Of all candidate 193 nm photoresist binder resins, transition metal catalyzed vinyl addition cyclic olefin (i.e., norbornene) polymers (PCO) hold the promise of high transparency and excellent etch resistance. In order to access lower molecular weight polymers, which are typically used in photoresists, α-olefin chain transfer agents (CTAs) are used in synthesizing vinyl addition poly(norbornenes). For example, HFANB (α,α-bis(trifluoromethyl)bicyclo
[2.2.1]hept-5-ene-2-ethanol) homopolymers (p(HFANB)) with molecular weights (Mn) less than 5000 have been synthesized using such chain transfer agents. However, the optical density (OD) at 193 nm of these materials was found to rise as their molecular weights decreased consistent with a polymer end group effect. Extensive NMR and MS analysis of these polymers revealed that olefinic end groups derived from the chain transfer agent were responsible for the deleterious rise in OD. Chemical modification of these end groups by epoxidation, hydrogenation, hydrosilation, etc. lowers the OD of the polymer by removing the olefinic chromophore, however, it does require a second synthetic step. Thus a new class of non-olefinic chain transfer agents has been developed at Promerus that allow for excellent control of vinyl addition cyclic olefin polymer molecular weight and low optical density without the need of a post-polymerization chemical modification. Low molecular weight homopolymers of HFANB have been synthesized using these chain transfer agents that exhibit ODs ≤ 0.07 absorbance units per micron. This molecular weight control technology has been applied to both positive tone and negative tone vinyl addition cyclic olefin binder resins. Lithographic and etch performance of positive tone photoresists based on these binder resins will be presented.
Alicyclic polymers, such as substituted polynorbornenes, are one potential material solution for providing photoresist polymer resins with high transparency backbones for photolithography at 193 nm and 157 nm wavelengths. In addition, the bis-trifluoromethyl carbinol functional group has been identified as a highly transparent base soluble group that can be used for producing photoresist resins from polynorbornene materials for 157 nm lithography. In this work, the interactions between commercial photoacid generators (PAGs) and bis-trifluoromethyl carbinol substituted polynorbornene (HFAPNB) are examined. It was found that photoacid generators can act as strong dissolution inhibitors for bis-trifluoromethyl carbinol substituted polynorbornene homopolymers. More importantly, it was found that a variety of photoacid generators can act as photoswitchable dissolution inhibitors for these materials, with exposure of the photoacid generator resulting in a reduction in the dissolution inhibition (i.e. increased dissolution rate) of the functionalized polynorbornene. The complete inhibition of unexposed HFAPNB polymers by iodonium photoacid generators allows for the formulation of photodefinable materials using a simple two component system consisting only of PAG and the HFAPNB polymer.
As features shrink below 100 nm, new exposure technologies such as 157 nm lithography are being developed. One of the critical challenges in developing these new lithographic tools and processes is the development of appropriate resist materials that can be used at these lower exposure wavelengths. Creating organic resist polymer resins for 157 nm exposure is a particularly challenging issue since many organic functional groups absorb at this wavelength. It has been previously shown that fluorinated polymers may offer the required low optical absorbance needed to serve as resist resins for 157 nm lithography. In particular, there has been interest in bis-trifluoromethyl carbinol substituted polynorbornenes (HFAPNB) and similar materials for use in photoresists. The bis-trifluoromethyl carbinol group offers a base soluble group that is sufficiently transparent to be used at 157 nm. This work has focused on the dissolution behavior and other characteristics of bis-trifluoromethyl carbinol substituted polynorbornenes. In particular, it was found that the dissolution behavior of the HFAPNB homopolymer is strongly controlled by its ability to hydrogen bond with both neighboring chains and also other small molecule additives such as dissolution inhibitors and photoacid generators. A detailed molecular level explanation for these effects is presented. The interaction of a series of commercial photoacid generators with HFAPNB polymers are presented. The use of such information for the rational design of advanced resist materials using these polymers will be discussed.
