Self-Aligned Triple Patterning to Extend
Optical Lithography for 1x Patterning
Yijian Chen*, Ping Xu, Yongmei Chen, Liyan
Miao, Xumou Xu, Chris Bencher, Chris Ngai
*Email: [email protected]
Maydan Technology Center Group (MTCG)
Applied Materials, Inc.
International Symposium on Lithography Extensions
10/21/2010
Public Presentation
Outline
§ Self-aligned triple patterning as an evolutionary
enhancement to double patterning
§ SATP material consideration
§ Preliminary results of SATP development
- 21nm and 16nm lines/spaces
§ SATP challenges and potential solutions
§ Summary and future work
2
Public Presentation
§ Self-aligned triple patterning as an evolutionary
enhancement to double patterning
§ SATP material consideration
§ Preliminary results of SATP development
- 21nm and 16nm lines/spaces
§ SATP challenges and potential solutions
§ Summary and future work
Public Presentation
Looking Backward: Negative and Positive Tone
SADP Processes for HP 37-20 nm
ü Variable line width
X Only one space
X Only one line width
ü Variable space
§ Two different design rules and restrictions
§ Both schemes co-existed in NAND flash manufacturing
4
Public Presentation
Looking Forward: Should We Keep or Remove Cores
for HP 19-13 nm?
37-20 nm
19-13 nm
In post-SADP era (19-13nm), self-aligned multiple patterning (SAMP)
will be needed for NAND flash, will the dual-track (keep & remove core)
scenario remain the same for SAMP?
Public Presentation
Motivations for Self-Aligned Triple Patterning
Nitride (300 A)
Resist
APF core
BARC
APF (880 A)
APF (880 A)
Substrate
(1)
Nitride
(4)
(3)
(2)
Nitride Spacer
(5)
Oxide Spacer
Two Motivations:
1. Increase density
(double à triple)
2. Different design
rules/restrictions.
(6)
Wet Strip Nitride
(7)
(8)
: APF
: Nitride
: Oxide
Example:
NAND 32-string with select lines
§ Ground select & string select by mandrel (wide)
§ 32-line array is mix of spacers and mandrels
ü Keep both mandrels (cores) and (2nd) spacers
ü Variable line width
ü Variable space
Public Presentation
Self-Aligned Quadruple Patterning (SAQP) Limitations
Film Stack
(1)
Quadruple
Patterning
Process 1
Litho/Spacer
(2)
Spacer & Core
(3) & (4)
Final Structure
(5)
APF 70 nm
Ox 30 nm
APF 70 nm
Poly 60 nm
Si
Quadruple
Patterning
Process 2
APF 110 nm
HTO 30 nm
Poly 60 nm
Si
X Only one line width
ü Variable space
3 Masks/critical layer :
(1) core mask (2) cut mask (3) pad & peripheral mask
Unlike spacer double patterning, SAQP does not even allow a “dual-track” (keep
& remove core) scenario, it still can not do the NAND string with one mask.
7
Public Presentation
SATP Reduces Number of Masks
APF core
Nitride Spacer
(3)
Oxide Spacer
(5)
Wet Strip Nitride
(7)
(6)
(3) Core mask
(5) 1st spacer
(6) 2nd spacer
: APF
: Nitride
: Oxide
(7-a) 1st spacer etch (wet)
(7-b) Cutting mask and etch
SATP process keeps the core patterns, thus allowing less masks
and more flexible design.
Public Presentation
§ Self-aligned triple patterning as an evolutionary
enhancement to double patterning
§ SATP material consideration
§ Preliminary results of SATP development
- 21nm and 16nm lines/spaces
§ SATP challenges and potential solutions
§ Summary and future work
Public Presentation
Many Different SATP Material Combinations
SATP
First
Candidate
Other
Candidates
SATP
Core / Spacer1 / Spacer2
Core/Mandrel
Poly Si
APF/ Oxide
Scheme 1
Poly Si / Nitride / Poly Si
1 Spacer
nitride
Oxide/ Poly Si
Scheme 2
Poly Si / Nitride / Oxide
Hard-stop Layer
oxide
TBD
Scheme 3
APF / Poly Si / Oxide
Poly Si
oxide
Scheme 4
APF / Nitride / Oxide
st
2
nd
spacer
Application example: use poly Si spacers as the hard mask to
etch oxide for NAND flash STI patterning.
