NCTU NFC Lithography-Related Tools Operation. Manual

Transcription

1 NCTU NFC Lithography-Related Tools Operation Manual A. General Procedures HMDS priming Resist coating Soft bake Exposure Development After development inspection (ADI) Hard bake Record sheet filling. B. Environment 1. Two doors separate the yellow-light room from outside to avoid inadvertent light penetration into this room that may cause resist being exposed. For the same reason, three doors designed for use in emergency (two in mask room) are closed during regular hours. (Principle: Yellow light has longer wavelength and lower energy, so it does not alter resist characteristics. Ambient white light is composed of various wavelengths in which the component with short wavelength tends to expose the resist.) 2. Put on mask and gloves in this room. They are stored in the cabinet under the hot plate. 3. Prior to your session, check if the required resist is available. If not, defrost the new resist stored in the fridge. Power on mercury lamp and let it get stabilized. Turn on hot plate and prime the wafer with HMDS. These preliminary steps take 20~30 min. 4. Arrangement of valves behind the spinner from top to bottom: CDA compressed air (used for stabilize the table of two-side aligner), two-side aligner N 2 (for cooling mercury lamp and aligner gas valve), spinner N 2 (N 2 gun), aligner A N 2 (for cooling mercury lamp and aligner gas valve). (aligner B N 2 is behind the aligner B) C. Resist 1. Inside the fridge, there are various types of resist, including positive-tone in red (FH6400, AZ6112, AZ4620) and negative-tone in yellow (AZ5200). Resist stored in large bottle is sometimes dispensed into smaller plastic bottles. New plastic bottles are stored in the cabinet under the hot plate. Use funnels corresponding to different types of resist when pouring the resist. Funnels are stored in the clean hood. When pouring, please place clean wipes around. Please practice the skill of pouring. Put the small bottle back into fridge if it won t be used for a while. 2. Resist components: photo-sensitizer, organic solvent and resin. Organic solvent evaporates during spin and soft bake. Positive-tone resist is dissolved in developer when it is exposed to light because acidic compounds generated

2 by photo-sensitizer during exposure in the positive-tone resist is soluble in the base developer. On the other hand, negative-tone resist crosslinks when subject to exposure so that it stays intact in developer. Resin determines the structural parameters of resist and needs to be hardbaked to enhance its mechanical properties to facilitate the following etching step. 3. Resist-related info and MSDS are located at the front door. 4. To bring your own chemicals, please file application first. D. Powering on mercury lamp 1. If it is off, check the record sheet first to see when it was turned off. Since the lamp can only be restarted after being cooled by N 2, please allow at least 30 min (with N 2 on) before turning it on. You can also touch the cooling plate to check the temperature. 2. Then check N 2 condition. Verify that N 2 valve on the wall is on (the pressure indicator should be near the drawn line). Switch on two powers on the bottom-right corner of aligner pressure panel (left is gas valve; right is N 2 for mercury lamp cooling). Verify that all the pressure gauges and pinball of flow gauges match the drawn positions. 3. Note that mercury lamp can only be turned on when aligner is off. 4. Hit POWER of lamp. Once rdy appears, hit START. The display shows cold until the power setpoint is reached. After a while, it displays 275 (depending on the setting). The light source is still not stable yet. 5. It takes 20~30 min to stabilize the wavelength of light source for consistent results. Filter installation can help reduce the time though light intensity would be attenuated and longer exposure time is needed as a consequence. 6. The purpose of filter is to increase the wavelength monochromaticity and reduce the pattern distortion caused by diffraction effects. E. HMDS Oven Purpose: to get rid of water vapor on the wafer. HMDS is able to improve adhesion between resist and substrate so that hydrophilic substrate can be coated with resist uniformly. It is especially effective for metal and SiO 2. Procedures: 1. Set= 0. Hit START to vent. Wait until yellow signal is on (it takes about 3 min). Hit RESET. 2. Open the oven door. Use HMDS holder to load the sample. For wafer pieces, rotate the holder for 90 deg to lie pieces on the holder. (holder is stored between two ovens) Close the oven door. Set= 2. Hit START. Yellow signal

