Chapter 4.24

Karl Suss MA6 Mask Aligner

(ksaligner)

1.0         Title

Karl Suss MA6 Mask Aligner (ksaligner)

2.0         Purpose

The Karl Suss MA6 is a top and bottom side contact printer used for fine lithography down to 1 micron or better. The MA6 is ideal for use with I-line (365 nm) resists. It is capable of processing both 4- and 6-inch substrates. After reading this manual, the User should be able to describe a typical MA6 (ksaligner) process for both top and backside alignment, explain the theory of operation, and state all hazards associated with the system. After successfully completing the qualification procedures for this tool (see section 12.0 Appendix), the User should be able to perform a full photolithography process for both TSA and BSA using this system. Only trained and approved (qualified) Users may use this tool. 

3.0         Scope

The system includes a number of unique features including:

3.1         1000 W mercury arc lamp with "smart power supply" capable of operating in constant power mode, or constant intensity mode. The default is constant intensity mode. In the constant intensity mode, as the lamp deteriorates, the power is automatically adjusted to keep the intensity of the wavelength. Also the Intensity of the lamp may be read from the power supply during exposure or during a lamp test.

3.2         Top side wafer alignment using a conventional microscope, wafer and mask stage assemblies.

3.3         Bottom side alignment using bottom viewing optics, CCD imaging with image frame grabber and TV monitor. This allows registration of features on the backside of a wafer to the topside of the same wafer (e.g. through wafer etching, backside window etching for membrane formation, back side masks for wafer-wafer bond alignment, etc.).

3.4         Automatic computer control with  LCD  status  for User prompting  and  keypad  entry.  Up to 100 programs may be stored with five on line at any one time. Each  program  may be  edited  for  key  parameters pertinent to the lithography mode.

3.5         1 of 5 lithography modes may be used for exposure. These include: soft contact, hard contact,  vacuum contact, low vacuum  contact,  and  proximity.  Each  mode  is  easily  selected  by  keypad  and  may  have  certain  parameters changed by the User.

3.6         Mask sizes from 5-inch to 7-inch may be used by selecting either of two mask holders.

3.7         Two different size chucks are available for patterning of either 4- or 6-inch diameter substrates.

3.8         Fast or slow scanning of mask/substrate with a memory toggle to quickly view between two locations is also available. This makes alignment using one objective easier.

4.0         Applicable Documents

Revision History

Karl Suss Ma6 Operating manual - hardcopy located at machine.

5.0         Definitions & Process Terminology

5.1         WEC – Wedge Error Compensation. After loading the substrate WEC will occur. It is the procedure by which the chuck automatically adjusts such that the substrate is perfectly parallel to the mask (see section 11, figures and schematics). There are two WEC options in the four basic contact mode programs: contact and proximity. Contact WEC relies on the overall flatness of the mask/substrate to produce a parallel pair. Prox WEC uses a three-point contact (via prox flags) procedure for parallel adjustment. Proximity WEC is always performed when exposing with a proximity program, while contact programs may use either WEC option.

5.2         MA6 – The Karl Suss mask aligner. This manual  describes all aspects of MA6 operation.

5.3         BA6 – The Karl Suss bond aligner. The ksaligner tool may to be converted BA6 operation; however, there is a separate qualification procedure for BA6 (See Chapter 9.1 in the Microlab’s Process and Equipment Operating Manual). Users must qualify on MA6 before they may qualify on BA6.

5.4         TSA – Top Side Alignment. The top microscope is used to align mask features to the topside of the substrate.

5.5         BSA – Back Side Alignment. The bottom side objectives are used to align mask features to the backside of the substrate. The topside of the substrate is then exposed.

5.6         Soft Contact – One of the five possible lithography modes. The substrate is brought into contact with the mask by a preset force during exposure.

5.7         Hard Contact - One of the five possible lithography modes. This is virtually the same as  soft contact mode save for a pillow pressure of Nitrogen that gives an additional upward force to the wafer.

