A New Dual Functionality Filter for Defect Reduction of Advanced Lithography Processes

1,545 views

Published on

The downward scaling of semiconductor circuits has put an increasing demand for contamination control in the lithography process. With the utilization of chemically amplified photoresists for enhanced photosensitivity, there have been widespread occurrences of various defects in the coated films. 193nm photoresist systems, typically consisting of a solvent system, a polymer system, photo acid generators (PAG), acid quenchers, additives, and surfactants, are particularly sensitive to particulate and bubble-induced defects. Microbridging defects in photoresist and cone defects in the anti-reflective coatings are particularly troublesome because they may form by contaminants smaller than the nominal size of the filter membrane pore and may only be evident in the subsequent process steps.

Microbridging defects manifest themselves as resist remaining in unwanted places after exposure and development. Examples of these defects are shown in Figure 1. Microbridging was recognized as one of the critical patterning defects that were frequently observed in 193nm lithographic process in different formulations from different manufacturers. The problem becomes remarkable particularly in dense line/space L/S feature and should seriously damage the production yield. While the cause of micro-bridging defects has not been definitely identified, a hypothesis has been proposed which states that some compositional inhomogeneity potentially existing in the 193nm polymer was suspected for the root cause of micro-bridging defects. These “less-soluble” species exist in the polymer at a trace amount, which is supposed to agglomerate and eventually grow up into the size that would bridge the lines. The photoresist filtration is known to influence this defect density.

With the continuous demands for defect reduction and high productivity, Entegris has developed a new and unique photochemical Point-Of-Use (POU) filter, Impact® Duo to address these demands particularly in advance lithography processes.

Published in: Technology, Business
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,545
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
26
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

A New Dual Functionality Filter for Defect Reduction of Advanced Lithography Processes

