Experiments and Results for CMP v.s. Etching Interaction of ET2 lot

Chapter 3 Experiments and Results

3.3 Etching Experiments and Results

3.4.2 Experiments and Results for CMP v.s. Etching Interaction of ET2 lot

In order to prove above assumption, we prepare some wafers with different combination of W-CMP and oxide touch-up CMP rotary direction and then implement Contact-1 etching in

either ET1 or ET2 with over etching recipe or without over-etching recipe to check the effects induced by CMP rotary direction and over etching on overlay control. The detail spilt table is listed in Table 3-8 and the result is shown in Fig 3-14.

The wafer rotation baseline for this experiment is as follows：

1. The wafer rotation baseline for slot 1 and slot 6 are very similar. It means that ET1 wafers is not sensitive to CMP rotary direction. It matches with the previous result that before we implement ET2 etcher for Contact-1 etching in production line.

2. The wafer rotation baseline for slot 4,5,9, and 10 are very close to slot 1 and slot6. It means that ET2 wafers with over etching show deeper alignment mark depth, therefore, not sensitive to CMP rotary direction.

3. ET2 wafers without over etching are very sensitive to CMP rotary direction. The wafer rotation baseline for slot2/3 and slot 7/8 are similar to results from spilt 1 and split 3 in

pervious W-CMP and oxide touch-up CMP rotary direction experiment.

The experimental results have proved the assumption that Contact-1 etching step dominates the poor overlay performance. If the alignment mark is not deep enough, CMP rotary direction will enhance the overlay baseline variation and induce a worse result.

18 -Chapter 4

Conclusion and Discussion

4.1 Conclusion of Experiments:

In this thesis, we discuss the CMP and the etching conditions induced lithography overlay error. Some important conclusions are summarized as follows

(a) Alignment mark depth is the most important factor influencing the overlay error. If the alignment mark depth is too shallow, the scanner alignment system either can not detect enough signal and then induce the alignment fail, or the alignment result can not well correspond to the wafer deformation and then make the overlay baseline variation too big.

(b) CMP process also plays an important role in overlay control. Especially in the condition of alignment mark not deep enough, the CMP rotary direction significantly influences the overlay baseline variation.

(c) In the condition of shallow alignment mark depth, scanner alignment system induced performance difference will become significant.

4.2 The discussion for alignment and overlay strategy:

In general, we separate the factors influence the alignment accuracy and the overlay error performance into 2 parts：

(A) Wafer Process：Including all wafer process that may influence the mark shape. Film deposition thickness, etching time, and CMP polish time, all possibly influence the step height of alignment mark. CMP rotary direction, erosions and dishing effect, etching uniformity, film deposition uniformity all possibly influence the alignment mark deformation and asymmetry.

In this study, we increase the etching time and fix the CMP rotary direction to improve the overlay error performance. But in some cases, the optimal process condition for alignment

mark may not be suitable for the features at circuit areas. Most common case is the alignment mark depth being too shallow. Therefore, it is necessary to coat photoresist to protect circuit area and use additional lithography and etching step to increase the alignment mark depth.

(B) Exposure tool alignment system and alignment mark：The hardware of exposure tool alignment system and the algorithm influence the alignment sensitivity of different alignment mark designs, and also the alignment mark step height and the deformation by wafer process affect the alignment sensitivity. The strategies are developed in lithography alignment technology to reduce the effect induced by wafer process and alignment mark in alignment sensitivity.

It includes

--- To use different wavelength for alignment light source.

--- To capture more high order alignment signal [2][12].

--- To optimize the algorithm to enhance the signal strength or the signal to noise ratio [9].

--- To optimize the algorithm to correlate the asymmetry signal [10][11].

In addition, the different type and the different dimension of alignment mark have different correlation with alignment algorithm. To evaluate a suitable alignment mark and algorithm combination is very important for better overlay control.

In advanced IC fabrication, lithography is no longer the only factor resulting in the misalignment, Wafer process optimizations and alignment system improvement both important for good overlay control.

20 -Reference

[01] C.P. Alex Chen, Brain Huang, Wilson Lee, W.J. Chung, T.K. Hou, “Chemical Mechanical Planarization Process Induced Within Lot Overlay Variation in 0.2um DRAM: Solution and Simulation Model”, SPIE Vol. 4344, pp 89-97, 2001.

[02] Yuanting Cui, Albert So, Sean Louks, “Fine Tune W-CMP Process with Alignment Mark Selection for Optimal Metal Layer Overlay and Yield Benefits”, SPIE Vol. 5375, pp827-838, 2004.

[03] Igor Jekauc, Bill Roberts, Paul Young, Paul Jowett, Reuben Ferguson, Sean Louks,

“Necessary Non-zero Lithography Overlay Correctables for Improved Device Performance for 110nm Generation and Lower Geometries”, SPIE Vol. 5378, pp228-236, 2004.

[04] Christopher J. Gould, Yuanting Cui, Sean Louks ,“Advanced process control applied to metal layer overlay process”, SPIE Vol. 5378, pp28-37, 2004.

