Questions & Answers
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.
How exactly is process control attained with FIBRotools™?
FIBRotools™ work because of ECSI Fibrotools’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.
Can IKo™ systems be used in a clean room, multi-user facility?
Yes. IKo™ systems are currently successfully operating in both single- and multi-user clean room facilities.
Are IKo™ systems easy to install?
Yes, all IKo™ system models are turnkey systems. Simply place on a bench, attach the hood, and plug it in.
Will the brushing damage the photoresist image?
No. The FIBRoplate™ mechanism is designed to minimize the boundary layer (see Boundary Layer Q&A), not to “scrub” the photoresist structure. With IKo™ systems, 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.
How frequently does the fibrilic applicator material need to be replaced?
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 IKo™ system packaging.
Do the microfibers used in IKo’s™ fibrilic applicators cause contamination of the plating solution?
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.
What are some examples of MEMS structures that have been successfully plated with FIBRotools™?
IKo™ systems 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 click for details |
| g. 300µ Micro-robot Soccer Player | IRIS of ETH Zurich produced a copper-nickel micro-robot using Iko system™ click for details |
| h. 100nm, 250nm, and 500nm Copper Film | 4″ wafers click for details |
For more examples see the News and Articles section of our website.
Is there a benchmark study using the FIBRotools™ technology?
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. IKo System’s™ 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.
click for details
What is the “boundary layer”? And why does it impede MEMS plating?
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. IKo Systems™ virtually eliminate the boundary layer, extending process control to the interface. (see process diagrams)
Can I maintain deposit quality by maintaining only the bulk solution composition?
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:
- 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. IKo systems™ are specifically designed to address this drawback of conventional plating systems.
How do IKo™ systems help produce high grade homogeneous alloy deposits such as Permalloy and Solder?
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.
How do FIBRotools™ maintain bulk solution composition?
IKo™ systems 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.
What is a “conventional” electroplating process?
Any electroplating process that relies exclusively on pumps, jets, paddles or nozzles to circulate the chemical solution.
What causes defects in MEMS electroplating?
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 the IKo™ system’s 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.
What is “deposit porosity?” And how does it happen?
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.
What is the smallest size feature/section that IKo™ systems can electroplate?
IKo™ systems have demonstrated exceptional performance with nanometer features.
For more examples see the News and Articles section of our website.
What wafer sizes can I electroplate with IKo™ systems?
With IKo™ systems, 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.
Can IKo™ systems be used for seedless (SL) electroplating of highly-doped silicon?
Yes, our proprietary technique enables seedless electroplating without physical modification of the silicon wafer. The IKo™ system ensures uniform current distribution without a copper current collector. See Add-on Options for more information.
Can IKo™ systems be used for electroplating under a magnetic field?
Yes, IKo™ systems can be used to perform electroplating under a magnetic field of nominally 1,000 oersted. See Add-on Options for more information.