5.8         Vacuum Contact - One of the five possible lithography modes. The vacuum seal inflates to form a chamber, which is then evacuated. The parameter “PreVac time” in this mode serves to allow the vacuum to proceed slowly. This aids in preventing alignment shift.

5.9         Low Vacuum Contact - One of the five possible lithography modes. This is the same as vacuum mode except that a small  amount of  Nitrogen  is bled into the chamber to reduce contact force.

5.10      Proximity - One of the five possible lithography modes. The mask and wafer are separated by an "exposure distance" which is User-specified in the proximity program. The mask and  wafer never actually make contact in this mode.

5.11      Prox Flags – The three pneumatically actuated components located on the bottom side of the mask holder. They serve as spacing elements between the mask and substrate during proximity WEC.

5.12      Overcurrent Error – This error will most likely appear during an attempt to expose. If WEC has been improperly performed, the exposure process will draw excessive current from the motor that brings the mask and substrate into contact. So, although this error will usually occur during an attempt to expose, it is likely that bad WEC prior to the exposure is the cause.  

6.0         Safety

6.1         Alpha particle N2 gun – This blow gun is mounted at the lower right hand side of the tool, and should be used to neutralize and clear charged particles from the desired substrate (e.g. chuck, wafer, mask etc.). The User should be aware that alpha particles (radioactive Polonium) are present when this gun is used. It does not present a hazard as long as it is used properly (e.g. solely to blow off chuck, wafer, mask, etc.). The User should never point the gun towards his or her face.

6.2         Moving Components – The User should be aware at all times of the moving components associated with this tool. For instance, the topside microscope assembly moves up and down,

and does present a potential hazard. The User must exert caution at all times such that a limb, finger, or article of clothing does not become trapped or entangled (or worse, violently detached) when components of the machine are in motion.

6.3         Ultra Violet Light – The MA6 uses an Hg bulb that is filtered to a 365 nm wavelength. The lamp intensity for exposure is set to 25 mW/cm2 by default, although the indirect light that escapes the lamphouse during exposure is much weaker. Nonetheless, the User should be aware that excessive ultraviolet radiation can be harmful to the eyes and skin. 

7.0         Statistical Process/Data

8.0         Available Processes, Process Notes

 

 

 

 

 

 

 


8.1         The correct default idle state of the MA6 should be as follows:

8.1.1          System power ON - machine in MA6 mode.

8.1.2          Power to the TV monitor is OFF.

8.1.3          Lamp power is ON with the LED power supply readout at 900 W in constant intensity mode. (Sometimes the display is set to intensity. It can be toggled back to  power mode by pressing the DS button.)

8.1.4          The 5-inch dummy mask and 4-inch MA6 lithography chuck are loaded. No wafer is on the chuck.

8.1.5          Pressure = 5-6 bar; Nitrogen = 1-2 bar.

8.1.6          If lamp power is OFF (no LED readout), inform staff.

8.2         Basic Exposure Programs

8.2.1          Soft Contact – The substrate is brought into contact with the mask by a preset force during exposure.

8.2.2          Hard Contact - This is virtually the same as  soft contact mode save for a pillow pressure of Nitrogen that gives an additional upward force to the wafer.

8.2.3          Vacuum Contact - The vacuum seal inflates to form a chamber, which is then evacuated. The parameter “PreVac time” in this mode serves to allow the vacuum to proceed slowly. This aids in preventing alignment shift.

8.2.4          Low Vacuum Contact - This is the same as vacuum mode except that a small  amount of  Nitrogen  is bled into the chamber to reduce contact force.

8.2.5          Proximity - The mask and wafer are separated by an "exposure distance" which is User-specified in the proximity program. The mask and  wafer never actually make contact in this mode.

8.3         WEC Types

8.3.1          Contact WEC – WEC is performed by bringing the wafer and mask into direct contact. This type of WEC should usually be used for all contact programs (as specified in the program editor).

