Vj Law

Rf probe technology for the next generation of technological plasmas

We describe radio frequency (rf) analysis of technological plasmas at the 13.56 MHz fundamental drive frequency and integer narrow-band harmonics up to n = 9. In particular, we demonstrate the use of harmonic amplitude information as a process end-point diagnostic. Using very high frequency (vhf) techniques, we construct non-invasive ex situ remote-coupled probes: a diplexer, an equal-ratio-arm bridge, and a dual directional coupler used as a single directional device. These probes bolt into the plasma-tool 50 Ohm transmission-line between the rf generator and matching network, and hence do not require modification of the plasma tool. The 50 Ohm probe environment produces repeatable measurements of the chamber capacitance and narrow-band harmonic amplitude with an end-point detection sensitivity corresponding to a 2 dB change in the harmonic amplitude with the removal of 1 cm(2) of photoresist.The methodology and design of an instrument for the measurement of the plasma-tool frequency response, and the plasma harmonic amplitude and phase response are examined. The instrument allows the monitoring of the plasma phase delay, plasma-tool short- and long-term ageing, and process end-point prediction.

Harmonic characterisation of a plasma-tool using a diplexer

AbstractAnon-invasiveex situharmonicprobetechniquethatcharacterizesplasma-generated-harmonicsofaparallel-plateplasma-toolisdescribed. The technique uses a calibrated diplexer to electrically isolate the external RF generator impedance from the plasma tooland to extract harmonic information in the frequency domain.Itisshownthat thetechniqueprovidesa reproducibleday-to-daysignatureofaHe-andN2-plasmaprocess.Thetechniqueshowsthattheplasmanonlinearityfallswithatomicmassandtotalchamberpressure.Plasmapowerdissipationinformationisgiveninthefrequency domain. ( 1999 Elsevier Science Ltd. All rights reserved. 1. IntroductionThe radio frequency (RF) generated low pressureplasma is the primary energetic environment employedin the manufacture of semiconductor devices. Theseplasma environments are conÞned and controlled bynumerous plasma-tools. Examples of the parallel-platereactortypeare:reactiveionetch(RIE);plasmaetch(PE)and; plasma enhanced chemical vapour deposition (PE-CVD).It is well known that the low pressure RF plasma isa rich source of harmonics, because of the nonlinearmechanism in the plasma. Parallel-plate plasmas thatoperate at a ISM designated excitation frequency of13.56MHz are essentially rectiÞers, because the excita-tion frequency is high compared to the ion plasma fre-quency and low compared to the electron frequency.Inthispaper,wepresentmeasurementsofRFplasma-generated-harmonics above the excitation frequency us-ing a diplexer to isolate the RF generator from thenonlinear plasma load. This innovation simpliÞes theinterpretation of the results, by reducing harmonics for-med by remixing at the RF generator. The diplexer isdesigned to be placed in the 50-) transmission-line be-tweentheRFgeneratorandmatchingnetwork(eitherL-

A frequency domain measurement diagnostic technique for plasma-tools

The design of a 10-500 MHz bridge is described and also its use with a tracking generator and spectrum analyser to form a scalar network analyser for the investigation of the internal electro-mechanical components of a parallel-plate and inductively-coupled plasma-tool. The non-invasive frequency scalar data obtained (with the plasma off) provides a frequency related registration of the internal components of the plasma-tool for given match network settings. Frequency data are presented for a parallel-plate chamber and a STS plc inductively-coupled plasma-tool as viewed via the lower electrode platen. Components identified relating to these chambers are the matching network, electrode position, wafer loading arm, wafer lift pin position and silicon wafer dislodgement. The data are used for comparing similar build configurations and fault conditions.

Remote-coupled sensing of plasma harmonics and process end-point detection

Abstract A remote-coupled dual-directional coupler used in the single-directional mode for process harmonic end-point detection is described. Harmonic end-point detection of photoresist stripping and chamber cleaning of silicon dioxide is demonstrated in three different plasma tools for two plasma chemistries (pure O 2 and 10% O 2 in CF 4 , respectively). The responding harmonic number is found to be determined by the frequency response of the plasma tool, whereas the harmonic amplitude response is proportional to the volume of injected etched material, either from a wafer surface or chamber wall. The technique described uses a non-invasive remote-coupled probe which can be employed without re-engineering the plasma tool.

A noninvasive rf probe for the study of ionization and dissociation processes in technological plasmas

A swept frequency absorbance plasma diagnostic technique for measurement of self-resonance frequency, intrinsic plasma-tool distributed capacitance, radiative energy loss, and effective plasma capacitance is described. The ex situ probe measures the plasma properties independently of all contributions from the plasma-tool and transmission line connection to the rf supply. The technique employs a swept frequency source and a balanced equal ratio arm bridge to measure the frequency response of the plasma tool after the plasma has been extinguished under plasma conjugate matching conditions. The resonant frequency of the combination of capacitances due to plasma-tool geometry (intrinsic capacitance, Ci) and the matching network (Cm) exhibits a shift from the excitation frequency (13.56 MHz) that is dependent on the effective plasma capacitance. Resonance frequency shift data are given for He, Ne, Ar, O2, N2, and N2O as a function of both pressure (0.02–0.8 mbar) and incident power (50 and 100 W). This techni...

Harmonic monitoring of the switched silicon etched process

A new non-invasive radio frequency technique for real-time monitoring of the STS ASE™ deep silicon etch process, or other forms of the Bosch switched etch process, is reported. The technique interrogates the plasma-generated harmonic and sideband noise floor level, which is a sensitive probe of the plasma. Using a narrow resolution bandwidth (9 kHz) spectral information discriminating between the alternating cyclo-C4F8 passivation step and the SF6 etch step is clearly and easily visualized. The real-time feedback has the potential to allow characterization and control of the plasma process, both from run-to-run and day-to-day. This measurement technique may provide a path to the understanding of passivation and etching of silicon, and a means of automated process feedback control. The technique is likely to find application in many other processes, as it provides a real-time evolving characteristic signature that may be used to characterize new processes.