Sou Kamimura

Development of materials and processes for negative tone development toward 32-nm node 193-nm immersion double-patterning process

A new negative tone imaging with application of new developer to conventional ArF immersion resist materials is proposed to form narrow trench and contact hole patterns, which is promising for double patterning process, since it is difficult to obtain sufficient optical image contrast to print narrow trench or contact hole below 60 nm pattern size with positive tone imaging. No swelling property in the developing step realized low LWR number at 32 nm trench patterns. Uniform de-protection ratio through the depth of resist film reduced cuspy resist pattern profile causing micro-bridges at narrow trench pattern, and low frequency LWR number down to 2.4 nm. High resolution potential was demonstrated with 38 nm dense S/L under 1.35 NA immersion exposure. Better CD uniformity and LWR number of trench pattern were obtained by negative tone development (NTD) process with comparison to positive tone development (PTD) process. Excellent defect density of 0.02 counts/cm2 was obtained for 75 nm 1:1 S/L by combination of 0.75 NA dry exposure and NTD process combination. NTD process parameters impacts to defectivity were studied.

Process parameter influence to negative tone development process for double patterning

Process parameter influence in resist process with negative tone development (NTD) to pattern size (CD), CD uniformity (CUD), and defectivity are studied to estimate the impact for process stability in high volume manufacturing (HVM) of semiconductor devices. Since double exposure process is one of the candidates in contact hole patterning, exposure to exposure delay was studied. There is a possibility to design the off-line system with NTD process, therefore, exposure - PEB delay and PEB - development delay were studied. As basic development parameter studies, development time, developer temperature, developer volume, and rinse time dependency on CD, CDU, and defectivity were investigated.

The material design to reduce outgassing in acetal-based chemically amplified resist for EUV lithography

In case of EUV lithography, resist material needs to be developed to improve high sensitivity and to minimize outgassing. The outgassing segments from resist were mainly from PAG decomposition. The new type PAG was synthesized by modifying cation group of the sulfonium salt. The sensitivity of the PAG could be enhanced by loading electron withdrawing group on the PAG, which has low volatility during EUV exposure. Then the newly developed PAGs were capable to reduce outgassing during EUV exposure maintaining high acid generating efficiency against EB and EUV exposure. The other approaches to improve the resist sensitivity and minimizing outgassing property were to design PHS based polymer platform with bulky acetal group. The various kind of acetal groups were simulated to determine the Van der Waals volume. The bulkiness of the protection group is effective to both a) increasing inhibition rate of the resist matrix and b) boiling points of deprotected group. The optimum protection ratio has been studied to obtain proper dissolution rate changes before and after exposure. The resist sensitivity is depend on the protection ratio of the bulky acetal group. By modifying PAG and optimizing bulky acetal group in the polymer, it is possible to minimize the amount of the outgassing segments during EUV exposure maintaining high resist sensitivity. The EUV exposure was demonstrated. It was observed that the resist had a high resolution capability in EUV exposure.

Resist material for negative tone development process

Methods for improving lithography performance with optimization of resist materials and formulation for negative tone development (NTD) process are discussed. Narrow pitch lithography performance comparison with NTD and PTD process for initial platform for NTD revealed the not enough maturity of the resist for NTD. Dissolution rate study suggested the optimizations of molecular weight and solvent parameter to NTD process are important to improve dissolution property. Larger dissolution rate and larger γ value in contrast curve gave larger process window at 40 nm half pitch dense contact hole pattern with double exposure and single development step.

High volume manufacturing capability of negative tone development process

High volume manufacturing capability of negative tone development (NTD) process were discussed in viewpoint of lithography performance, necessary developing time impacting throughput, pattern defectivity, and CD-uniformity (CDU). Dense C/H pattern lithographic performances of the latest resist materials dedicated NTD process were introduced, and the design strategy of these resists were discussed. Best condition of development time was fixed with the study on development time dependences on CD-uniformity and defectivity. Throughput performance of NTD was discussed with the necessary development time. Pattern defectivity studies and CDU studies were carried out on L/S pattern and C/H pattern.

