W. Lee Smith

Ion implant monitoring with thermal wave technology

A new method, based on thermal wave technology, is used to monitor the ion implantation process in silicon. It is a noncontact, nondestructive technique that requires no special sample preparation or processing, has high sensitivity even at low dose, and provides a one‐micron spatial resolution capability. This method allows, for the first time, the ability to monitor the critical ion implantation process directly on the patterned product integrated circuit wafers as well as on the usual test wafers.

Temporal behavior of modulated optical reflectance in silicon

We report on the results of a study of the temporal behavior of the laser‐induced modulated optical reflectance from the surfaces of crystalline silicon wafers, epitaxial silicon films, and ion implanted but unannealed silicon wafers. The observed temporal behavior of this signal appears to be associated with the presence and temporal evolution of electronic surface states.

Study of reactive‐ion‐etch‐induced lattice damage in silicon by Ar, CF4, NF3, and CHF3 plasmas

Reactive‐ion‐etch‐induced damage in silicon has been investigated using transmission electron microscopy (TEM), Rutherford backscattering (RBS) ion channeling, and laser‐induced thermal waves (TW). A correlation has been found between lattice damage in silicon due to reactive ion etching and leakage current properties of thermal oxide films subsequently grown on the damaged silicon. The silicon wafers were plasma etched using Ar, CF4, NF3, and CHF3 etch gases at dc bias voltages ranging from 150 V to 450 V. Lattice damage at the silicon surface, as determined by TEM and RBS, was found to depend on both the dc bias voltage and the etch chemistry. Subsequent leakage current measurements of the silicon oxides show that the samples with more silicon substrate lattice damage prior to oxidation also have correspondingly higher leakage. The thermal wave technique also indicates a damage dependence on dc bias and on etch chemistry; however, the thermal wave measurements indicate a damage dependence on etch chemistry different from TEM and RBS measurements. The source of this difference is not yet understood.

Nondestructive technique for the detection of dislocations and stacking faults on silicon wafers

We demonstrate the imaging of dislocations and stacking faults in silicon wafers in a noncontact, nondestructive fashion using laser based modulated optical reflectance. By comparison with conventional wet decoration etching, we show that the sensitivity of the modulated optical reflectance method can resolve the difference between two types of dislocations.

Ultra-High-Resolution Dose Uniformity Monitoring With Thermal Waves

We demonstrate the ability of thermal-wave techniques to nondestructively measure ion-implanted dose and dose uniformity on the same spatial scale as the implanted features of micro-electronic devices. We present results on the variation of the thermal-wave signal with implanted dose, ion energy, surface oxide thickness, and silicon substrate resistiv-ity. We demonstrate ion dose measurements over the 1011 -1015 ions/cm2 range, automatic wafer mapping of ion dose uniformity, and measurement of dose variations on actual integrated circuit features. The attributes of this measurement technique make it particularly suited for production monitoring of ion implantation, especially in the critical threshold-voltage-adjust implant regime.

Damage formed by ion implantation in silicon evaluated by displaced atom density and thermal wave signal

Damage formed by BF+2 and As+ implantations in Si was evaluated quantitatively. The density of displaced atoms (Dda) was determined from 1.5 MeV He+ Rutherford backscattering spectrometery. Dda increased from 4.7×1016 to 1.6×1017 cm−2 with the dose increased from 6.0×1013 to 1.3×1014 cm−2. However, Dda saturates at around 4×1017 cm−2 for all doses above 5×1014 cm−2. The thermal wave signal intensity shows the same dose dependence as Dda. This result shows that thermal wave signal intensity has a close relation with the density of displaced atoms formed by ion implantation. Therefore, quantitative damage monitorings can be achieved by thermal wave intensity measurements. Also, the variation of thermal wave signal intensity with ion implant energy was studied.

Relaxation of ion implant damage in silicon wafers at room temperature measured by thermal waves and double implant sheet resistance

Abstract We have detected and measured the room-temperature relaxation of ion implant damage in silicon wafers. Measured with thermal wave modulated reflectance and with double implant (i.e., damage dependent) sheet resistance the duration of the relaxation varies from as short as a few hours to as long as a few days, depending on dose and species. For dose monitoring techniques which rely on the effects of implant damage and which do not correct the relaxation effect, large errors in the measured dose values may result. We describe the thermal wave method for automatic measurement and correction for the relaxation effect, thus preserving the ability to make real-time, post-implant dose measurements with thermal wave techniques.

Thermal wave implant dosimetry for process control on product wafers

Abstract The ability of thermal wave techniques to nondestructively measure ion implant doses on NMOS product wafers is demonstrated. The correlation of thermal wave measurement signal to electrical parameters and as-dialed dose is examined. Results are presented for thermal wave measurements over an implant dose range of 4.0–8.0E11 ions/cm 2 for a 50 keV boron enhancement implant and 1.5-2.5E12 ions/cm 2 for a 25 keV arsenic depletion implant.

Thermal‐wave measurements and monitoring of TaSix silicide film properties

There presently exists the need to measure the postanneal thickness of silicide films deposited on Si. In addition, there exists the need to monitor the deposition parameters of silicide films, since variations in the deposition process may alter the film stoichiometry, density, and preanneal electrical resistivity. In this paper we describe results of efforts to satisfy these needs using a thermal‐wave Therma‐Probe 100.

Laser‐induced breakdown and nonlinear refractive index measurements in phosphate glasses, lanthanum beryllate, and Al2O3

We present results of measurements of the laser‐induced dielectric breakdown threshold in two phosphate composition laser glasses, in lanthanum beryllate:Nd, and in Al2O3. The nonlinear refractive indices for these materials are also presented. The measurements were made with single 30‐psec 1.064‐μm pulses. The results are compared with those for other laser materials in the 1.06‐μm spectral region.