Chemically Amplified Photoresists Research Articles

Challenges in Lift-Off Process Using CAMP Negative Photoresist in III–V IC Fabrication

In III–V IC processing, lift-off patterning is universally used. Historically used negative resist has its limitations; hence the image reverse process using positive tone resist has been utilized as the main work horse in lift-off applications. Metal lift-off processes using a specially designed chemically amplified (CAMP) negative tone resist have been evaluated for thin and thick metal layers to have a varying degree of success. Lift-off using CAMP photoresists has made it possible to reduce cycle time (~57% reduction in $1\times$ theoretical cycle time per layer) and reduce cost (due to elimination of steps) as compared to the image reverse process. However, achieving consistent lift-off and critical dimension (CD) control presents challenges, which are discussed in this paper.

A new type of sulfonium salt copolymers generating polymeric photoacid: Preparation, properties and application

Photoacid generators (PAGs) are critical components in chemically amplified (CA) photoresists system, among which small molecular sulfonium salts are commonly used but possess inherent incompatibility with polymer matrixes and acid migration during the post exposure baking (PEB) processes. PAG-bound polymers would be better choices for CA photoresists to acquire excellent lithographic performance. In this work, a new and convenient way is designed to prepare polymeric PAGs which generate polymeric photoacids and with this method the existing small molecular sulfonium salts can be transformed into polymeric compounds with convenience. Poly (sodium p-styrenesulfonate-co-tertiary-butyl methacrylate) (p(SSNa-co-t-BMA)) was prepared through free radical polymerization and then was further reacted with various sulfonium halides to give sulfonium salt copolymers. Different molecular weights of the copolymers can be obtained from Mn 5.5 × 103–2.5 × 104 with distribution coefficient between 1.18‐1.88. The ionic copolymers display good solubilities in common resist solvents. The thermal decomposition temperatures (Td) are around 150–155 °C and the glass transition temperatures (Tg) are above 130 °C. After exposed to light, the copolymers can generate polymeric photoacids. The photoacid generation efficiencies are determined around 0.31–0.34. UV spectra show big difference between the polymeric PAGs and the mixture of the corresponding small molecular sulfonium salts and framework polymers and demonstrate much better transparency of polymeric PAGs. Thick film 248-nm CA photoresist can be formed by one of the polymeric PAGs and partly protected poly(4-hydroxystyrene-co- tertiary-butyl methacrylate) (p(4-HS-co-t-BMA)), and display excellent performance with high height/width (H/W) ratio of 5:1 and resolution of 0.35 μm. These polymeric PAGs also have potentiality to be used in CA photoresists for other photolithography technologies such as 193-nm immersion technology.

Patterning highly ordered arrays of complex nanofeatures through EUV directed polarity switching of non chemically amplified photoresist.

Given the importance of complex nanofeatures in the filed of micro-/nanoelectronics particularly in the area of high-density magnetic recording, photonic crystals, information storage, micro-lens arrays, tissue engineering and catalysis, the present work demonstrates the development of new methodology for patterning complex nanofeatures using a recently developed non-chemically amplified photoresist (n-CARs) poly(4-(methacryloyloxy)phenyl)dimethylsulfoniumtriflate) (polyMAPDST) with the help of extreme ultraviolet lithography (EUVL) as patterning tool. The photosensitivity of polyMAPDST is mainly due to the presence of radiation sensitive trifluoromethanesulfonate unit (triflate group) which undergoes photodegradation upon exposure with EUV photons, and thus brings in polarity change in the polymer structure. Integration of such radiation sensitive unit into polymer network avoids the need of chemical amplification which is otherwise needed for polarity switching in the case of chemically amplified photoresists (CARs). Indeed, we successfully patterned highly ordered wide-raging dense nanofeatures that include nanodots, nanowaves, nanoboats, star-elbow etc. All these developed nanopatterns have been well characterized by FESEM and AFM techniques. Finally, the potential of polyMAPDST has been established by successful transfer of patterns into silicon substrate through adaptation of compatible etch recipes.

Synthesis of Novel Photoacid Generator Containing Resist Polymer for Electron Beam Lithography

Photoacid generators (PAGs) have been widely used as a key material in the development of novel photoresist materials. One of the important uses of PAGs is found in chemically amplified photoresists (CARs) because of their high photosensitivity and high resolution capability. Triphenylsulfonium salt methacrylate (TPSMA) as the PAG has been bounded in the main polymer backbone. TPSMA was employed for synthesis of terpolymers, poly(MMA-co-tBVPC-co-TPSMA) and poly(tBVPC-co-tBOCPOMI-co-TPSMA) as a positive tone photoresists by free radical polymerization using AIBN. Terpolymers with various ratio of TPSMA, MMA, tBVPC and tBOCOPMI were synthesized and well characterized by FTIR, NMR. Molecular weight distribution was analyzed by GPC. Thermal properties were studied using TGA, DSC which showed thermal stability of terpolymer up to 150 degrees C. We have applied E-beam lithography and KrF lithography in order to demonstrate the effect of the polymer bounded PAG resists. These positive tone resists were successfully applied for fabrication of nano-scale patterns.

Chemically amplified photoresists for 193‐nm photolithography: Effect of molecular structure and photonic parameters on photopatterning

AbstractNext generations of microelectronic devices request further miniaturized systems. In this context, photolithography is a key step and many efforts have been paid to develop new irradiation setup and materials compatible with sub‐100 nm resolution. Among other resist platforms, chemically amplified photoresists (CAR) are widely used because of their excellent properties in terms of resolution, sensitivity, and etching resistance. However, low information on the impact of the polymer structure on the lithography performance is available. CAR with well‐controlled polymer structures were thus prepared and investigated. In particular, the impact of the polymer structure on the lithographic performance was evaluated. Linear and branched polymers with various molecular weights and polydispersities were compared. We focused on the dependency of the photosensitivity of the resist with the structural parameters. These results allow further understanding the fundamental phenomena involved by 193‐nm irradiation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1271–1277, 2010

Dependence of Acid Yield on Acid Generator in Chemically Amplified Resist for Post-Optical Lithography

Acid generators are a key component of chemically amplified (CA) resists. They have been intensively investigated during the development of CA photoresists. However, the role of acid generators in acid generation processes is different between photoresists and electron beam resists. In this study, the dependence of acid yield on the kind of acid generator was investigated in CA resists for post-optical lithography. On exposure to ionizing radiation, a difference in acid yield was observed among four kinds of acid generator. The role of acid generators and their reaction mechanisms were discussed.