Mike Wagner

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.

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.

Development of molecular resist derivatives for EUV lithography

As part of the continued effort of Dows Electronic Materials business unit to generate novel resists for advanced semiconductor technologies, there has been a recent emphasis on the development of several new photoresists and ancillary platforms to enable EUV lithography. An important aspect for the success of EUV lithography is the development of photoresist materials that can meet the stringent requirements for Resolution, Line width roughness (LWR) and Sensitivity (RLS). While, a great portion of industrial research is focused on the development of polymeric resists like Polymer Bound PAGs (PBPs), small monodisperse organic molecules called molecular glasses (MGs) have gained increased attention over the past several years. If properly designed, MGs could possess physical properties that are very similar to polymeric resists while offering superior performance, specifically towards improving LWR. We have developed several MG resists based on calixarene cores that exhibit promising lithographic performance. We have continued to study the structure-property relationship of these materials with special emphasis on molecular architectures and design strategies for improved photoresist performance. In this paper, we summarize the promising lithographic performance of these MG resists that are considered as alternative choices to polymeric resists for enabling next generation lithography.

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.

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.

Advanced hole patterning technology using soft spacer materials (Conference Presentation)

A continuing goal in integrated circuit industry is to increase density of features within patterned masks. One pathway being used by the device manufacturers for patterning beyond the ~80nm pitch limitation of 193 immersion lithography is the self-aligned spacer double patterning (SADP). Two orthogonal line space patterns with subsequent SADP can be used for contact holes multiplication. However, a combination of two immersion exposures, two spacer deposition processes, and two etch processes to reach the desired dimensions makes this process expensive and complicated. One alternative technique for contact hole multiplication is the use of an array of pillar patterns. Pillars, imaged with 193 immersion photolithography, can be uniformly deposited with spacer materials until a hole is formed in the center of 4 pillars. Selective removal of the pillar core gives a reversal of phases, a contact hole where there was once a pillar. However, the highly conformal nature of conventional spacer materials causes a problem with this application. The new holes, formed between 4 pillars, by this method have a tendency to be imperfect and not circular. To improve the contact hole circularity, this paper presents the use of both conventional spacer material and soft spacer materials. Application of soft spacer materials can be achieved by an existing coating track without additional cost burden to the device manufacturers.