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Device Chip and Materials Properties Sample Processing Description

MOSFET/CAPACITOR/DIODE/DIFFUSED RESISTOR FABRICATION

Lab 2 and 3: First Photoresist, Diffusion Mask

Required reading: pp. O-6 - O-10, pp. 1-7, pp. 35-47, OP-L, OP-O, OP-R

1. Obtain (two each) clean, oxidized n- and p-type silicon chips from your T.A. Record the number scribed on the back of each chip. Store the chips in a clean petri-dish until you are ready to use them.

Note: Wafers are cleaned (e.g., OP-J) and wet oxidized for an oxide to serve as a diffusion mask. See the Wet Ox Log Book for oxidation time used on your sample.

On the oxidized samples provided, measure the oxide thickness on one n-type and one p-type sample using the ellipsometer and OP-R. Make sure to record the sample numbers on these chips in your notebook, and keep track of them as the materials properties test chips(here after referred to as the MPT chips). Also make sure to mark these chips so you can tell which half will be oxide-etched and doped. You will use the other two chips for your device arrays. 
DEVICE CHIP NUMBERS:

n-type device chip #: t= Å (if measured)

p-type device chip #: t= Å (if measured)

MPT CHIP NUMBERS AND INITIAL FIELD OXIDE THICKNESS:

n-type MPT sample #: t= Å

p-type MPT sample #: t= Å
2. PHOTO-RESIST I (PRI): Windows for 1st diffusion.

____ a. Bake-out the sample for 5 mins. in post-bake oven. (This step may be skipped if sample did not go through any wet processing prior to PRI).

____ b. Spin-on the Adhesion Promoter (HMDS) at 4000 rpm for 30 sec.

____ c. Spin-on positive-resist (1350J) at 4000 rpm for 30 sec.

____ d. Pre-bake sample for 10 mins in the Pre-bake oven, 95C.

____ e. On your device samples, use OP-O to align the sample with the 1st diffusion mask, MASK I, so that its edges are approximately parallel to the edges of your chip.

____ f. Using the same OP, do a 15 sec exposure to UV light. CHECK THE LOG BOOK FOR UPDATED EXPOSURE TIMES. Make sure you enter your exposure times into the log Book!

____ g. Dip the sample in developer for 60 sec followed by two rinses in the high purity H2O beakers. Blow dry the sample. Inspect pattern under microscope. 
chip number: Mask Level:  exposure time:sec

minimum resolution line:  um

minimum resolution space:  um
____ e'.On your materials properties test chips align the samples to the 50% opaque/50% clear mask so that l/2 your chip is covered. NOTE WHICH SIDE OF THE CHIP IS EXPOSED FOR LATER REFERENCE!!!!!!!!

____ f'. Expose as above.

____ g'. Develop as above.

____ h. Flood expose the chips under the U.V. lamp. Use a 5 sec exposure /pause 5 sec/ 5sec exposure sequence. CHECK FOR UPDATES ON THE TIMING OF THE FLOOD EXPOSURE!

NOTE IF BACK SIDE RESIST COATING PROCEDURE IS USED, IT MUST BE DONE BEFORE POST-BAKE! IF USING RESIST FOR BACK SIDE PROTECTION, FOLLOW THE NEXT TWO STEPS (steps i1 and j1; IF USING THE WAX PROCEDURE, SKIP TO steps i2 and j2. Check with TAs for updates on these steps.

********************

____ i1. To protect the oxide on the back side of the chip during etching we need to coat it. Resist coating procedure: Working in the small hood, place a VERY SMALL drop of resist on a clean microscope slide. Now CAREFULLY place your chip BACKSIDE DOWN onto the resist. Using forceps, gently press down on the corners of the chip, and rotate the chip to evenly distribute the resist over the back. CAREFULLY slide your chip off the the microscope slide (DO NOT TRY TO PULL IT VERTICALLY OFF) and inspect for good resist coverage. Place the chip vertically in the teflon carrier with the other chips; now procede to post bake.

____ j1. Post-bake samples for 15 min in the Post Bake Oven, 125C.

********************

____ i2. Post-bake samples for 15 min in the Post Bake Oven, 125C.

____ j2. To protect the oxide on the back side of the chip during etching we need to coat it. Wax coating procedure: In the small hood turn the hot plate on, set for LOW, and allow it to warm up. Place a clean microscope slide on the hot plate, and place a SMALL amount of clear wax on the slide by rubbing the wax stick on the slide. Now CAREFULLY place your chip BACKSIDE DOWN onto the molten wax. Using q-tips, gently press down on the corners of the chip, and rotate the chip to evenly distribute the wax over the back. Quickly slide your chip off the the microscope slide (DO NOT TRY TO PULL IT VERTICALLY OFF) and inspect for good wax coverage. The chip will cool quickly, then place it back in your petri dish.