3 is on after 30 min. Hit RESET to open the door and retrieve the sample. Close the door. 3. Set= 2. Hit START. When pressure gauge reads 20 torr, hit RESET. Adjust set to 0. Note: a. Check if the tool is occupied before use. If unoccupied, set is at 0, pressure is around 20 torr, and display reads free. b. For baking purpose, follow step. 3 after loading the wafer and let set be 2. If display shows free and set=2, someone else might be doing the bake. Please put a note outside when doing the bake. c. Set=number represents different programs. For instance, 2 =2 min prime. d. Any weird noise during pumping means door is not closed completely. Check if the O-ring inside the door is placed properly. e. Hit RESET and leave immediately in case of toxic gas leakage. f. There are two ovens for different materials (A for Si. B for III-IV). Do not put any flammable such as filter paper inside the oven since it causes contamination. g. Power switch is on the right hand side behind the oven. Colorless HMDS is stored on the left. Pump is under the oven. h. Please adjust set to 0 after use and tell the following user that it is unoccupied unless it is doing the bake. F. Spinner Purpose: to coat resist uniformly across the wafer. 1. Use tweezer to hold clean wipe to remove redundant resist (tweezers are stored near hot place). Then use tweezer to hold acetone-covered clean wipe to clean the table. Be sure not to touch O-ring to avoid corrosion. Place foils and clean wipes around before coating to prevent resist from spreading all over the place. Please practice the skill. 2. Select the proper chuck based on the wafer size (wafer pieces, 3-inch, 4-inch). The chuck must be smaller than wafer size so as not to cause resist accumulation near the chuck or below the sample and result in drain clog. Oversized chuck can lead to vacuum failure and cannot effectively hold the sample. 3. Hit POWER to power on spinner. There are two steps during spinning. The first step would automatically switch to the second one when it is done. The first step is with slower rotating speed at 1500 rpm for 5 sec to spread resist uniformly across the wafer. The second one is with faster rotating speed at 4500 rpm for 25 sec to control the final resist thickness.

4 4. Put the wafer on the chuck. Hit VACUUM. Verify that pressure gauge reading is above 30 or use the tweezer to confirm the wafer is indeed firmly sucked by the chuck before hit START to begin the coating. Hit RESET to abort spin if necessary. 5. Without coating resist, once the wafer is in place, test the spinning speed first. To begin, increase the spinning time. Hit START to begin the spinning. When spinning speed for each step is defined, adjust the spinning time to its initial setpoint. When adjusting, place a sample on the chuck; otherwise, the sample weight might not be evenly distributed and the friction between sample and spinning axis might cause abrasion of Teflon on the chuck. 6. When pouring the resist, check if there is any dried resist clogged near the bottle open. Pour a few drops on the clean wipe near the chuck to remove the clog. Start with the sample center when pouring. Spread the resist on at least one-third of the sample area. Excessive resist will be spun out. Try not to form any bubble which might result in inhomogeneity. Replace foil and clean wipe when necessary. 7. Be sure to do cleaning after use. Do not leave resist residue outside the trash can. Wipe out resist immediately if spread accidentally. Keep the sash closed at all times. The same procedures apply for negative-tone resist. 8. Separate the trash according to its category. The can without ventilation feature is for non-pollutants such as gloves and filters. The other one with ventilation feature is for resist-covered stuff and other volatile organic compounds. In case of the can being almost filled up, use the gadget beside to compress the trash. Make sure the lid is closed; otherwise, organic odor will permeate the whole room. Resist is carcinogen so ensure that it is completely cleaned up after use. G. Soft and hard bake 1. Do not adjust the temperature of two hot plates. Allow the temperature to be stable before using hot plates. Verify that hot plates are on when entering the room. Pay attention to the ventilation system as in the wet bench system. 2. Hot plate heats the sample from the bottom, so resist would become thin and tend to collapse. Oven heats the sample from the top, so resist pattern could have better fidelity. 3. Soft bake: 90 deg. This step removes most solvent of resist to improve resist adhesion to sample. 4. Hard bake: 120 deg. This step strengthens the resin component of resist to improve its anti-etching ability. 5. Turn off hotplate if you are the last one to leave the room. Oven is recommended for long-time baking or thick resist.

