Leo L. Linehan

New negative tone resists for subhalf micron lithography

Abstract New crosslinking type resist systems are described which use benzylic carbocation precursors carrying phenolic hydroxy group. The special feature of the new resists is the versatility of applications, ease of synthesis, high sensitivity, high contrast and a large process window. One such resist system has been used successfully in the back-end-of-the-line personalization for manufacturing advanced bipolar devices which required an exceptionally large process window. The new resist system is a promising candidate for surface imaging as well as for I-line, DUV and X-Ray applications.

Shot-size reduction of photoresist formulations

The cost of expendable chemicals in the resist process is increasing and with this the economic impetus to conserve usage. The volume of liquid resist dispensed (shot size) determines the consumption rate and disposal volumes of liquid resist. The choice of resist solvent can influence the shot volume. Three formulation factors influence the shot size: (1) the surface tension of the resist and the interfacial energy of the coating surface, (2) the viscosity of the resist formulation, and (3) the evaporation rate of the solvent. The suitable resist formulation and subsequent solvent choice should be of the lowest surface tension and lowest viscosity and be balanced by an evaporation rate which allows a minimum shot volume to be spread on the surface without significant solvent loss. Of all the solvents examined, ethyl 3-ethoxy propionate (EEP) gave the lowest shot size relative to the old resist solvent standard of 2- ethoxy ethyl acetate (ECA).

0.25-μm lithography development using positive mode top surface imaging photoresist

As design rules for ULSI chip sets continue to require sub-O.3j.un resolution for high density patterns the drive toward shorter wavelength (248nm), and higher numerical aperture (<O.5NA) steppers will continue. Process development on these advanced lithography systems is made difficult for a variety of reasons. The first of these is cost, the most modem steppers available today can cost <

Investigation into the origin of microbridging in chemically amplified negative-tone photoresists

5 million per system making it necessary to keep manufacturing cost in check by extending life times to more than one generation chip set. Secondly, working at 248nm and high numerical aperture tends to reduce process latitudes making manufacturing processes inherently more difficult to control. Last but not least, photoresist and antireflective coatings needed for even the simplest processes historically have had major environmental sensitivity problems or material compatibility problems associated with them. These issues have been addressed by such developments as phase shift masks, off axis illumination techniques, and major advances in resist technology. So far these types of cures have proven to be both costly and extremely complicated to implement in a manufacturing environment.

Acid diffusion in a chemically amplified negative i-line photoresist

Microbridge formation in a CAMN photoresist we have developed is dependent on the ratio of dose to print (DTP) to dose to gel (DTG) as well as resist contrast. Photoresists formulated with poly(p-hydroxystyrene) (PHS) have a very high tendency to form microbridges when developed in 2.38 wt% TMAH due to high contrast and high DTP/DTG ratio. When photoresists formulated from PHS were developed in 1.2 wt% TMAH contrast and DTP/DTG ratio were reduced resulting in microbridging being nearly eliminated. Using this observation we developed an I-line CAMN photoresist with PHS type thermal stability and high resolution capabilities which can be developed in industry standard 2.38 wt% TMAH.

Polymer-bound sensitizer in i-line resist formulations

One of the major factors which determines the success of resist photochemistry is acid diffusion. Inadequate or excess diffusion can cause undesirable resist profiles, limit resolution and adversely impact process windows. Both formulation and process parameters effect acid diffusion. Formulation factors include such things as intrinsic properties of the acid, resin, and solvent. The process parameters which effect acid diffusion are mainly exposure dose, post-apply (PAB) and post-exposure bake (PEB). A practical study has been conducted which investigates the effect of PAB and PEB times and temperatures on acid diffusion in a chemically amplified negative i-line photoresist. Acid diffusion was measured by determining the change in linewidth of an isolated resist line. The goal of the study was to maximize acid diffusion through PAB and PEB conditions with minimal impact on profile quality and process windows. Maximum acid diffusion was required to combat a minimum light intensity at the surface of oxide wafers. Data on quantifying acid diffusion through linewidth change, maximizing acid diffusion at low light intensities as well as the role of the resist formulation will be discussed.

INR negative resist: a negative-tone I-line chemically amplified photoresist

An important component of a photoresist formulation is the photoactive compound. In conventional I-line resist, it is the DNQ molecule. In chemically amplified resists, it is the photoacid generator or the PAG. This component acts as the link between the exposure tool and the photoresist system. While PAGs for the 248 nm or DUV application are plenty, there is little effort in the arena of i-line PAGs. Typically, energy transfer in i-line lithography is achieved by using a DUV PAG in conjunction with an i-line energy transfer agent called sensitizer. This combination works very well, as described by workers before. This paper describes a polymer-bound sensitizer, which while maintaining the performance characteristics of a monomeric sensitizer, also enhances the solubility characteristics and the thermal stability of the resist.

Antireflective coating for microlithography

INR, an I-line negative photoresist, is described. Acid catalyzed cross-linking of phenolic resins using a non-metallic photoacid generator, 2,6-bishydroxymethyl-p-cresol as a cross- linker, and 9-anthracene methanol as an I-line sensitizer results in a very high photospeed aqueous TMAH developable photoresist. Poly(p-hydroxystyrene) was found to have advantages over novolac resins for formulation of high performance negative I-line photoresist. Advantages obtained by using PHS rather than novolac include higher thermal stability, elimination of undercut on nuleophilic surfaces and compatibility with 2.38 percent TMAH puddle develop processes. A high resolution version, INR-X, is described. Resolution to 0.30 micrometers and linearity to 0.35 micrometers was obtained using a 0.54NA ASML I-line stepper. 0.35 micrometers line-spaces arrays had 1.2 micrometers depth of focus and 0.40 micrometers line-space arrays had a depth of focus greater than 1.6 micrometers . An unusual characteristic found in INR-X is a very low sensitivity to variation in PEB temperature. A 3nm/ degree(s)C line-width dependency was found.