The resist materials study for the outgassing reduction and LWR improvement in EUV lithography

The continuous studies for both the outgassing reduction and the sensitivity improvement by applying low outgassing photo acid generator with a various kinds of polymer protection group were discussed in this paper. Further reduction of the outgassing segments from the resist was demonstrated to achieve the total outgassing amount below the detection limit of GC-MS (ca. less than 1E+10 molecules / cm2). Loading a large sized acetal group could be successfully reduced the amount of the outgassing segments from polymer below the tool detection limit, which would be acceptable for a high volume manufacturing tool usage. The development properties of PHS based bulky acetal polymers were measured by changing molecular weight. The high dissolution rate contrast was obtained with the bulky acetel protected low molecular weight polymer. A resolution capability study was carried out with micro exposure tool (MET) at LBNL and Albany. The correlation between LWR through CD and DOF was measured by loading various amounts of quencher. The resolution capability of newly developed EUV resist had been successfully improved by modifying both resist polymer matrix and quencher amount optimization. It was possible to obtain 27.7nm lines with MET tool, where LWR value at 35 nm L/S was 3.9 nm with reasonable sensitivity range.

Cost effective processes by using negative-tone development application

The high volume manufacturing with extreme ultraviolet (EUV) lithography is delaying due to its light source issue. Therefore, ArF-immersion lithography has still been the most promising technology for down scaling of device pitch. As the limitation of ArF-immersion single patterning is considered to be nearly 40nm half pitch (hp), ArF-immersion lithography has necessity to be extended by combining processes to achieve sub- 20nm hp patterning. Recently, there are many reports about the extension of ArF-immersion lithography, e.g., self-aligned multiple patterning (SAMP) and litho-etch-litho-etch (LELE) process. These methods have been realized by the combination of lithography, deposition, and etching. On the other aspect, 1-D layout is adopted for leading devices, which contains additional cut or block litho and etch processes to form 2-D like layout. Thus, according to the progress of down scaling technologies, number of processes increases and the cost of ownership (CoO) can not be neglected. Especially, the number of lithography steps and etching steps has been expanded by the combination of processes, and it has come to occupy a large portion of total manufacturing cost. We have reported that negative tone development (NTD) system using organic solvent developer have enough resolution to achieve fine narrow trench or contact hole patterning, since negative tone imaging enables to apply bright mask for these pattern with significantly high optical image contrast compared to positive tone imaging, and it has contributed high throughput multiple patterning. On the other hand, NTD system is found to be useful not only for leading device node, but also for cost effective process. In this report, we propose the cost effective process using NTD application. In the viewpoint of cost down at exposure tool, we have developed KrF-NTD resist which is customized for organic solvent developer. Our KrF-NTD resist has resolution comparable with ArF positive tone development (PTD) resist in narrow trench pattern, and it realizes downgrade of exposure tool. Also, we propose litho-litho-etch process with NTD resist. This method can reduce etching process and decrease total manufacturing cost more directly.

Experimental characterization of NTD resist shrinkage

Simulation of negative tone development (NTD) resist has become a challenge for physical resist modeling. Traditionally, resist modeling was mainly limited to reaction-diffusion models for post exposure bake (PEB) and standard development rate models for simulating the pattern formation during the final development step. With some minor extensions, this simulation approach sufficiently predicted resist CDs and resist profile shapes that were in agreement with experimental data.3 For the latest NTD resists, this situation has changed. In contrast to positive tone development (PTD) resists, resist shrinkage is strongly impacting resist profile shapes. Furthermore, NTD resists induce strong proximity effects that require consideration of additional chemical resist properties in modeling and model calibration. In this paper we experimentally characterize and model the main properties of NTD photo-resists.