in the production of semiconductor devices and liquid crystal display panels. Moreover, these known stripping agents are reported to show negative effect on the PCB production process with problems such as high metal corrosion rates which can lead to tin transfer and etch retardation. Therefore, it has been a high demand for further improvement of the stripping ability. Up to date, the stripping agents we used are capable of dry films removal processes within a short period of time. However, the existing stripping agents are not powerful enough to clean the liquid photoresists efficiently. The liquid photoresists removal process performs much worse with high level of residues which requires a second exposure and lead to unacceptable scrap rates after etching. Furthermore, corrosive attack on copper substrate by these existing stripping agent results in an uneven wire width after gold plating. In order to resolve such issues, development of the next generation of photoresist stripping agent which can be applied to both dry and wet film with minimal attack on the metal base is an urgent issue in the immediate future. In this paper, a photoresist stripping agent containing a combination of amine compounds in aqueous alkaline based solutions is proposed. By using this new photoresist stripping agent, the circuit appears to have been fully stripped of all dry film with increasing stripping rate and the production was increased by 60%. New product is also capable of completely removing the liquid photoresists without secondary processes, and the production was increased by 25%. The use of new formulation avoids any undesirable metal attack. In addition, the cost of the new formulation is much less than the existing stripping agent. With the advantages of lower cost, better stripping ability and increase of production rates, the new stripping agent is aimed to replace the older stripping agent in order to produce high quality product.