Dr. Lynn Fuller, Ivan Puchades

Transcription

1 ROCHESTER INSTITUTE OF TECHNOLOGY MICROELECTRONIC ENGINEERING Bulk Micromachined Laboratory Project Dr. Lynn Fuller, Ivan Puchades Motorola Professor 82 Lomb Memorial Drive Rochester, NY Tel (585) Fax (585) Rev Page 1

2 OUTLINE Lab Project Expectations Lab requirements Design considerations Maskmaking Testing Approach Test Results Page 2

3 LAB PROJECT EXPECTATIONS Objective: design, fabricate and test a MEMS device utilizing the provided process flow. Lab project is 50% of grade Meet all required project timelines 33% Weekly attendance and participation 33% Quality of work 33% Project timelines 2 References, design calculations and 1 st Draft layout design 2 nd week Final layout design in dropbox Report theory section and test plan Final presentation Final report 3 rd week 5 th week 11 th week 11 th week Page 3

4 LAB REQUIREMENS AND TOOLS Design: Mentor graphics IC Layout in CE VLSI lab Account to be provided by TA during second week Review mems_cad bulk.pdf posted on Fabrication Complete safety training and pass safety exam by 3 rd week Complete your lab notebook, sign each page, date each page, diary format, comments and observations, etc. Fabrication schedule will be reviewed and ed to students on Fridays. TA (ixp6782@rit.edu) with available hours during the week. One 3-hour block (AM or PM) is required per week plus the 1 hour review session on Friday at 10:00am Page 4

5 DESIGN GUIDELINES Microelectromechanical Systems The basic unit of distance in a scalable set of design rules is called Lambda, λ For the current MEMS process λ is ten microns (10 µm) The process has seven mask layers, they are: P+ Diffusion (Green) (layer 1) N+ Diffusion (Yellow) (layer 2) Poly Resistor (Red) (layer 3) Contact (Gray) (layer 4) Metal (Blue) (layer 5) Diaphragm (Purple) (layer 6) Top Hole (White)(layer 7) /shared/ /mems_bulk_092 Page 5

6 RIT MEMS BULK PROCESS 1 P+ Diffused Layer (110 Ohm/sq) 1 N+ Layer (50 Ohm/sq) 1 N-Poly layer (40 Ohm/sq) 1 metal layer (Al 1µm thick) Top Passivation Top hole µm Si diaphragm Page 6

7 TOP HOLE DESIGN RULES Top hole defines Silicon hole and also openings to metal pads. Silicon hole also needs to be defined with contact layer. Etch will remove oxide and Silicon around them but metal will protect etching of the pads. Contact to P+/N+ diffusion and poly should be made outside the top hole areas. Page 7

8 TOP HOLE DESIGN RULES B A C A. Distance from edge of top hole to metal line >50µm B. Distance from edge of top hole to poly/diffusion line >100µm C. Distance from edge of top hole to edge of diaphragm >300µm D. No top hole over diffusion/poly 51µm Page 8

9 POSSIBLE DEVICES Pressure Sensor, diffused resistors or poly resistors Microphone with top hole to make more sensitive pressure sensor Speaker diaphragm with coil on it, magnet below Accelerometer beam or suspended mass Diaphragm Actuator with coil and resistors for sensing and feedback Optical pyrometer with thermocouples on diaphragm Micro mirror with two moving surfaces Heater on diaphragm either poly or diffused resistor heater Heater plus temperature sensor (diffused heater, poly resistor sensor) Heater plus interdigitated chemical sensor Gas flow sensor single resistor anemometer Gas flow sensor with heater and two resistors PN junction temperature sensors Transistors and logic RF Inductors Page 9

10 POSSIBLE DEVICES Pressure sensor Accelerometers Flow sensor Thermopile Micro-pump Page 10

11 POSSIBLE DEVICES Beam Accelerometer Av=-12V/V buffer opamp Circuitry to amplify the output Signal Plug accelerometer here Accelerometer Cantilever beam with weight Sensitivity can be targeted Low g s test set up Page 11

