How to Adjust RF Reflected Power on Applied Materials® Ultima HDP CVD® Chamber
Categories: Equipment, Parts, Service
Background:
With Fault Detection and Classification (FDC) monitoring used at most semiconductor fabs, only a small variation in temperature, gas flow or rf power may cause a chamber to be taken out of production.
Many of our customers have asked for support when there is an excursion in rf reflected power on the Applied Materials Ultima HDP CVD chamber. Here we will cover one of the simpler adjustments that can be made to quickly get a chamber up and running and back into production.
First we will briefly review the rf hardware. The top and side rf sources have matches that can be manually adjusted; each match has two capacitor knobs. The generators are variable frequency in the 1.8-2.2 MHz range. In normal operation the frequency is varied automatically in order to keep the top and side rf sources matched to the load. The manual capacitor adjustments are made only for setup purposes. It is important to note that one consequence of having frequency tuning is that there will generally be a compromise to be made in terms of the manual capacitor settings. A single set of capacitor settings will not give a perfect match across a range of different processes.
Adjustments are not normally made to the bias matchbox, as in this case the generator operates at a fixed frequency of 13.56 MHz and the match is auto-tuning.
The most effective way to adjust the reflected power on the top and side rf sources is during the deposition step. If there is more than one recipe or two deposition steps then this can be challenging. As mentioned above, frequency tuning alone cannot perfectly match processes that have widely differing impedances. The key is to find the right balance in setting the manual matches so that the different processes are all acceptably well matched. Adjusting one process recipe or step for a really close match might in some cases cause a second recipe or step to have an unacceptably high amount of reflected power.
Performing the Manual Matchbox Adjustments:
Start by removing the black covers on the top and side matches. There are two adjustment knobs on each match. The smaller knob at the top is the tune adjustment and is primarily for adjusting the generator center frequency. The larger one at the bottom is the load adjustment and is for adjusting the matching capacitor position. Make sure they are in the unlocked position before turning. The match for the top coil is on the left and the match for the side coil is on the right.
Next run some test wafers. When the deposition step begins adjust the reflected power using the load knob. Turn the knob in either direction until the lowest reflected power is found. Do this for both the top and the side matches.
For the next step you will need to see the front of your generator rack. This may require two people, depending on where the rack is located. On configurations using either ETO or ENI generators, the frequency is displayed on the front of the generator when it is running. The generator for the top rf coil is at the very top of the rack and the generator for the side rf coil is the one in the middle.
Run another test wafer. Again wait for the deposition step and look at the generator frequency. The top generator should be between 1.90 and 1.96 MHz. 1.93 MHz is good. The side generator should be between 2.07 and 2.17 MHz. 2.11 MHz is good. To adjust the frequency, use the tune knob and turn clockwise to increase. If you make an adjustment to the side match double-check the top match and vice versa, as they can affect each other. The tune knob will also change reflected power.
If you are unable to get to your desired level of reflected power by using the load knob, use the tune knob. Just keep the frequencies within the desired ranges to prevent cross talk between the generators. It may be necessary to repeat these adjustments several times in order to get to an appropriate level of reflected power across a range of processes.
If you find that any of the knobs will not move, most likely the associated match unit will need service. Semiconductor Support Services can supply that service.
This note applies to the Applied Materials Ultima®, Ulitma Plus®, Ultima TE® and Ultima X® HDP chambers.