Although electrochemistry may have its roots in alchemy, today it is far from being "black magic." To help take the mystery and guesswork out of this potentially predictable, law-abiding science we have compiled the following list of frequently asked questions.
01. How exactly is process control attained with FIBRotools™?
02. Can FIBRotools™ be used in a clean room, multi-user facility?
03. Are FIBRotools™ easy to install?
04. Will the brushing damage the photoresist image?
05. How frequently does the fibrilic applicator material need to be replaced?
06. Do the microfibers used in FIBRotools'™ fibrilic applicators cause contamination of the plating solution?
07. What are some examples of MEMS structures that have been successfully plated with FIBRotools™?
08. What is the "boundary layer"? And why does it impede MEMS plating?
09. Can I maintain deposit quality by maintaining only the bulk solution composition?
10. How do FIBRotools™ help in producing high grade heterogeneous alloy deposits such as Permalloy and Solder?
11. How do FIBRotools™ maintain bulk solution composition?
12. What is a "conventional" electroplating process?
13. What causes defects in MEMS electroplating?
14. What is "deposit porosity?" And how does it happen?
15. What is the smallest size feature/section that FIBRotools™ can electroplate?
16. What wafer sizes can I electroplate with IKo CLASSIC?
01.How exactly is process control attained with FIBRotools™?
The FIBRoplate™ process also enables a better electric field distribution, minimizing the so-called "edge effect" – the tendency to create excess current density in the isolated sharp edges of the pattern.
These two critical elements give the operator the ability to prepare high-quality MEMS samples regardless of design complexity.
02.Can FIBRotools™ be used in a clean room, multi-user facility?
Answer:Yes. FIBRotools™ are currently successfully operating in both single- and multi-user, 10,000 class facilities.
03. Are FIBRotools™ easy to install?
Answer: Place IKoClassic and IKo-2W6 on a bench. Attach the hood. Plug it in.
04.Will the brushing damage the photoresist image?
Answer: No. The FIBRoplate™ mechanism is designed to minimize the boundary layer (see Boundary Layer Q&A), not to "scrub" the photoresist structure. With FIBRotools™, the operator maintains complete control of both the reciprocating action of the FIBRoplate™ mechanism and its exact distance from the pattern. These parameters are based on the MEMS thickness and pattern density.
05.How frequently does the fibrilic applicator material need to be replaced?
Answer: Fibrilic applicator, or "brush", wear is practically nonexistent. We have been using the same material for hundreds of wafers and several hundred hours of operation. In the unlikely event that the original material does wear out, extra material is included in the FIBRotools™ package.
06.Do the microfibers used in FIBRotools'™ fibrilic applicators cause contamination of the plating solution?
Answer: No. The microfibers are securely attached and do not "shed." In fact, it is the combination of our microfiber material and our fine filtration process that eliminates particulates that cause plating problems in traditional plating systems.
07.What are some examples of MEMS structures that have been successfully plated with FIBRotools™?
Answer: FIBRotools™ have been used very successfully to plate various MEMS structures, including:
| a. HD Interconnects: | 5" wafers
|
| b. Au Power lines: | 4" wafers
|
| c. Robotics Accelerometers: | 6" wafers
|
| d. RF devices, Au: | 4" wafers
|
| e. Au bumps for Chips: | 6" wafers 35 and 50µ bumps 25µ thick 3.7% St. deviation 1.3 million bumps Plating time, 60 min
|
| f. 4.5" x 4.5" aluminum substrate | 50 micron Cu deposit, low density pattern 1.0% St. deviation, 60 minutes |
For more examples see the News and Articles section of our website.
08.What is the "boundary layer"?
And why does it impede MEMS plating?
Answer:The boundary,
or diffusion, layer is the stagnant layer at the interface where
process control is minimal. During conventional processing, this
layer can extend 50-100 microns above your resist. Since many MEMS
features are themselves 100 microns deep, you essentially lose process
control 200 microns from the bottom of the resist mold. FIBRotools™ virtually eliminate the boundary layer, extending process control
to the interface. (see process diagrams)
09. Can I maintain deposit quality by maintaining only the bulk solution composition?
Answer: Maintaining bulk solution composition quality is only one of several prerequisites for maintaining deposit quality. When plating features smaller than 50-100 microns (i.e. MEMS, ICs, etc.), it becomes a secondary issue because the bulk solution never reaches the solid interface where the plating is supposed to occur.
