Probing of pyroelectric distributions from thermal wave and thermal pulse measurements

Thermal wave physics is playing an ever increasing role in the on-line characterization of semiconductor materials and devices. This is especially true for thermal wave methods that employ laser beams for both the generation and detection of thermal waves. For the modulated reflectance method discussed here, the pump and probe beams are focused on the same spot. They therefore achieve the noncontact advantage of optical methods in addition to the optimum condition for high spatial resolution, a necessary condition for thermal wave measurements on product wafers.When a material is excited with an intensity-modulated laser beam or pump, a thermal wave is generated in the material and in the air above the sample. The material within this heated region will undergo a thermal expansion which can be detected with a probe beam interferometer or by deflecting the probe beam from the thermoelastic deformation of the surface. Since the complex refractive index of most materials depends on temperature, a modulated temperature will also induce a corresponding modulation in the refractive index and consequently a modulation on a probe beam passing anywhere near the thermal wave. A probe beam directed along the heated surface of the sample, for example, will be deflected as it passes through the heated region above the surface. This mirage effect can also be observed within the sample by directing a transmitting probe through the heated region beneath the surface. Likewise, using a probe beam directed onto the sample surface one can observe a modulation in reflection, transmission, or scattering. A related noncontact method is the photothermal measurement of infrared radiation emitted from the material's heated region. Note that with all these detection methods, thermal wave measurements can be, and most often are, done in air and at room temperature.

Starting from the basic principles of photon detection, a general theoretical description is here given for the incoherent background fluctuation limit of thermal wave detection. Different imaging conditions of IR detection of thermal waves and different detectors are considered. The theoretical limits are compared with measurements obtained for a MeT detector. Good agreement between the observed detection limits and the theoretical prediction is obtained. Thermal waves, excited in solids by intensity-modulated heating, can be used to determine thermo physical parameters, e.g. the thermal diffusivity and effusivity. Since the penetration depth of thermal waves decreases with the modulation frequency of heating, depth-selective information about the thermal properties can be obtained by measuring the amplitude and phase as functions of the modulation frequency. In general, thermal wave measurements are nondestructive and in the case of IR detection of the thermal wave response, thermal waves are most appropriate for non-contact remote measurements of thermal properties and thermal depth profiles. The limit of detection of thermal waves for a given measurement setup, is affected by the total noise of the setup within the measured bandwidth. The total noise is mainly caused by the noise produced in the detector itself, the noise of the electronic system following the detector, and the noise of the incident radiation to which the detector responds. The ultimate limits of detection are set by the fluctuations of the incident radiation, which can be identified, when a cooled detector with low internal noise and a low-noise preamplifier are used. There are two types of fluctuations of the incident radiation: fluctuations of the signal radiation and fluctuations of the background radiation. For the detection of thermal waves, usually the fluctuations in background radiation are dominant and the fluctuations in signal radiation are negligible. 2. Background fluctuations The small variations of the detector signal which correspond to the thermal wave response are distinguished from the background radiation level by filtering the detector signal with the help of a lock-in amplifier at the modulation frequency f of the thermal wave. Nevertheless, the detection is affected by incoherent and coherent fluctuations: - Coherent fluctuations may be due to secondary thermal waves produced in the compo­ nents of the IR optics (lenses and filters) by the modulated laser beam used for the excita­ tion of the thermal wave or by the thermal wave response itself [1]. Since the thermal wave signal depends on the stationary temperature T, coherent noise may also arise from slow changes in the stationary temperature of the sample [2].

This paper will describe how methods developed in structural dynamics may be used to solve a problem of microsystem technologies. In microsystem simulation, determination of the physical properties is of considerable interest. The method of thermal wave measurement is often used today to describe the thermal behaviour of microstructures. The simulation of thermal wave effects based on thermal mode vectors and followed by a sensitivity analysis enables the correction of primarily estimated thermal parameters by fitting calculated results with measured information. Model description and sensitivity analysis offer an effective tool for determining thermal parameters by thermal wave measurement in a fast and clear manner. Thermal wave measurement, simulation and sensitivity analysis together may be used for device design as well as for testing.

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.

Thermal wave implant dosimetry for process control on product wafers

In this paper, a thermal wave in the bath of superfluid helium II is measured by a new type of superconductor temperature sensor under different heat fluxes and bath temperatures, and at the same time, a thermal shock wave is also studied experimentally and theoretically. © 2001 Scripta Technica, Heat Trans Asian Res, 30(5): 419–425, 2001