8.3.2          Prox WEC – Three prox flags act as spacers between the wafer and mask during WEC. Therefore the mask and wafer never actually touch. This type of WEC has associated with it 3 microns of error, although it is necessary for the proximity exposure program.

8.4         Compatible Resists –  The following resists are compatible for use with the MA6: OCG Oi R-897 10I;  OCG 825;  Shipley STR-1075 thick resist and Shipley SPR 220 thick resist. For questions on compatibility of other types of resist, please contact a ksaligner superuser.

9.0     Equipment Operation

The MA6 allows 5 different program recipes (one for each  contact  mode)  to  be in online memory at one time: a low vacuum contact program, a vacuum contact program, a hard contact program, a soft contact program, and a proximity program. One of these 5 programs may be immediately chosen by  simply  pushing the Select  Program key until the appropriate program appears in the display. 100  programs  (numbered 0-99) may be stored in archived memory. These programs must be loaded before they can be executed. Only one program per contact mode may be loaded into online memory at a time.

9.1         Viewing, loading, saving, and editing a program

9.1.1          Viewing a program

9.1.1.1    Press the Edit Program key. The keypad will flash.

9.1.1.2    Press the Y (up/down arrow) keys. Each program #, contact mode, alignment  gap  and  exposure  time will be displayed as you scroll through each program. You can scroll  up or down through the list by pressing the Y-up or Y-down key.

9.1.1.3    To exit viewing a program, press the flashing Edit  Program key.

9.1.2          Loading an already stored program

9.1.2.1    Press the Edit Program key. The keypad will flash.

9.1.2.2    Press the X-lateral key to scroll among: 1; save prgm  to, 2;  load prgm from, 3; delete prgm #, and 4; exit prgm editor without change. Scroll to 2; load prgm from.    

9.1.2.3    Press the Y –up/down key until the desired program number appears  in  the LCD display

9.1.2.4    Press the flashing Edit Program key to load the stored  program into online memory.         

9.1.2.5    EXAMPLE: Loading program 9: 

9.1.2.6    Press the Edit Program key. The keypad will flash.

9.1.2.7    Press the X-lateral key once to scroll to load prgm from.

9.1.2.8    Press the Y-up/down key 9 times to scroll to recipe 9.

9.1.2.9    Press the Edit Program key again to both load the recipe and exit the editor.

9.1.3          Changing parameters in a program

9.1.3.1    Load the desired program as described previously.

9.1.3.2    Press the Edit Parameter key. The keypad will flash.

9.1.3.3    Press the X-lateral key to scroll  through  the parameters.  For soft  or  hard contact modes the parameters are: Expose Time, Alignment Gap, and Wedge Error Compensation (WEC) type. NOTE: For vacuum mode there are additional parameters. Select the parameter(s) to be changed.

9.1.3.4    Press the Y-up/down key to change a parameter to the desired value.

9.1.3.5    Press the Edit Parameter key again.  The change should appear on the display  (pad stops flashing). Note that this program must still be saved for future use.

9.1.4          Saving the current program to a different memory slot

9.1.4.1    Press the Edit  Program  key. The pad will flash, and save prgm to should be displayed.

9.1.4.2    Press the Y-up/down key to select the program # to save to. When you save a  program the position of the objectives is also saved. NOTE: DO NOT save programs to memory slot #’s 1-10.

