Yuki Usui

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.

Gradation of proteins and cells attached to the surface of bio-inert zwitterionic polymer brush.

A self-assembled monolayer (SAM) of a 2-bromoisobutyryl end group-carrying initiator for atom transfer radical polymerization (ATRP) was constructed on the surface of silicon wafer or glass substrates via a silane-coupling reaction. When the initiator SAM was irradiated with UV light at 254nm, the surface density of bromine atoms was reduced by the scission of CBr bonds as observed by XPS. With the surface-initiated ATRP of the zwitterionic vinyl monomer, carboxymethyl betaine (CMB), the surface density of PCMB brushes could be easily varied by changing the irradiation period of UV light prior to the polymerization. Furthermore, by using a UV-cut shutter sliding above the initiator SAM-modified substrate at a constant speed, the degree of bromine atom removal could be linearly varied along the direction of movement of the shutter. Consequently, the amount of both proteins adsorbed and cells adhered to the PCMB brush-covered substrate could easily be controlled by the gradation of the surface density of PCMB brushes, which suppressed protein adsorption and cell adhesion. Such a technique is very simple and useful for the regulation of the surface density of adsorbed proteins and adhered cells on an originally bio-inert surface.

Helium ion microscopy (HIM) for imaging fine line features patterned organic film with less damage

Helium ion microscopy (HIM) was applied to image an organic film filled into narrow trenches. The film was characterized to examine structural changes after the HIM helium ion irradiation comparing with a SEM electron beam irradiation. In the HIM case, the change was seen in a deep region of the film, while it occurred at the surface in the SEM case. This depends on penetration properties of helium ions and electrons to the material, and surface imaging of the film looks more realistic by the HIM than the SEM.

Novel gap filling BARC with high chemical resistance

In the recent of the semiconductor manufacturing process, variety of properties (narrow gap-filling and planarity etc.) are required to organic BARC in addition to the conventional requirements. Moreover, SC-1 resistance is also needed because BARC is often used as a wet etching mask when TiN processing. But conventional BARC which include crosslinker doesn’t have enough SC-1 resistance, and we found that it is also difficult to obtain good gap-filling and good planarity because of outgassing and film shrinkage derived from the crosslinker. In this study, we have developed the new self-crosslinking BARC. The new crosslinking system shows low outgassing and film shrinkage because of not including crosslinker. So, novel BARC has better gap filling property and planarity and over 3 times higher SC-1 resistance than that of conventional BARC. Moreover, by adding the low molecular weight additive which has high adhesive unit to TiN surface, the novel BARC has over 10 times higher SC-1 resistance than that of conventional BARC. And this novel BARC can be applied both ArF and KrF lithography process because of broad absorbance, high etching rate, chemical resistance (SC-1, SC-2, DHF, and others) and good film thickness uniformity. In this paper, we will discuss the detail of new self-crosslinking BARC in excellent total performance and our approach to achieve high chemical resistance.