12 POSSIBLE DEVICES Plate Accelerometer Accelerometer Silicon plate with weight Sensitivity can be targeted with mass High g s test set-up glued PZT actuator Frequency f=10,000 Hz x o =5 µm Max a=28000 m/s^2 Mass=11mg R06 Max Height Amplitude (nm) R06 Max Height Amplitude to reference (nm) f=6,800 Hz x o =5 µm Max a=9000 m/s^2 Mass=14.64mg Frequency sweep R03 Max Height Frequency (Hz) R08 Min Height Page 12

13 POSSIBLE DEVICES Plate Resonators f=61,000 Hz Plate Resonator Resonance of plate is monitored Changes in resonance are due to added mass (real or virtual) Glued PZT actuator Examples shows sensitivity to density of air (vacuum vs psi)) Normalized Maximum Amplitud Frequency Response of MEMS Plate Vacuum Air Frequency Hz Page 13

14 POSSIBLE DEVICES Beam Resonators f=10,100 Hz Beam Resonator Similar to previous Resonance of beam is monitored Changes in resonance are due to added mass (real or virtual) Glued PZT actuator Page 14

15 POSSIBLE DEVICES EM Actuator/Sensor EM actuator/sensor Silicon plate - coil or magnet Electromagnet needed for actuation Changes in resonance due to environmental changes Also vibration energy harvesting Need to develop test set-up Page 15

16 DESIGN AREA Probe pads and connections must be as large as possible and placed around the perimeter Design space is 4mmx4mm. 4mm 4mm Page 16

17 20072 LAB Page 17

18 20072 LAB Page 18

19 MASK ORDER FORM Individual Student Designs are sent to a dropbox to be combined with other designs. Click: File/Cell/Save/as: /shared/ /your_name_design Example: /shared/ /lynn_fuller_mirror Page 19

20 WEDNESDAY LAB SECTION 1X ARRAY Page 20

21 MASKS Page 21

22 ETCHED BULK MEMS PROCESS FLOW 1 Obtain qty 10, 4 n-type wafers 34 RCA Clean 2 Wafer grind to 300um 35 Deposit 6000Å Poly LPCVD 3 Polish back side 36 Spin on Glass, N CMP Clean 37 Poly Diffusion, Recipe RCA Clean 38 Etch SOG 6 Grow masking oxide 5000 Å, Recipe pt Probe 7 Photo 1: P+ diffusion 40 Photo 3, Poly 8 Etch Oxide, 12 min, Rinse, SRD 41 Etch poly, LAM490 9 Strip Resist 42 Strip resist 10 Spin-on Glass, Borofilm 100, include dummy 43 RCA Clean 11 Dopant Diffusion Recipe Oxidize Poly Recipe Etch SOG and Masking Oxide, 20min BOE 45 Deposit 8,000Å TEOS or LTO Oxide 13 Four Point Probe Dummy Wafer 46 Photo 4, Contact Cut 14 RCA Clean 47 Etch Oxide in BOE, Rinse, SRD Å Pad Ox - recipe Strip Resist 16 Deposit 1500Å Nitride 49 RCA Clean, include extra HF step 17 Coat back of wafer and protect edge 50 Deposit Aluminum, 10,000Å 18 Plasma Etch Nitride on front of wafer, Lam Photo 5, Metal 19 Strip backside resist 52 Etch Aluminum, Wet Etch 20 Remove pad oxide - 1min BOE 53 Strip Resist 21 RCA Clean 54 Deposit 10,000Å LTO2 22 Grow 5,000Å of oxide - recipe Deposit top hole mask - Aluminum 5,000Å 23 Photo 2: N+ diffusion 56 Photo 7, Top Hole 24 Etch oxide 57 Top Hole Aluminum etch 25 N+ SOG 58 Deposit 4,000Å LTO PROTEK Adhesion 26 Strip resist, RCA clean 59 Spin coat PROTEK on front of wafer 27 N+ drive -in 60 Etch Diaphragm in KOH, ~4 hours 28 Photo 6: Backside Diaphragm 61 Strip PROTEK 29 Coat front of wafer and protect edge 62 Decontamination clean 30 Etch oxynitride, 1 min 10:1HF 63 Top Hole Silicon etch 31 Plasma Etch Nitride on back of wafer, Lam Remove aluminum top layer min 10:1 HF to remove Pad ox 65 Test 33 Remove resist - solvent strip 5min + 5min rinse Page 22