  1. 1. APPLICATION NOTE A NEW DUAL-FUNCTIONALITY FILTER FOR DEFECT REDUCTION OF ADVANCED LITHOGRAPHY PROCESSES Author: Aiwen Wu Introduction The downward scaling of semiconductor circuits has put an increasing demand for contamination control in the lithography process. With the utilization of chemically amplified photoresists for enhanced photosensitivity, there have been widespread occurrences of various defects in the coated films. 193 nm photoresist systems, typically consisting of a solvent system, a polymer system, photo acid generators (PAG), acid quenchers, additives and surfactants, are particularly sensitive to particulate and bubble-induced defects. Micro- bridging defects in photoresist and cone defects in the anti-reflective coatings are particularly troublesome because they may form by contaminants smaller than the nominal size of the filter membrane pore and may only be evident in the subsequent process steps. Microbridging defects manifest themselves as resist remaining in unwanted places after exposure and development. Examples of these defects are shown in Figure 1. Microbridging was recognized as one of the critical patterning defects that were frequently observed in 193 nm lithographic process in different formulations from different manufacturers. The problem becomes remarkable particularly in dense line/space (L/S) feature and could seriously Figure 1. Microbridging type defects damage the production yield. While the cause of microbridging defects has not been definitely identified, a hypothesis has been proposed which Polymer Materials Used states that some compositional inhomogeneity potentially existing in the 193 nm polymer was for POU Photochemical suspected for the root cause of microbridging Applications defects. These “less-soluble” species exist in the polymer at a trace amount, which is supposed to POU filtration acts as the last barrier to wafer agglomerate and eventually grow up into the contamination from the process tool, fluid size that would bridge the lines. The photoresist handling and system upsets. The ideal filter filtration is known to influence this defect density. should have a combination of physical properties that produces a structure capable to remove With the continuous demands for defect reduction contamination from a photochemical. Some and high productivity, Entegris has developed a key properties for a filter at the POU for new and unique photochemical point-of-use (POU) photochemical filtration include: filter, Impact® Duo, to address these demands • Filter membrane is wet spontaneously by particularly in advanced lithography processes. photochemical ENTEGRIS, INC. 1
  2. 2. A NEW DUAL-FUNCTIONALITY FILTER FOR DEFECT REDUCTION APPLICATION NOTE UPE Membrane Photoresist Solids • Fast priming/bubble clearance • Good retention • High flow rate/low pressure drop • Complete chemical compatibility with photochemical • High cleanliness/low extractables 1800 1500 1200 900 The most common materials used to manufacture Wavenumbers (cm-1) particle filters for POU photochemical filtration Nylon Membrane are ultra-high molecular weight polyethylene Photoresist Solids (UPE) and polyamide. While both material membranes wet spontaneously with all solvent- based photochemicals and have been used as photochemical filters, each membrane material has its specific structure and associated properties. The principle particle retention mechanism of microporous membranes is based on sieving or 1800 1500 1200 900 screening, that is, particles larger than the pore Wavenumbers (cm-1) size do not pass through the filter. The decrease Figure 2. FTIR spectra of used filters in 193 nm photoresist of critical linewidths is requiring the use of tighter filtration for photochemicals. 10 nm and 20 nm nylon and UPE filter surfaces after filtering a filtration has been implemented in both the 193 nm photoresist. None of the membranes photoresist manufacturing process and in the initially had peaks evident at 1790 to 1720 cm-1. POU spin-coating process in track systems, and The nylon membrane shows the adsorption of some has been shown to be effective to reduce defects. material from the photoresist in the area while the While finer pore size filters are advantageous for UPE membrane shows no adsorption at all. reducing wafer defects, small pore alone will not eliminate some process-specific defects such as It was hypothesized that the adsorption effect microbridging. In addition, the implementation of of polyamide membrane was due to the polar finer filtration raises concerns as high differential functional groups of polyamide polymer. Figure 3 pressure across the filter causes outgassing of the shows the chemical structure of polyamide and photoresist and finer pore size approaches the polyethylene polymers and the polar functional size of large molecular weight polymers in the groups of polyamide polymer. This nonsieving photoresist. retention capability of polyamide membrane would be instrumental in reducing the wafer defect level In addition to the size exclusion, there may be without further reducing the membrane pore size. some adsorption effects of the membrane. Trace contaminants, even smaller than membrane pore in size, are attracted and captured by the membrane surface due to hydrophobic binding or charge effect. This is referred as nonsieving retention. While the membrane surface can be well Polar Functional Groups characterized, the interactions with complicated photochemical chemistry can be difficult to predict. Empirical evidence indicated that there appeared to be an adsorptive interaction of the polyamide membrane surface with the photoresist, in which UPE “less-soluble”, polar, defect-causing high molecular Polyamide weight polymers in the resist were adsorbed by the membrane. Figure 2 shows the FTIR spectra of Figure 3. Chemical structure of polyamide and polyethylene 2 ENTEGRIS, INC.
