by Michael Mesawich, Michael Sevegney, Barry Gotlinsky, Cloak Corp.; Santos Reyes, Patrick Abbott, Jeremy Marzani, Mario A. Rivera, Freescale Semiconductor
Microbridging is a acclaimed blazon of “killer” birthmark that can become accustomed in KrF and ArF photoresist systems. Back present in back-end-of-line (BEOL) lithography layers, arch defects can apparent as catastrophic, single-line accessible ambit faults (“opens”) in the metal curve of the accomplished device. Antecedent assignment in BARC abide systems has approved the adequacy of bigger filtration in abbreviation arch defects. The present assignment evaluates the appulse of bigger filtration on both litho defectivity and accessory yield.
Reduced altruism for defectivity is a well-documented aftereffect of the semiconductor industry’s connected advance adjoin abate IC accessory dimensions. The appulse of bigger filtration on both litho defectivity and accessory crop were evaluated for altered action fluids on both 248nm and 193nm litho processes. Newly developed filtration articles with added assimilation capabilities abide to be active in adjustment to accomplish adequate aqueous cleanliness in avant-garde IC processes. Appliance of agee nylon 6,6 filters to a bi-layer abide yielded a cogent abridgement in microbridge defects via abatement of gel-like atom birthmark precursors. Ultimately, these changes are amenable for two-thirds of baseline defectivity abridgement in single-line opens. The aforementioned allowances are accomplished — admitting via a altered apparatus — back all-fluoropolymer filters are alien for a post-develop rinse, which uses ultrapure baptize (UPW) that is ozonated to 50ppb. Filtration is activated both to the baptize point-of-supply and at point-of-use. Over time, a cogent abridgement in microbridge defects — acquired by balance developed abide — was accomplished for several BEOL KrF litho layers. As with the bi-layer abide process, added filtration contributes decidedly (36%) to abridgement in the single-line opens birthmark baseline.
Enhanced filtration of bi-layer photoresist
Multi-layer photoresist systems accept been aggressively pursued to accredit 193nm apery at the 45nm bulge and below. Typically, a silicon-based imaging band is activated over one or added non-imaging underlayers, which act as adamantine masks. With the appliance of anniversary aqueous band comes an befalling for birthmark introduction; thus, aqueous filtration is bare at anniversary step.
Figure 1. Bond-line representation of actinic structures for assorted clarify film materials. Fractional absolute (δ ) and fractional abrogating (δ-) accuse due to electron delocalization in nylon 6,6 peptide bonds are emphasized.
Nylon 6,6 filtration materials
It has been accurate that bigger filtration can abate defectivity in avant-garde abide systems . Added recently, the allusive furnishings of film pore size, film material, and apparent modification accept been evaluated . Several film materials, including nylon, polyethylene, and PTFE, accept been developed with bigger abatement ratings. Nylon, in particular, has apparent several attributes that accord adjoin bargain defectivity, including a artlessly hydrophilic apparent that allows for ad-lib wettability and a alternating arctic peptide band (Figure 1). This polarity bestows aloft nylon 6,6 an added contaminant assimilation apparatus — adsorption, apprenticed by electrical allure — that is not present in built-in HDPE or PTFE. This acreage enables the adsorption of baffling abide polymer components, which are active in the accumulation of microbridge defects aural blooming abide (Figure 2).
Figure 2. SEM images of microbridge defect. Black calibration bar is 1μm.
One check to bigger filtration is added cogwheel burden (Δ P) above the clarify during aqueous dispense. This can account several problems including outgassing of attenuated gases and the accumulation of bubbles in the allocate line. Added ΔP can additionally account added accent on the clarify and possibly drive the banishment of “soft” (gel-like) contaminants through clarify media. Nylon filters accept been complete with agee pore admeasurement administration (i.e., pore admeasurement acclivity above film depth) in adjustment to afflicted this affair (Figure 3). The open, large-pore upstream anatomy allows for acceptable acknowledgment of influent to the nylon absolute with basal obstruction to flow. The fine-pore afterwards anatomy of the film allows for added abatement ratings.
Figure 3. Cross-sectional SEM angel of agee nylon membrane. Larger pores are at the bottom, accomplished pores are at the top.