9.1.4.3    Press the Edit Program key again to execute the save.

9.1.5          Deleting a program

9.1.5.1    Press the Edit Program key. The pad should flash.

9.1.5.2    Press the X-lateral key twice to scroll to option 3;  delete prgm #.

9.1.5.3    Press the Y-up/down key until  the program  you  wish  to  delete appears.

9.1.5.4    Press the flashing Edit Program key again. The flashing  should stop, and the program should now be deleted.

9.1.6          Exiting Edit Program mode without making a change

9.1.6.1    Press the Edit  Program key. The pad will flash.

9.1.6.2    Press the X-lateral key until option 4, exit prgm editor is displayed.

9.1.6.3    Press the Edit Program key again to exit.

9.1.7          Changing a parameter without loading a new program

9.1.7.1    EXAMPLE 1: Changing the exposure  time  for  the  next  substrate only.

9.1.7.1.1     Press the Edit Parameter key. Exp time should be displayed.

9.1.7.1.2     Press the Y-up/down key to increase/decrease the exposure time.

9.1.7.1.3     Press the flashing Edit Parameter key once more. The new exposure time should now be displayed.

9.1.7.2    EXAMPLE 2: Changing the alignment gap for the next substrate only:

9.1.7.2.1     Press the Edit Parameter key.

9.1.7.2.2     Press the X-lateral key until Al Gap is displayed.

9.1.7.2.3     Press the Y-up/down key to set the desired value of  Al Gap.

9.1.7.2.4     Press the flashing Edit Parameter key again to save this new value. NOTE: The separation key pads (^) also serve to adjust the parameter Al Gap without having to enter the program editor.

9.2         Mask Loading

There are two different size mask holders (trays); one for 5-inch masks, and one for 7-inch masks.

9.2.1          Press the Change Mask key. This key and the Enter key will flash.

9.2.2          Verify on the LCD display that the vacuum holding the mask is ON before pulling out the tray. If the vacuum is OFF, press the Enter key to toggle the vacuum ON. Pull the mask tray out, gently flip it over, and place it on the special shelf at the left of the machine.

9.2.3          Release the spring-loaded clip to the mask and  toggle the vacuum OFF by pressing the Enter key. The mask may then be carefully removed.

9.2.4          If a different size mask tray is desired, disconnect the vacuum hose at the machine (not tray). Push in on the red knurled knob and gently pull on the hose. Place the unwanted tray in the Karl Suss storage cabinet. Place the new tray upside down on the special shelf to the left of the machine. The vacuum hose should be facing toward the User and to the right. Reconnect the vacuum hose. Note that the 5-inch mask  tray is the default for this system. Users who change to a 7-inch tray should change it back to the 5-inch once they are done.

9.2.5          Place the mask to be used onto the tray, emulsion/chrome side up. Use the three alignment pins to center the mask over the tray aperture.

9.2.6          Press the flashing Enter key  to  turn  the vacuum ON.  Verify that the vacuum  is ON by reading the vacuum gauge. It should read less than –0.7.

9.2.7          Push the silver tab down on the spring loaded clip to engage it against the mask. CAUTION: This clip may not be strong enough to hold  the mask  in  place when the tray is inverted. The vacuum should always be ON before the tray is inverted or the mask will drop and possibly break.

9.2.8          Turn the tray over such that the mask is on the bottom facing up. Carefully slide the tray back into the mask frame’s dovetail grooves.

9.2.9          Press the Change Mask key again. The flashing light will extinguish, and the mask  tray will be locked into place. A Ready for Load message should then appear on the LCD display.

9.3         Substrate Loading

There are two wafer chucks; one for 4-inch and the other for 6-inch size substrates. The vacuum grooves on the chuck must be completely covered by your substrate. These chucks are meant to be used with the correct size mask tray only. In other words, the 4-inch chuck must be used in conjunction with the 5-inch mask tray, and the 6-inch chuck with the 7-inch mask tray.

CAUTION: These chucks are  made  by  precision machining and should be handled with extreme care. Do not drop, scratch or otherwise damage them. Store an unused chuck at its proper location in the Karl Suss storage cabinet (shelf on the wall).

9.3.1          Adjust the stage rotation knob to 0 (zero) (such that the rotation indicator is centered) and set the X and Y stage micrometers to 10 (ten).

9.3.2          Press  the Load  key  and  pull  the substrate slide straight out. The Enter and Unload lights should flash.

9.3.3          Verify that the chuck and red vacuum seal are clean from stains or particles. Use the alpha-particle Nitrogen gun to remove particles from the chuck. Use IPA (Isopropyl Alcohol) and a clean wipe to remove any stains. DO NOT allow IPA to get on the seal. DO NOT use acetone to clean the chuck. If the chuck is dirty enough to require an acetone clean, inform staff. Furthermore, leaving resist or particles on the chuck can be grounds for disqualification. Ensure that the chuck, and tool in general is left in a clean state when finished.  

