Takanori Kawakami

Polymer-bound photobase generators and photoacid generators for pitch division lithography

The semiconductor industry is pursuing several process options that provide pathways to printing images smaller than the theoretical resolution limit of 193 nm projection scanners. These processes include double patterning, side wall deposition and pitch division. Pitch doubling lithography (PDL), the achievement of pitch division by addition of a photobase generator (PBG) to typical 193 nm resist formulations was recently presented.1 Controlling the net acid concentration as a function of dose by incorporating both a photoacid generator (PAG) and a PBG in the resist formulation imparts a resist dissolution rate response modulation at twice the frequency of the aerial image. Simulation and patterning of 45 nm half pitch L/S patterns produced using a 90 nm half pitch mask were reported.2 Pitch division was achieved, but the line edge roughness of the resulting images did not meet the current standard. To reduce line edge roughness, polymer bound PBGs and polymer bound PAGs were investigated in the PDL resist formulations. The synthesis, purification, analysis, and functional performance of various polymers containing PBG or PAG monomers are described herein. Both polymer bound PBG with monomeric PAG and polymer bound PAG with monomeric PBG showed a PDL response. The performance of the polymer bound formulations is compared to the same formulations with small molecule analogs of PAG and PBG.

Design and synthesis of a photoaromatization-based two-stage photobase generator for pitch division lithography.

The synthesis of a two-stage photobase generator (PBG) based on photoinduced aromatization is described. This material was designed for use in resolution-enhanced photolithography. Computer modeling predicts that a delay in the onset of base generation can lead to improved image quality. This delay can be realized by a PBG that must undergo two sequential photoreactions for each molecule of base generated. Toward that end, latent PBGs were designed that are oxime esters of aliphatic acids, which undergo Norrish type II reactions to yield oxime esters of aromatic acids that are efficient PBGs.

Various factors of the image blur in chemically amplified resist

In the current optical lithography, the resolution is being pushed for 45 nm half-pitch, and the chemically amplified resist will be used for wide variety of applications including immersion lithography. So far the chemical amplification has brought high performance for lithography. In the future, for the ArF lithography beyond 45nm half-pith, it will be important to control pattern size. On the other hand, chemically amplified resist which utilized acid catalyzed deprotecting reaction is sensitive to physical and chemical factor. Thus, there are various factors in the each process (Resist coating, Pre bake, Exposure, Post exposure bake, Development and Rinse) to cause the resist blur. For example, its acid diffusion on PEB. The influence of these factors for the resist blur is a significant issue for lithography beyond 45 nm half-pitch. Therefore the need to reduce these factors on the resist blur becomes higher in order to extend the ArF lithography beyond 45 nm half-pith. In this paper, acid diffusion coefficient (D) and resist blur with changing anion size of PAG, size of protecting group in typical ArF resist was reported. The relationship between acid diffusion coefficient and resist blur was discussed on the basis of their difference in structure and characteristics.

Photobase generator enabled pitch division: a progress report

Pitch division lithography (PDL) with a photobase generator (PBG) allows printing of grating images with twice the pitch of a mask. The proof-of-concept has been published in the previous paper and demonstrated by others. Forty five nm half-pitch (HP) patterns were produced using a 90nm HP mask, but the image had line edge roughness (LER) that does not meet requirements. Efforts have been made to understand and improve the LER in this process. Challenges were summarized toward low LER and good performing pitch division. Simulations and analysis showed the necessity for an optical image that is uniform in the z direction in order for pitch division to be successful. Two-stage PBGs were designed for enhancement of resist chemical contrast. New pitch division resists with polymer-bound PAGs and PBGs, and various PBGs were tested. This paper focuses on analysis of the LER problems and efforts to improve patterning performance in pitch division lithography.

Photobase generator assisted pitch division

The drive to sustain the improvements in productivity that derive from following Moores law has led the semiconductor industry to explore new technologies that enable production of smaller and smaller features on semiconductor device. Pitch division techniques and double exposure lithography are approaches that print features beyond the fundamental resolution limit of state-of-art lenses by modifying the lithographic process. This paper presents a new technique that enables pitch division in the printing of gratings using only a single exposure that is fully compatible with the current manufacturing tools. This technique employs a classical photoresist polymer together with a photoactive system that incorporates both a photoacid generator (PAG) and a photobase generator (PBG). The PBG is added to the resist formulation in higher molar concentration than the PAG, but has a base production rate that is slower than the acid production rate of the PAG. The PBG functions as a dose-dependent base quencher, which neutralizes the acid in high dose exposure regions but not in the low dose regions. This photoactive system can be exploited in the design of both positive tone and negative tone resist formulations that provide a developed image of a grating that is twice the frequency of the grating on the mask. A simulation of this process was performed for a 52 nm line and space pattern using PROLITH and customized codes. The results showed generation of a 26 nm half pitch relief image after development. Through this new technique, a 45 nm half pitch line and space pattern was experimentally achieved with a mask that produces a 90 nm half pitch aerial image. This corresponds to a k1 factor of 0.13. The principles, the materials design and the first lithographic evaluations of this system are reported.

High-performance 193nm photoresists based on fluorosulfonamide

The combination of immersion lithography and reticle enhancement techniques (RETs) has extended 193nm lithography into the 45nm node and possibly beyond. In order to fulfill the tight pitch and small critical dimension requirements of these future technology nodes, the performance of 193nm resist materials needs to further improve. In this paper, a high performance 193nm photoresist system based on fluorosulfonamide (FSM) is designed and developed. The FSM group has good transparency at 193nm. Compared to the commonly used hexafluoroalcohol (HFA) group, the trifluoromethyl sulfonamide (TFSM) functionality has a lower pKa value and contains less fluorine atoms. Polymers containing the TFSM functionality have exhibited improved dissolution properties and better etch resistance than their HFA counterparts. Resists based on the FSM-containing polymers have shown superior lithographic performance for line, trench and contact hole levels under the 45nm node exposure conditions. In addition, FSM resists have also demonstrated excellent bright field and dark field compatibility and thereby make it possible to use one resist for both bright field and dark field level applications. The structure, property and lithographic performance of the FSM resist system are reported.

Feasibility study of non-topcoat resist for 22nm node devices

Subsequent to 45 nm node, immersion lithography using topcoat process is approaching its next step for mass production. However, microfabrication using immersion topcoat leads to increase in cost due to increase in process steps. In order to deal with this problem, high throughput scanners equipped with a wafer stage which moves at higher speed are under development. Furthermore, as resist process compatible with such high speed scanners, non-topcoat resist is available and seems promising in reducing costs of the resist process. Non-topcoat resist contains hydrophobic additives which are eccentrically located near the film surface. Because non-topcoat resist enables the formation of a more hydrophobic surface, non-topcoat resist process is more suitable for high-speed scanning than topcoat resist process. In the topcoat process, the function of topcoat material and resist material is separated. That is, the resist material and the topcoat material are responsible for lithographic performance and immersion scanning performance, respectively. However, the non-topcoat resist is expected both performances. That is, the non-topcoat resist are required a fine resist profile, small LWR, and low development defects at high speed immersion scanning. In this paper, we report the application of non-topcoat resist in 22 nm node devices. We investigate the influence of hydrophobic additives on imaging performance in several base polymers. Additionally, the influence of chemical species, molecular weight and amount of hydrophobic additive are investigated. Scan performance is also estimated by dynamic receding contact angle using pin scan tool. 22nm node imaging performance is evaluated using Nikon NSRS610C. The surface characteristics and lithographic performance of non-topcoat resist for 22 nm node devices are discussed.