Si was etched with a plasma generated by an electron cyclotron resonance (ECR) source and the effects of etch‐induced damage were studied. Surface damage was evaluated by electrical characterization and surface analysis. Low ion energy and optimized reactive species concentration are necessary to minimize etch‐induced damage. The reactive species concentration is optimized when the etch conditions provide high concentration of reactive species and high etch rate. As RF power was increased from 20 to 250 W, the ideality factor for Schottky diode increased from 1.08 to 1.90 and the breakdown voltage decreased from 60 to 6 V. Using transmission electron microscopy, defect density increased from while the damage layer thickness decreased from 134 to 91 nm as RF power was increased from 50 to 500 W. The etch‐induced defects are mainly dislocation loops ranging from 1.2 to 2.4 nm. Higher RF power also caused an increase in thermal wave signal. At low self‐induced bias voltage (−50 V), leakage current and thermal wave signal increased with increasing microwave power. However, Schottky diode characteristics improved at higher microwave power when high self‐induced bias voltage (−150 V) was used. Addition of Ar degraded the Schottky diode performance and increased thermal wave signal. After removing 60 nm from the etched surface using low energy chlorine species, full recovery in the device performance is observed as indicated by the electrical and thermal wave measurements. A new damage model is proposed to relate the generation of defects to the etch conditions by comparing the increase in leakage current of the Schottky diodes after dry etching. The defect density is found to increase with self‐induced bias voltage and microwave power, but to decrease with etch rate and distance from the etched surface. Good agreement is obtained between the measured and the predicted Schottky diode characteristics.

Thermoacoustic techniques are becoming popular in both laboratory and industrial environments because they provide a very sensitive method for investigating the properties of solids and liquids, through their effectiveness in absorbing an “exciting” radiation. In this paper we report some application of thermal wave measurements to silicon science and correlate the thermal wave response to the properties of the sample under investigation, obtained with techniques such as secondary ion mass spectrometry, transmission electron microscopy and carrier depth profiling.

A short review of thermal wave measuring methods is presented in the paper. Based on fundamental laws of heat transport, experimental methods for determination of thermal properties of solids are divided into two groups – steady flux techniques and variable flux ones. Special attention is paid to the wave methods belonging to the second group and methods used by the author in his experiments. The idea of Angstrom's method for determination of the thermal diffusivity of metals is reminded. Then different modifications of this classical technique using in investigations of bulk materials and thin films are described. Examples of a few thermal wave measurements are also presented.

Thermal wave measurements and images are presented that illustrate the sensitivity to damage and defect resolution attainable in a laser-based thermal wave system.

ABSTRACTThe Greater Silicon Valley Implant Users' Group (GSVIUG) has conducted a round robin to determine the uniformity and repeatability available in wafers processed with modern RTP equipment. High-dose ion implantation (As, 5E15, 80keV) of 150mm wafers was used to monitor temperature distribution through sheet resistance. Sheet resistance maps were then used to compare the uniformity and repeatability of each vendor. As previously reported, the actual uniformity results varied significantly with RTP vendor and implant conditions, ranging from 0.77% (one sigma/mean) to 3.55%. In addition, some contour patterns were quite representative of specific vendors.Subsequently, wafers from each participating vendor were evaluated by three techniques in order to determine what damage or defects might have resulted from the RTP process: laser flatness measurement, optical-imaging inspection, and thermal wave measurement. The flatness measurement system was used to measure the warpage of each sample. The reflective-optical inspection technique is a full-field, non-destructive technique that provides a real-time visual display, evidenced by light and dark field contrast over the entire wafer. The thermal wave measurement system uses two laser probes to measure a difference in modulated reflectance which results from damage or defects within the wafer.This paper describes each of the three techniques and summarizes the measured results of wafer defects and damage due to the processing by various RTP vendors. Comparisons between the three measurement techniques are made.

The measurement of the thermal properties of thin films and small samples are difficult, if not impossible, when using conventional thermal measurement techniques [1–3]. Such methods typically require extensive sample preparation and have many potential sources of error (e.g. contacts, absolute temperature measurement, emissivity, etc.). Measurement of the thermal conductivity of a thin film is especially difficult, when that film resides on a substrate that also has a reasonably good thermal conductivity, such as polycrystalline diamond on silicon. In this paper, we present a brief introduction to the Mirage Effect Thermal Wave Technique and demonstrate the application of that technique to the making of such thin polycrystalline diamond film measurements. We present experimental results for polycrystalline diamond films on silicon that show that a correlation exists between the “graphitic” content of a thin diamond film, as estimated by Raman spectroscopy, and the thermal diffusivity (conductivity) of those films.KeywordsThermal DiffusivityDiamond FilmMirage EffectSingle Crystal DiamondThin Diamond FilmThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Observation of anomalous high resistance to implanted areas caused by reactive ion etching (RIE)

Analysis of influence of Yb concentration on thermal, elastic, optical and lattice parameters in YAG single crystal

In this paper, a method of determination of thermal properties of multilayer structures using thermal wave measurements and artificial neural networks (ANN) is described. The copper-corundum bondings were examined. The presented method is based on analysis of amplitude and phase characteristics of the photoacoustic signal and usage of ANN for determination of thermal parameters.