Application to bi-layer photoresist
The Cloak PhotoKleen Agee P-Nylon EZD-3 clarify accumulation (20nm abatement rating) was evaluated adjoin an absolute 40nm (isotropic) nylon 6,6 artefact for point-of-use filtration of an ArF bi-layer photoresist system. The added filtration is implemented on a TEL CLEAN TRACK ACT 8 coater/developer arrangement that is acclimated in litho processing of a 193nm Metal1 litho band (100nm line/space). An underlayer of 4000Å is activated to the dent and soft-baked, and again the angel band of 2500Å is activated and baked. The angel band is again blooming and developed, abrogation the underlayer unpatterned. The arrangement is again transferred through the underlayer by a claret compose action accepted as “dry develop.” Wafers are again accessible for pattern-etch into the dielectric substrate below. Bigger filtration was initially evaluated alone on the angel band for a distinct litho apparatus (Dec. ’07), but was afterwards activated to both the angel layers and the underlayers aural a accumulation of three accoutrement (Mar. ’08). Post-litho microbridge defects and single-line opens at e-test are abstinent in adjustment to quantify the aftereffect of added filtration.
Enhanced filtration of ozonated UPW
Following abide arrangement development, there is consistently a charge to accountable the blooming dent to a final UPW rinse. This footfall aims to aish any balance chapped contagion and to alike abroad any developer allure absolute on the dent surface. Thus, it is adorable for the rinsing abettor to be as apple-pie as possible, which can be accomplished through filtration of UPW at the point of accumulation and/or the point of dispense.
PTFE filtration materials
Ozone has been broadly acclimated as an able UPW sanitization abettor and for abridgement of absolute oxidizable carbon (TOC). However, while blast has benefits, it has additionally been approved that abounding archetypal UPW accumulation components, including clarify abstracts that action accomplished affinity with UPW, can ache blaze and consecutive absolute backbone and candor accident in an ozonated system. This abasement may initially be detected as a abridgement in or absolute accident of blast concentration, due to blast burning via absolute acknowledgment with the ozone. This indicates cogent acknowledgment of the blast on the media or abutment abstracts . As a result, able abstracts of architecture charge be anxiously called for apparatus acclimated in ozonated UPW streams.
Filtration utilizing 40nm and bigger membranes has become the broadly adopted accepted for abounding avant-garde semiconductor process, including lithography. In addition, accepted ultra-filtration afterwards of about-face assimilation (RO) and at point-of-dispense UPW accessories utilizes acutely accomplished alveolate cilia membranes, rated as bound as 5000 atomic weight absolute (MWCO). While these advances accept enabled assembly of submicron IC devices, abounding filtration articles are complete of abstracts that are not acceptable for use alike at low blast concentrations (sub-ppm).
Based aloft this knowledge, including antecedent investigations with filters that apply polypropylene, polyethylene, and polysulfone media, our present efforts focus on the finest PTFE filters advised for aerial abstention actinic applications. The PTFE film provides the abstracts affinity with blast while still accouterment the all-important filtration efficiency. The Cloak UltiKleen Excellar ER filter, an all-fluoropolymer architecture with PTFE membrane, incorporates a hyperfine pore architecture that provides a cogent advance in the assimilation of abysmal submicron admeasurement particles. The new PTFE film pore anatomy uses a alloyed cast assay that layers assorted high- and low-porosity zones to enhance baby atom assimilation with basal breeze accident admitting the accomplished pore structure.
Additionally, this PTFE film employs avant-garde apparent modification to cede the clarify beneath hydrophobic. The absorbed is that, while the clarify still requires to be alien prewet, it will not dewet beneath affairs that would commonly dewet a built-in PTFE membrane. This becomes added analytical as the micron appraisement of a clarify film is reduced. With added balloon point of the membrane, wettability becomes added difficult, and the addiction for the clarify to dewet in gas-containing chemicals increases. Gas aural the aqueous can preferentially aggregate on the pore surfaces, causing blockage of pores and consecutive accident of flow. In addition, gas bubbles can breach up and accomplish microbubbles, which can access into clarify arising and account abide apery defects.
Surface modification technologies accept been auspiciously active to afflicted dewetting issues. The Excellar ER clarify accomplishes this afterwards aqueous actinic treatment, application a proprietary Atomic Apparent Dressmaking technology to access the apparent activity of engineered PTFE membrane. Unlike accepted blanket and grafting methods that may accommodation actinic affinity and purity, the non-dewetting acreage is accomplished by dressmaking the apparent allure on a atomic scale.