  3. 3. A NEW DUAL-FUNCTIONALITY FILTER FOR DEFECT REDUCTION APPLICATION NOTE While the surface of polyamide is beneficial for On the other hand, ultra-high molecular weight particle removal, there are some concerns about polyethylene membranes offer outstanding polyamide membrane. chemical resistance to organic solvents used in photoresist and bottom anti-reflective coatings Lifetime concerns (BARC) and have found considerable success as photoresist and BARC filters in the lithography Improvement in defectivity due to nonsieving processes. The UPE membrane and high-density mechanism is likely volume dependent. Once a polyethylene (HDPE) filter components are prescribed volume of photoresist has been processed, compatible with almost all photochemical solvents. defects would break through as functional groups Highly sieving UPE filters down to 10 nm have become saturated. It is difficult to predict the been demonstrated to be effective to reduce breakthrough point, since this point is affected by defects on the wafers. many external factors. Side effects concerns Impact Duo Filter Design The adsorption of polar functional groups of The Impact Duo filter is specifically designed polyamide membrane is non-selective. The polar to meet the unique requirements of advanced functional groups may adsorb the defect-causing lithography processes. It uses Entegris’ dual- impurities while at the same time they may also functionality technology, which is the combination adsorb the additives which are important to of a polyamide layer and a tight UPE membrane. photoresist properties, such as PAGs, acid quenchers Figure 4 is a schematic representation of membrane etc. The adsorption of these important additives layout in the filter. The filter is constructed with may induce some CD variations. the pleated dual layer membranes and with HDPE supports, components and housing. Compatibility concerns Polyamide is a highly crystalline form with a Support Polyamide UPE 0.03 µm or 0.01 µm high degree of hydrogen bonding. It tends to be decomposed in solvents with high polarity. Moisture, chemical attack, photolysis and oxidation are all routes to attack polyamide. The degradation of Upstream Downstream polyamide filter membrane can be detected in the process in a number of ways. The most common effect is loss of particle performance. As a result, Impact Duo (4 layers) small particles can be released, known as particle shedding, or the pore size can increase, releasing Figure 4. Schematic of membrane layout of the “Duo” filter retained particles back into the process stream. The mechanical properties of the filter can also be The “Duo” filter provides superior sieving and compromised, resulting in a weakened membrane nonsieving (adsorptive/purification) retention. and defects in the membrane structure, which The technology is targeted at specific 193 nm could allow unfiltered chemicals to come in photoresist and BARC applications where the contact with the wafer. customer is experiencing defects caused by The lifetime of POU photochemical filters is impurities not removed by standard sieving generally in the 3- to 12-month range because the technology. The upstream polyamide layer uses particle loading is low and the tool downtime costs an asymmetric membrane structure, where the involved with filter changeout are quite high. In downstream surface of the membrane is very the POU application, the filter must have exemplary thin and has more retentive pore structure. The chemical compatibility because it is in contact remaining membrane thickness has a more open with the chemical for up to one year. Even if the pore structure, providing strength and some depth filter is idle, chemical attack can occur, with the filtration. This kind of composite pore structure by-products of degradation being released into the provides the retention capacity of the microporous process on startup. membrane without the sacrifice of the flow. Figure 5 shows the scanning electron microscope (SEM) of the cross-section of the symmetric UPE and asymmetric polyamide membranes used in the Impact Duo filter. ENTEGRIS, INC. 3
  4. 4. A NEW DUAL-FUNCTIONALITY FILTER FOR DEFECT REDUCTION APPLICATION NOTE In addition, the polar functional groups of The Impact Duo’s superior sieving retention is polyamide membranes may remove difficult accomplished mostly by the UPE membrane contaminants from specific photoresists due to used as the downstream membrane layer. Sieving an adsorptive property, where a single retention retention of 30 nm and below is effective at technology might not succeed. However, by its reducing gels, hard/soft particles and some nature, the capacity of an adsorptive removal molecular contaminants that can lead to defects. mechanism is limited. The number of sites on the The defect-causing substances adsorbed in the surface and the amount of contamination in the first nonsieving layer may nucleate and become photoresist control the lifetime of the filter. By larger gels. These large gels may penetrate using an asymmetric pore structure, the thickness through the nonsieving layer. The sieving UPE of the polyamide membrane can be increased, layer downstream of the nonsieving layer can resulting in higher numbers of adsorptive sites on protect the processes from these gels or other the surface, longer residence time of the photoresist variables, such as compatibility