Changil Oh

Novel spin-on organic hardmask with high plasma etch resistance

In recent years for memory devices under 70nm using ArF lithography, spin-on organic hardmask has become an attractive alternative process to amorphous carbon layer hardmark (ACL) in mass production due to ACL hardmasks limited capacity, high cost-of-ownership, and low process efficiency in spite of its excellent etch performance. However, insufficient plasma etch resistance of spin-on hardmask makes the etch process an issue resulting in inadequate vertical profiles, large CD bias, and narrow etch process window compared to ACL hardmask. In order to be able to apply these spin on hardmasks to varies layers including critical layers, the aforementioned problems need to be resolved and verified using several evaluation methods including etch pattern evaluation. In this paper, we report the synthesis of novel organic spin-on hardmasks (C-SOH) that incorporate various fused aromatic moieties into polymer chain and the evaluation of etch performance using dry etch tools. Organic spin-on hardmasks with 79-90 wt% carbon contents were synthesized in-house. Oxygen and fluorine based plasma etch processes were used to evaluate the etch resistance of the C-SOH. The results show our 3rd generation C-SOH has etch profiles comparable to that of ACL in a 1:1 dense pattern.

Spin-on organic hardmask materials in 70nm devices

In ArF lithography for < 90nm L/S, amorphous carbon layer (ACL) deposition becomes inevitable process because thin ArF resist itself can not provide suitable etch selectivity to sub-layers. One of the problems of ACL hardmask is surface particles which are more problematic in mass production. Limited capacity, high cost-of-ownership, and low process efficiency also make ACL hardmask a dilemma which can not be ignored by device makers. One of the answers to these problems is using a spin-on organic hardmask material instead of ACL hardmask. Therefore, several processes including bi-layer resist process (BLR), tri-layer resist process (TLR), and multi-layer resist process (MLR) have been investigated. In this paper, we have described spin-on organic hardmask materials applicable to 70nm memory devices. Applications to tri-layer resist process (TLR) were investigated in terms of photo property, etch property and process compatibility. Based on the test results described in this paper, our spin-on hardmask materials are expected to be used in mass production.

EUV-patterning characterization using a 3D mask simulation and field EUV scanner

In the field of lithography technology, EUV lithography can be a leading candidate for sub-30 nm technology node. EUVL expose system has different characteristics compared to DUV exposure system. EUV source wavelength is short and no material is transparent to the source. So off-axis reflective optic system is used for patterning in place of on-axis refractive system of DUV system. And different reticle design is needed that consists of 40 pair of Mo/Si multi layer and absorber layer in place of conventional mask. Because of the oblique incidence on the mask, shadowing effect is occurred such as pattern asymmetry, shift and pattern bias depending on pattern orientation. For non-telecentric characteristics of EUV scanner, shadowing effect produces CD variation versus field position[1][2]. Besides, it is well known that EUV scanner has bigger flare than conventional DUV scanner. Therefore, the correction of mask shadowing effect and flare level are one of the important issues for EUV lithography. In this paper, process window and MEF of EUV lithography has been examined by 3D mask simulation. CD variation by shadowing is simulated for various pattern orientations. A shadowing correction method has been calculated due to field position to reduce shadowing effect. And the correction effect is examined by simulation and Experimental results. Principle of radial overlay shift due to field position is verified then the shift length of line and space pattern is calculated.

Comparison of EUV patterning performance between PTD and NTD for 1Xnm DRAM

Recently in the R&D area DRAM has shrunk to 1X nm, at the same time patterning technology has been one of the major challenges on 1X nm DRAM. Less than 20nm line and space and less than 30nm contact hole patterning are basically needed for 1X nm DRAM. Currently ArF immersion extension such as DPT (Double Patterning Technology), SADP (Self-Aligned Double Patterning) and SAQP (Self-Aligned Quadruple Patterning) shows robust patterning performance relative to EUV/DSA and become established process as a baseline for 1Xnm DRAM. But cost of ownership and process complexity of DPT/SADP can be the big burden for volume production. Furthermore too many DPT/SADP can make DRAM shrink meaningless. In spite of current issues on DPT/SADP, EUV source power has been the most critical issue so far. And now source power issue is pushing development of high sensitive EUV resist and related process. In this paper, author will compare EUV PTD and NTD in view of image contrast and swelling, also evaluate patterning performance between EUV PTD and NTD, and finally describe current status and issues of EUV NTD.

