Tom Ni

Studies of the low-pressure inductively-coupled plasma etching for a larger area wafer using plasma modeling and Langmuir probe

As semiconductor wafer size increases (from the current 200 to 300 mm), scaling up a process chamber to meet the same or even more stringent requirements becomes difficult due to complexity of the nonequilibrium plasmas. Designing 300 mm etching reactors can be costly and time consuming for developers without an understanding of fundamental physical and chemical processes. To expedite development and reduce cost, plasma modeling and plasma diagnostics are used to gain insight and assist the 300 mm etching reactor development. In this article, it is demonstrated that plasma modeling and Langmuir probe measurement can be used to study various plasma properties including the effects of inductively coupled power, chamber pressure, aspect ratio, and coil configuration, for a planar inductively-coupled plasma. The results from these studies are used to optimize an inductively-coupled plasma R&D chamber capable of etching 300 mm wafers.

HBr concentration and temperature measurements in a plasma etch reactor using diode laser absorption spectroscopy

In situ measurements of HBr concentrations and rotational temperatures were recorded in a 300 mm planar inductively coupled plasma (ICP) etch reactor using diode laser wavelength modulation spectroscopy. A pair of diode lasers operating near 1.95 and 2.00 μm were wavelength tuned over the R(7) and P(2) transitions of HBr (2–0 band), time-division multiplexed, and directed through an industrial wafer etch reactor. The rotational temperature (typically 435±8 K) was determined from the ratio of peak absorption signals and the HBr concentration was determined from the measured temperature and absorbance from a single line. The measured rotational temperature in the plasma was relatively independent of conditions studied. The estimated HBr dissociation fraction ranged from 25%–60%, depending on the ICP power applied, gas flow rate, and chamber pressure. Decreases in HBr concentration were detected 1 cm above the wafer surface during blank silicon wafer etching. The HBr dissociation fractions were measured befo...

Optical self-absorption technique for qualitative measurement of excited-state densities in plasma reactors

Measurements of excited-state populations in processing plasmas can be useful because those populations often are indicators of, or participants in, chemical reactions. An optical self-absorption technique has been used to measure the relative densities of species in long-lived excited states in high-density plasma reactors. The technique is advantageous because it is simple and inexpensive compared to many laboratory diagnostic techniques, and thus it has potential for industrial manufacturing applications. The technique is useful when absorption strength and wavelength are in acceptable ranges. This paper describes the technique, compares its performance to a more sophisticated laser-absorption technique, and presents self-absorption data from a laboratory reactor and from a 300 mm production-prototype reactor.

Critical dimension control of a plasma etch process by integrating feedforward and feedback run-to-run control

In this article, we have derived a run-to-run (R2R) control design technique that integrates feedforward and feedback control on the etch process. The purpose is to minimize the effect of an oxygen flow disturbance during the resist trim on the polysilicon critical dimension (CD) after the main etch. The R2R controller manipulates the resist trim time based on feedforward measurements of the resist CD at the end of the lithography and feedback measurements from polysilicon CD at the end of the etch process. The purpose of the feedforward measurement is to adjust the resist trim time using a model of the relation between trim time, resist CD before the resist trim and polysilicon CD after the main etch. The purpose of the feedback measurement is to adjust this model to compensate for the oxygen flow disturbance during the resist trim. The resulting controller is called feedforward/feedback (FF/FB) controller. The FF/FB controller is tested using simulations and experiments conducted on an etch tool manufactured by Lam Research. The simulations and experimental results show that the FF/FB controller attenuates linear drift and shift in the polysilicon CD caused by the oxygen flow disturbance. Moreover, the results quantify the significant benefit of integrating feedforward and feedback control in addition to only using a feedforward control in minimizing the polysilicon CD deviations from the etch target.