[05] Chun-Yen Huang, Boris Habets, Hans-Georg Froehlich, “Alignment improvement for sub 70nm DRAM technology”, 2^nd NTC Technical Paper Collection, pp 59-62, 2004.

[06] Ai-Yi Lee, Chun-Yen Huang, Chung-Hsin Lin, “Improvement of Overlay Control on Metal Layer”, 2^nd NTC Technical Paper Collection, pp73-76, 2004.

[07] Chi-Long Chung, Hsu-Cheng Fan, “The Investigation of Wafer Bow for sub-0.09um DRAM Technology in 300mm Fab”, 2^nd NTC Technical Paper Collection, pp260-264, 2004.

[08] Hong Xiao, “Introduction to Semiconductor Manufacturing Technology”,pp505-544, 2001.

[09] Tadashi Nagayama, Shinichi Nakajima, Ayako Sugaya, Yuho Kanaya, Ayako Sukegawa

“New Method to Reduce Alignment Error Caused by Optical System”, SPIE Vol. 5038,

pp849-860, 2003.

[10] Ayako Sugaya, Yuho Kanaya, Shinishi Nakajima, Tadashi Nagayama, Naomasa Shiraishi

“Innovative Optical Alignment Technique for CMP Wafers ”, SPIE Vol. 4691, pp959-970, 2002.

[11] Shinishi Nakajima, Yuho Kanaya, Akira Takahashi, Shinishi, Koji Yoshida, Hideo Mizutani, “Improving the Measurement Algorithm for Alignment ”, SPIE Vol. 4344, pp572-582, 2001.

[12] Jeroen Huijbregtes, Richard van Harren, Andre Jeunink, Paul Hinnen, Bart Swinnen, Ramon Navarro, Geert Simons, Frank van Bilsen, Hoite Tolsma, Henry Megens

“Overlay Performance with Advanced ATHENA Alignment Strategies”, SPIE Vol.

5038, pp918-928, 2003.

[13] Hideki. Ina, Takahiro Matsumoto, Koichi Sentoku, Katsuhiro Matsuyama, Kazuhiko Katagiri, “New criterion about the topography of W-CMP wafer’s alignment mark”, SPIE Vol. 5038, pp445-452, 2003.

[14] Koichi Sentoku, Takahiro Matsumoto and Hideki Ina, “Novel Strategy for Wafer Induced Shift(WIS)”, SPIE Vol. 4691, pp981-989, 2002.

Process Flow from Contact-1 to Metal-1 lithography 0. Pre Contact-1 process

1. Contact-1 SiON / Oxide Deposition 2. Contact-1 Lithography

3. Contact-1 Etching

4. Contact-1 TiN Deposition 5. Contact-1 W Deposition 6. Contact-1 W-CMP

7. Contact-1 Oxide Touch-up CMP 8. Metal-1 Deposition

9. Metal-1 DARC Deposition 10. Metal-1 Lithography

Table 2-1 Process Flow from Contact-1 to Metal-1 lithography

Table 3-1 W-CMP and oxide touch-up CMP rotary experiment spilt table

22

-Table 3-2 W-CMP over polish experiment spilt table

Table 3-3 Oxide touch-up CMP over polish experiment spilt table

Lot Count

C1 Etching Tool CMP unify Rotation M1 Litho Tool

Mean 3-Sigma Mean 3-Sigma Mean 3-Sigma

- 0.024 0.010 0.026 0.012 0.026 0.21 79

Yes 0.026 0.009 0.026 0.011 0.076 0.11 420

- 0.026 0.009 0.025 0.011 -0.055 0.17 197

Yes 0.025 0.012 0.025 0.014 -0.044 0.11 351

- 0.039 0.033 0.041 0.039 0.203 1.05 21

Yes 0.032 0.023 0.035 0.026 0.567 0.59 45

- 0.032 0.022 0.032 0.028 0.078 0.57 79

Yes 0.027 0.016 0.028 0.019 0.237 0.20 61

ET1

PH1 PH2

ET2

PH1 PH2

Vintage/Overlay

Overlay X-3S Overlay Y-3S Wafer Rotation Baseline

Table 3-4 overlay performance by vintage summary table-1

24

-C1 etching tool Condition/Slot #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 #15 #16 #17 #18 #19 #20 #21 #22 #23 #24 #25

ET1 POR

Step1:80 Step2:30 Step1:85 Step2:15 ET2

Step1:90 Step2: 0

Table 3-5 C1 over etching experiment spilt table-Lot1

C1 etching tool Condition/Slot #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 #15 #16 #17 #18 #19 #20 #21 #22 #23 #24 #25

