As IC manufactures explore different paths to meet the resolution requirements for next generation technology,
patterning schemes which utilize a double photoresist patterning process are under extensive evaluation. One dual
patterning process under consideration uses a 172nm UV cure to render the first photoresist pattern insoluble to the
casting solvents and developer chemistries used to define the second photoresist pattern. Line-space resist patterning is
used to understand the effect of the 172nm UV light on the SiBARC, under-layer film stack and how it influences the
patterned CD. This is followed by cross-grid and pitch-split double patterning using 172 nm UV light of varying dose to
freeze the first photoresist layer patterned using a tri-layer film configuration. In the final section we discuss the effects
of the 172nm UV cure on the SiBARC film thickness and optical properties. Simulations are run to understand the
change in the focus-exposure process window due to changes in the SiBARC film due to the 172nm UV cure.
We describe progress in low-k1 factor double patterning using 172 nm ultraviolet (UV) curing as a resist stabilization
method. Factors that have contributed to enhanced patterning capability include a) resists design and optimization for
both patterning and UV curing; b) use of unique R&D tooling capabilities to rapidly identify and optimize key process
variables; c) development of simple process metrics for characterizing double patterning process quality, and d) use of
172 nm-resistant antireflective materials. A designed resist, XP-7600A, was selected for detailed evaluation based on
superior patterning and curing behavior (less than 10 percent volumetric shrinkage during cure.) Process optimization
on 172 nm damage-prone antireflective coatings produced 60 nm cross-grid contact holes at 0.93 NA (litho k1 = 0.28)
with good uniformity when an ancillary 150 °C post-UV bake was used. Additional optimization on improved
antireflective coatings yielded superior process latitude (>20 percent 172 nm dose latitude) and also demonstrated that a
UV-cure-only resist stabilization process flow may be attainable. Under optimized conditions, highly uniform 60 nm
half-pitch cross-grid contacts with cross-sectional area uniformity (1σ) of approximately 200 nm2 (5 percent) are
produced at 135 nm resist film thickness.
As IC manufactures explore different paths to meet the resolution requirements for next generation technology,
patterning schemes which utilize a double photoresist patterning process are under extensive evaluation. One dual
patterning process under consideration uses a 172nm UV cure to render the first photoresist pattern insoluble to the
casting solvents and developer chemistries used to define the second photoresist pattern. In this work we investigate the
change in the material properties such as thickness, optical, bond structure, adhesion and stability of the SiBARC film
due to the UV cure. Simulations are included to assess the change in substrate reflectance due to the change in the optical
properties of the SiBARC film as a result of the UV cure. Single patterned photoresist line space features versus UV cure
dose of the SiBARC - under layer film stack is presented. This is followed by cross-grid and pitch-split double patterning using 172 nm UV light of varying dose to freeze the first photoresist layer patterned using a tri-layer film configuration.
We have developed a unique resist stabilization process for double patterning that uses 172 nm UV curing to 'freeze' a first photoresist pattern prior to application and patterning of a second photoresist film. 172 nm cure offers many potential advantages over other resist stabilization processes, including improved pattern fidelity vs. other cure processes and track-based implementation scenarios that are relatively simple, compact, and inexpensive. Assessment of 172 nm double imaging process requirements and limitations indicates that pattern distortions in the 'frozen' first photoresist may arise during all 2nd patterning steps, including coating, exposure, and development. Careful optimization to maximize overall pattern fidelity is needed. Process optimization using a conventional 193 nm photoresist suggests that pattern freeze approaches based on resist cure are best suited to extremely regular structures due to line-end and other resist distortions. Nevertheless, the method allows cross-grid contact printing at lithographic k1 = 0.385.
This paper investigates the feasibility of using an electrostatic chuck (ESC) on a post exposure bake (PEB) plate in the
track to improve the critical dimension uniformity (CDU) for bowed wafers. Although it is more conventional to
consider vacuum chucking during PEB, electrostatic chucking offers some potential advantages, chief among which is
the fact that electrostatic chucking does not require any type of a seal between the wafer and the PEB plate whereas
vacuum chucking does. Such a seal requires contact and therefore has the potential to generate backside particles on the
wafer. Electrostatic chucking therefore has the potential for a cleaner overall process. Three different PEB plates were
tested in the course of this investigation, a non-chucking PEB plate (SRHP), a PEB plate equipped with a vacuum chuck
(VRHP), and a PEB plate equipped with an ESC (eBHP). It was found that CD uniformities were up to 84 percent lower
for bowed wafers that were chucked during PEB relative to wafers that were not chucked. In every case tested, wafers
processed through chucking PEB plates showed lower CDUs than wafers processed through the non-chucking plate.
CDU results were similar between vacuum chucked wafers and electrostatic chucked wafers. Based on the results
presented in this paper, it can be concluded that electrostatic chucking during PEB is a feasible method for controlling
CD uniformities on bowed wafers.