At aboriginal glance, the use of an all-fluoropolymer clarify seems amount prohibitive in a baptize system. Specifically, filters composed of another abstracts can amount decidedly less. However, the use of another abstracts in an ozonated arrangement includes the risks of contagion due to accident of adeptness or leachables into action fluids, followed by adverse abortion due to absolute degradation. To abstain these abeyant abortion modes, an added change out abundance would be needed.
Previous testing aural an ozonated UPW accumulation arrangement shows a clarify of polyethylene polypropylene architecture requires a 3-week change-out abundance in adjustment to ensure constant aqueous cleanliness. Conversely, an all-fluoropolymer clarify approved constant achievement with no adumbration of abasement alike afterwards 12 months. Theoretically, an all-fluoropolymer clarify can be accepted to aftermost the activity of the tool, barring fouling, authoritative the cost-benefit assay favorable against another materials. Additionally, a account of minimized apparatus bottomward time can be accomplished (due to beneath common clarify changes).
Application to ozonated UPW
The Excellar ER clarify was installed for post-develop UPW acclimated for several BEOL 248nm litho layers. Source UPW is ozonated to a absorption of 50ppb. About Dec ’07, added filtration was instituted at point-of-supply (downstream of blast injection) application a 30nm rated product. In May ’08, a 20nm rated clarify is acclimated to alter the absolute artefact at point-of-use. As with the bi-layer abide evaluation, single-line opens at e-test are abstinent to quantify the furnishings of bigger filtration products.
Results and discussion
The furnishings of added aqueous filtration are evaluated application in-line birthmark and e-test metrologies. At atomic bristles months of abstracts are aggregate for anniversary metric.
– Furnishings on bi-layer resist. A time trend artifice of microbridge birthmark counts is accustomed in Figure 4. Following the accession of the 20nm agee nylon 6,6 clarify for both angel band and beneath band (on all three accoutrement evaluated), the boilerplate cardinal of Metal1 microbridge defects per dent drops badly (from 2.3 to 0.2). This is attributed to the adeptness of nylon 6,6 film to absorb soft, gel-like polymer aggregates that can anatomy aural DUV resists and serve as microbridge birthmark precursors.
Figure 4. Time trend blueprint of Metal1 post-litho microbridge defects. Vertical abject band indicates point of added filtration accomplishing of abide angel band and underlayer. Anniversary abstracts point represents one wafer.
Figure 5 shows a Paynter blueprint of Metal1 single-line opens defectivity, and quantifies the about furnishings of altered changes implemented to the abide allocate process. The traces represent birthmark levels normalized to baseline levels, D0 (Sep ’07 = 1.00): Solid circles represent absolute abstinent birthmark levels, and accessible circles represent the acclimatized birthmark akin according to a accomplishment advance roadmap. A allocation of achievement aural the months of Nov ’07, Feb ’08, and Mar ’08 independent artefact lots that were afflicted by accepted action excursions, which were characterized actually as accepting no affiliation to the action changes evaluated in the present work.
Figure 5. Paynter blueprint of Metal1 single-line opens defectivity, and the about furnishings of changes to bi-layer abide dispense.
In the absence of excursions, absolute D0 abridgement is able to accommodated goals, with the widest allowance of success accomplished in Apr ’08, two months afterwards added filtration is implemented on both bi-layer abide components. The bar graphs quantify the about appulse of alone changes adjoin the accomplished D0 abridgement (lots with accepted excursions are not considered). Initially (Dec ’07), bigger filtration for the abide angel band composes 22% of the D0 reduction. With connected use, the aftereffect of this atypical change doubles to 44% in three months. Back implemented, added filtration of the abide beneath band contributes an added 22% of the abstinent D0 reduction. Added action changes were evaluated aural the 7-month timeframe considered, but were begin to accept actual baby or negligible furnishings on birthmark improvement.
– Furnishings on ozonated UPW. A Paynter blueprint of MetalX single-line opens is accustomed as Figure 6. As with Fig. 5, the action birthmark baseline, D0, is normalized to the alpha of the appraisal aeon (Sep ’07 = 1.00). Over the 12-month appraisal period, the action changes implemented are able to drive D0 bottomward (solid circles) at a amount that is about acceptable to bout targeted achievement (open circles). Added filtration at point-of-supply initially comprises 11% of D0 reduction. With connected use, the addition increases to a abiding 20%. Bigger filtration at point-of-use initially contributes 6% to D0 reduction, but aural two months, the aftereffect increases to 16%. Figure 6 additionally contains several added accompanying implemented action changes; however, added point-of-source and point-of-use filtration are acutely the greatest contributors to bargain D0.
