Renee Koch

Photomask etch challenges for future technology nodes

Requirements to meet the 45nm technology node place many challenges on photomask makers. Resolution Enhancement Techniques (RET), employed to extend optical lithography in order to resolve sub-resolution features have burdened mask processes margins. Also, yield compromises rise with every nanometer of error incurred on the photomask (and device) platforms. As photomask costs rise, strict performance control is required for all photomask varieties utilized in the mask shop. Mask etching for future technology nodes, requires a system-level data and diagnostics strategy. This necessity stems from the need to control the performance of the mask etcher at increasingly stringent and diverse requirements of the photomask production environment. From etch applications perspective, alternating phase-shift masks (APSMs) and OPC masks pose key challenges. Specifically, the etcher needs to provide highly uniform CD performance across the entire active area of the photomask - for various feature sizes and load distributions, with no degradation to profiles. It is challenging to strike this balance, yet maintain adequate process window. Future etch systems require sensitive controls and knobs to provide this high precision and repeatable performance. Additionally, incoming variation in plate characteristics and quality necessitate tuning knobs capable of targeting the optimum performance across a diversity of applications.

Evaluation of quartz dry etching performance for next generation phase-shift mask applications

The photomask industry is constantly reaching towards next-generation technology that can advance todays semi-conductor applications. One of the most successful and widely used techniques for advancing the current lithography capability and meeting many of the next-generation requirements is through the use of phase-shifting photomasks (PSM). Resolution enhancements techniques implemented through the use of PSMs can be a powerful tool in meeting both todays and tomorrows demanding lithographic requirements. For this work, effects of changing etch process parameters on the quartz dry-etching process performance is investigated. Considerations are given to phase depth uniformity, sidewall profile and reactive ion etch lag in the analysis of the quartz etch performance.

Approaching zero etch bias at Cr etch process

Increasing demand for high end lithography mask especially phase shift masks and narrowing the specification, lead to development of etch processes with minimum critical dimension uniformity (CDU) and very low etch bias. The etch bias becomes one of the limiting parameters for the Cr etch process, due to strong cross links between etch bias and other etch characteristics like linearity and loading effect, thus contributing strongly to the CDU for masks with non uniform pattern distribution. The goal was to develop a Cr etch process with very low etch bias, keeping the other parameters at the same level and providing a wider process window for further optimization of the CDU, loading effect and linearity. In the paper we want to present a feasibility study of one specific approach to the mentioned methods and compare different ways for measurement of the CDU and etch bias. The work presented was done on the Applied Materials Tetra II Mask Etch system.