Virtual Image with Employee |
Top View of Machine w/Mask |
Top View of Machine w/Top Ring & Wafer |
Full Vertical View of Machine |
CAD Drawing, Frontal View |
It all started with that familiar phrase, “I have a problem”.
A Production Engineer from a prominent semiconductor company met with the president of Hi-Tech Products, Inc., (HTP), and started to describe his dilemma. His company was licensed to run the IBM ‘C4’ evaporation process on their wafers. This process uses a metal ‘shadow’ mask held in place with specialized tooling consisting of a top and bottom ring with tension clips to hold the assembly together. During the process appropriate metals are transferred through holes in the mask and deposited onto the wafer. The metals deposited on the wafer protrude through the mask and is in contact with the sides of the holes. There is also metal deposited on the top of the mask and that material forms a bond with the deposited bumps.
The existing process of mask removal was, at the time, manual.
An operator must remove the retaining clips, lift off the top ring, and then the operator peels off the mask away from the wafer. Mask removal seems to offer the least amount of resistance the moment it leaves the evaporation chamber. As the product cools to room temperature, the mask removal process becomes more difficult. Also, the manual removal process can cause many failures, lifted bumps, broken wafers, and kinked masks. As the current trend moves towards smaller, faster components, the mask hole pattern likely becomes denser in direct proportion. Structural integrity and expense of the mask tend to increase with a denser hole pattern, thus making the masks more susceptible to damage. The trend to go denser has made the manual mask removal a serious problem and mask damage has increased, resulting in a lower ROI.
The design team at HTP began to brainstorm the problem(s) and identified the following issues to complete the operation of removing the mask from the wafer:
a) The 6 clips holding the Top Ring Assembly together need to be removed.
b) The top ring itself, needs to be lifted off next.
c) Then the shadow mask needs to be removed off the wafer, (without damaging the mask or wafer).
d) Next the wafer needs to be removed.
e) And lastly, the bottom ring needs to be removed, (end of cycle).
Time was of the essence to solve the mask damage issue(s). The semiconductor company estimated losses in the range of $15-20 thousand per week due to mask damage.
After several concepts were developed and evaluated with the requesting engineer, a decision was made to build a semi-automatic machine. The wafer size for the prototype was to be for the 200mm, (8”) Top Ring Wafer Assembly. Initially, the concept was to automate (a) and (c) only. All other operations of the process were deemed of lower priority since they could be performed manually by the operator quickly.
The venture to prove concept began.
The HTP design team began the complicated process of designing the machine and marrying all the components into a cohesive unit. A parametric solid design package was used to complete the equipment and tool design into a 3D model. This aided in theorizing and virtual motion testing before the first component was built. The virtual machine concept proved to be an invaluable tool to help our customer clearly see the approach we were taking in early development phases. This approach was also invaluable to our manufacturing team by the clarity it brought prior to the build.
Hi-Tech Products’ design team incorporated a pneumatic actuated de-clip tool it had previously developed into the design concept to deal with the clip removal. HTP was supplied with a number of sample product wafer/mask assemblies for testing. A vacuum holding device was built into the de-clip station to hold and support the wafer. A wedge was designed and mounted onto a horizontal actuator. A second motor was used to raise and lower the chuck vertically to meet the wedge. A third motor was employed to rotate the chuck and reduce the friction induced during the mask removal process. The pneumatics, motor & motion were united by use of a special controller with a built-in processor. This important option made it possible for an administrator to develop and maintain programmable routines for varying mask types. The team took the empirical approach to defining the rotation, feed, and lift height.
The requesting company was anxious to incorporate the ‘new machine’ into their production cycle. The design was finalized on a compact, (space is also a premium in the cleanroom facility), manual load/unload machine. The system utilized three axis of motion. Electro-mechanical linear actuators and servomotors precisely controlled each axis of motion. All motions and actions to remove the clips & masks were refined with programmable flexibility. A touch screen monitor using step by step screen graphics was used for ease of operation and training.
After the machine was delivered and used for a period of time, sources at the facility told us, “We will not run the masks for our new processors without this machine.”
In the future, the equipment may be upgraded to deal with more fully automated removal of top & bottom rings and placing said rings in inventory trays. Also, with some redesign, a variation of the machine can be made to handle smaller & larger top ring assemblies, like the 4”, 5”, 6” wafer assemblies or the newer 300mm, (12”) wafers. It appears that machine tools such as these may extend the life of the IBM ‘C4’ metal evaporation process.