ET1 POR

Step1:80 Step2:30 Step1:85 Step2:15 ET2

Step1:90 Step2: 0

Table 3-6 C1 over etching experiment spilt table-Lot2

Lot Count

C1 Etching Tool CMP unify Rotation M1 Litho Tool

Mean 3-Sigma Mean 3-Sigma Mean 3-Sigma

- 0.024 0.010 0.026 0.012 0.026 0.21 79

Yes 0.026 0.011 0.027 0.014 0.080 0.11 801

- 0.026 0.009 0.025 0.011 -0.055 0.17 197

Yes 0.024 0.011 0.026 0.013 -0.039 0.12 780

- 0.039 0.033 0.041 0.039 0.203 1.05 21

Yes 0.032 0.023 0.035 0.026 0.567 0.59 45

- 0.032 0.022 0.032 0.028 0.078 0.57 79

Yes 0.027 0.016 0.028 0.019 0.237 0.20 61

Yes PH1 0.025 0.013 0.026 0.013 0.095 0.14 20

Yes PH2 0.023 0.010 0.027 0.011 0.045 0.13 84

ET1

Vintage/Overlay

Overlay X-3S Overlay Y-3S Wafer Rotation Baseline

Table 3-7 overlay performance by vintage summary table-2

Table 3-8 CMP rotary direction v.s. etching interaction on overlay baseline wafer rotation experiment spilt table

Figure 2-1 Schematic of overlay offset linear items

26

-Figure 2-2 Schematic of a CMP system

Figure 2-3 Schematic of erosion and dishing effect after W-CMP

Key Components of Nikon Scanner System (1) Illumination System

28

-Figure 2-4 Schematic of Nikon Scanner System (2) Reticle Alignment System (3) Reticle

(4) Reticle Stage (5) Projection Lens

(6) Wafer alignment System ‘FIA’

(7) Wafer (8) Wafer Stage

Light travels through (a) Lamp Unit (b) Optical Fiber and (c) Illumination Optics, falling on (d) Half Prism. The Half Prism reflects the light onto the wafer through (e) the Objective Lens, illuminating (f) the Alignment Mark on the wafer. The Alignment Mark thus illuminated is captured by (i) the CCD’ Cameras through (g) the FIA Microscope. The CCD’ Camera then transmits electronically this image signal to (j) the Image Processing Unit (IPU). The IPU automatically measured the image position on the CCD which ultimately is the wafer alignment position

Figure 2-5 Schematic of FIA Alignment System

Figure 2-6 Metal-1 Overlay X/Y 3 Sigma and wafer rotation baseline on ET1 and ET2

Figure 3-1 the wafer rotation baseline result of W-CMP and touch-up CMP experiment

30

-Figure 3-2 the wafer rotation baseline result summary of W-CMP and touch-up CMP experiment

1 2

Figure 3-3 Schematic of CMP system with two polish head

Wafer Rotation Baseline vs. W-CMP over plish experiment

OP 15sec(POR) OP 11sec OP 23sec

Figure 3-4 W-CMP Over-polish experiment result

32

-W a fe r R ot a t i on B a se l i ne vs. oxi de t ouc h-up C MP ove r pol i sh

W02 W03 W04 W05 W06 W07 W08 W09 W10 W11 W12 W13 W14 W15 W16 W17 W18 W19 W20 W21 W22 W23 W24 W25

Wafer

Wafer Rotation Baseline [urad]

OP 350A(POR) OP 230A OP 480A

W a fe r S c a l ing X B a se l ine vs. Oxide Touc h-up C MP ove r pol ish

W02 W03 W04 W05 W06 W07 W08 W09 W10 W11 W12 W13 W14 W15 W16 W17 W18 W19 W20 W21 W22 W23 W24 W25

Wafer

Wafer Scaling X Baseline [ppm]

OP 350A(POR) OP 230A OP 480A

W a fe r S c a ling Y B a se l ine vs. Oxi de Touc h-up C MP ove r pol ish

W02 W03 W04 W05 W06 W07 W08 W09 W10 W11 W12 W13 W14 W15 W16 W17 W18 W19 W20 W21 W22 W23 W24 W25

Wafer

Wafer Scaling Y Baseline [ppm]

OP 350A(POR) OP 230A OP 480A

Figure 3-5 oxide touch-up CMP over polish experiment result

Unify the CMP rotary direction

Figure 3-6 overlay X/Y 3 sigma and overlay baseline wafer rotation before and after unify the CMP rotary direction

34 -Unify the CMP rotary direction

Unify the CMP rotary direction

Figure 3-7 Overlay X/Y 3 Sigma and Overlay baseline wafer rotation, before and after unify the CMP rotary direction, by tool and condition vintage

(Alignment mark cross section SEM by ET1 etcher)

(Alignment mark cross section SEM by ET2 etcher)

Figure 3-8 Alignment mark cross section SEM comparison on ET1 and ET2 etchers

36

-FIA alignment signal of alignment mark 1 by ET2

FIA alignment signal of alignment mark 1 by ET1

Figure 3-9 FIA alignment signal of alignment mark 1 comparison on ET1 and ET2 etchers

FIA alignment signal of alignment mark 2 by ET2

FIA alignment signal of alignment mark 1 by ET1

Figure 3-10 FIA alignment signal of alignment mark 2 comparison on ET1 and ET2 etchers