Kaveri Jain

Resist freezing process challenges of cross pattern applications

Three resist freezing methods (fluoride plasma, chemical and thermal freezing) were studied for double patterning cross pattern by printing the second layer directly on top of the first resist layer. Different methods show different challenges: plasma freezing is very hard to remove footing on both layers; Chemical freezing first layer CD will grow after completion of second pattern; thermal freezing will change line curvature when the CD is smaller than 50nm, if first layer is wave type pattern.

Characterization of resist and topcoat properties for immersion lithography

For this paper, we have performed a fundamental characterization of various resists and topcoats supplied by different vendors. The resists and topcoats were selected based on the inherent properties of these chemicals (elemental composition, contact angle, etc.). The goal of this study is to better understand the resist and topcoat interaction under various process conditions. We have characterized these materials using a number of analytical techniques such as atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). We have also provided data on the effect of the constitution of the resist and topcoat materials on the resist profile, under both dry and immersion exposure.

Characterization of array CD uniformity with respect to pattern density in 193nm dry photolithography

As we move toward printing sub-100nm features using 193nm dry photolithography with high-contrast photoresists, effects of mask transmission and pattern density start to play an important role in critical dimension uniformity (CDU). With these two factors in existence, the linewidth for a dense feature block gradually increases from the center to the edge of the array of the block. This change in CD is typically observed for low-transmission reticles. In this paper, we have characterized variables, such as reticle tone and resist processing parameters, which have an effect on the CD uniformity. Use of high-contrast photoresist can increase the effect of chemical flare and can have higher CDU. We have further shown that by using a topcoat or by making changes in the resist bake temperature and time, the effect of chemical flare can be reduced. We also propose a mechanism by which resists exhibit this characteristic and show that both the photoacid generator and quencher can contribute to chemical flare.

Fundamental characterization of shrink techniques on negative tone development based dense contact holes

Enormous advances have been made in recent years to design sub 40nm dense contact hole pattern with local CD uniformity (CDU) that the process can tolerate. Negative tone development process (NTD) on 193nm photoresists has achieved this to a large extent without the requirement of additional processing steps on the patterned layer. With further shrinking of size of the subsequent nodes, the demand to produce smaller patterns with wider process window, low defectivity, and improved CDU is increasing, and reaching beyond what can be achieved through NTD alone. A number of techniques are in practice today to achieve this, most notably, implementation of a collar of Atomic Layer Deposited SiO2 (ALD) on photoresist or substrate. However, in recent years, various material suppliers have also proposed shrink chemistries to achieve this. In this paper, we have provided fundamental characterization of shrink via application of spin-on agents (organic as well as aqueous) on the post-imaged pattern. We have also compared them for their shrink capacity, defect tendency, dry etch capability and ease of implementation in the process flow. In addition, we have provided recommendations on which technique is suitable for a given set of process prerequisites.

Predicting resist sensitivity to chemical flare effects though use of exposure density gradient method

Chemical flare has been shown to be a process limiter for patterns that are surrounded by areas of unexposed resist for certain chemically amplified resists. Using a pattern known to be susceptible to chemical flare effect a method was developed and tested on several materials. Details of the testing patterns, consisting of placements of small and large pattern density areas set to provide multiple degrees of resist loading; and a second level of loading variation achieved by selective exposure locations of those patterns across the wafer are given. Descriptions of the determination of slopes from linear trend-lines of the critical dimensions responses can be used to provide a gauge for internal evaluations as well as feedback to the vendors for chemical flare sensitivity.