Suzanne Coley

Methacrylate resists and antireflective coatings for 193-nm lithography

Methacrylates were the first class of resist to be examined for use in 193nm lithography. They are still useful today, but have a very different molecular structure because of the requirements for development in 0.262N tetramethyl ammonium hydroxide and high etching resistance. A major driving force for their continued use is the availability of a wide variety of methacrylate monomers and the use of free racial polymerization which imparts a wide range of properties to the polymers and makes them very cost effective.

High sensitivity chemically amplified EUV resists through enhanced EUV absorption

Resolution, line edge roughness, sensitivity and low outgassing are the key focus points for extreme ultraviolet (EUV) resist materials. Sensitivity has become increasingly important so as to address throughput concerns in device manufacturing and compensate for the low power of EUV sources. Recent studies have shown that increasing the polymer linear absorption absorption coefficient in EUV resists translates to higher acid generation efficiency and good pattern formation. In this study, novel high absorbing polymer platforms are evaluated. The contributing effect of the novel absorbing chromophore to the resultant chemically amplified photoresist is evaluated and compared with a standard methacrylate PAG Bound Polymer (PBP) platform. We report that by increasing EUV absorption, we cleanly resolved 17 nm 1:1 line space can be achieved at a sensitivity of 14.5 mJ/cm2, which is consistent with dose requirements dictated by the ITRS roadmap. We also probe the effect of fluorinated small molecule additives on acid yield generation (Dil C) at EUV of a PBP platform.

Impact of polymerization process on OOB on lithographic performance of a EUV resist

Several approaches have been used to minimize LWR in advanced resists. Various polymer and matrix properties, such as polymer molecular volume and free volume fraction, polymer dissolution, impact of activation energy of the deprotection reaction and distribution of small molecules in the polymer matrix have been shown to influence the functional behavior of the resist. We have developed polymerization methods to improve the incorporation and homogeneity of monomers, including PAG monomer, in an EUV resist polymer. Further, we report on use of a new cation which imparts reduced OOB character and a 30% improvement in LWR for a 28nm L/S feature with sensitivity of 10mJ/cm2 versus a control containing the TPS cation. Additionally this new material is capable of 21nm resolution. We also tested the new cation for outgassing by RGA and observed a 60% reduction in outgassing versus a TPS control.

Effect of leaving group design on EUV lithography performance

In this paper, we will describe some of our efforts on various leaving group designs and their impacts on resist performance, mainly focusing on the leaving group polarity, activation energy and molecular volume. The EUV lithographic performances of the newly designed leaving groups are evaluated on a standard methacrylate polymer bound photoacid generator (PBP) platform. With our low activation energy and hydrophobic leaving group PBP, we report good line and space and contact hole performance using the Albany eMET and LBNL BMET tool.

Progress in resolution, sensitivity, and critical dimensional uniformity of EUV chemically amplified resists

This paper will discuss further progress obtained at Dow for the improvement of the Resolution, Contact critical dimension uniformity(CDU), and Sensitivity of EUV chemically amplified resists. For resolution, we have employed the use of polymer-bound photoacid generator (PBP) concept to reduce the intrinsic acid diffusion that limits the ultimate resolving capability of CA resists. For CDU, we have focused on intrinsic dissolution contrast and have found that the photo-decomposable base (PDB) concept can be successfully employed. With the use of a PDB, we can reduce CDU variation at a lower exposure energy. For sensitivity, we have focused on more efficient EUV photon capture through increased EUV absorption, as well as more highly efficient PAGs for greater acid generating efficiency. The formulation concepts will be confirmed using Prolith stochastic resist modeling. For the 26nm hp contact holes, we get excellent overall process window with over 280nm depth of focus for a 10% exposure latitude Process window. The 1sigma Critical dimension uniformity [CDU] is 1.1 nm. We also obtain 20nm hp contact resolution in one of our new EUV resists.

