Sputter system update

Last Friday, Chris and I met with Dave Glocker from Isoflux Inc., an expert in physcial vapor deposition.  Specifically, we wanted to get advice on the recent problems we’ve had with the AJA tool.

Arcing from Lesker targets

We recently decided to try new oxide targets from Lesker because the last batch of AJA targets were contaminated.  Unfortunately, the Lesker targets were arcing between the target and clamping ring.

Arcing is a quick, localized draining to ground of an electron charge build-up which can eject particles/contaminants onto the substrate and compromise the integrity of the film (i.e. source of pinholes).  Ideally, the clamping ring and target should be at the same potential.  However, it appears that there is a potential difference that’s developed between the ring and target and causing the arcs.  Dr. Glocker suggested that this potential developed because rf power was being delivered to the target over a larger surface area than the ring (rf through 4 small screws).  To address this issue, we’re going to try placing a thin strip of copper in between the clamping ring and gun to increase the rf conductance.

AJA targets “contaminated”

It seems that our latest batch of AJA oxide targets were producing wrinkled membranes because of a contaminant.  Glocker suggested that we perform elemental analysis on the targets because aluminum oxide has an optical density similar to SiO2 and that it’s possible AJA sent us the wrong material.  We have a new set of targets from AJA that I will begin testing this week.

Miscellaneous

• Film build-up along the chamber walls is now causing flaking that falls on the targets.  A thorough wall cleaning will need to be done in the near future.  This includes disassembling the main pump to the chamber as well as all the guns.  This will probably be a two day job.
• The grounding of the tool is currently being provided by a 14 gauge wire.  Both Glocker and our power supply manufacturer suggests we use a wide copper strip to ground the system because rf travels on the surface (skin effect) of conductors.  We have the copper strips and installation will take place this week.  Correct grounding will help with power supply stability.

Hopefully with these problems resolved we can get back to good material.