Study of gap drive system
(1 hour for question 1, 2, 1 hour for q3 report time included in there)
Safety: Lock out tag out main power from wall outlet. Make sure that the process chamber metal cover is put back securely without RF leak at the end of the study.
Overall goal: you are to understand how the gap distance (the distance between upper and lower electrode) can be adjusted by the etcher and how the etcher keeps track of how large that distance is.
Questions:
1. can you guess which physical blocks of the gap drive and upper electrode assembly move and which blocks are stationary when the gap closes/opens.
2. Review the location and functions of the following components:
DC motor, gap drive controller, lead screws, gang chains, gap distance encoder, limit switches, mechanical limit stops, electromechanical break, quad vacuum seal (related to the vacuum seal problem #L below)
Based on the review, can you put together a story on how the gap drive works, including how it performs the following functions:
a)what drives the up and down motion
b)How is the rotation of the motor translated to the up and down motion? Refer to MT224 text book p402 for an explanations on lead screws with ball bearings.
c)What couples the motor shaft and the lead screw?
d)What ensures that the upper and lower electrodes are parallel to each other while the gap moves?
e)How does the system tell the gap distance?
f)What type of encoder is used? Describe the mechanism through which the encoder measures the gap distance?
g)How does the system establish the reference “home” position during gap initialization?
h)How can the system tell if the gap is moving up or down? If it uses a sensor to do that, describe how the sensor can tell that. Refer to MT224 text book.
i)To what accuracy can the gap distance be measured? What are the factors involved in determining the accuracy? (for example, if a distance is measured by a ruler, the accuracy of the system is determined by one factor here—how many marks there are in one unit length on the ruler.)
j)How is the motion limited to make sure the gap is not too small or large or the upper electrode crashes into the lower one? There maybe multiple ways that the system ensures this.
k)What is used to lock the upper electrode from slipping down from atmospheric pressure while the gap motors are not actuated? How does the locking work? Refer to p198 of MT224 text book for an explanation on the electromagnetic brake.
l)How is the vacuum sealed inside the process chamber when the gap moves up and down?
3. How can you determine if upper and lower electrodes are parallel to each other? If not, how can you adjust it? How can you calibrate the actual gap distance against the encoder reading? Study procedure in the manual—electrode parallelism and gap spacing calibration. (not applicable to 2012 students)
4. Study of the rest of the process chamber, questions: (Only part b and d applicable to 2012 students)
a)how is RF power and process gas and coolant delivered to the upper electrode?
b)How is He delivered to underneath of the wafer? Draw a diagram of the He delivery path from where He enters into the etcher to where it gets to the back side of the wafer.
c)How is wafer clamping done?
d)At what places(s) is the chamber pressure measured?
e)At what place(s) is the upper/lower electrodetemperature measured (optional question)?