The demands for high resolution and issues of line edge roughness require a reconsideration of current resist design strategies. In particular, EUV lithography will provide an opportunity to examine new resist concepts including new elemental compositions and low molar mass resists or molecular resists. In the former case, resist compositions incorporating elements such as silicon and boron have been explored for EUV resists and will be described. In an example of the latter case, molecular glass resists have been designed using synthetic architectures in globular and core-arm forms ranging from one to multiple arms. Moreover, our studies include a series of ring and irregularly shaped small molecules modified to give imaging performance. These materials have been explored to improve line edge roughness (LER) compared to common polymer resists. Several examples of polymeric and molecular glass resists will be described. Several compositions showed high glass transition temperatures (Tg) of ~ 120°C and possessed no crystallinity as seen from XRD studies. Negative-tone molecular glass resists with a T-shaped phenolic core structure, 4-[4-[1,1-Bis(4-hydroxyphenyl)ethyl]]-α,α-dimethylbenzylphenol, have demonstrated feature sizes as small as 50mn. Similarly, negative-tone images made using spiro-based compounds showed feature size as small as 60nm in lines/space patterns using e-beam lithography. Most recently we have demonstrated that fully and partially tert-butoxycarbonyl (t-Boc) protected calix[4]resorcinarene derivatives can be successfully studied as a positive-tone resist using EUV and E-beam lithography. Resolution as low as 35nm was obtained by EUV exposure.
Lithography and the processes associated with it are the backbone of the nanotechnology revolution. Several developments are occurring simultaneously: a drive to reduce minimum feature size leading to advances in microelectronics, the use of lithographically patterned structures to prepare devices for photonics, biotechnology and other forms of nanotechnology and finally the drive to create three-dimensional (3D) structures for device and new materials creation. Thus the controlled formation of nanometer scale structures in two and three dimensions is of increasing interest in many applications. This paper will overview new approaches for the construction of small-scale structures using methods generally considered as next generation lithography. New approaches derived from two photon processes for the formation of complex images and the development of patterned structures will be described. Finally in the production of 3D patterns, the possible role of self-assembly coupled to lithography will be examined. Photodefinable block copolymers with erodable microstructures have been successfully used to form mesoporous materials and will be discussed.
EUV lithography is to date the most promising NGL technology for the sub-50nm technology node. In this work, we have designed and synthesized several types of organoelement resists with low oxygen content for high transparency. Boron was incorporated in the resist structures to improve both etch resistance and transparency. Both negative-tone and positive-tone resists were made containing the carborane group. In a preliminary study, these polymers were imaged using a 248nm stepper to produce images with good resolution. The incorporation of a carborane structure provides these polymers with excellent oxygen etch resistance. Hall effect measurements were performed and no contamination was found in the substrate after applying boron-containing polymers.
EUV lithography is to date the most promising NGL technology for the sub-50nm technology node. In this work, we have designed and synthesized several types of organoelement resists with minimum oxygen content for high transparency. Either silicon or boron was incorporated in the resist structures to improve both etch resistance and transparency. In the exposure studies, it was possible to image the silicon-containing polymers to 22.5 nm line/space patterns using EUV interferometry. A second type of EUV transparent resist platform was studied involving boron-containing polymers. Carborane carboxylic acid was attached to a copolymer backbone to introduce boron atoms with controlled structure attachment level. In a preliminary study, these polymers could be imaged by 248nm exposure. Effect of structure on line edge roughness is also to be included in the discussion.
EUV lithography is perhaps the most promising of the NGL technologies for sub-100nm resolution. To address needs in this area, we have designed and synthesized several types of organoelement resists using only low absorbing elements, including H, C, Si and B. One category is based on silicon-containing block and random polymers. They show high transparency according to theoretical simulations and have high oxygen reactive ion etch resistances compared to Novolac resins. In a preliminary study, we were able to image these polymers to 180 nm line/space patterns using EUV exposure. A second type of EUV transparent resist platform involves boron-containing polymers. Carborane carboxylic acid was attached to a copolymer backbone to introduce boron atoms with controlled attachment level. It was found that incorporation of a small amount of B provides remarkably high oxygen etch resistance.
Recently, there is significant interest in using chemically amplified (CA) resists for electron beam (E-Beam) applications including mask making, direct write, and projection printing. CA resists provide superior lithographic performance in comparison to traditional non CA E-beam resists in particular high contrast, resolution, and sensitivity. Due to the electron scattering effect and the image collapse problem, thinner imaging layer is desirable. Sufficient etch selectivity is needed to compensate reduced resist thickness. Therefore, there is a need to have a high etch resistant resist system which can survive Cr etch (Cl2/O2RIE etchant) process in mask making. For device making, the thin film bilayer approach needs a resist that can withstand O2 etch for image transfer to the underlayer. We have found Si-O containing polymer has the etch characteristics for both applications. In the first approach, using a blend of KRS-XE and silsesquioxane polymer, we have been able to resolve resist images down to 50nm with etch rate 20% slower than conventional novolak I- line resist systems. In the second approach, we have investigated the copolymer of vinyl phenol and acrylate siloxy silane systems. Superior litho performance and etch properties have been observed. In this presentation, we will discuss the chemistry, the miscibility in blends, etch characteristics and lithographic performance of these resist systems.
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