Resist Dissolution Rate Research Articles

Validation of X-Ray Lithography and Development Simulation System for Moving Mask Deep X-Ray Lithography

This paper presents a newly developed 3-Dimensional (3-D) simulation system for Moving Mask Deep X-ray Lithography (M/sup 2/DXL) technique, and its validation. The simulation system named X-ray Lithography Simulation System for 3-Dimensional Fabrication (X3D) is tailored to simulate a fabrication process of 3-D microstructures by M/sup 2/DXL. X3D consists of three modules: mask generation, exposure and resist development (hereafter development). The exposure module calculates a dose distribution in resist using an X-ray mask pattern and its movement trajectory. The dose is then converted to a resist dissolution rate. The development module adopted the Fast Marching Method technique to calculate the 3-D dissolution process and resultant 3-D microstructures. This technique takes into account resist dissolution direction that is required by 3-D X-ray lithography simulation. The comparison between simulation results and measurements of stairs-like dose deposition pattern by M/sup 2/DXL showed that X3D correctly predicts the 3-D dissolution process of exposed PMMA.

Advances in Immersion Related Defectivity on XT:1250i at IMEC

The immersion-specific watermark defect is discussed in its formation mechanism and in the influence of materials and exposure process. The non-topcoat approach was the basis of the work, where the properties of resist surface itself played the key role. Water droplets left on the resist surface were considered to induce the watermark defect in two possible ways; (1) the droplet is carried over to PEB process and impact the resist properties under the heat, (2) the droplet already evaporates before the PEB leaving some residue on the surface. A notable reduction in the resist dissolution rate was observed in the former case, which could be due to either physical or chemical change in the resist materials triggered by the water, and thereby would result in an unavoidable patterning failure. Therefore it is essential not to leave any water droplets on the surface in preventing the watermark formation. A very much hydrophobic materials design was proven effective in achieving this. The watermark formation was correlated to the scanning speed of immersion showerhead and the defectivity was evaluated in this perspective. The receding contact angle of the resist surface was found to well correlate to the allowable scanning speed, and was concluded that the higher was the better. A resist material was newly designed by using a hydrophobic polymer on this basis and the resist demonstrated a promising results not only in the watermark defectivity but also in lithographic performance.

The effect of photoacid generator structure on deep ultraviolet resist performance

The structural influence of photoacid generators on deep ultraviolet resist performance is investigated in both high and low activation energy resist systems. The lithographic behavior of the photoacid generator is considered in terms of the structure of the photogenerated acid and the light sensitive chromophore. First, the lithographic impact of the photogenerated acid is investigated in terms of acid strength and acid size in resists optimized for high and low temperature processing, respectively. Dissolution kinetics, contrast curve data, and absorbance data are presented for a series of high and low activation energy resists in which the structure of the photogenerated acid is systematically varied. The results of these studies are discussed in terms of the photogenerated acid, emphasizing the impact of acid strength and size on lithographic performance and resist dissolution rate kinetics for each resist platform. Second, the structural influence of the light sensitive photoacid generator (PAG) chromophore is investigated by comparing the lithographic performance and acid generating efficiency of iodonium and sulfonium salt PAGs. Last, correlations of lithographic performance and dissolution rate kinetics are probed in terms of resist type (high and low temperature systems) and PAG structure.

Design and Chemistry of Advanced Deep-UV Photoresists. The Role of the Photoacid Generator.