induced by the in the tortuous membrane pore structure and, first layer and extend the filter lifetime after active therefore, enhanced nonsieving retention sites of the first layer are saturated. In addition, efficiency and filter lifetime. this filter design mimics photoresist manufacturing process (PMP) of most advance chemicals, where nonsieving technology is used as a pre-filter and a highly retentive sieving UPE membrane is used as a final filter. By using the combination of a thick, asymmetric polyamide layer and a thin, tight UPE membrane, the “Duo” technology provides superior sieving and nonsieving particle retention, flow and chemical compatibility. Improving Filter Performance Particle Retention The finer feature size of advanced lithography processes requires even finer filtration for Asymmetric polyamide membrane photoresists. The filters with 30 nm, 20 nm, even 10 nm retention ratings have become the standard for ArF resists. These filters were tested for particle retention with monodispersed 0.034 µm polystyrene latex (PSL) beads using a modified SEMATECH test method1. In the testing, the filters were continually challenged with 0.034 µm PSL beads and filter retention values were measured as a function of particle loading. The retention capability of the filters is reported as log reduction value (LRV), a very sensitive method for detecting slight passage of particles. LRV is defined as the logarithm of the ratio of the number of particles in the feed to the number of particles in the filtrate. Symmetric UPE membrane Figure 5. Membrane cross-section 4 ENTEGRIS, INC.
  5. 5. A NEW DUAL-FUNCTIONALITY FILTER FOR DEFECT REDUCTION APPLICATION NOTE Figure 6 shows the particle retention comparison METAL EXTRACTABLES RESULTS FOR IMPACT DUO FILTERS of the newly developed Impact Duo 30 nm and Filter Impact Duo Impact Duo Competitor’s Nylon 10 nm filters, and a 50 nm polyamide single-layer Pore Size 10 nm 30 nm 40 nm filter. The Impact Duo filters show improved retention compared to a 50 nm polyamide single- Metal µg/device µg/device µg/device layer filter. Both the 30 nm and 10 nm rated Na 0.40 0.26 2.80 Impact Duo filters are extremely efficient in Mg 0.92 0.96 0.79 removing PSL particles from the process fluid, Al 0.43 0.46 0.96 even with very high particle loading. The Impact K 0.14 0.07 0.62 Duo 10 nm filter maintains superior particle Ca 0.08 0.08 2.48 removal performance throughout the whole Ti 0.01 0.04 0.55 particle challenge period. This represents an Cr 0.00 0.00 0.11 extended lifetime in fluids containing high concentrations of contaminating particles. Mn 0.00 0.00 0.18 Fe 0.05 0.11 0.04 30 nm LRV vs. Particles/Filter Ni 0.02 0.01 2.35 Cu 0.05 0.03 0.55 50 nm polyamide Impact Duo 30 nm Zn 0.09 0.04 0.65 Impact Duo 10 nm Pb 0.00 0.00 0.24 10.00 Total 2.19 2.07 12.32 Table 1. Metal extractables results for Impact Duo filters Retention (LRV) 1.00 The organic extractables of the Impact Duo filters was measured as non-volatile residue (NVR). The filters were soaked with a solvent for a period of time and the solvent drained into a clean beaker. The solvent in the beaker was then evaporated 0.10 and the mass of the residue was weighed with an 1E+11 1E+12 1E+13 analytical balance. As seen in Table 2, the Impact Number of 0.034 µm PSL Challenge Particles Duo filters have very low organic extractables Figure 6. Particle retention of Impact Duo filters using levels. PSL beads ORGANIC EXTRACTABLES RESULTS MEASURED BY NVR Cleanliness/Extractables Filter NVR (mg/device) Competitor Nylon 20 nm 8.6 Impact Duo filters are much cleaner and have much lower metal extractables and organic Competitor Nylon 40 nm 8.2 extractables than other commercially available Impact 2 UPE 3.0 photochemical POU filters. The metal extractables Impact Duo 1.3 of the Impact Duo filters was determined after Table 2. Organic extractables results for Impact Duo filters as placing the filters in a known volume of an measured by NVR extracting fluid over a period of time. The filters were drained of the fluid and the extracting fluid was analyzed for key metal elements using ICP-MS The Impact Duo filters use ultra-clean raw technique. The metal concentrations measured in materials and are cleaned using Entegris’ most ppb (parts-per-billion) were multiplied by the advanced proprietary cleaning technology for extract volume and the total reported as µg/device. ultra-low organic extractables. Careful handling, Table 1 provides a summary of the metal extractables manufacturing and flushing techniques are also results for Impact Duo filters and a competitor’s responsible for the Impact Duo filters’ extractables nylon filter. The metal extractables results show performance. the Impact Duo filters are much cleaner as indicated by the total metals extracted from the filters compared to a competitor’s nylon filter. ENTEGRIS, INC. 5