23 Example of Design Calculations Page 23

24 FINITE ELEMENT ANALYSIS Points of Maximum Stress Page 24

25 +5 Volts Vo1 Bulk Micromachined MEMS Laboratory CALCULATION OF EXPECTED OUTPUT VOLTAGE R1 R3 R2 R4 Gnd Vo2 The equation for stress at the center edge of a square diaphragm (S.K. Clark and K.Wise, 1979) Stress = 0.3 P(L/H) 2 where P is pressure, L is length of diaphragm edge, H is diaphragm thickness For a 3000µm opening on the back of the wafer the diaphragm edge length L is (500/Tan 53 ) = 2246 µm Page 25

26 CALCULATION OF EXPECTED OUTPUT VOLTAGE (Cont.) Stress = 0.3 P (L/H) 2 If we apply vacuum to the back of the wafer that is equivalent to and applied pressure of 14.7 psi or 103 KN/m 2 P = 103 N/m 2 L= 2246 µm Stress = 2.49E8 N/m H= 25 µm 2 Hooke s Law: Stress = E Strain where E is Young s Modulus σ = E ε Young s Modulus ofr silicon is 1.9E11 N/m 2 Thus the strain = 1.31E-3 or.131% Page 26

27 CALCULATION OF EXPECTED OUTPUT VOLTAGE (Cont.) The sheet resistance (Rhos) from 4 point probe is 61 ohms/sq The resistance is R = Rhos L/W For a resistor R3 of L=350 µm and W=50 µm we find: R3 = 61 (350/50) = ohms R3 and R2 decrease as W increases due to the strain assume L is does not change, W becomes 50+50x0.131% W = µm R3 = Rhos L/W = 61 (350/ ) = ohms R1 and R4 increase as L increases due to the strain assume W does not change, L becomes x0.131% R1 = Rhos L /W = 61 ( /50) = ohms Page 27

28 CALCULATION OF EXPECTED OUTPUT VOLTAGE (Cont.) 5 Volts R1=427 R3=427 Vo1=2.5v Vo2=2.5v No stress Vo2-Vo1 = 0 R1=427.6 Vo1=2.4965v 5 Volts R3=426.4 Vo2=2.5035v R2=427 R4=427 R2=426.4 R4=427.6 Gnd With stress Vo2-Vo1 = 0.007v =7 mv Gnd Page 28

29 BUFFER / DIFFERENTIAL AMPLIFIER / FILTER Vsupply Rf R1 R3 - + Va Rin Rin - + Rf Vo R2 R4 Gnd Gnd - + Vb Electronics Off-Chip May not be needed Page 29

30 REFERENCES 1. Process Development for 3 D Silicon Microstructures, with Application to Mechanical Sensor Devices, Eric Peeters, Katholieke Universiteit Leuven, March 1994.] 2. United States Patent 5,357, S.K. Clark and K.D. Wise, Pressure Sensitivity in Anisotropically Etched Thin-Diaphragm Pressure Sensors, IEEE Transactions on Electron Devices, Vol. ED-26, pp , Page 30

31 HOMEWORK - BULK PRESSURE SENSOR LAB 1. Fill in the missing details for the process outlined above. 2. What measurements should be made at each step in the process outlined above? Page 31

32 FINAL LAB REPORT AND NOTEBOOK 1. Complete your lab notebook, sign each page, date each page, diary format, comments and observations, etc. 2. Write a ~4 page technical paper on this laboratory project. Use the standard IEEE conference proceedings format. See attached format and example paper. Both Due 1 st day of Finals Week Page 32

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