Advanced deep-UV photoresists are studied from the standpoint of understanding the chemical design principles behind resist lithographic performance. The role of the photoacid generator in defining lithographic performance of deep-UV photoresists is investigated for high and low activation energy resists respectively. State of the art high and low temperature processed resists are studied with emphasis on the structure of the acid sensitive protecting group. The acid sensitive protecting group is considered in terms of the activation energy for resist deprotection. The lithographic behavior of the photoacid generator in each resist platform is probed in terms of the structure of the photogenerated acid and the light sensitive chromphore. Firstly, the lithographic impact of the photogenerated acid is investigated in terms of acid strength and acid size in resists optimized for high and low temperature processing, respectively. Dissolution kinetics, contrast curve data and absorbance data are presented for a series of high and low activation energy resists in which the structure of the photogenerated acid is systematically varied. The results of these studies are discussed in terms of the photogenerated acid, emphasizing the impact of acid strength and size on lithographic performance and resist dissolution rate kinetics for each resist platform. Secondly, the structural influence of the light sensitive PAG chromophore is investigated by comparing the lighographic performance and acid generating efficiency of iodonium and sulfonium salt PAGs.

Resist dissolution rate and inclined-wall structures in deep x-ray lithography

We investigate the chemical dissolution rate of PMMA resist (polymethylmethacrylate) in the case of deep x-ray lithography with the aim of intentionally producing microstructures with inclined side walls. This can be achieved by controlling the dose distributions and their related dissolution rates in both exposed and shaded areas. We specialize in the fabrication of pyramidal microstructures using thin mask absorber patterns. Controlling dissolution conditions in the developer bath such as bath temperature or stirring, microstructure aspect ratios are investigated.

Characterization of exposure and processing of thick PMMA for deep x-ray lithography using hard x-rays

The first step for the fabrication of microstructures using deep x-ray lithography (DXRL) is the radiation of a sensitive polymer like poly(methyl methacrylate) (PMMA) by hard x-ray. At the Advanced Photon Source a dedicated beamline1 allowed the proper exposure of very thick resist (several mm). In this work we give a characterization of the PMMA/development system. As a result the resist dissolution rate (μm/min) of the exposed PMMA in different developer is calculated. We also analyze the conditions that produce bubbles and cracks in the thick exposed resist and investigate the scanning parameters that reduce them.

Relationship between Dissolution Inhibitors and Dissolution Rate of Resist in Chemically Amplified Three-Component Positive Resist

For chemically amplified electron beam (EB) resist composed of partially tert-butoxycarbonyl (tBOC) protected poly(p- vinylphenol) (PVP), a dissolution inhibitor, and an acid generator, the effect of the dissolution inhibitors on the dissolution characteristics of resist are investigated. As dissolution inhibitors, hydroquinone protected by a tert-butoxycarbonyl group (B-HQ) and isophthalic acid protected by a tert-butyl group (B-IP) are used. Dissolution inhibitors (B-HQ and B-IP) become dissolution promoters (HQ and IP) after exposure. The dissolution rate of the resist consisting of B-IP was faster than that of B-HQ in the exposed area. pKa of IP is smaller than that of HQ, and the acidity of IP is higher than that of HQ. Therefore IP enhances the solubility of the matrix resin in the alkaline developer. A 0.14 µ m line and space pattern is fabricated at 17.5 µ C/cm2 using 50 keV EB in the resist consisting of B-IP.

Positive photosensitive polyimides using polyamic acid esters with phenol moieties

AbstractPolyimide resists developable with basic aqueous solutions were realized by polyamic acid esters with phenol moieties (PPh's) and naphthoquinone diazides. The polyimide precursors (PPh's) were synthesized from diamines and dicarboxylic acids that have phenol moieties through ester linkage. A selective reaction of alcohol groups with acid dianhydride groups made the synthesis of the PPh's possible, even if the phenol groups were in the reaction mixtures. The PPh's were soluble in basic aqueous developer, but their dissolution rates were too low for use as resists. To increase the resist dissolution rate, polyamic acids were added to the PPh's. By adjusting the dissolution rates in basic aqueous developers, fine patterns could be realized. The polyimide resists had high thermal stability and reliable adhesive property to silicon substrate. © 1994 John Wiley & Sons, Inc.

