As 193 nm resist moves into production with minimum feature sizes approaching 100nm, bilayer resist is being evaluated more closely for certain applications. Our polymer design has been evolving to meet tighter outgassing requirements. Optical density, etch resistance and dissolution behavior are other considerations. The protecting group used in our 248 nm bilayer is not useful for 193 nm lithography because of the high optical density contribution from Si-Si linkage. Silicon was incorporated into a COMA platform for the first generation polymer. Maleic anhydride is used to modulate dissolution characteristics. The first generation 193 nm bilayer was optimized to print 120 nm L/S patterns with an attenuated PSM on a 0.6 NA Nikon S302. We will describe next generation platforms that address silicon outgassing concern. The lithographic performance of these resists was evaluated on a 0.6 NA Nikon S302 with a dark field mask. Results for 280nm pitch (1:1 L/S) and 245 nm pitch (105 nm L, 140 nm S) lithography are presented. Also shown is result for a 245 nm pitch (1:1 L/S) and 210 nm pitch (1:1 L/S) on a 0.75 NA ASML PAS 5500/1100. Outgassing data generated at MIT Lincoln Laboratory will be discussed.
The objective of this report will be to clarify the maturity of the current 193 SLR materials. We are going to report on all major platform chemistries, i.e.,(meth) acrylate system, ROMP system, cyclic olefin addition system, cyclic olefin/maleic anhydride system, vinyl ether/maleic anhydride system, and cyclyzed system at the same time. We are going to discuss maturity of each platform from several viewpoints such as polymerization process, physical properties of the resins, lithographic performances of the resists, and process latitude of the resists including etch performances. We are also referring to several critical issues such as etch resistance, surface roughness after etch, line slimming, etc. Three major platform chemistries, (meth)acrylate, COMA, and addition, are selected in order to cover the whole spectra of layer requirements. Those three systems respectively show characteristics lithographic performances.
In building the cyclic olefin addition polymer as a potential platform for 193nm contact hole application, we have encountered an unusual bottlenecking or lipping profile. We have investigated the causes and possible cures of this lipping profile in contact hole printing. The lipping was found to be tool dependent, mask dependent as well as duty cycle dependent. Several treatments were evaluated in terms of their ability to reduce or eliminate the lipping profile. These included various flood exposures, pre wet during development, the use of additives in the resist formulation and various surfactants added to TMAH developer. Among them, the most effective way to eliminate the lip profile was found to be modification of the developer by the addition of surfactants. A proper surfactant was selected to provide better wetting for the resist which resulted in the elimination of the lip profile. In addition, resist formulation changes were also beneficial in reducing the lipping profile. This study will present the results of designed experiments which investigated several different treatments and the resultant impact on profile quality.
In this paper, we have shown the progress we have made in improving reactive-ion-etch stability and lithographic performance of IBM 193 nm resist materials. Using selectively functionalized cyclicolefins, we have developed 193 nm resists with etch stability and post-etch surface roughness comparable to those of the matured, state-of-the-art DUV resists. Furthermore, we have also demonstrated dramatically improvement in dense line (100 nm 1:1 L/S) and semi-dense line (< 100 nm 1:2, 1:3 L/S) resolution using resolution enhancement techniques such as alternate phase shift mask.
KEYWORDS: Deep ultraviolet, Lithography, Phase shifts, Bridges, Polymers, Photoresist materials, Manufacturing, Signal to noise ratio, Reticles, Temperature metrology
While positive photo resists make up the majority of the DUV market, negative resists have gained acceptance in IC manufacturing. Typically, negative photo resists can be used for a wide variety of feature types with minimal print bias including posts, lines/spaces and isolated lines. In some instances, negative resist are being investigated to print trenches and contact holes. Although negative resists are promising, there has been one issue. Dense line resolution has been limited by the onset of microbridging. Currently, minimum resolution for equal lines and spaces is about 200 nm with 0.26N developer, using conventional illumination. Recent developments in negative DUV resist technology have eliminated microbridging in 0.26N developer and has resulted in a significant increase in resolution. In addition to resolution and overall lithographic performance for sub 200 nm features, the PEB sensitivity, PED stability and other key resist performance capabilities will be demonstrated.
