UV NIL mask making a nd imprint evaluationcnt.canon.com/wp-content/uploads/2014/11/PMJ-2008-DNP...The trench profile of the imprint masks was measured by an AFM as shown in Fig. 16

UV NIL mask making and imprint evaluation

Akiko Fujii, Yuko Sakai, Jun Mizuochi, Takaaki Hiraka, Satoshi Yusa, Koki Kuriyama, Masashi Sakaki, Takanori Sutou, Shiho Sasaki, Yasutaka Morikawa, Hiroshi Mohri,

and Naoya Hayashi Electronic Device Laboratory, Dai Nippon Printing Co., Ltd.

2-2-1 Fukuoka, Fujimino-shi, Saitama, 356-8507 Japan

ABSTRACT

UV NIL (nano-imprint lithography) shows excellent resolution capability with remarkable low line edge roughness, and has been attracting pioneers in the industry who were searching for the finest patterns. We have been focused on the resolution improvement in mask making, and with a 100keV acceleration voltage spot beam (SB) EB writer process, we reported down to hp(half pitch)18nm resolution in our previous papers1-3. In this paper, as a continuation of our previous works, we have achieved further resolution by optimizing the materials, processes, as well as the writing parameters of the EB writer. At the best resolved point on the template, resolutions down to hp 15nm dense line patterns were confirmed.

Now, UV NIL exploration seems to have reached the step of feasibility study for mass production and a full field mask is required, though the resolution demand is not as tough as for the extremely advanced usage. The 100keV SB EB writers have a fatally low throughput if we need full field writing.

We focused on the 50keV variable shaped beam (VSB) EB writers, which are used in current 4X photomask manufacturing. The 50keV VSB writers can generate full field pattern in a reasonable time, and by choosing the right patterning material and process, we could fabricate masks with hp32nm actual device-like pattern with an acceptable CD (critical dimension) uniformity.

We also studied the imprint capability of our masks, and both the hp32nm patterns made by the 50keV VSB writer and the hp22nm patterns made by the 100keV SB writer were well imprinted onto the wafer.

Keywords: NIL, EB pattern writer, spot beam, VSB, full field, imprint

1. INTRODUCTION NIL masks are 1X masks and require mask process with higher resolution compared to that of the 4X photomasks.

For the NIL mask pattern making, we evaluated two different process with 100keV SB EB writer and 50keV VSB EB writer.

The 100keV SB writer is for R&D purpose, and has high resolution capability. But it has a fatally low throughput for full field writing. On the other hand, the 50keV VSB writer is actually used in today’s advanced photomask manufacturing, and can write full field in a reasonable time. However, they are designed for 4X pattern generation and show relatively low resolution capability compared to the 100keV SB writer.

In this paper, we will show the high resolution pattern mask making with the 100keV SB EB writer, and full field pattern mask making with the 50keV VSB EB writer.

2. EXPERIMENTAL Fig. 1 shows our manufacturing process flow of imprint masks. A thin chrome film was coated between the EB

resist and the quartz substrate. The thin chrome enabled us to make the resist thickness thinner compared to the 4X photomask resists, and made the resolution remarkably finer. The thin chrome might also reduce charge up problem during EB writing, and decrease resist peeling caused by poor adhesion between resist and quartz.

Photomask and Next-Generation Lithography Mask Technology XV,edited by Toshiyuki Horiuchi, Proc. of SPIE Vol. 7028, 70281W, (2008)

0277-786X/08/$18 · doi: 10.1117/12.793073

Proc. of SPIE Vol. 7028 70281W-1

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In general, though the thicknesses are different, the processes are already used in current photomask manufacturing, for example in the manufacturing of alternating PSMs. Only the conditions and parameters are modified to achieve higher resolution.

Table 1 shows the experimental tools and materials. We used the “JBX9300” (JEOL) and “ELS-7000” (Elionix) as the 100keV SB writer. As the 50keV VSB EB writer, machines used in current 4X photomask manufacturing were used. A positive tone non-CAR (non-chemically amplified resist) was used as the resist material. For measurement tools, we used “LWM9000” (Vistec) CD-SEM, “LMS IPRO” (Vistec) image placement measurement tool, and “ULTRA” (Carl Zeiss) SEM. Imprint performance test was done by an “Imprio250” (Molecular Imprints Inc) tool.