Profile abnormality in a chemical amplification resist system

Pattern profile abnormality on a spin-on glass (SOG) substrate is investigated for the chemical amplification resist system SAL601. The resist dissolution rate, which is strongly related to the generated catalyst concentration, is abnormally enhanced near the SOG substrate. Resist profile simulation suggests that this phenomenon depends on the diffusion effect of a catalyst or its scavenger. Based on resist sensitivity variation due to humidity, and FTIR analysis of the SOG, it is considered that H 2O in a SOG substrate is the diffusion component acting as the catalyst scavenger.

Profile abnormality in a chemical amplification resist system

Pattern profile abnormality on SOG substrate in chemical amplification resist system SAL601-ER7, has been investigated. A resist dissolution rate, strongly related to a generated catalyst concentration, is abnormally enhanced near the SOG substrate. Resist profile simulation suggested that this phenomenon depends on the diffusion effect of a catalyst or its scavenger. According to resist sensitivity variation due to humidity, and FTIR analysis of the SOG, it is considered that H2O in the SOG substrate is the diffusion component acting as the catalyst scavenger.

Thermodynamics of Development Process of Positive Resists in Binary Mixed Developer

The sensitivity of positive e-beam resists depends strongly on the development condition. We have found that a small amount of water in an organic developer enhances the resist dissolution rate resulting in development instability. The addition of polar solvents to a developer causes a large increase of the dissolution rate. The reason for this enhancement of the dissolution rate is explained by thermodynamic compatibility between the resist and the developer. It is shown that thermodynamic consideration of the development process is very useful to comprehend the dissolution characteristics of positive resists in binary mixed developers.

Evaluation of deep UV ANR photoresists for 248.4 nm. excimer laser photolithography.

This paper describes further work on XP-8843, a novel Advanced Negative Resist (ANR) system developed specifically for Kr-F excimer laser and broadband DUV advanced imaging systems. Optical changes in the resist film have been measured for exposed and post-exposure baked samples. At lithographically useful doses, 10mJ/cm2, virtually no change in % transmittance occurs upon exposure. The post-exposure bake at 130°C leads to slight darkening (62 to 54%T). Resist modelling studies have shown that 10-6 moles of acid per gram of resist are necessary to induce sufficient crosslinking to decrease resist dissolution rate in aqueous base by fifty-fold. Based on the concentration of acid, the average distance between nearest acid neighbors is 100A in the exposed film. Contrast curves were generated on a 0.35 NA GCA ALS LaserstepTM 200 5:1 stepper. Contrast was as high as 6 at 130°C post-exposure bake. Arrhenius plots of XP-8843 and the poly(p-vinyl)phenol-modelled resist vs. post-exposure bake temperature both gave Ea of 43kJ/mole. The XP-8843 resist exhibited high resolution (0.45 micron 1/s pairs) and vertical sidewalls when imaged at 1.35 micron thickness. The XP-8843 resist also shows high thermal resistance, maintaining linewidth at 210°C.

The radiation chemistry of poly(methyl methacrylate) polymer resists

Poly(methyl methacrylate) (PMMA) films of approximately 2.5 μm have been irradiated to various doses using Al x rays. The effect of this irradiation is shown by monitoring the variation in intensity of the Raman vibrational bands of the major constituent species of PMMA, as a function of dose. It is shown that at low doses the molecular weight is reduced as a consequence of main chain scission arising from abstraction of the ester group. This substantiates the previously reported increase in dissolution rate in this dose regime. However, at larger doses it is shown that a cross‐linking reaction generated primary C=C bonds between chain molecules at end‐group sites previously activated by the scission process. This is believed to increase the molecular weight of the polymer resist at larger doses and explains the previously reported drop in the resist dissolution rate at large x‐ray doses. The Raman data suggest that scission and cross‐linking proceed concurrently in response to incident radiation. A model to predict the dissolution rate of the resist as a function of dose based on this dependence of cross‐linking on scission is presented. The results generated from this model are compared to our previously reported experimental resist dissolution data to substantiate conclusions drawn from the Raman results.