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Check your pattern by examining your chips with the Nikon Microscope; make sure you know what is photoresist and what is bare substrate.

3. Etch windows for 1st diffusion (all chips).

____ a. Etch oxide in buffered HF (BHF) for approximately 4 min. Etch rate is about 1000 Å/min. When etching is complete the etched areas should de-wet. Rinse and blow dry. Check with TAs for updated etch times.

____ b. Clean the photoresist off the chips after etching: rinse in acetone/ethanol/HP H2O.
minimum resolution line etched: ________ um

minimum resolution space unetched: ________ um
4. Strip remaining photoresist (all chips).

____ a. Place chips in the boat inside the Plasmod (see OP-K) and oxygen ash at full power for 5 min.

Lab 4: Boron, Phosphorus Predeposition

Required reading: OP-A, OP-D, OP-E, OP-F, OP-H

PRELAB QUESTION: ANSWER IN LAB NOTEBOOK BEFORE LAB PERIOD BEGINS!
1. The operating procedures for the pre-dep furnaces specify that you use several different flow meter settings, but do not give the actual flow rates. Using the settings given and the data in OP-A determine how long it takes to completely displace the volume of gas contained in the furnace tube for each flow rate given. Why might each of theses rates have been chosen?

2. For the sheet resistance measurements on the MPT chips, what are the dimensions you should use in order to find the correction factors CFd and CFt in order to convert I and V measurements into true sheet R's? Remember you have doped only one half of the sample, and think about where the current will be confined to flow.
5. Pre-deposition

____ a. Immediately prior to predep, perform a 5 sec BHF etch to remove any native oxides.

____ b. On the n-type substrates, perform a 30 min. boron pre-dep (see OP-A, OP-D). CHECK FOR UPDATED TIME.

____ c. On the p-type substrates, perform a 20 min. phosphorus pre-dep (see OP-A, OP-E).

6. Predep sheet resistances and Oxide thickness measurement.

____ a. Strip boro-silicate/phospho-silicate glass from all chips with BHF etch:

n-type chips (boron-doped): 30 sec.

p-type chips (phosphorus-doped): 15 sec.

Rinse and spin dry.

____ b. Measure the sheet resistance of the doped layers on the materials test chips using the 4 point probes and OP-H. Make three (3) measurements at slightly different locations on each chip to check the accuracy of the measurement.
n-type substrate, boron-doped: Rs = __________

p-type substrate, phosphorus-doped: Rs = __________
Record these results in the appropriate Furnace Log Books.

____ c. Using the ellipsometer and OP-R, measure the oxide thickness on both the doped and undoped sides of your MPT chips.
ox thickness, n-type : doped_________ undoped_________

ox thickness, p-type : doped_________ undoped_________
Labs 5 and 6: Drive-in, 2nd Photoresist pattern.

Required reading: OP-F, OP-L, OP-O, OP-H, OP-R

PRELAB QUESTION: ANSWER IN LAB NOTEBOOK BEFORE LAB PERIOD BEGINS!
1. The procedure described below for the drive-in specifies that you use several different flow rates and gases, but does not give the actual flow meter settings. Using the rates given and the data in OP-A determine the meter settings necessary.

2. How long does it take to completely displace the volume of gas contained in the furnace tube for each flow rate given? Why might each of theses rates have been chosen? During the drive, roughly how much time is spent in an oxidizing ambient, and how much in a non-oxidizing one?
7. Drive-in

____ a. On all your samples, perform a 30 min. drive-in at 1100C:
i) initiate drive-in in O2, 1 liter/min., for 5 min.

ii) conclude with N2, 1 liter/min., for 25 min. (see OP-A, OP-F)
____ b. After drive, on your material properties samples measure the oxide thickness using OP- R. Make sure to measure the thickness on both the doped and undoped sides of the samples.
ox thickness, n-type : doped_________ undoped_________

ox thickness, p-type : doped_________ undoped_________
8. PR II: Gate oxide pattern, Mask 2, on device chips ONLY.

____ a. Dehydration bake, 5 min. at 125C (use the Post Bake oven).

____ b. Spin on adhesion promoter, 4000 rpm, 30 sec.

____ c. Spin on photoresist (1350J), 4000 rpm, 30 sec.

____ d. Pre-bake: 10 min, 95C.

____ e. Using OP-O, align the sample pattern to the pattern on Mask 2. Be very careful; do the rotational alignment first, then the x-y alignment. Use the split-field technique.