Understanding EUV resist mottling leading to better resolution and linewidth roughness

We have shown that the dissolution properties can be successfully modified to improve the line/space profile and LWR of a low diffusion EUV CA resist. The surface roughness is a function of hot spots in the nominally unexposed regions of the resist material. We conjecture that the photoacid hot spots are formed due to DC flare present in the optical train of the exposure system. We also have shown that the PAGs can be further improved for out-of-band radiation (OOB) response. The improvement can be as much as 557% for 193nm exposure, and 838% by 248nm exposure. The improved OOB response leads to better contact hole performance. We also shared our continued improvement in resist witness plate performance with the majority of our resists passing for carbon growth, and all samples passing for non-cleanables. There does appear to be a site-to-site bias which we attribute to differences between e-beam and EUV exposure and/or substrate working distance from the source. Lastly, we show outstanding lithographic process window for 24 nm contact arrays on an NXE 3300 stepper as well as 15 nm half pitch lines and spaces on the PSI interferometric tool.

Planarizing AR for DUV lithography

A systematic approach was taken in order to improve the planarity of a DUV anti reflectant (AR) utilized for various lithographic steps, particularly those involving a patterned transparent layer. These layers can occur in both front and back end processing. Two approaches were pursued to accomplish this. The first approach was to minimize the molecular weight of the AR polymer. Polymers with weight average molecular weights from 45,000 daltons to as low as 2,300 daltons were evaluated. The planarity of the AR improved significantly for polymers with Mws below 20,000 daltons. The second approach was to add plasticizers in order to reduce the glass transition temperature of the precrosslinked film. The addition of plasticizers to the AR was effective in increasing the planarity. One of the plasticizers contained a DUV chromophore used to maintain the required optical density of the AR. It was proven possible to make these changes while maintaining lithographic performance in both resist profiles and reflection control.

Optimization of low-diffusion EUV resist for linewidth roughness and pattern collapse on various substrates

This paper will report on our development of low diffusion EUV resists based on polymer-bound PAG technology. With our low diffusion resist, a wide process window for 30-nm hp of 280nm DOF over a 10% exposure range is achieved on a prototype ADT fullfield scanner. Linewidth roughness of 3.1nm is also achieved. Excellent resist profiles can be achieved on organic ULs or Si hardmask materials. This resist also shows only 1.1 nm carbon growth on witness plate mirrors for cleanables, and no reflectivity loss after mirror cleaning. These results clearly pass for use on all NXE exposure tools. We also have shown good pattern transfer for a Si HM stack using this resist. Finally, we report 17-nm hp resolution at a dose of 14.5mj for a higher absorption resist.

Comparison of EUV and e-beam lithographic technologies for sub-22-nm node patterning

Prompted by the fact that the International Technology Roadmap for Semiconductors (ITRS) has declared no proven optical solutions are available for sub 22nm hp patterning, we have investigated e-Beam and Extreme Ultraviolet (EUV) resist performance with a view to High Volume Manufacturing (HVM) at these design rules. Since these patterning technologies are considered the leading candidates to replace Immersion ArF (ArFi) multilevel patterning schemes, it was deemed prudent to assess the readiness of these imaging options. We review the advantages and disadvantages of each patterning method and highlight general technology challenges as well as resist specific challenges. In terms of resist specific challenges, we primarily focus on Resolution, Linewidth roughness and Sensitivity (RLS) tradeoffs for both e-Beam and EUV patterning. These metrics are of particular relevance as the industry continues to contend with the well known tradeoffs between these performance criteria. The RLS relationship is probed for both line space and contact hole patterns with each exposure wavelength. In terms of resist selection, we focus on our advanced Polymer Bound PAG (PBP) resist platform as it has been designed for high resolution applications. We also assess resist outgassing during EUV exposure as it is a potential barrier to adoption of EUV for HVM.

Planarizing ARs for dual-damascene processing

Via fill performance of AR7 (KrF anti-reflectant) and a prototype 193nm anti-reflectant were measured for 600 and 1000 nm deep vias in thermal oxide. Simple fitting functions were found which gave good agreement with experimental data (Rsq over 0.84). The most important factors were AR thickness, via duty ratio and via depth. The importance of these factors was different for the different anti-reflectants.