High hydrophobic topcoat approach for high volume

High hydrophobic topcoat approach for high volume production and yield enhancement of immersion lithography Natsuko Sagawa*, Katsushi Nakano and Yuuki Ishii Nikon Corporation, 201-9 Miizugahara, Kumagaya, Saitama, Japan 360-8559 Kazunori Kusabiraki and Motoyuki Shima JSR Corporation, 100 Kawajiri-cho, Yokkaichi, Mie, 510-8552, Japan ABSTRACT Immersion scanner performance is being improved generation by generation. Faster scan speed is required to increase scanner productivity. There are, however, several papers reporting defect increase with higher scan speed1, 2, 3. To overcome this challenge, both material and immersion scanner requires special tuning and optimization. This high stage speed is possible by employing topcoats that have higher hydrophobicity. In general, blob defect are generated at a higher rate with increase in hydrophobicity of topcoat. Nikon and JSR have collaborated to address this challenge by using next generation scanner and a newly developed topcoat material, respectively. JSR, as a topcoat supplier, introduces a new topcoat (TCX279), which shows low blob defects even with very high hydrophobicity. Nikon’s latest immersion scanner S621D, equipped with latest nozzle design for optimizing immersion water flow, and an improved tandem stage system to reduce edge particles, resulted in achieving 5x defect reduction compared to S620D. Ultimately, zero immersion defects were realized by a combination of Nikon’s S621D scanner and JSR’s new topcoat, TCX279. Keywords: immersion, topcoat, defectivity, hydrophobicity

1. INTRODUCTION High throughput and yield enhancement of immersion lithography is required in semiconductor industry. To meet these industry demands, highly hydrophobic material and reliable immersion scanner is needed. There are two immersion lithography processes: One is topcoat process and the other is topcoat-less process. The beauty of the topcoat process is that it allows the chip manufacturers to optimize their resist and topcoat process independently. This leads to an increase in flexibility of process material choice for the users. Therefore, the topcoat suppliers can focus on the immersion related topcoat performance improvement, while the chip manufacturers can continue using their own optimized resist process in combination with the latest highly hydrophobic topcoat material to meet the requirements of the next generation immersion scanner. Therefore higher hydrophobic topcoat is highly attractive to improve overall performance of immersion lithography.

* [email protected]; phone +81-48-533-2111; fax +81-48-533-7458

Optical Microlithography XXV, edited by Will Conley, Proc. of SPIE Vol. 8326, 832627 © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.916271

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2. NOTICEABLE DEFECTS Defect reduction is important for yield enhancement of immersion lithography. In this paper, both track defect and immersion defect are studied. These defects are shown in Figure1. Blob defects are generated during development process. One approach to reduce blob defect is to improve topcoat material. Immersion defects, on the other hand are generated during immersion exposure. Large bridge, deformation, watermark and bubble defect are included in immersion defect. Immersion scanner improvement is needed to reduce these immersion defects.

Immersion defect

Track defect Blob defect

Large bridge

Watermark

Deformation

Bubble

Wafer

Figure 1. Defect SEM images of track defects and immersion defects

3. TOPCOAT MATERIAL IMPROVEMENT 3.1 Challenge of topcoat design Higher hydrophobicity of topcoat helps to reduce immersion defectivity. However, the trade-off for increasing hydrophobicity is the increase in blob defect generation. Typically, it is necessary to increase the fluorine content in topcoat for increasing the hydrophobicity of topcoat (Figure 2(a)), but the high hydrophobic topcoat with high fluorine c ontent tend to increase blob defects (Figure2(b)). Thus, topcoat material improvement is needed to reduce blob defect. The blob defect generation mechanism is explained as follows.

(b)

D-RCA [deg]

Blob Defect Count

(a)

Low

High

High

Low

Fluorine Content

D-RCA [deg]

Figure 2. (a) General relationship between hydrophobicity (D-RCA) and fluorine content of topcoat. (b) General relationship between blob defect and hydrophobicity (D-RCA)


Blob defect is not an immersion scanner related defect but development process related defect. The blob defect generation mechanism is shown in Figure 3. For wafer development, developer is applied to the wafer surface which dissolves topcoat polymers. Even with dynamic development, during which wafer is rotated, flow speed of developer at wafer proximity is actually very slow therefore the dissolved topcoat polymers nearly saturate the developer at wafer proximity region (Figure 3(a)). When the water rinse process starts, sudden pH change occurs which separates out topcoat polymers from developer (Figure 3(b)). When the final spin dry process starts, wafer surface starts drying up from the center and receding meniscus moves toward the wafer edge. During this period, if the resist surface was very hydrophobic, small rinse water droplets that contain topcoat polymers may be left behind which upon drying up can leave topcoat polymer residues on the wafer (Figure 3(c)). These are blob defects. Blob defect generation is related to solubility of topcoat in developer. Generally, better solubility in developer decreases blob defect.

(a)

(b)

Developer

(c)

Water rinse

Spin dry

Separated out polymer

Dissolved polymer

Blob

Figure 3. Blob defect generation mechanism. (a) Topcoat polymers dispersed into developer during development. (b) Topcoat polymers separate out from developer during water rinse step. (c) Small droplets remain and dry during spin dry step and cause blob defect.

3.2 Material improvement approach To overcome this challenge, JSR has developed a new technology. While conventional topcoat requires high fluorine content to increase hydrophobicity, newly developed TCX279 topcoat series offers high hydrophobicity even with low fluorine content compared to conventional topcoats (Figure4). 80

TCX279 series

78 D-RCA [deg]

76 74 72 70 68 66 64 62

Conventional Topcoats Low High Fluorine Atomic%/CarbonAtomic%

Figure 4. Hydrophobicity (D-RCA) vs fluorine content of topcoats. Newly developed topcoat with low fluorine content shows high hydrophobicity.


