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.

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. Is there a benchmark study using the FIBRotools™ technology?

09. What is the "boundary layer"? And why does it impede MEMS plating?

10. Can I maintain deposit quality by maintaining only the bulk solution composition?

11. How do FIBRotools™ help in producing high grade homogeneous alloy deposits such as Permalloy and Solder?

12. How do FIBRotools™ maintain bulk solution composition?

13. What is a "conventional" electroplating process?

14. What causes defects in MEMS electroplating?

15. What is "deposit porosity?" And how does it happen?

16. What is the smallest size feature/section that FIBRotools™ can electroplate?

17. What wafer sizes can I electroplate with FIBRotools™?

18. Can FIBRotools™ be used for seedless (SL) electroplating of highly-doped silicon?

19. Can FIBRotools™ be used for electroplating under a magnetic field?

 

ANSWERS

01.How exactly is process control attained with FIBRotools™?

Answer:FIBRotools™ work because of ECSI's FIBRoplate™ (Fiber-Initiated Boundary-layer Removal) process. It utilizes a unique fibrilic applicator to agitate and effectively reduce the boundary layer by up to 90%. Process control extends to the interface.

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 clean room facilities.

03. Are FIBRotools™ easy to install?

Answer: Yes, all FIBRotools™ models are turnkey systems. Simply place on a bench, attach the hood, and plug it in.

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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.

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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
Cu on Silicon
15µ thick Cu
6µ lines 4µ spaces
10% st. deviation
Plating time, 20 min
b. Au Power lines: 4" wafers
5 cm long
20µ thick
5% St. deviation
10µ spaces between three lines
Plating time, 20 min
c. Ni Accelerometers: 6" wafers
1 to 5 mm interdigitated resonant forks
100µ thick
10µ wide
Aspect ratio 10:1
Plating time, 90 min
d. RF devices, Au: 4" wafers
1.5µ thick
500 nanometers resolution
Mirror finish, 50Å RMS
2.5% St. deviation
Plating time, 3 min
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. 5.5" x 5.5" aluminum substrate 50 micron Cu deposit, low density pattern
1.0% St. deviation, 60 minutes
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g. 300µ Micro-robot Soccer Player IRIS of ETH Zurich produced a copper-nickel micro-robot using FIBRotools™
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h. 100nm, 250nm, and 500nm Copper Film 4" wafers
click for details

For more examples see the News and Articles section of our website.

08. Is there a benchmark study using the FIBRotools™ technology?

Answer:Yes. The test results were obtained over a 5.5" x 5.5" square Cu seeded aluminum substrate with Cu plating duration 60 minutes. The nominal thickness was to be 50 microns. FIBRotools™ test sample was at 51.5 micron with 1.04% Std Deviation compared to 3-7 fold bigger for the benchmark samples in a state-of-the-art commercial plating tool currently at the customer's site.
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09.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)

10. 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 occurs.

In order to maintain deposit quality for these microscopic features the plating equipment must be able to:

  1. 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.]
  2. maintain interfacial solution uniformity across the entire wafer
  3. maintain the interfacial solution level (next to the bulk solution) across the entire wafer
  4. 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.

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11.How do FIBRotools help in producing high grade homogeneous 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. By changing of the thickness of the boundary layer that forms at the solid/liquid interface (see "Boundary Layer" Q/A), the composition of the resulting alloy can be modified. FIBRotools™ unique reciprocating technology gives the user an unprecedented level of control over this boundary layer thickness, and consequently the ability to manipulate the composition of the deposited alloy.

12.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.

13.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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14.What causes defects in MEMS electroplating?

Answer: Aside from an inappropriate selection of electroplating solution, defects can be attributed to:

  1. 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.
  2. 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.
  3. 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.

15.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.

16.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.

17. What wafer sizes can I electroplate with FIBRotools™?

Answer: With FIBRotools™, 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.

18. Can FIBRotools™ be used for seedless (SL) electroplating of highly-doped silicon?

Answer: Yes, our proprietary technique enables seedless electroplating without physical modification of the silicon wafer. The FIBRotools™ system ensures uniform current distribution without a copper current collector. See Add-on Options for more information.

19. Can FIBRotools™ be used for electroplating under a magnetic field?

Answer: Yes, FIBRotools™ can be used to perform electroplating under a magnetic field of nominally 1,000 oersted. See Add-on Options for more information.

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