This new photoresist system extends the capability of the ESCAP platform previously discussed. (1) This resist material features a modified ESCAP type 4-hydroxystyrene-t-butyl acrylate polymer system which is capable of annealing due to the increased stability of the t-butyl ester blocking group. The resist based on this polymer system exhibits excellent delay stability and enhanced etch resistance versus previous DUV resists, APEX and UV2HS. Improved stabilization of chemically amplified photoresist images can be achieved through reduction of film volume by film densification. When the host polymer provides good thermal stability the soft bake conditions can be above or near the Tg (glass transition) temperature of the polymer. The concept of annealing (film densification) can significantly improve the environmental stability of the photoresist system. Improvements in the photoacid generator, processing conditions and overall formulation coupled with high NA (numerical aperture) exposure systems, affords linear lithography down to 0.15 micrometer for isolated lines with excellent post exposure delay stability. In this paper, we discuss the UV4 and UV5 photoresist systems based on the ESCAP materials platform. The resist based on this polymer system exhibits excellent delay stability and enhanced etch resistance versus APEX-E and UV2HS. Due to lower acrylate content, the Rmax for this system can be tuned for feature-type optimization. We demonstrate sub-0.25 micrometer process window for isolated lines using these resists on a conventional exposure tool with chrome on glass masks. We also discuss current use for various device levels including gate structures for advanced microprocessor designs. Additional data will be provided on advanced DRAM applications for 0.25 micrometer and sub-0.25 micrometer programs.
The synthesis, characterization, and lithographic evaluation of a polyhydroxystyrene (PHS) modified with isopropyloxycarbonate groups is described. The inert blocking group is attached to the hydroxyl sites on PHS resin to slow the dissolution rate and make the resin useful in resists designed for 0.263 N TMAH developers. A negative tone resist (CGR-IP) that is formulated with the modified polymer is compatible with the industry standard 0.263 N TMAH developer and is capable of resolving 0.22 micrometer L/S features and 0.14 micrometer isolated lines on a 0.50 NA imaging system. Reaction with PHS resin occurs primarily at the phenolic sites as shown by carbon-13 NMR and 10% protection is sufficient to lower the dissolution rate to an acceptable level so that there is less than 50 angstrom film loss in exposed areas. The blocking group described here is not acid labile and reaming intact after the resist film is baked at 150 degrees Celsius.
Improved stabilization of chemically amplified photoresist images can be achieved through reduction of free volume by film densification. When the host polymer has good thermal stability, the softbake temperature can be above or near the glass transition temperature (Tg) of the polymer. Annealing (film densification) can significantly improve the environmental stability of the photoresist system. Improvements in the photoacid generator, processing conditions, and overall formulation coupled with high NA (numerical aperture) exposure systems afford 200 nm linear resolution with excellent post-exposure delay stability. In this paper, lithographic data is shown for the improved ESCAP photoresist system (now called UVIIHS) currently under development for DRAM and logic device technology. We review the photoresist system, along with process- and formulation-related experiments on device levels and substrates demonstrating excellent 250 nm and sub-250 nm process windows.
This study evaluates the effect of dyes, including photosensitive dyes, on resist performance such as: swing curve reduction, resist dissolution rate, resolution, dose and focus latitude, scumming, etc. The paper demonstrates good correlation between modeling of the dyed resist performance and experimental results.
Conventional acid catalyzed, chemically amplified DUV photoresists are susceptible to environmental contamination and post exposure delay effects resulting in `T-topping' and linewidth variation. These phenomena are directly relatable to uncontrolled diffusion of the photoactive acid generator within the photoresist or from the diffusion of basic contaminants into the resist. The diffusion process can be controlled by a combination of materials and processing optimization. This paper describes a new positive tone DUV photoresist based on poly(4-hydroxystyrene) protected with the isopropyloxycarbonyl (i-POC) functionality. This protecting group is considerably less acid labile than the tert-butyloxycarbonyl (t-BOC) group and the resulting polymer is considerably more thermally stable than a t-BOC protected poly(4-hydroxystyrene). As such, the i-POC based polymer is more amenable to processing at higher temperatures.
Iodine containing diazoquinone photoactive compounds (PAC) were synthesized and formulated with novolak and other resins in an effort to develop a positive photoresist for the synchrotron beam line at IBM's Advanced Lithography Facility. The studies focused on the effect of synchrotron radiation on the PACs themselves and in various halogenated resins. These materials were tested by exposing the resist materials to various doses of radiation and then measuring the loss of diazo from the PAC. An enhanced sensitivity x-ray (ESX) photoresist system was developed by combining an iodinated PAC with a novolak resin. ESX was compared to a conventional DQ/novolak photoresist system TNS. ESX was able to print at approximately half the dose needed for TNS. Features as small as 175 nm resolved. These set of experiments demonstrate the potential of significantly improving the photospeed of DQ/novolak photoresist system by utilizing a more x-ray efficient PAC.