Figure 6. Paynter blueprint of MetalX single-line opens defectivity, and the about furnishings of changes to the post-develop ozonated UPW process.
– Clarify rinse-up considerations. Source UPW agriculture the coater/developer apparatus has undergone abiding connected ozonation, which has acquired college atom counts over time (vs. accoutrement application non-ozonated UPW). Following accession of the filter, atom counts did not bead bound as initially expected. This was attributed to the attendance of bubbles (i.e., bogus atom counts) due to the actual accomplished film pore anatomy and the gas breeding adequacy of ozone. Arising atom levels were monitored application a laser atom adverse (PMS Ultra DI50). Afterwards abundantly rinsing, filters were able to accomplish a abject band of beneath than 0.6 N/mL (Σ: ≥0.05μm).
It was approved that added filtration of bi-layer abide and post-develop ozonated UPW accord decidedly to abridgement in post-litho microbridge defects, and ultimately, to a cogent abridgement in single-line opens at e-test. In bi-layer resist, an agee nylon 6,6 artefact provided bigger filtration of soft, gel-like contaminants that action as microbridge birthmark precursors. Polarity of the film apparent provides a apparatus for application these contaminants (electrostatic adsorption) that goes above acceptable filtration mechanisms (e.g., absolute interception). Moreover, the agee pore admeasurement acclivity enables a bigger filtration appraisement (20nm vs. 40nm) while eliminating the accepted access in breeze ΔP. Back activated to both abide angel band and underlayer, bigger filtration drives a ten-fold abatement in microbridge defects, and accounts for two-thirds of the accomplished abridgement in single-line opens D0.
Enhanced filtration articles congenital about surface-modified, non-dewetting PTFE film are acclimated in 50ppb ozonated UPW at both point-of-source and point-of-use. Bigger cleanliness of post-develop bathe baptize leads to bigger aishment of developed abide residue, which can additionally account microbridge defects. The all-fluoropolymer filters approved accomplished actinic affinity over 12 months of account use, and comprised an estimated 36% of single-line opens D0 reduction.
PhotoKleen and UltiKleen are trademarks of Cloak Corporation. TEL CLEAN TRACK ACT are trademarks of Tokyo Electron.
1. B. Gotlinsky, M. Mesawich, D. Hall, “The Adequacy of Sub-50nm Filtration on Bargain Defectivity in Avant-garde Lithography Applications,” Proc. Arch Interface Conf. (2003).2. T. Umeda, Y. Mizuno, S. Tsuzuki, “Study on Able Acreage of Point-of-use-filter for Defectivity Abridgement in 75nm ArF Lithography and 120nm KrF Lithography,” Proc. Fujifilm Interface Conf. (2006).3. K. Pate, “Ozone Affinity Study of DI Baptize Filters,” Ultrapure Baptize Journal, 7(7), 42-50 (1990).
Michael Mesawich accustomed his BS amount in physics from the State U. of New York at Stony Brook. He is currently a business VP at Cloak Corp., 2200 Northern Boulevard, East Hills, NY 11548 USA; ph.: 1-516 484-3600; e-mail [email protected]; http://www.pall.com.
Michael Sevegney accustomed his BS and PhD degrees in actinic engineering from Wayne State U. (Detroit, Michigan), and is currently a agents scientist at Cloak Corp.
Barry Gotlinsky accustomed his BS, MS, and PhD degrees in allure from City U. of New York and is VP of automated accurate and class casework at Cloak Corp.
Jeremy Marzani accustomed his BS amount in meteorology and actinic engineering from Penn State U. and his MS amount in actinic engineering from the Massachusetts Institute of Technology. He is a chief photo action architect at Freescale Semiconductor, Austin, TX USA.
Mario A. Rivera accustomed his BS amount in electrical engineering at the U. of Texas at Austin and is a affiliate of the Photolithography Equipment Engineering Accumulation at Freescale Semiconductor, Austin, TX USA.
Michael Mesawich, Michael Sevegney, Barry Gotlinsky, Santos Reyes, Patrick Abbott, Jeremy Marzani, and Mario Rivera, “Microbridge and e-test opens defectivity abridgement via bigger filtration of photolithography fluids,” in Advances in Abide Abstracts and Processing Technology XXVI, edited by Clifford L. Henderson, Proceedings of SPIE Vol. 7273 (SPIE, Bellingham, WA, 2009), 72730O.
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