Thermal oxidation of Si and oxide thickness measurement

半導體專題實驗 實驗四 氧化層之成長與厚度量測 Thermal oxidation of Si and oxide thickness measurement 1

Oxidation in Semiconductor A Typical MOS Profile Screen Oxide (for imp. ), Pad Oxide(buffer oxide, protect active areas) 3 Barrier Oxide, LOCal Oxidation of Silicon

Pad Oxide Bird’s beak effect 4

Channeling 5

J. F. Ziegler, and R. F. Lever Appl. Phys. Lett. 46, 358 (1985); 6

Kevin M. Klein et al. , J. Electrochem. Soc. , Vol. 138, No. 7, July 1991 7

Color chart of Si. O 2: 12

熱成長氧化層的機制與模型(II) No Ni o Model: n Ficker’s Law: J=D(No-Ni)/Xo Si. O 2 n Reaction rate: J=Ks*Ni Si J=D*No/(D/Ks+Xo) n d. Xo/dt = J/M =(D*No/M) / (Xo+D/Ns) o A=2 D/Ks , B=2 D*No/M o = Xi 2/B + A*Xi/ B n n Xi為一開始氧化層的厚度 X 0可以看成 Xo(t)=B/A (1+ ) 當經過一段長時間後, Xo(t)=(Bt) 1/2 15 Deal－Grove Model

Deal－Grove Model X 2＋A*X＝B*（t＋τ） 當t很短時，X很薄，X 2＜＜A*X，上式趨近 為 A*X＝B*（t＋τ）/A 此時稱為linear growth regime 或linear rate regime B/A稱為Linear rate Constant，受控於K（反應速率） 17

Deal－Grove Model X 2＋A*X＝B*（t＋τ） 當t很長時，X變厚，X 2＞＞A*X，上式趨近為 X 2＝B*（t＋τ） 此時稱為diffusion-limited regime 或parabolic rate regime B稱為Parabolic rate Constant，受控於D （oxidant在Si. O 2內之擴散速率） 18

DRY & WET 21

B=C 1*exp(-E 1/k. T) B/A=C 2*exp(-E 2/k. T) Dry C 1 =7. 72 x 102 mm 2 hr-1 E 1 =1. 23 e. V C 2 =6. 23 x 106 mmhr-1 E 2 =2 e. V Wet C 1 =2. 14 x 102 mm 2 hr-1 E 1 =0. 71 e. V C 2 =8. 95 x 107 mmhr-1 E 2 =2. 05 e. V 22

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Molecular density � (100): � (111): � Thus here the molecular density is (110) > (111) > (100) 24

Distance between layers � (100): � (111): � Hence the distance between two layers: (110) > (111) > (100) � Thus if the oxidation rate on each plane, concerning the molecular density, is not the dominant factor, the rate of thickening the oxide should be fastest for plane (110). 25

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Dry oxidation E. A. Irene et al. , Journal of The Electrochemical Society, 133 (6), (1986) Initially, (110) > (111) > (100). Eventually, (111) > (110) > (100). 27

Wet oxidation o Atmospheric pressure, wet oxidation, ~785 degrees Celsius o Initially, (110) > (111) > (100). Eventually, (111) > (110) > (100). 28

Intrinsic Si. O 2 Film Stress Measurements on Thermally Oxidized Si E. Kobeda and E. A. Irene, J. Vac. Sci. Technol. B, 5, 15 ~1987. 29

橢圓儀(ellipsometer) 35

表面軌跡分析儀(SPM)示意圖 Scanning Probe Microscope 39

數據處理 1. Find and compare the oxide thickness from the following methods 1. Table 2. Deal-Grove Model 3. Color chart (optical) 4. Ellipsometer (optical) 5. C-V (electrical) 2. Find VFB 3. Find Qox 4. Find Na, Nd 跟過去實驗的濃度做比較 45

結報問題 1. Check out RTA/RTO (Rapid Thermal Annealing/Oxidation). What heating mechanisms are used? What are the applications. Is it possible to achieve rapid cooling? 2. Look up for SOI (Silicon on insulator), how are they fabricated? What are the applications? 3. Look up for the concept of “thermal budget”. What are the critical issues that cause the lowering of thermal budget. 4. What is the highest possible resolution of ellipsometers? 5. Check out about the XRD diffraction technique, what is their difference with ellipsometry? Discuss their working mechanisms, applications, limitations, and advantages. 6. Check out about AFM. Discuss their working mechanisms, applications, limitations, and advantages. 7. Check out about High-K technology, what is it about? what part of the electronic device is it used for? How could it improve the IC performance? 8. Look up for possible mechanisms for gate oxide leakage (Hint: direct tunneling, trap assisted tunneling, Fowler-Nordheim tunneling etc. ) 9. Capacitors are an essential part in memory devices. Check out for capacitors used in DRAM technologies (hint deep trench capacitor etc. ) 46