We have performed simple accelerated blob defect test of the newly developed TCX279 topcoat series. Accelerated test method is shown in Figure 5. Line and space patterns were exposed and the surrounding areas were unexposed. Then the wafers were developed and unexposed areas were inspected. The detailed test conditions are shown in Table 1. The obtained results are shown in Figure 6. While conventional topcoats show many blob defects with increasing hydrophobicity, newly developed TCX279 series shows less blob defect even with high hydrophobicity. Table1. Blob defect test condition

Exposure condition Exposure :S610C Pattern :45nmL90nmP Process condition Inspection Area

TRACK Substrate Resist FT PB/PEB Topcoat PAB Develop

:Lithius Pro-i :ARC66 (105nm, 205C60s)/ Bare-Si :Typical ArF Resist :100nm :100C60s/100C60s :TCX material :90C60s :TMAH 2.38wt%, -GP nozzle 4 times Rinse 15s (w/o PDR, ADR) Inspection condition

Exposed 45nmLS Un-exposed

1 shot

Figure 5. Accelerated blob defect test method. LS patterns are exposed and the surrounding unexposed areas are inspected.

Tool :KLA2810 Spectral Mode :Broadband-DUV Imaging Mode :High Performance Edge Contrast Pixel Size :0.230um Threshold :20 Coverage :100%

Blob Defect [A.U.]

100

10

Conventional Topcoats

1 TCX279 series 0.1 62 64 66 68 70 72 74 76 78 80 D-RCA [deg]

Figure 6. Blob Defect vs Hydrophobicity (D-RCA) of topcoats. Newlu developed topcoats with high hydrophobicity achieved low blob defect density.


Hydrophobic character of finalized new topcoat product, TCX279, is shown in Table2. Measurement methods are shown in Figure7.

Table2. Blob defect test condition

S-ACA S-RCA D-RCA 102

81

S-ACA Static Advancing Contact Angle

S-RCA Static Receding Contact Angle

77 Sliding angle

[deg]

Mimic immersion nozzle

D-RCA Dynamic Receding Contact Angle

Wafer Scan 250mm/s

Figure 7. Measurement method of S-ACA (static advancing contact angle),S-RCA (static receding contact angle) and DRCA (dynamic receding contact angle)

4. FURTHER DEFECT REDUCTION Defectivity is one of the important aspects of immersion lithography. For immersion defect test, S621D (Figure 8) which is the Nikon’s 4th generation immersion volume production scanner, was utilized. S621D is equipped with two important immersion key technologies, local fill nozzle (Figure 8) and tandem stage (Figure 10). They are further improved from S620D to reduce immersion defectivity. Inside the new nozzle, water flow was optimized for maximum particle discharge. Tandem stage design was improved to reduce particle stagnation generated from the wafer edge. The detailed defect test conditions are shown in Table 3. Exposure shot map is shown in Figure 9. For immersion defectivity analysis, a bright field defect inspection system (KLA-Tencor 2800) was used.

Figure 9. Improved local fill nozzle. Immersion water flow is optimized.

Projection Lens Water

Calibration Tool

Figure 8. Nikon’s 4th generation immersion volume production tool, S621D.

Exposure Stage

Calibration Stage

Figure 10. Improved advanced tandem stage design


Table 3. Defect test condition

Exposure condition Exposure : S621D Scan : 700mm/s (200WPH condition) Pattern : 100nm LS, binary, v-line, full field Process condition TRACK Substrate Resist Topcoat PEB Develop

:Lithius Pro-i : HMDS, AR26N (bevel 170um), : AIM6784 (EBR3mm), : bevel 150um : 95C/ 60sec : TMAH 2.38wt%, GP 10 sec + ADR w/o pre, post rinse

Inspection condition Tool :KLA2800 Mode : Array mode Sensitivity : 100% capture of 30nm defect Inspection area: 536.9 [cm2]

Figure 11. Exposure shot map

Defectivity test was performed at 700mm/s scan speed using several topcoats. The obtained defectivity data is shown in Figure 12. Immersion lithography tool (S621D) offered 5x defect reduction compared to S620D, thanks to the enhanced immersion nozzle and tandem stage performance. In addition to the improvement seen from S621D scanner, there is a general tendency in decreasing defect count with increasing hydrophobicity of topcoat. Hence, newly developed TCX279 topcoat achieved zero immersion defects in combination with S621D.

S 620D S 621D

12

0.025 0.020

9

0.015

Better

6

0.010

5x reduction 3

TCX279

TCX121

0 55

60

0.005

Defect Density [/cm2]

Immersion defect Count

15

0.000 65

70

75

80

D-RCA [deg] Figure 12. Defect vs Hydrophobicity of topcoats. 5x defect reduction by S621D. Newly developed TCX279 (high hydrophobic topcoat) shows zero immersion defect.


6. SUMMARY In this paper we described two technical breakthroughs: 1. TCX279 showed low blob defect with high hydrophobicity. 2. 5x defect reduction was realized by S621D In conclusion, the combination of Nikon’s next generation S621D scanner and JSR newly developed topcoat TCX279 series resulted in achieving zero immersion defects at last.

REFERENCES [1] D. Gill et al., “The Role of Evaporation in Defect Formation in Immersion Lithography”, Presentation at the 2nd International Symposium on Immersion Lithography, Sep. (2005) [2] S. Brandl et al., “Immersion Defect Studies on the 1150i α-tool”, Presentation at the 2nd International Symposium on Immersion Lithography, Sep. (2005) [3] U. Okoroanyanwu et al., “Prospects & challenges of defectivity in water immersion lithography”, Presentation at the 2nd International Symposium on Immersion Lithography, Sep. (2005)