3. RESULTS AND DISCUSSION 3.1 NIL mask resolution improvement with the 100keV SB EB writer

For the improvement of resolution on the imprint mask, we optimized the process parameters and conditions with the 100keV SB EB writer. Figs. 2 to 8 are pattern images on the imprint masks. Fig. 2 shows resolution results of the line and space resist pattern. Fig. 3 shows patterns of the line and space pattern after the quartz etch, where the thin chrome is left on the top (resist and quartz image). At our previous work3, we reported resolution down to hp18nm. But with further improvement, we confirmed resolution down to hp16nm. Fig. 4 is the resist and quartz images of dense hole patterns. These are the same as the achievements at the previous work, and resolution down to hp20nm was confirmed. Regarding dots, the resolution limit was hp26nm as shown in Fig. 5, and was the same as our previous work.

We also checked the proximity effect correction of the 100keV SB EB writer. Fig. 6 shows the center and corner of a 250 micron square filled area, both for line and spaces and dense holes. There is still room for improvement, and we can see difference of around 1.5nm. But for current phase of imprint mask development, we believe this is a good and acceptable result.

For further improvement of resolution, we are trying better exposure process and resist optimization. Fig. 7 shows the preliminary result of the line and space resist patterns, and we confirmed that hp15nm pattern was resolved. Fig. 8 is the resist and quartz image of the hp15nm pattern. This resolution is still for a very limited area, and we have to check the actual availability, but we can see that from this picture we will be able to supply hp15nm masks in near future.

Fig. 9 shows the writing time comparison between 100keV SB and 50keV VSB writer. Actual writing time estimation for a temporary hp32nm device pattern, with no OPC (optical proximity correction) pattern was done. The 50keV VSB EB writer used in this estimation was a writer designed for 65nm node manufacturing and 45nm node R&D. The 100keV SB EB writer needs more than 50 times of writing time compared to that of the 50keV VSB EB writer, and while an average 100keV SB writer will need about 1 month for full chip writing even without OPC, the 50keV will just need around 12hours. So, it is clear that the high resolution 100keV can not be used for mask manufacturing for actual device pattern, though they are good for R&D use.

3.2 NIL mask resolution improvement with 50keV VSB EB writer

Next, we checked the resolution capability of the 50keV VSB EB writer process. We optimized the materials and process condition, as we have learned through the 100keV SB EB writer process resolution improvement. Fig. 10 is the resist patterns of our achievements, and we can see that hp28nm line and spaces and hp32nm dense holes were well formed. Fig. 11 shows the pictures of the resist and quartz images. We can see that the resist patterns are well printed into the quartz plate. With the 50keV VSB EB writer, we could start actual device-like pattern writing for hp32nm, and Fig. 12 shows the result of an actual pattern with hp32nm.

3.3 NIL mask metrology results

Fig. 13 shows the CD uniformity of the 50keV SB and 100keV VSB process masks. For both process, a hp32nm dense line were measured. We can see that the 100keV SB process shows better uniformity of 1.2nm in 3 sigma, while the 50keV VSB process was 3.2nm in 3 sigma. The distribution of the 50keV VSB process shows a clear signature, which probably could be improved. But we can say that while the 50keV VSB process is close to its resolution limit, the



100keV SB process has still a margin in terms of resolution, and the 100keV could have potentially better capability for the uniformity.

Fig. 14 shows the edge roughness of the 50keV VSB mask and 100keV SB mask. Here again, the 100keV SB mask shows better result, and 50keV VSB mask shows 4.3nm 3sigma, while the 100keV SB mask gives 2.9nm 3sigma. At this moment we believe these numbers are acceptable for the imprint process development.

Fig. 15 shows the registration results. Both process masks show similar results, and the maximum error is about 4nm.

The trench profile of the imprint masks was measured by an AFM as shown in Fig. 16. An “Insight 3D” CD-AFM system (Veeco) was used. We can see that with the high density carbon tip “CDP15-150C”, the narrow spaces could be measured. But we can see that for 28nm and finer trenches, the measured depth were not uniform, which we think, judging from the SEM cross section, was a matter of metrology, not a matter of the profile. We can see that the CD-AFM metrology has a capability down to 32nm trench, and might have a possibility for finer dimension, with sharper tips. 3.4 Imprint pattern results

Figs. 17 and 18 show the imprinted wafer picture using the 50keV VSB process mask. As is shown in Fig. 17, hp32nm SRAM patterns were well printed onto the wafer. Fig. 18 shows the line edge roughness of the imprinted pattern. We should note that the edge roughness is about 1nm smaller than that on the mask.

Figs. 19 and 20 show the imprint results of the 100keV SB process mask. We can see that the hp22nm patterns were successfully formed on the wafer. Again, the edge roughness is around 1nm better than that on the mask.

4. SUMMARY

NIL mask process with a 100keV SB EB writer and 50keV VSB EB writer was evaluated. We confirmed that 100keV SB process was effective for R&D mask making with high resolution and 50kev VSB process was effective for full field mask making.

