Sang-mun Chon

Development of automated contact inspection system using in-line CD SEM

We have developed an automated contact inspection system using an in-line CD SEM and applied it to monitor contact etching processes. As the design rule shrinks, monitoring of the contact etching, which cannot be detected by the conventional optical inspection systems, are becoming one of the most critical issues in semiconductor processing. Though there are e-beam based inspection systems or manual inspection sequence with in-line SEM (Scanning Electron Microscope), monitoring small and electrical defects has a few fundamental limitations. E-beam inspection systems have low throughput and a high price as a mass production tool. In the case of the manual inspection system, the inspection result depends on the operator and it is difficult to quantify the defect data. We have developed an automated contact inspection system to overcome these limitations. The system is composed of a data processing system and an in-line SEM. The automated in-line SEM inspects and stores the images of specified points on the wafer. The data processing system receives and manipulates the images to indicate the etching problem. It was shown that the scanning electron image of the contact is related to failures such as insufficient etching or residuals inside the contact.

Influence of activation energy on LER in chemically amplified KrF photoresists

LER of an acetal-type photoresist (PR) and an annealing-type PR was measured by Atomic Force Microscopy, with which LER is more quantitatively measurable than using SEM. The annealing-type PR showed smaller LER than acetal-type did. Acid diffusion length measurement of these two types of KrF photoresists with a practical method that is a measurement of the thickness loss in a resist film after development which follows placement of exposed resist powder on the surface and applying PEB was also executed. The annealing-type PR has been found to show longer acid diffusion length than that of acetal-type PR. Considering deblocking temperature, acetal group is cleaved right upon exposure before PEB due to its relatively low activation energy. This means that there would be more hydroxystyrene units in acetal-type PR at the beginning of PEB than in annealing-type one. Tg of photoresist samples before and after deblocking reaction was also measured by DSC. After deblocking reaction, it was found that Tg of acetal-type PR is much higher than that of annealing-type PR. This relatively high Tg will make acetal-type PR to have shorter acid diffusion length in conjunction with relatively low PEB temperature comparing with annealing-type in general. The absolute Tg value and Tg change with deblocking reaction depending on types of PRs were correlated to explain the inherent difference in LER performance in different types of PRs.

Impact of BARC on SEM shrinkage of ArF resist

The shrinkage of resist pattern during in-line SEM measurement has been argued and studied as one of the problems unsettled for manufacturing with ArF photolithography. Many of attempts to solve this problem have focused their attentions on the improvement of resist and inspection equipment. We bring up BARC (bottom anti-reflective coating) as a new impact factor on SEM shrinkage of resist. Practically, although the same resist was employed, our shrinkage tests gave the results depending on the kind of BARC. Feature size and depth of focus also affect SEM shrinkage of resist. Effect of reflectivity on SEM shrinkage was evaluated by changing thickness of BARCs and resultantly was somewhat significant. In this paper, the BARC-dependent results of SEM shrinkage are analyzed and discussed to provide a possibility that BARC may have another function of reducing SEM shrinkage.

New polymer platform of BARC for ArF lithography

We found a new polymer platform for ArF BARC that can be prepared by addition polymerization. This system not only improves resist pattern collapse, but also allows control of the optimum film thickness, and etch rate by combination of compounds, method of polymerization (molecular weight control), and additives. Moreover, these materials have the unique characteristic that the resist profiles change little even if the type of resist changes.

Influence of resin properties to resist performance at ArF lithography

The ArF resist has been evaluated focusing on resin character such as molecular weight, monomer composition and polydispersity (Pd). The resin properties were investigated to elucidate that which parameter was affected to the line edge roughness (LER). The Pd was correlated with LER. As the Pd was large, the LER was small. The resin molecular weight and monomer composition were affected to their vertical profile. Low molecular weight portion rich resin resulted in round and t-top profile, whilst high molecular weight rich resin resulted in square profile. The amount of lower molecular weight fraction was changed by purification method. The lower molecular weight resin caused severe tapered profile. It was concluded that 1) shift of Mw to smaller and 2) higher content of low molecular size fraction lead to rounded and tapered pattern profile. Lot-to-lot stable good pattern profile has achieved by controlling polymer molecular weight and content of low molecular size fraction in small variation range.

Analysis of solvent effect to control the BARC coating uniformity

There are many considerations to the design of BARC materials. Among those many properties, one important property that can effect lithographic performance is BARC coating uniformity. In general, the basic coating property (conformal or planar) depends on basic characteristics of polymer (Mw, chemistry, etc). But another major factor to control the coating uniformity is the choice of solvent system in the formulation of the BARC. According to our experimental results, two major factors that can affect the coating uniformity of one BARC are the vapor pressure and the hydrophilicity of solvents. If any solvent has too high vapor pressure and high hydrophilicity relatively, polymer segregation occurs in BARC surface area in case of high humidity condition, resulted in bad coating uniformity. In this paper, we will show basic evaluation results including the morphology change of BARC surface with several solvents which can be used in BARC formulation according to various humidity and temperature conditions. And also we will show the solution to overcome this problem in device manufacturing.