Yoshiomi Hiroi

Patterning of photocleavable zwitterionic polymer brush fabricated on silicon wafer.

Brushes of a polymer, namely poly(carboxymethylbetaine) (PCMB), were fabricated on silicon wafers by reversible addition-fragmentation chain-transfer (RAFT) polymerization using a surface-confined RAFT agent having an aromatic group at its bottom. The polymer brush showed effective suppression of the non-specific adsorption of bovine serum albumin (BSA) and adhesion of fibroblasts (3T3 cells). In contrast, BSA and 3T3 cells significantly adsorbed on and adhered to positively or negatively charged polymer brushes fabricated by the same procedure. Upon UV irradiation at 193 nm, the thickness of the PCMB brush with an aromatic group at its bottom decreased significantly whereas PCMB prepared using a surface-confined RAFT agent without an aromatic group needed a much higher irradiation dose to afford a comparable decrease in thickness. These results indicate a preferential cleavage of the PCMB brush due to photodecomposition of the phenyl group at the bottom. BSA and 3T3 cells non-specifically adsorbed on and adhered to the UV irradiation-induced hollow spaces, respectively. Furthermore, a designed pattern with a resolution of 5 μm was successfully made on the PCMB brush above the silicon wafer by simple UV irradiation. These results suggest that the surface-confined aromatic RAFT agent will be quite useful for simple photolithography in biomedical fields.

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.

BARC (bottom anti-reflective coating) for immersion process

193nm immersion Lithography will be installed at 45nm and beyond. For severe CD control, BARC (Bottom Antireflective Coating) has been used and this material must be used for immersion lithography. So far, we have developed several BARCs with various advantages (fast etch rate, broad resist compatibility, high adhesion, conformal...etc). Especially in an immersion process, development of BARC has to satisfy for the optical control and defectivity. The reflectivity control at Hyper NA is not same as the lower NA, because optical pass length in the BARC is not the same between low NA and High NA. In order to achieve enough etch selectivity to the substrate, hard mask materials are necessary. These under layers have absorption at 193nm. As a result of simulation, target optical parameters of next BARC should be low k value (k = ~0.25) for multi BARC stack. On the other hand, the defect issue must be decreased in the immersion process. However, the generation of many kinds of defects is suspected in the immersion process (water mark, blob defect, sublimation defect...etc). Regarding the BARC, there are also several specific defects in this process. Especially, after edge bead rinse, film peeling at edge area is one of the concerns. We researched the root cause of edge peeling and a solution for this defect. In this paper, we will discuss the detail of our BARC approach for litho performance, optical parameter, leaching, sublimation, edge peel defects and etch selectivity, and introduce new BARC for 193nm immersion lithography.

Diffusion of acid and amine at resist/BARC interface

In chemically amplified (CA) resist process, photo-chemically generated acid is needed to diffuse in resist matrix to induce the de-blocking reaction. The concentration of acid in resist matrix should be constant during the post-exposure-bake (PEB) treatment. Organic bottom anti-reflective coating (BARC) is essentially important to provide reflectivity control for resist patterning. In some cases, the photochemically generated acid and amine added as a quencher can diffuse from resist layer to BARC layer, which causes the footing or undercut of resist patterns. In this study, we have devised novel concept to qualitatively observe the diffusion of acids and amines from resist layer to BARC layer and vice versa. The rate of de-blocking reaction of CA resist was used to estimate the amount of acid in resist layer. It was found that the acid in resist layer can diffuse into BARC layer and the acid in BARC layer can also diffuse into resist layer during PEB treatment. Diffusion efficiency of the acid at resist / BARC interface was dependent on the chemical structure of resist and crosslinking density of BARC materials. Diffusion of amines from resist layer to BARC layer was negligible.

Bottom-Anti-Reflective coatings (BARC) for LFLE Double patterning process

Double patterning process with ArF immersion lithography has been developed as one of the most promising candidate for hp32 node and beyond. However the complicated process flow and cost of ownership are the critical issue for this process. LELE (Litho-Etch-Litho-Etch) is the one of the standard process, but in order to reduce the process and cost, that LPLE(Litho-Process-Litho-Etch) process have been investigated as the alternative process. In these processes, organic Bottom-Anti-Reflective Coating (BARC) is used two times with same film in both 1st Litho and 2nd lithography process. In 2nd lithography process, resist pattern will be printed at space area where exposed and developed in 1st lithography process. Therefore, organic BARC needs to have process stability in photo and development step to keep good litho performance between 1st and 2nd lithography in LPLE process. This paper describes the process impact of 1st exposure and development for organic BARC, and the LPLE performance with optimized organic BARC will be discussed.

The design and evaluation of high barrier performance organic BARC material

The pattern shrinkage of semiconductor devices has been achieved by moving to shorter and shorter wavelengths in the optical lithography technologies. According to the ITRS, it is estimated that this trend will be continued through advanced lithography techniques such as Hyper NA immersion lithography, double patterning technique and EUV lithography. In the future, photo-resist film thickness requirements will approach 100 nm or less to achieve suitable aspect ratios. Therefore, organic bottom anti-reflective coating (BARC) film thicknesses must also be reduced from the viewpoint of the etching process. Due to these design changes, the performance of BARCs, especially photo-resist profile control and maintaining enough of a lithography process margin at the critical CD has become more crucial. Problem of photo-resist profiles, such as missing holes or scumming for contact holes (C/H) and footing in line-space (L/S) patterns by contamination from the substrate are known as resist poisoning. In order to prevent this issue, BARC films need to have not only reflection control properties but they also need to capable of contamination or poison blocking. Therefore, barrier properties to prevent contamination or poisoning should be included in the design of these new BARC materials. For developing these BARC that are designed to have both barrier properties and reflection control at around 30 nm thickness, we investigated their performance by evaluating both the chemical and physical property of BARC film. The design of these barrier films and details of evaluation experiments are discussed in this paper.

New 193-nm bottom anti-reflective coatings

Currently, a reduction in the critical dimension (CD) of integrated circuits is needed. Therefore, 193nm (ArF Excimer laser) optical lithography technology is introduced to manufacture IC in the semiconductor industry. In these circumstances, Bottom Anti-Reflective Coatings (BARCs) for 193nm optical lithography are required for high performance. New spin-on organic 193nm BARC chemistries (chromophore-attached polymers) have been developed with the objective being a commercial product. This paper discusses the development of new spin-on organic 193nm BARC (ARC29A). New 193nm BARC had many useful properties considered important for a successful product. In addition to the control of the reflectivity, new 193 BARC was developed with the purpose of increasing adhesion between photoresist and BARC to restrain pattern collapse at interface. It has been strongly required to restrain pattern collapse recently, because of the continuing demand for decreasing feature size. It was accomplished by optimize polymer structure, increasing the affinity to the photoresist and so on. The development process plan details in the releasing in the day. And in litho performance, new 193nm BARC has good compatibility (photoresist-profile, DOF, EL etc) with various photoresists. At IMEC, 80nm resolution was achieved. The plasma etch rate was about 1.3 times leading 193nm photoresist, using CF4 as etchant.