Resolution limit after improvement of the NIL mask manufacturing process for both process were shown. With the 100keV SB process we achieved hp16nm resolution for line and spaces, and promising preliminary results for further finer patterns. On the other hand, 50keV VSB process showed hp32nm resolution for line and spaces with acceptable writing speed.

In both process, CD uniformity, pattern roughness, and registration results were acceptable for NIL process development.

Imprint capability of our templates were also confirmed. 100keV SB process mask with patterns down to hp22nm, and 50keV VSB process mask with patterns down to hp32nm pattern were well imprinted.

ACKNOWLEDGEMENT

The authors would like to thank Molecular Imprints, Inc. for sharing imprint results. We also thank Sean Hand, Max Ho, Marc Osborn (Veeco Instruments Inc.), and DNP members involved in this work, including the Electronic Materials Research Department members.

REFERENCES

1. S. Yusa, T. Hiraka, A. Kobiki, S. Sasaki, K. Itoh, N. Toyama, H. Mohri, and N. Hayashi, “Progress of NIL template making”, Proceeding of SPIE vol 6607, pp. 66073H ,2007 2. T. Hiraka, S. Yusa, A. Fujii, S. Sasaki, K. Itoh, N. Toyama, M. Kurihara, H. Mohri, N. Hayashi" UV-NIL template for the 22nm node and beyond ", Proceeding of SPIE, vol.6730, 67305P , 2007, to be printed 3. S. Yusa, T. Hiraka, J. Mizuochi, A. Fujii, Y. Sakai, K. Kuriyama, M. Sakaki, S. Sasaki, Y. Morikawa, H. Mohri, and N. Hayashi, “Progress of NIL template making”, Proc. of SPIE, Vol.6792, 2008, to be printed.



Fig. 1 Nano-imprint mask process flow

Table1 tools and materials

Fig. 2 Resist resolution images with 100keV EB writer (Dense line)

Quartz template !!

Quartz

Electron beamResistChrome

Exposure Development Chrome etching

Quartz etching Chrome strippingResist stripping

Quartz template !!

Quartz

Electron beamResistChrome

Exposure Development Chrome etching

Quartz etching Chrome strippingResist stripping

Exposure tool 100keV spot beam EB writer (JBX9300, ELS-7000) 50keV VSB EB writer (4X photomask manufacturing tool)

Resist materials Non CAR (Positive tone)Measurements tool CD-SEM (LWM9000)

Image placement measurement (LMS IPRO) Cross section-SEM (Ultra)

Imprint tool Imprio 250

hp32nm hp24nm hp22nm hp20nm hp18nm hp16nm

Resist images (top view)

Resist images (cross sectional view)

Magnification: 150k




Magnification: 150k



Fig. 3 Quartz resolution images with 100keV EB writer (Dense line)

Fig. 4 Resolution images with 100keV EB writer (Hole)

hp32nm hp24nmhp28nm hp22nm hp20nm

Resist images

Chrome images after quartz etching

Cross sectional images

Magnification: 150k

hp32nm hp24nmhp28nm hp22nm hp20nmhp32nm hp24nmhp28nm hp22nm hp20nm

Resist images



Magnification: 150k



Quartz images (cross sectional view)

Magnification: 150k

hp32nm hp24nm hp22nm hp20nm hp18nm hp16nmhp32nm hp24nm hp22nm hp20nm hp18nm hp16nm


Quartz images (cross sectional view)

Magnification: 150k



Fig. 5 Resolution images with 100keV EB writer (Dot)

Fig. 6 250um square pattern images with 100keV EB writer

hp26nmhp32nmhp24nmhp32nm




19.8nm29.4nm 34.7nm 25.2nm

21.0nm30.7nm 36.1nm 26.3nm

*SEM Measurement CD

Magnification: 150k

center

corner

Dense line Hole


Resist images



Magnification: 150k


Resist images



Magnification: 150k



Fig. 7 Next trial Exposure condition and resist optimization

Fig. 8 hp 15nm Dense line

Fig. 9 EB writing time calculation

0

10

20

30

40

50

60

50keVVSB

100keVSpot Beam

100kev SB: 1month

50keV VSB: 12h

・Condition Writing data for positive resist(non CAR)

・Temporary hp32nm full field chip

Data area: 33 x 26mm

1

52

0

10

20

30

40

50

60

50keVVSB

100keVSpot Beam

100kev SB: 1month

50keV VSB: 12h

・Condition Writing data for positive resist(non CAR)