Characteristics analysis of RELACS process from an OPC point of view

There are strong demands for techniques which are able to extend application of ArF immersion lithography. Especially, the leading edge techniques are required to make very small hole patterns below 50nm. Several techniques such as double patterning technique, free-form illumination and resist shrinkage technology are considered as viable candidates. Most of all, NTD (Negative Tone Development) is being regarded as the most promising technology for the realization of small hole patterns When NTD process is applied, hole patterns are defined by island type features on the reticle and consequently its optical performance shows better result compared with PTD (Positive Tone Development) process. However it is still difficult to define extremely small hole patterns below 40nm, new combination process of NTD with RELACS is being introduced to overcome resolution limitation. NTD combined with RELACS, which is the most advanced lithography technology, definitely enable us to generate smaller size hole patterns on the wafer. A chemical shrinkage technology, RELACS (Resolution Enhancement Lithography Assisted by Chemical Shrink), utilizes the cross linking reaction catalyzed by the acid component existing in a predefined resist pattern. In case of PTD combined with RELACS process, we already know that CD change after the shrinkage process is not influenced by duty ratio. So we could easily reflect the RELACS bias to meet the CD target during OPC (Optical Proximity Correction) procedure. But NTD combined with RELACS process was not understood clearly, nor verified. It requires more investigation of physical behavior during combined process in order to define exact hole patterns. The newly introduced process might require additive OPC modeling procedure to satisfy target CD when NTD RELACS bias has different values according to pitch and shape. This study is going to include the investigation on two types of resist shrinkage process, PTD and NTD. The optimized OPC methodology will be discussed through the evaluation on simple array hole patterns and random hole patterns.

Defect printability analysis in negative tone development lithography

In general, contact hole patterning has various challenges such as narrow process window, large mask error enhancement factor (MEEF), poor circularity, and low image contrast compared to line & space patterning. For that reason, it is difficult to make sub-50nm size contact hole with 193nm ArF immersion single exposure. In order to achieve sub-40nm contact hole patterning, we have need of shrink bias over 20nm. However, conventional pattern shrink technology such as resist reflow process is difficult to get shrink bias over 20nm because the shrink volume gets smaller as the pitch gets narrower. Recently several authors have specifically noted the advantages of using negative tone development for patterning narrow trenches. A new negative tone imaging with application of new developer to conventional ArF immersion resist materials is proposed for small contact hole pattern formation. Significantly better LWR and resolution on small contact hole pattern were observed with this negative tone development compared with positive tone development. In this paper, we will introduce the experimental results of sub-40nm contact hole patterning using negative tone systems for contact hole patterning. We will report the results of comprehensive studies of defects originating in negative tone photolithography and reveal the defect generation mechanism of each negative tone imaging-specific defect types.

Topcoat-less resist process for 2Xnm node devices

In recent years ArF immersion lithography in memory devices, topcoat process has become baseline process in mass production in spite of its additional process steps and high cost-of-ownership. In order to overcome low process efficiency of topcoat process, high throughput scanner with higher scan speed and advanced rinse modules for decreasing defectivity are under development. Topcoat-less resist is also upgraded gradually which contains hydrophobic additives enables the extreme patterning without topcoat and high speed scanning. But current topcoat-less process has not matured yet for the dark-field mask compared to bright-field because of the blob defect in unexposed area. To minimizing blob defect level both material and process sequence should be optimized effectively. The authors have focused on blob defect and litho performance of topcoat-less resist process for dark field application in 2Xnm node devices.