A statistical design of experiments for the post-applied bake and post-exposure bake temperatures for two types of resists, the commercial formulation AZ FX 1000P and an experimental resist AZ EXP 20 X, was carried out using contrast, clearing dose and dark erosion as response variables examined. It was found that for AZ FX 1000P dark erosion could be suppressed entirely and contrast improved by employing a lower PEB without significant impact on the contrast. In this manner, a substantial improvement in the image quality for AZ FX 1000P was obtained. AZ EXP 20X was not susceptible to dark erosion at higher post-applied bakes as was AZ FX 1000P. Both resists gave better imaging at lower post-exposure bake temperatures in the range of ~110°C, presumably because of excessive acid diffusion at higher temperatures, such as 150°C. Generally, the contrast achievable with AZ EXP 20 X (>16) is much higher than that possible for AZ FX 1000P (~6).
As part of a new generation of more transparent 157 nm resist platforms we are developing, a novel resist system is described that has higher transparency and contrast than AZ FX 1000P. Using a new protecting group strategy, encouraging results have been obtained with both poly(α,α-bis(trifluoromethyl)bicyclo(2.2.1)hept-5-ene-2-ethanol) and a more transparent perfluorinated resin (TFR). These new resist systems show absorbance values as low as 1 μm-1 at 157 nm, have twice the contrast (i.e., 12 instead of 7) of AZ FX 1000P, and have neither significant dark erosion nor do they switch to negative tone behavior within the dose range studied. The dry etch resistance of the TPR platform is found to be superior to APEX-E DUV resist for polysilicon but somewhat lower for oxide etches. Features as small as 50 nm lines and spaces were resolved for slightly relaxed pitches (1:1.5 micron). By adjusting the base level it is possible to improve the photospeed by a factor of more than 10 while still maintaining a resolution of 70 nm L/S features.
The aqueous base dissolution behavior and hydrogen bonding interaction of polymers bearing hexafluoroisopropanol (HFA) as an acid group have been investigated. While pKa of HFA is similar to that of phenol, the dissolution rate of HFA polymers in aqueous base varies from one structure to another. Poly(norbornene hexafluoroisopropanol) (PNBHFA) dissolves in 0.26 tetramethylammonium hydroxide (TMAH) aqueous solution at a rate of 1,500-8,000 A/sec, which is not correlated to the number-average or weight-average molecular weight. Furthermore, PNGHFA exhibits a complex multi-stage dissolution kinetics in 0.21 N TMAH, depending on the molecular weight and molecular weight distribution. Hydrogen bonding of HFA polymers has been investigated using FTIR. Polynorbornene and polystyrene bearing HFA (PNBHFA and PSTHFA) are much less hydrogen-bonded than poly(4-hydroxystyrene)(PHOST). HFA-ester copolymers tend to have more free OH groups than a HOST/t-butyl acrylate copolymer. The carbonyl bond in 2-trifluoromethylacrylic units is less polarized and therefore less prone to hydrogen bonding with OH than C=O in (meth)acrylate units. The interaction of acid generators with the HFA group can be studied by 19F NMR. Both ionic iodonium and nonionic imidesulfonate acid generators interact strongly with HFA and inhibit the dissolution of HFA polymers in aqueous base while ionic acid generators are better dissolution inhibitors of phenolic resins.
Electronic packaging and chip-to-module connections have evolved to meet the needs of electronic systems. The rate of change of the technology will accelerate as the package disappears and optical interconnects come into play. Compliant wafer-scale packaging is an approach which can be used to provide acceptable electrical and mechanical functions for future electronic packaging. In this work, buried air-cavities using sacrificial polymers are used to provide compressible input/output leads.
The copolymerization reaction between methyl cyanoacrylate (MCA) and a variety of cycloolefins (CO) was investigated. Cycololefin/cyanoacrylate (COCA) copolymers were obtained in good yields and with lithographically interesting molecular weights for all cycoolefins studied. Anionic MCA homopolymerization could be largely suppressed using acetic acid. Based on NMR data, the copolymerization may tend to a 1:1 CO:MCA incorporation ratio but further work with better suppression of the anionic component is needed to confirm this. Lithographic tests on copolymers of appropriately substituted norbornenes and MCA showed semi-dense and isolated line performance down to 90 nm.