9.3.4          If a different size chuck is desired, gently lift the chuck from the bottom side of the slide and place it in the KS storage cabinet. Then place the desired chuck into the circular opening within the slide (seal faces up). Ensure that the white tick mark on the chuck is aligned to the steel pin on the slide. Always handle the chuck by its metal rim. DO NOT touch the center of the chuck.

9.3.5          Place the substrate on the center of the chuck with the major flat facing the User. Ensure that all the vacuum grooves are covered. When placed properly, the substrate should touch up against the three small steel alignment pins on the chuck.

9.3.6          Press the Enter key to toggle the substrate vacuum ON.

9.3.7          Slowly push the slide all the way back into the machine.

9.3.8          Push the Enter key again. WEC will then be performed. After WEC, the substrate is ready to be aligned to the mask.

9.4         TSA Setup

9.4.1          Position both objectives over the mask using the X-Y arrow  keys. A swifter movement of the objectives may be obtained by toggling the Fast key . The key will illuminate when in “fast” mode.

9.4.2          The distance between the left and right objectives may be adjusted by means of the lateral separation knobs. Each separation knob is located on the left and right side of the objectives. In general, it is best to find an alignment mark at the extreme left and right side of the mask. The rotation knob located at the front of the microscope allows the “theta”, or rotational angle of both objectives to be adjusted.

9.4.3          Rotate the field select knob to the center position to obtain a split-field view on the monitor. A split-field view denotes when the left and right objective images may be seen simultaneously. It is also possible to view a full-screen image of the left or right objective by adjusting the field select knob accordingly.

9.4.4          The intensity of illumination from the objectives may be adjusted by means of the illumination control knobs. First ensure that TSA is selected, then adjust to the desired intensity using the illumination knob for TSA.

9.4.5          The large coarse focus knob is located at the top of the TSA microscope. Naturally, this is used for bringing the objective’s depth of focus into the fine focus range. Fine focusing may be adjusted by means of the focus control knobs. The fine focus knobs labeled Top Substrate should be used to focus on the mask. The fine focus knobs labeled Bottom Substrate should be used to focus on the wafer. The Top/Bottom key may be toggled to switch focus control between the two sets of fine focus knobs. When illuminated, the Top/Bottom key will provide focus control to the Top Substrate knobs. When the Top/Bottom key is not lit, focus control is allotted to the Bottom Substrate knobs. Note: This logic applies to both TSA and BSA processes.

9.4.6          MA6 has the ability to remember microscope position via  the  Set Reference key. To use this option, position the microscope to the first reference location using the X-Y arrow keys. Then press the Set Reference key (key becomes illuminated). Next, reposition the microscope to the 2nd desired location using the X-Y arrow keys. Finally, press the Scan key. The microscope will automatically move back to the first reference location. Pressing the  Scan key once more will move the microscope to the 2nd location. Note: This feature is also available for use with the bottom side microscope.

9.5         Wafer Alignment

CAUTION: Before any attempt to align, ensure that the machine is in alignment mode. The Alignment/Cont key will be illuminated when the machine is in alignment mode. If the system is in contact mode (orange contact LED illuminated), any attempt to align will scratch/ruin the mask and wafer, and possibly damage the machine.

9.5.1          Locate the three micro-manipulators near the bottom left and right sides of the stage. These allow the chuck (upon which the wafer rests) to be moved (X, Y, and R-rotation) relative to the mask.

9.5.2          If resistance is felt during wafer movement, press the separation key labeled “v” to increase the distance between the wafer and mask (z value becomes more negative). The other separation key labeled “^” will decrease the distance between the wafer and mask (z value on LCD display  becomes less  negative).

