Modified waveforms to simplify electroplating

Semiconductor and PCB manufacturers could soon be using Faraday Technology’s Faradaic Levelling process to selectively deposit metals in order to create devices with submicron features.

One goal of semiconductor and printed circuit board manufacturers is to create devices having submicron features, but making such devices has been held back because depositing metallic films inside high-aspect-ratio features is very difficult.

Currently, high-aspect-ratio features are electroplated and filled using simple variations in current at different stages in the electroplating process and by using chemical additives (levellers) to suppress plating at various locations on the substrate.

Levellers require strict monitoring and control of the chemistry of the electroplating solution, subsequently increasing production costs. Because of their toxicity to the environment, using these chemicals incurs additional costs for proper handling and disposal.

To enable precise control of electroplating using electrical rather than chemical means, Faraday Technology, Inc. (Clayton, Ohio), has developed their Faradaic Levelling process that uses modified current or voltage waveforms to selectively deposit metals in certain submicron features.

In the process, a substrate having an electrically conductive ‘seed layer’ and a counter electrode are immersed in an electroplating bath containing ions of the metal to be deposited.

A short cathodic pulse causes a thin layer of metal to be deposited onto one area of the substrate. This may be followed by a short anodic pulse to remove unwanted, excess material from another area. This waveform-modulated, polarity-reversing current is specifically selected to provide proper coverage and fill.

Simplicity is at the heart of the technology. ‘Conventional electroplating relies on complicated chemical formulas to deposit and remove metals,’ said Philip Miller, Faraday’s business development manager. ‘The situation gets even more confusing when many different metals must be deposited. With our additives-free Faradaic Levelling process, deposition is controlled simply by asymmetric waveforms.’

High-density interconnects, which are key to making advanced electronic modules used in missile defence systems, can now be made faster and more affordably.

Faraday’s process is said to have additional uses. It can be used to deposit uniform layers of metals on the surfaces of large semiconductor wafers and objects with intricate geometries.

The process can also be used to selectively etch material by modulating voltage rather than current. Faraday has used the process for special etching applications, including electropolishing of the internal surfaces of stainless steel semi-conductor fluid delivery valves. Very passive metals, such as nickel, titanium, aluminium, chromium, and their alloys, can be etched using the Faradaic process.

Several alliances have been formed to develop an integrated electrochemical deposition system based on the Faradaic Levelling technology. Faraday has teamed with Ludy, an electroplating equipment supplier that is providing specialised processing tanks. Faraday has also allied with Dynatronics, which supplies the electronics to control the waveforms.

In a strategic technology alliance, Faraday and Multilayer Technology, Inc. (Multek), a wholly owned subsidiary of Flextronics International, Ltd., have agreed to jointly develop and refine this technology. As part of this arrangement, Multek has provided approximately $700,000 in development funding and is allowing Faraday personnel access to one of its advanced plating facilities to conduct experiments. Faraday is scaling up the process using test panels supplied by Multek.

Source: P. Hartary