____ f. Expose for 15 sec.; check for current exposure time.

____ g. Develop (60 sec), rinse, blow dry. Inspect pattern with Nikon microscope! Is it OK?? Check the resolution sections: 
chip number: Mask Level:  exposure time:sec

minimum resolution line:  um

minimum resolution space:  um
Check the alignment verniers at the following locations on your chips: 
top left reg error  
x :  microns  
y :  microns
 
Mask level: 
Chip #: 
top right reg error  
x :  microns  
y :  microns
  
center reg error  
x :  microns  
y :  microns
  
bottom left reg error  
x :  microns  
y :  microns
   

bottom right reg error
x :  microns  
y :  microns
____ h. Flood expose: use a 5 sec. exposure, pause 5 sec., then 5 sec. exposure.

____ i. Post-bake: 15 min, 125C.

9. Etch all oxide from gate/capacitor areas and all oxide from materials chips.

____ a. Using buffered HF, perform a 4 min. oxide etch. When complete the back side of the chip should de-wet. Remember to include your materials properties test chips. Check with TAs for updated etch times.

____ b. Inspect pattern with microscope.

____ c. On the material properties test chips (which should now be completely free from all oxides) measure the sheet resistance of both the doped and undoped sides of the chips using OP-H. Again take three different measurements.
n-type : B doped Rs = ______ undoped Rs = ______

p-type : P doped Rs = ______ undoped Rs = ______
Record these results in the appropriate Furnace Log Books.

10. Strip Photoresist from device chips

____ a. Rinse sample: acetone/ethanol/HPH2O.

____ b. Strip sample in Plasmod (OP-K), full power, 5 min.

____ c. Inspect pattern with microscope.

Lab Report I (see p.19) is due on SOON: see course schedule!

Labs 7 and 8: Gate Oxidation, 3rd Photoresist Pattern, Contact Windows

Required reading: OP-J, OP-N, OP-C

11. Gate oxide growth on ALL chips.

____ a. Immediately prior to oxide growth, perform a 5 sec. BHF etch, rinse, dry.

____ b. Immediately after the BHF dip perform the RCA cleaning step for inorganic contamination using a 5:1:1 solution of HP H2O: 30% H2O2: 37% HCl for 5 min. (see OP-J). Rinse thoroughly in HP H2O.

Note: TA's should check temperature of Dry Ox Furnace prior to this step.

____ c. Grow oxide in Dry Ox Furnace, as per OP-C, but before pushing samples into furnace center zone, allow them to heat in the furnace neck for 5 min. Make sure to oxidize all four of your samples.Perform the oxidation WITH CHLORINE INJECTION, for the time indicated by your lab TA.

time in O2:_________;

time in O2 + TCE/chlorine:_________;

time in N2:________.

Record in Furnace Log Book!!!! CHECK FOR UPDATES

____ d. On your material properties test samples, measure the thickness of the oxide just grown using OP-R. Measure the oxide thickness over both doped and undoped regions.
n-type, thickness : doped______ undoped______

p-type, thickness : doped______ undoped______
Record in Furnace Log Book!!!!

12. PR III: Contact window pattern, Mask 3, on device chips only.

____ a. Dehydration bake, 5 min. at 125C.

____ b. Spin on adhesion promoter, 4000 rpm, 30 sec.

____ c. Spin on photoresist (1350J), 4000 rpm, 30 sec.

____ d. Pre-bake: 10 min., 95C.

____ e. Using OP-O, align the sample pattern to the pattern on Mask 3. Be very careful; do the rotational alignment first, then the x-y alignment.

____ f. Expose for 15 sec. Check for current exposure time.

____ g. Develop (60 sec) in AZ developer, rinse, blow dry. Inspect for proper results with Nikon microscope.

chip number: Mask Level: exposure time:sec

minimum resolution line: um

minimum resolution space: um

Check the alignment verniers at the following locations on your chips:


 top left reg error

x : microns

y : microns		            Mask level:
Chip #: 		 top right reg error  

x : microns  

y : microns
 

 center reg error  

x : microns  

y : microns		  
       


 bottom left reg error  

x : microns  

y : microns		    

 bottom right reg error

 x : microns  

y : microns
           
____ h. Flood expose (5 sec. exposure, 5 sec. pause, 5 sec. exposure).

Note: Do NOT cover back side of chip with wax or photoresist.