9.5.3          Alignment shift between the mask and substrate may sometimes occur during the contact exposure process. To ensure proper alignment before exposure, press the Alignment Check key. When this is done, the machine will undergo all the steps in the contact program up to the actual exposure (i.e. vacuum pump down, N2 boost, etc.). Any shift  may then be observed through microscope. If unacceptable shift is observed, the substrate or mask may need to be  re-cleaned,  WEC  may  need to be redone, or a pressure adjustment may need to be made (inform staff). DO NOT attempt to re-align the substrate in “contact” Mode. Ensure the wafer and mask are separated before re-aligning the wafer (toggle with Alignment Check key). If the alignment is acceptable, the wafer may be subsequently exposed. Note: The Alignment Check key is not available for proximity or soft contact modes. Use the Alignment/Cont key instead.

9.6         Wafer Exposure

The lamp power supply is by default set to CI (constant Intensity at 365 nm) mode with  a 900 W LED readout prior to exposure. The system’s intensity is set at 25 mW/cm2 under normal conditions. If different intensities are required, discuss with staff beforehand. Check the WAND header file when enabling the tool, or perform an exposure test to determine proper exposure times. NOTE: A steady beep during exposure implies that the power supply has reached maximum output, as shown in the chart below. At this point constant intensity can no longer be maintained, and the exposure time must be increased to compensate. Linear approximation is usually sufficient for the time adjustment.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


9.6.1          If the exposure time must be changed, press the Edit Parameter  key (do this prior to loading the wafer). Use the Y-arrow keys to change the exposure time. Then press the Edit Parameter key again. The LCD readout in the program should reflect the changed exposure time.

9.6.2          Press the Exposure key. The top side microscope assembly will lift, and the exposure assembly will slide out over the mask.

9.6.3          After exposure, the microscope will drop back down over the mask. The exposed wafer is then ready to be unloaded.

9.6.4          Pull the wafer tray out and press the Enter key to toggle the vacuum OFF. Remove the exposed substrate, and slide the wafer tray back into the machine.

9.7         Bottom Microscope Setup

The bottom microscope is used to print a pattern on the backside of a substrate that is aligned to a pattern on the front side of the substrate. It  accomplishes this by using a stored image of the mask prior to loading the substrate. The mask and microscope then lock into place while the substrate is loaded patterned side down,  resist side up. The patterned wafer may then be viewed by the bottom microscope, and alignment may be accomplished by  moving  the wafer. Both the mask's stored image and the real time wafer image are viewed on the TV monitor during this procedure. NOTE: The top microscope may NOT be used during the following procedure.

9.7.1          Verify that MA6 is in the default idle mode.

9.7.2          Select the desired program and parameter settings as described previously.

9.7.3          Load the desired mask as previously described.

9.7.4          Select BSA/IR on the front panel’s illumination switch.

9.7.5          Activate the bottom microscope movement controls by  pressing the BSA  Microscope key (key should illuminate). The X-Y and Fast keys may now be used to move the bottom microscope objectives. 

9.7.6          Three keypads, Left, Both, and Right  determine  the bottom objectives’ mode of movement. When the Left key is selected (key illuminated) , the left objective movement only is controlled by the X-Y keys. The Right key controls the right objective movement only. The Both key controls movement of both objectives at the same time.

9.7.7          Press the Top/Bottom key to activate mask focus (key should be illuminated).

9.7.8          Adjust the Top Substrate (mask)  left  and  right  focus knobs to obtain a sharp image on the monitor.

9.7.9            The bottom microscope  position  may  be  read from the LCD. XL = left objective x position; XR = right objective x position, YL = left objective Y position etc.. The following coordinates place the BSA objectives directly under the windows on the chuck: XL 23 mm; YL 48 mm; XR 23 mm; YR 48 mm. Effective rotation may be accomplished  by  moving  one  objective  relative to the other. The Set Reference key may  be  used  as  described previously.

9.7.10      Find the alignment marks on the mask (use split field mode). Adjust the left and right illumination knobs if necessary to obtain a clear image on the monitor.

9.7.11