5 H. Differentiation between front and back side of mask Here the front side is defined as the side coated with Cr. When the front side faces up, a shadow with patterns of metal can be seen on the other side. This shadow is seen because quartz and glass have different dielectric constants. When the front side faces up, light penetrates metal film first followed by quartz, so the light experiences refraction upon coming out of the quartz, generating double-layer patterns (metal layer and shadow) observable by the naked eye. If the back side faces up, light goes through quartz first and then metal layer, so no shadow can be seen. In case of large metal pattern area, you can directly check the Cr color to determine which is front side. The side with silver-like color (similar to mirror surface) is back side while the one with dark brown color is front side (with Cr). Since the exposure is done in contact mode, front side touches the sample during exposure. During ADI, front side also faces up to prevent lens damage caused by inappropriate focal length adjustment. I. Aligner 1. Switch on the power of mask pump (underneath the desk edge). Power on aligner. Turn on the power of microscope lamp (top). Light source of microscope is to its left and has a knob for intensity adjustment. 2. Reset X, Y, and θ axis. Use a 3-inch wide opening at the mask holder center to visually verify that chuck is right at the bottom. Use the coarse adjustment feature of X and Y axes to reset chuck. θ axis is reset by making the two sides of wafer stage perpendicular to the edges of mask holder. Reset is to allow sufficient shift tolerance in any direction during alignment. 3. There are two knobs for fixing mask holder position. Use two hands simultaneously to loosen knobs in order to maintain the balance of holder. Reverse the holder and place it on the table. Put the mask with its front side facing up on top of the holder. Hit VACUUM to attach mask firmly on the holder. Ensure that mask is completely fixed. Reverse the holder again and put it back into aligner. Corners of mask should be held with two hands to prevent it from falling. Use two hands simultaneously to tighten knobs. 4. Slide out the wafer holder and reset the chuck. If it is seriously mis-oriented, shift it toward the center (with respect to the notch on chuck). Load the sample and slide the holder back. For wafer pieces, use holders with an opening in the center. Sample must cover all sucking holes to be firmly attached. When replacing the holder, make sure the dent on the edge of holder is aligned with the circular

6 button to the left. To fix sample position, press and hold the black button to prevent the sample from moving. 5. Rotate the contact knob by 160 deg counter-clockwise. Then adjust the Z axis to appropriate position. Any strips appeared on the resist indicates that wafer and mask are too close to each other. Verify that wafer is flat and slightly touches the mask, and then rotate the contact knob to 180 deg. Z axis is fixed when contact signal is on. Do not attempt to adjust Z axis once contact is reached. 6. Rotate the objective lens (right in the front). Focus the sample. Enable separation on (separation rod is on the bottom-left side). Adjust X,Y, and θ axes so that they are aligned to the mask. Adjustment can be done in a coarse and fine manner. Be sure not exceed one scale during fine adjustment. Please practice the alignment skills diligently. 7. When aligning, align the pattern edge to the mask first. Then move the center to tune X and Y axes. Next, move to outer area to adjust θ axis. Doing this step repeatedly can achieve alignment before long. 8. After alignment is done, enable separation off. Verify if filter is needed (requires longer exposure time), set the exposure time (for A tool, x0.1s; for B tool, x0.01s), and tune the objective lens to the lowest mag to prevent collision with the mask holder. Notify other users and hit EXPOSURE to start exposure. Note that sometimes the tool would dash out and result in misalignment, which can be avoided by gently holding the tool. 9. Filter usage. If mask patterns consist of small openings in a large area or isolated thin lines (less than 5 μm), using additional filters can help mitigate pattern distortion. Filters are to be installed to the left side of the rear of microscope. Circular handle of the filter should face toward the outside. Do not let lens surface collide with the corners of mask holder edge during installation. If filter is not needed, store it in the box to the right of tool and let the lens surface face up to prevent possible damage from the friction between the surface and the box. 10. When exposure is done, rotate the knob clockwise to its initial position. Slide out the holder and retrieve the sample. When all samples have been exposed, unload the mask holder. Reverse it and put in on the table. Only disable VACUUM when mask is retrieved. Reset the chuck. 11. Dismount the filter and let the lens surface face up to avoid scratch. Adjust the exposure time to the initial setting 25 sec. 12. If no other tool reservation after this session, reverse the sequence of the previous procedures to power off tool (switch off microscope light source, aligner power, mask pump, and mercury lamp). Allow 30 min to let mercury lamp to cool before switching off N 2.