・Temporary hp32nm full field chip

Data area: 33 x 26mm

1

52

hp16nm hp15nm hp14nm hp13nm



Magnification: 300k

hp16nm hp15nm hp14nm hp13nmhp16nm hp15nm hp14nm hp13nm



Magnification: 300k

hp15nm

Magnification: 300k

Chrome images after quartz etching (top)

hp15nm

Magnification: 300k

Chrome images after quartz etching (top)



Fig. 10 Resist resolution images with 50keV EB writer

Fig. 11 Quartz resolution images with 50keV EB writer


Resist images (Dense line)

Resist images (Hole)

Magnification: 150k


Resist images (Dense line)

Resist images (Hole)

Magnification: 150k


Chrome images after quartz etching (Dense line)

Chrome images after quartz etching (Hole)

Magnification: 150k


Chrome images after quartz etching (Dense line)

Chrome images after quartz etching (Hole)

Magnification: 150k



Fig. 12 Quartz pattern images with 50keV EB writer

Fig. 13 CD uniformity results

hp44nm hp36nmhp40nm hp32nm

SRAM patternMagnification: 75k

hp44nm hp36nmhp40nm hp32nmhp44nm hp36nmhp40nm hp32nm

SRAM patternMagnification: 75k

Area 30X24mm (6X5 arrays)hp 32 nm dense line


Average : 27.5 nmRange : 5.0 nm

3σ : 3.2 nm

50keV 100keV


3σ : 1.2 nm




3σ : 3.2 nm

50keV 100keV


3σ : 1.2 nm



Fig. 14 LER results

Fig. 15 Registration results

50keV 100keV

CD : 30.2 nmLER 3σ : 4.3 nm

CD : 32.8 nmLER 3σ : 2.9 nm

Magnification: 150k

* Average : 10 linesBox length : 700nm

50keV 100keV

CD : 30.2 nmLER 3σ : 4.3 nm

CD : 32.8 nmLER 3σ : 2.9 nm

Magnification: 150k

* Average : 10 linesBox length : 700nm

X Y 3σ : 6.0 nm 6.0 nm

Min : -4.0 nm -4.0 nmMax : 3.0 nm 4.0 nm



50keV 100keV

-20 -15 -10 -5 0 5 10 15 20

[mm]15

10

5

0

-15

-10

-5

X Y 3σ : 6.0 nm 6.0 nm

Min : -2.0 nm -3.0 nmMax : 4.0 nm 4.0 nm

15

10

5

0

-15

-10

-5

-20 -15 -10 -5 0 5 10 15

[mm]

[mm] [mm]

X Y 3σ : 6.0 nm 6.0 nm

Min : -4.0 nm -4.0 nmMax : 3.0 nm 4.0 nm



50keV 100keV

-20 -15 -10 -5 0 5 10 15 20

[mm]15

10

5

0

-15

-10

-5

X Y 3σ : 6.0 nm 6.0 nm

Min : -2.0 nm -3.0 nmMax : 4.0 nm 4.0 nm

15

10

5

0

-15

-10

-5

-20 -15 -10 -5 0 5 10 15

[mm]

[mm]

15

10

5

0

-15

-10

-5

-20 -15 -10 -5 0 5 10 15

[mm]

[mm] [mm]



Fig. 16 AFM measurements trial

Fig. 17 Imprint results using by 50keV template

Space 31.9nm

Tool：InSight 3DAFM ((Veeco Instruments Inc.)Measurement mode ：Enhanced DT mode

AFM profileSEM profile

CDP15-150CHigh density Carbon

Space 27.3nm

Space 21.9nm

hp32nm

hp28nm

hp24nm

*SEM Measurement CD

Space 31.9nm




Space 27.3nm

Space 21.9nm

hp32nm

hp28nm

hp24nm

Space 31.9nm





Space 27.3nm

Space 21.9nm

hp32nm

hp28nm

hp24nm

*SEM Measurement CD

32nm 35nm

SRAM pattern

32nm 35nm

SRAM pattern



Fig. 18 Imprint LER measurements using by 50keV template



[nm]

Parameter meanstandarddeviation

Line width 33.20 1.70LWR 3σ 3.02 0.74Pitch 66.93 2.37LER 3σ 2.26 0.40



32nm 35nm

[nm][nm]





32nm 35nm

[nm]

Hp22nm LS and pillar pattern

[nm]





32nm 22nm

[nm]





32nm 22nm



Documents

UV NIL mask making a nd imprint evaluationcnt.canon.com/wp-content/uploads/2014/11/PMJ-2008-DNP...The trench profile of the imprint masks was measured by an AFM as shown in Fig. 16