The ever-increasing need for economical, reliable, and high- performance optical interconnects for telecommunication and data communication markets demands new innovative solutions. Polymer technology being developed at BFGoodrich is focused on satisfying this demand. It is based on proprietary polynorbornene polymers that exhibit excellent optical, thermal and mechanical properties essential for fabrication of reliable components for integrated optics. Typical polymer waveguide systems exhibit a tradeoff between thermal and optical performance. The uniqueness of the polynorbornene system is that these tradeoffs are minimized. The intrinsic properties of the polynorbornene system include low transmission loss (<0.1 dB/cm at 820 nm), wide spectral range (<0.4 dB/cm at 450 nm and <0.1 dB/cm at 515-870nm), low birefringence ((Delta) n(in plane)<10-5, (Delta) n(out of plane) <10-3 at 820 nm, consistent difference in index over a wide temperature range, long-term thermal stability (>2000 hours at 125 degree(s)C), high glass transition temperature (>280 degree(s)C), and low moisture absorption (<0.1%). The combination of these characteristics offers advantages over existing plastic materials for visible and near IR applications such as those used in the datacom market. Candidate materials have been identified as core and cladding components for optical waveguides. The refractive index of a typical core material is 1.53, and of a typical clad material, 1.50 at 820 nm. The difference in index between core and cladding is approximately 0.03 over a broad range of wavelength (515-870nm). Preliminary results indicate that the difference in index between core and cladding tracks with temperature, which is in line with out expectation since these polymers have similar structures at the molecular level. Fabrication of functional waveguides has been demonstrated using a conventional cast and cure process at the lab scale. Optical performance of the constituent materials and the waveguide devices will be discussed in the paper.
We have investigated three substantially different routes to 193nm single layer resists. This paper will attempt to shed light on the strengths and weaknesses of each approach. Design principles, polymer synthesis and properties, and resist properties will be discussed for the three main branches of 193nm resists.
We have examined the reactive ion etch (RIE) resistance of two families of 193 nm photoresist candidates, poly(methacrylates) and vinyl-polymerized poly(cyclic olefins), in three RIE processes. Correlation of these measurements to polymer structure and composition using known methods (Ohnishi and Ring Parameter fits) was moderately successful in demonstrating global trends but proved generally inadequate for providing quantitative predictions. To address this shortcoming, we have developed a new empirical structural parameter which provides a much more precise model for predicting RIE rates within a given family of polymers. The model is applicable across polymer platforms, with two caveats: (1) The methacrylate and cyclic olefin families examined to date fall on essentially parallel, offset curves when examined with the new model, (2) The offset between polymer family curves is RIE tool- and process-dependent. While these caveats imply a setback to the idea of a truly `universal' model, they may in fact represent a powerful and unanticipated feature; the model appears to separate chemical RIE processes which affect individual functionalities within a polymer from predominantly polymer-family dependent processes such as global backbone degradation. In the course of conducting these studies, we have encountered several potential pitfalls in the measurement of etch rates. These illustrate the complex nature of plasma: resist interactions and highlight the careful experimental design and controls that are required if meaningful RIE rate comparisons between polymer and resist families are desired.
In the quest for a high performance 193 nm photoresist with robust plasma etching resistance equivalent to or better than the DUV resists of today, we have focused on the use of cyclic olefin polymers. In this paper, we will discuss monomer synthesis, polymerization approaches, polymer properties and early lithographic results of 193 nm photoresists formulated from cyclic olefin polymeric materials made from a metal-catalyzed addition polymerization process. The goal of this work is to produce a 193 nm photoresist with excellent imaging performance and etch resistance exceeding DUV resists, and in fact approaching novolak-based photoresists.