Izpitec and a new plasma potential measurement

Izpitec and the PNBP

Izpitec, LLC is a high technology company founded in April 2009 in Austin, TX to develop a new measurement technique for plasmas crucial to semiconductor manufacturing.  The current goal of Izpitec is to develop a prototype of a diagnostic tool, called the Photon-assisted Neutral Beam Probe (PNBP), for the semiconductor manufacturing industry.  The PNBP (patent-pending) offers the possibility of making direct, nonperturbing measurements of plasma potential (voltage).

Importance of Plasma Potential

The difference between the plasma and wafer potential governs the processing rates, degree of anisotropy, and the damage imparted to the chips in modern semiconductor manufacturing.  The wafer potential is controlled by external circuitry, but the plasma potential is difficult to determine.  If the plasma potential were known, the wafer potential could be programmed to follow the plasma potential at all times by a predetermined amount.

Shortcomings of Langmuir Probes

A Langmuir probe is commonly used to determine the plasma potential, but this method perturbs the plasma and gives data that is difficult to reconcile with the true plasma potential.  In order to understand the dynamics of the system, we must directly determine the true parameters of the plasma.  The PNBP will accurately measure the plasma potential, a measurement that until now has evaded researchers of low temperature plasmas.

The PNBP diagnostic is based on the well established Heavy Ion Beam Probe.  It operates under the same measurement principles, but can measure low temperature plasmas (below 10 eV electron temperature).

Overetch Problem

In the case of plasma etching, the variation of the plasma potential over the wafer leads to a variation in the etch rate from location to location.  To ensure complete etching everywhere on the wafer, an overetch is performed.  This results in longer processing time (10-20%) and some damage to the underlying material that is not intended to be etched.  An improvement in the uniformity of the plasma potential profile, aided by the PNBP measurements, could reduce this problem.

Other Plasma-semiconductor Problems

In addition to plasma etch, deposition rates also depend on the plasma potential as does a phenomenon known as ``plasma charging damage.''  An in situ diagnostic would reduce guess work when a plasma tool fails and save hours or days of fab time.  Additionally, it would detect abnormal conditions and stop the production line before all the processing and testing steps are done with a corresponding loss of time and money.

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