7 13. Fill out the record sheet, including session time, condition of mercury lamp and N Make sure to leave info on the notebook on the door, including the used chemicals. J. Development 1. Developers are stored in the cabinet below the cleaning hood. FHD5 is for developing positive-tone resist FH6400. AZ300 is for developing positive-tone resist AZ6112 and AZ4620. FHD5 with different development time can also substitute AZ300 if AZ300 is running low. Water is fixer for positive-tone resist. WNRB is for developing negative-tone resist. NBA is fixer for negative-tone resist. Acetone is for removing positive-tone resist (useless for negative-tone resist). Stripper is to strip resist (it needs to be heated to do so). 2. This cleaning hood is for development and fixing. All chemicals are to be recycled. Bottles for storing FHD5 and acetone are located on the left side or behind the spinner. If you need to reuse the developer, please cover it and leave a note. Pay attention to the ventilation system. If the bottle is filled up, store it inside the recycle bin and put a new bottle in the hood. 3. When developing, immerse the sample in developer and agitate it gently until the thin fog above disappears (in a few tens of seconds). Then use water to do fixing (for positive-tone resist) and blow dry the sample. Please practice this step, which will be tested during tool qualification. 4. Acetone is often used to rework resist and remove resist on metal. For Si/SiO 2 materials, sulfuric acid in the wet bench is recommended to completely strip resist without any residue. 5. Clean up any self-brought tools, filters, and clean wipes after the session. 6. Chemicals are stored in the cabinet near the cleaning hood. Please sign on the sheet when taking a new bottle. Discarded chemicals and empty bottles are to be stored beneath the cabinet. K. Spinning and development for negative-tone resist 1. Negative-tone resist processing steps can be done either manually or automatically. Resist coating procedures are the same as those for positive-tone resist. 2. Mask production is typically done with automatic development and fixing. Verify that the recycle bin below is not yet full. This bin is to store used developer and fixer. Remove foils and clean wipes to facilitate the flow of developer and fixer into the bin.

8 3. Verify that spinner N 2 is on and the pressure is at a normal level. Rotate the 4 black valves on the bins of developer and fixer so that they are parallel with the piping. 4. Verify there is enough developer (WNRM) and fixer (NBA) in the bin. Refill them if not enough. Also verify that the lid of bin is properly closed and 6 screws tightened. If not closed, automatic operation is not possible owing to insufficient pressure in the bin. 5. Set the timer parameters. You may try your own parameters, refer to instructions near the spinner, or consult technician. General procedures are to set timers for N 2 blowing development development and fixing fixing. To start, move the nozzle to the center and hit START. The process will run all the way till it ends. 6. Be sure to clean the hood after use. Adjust the timer to its initial settings (settings for resist coating). Turn off N 2 for negative-tone resist. Adjust the rods on the pipelines of developer and fixer to their original positions. 7. Refer to lab notes for other details. L. Microscope 1. Before hard bake, check the patterns using microscope. This step is called after development inspection (ADI). Microscope can also be used to monitor wafer condition after etching and mask patterns. 2. Verify the proper settings of the following items: main power, power of light source and monitor, reflection and incidence light adjustment, coarse/fine knob, objective lens knob, sample holder knob, aperture, and filter position. 3. When using the microscope, sample front side should face up. For mask inspection, reflection light is used for better contrast and clearer image. 4. Adjust the objective lens to the lowest mag and sample holder to its lowest position. Use the sample holder knob to slide out the holder. Put down the sample and move it under the objective lens. Start with low mag focus, and then proceed to high mag and tune the focus. 5. The actual length is 1 cm/[mag of eye lens (10X) x mag of objective lens]. One partition in eye lens is 1 cm or 10 sub-partitions. One loop of rotation (marking of ruler starts from 0 to 100) shifts the marker by one partition. 6. Note that counter-clockwise rotation of the objective lens knob is to magnify while demagnification is done via clockwise rotation. Never switch to the highest mag directly from the lowest mag to avoid lens scratch by the collision between lens and sample.