§ Post-etch profile of core lines.
§ Etch (wet/dry) selectivity when strip 1st (sacrificial) spacer.
§ Stress minimization to reduce line bending.
§ A relevant hard-stop layer is available.
§ Satisfactory final structures for continuous integration.
SATP process flows with different film combinations can be used as
hard mask for many different applications.
Public Presentation
§ Self-aligned triple patterning as an evolutionary
enhancement to double patterning
§ SATP material consideration
§ Preliminary results of SATP development
- 21nm and 16nm lines/spaces
§ SATP challenges and potential solutions
§ Summary and future work
Public Presentation
SATP Process Development Using Dry Litho
APF Core
Oxide
Nitride
§ SEM top views at different process steps:
• Core Patterning
(HP: 6x nm)
• Nitride dep
• Nitride spacer
21nm L/S
Public Presentation
• Oxide spacer
• Wet etch nitride
(HP: 2x nm)
SATP Process Development Using Immersion Litho
Poly Core
Poly
Nitride
§ SEM top views at different process steps:
• Core Patterning
(HP: 4x nm)
• Nitride dep
• Nitride spacer
16 nm L/S
Public Presentation
• Poly spacer
• Wet etch nitride
(HP: 1x nm)
§ Self-aligned triple patterning as an evolutionary
enhancement to double patterning
§ SATP material consideration
§ Preliminary results of SATP development
- 21nm and 16nm lines/spaces
§ SATP challenges and potential solutions
§ Summary and future work
Public Presentation
Challenges and Potential Solutions
(1) Problem: poly core footing & sidewall of the 2nd spacers NOT vertical.
Possible solution: CMP may be used to polish off rounding corner of
core & 1st-spacers (at the price of extra trench-fill & etch-back steps).
Poly Si
mandrel
2nd spacer (poly)
(2) Problem: LWR of poly Si core is NOT satisfactory.
Possible solution: other core & hard-mask materials may be considered.
APF
mandrel
LWR
good
Mandrel
(APF)
Poly
mandrel
LWR
poor
Spacer
(Oxide)
Mandrel
(Poly)
Public Presentation
Spacer
(Poly)
Investigation of Core Line LWR Issue
Resist (90nm pitch) core line CD/3σ : 33.0/1.3nm
→ Post BARC open line CD/3σ : 24.9/2.6nm
→ Post plasma treatment line CD/3σ: 14.4/2.0nm (LWR: 3.2nm)
Final resist/BARC
Top
Final resist/BARC
Center
Final resist/BARC
Left
It remains a challenge to keep low LWR when we etch core lines
from resist/BARC to substrate.
Public Presentation
Further Optimization of Mandrel Etch Needed
MTC
MTC
10 nm lines
16 nm lines
§ In our first try, we were not able to keep low LWR when
etching mandrel lines from resist/BARC to substrate.
§ Our industry’s small-line patterning capability (e.g., FinFET)
is quite mature, and we just need to implant it into SATP.
§ Mandrel etching should not remain a bottle-neck of SATP
process.
Public Presentation
§ Self-aligned triple patterning as an evolutionary
enhancement to double patterning
§ SATP material consideration
§ Preliminary results of SATP development
- 21nm and 16nm lines/spaces
§ SATP challenges and potential solutions
§ Summary and future work
Public Presentation
Summary and Future Work
§ Self-aligned triple patterning (SATP) to extend optical
lithography for 1x patterning is proposed.
§ 21 nm and 16 nm HP lines/spaces based on dry and
immersion litho are demonstrated, while LWR of core lines
remains a challenge.
§ By keeping the core/mandrel lines, 2-mask SATP process
may pattern dense lines/spaces with pads and peripheral
circuits for each critical layer.
§ Potential solutions to overcome the technical barriers of
SATP process are identified for future research.
§ Stay tuned for a whole packet of various SATP & SAQP
process schemes and results in SPIE 11.
Public Presentation
Acknowledgement
§ We would like to thank MTCG operation
team for process support.
§ Sincere thanks go to Raymond Hung for
valuable discussion and revision of this
presentation, and Bingxi Wood for providing
the SEM pictures showing our small-line
etching capability.
§ We appreciate your time and interest in this
project.
Public Presentation