In previous papers, we described initial evaluations of CGR 248 negative resist using a variety of exposure tools. During subsequent studies, the emphasis has been placed on optimizing material and process for Micrascan and Micrascan II pilot line and manufacturing operations. The formulation is based on polyhydroxystyrene (PHS), tetramethoxymethyl glycoluril, and a sulfonate ester of an N-hydroxy compound. We will discuss image stability as a function of delay time between post apply bake (PA) and expose and as a function of delay time between expose and the post expose bake (PEB). Further, data will show that immersion or puddle development provides a larger process window than spray development for features in the 0.30 to 0.35 micrometers range. The thermal stability of the imaged resist will be discussed as well as the shelf life which is at least 6 months at 23 degree(s) C. Finally, additional data is available concerning image uniformity and how print bias and etch bias contribute to the overall nested-isolated line offset for positive tone (APEX-M) and negative tone (CGR) resists. Data obtained from Micrascan II exposures with test reticles will demonstrate an acceptable process latitude for 0.30 and 0.35 micrometers features and a wafer to wafer image uniformity similar to that observed for APEX.
This paper discusses a new negative tone aqueous base developable photoresist that has demonstrated excellent sub-half micron resolution with commercially available DUV (deep ultraviolet) exposure systems. This system which consists of a phenolic resin (pHOST), a glycoluril crosslinker (TMMGU), and a triflic acid generating material is currently in use for the manufacturing of 16 M b-DRAM and related CMOS logic technology. We provide supporting manufacturing data relating to our experiences with this program, along with the benefits realized by the implementation of a negative tone photoresist system.
A chemically amplified silicon-containing resist has been formulated and evaluated as a thin imaging layer in a positive tone deep UV (DUV) bilayer scheme. The key component is a silicon-containing polymer which has been characterized by GPC, UV, and dissolution rate studies. Dose and focus latitudes were determined for 0.4 and 0.5 micrometers patterns exposed on a SVGL Micrascan I step and scan system and on KrF excimer laser steppers. The dose latitude on a GCA (0.35 NA) excimer was found to be 20% for 0.4 micrometers features and about 30% for 0.5 micrometers features (+/- 10% CD variation). Focus latitude was at least 2 micrometers for 0.5 micrometers patterns. Wafer to wafer LW uniformity as well as within water uniformity is shown. Typical processing involves 5 - 10 mJ/cm2 exposure doses, employing a 90 degree(s)C post-expose bake (PEB) and a 60 sec 0.21 N TMAH develop. The dependence of linewidth upon PEB was found to be about 13 nm per degree C for 0.5 micrometers features. Pattern transfer into the hardbaked i-line resist underlayer was done in an MLR chamber on an AME 5000. A low pressure etch is preferred to eliminate residue but this can lead to a higher non-uniformity across the wafer. Sidewall roughness was prevalent and this could be partially attributed to `feet' on the silicon-containing imaging layer.
The use of i-line lithography for the 16 to 64 Mbit DRAM device generations calls for increased performance of i-line resists. This paper reports on investigations on novel sensitizers for advanced i-line lithography, starting out with a discussion of general design criteria, then discussing methodology and results of a screening phase, and examining in greater detail a small number of selected candidates for which resolution, exposure latitude, and depth-of-focus data were obtained. Finally, a new advanced resist for i-line lithography, AZR 7500, is presented, and its performance is evaluated in terms of the above criteria as well as thermal flow resistance.
Here we report two novel nonmetallic acid generators, derived from N- hydroxy-2,3-diphenylmaleimide, which absorb in the Deep UV and Near UV regions and do not require sensitization by additives. We have formulated a base developable positive tone resist containing these acid generators and have demonstrated 0.6 micrometers resolution on g-line and i- line steppers with sensitivity less than 50 mJ/cm2. We will show data characterizing the new materials and describe lithographic results relating to the performance of the resist.
This paper describes methods used and results obtained in the production of 1-megabit
(Mb) DRAM chips, using a chemically amplified tertiary-butoxy carhonyl
hydroxystyrene (t-BOC) resist and 1X lithography. 'Flie internally developed resist
provided high sensitivity and contrast, for I rn resolution on a Perkin Elmer Micralign
model 500 (PE 500) in the deep UV. Characterization, and modification of the PE 500
were required for this first application in the deep UV. The manufacturing process had
photo limited yield in excess of 95% with throughput of 100 wafers per hour.
The addition of phenolic compounds to positive tone chemically amplified resists has increased sensitivity
by approximately 2X for Deep UV exposures and up to 5Xfor X-ray imaging. Sensitivity enhancement
during e-heam exposures was only 20%. Additives like hydroquinone sensitize various acid generators
including triphenyl sulfonium triflate (TPS) and N-tosyloxyphthalimide (PTS) without affecting contrast and
image profiles. The sensitization occurs in poly(t-butyloxycarbonyloxystyrene) as well as in base soluble
resins. With PTS, the predominant mechanism is believed to involve electron transfer from the excited
singlet or triplet state of the additive to the acid generator. For onium salt, direct photolysis plays a significant
role in acid generation so that the effect of the additives is not as great as with PTS.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.