In order to maintain deposit quality for these microscopic features the plating equipment must be able to:
- minimize the Boundary layer that forms at the solid/liquid interface (see Boundary Layer Q&A). [If the boundary layer is not minimized, 2. and 3. below become unachievable.]
- maintain interfacial solution uniformity across the entire wafer
- maintain the interfacial solution level (next to the bulk solution) across the entire wafer
- and, maintain bulk solution composition at the prescribed level. Conventional electroplating systems have an inherent limitation for sub 100 micron features – they are not able to sufficiently and uniformly minimize the boundary layer. Thus, they are not able to extend deposit control to where it is needed – at the solid/liquid interface. FIBRotools™ are specifically designed to address this drawback of conventional plating systems.
10.How do FIBRotools™ help in producing high grade heterogeneous alloy deposits such as Permalloy and Solder?
Answer: Deposit composition and quality (regardless of the metal used) depend primarily on the solution composition at the solid/liquid interface where electroplating takes place. FIBRotools™ are designed to minimize the boundary layer that forms at the solid/liquid interface (see "Boundary Layer" Q/A), thus extending deposit control to the solid surface.
11.How do FIBRotools™ maintain bulk solution composition?
Answer: FIBRotools™ are designed to operate with both insoluble and soluble anodes, depending on the type of metal and thickness of deposit required. For insoluble metals such as Gold, Palladium and Platinum an insoluble anode is recommended. For soluble metals such as Ni, Cu, Sn, SnPb the choice of the anode depends on the thickness of the deposit. Specially designed Titanium baskets enable users the choice of soluble material and dual or multiple anode, for maintaining solution composition in long runs and thick deposits.
12.What
is a "conventional" electroplating process?
Answer: Any electroplating process that
relies exclusively on pumps, jets, paddles or nozzles to circulate
the chemical solution.
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13.What
causes defects in MEMS electroplating?
Answer: Aside from
an inappropriate selection of electroplating solution, defects can
be attributed to:
- Inadequate substrate preparation. A uniform seed
layer must adhere to the substrate. In addition, all exposed seed
layer areas, at the bottom of the mold formed by the resist, must
be free of resist leftovers and organic contamination. This is
true, regardless of what electroplating equipment you use.
- Inadequate exchange of matter at the interface.
Electroplating solution, all by itself, works perfectly well on
easy to access surfaces – where the boundary layer is insignificant.
But, it fails in the hard to reach areas of microscopic features
-- where the boundary layer is greater than the features being
plated. Eliminating the boundary layer and getting matter to exchange
in these areas is one of FIBRotools’™ primary tasks.
- Inadequate electric field distribution. A non-uniform electric field can cause the "edge effect" or uneven thickness within a single MEMS and across the entire wafer. There are several ways to improve electric field distribution. One is by redesigning the pattern. Another is by applying a pulsing current. Yet another important way is by reducing the distance, while altering the resistance, between the wafer and the anode – a proprietary feature of the IKo family of products.
14.What
is "deposit porosity?" And how does it happen?
Answer: Bubbles. A
byproduct of electroplating is hydrogen gas. Bubbles of this gas
get trapped in your deposit. FIBRotools™ reduce these gas bubble
occlusions by two means: first, the wafer is positioned so that
the plated surface is facing solution surface so that the bubbles
tend to escape by buoyancy; secondly, the solution is forced into
the pattern cavities where the bubbles may form thus forcing the
bubbles to leave the plated surface. Whatever gas bubbles appear
are quickly removed from the site.
15.What is the smallest size feature/section that FIBRotools™ can electroplate?
Answer: FIBRotools™ have demonstrated exceptional performance with nanometer features.
For more examples see the News and Articles section of our website.
16. What wafer sizes can I electroplate with ECSI's IKo CLASSIC?
Answer: With ECSI's IKo CLASSIC wet processor, you can electroplate any wafer between 2" and 8 " diameter as well as wafer chips 2 centimeter square and up. In addition, you can electroplate square and other shape substrates less then 100 microns up to 10 mm thick.