Directed self-assembly (DSA) process of block copolymers (BCPs) has been considered as a candidate for sub-20nm
contact patterning. In recent years the semiconductor manufacturers have been interested in use DSA in production. DSA
is based on the intrinsic property of the BCPs which is phase-separation in the molecular scale, but significant problems
remain for device application. Process time, high process temperature, defect, and CD distribution make the using of
DSA difficult in mass production. One of the most considered problems for DSA is the CD Distribution. A guide
material for grapho-epitaxy DSA process requires resistance against high temperature and solvent. We use negative tone
develop (NTD) photoresist (PR) guide for simple process and thermal resistance, and additional treatment for resistance
against high temperature and solvent. The CD distribution of DSA is highly related to the phase separation itself. In
order to get better performance, the polymer chains should have sufficient mobility under heating above their glass
temperature. Therefore, film thickness and molecular weight of BCPs are very important parameters for CD distribution
of DSA process. From the results, it is proven that guide materials, film thickness of BCPs, and molecular weight of
BCPs are significant parameter in order to improve CD distribution of DSA patterns.
In this paper we investigate fundamental resist properties to enhance resolution and focus margin for immersion
contact hole patterning. Basic chemistry factors have been used to manipulate the iso-focal region (the region of
smallest critical dimension variation through focus) of the photoresist and study the impact on resolution and focus
margin for small isolated contact holes. Acid diffusion length is one of the key factors investigated, which can be
controlled by polymer, PAG, quencher, bake temperature and bake time. The various criteria investigated for this study
were: focus and exposure latitude for dense L/S, dense C/H and semi-dense C/H. The effect of manipulating the acid diffusion of the photoresist on imaging small contact holes was verified using ultra-high NA immersion imaging at 1.35
Reflectivity comparison study of bottom anti reflectivity coating (BARC) was investigated at 30nm node devices with same gate width at different pitch sizes. The goal of this study is to elucidate the practical target of reflectivity for high NA immersion lithography especially focusing on the changes in the CD variation. Using double patterning technology (DPT) and single patterning technology (SPT) patterns in high NA systems, we studied the impact of reflectivity to the lithography performance for various ARC thicknesses.
A strong dependence of n, k values (of BARC and substrate) on reflectivity was confirmed by simulation. Standing wave effects were investigated by vertical profiles inspection and changes in lithographic performances. Finally, we investigated the critical dimension uniformity (CDU), and line width roughness (LWR) variations for various reflectivities using hard mask substrates. Our experimental and simulation results clearly show that a 0.1% reflectivity target is highly recommendable for the sub-30 nm device process using high NA immersion lithography.
Bi-Layer Resist (BLR) process has been developed as an alternative method to overcome the limit of Single-Layer Resist lithography. Compared to other methods such as Single-Layer Resist (SLR) and Multi-Layer Resist (MLR), BLR has distinct advantages in cost down effect and quick Turn-Around-Time (TAT) due to the reduced number of process steps. In addition, it yields acceptional improvement in the Line-Width Roughness (LWR) on smaller CD. We have obtained feasible results of dense line and space patterning on various devices, which has 70 nm design rule. In this paper, a scanner of NA 0.85 is used and then appropriate condition of dry etch without any grass defect is developed. We are certain that BLR process is a strong candidate approach for the extension technology of ArF lithography and has potentially applicable in various devices.
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.
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.
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.
ArF lithography has been successfully implemented for the development of sub-90nm DRAM devices. Line width control for the ArF lithography is becoming increasingly challenging as design rules shrink. Many works have been performed on the mask, exposure tools, and tracks to obtain better critical dimension (CD) uniformity, however in-field uniformity, in-wafer uniformity, and wafer-to-wafer uniformity from resist itself was not considered thoroughly. In this experiment, resist parameters that contributes to line width variation were considered in resist perspective. For the in-field uniformity, mask CD uniformity is very important. However, the mask error enhancement factor (MEEF) was different ranging from 3.27 to 5.12 depending on the resists in the k1 0.35 processes even though the screened resists met all the required resolution, depth of focus (DOF), exposure latitude (EL), line edge roughness (LER), and profile. For the resists having good MEEF, the in-filed uniformities of the critical layers were highly improved. The PEB sensitivities of the screened resists were evaluated again in terms of post exposure bake (PEB) sensitivity, which were quite higher than those of KrF resists. They ranged from 4.0 to 11.3 nm/°C. In-wafer uniformity was evaluated and compared using the resists having different PEB sensitivity. The resist with better PEB sensitivity showed better result in in-wafer uniformity. Finally, the wafer-to-wafer uniformities of the resists were evaluated. There was different delay after exposure depending on the sequence of the loaded wafers because it was not easy to control the delay time at the interface of a scanner and a track. The CD increased depending on the sequence, and it coincided well with the delay time of the wafers after exposure. The wafer-to-wafer CD variations were improved using the resists having strong resistance to the delay.