____ i. Post-bake: 15 min., 125C.

13. Etch oxide from contact windows and oxide from materials properties test samples.

____ a. Using the BHF etch station, perform a 4 min. oxide etch. When complete the back side of the chip should de-wet.

____ b. Inspect pattern with microscope.

____ c. Using OP-H, measure the sheet resistance of the doped layers on your materials properties test samples.
n-type substrate, B-doped : Rs = _______________

p-type substrate, p-doped : Rs = _______________
____ d. Using OP-N, measure the junction depth on the doped side of your material properties test chips.
n-type substrate, B-doped Rj = _______________

p-type substrate, P-doped Rj = _______________
Lab 9, 10, and 11: Complete Device Fabrication

Required Reading: OP-G, Vacuum Evaporation

14. Back side damage chip (device samples only for rest of processing).

____ a. Place chip face down on a piece of filter paper. While holding one corner down with your forceps, CAREFULLY damage the back side of your chip with the fine sandpaper provided. It is not necessary to damage a large area of the chip.

15. Strip photoresist.

____ a. Rinse sample: acetone/ethanol/HPH2O.

____ b. Strip sample Plasmod (OP-K), 1/2 power, 5 min.

____ c. Inspect pattern with microscope.
minimum resolution line etched: ________ um

minimum resolution space unetched: ________ um
16. Aluminum evaporation

____ a. CAREFULLY follow OP-G to vent and raise the vacuum system bell jar.

____ b. Load the aluminum evaporation filament with 4 inches of aluminum wire. The wire should be very carefully wrapped around the center of the filament. See TAs for help.

____ c. Clamp your sample front-side down using the clips on the the chimney cover plate. Remember to put at least one clear glass slide on the cover plate to double check metallization thickness.

____ d. Follow OP-G to pump down the vacuum system. Allow 15 min. for vacuum to improve.

____ e. Evaporate aluminum: see lab TA for up-date on evap system operation.

____ f. After concluding evaporation, allow 5 min. for the filament to cool, then vent and remove your sample as per OP-G.

17. PR IV: Aluminum contact pattern, Mask 4.

____ a. Spin on adhesion promoter, 4000 rpm, 30 sec.

____ b. Spin on photoresist (1350J), 4000 rpm, 30 sec.

____ c. Pre-bake: 10 min., 95C.

____ d. Using OP-L, align the sample pattern to the pattern on Mask 4.

____ e. Expose for 25 sec. Note the increased exposure time used when exposing resist over metal. Check for current exposure time.

____ f. Develop (60 sec), rinse, dry. Inspect for proper pattern with Nikon microscope.

chip number: Mask Level: exposure time:sec

minimum resolution line: um

minimum resolution space: um

Check the alignment verniers at the following locations on your chips:


 top left reg error

x : microns

y : microns		            Mask level:
Chip #: 		 top right reg error  

x : microns  

y : microns
 

 center reg error  

x : microns  

y : microns		  
       


 bottom left reg error  

x : microns  

y : microns		    

 bottom right reg error

 x : microns  

y : microns
           
____ g. Flood expose (5 sec. exposure, 5 sec. pause, 5 sec. exposure).

____ h. Post-bake: 15 min., 125C.

18. Aluminum etch.

____ a. Etch aluminum in Transene Type A Aluminum Etchant. Etch time should be approximately two minutes; continue etch until pattern is clearly visible.

____ b. Rinse thoroughly in HPH2O.

19. Strip photoresist.

____ a. Rinse sample: acetone/ethanol/HPH2O.

____ b. Strip sample Plasmod (OP-K), 1/2 power, 5 min.

____ c. Inspect pattern with microscope.
minimum resolution line etched: ________ um

minimum resolution space unetched: ________ um
20. Metallize chip back side.

____ a. Follow OP-G to vent and raise the vacuum system bell jar.

____ b. Load the aluminum filament with metal (4" wire length).

____ c. Load sample back side down. Remember to put in a blank slide to monitor the evaporation.

____ d. Follow OP-G to pump down the vacuum system. Allow 15 min. for pump down.

____ e. Evaporate aluminum at 40 amps for 2 min.

____ f. After completing evaporation, allow 5 min. for cooling, then vent and remove sample as per OP-G.

21. Form ohmic contacts and anneal gate oxide.

____ a. Set N2 flow in small annealing furnace #1 to 100 with steel ball (160 cc/min). Flush furnace for 5 min. before loading samples.

____ b. Load samples into quartz boat, push into center of furnace. Anneal for 15 min. at 450C.

Note: This furnace controller gives temperature in Fahrenheit, so be careful. Sample fabrication is now complete.

Lab Report II (see p.20) is due SOON, see course schedule for date!

You should now proceed to the Device Testing section, p.25 in the Lab Manual.

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