  6. 6. A NEW DUAL-FUNCTIONALITY FILTER FOR DEFECT REDUCTION APPLICATION NOTE Filter Priming Bubble Flushup of Impact Duo Filters The most noticeable attribute of photochemical on a Two-stage Dispense Pump POU filters is the ability to purge air and contaminants introduced during system Impact Plus 10 nm UPE single-layer Impact Duo 10 nm maintenance or filter changeout. Many fabs are Impact Duo 30 nm reluctant to perform filter change prior to failure due to chemical consumption and tool downtime. 1000 >= 0.15 µm Particle Counts (pts/ml) With constant throughput fab processes, lengthy fabrication tool downtime means corporate profitability is reduced. The Impact Duo filter’s @RION KL-27 100 unique design ensures a high level of retention to reduce advanced process defects, while also maintaining the ability of fast priming during 10 filter changeout. Laboratory experiments were conducted to examine the priming performance of Impact Duo filters 1 -25 0 25 50 75 100 125 150 and compare it to a standard Impact Plus UPE Operation Cycle single-layer filter on an Entegris IntelliGen® Mini dispense pump or a single-stage dispense pump. A Figure 7. Bubble flush-up of Impact Duo filters on a two- recirculating chemical test stand was assembled stage dispense pump using a chemical reservoir, a dispense pump, a filter manifold, a test filter and an optical particle Bubble Flushup of Impact Duo Filters counter (OPC). The OPC is a Rion KL-27, capable on a Single-stage Dispense Pump of detecting and sizing particles 10 nm to 50 nm. This OPC was installed on the outlet line of the Impact Plus 10 nm UPE single-layer Impact Duo 10 nm dispense system, monitoring the entire downstream Impact Duo 30 nm of the testing filters. The effluent was recycled to the reservoir. The filters were primed with the 1000 >= 0.15 µm Particle Counts (pts/ml) solvent propylene glycol monomethyl ether acetate (PGMEA) and the dispense recipe was continually performed until particle counts leveled off. Since @RION KL-27 100 each new testing filter was installed after the particle counts reached very low background with a filter in place, the particle levels shown by the 10 counter indicated the level of microbubbles in the dispense line during the testing. While optical particle counters are not designed to count bubbles, 1 the results can be used in a semi-quantitative -25 0 25 50 75 100 125 150 manner to see differences in filter performance. Operation Cycle The results of filter priming testing are showed Figure 8. Bubble flush-up of Impact Duo filters on a single- in Figures 7 and 8. The priming speed of Impact stage dispense pump Duo filters is slightly better or equal to a standard Impact Plus 10 nm UPE single-layer filter on both a two-stage dispense pump and a single-stage dispense On-wafer Performance pump. These results show that when the device design and membrane structure are combined The benefits of Impact Duo filters have been correctly, Impact Duo filters can maintain the fast demonstrated under actual production conditions priming speed. As a result, the chemical waste and at a number of different semiconductor dispense-point downtime are reduced. manufacturing sites. One customer in Asia had been facing bottom bridge defect issue for latest 6 ENTEGRIS, INC.
  7. 7. A NEW DUAL-FUNCTIONALITY FILTER FOR DEFECT REDUCTION APPLICATION NOTE ArF resist. The customer evaluated several filters Particle for Duo Filter Evaluation to reduce this defect issue. Figure 9 summarizes Pct_duo Control limit the results of the evaluation over a period of time. 15 While tighter filtration for BARC reduced the defect level, Impact Duo technology resulted in 10 almost “zero” bottom bridge defect. 5 Effect of Impact Duo Filter on Bridge 0 Defect Reduction in ArF Resist -5 ArF Resist: UPE 50 nm ArF Resist: UPE 50 nm ArF BARC: UPE 50 nm ArF BARC: UPE 10 nm -10 1 3 5 7 9 11 13 15 17 19 21 23 25 27 Number of Bottom Bridge Defects 12 Weeks Particle Pre-pump Change 2 Weeks (Nylon 40 nm) ArF Resist: Duo 10 nm ArF BARC: UPE 10 nm PC0001_C Control limit 15 8 Weeks 10 5 1 2 3 4 5 6 7 8 9 10 11 12 0 Figure 9. Effect of Impact Duo filter on bridge defect reduction in ArF resist -5 Impact Duo filters were also evaluated at an Asian -10 1 3 5 7 9 11 13 15 17 19 21 23 25 27 semiconductor foundry. The 30 nm Impact Duo Figure 10. Comparison of wafer defects as measured by filter was installed in a RDS-01 dispense pump in surface scanning a TEL® Act 8 track with a DUV resist. The resist- coated wafers were analyzed for defects with a KLA-Tencor® AIT. As shown in Figure 10, particle semiconductor manufacturing conditions, to counts on wafer were variable when a nylon 40 nm provide superior sieving and nonsieving (adsorptive/ single-layer filter was installed as the standard purification) retention that can lead to defect filter. However, for the Impact Duo filter, particle reduction in advanced lithography processes and levels on wafer were not only reduced, but also superior chemical compatibility and lifetime, were more stable. especially for certain resists where bridging defect or cone defect is a problem. Entegris’ proprietary These tests demonstrated that Impact Duo filters cleaning technology ensures the cleanliness of were effective at reducing bridge defects and Impact Duo filters. The fast priming speed due to provided lower particle concentrations on wafer optimized device design and membrane structure than comparable pore size single-layer filters for effectively reduces tool downtime and chemical the testing photoresists. consumption required for filter changeout. Conclusion References Impact Duo, a new photochemical point-of-use 1.Lee, J.K. et al, “Latex Sphere Retention by filter based on dual-functionality membrane Microporous Membranes in Liquid Filtration,” technology has been shown, under laboratory and Journal of the IES, January/February 1993, 26-36. TEL® is a registered trademark of Tokyo Electron, Inc. KLA-Tencor® is a registered trademark of KLA-Tencor, Inc. Entegris®, Impact® and IntelliGen® are registered trademarks of Entegris, Inc. Rion KL-27 is a trademark of Rion Company, LTD. Sematech® is a registered trademark of Sematech, Inc. ENTEGRIS, INC. Corporate Headquarters / 3500 Lyman Boulevard / Chaska, Minnesota 55318 USA Customer Service Tel. 952-556-4188 / Customer Service Fax 952-556-8022 www.entegris.com ©2007 Entegris, Inc. All rights reserved Printed in USA 4423-5376ENT-1207

×