9 7. The right eyepiece can adjust the focal length for size measurement and the left eyepiece can adjust the focal length for TV monitor. The separation can be widened to adjust to the distance between eyes. 8. There is a camera to the right. Users can bring thermo-sensitive paper for print. 9. After use, power off light source and camera/monitor. Adjust the lens to the lowest mag. At night, switch off main power. M. Handlings of power/outage and toxic gas alarm 1. All powers are to be turned off prior to power outage to avoid power shock when it is restored. 2. Do not attempt to continue the experiment during gas outage. Power of the mercury lamp needs to be turned off due to the lack of N Hit RESET on HMDS tool during toxic gas alarm to avoid possible reaction with the toxic gas. Evacuate immediately. 4. When fire alarm is activated, turn off powers of tools and gas valves near you. Put on an oxygen mask and evacuate immediately. Extinguishers in the clean room are CO 2 -based. N. Other important info 1. Fill out record sheet after use. Do not reserve the tool under others names. Heed announcement and feedback bulletin regarding tool regulations (on the exit door) hr tool operation eligibility can be applied after personal operation for 10 times. Application form is available online. 3. Additional qualification is required for double-side aligner. 4. Evacuate route on the left side is toward the rear of building (through a smaller-sized door). Please be aware of its location. 5. Aligner regulations are listed in the record sheet and are revised when necessary. O. Aligner reservation 1. Each user can reserve up to 1 hr per day (one can continue the experiment if there is no other user after you). 2. Reservation is available for the same day and the next two days. 3. Users eligible for 24 hr tool operation are recommended to reserve sessions at night. 4. Those who miss reservation twice (including reservation cancellation) are required to perform voluntary service in the yellow-light room or provide assistance in processing.

10 5. Reserve the tool in the instrument reservation system. Each group is required to reserve the tool at least twice per month. When there is no reservation by a particular group, two of its members must perform voluntary service in the yellow-light room. P. Tool qualification regulations 1. Be sure to read thoroughly the notes and instructions, and personally operate the tool several times under the guidance of a senior user. 2. There are two sets of exam sheets in the yellow-light room. Return them to the original place when finishing reading. 3. Personal operation is mandatory during tool qualification. Tweezer is to be prepared by the testee. 4. Qualification list of items: personal operation of the whole set of procedures, oral description of HMDS step, spin coating operation, soft bake, alignment, exposure, development, PDI (linewidth measurement), and hard bake. Rework the sample by using acetone to strip resist. 5. Grade is determined by the grader. Oral inquiry by the grader is also possible. 6. Make sure you understand all relevant processing and principles. Please take the related course such as IC Technology or refer to the following textbooks. a. Michael Quirk and Julian Serda, Semiconductor Manufacturing Technology (Prentice Hall, 2001), Chapters 13~15. b. Hong Xiao, Introduction to Semiconductor Manufacturing Technology (Prentice Hall, 2001), Chapter 6. c. James Plummer, Michael Deal, and Peter Griffin, Silicon VLSI Technology: Fundamentals, Practice and Modeling (Prentice Hall, 2000), Chapter 5. d. Stanley Wolf and Richard Tauber, Silicon Processing for the VLSI Era, Volume 1: Process Technology, 2nd Edition (Lattice Press, 1999), Chapters 12 & 13. Schedule qualification appointment only when you are fully proficient in all the steps.

11 NCTU NFC Yellow-Light Room Arrangement Map Resist and diluter fridge New and user chemicals storage place Development and fixing hood Developer and fixer Aligner-A Evacuation route Double-side aligner microscope Aligner-B Evacuation route funnel Trash can Soft bake Gas valve filter Record sheet hard bake