in situ Spectroscopic Ellipsometry (SE) is an optical technique which is well suited for the monitoring of epitaxial semiconductor growth, due to its high surface sensitivity and non-invasive nature. In this work, SE systems were installed on both MBE and MOCVD deposition systems to monitor the epitaxial growth of InxGa1−xAs and InxAl1−xAs compounds on InP substrates. The structures grown include thick lattice matched In0.53Ga0.47As buffer layers (for HBT collectors), and strained RTD structures. SE was used to monitor in real-time layer composition and thickness during growth. To enhance the precision and accuracy of the SE determined growth parameters, it was necessary to optimize the SE data analysis strategies. A methodology to determine the best spectral region for the SE data analysis in the presence of noise and systematic effects (such as angle of incidence uncertainty, detector wavelength shifts, surface roughness, uncertainty in surface temperature, non-ideal growth modes, etc.) is presented. Using the optimized data analysis strategies, long term SE-determined InxGa1−�As composition accuracy (as verified by ex situ x-ray measurements) of ±0.002 in ‘x’ was achieved. SE thickness measurements of ultra-thin (<30Å) strained AlAs barrier layers were also in excellent agreement (±0.5Å) with real-time photo-emission oscillation measurements.

Infrared spectroscopy is a versatile tool that is well adapted to in-situ diagnostics of many thin film properties and processes. In this paper, we will describe the application of infrared instrumentation for real-time in-situ measurements of film temperature, emissivity, thickness, free carriers, and optical constants using model based spectral analysis. We will illustrate the use of Fourier transform infrared (FT-IR) emission and reflection spectroscopy to monitor the fabrication of stacks of ferroelectric and conductive oxides on silicon substrates during pulsed laser deposition. The ability to measure the infrared optical constants of dielectrics such as silicon dioxide, including the detailed spectral dependence of the vibrational absorption bands at high temperatures, will be presented. The suitability of the technique for real-time sensing during rapid thermal processing will be illustrated using the example of carrier activation during a shallow-junction rapid thermal anneal.

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to characterize nanocrystalline diamond thin film growth processes by plasma-enhanced chemical vapor deposition (PECVD). With the newly-designed instrument, a time resolution of 32 ms is possible for spectra (1.5˜4.0 eV) in the Stokes vector of the light beam reflected from the surface of the growing film. Several advantages of the rotating-compensator over the simpler rotating-polarizer multichannel ellipsometer design are demonstrated here for diamond thin film growth. These include the ability to: (i) resolve the sign ambiguity in the p–s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the film/substrate. The degree of polarization has been applied to characterize the time evolution of light scattering during the nucleation of the diamond, as well as the time evolution of thickness non-uniformity over the probed area of the growing film. In this paper, a brief description of calibration and data reduction for the new instrument is also provided.

For the purpose of clarifying the growth mechanism of GaN metal-organic vapor phase epitaxy (MOVPE), the GaN surface during the growth on the (0001) sapphire substrate were in-situ monitored by surface photo-absorption (SPA) method. Ga-rich and N-rich surfaces can be distinguished by their reflectivities. It is found that the surface stoichiometry changes with the substrate temperature and with the carrier gas. In the nitrogen carrier gas, a N-rich GaN surface is stably formed at temperatures up to about 1000°C under NH3 flow. In contrast, the surface in H2 carrier gas is N-rich below 720°C, but becomes Ga-rich above 850°C. The desorption kinetics indicates that H2 enhances the N desorption.

As wafer diameters increase, monitor wafers become more costly for process characterization and real-time sensors become more attractive. Process-state sensors are generally easier to implement than direct wafer-state sensors, but process-state sensors are usually not thought to provide wafer-state analysis. Utilizing a process-state sensor, such as a mass spectrometer, for wafer-state information will result in new approaches for sensing, optimizing, and controlling integrated circuit fabrication processes. We used a two stage differentially pumped mass spectrometer system sampling directly from an electron cyclotron resonance (ECR) chamber to sense the process-state and monitor end-point during silicon dioxide etch. The end-point uniformity is characterized using mass spectroscopy and material balance modeling. Specifically, using CF4 and D2 etch gases, the partial pressure of CO-containing etch products decays near the endpoint, and the average initial slope is directly correlated with the uniformity determined from optical interferometry thickness measurements. Changing the ECR magnet geometry defines the etch uniformity, and the resulting CO+ end-point signal is sensed with the mass spectrometer. By analyzing the initial slope of the CO+ signal near the end-point, a correlation exists between uniformity and the mass spectrometry signal. A COF2 etch product material balance provides a concentration versus time end-point model which substantiates the correlation between the mass spectrometer signal and the etch uniformity. This model is valid for any sensor that detects a change in the COF2 concentration at the end-point.

A new approach is introduced for identifying a relation between the growth parameters measured in two molecular beam epitaxy systems, thereby realizing transfer of optimized growth conditions transfer. Test results show that the proposed approach is promising.

The fabrication of advanced integrated circuits requires increased accuracy in process monitoring and active control. As higher production yields are required, the technology is moving from statistical process control to in-situ diagnostic techniques. A set of experiments was conducted to explore the feasibility of using radio frequency (RF) impedance probes to detect deviation of electrical characteristics of process chambers during wafer fabrication. A probe was integrated on a plasma-enhanced chemical vapor deposition (PECVD) chamber to explore the sensitivity of the reactor electrical characteristics on the events of process drift or input parameter variation. We measured RF the voltage, current and harmonics, the phase angle and the impedance magnitude for a capacitively coupled reactor. A single frequency (13.56MHz) process for depositing Si0 2 and a dual frequency (13.56MHz+35OkHz) process for Si3N4 deposition were characterized. We investigated the dependence of the RF signature and process parameters such as RF power, pressure, gas flow and electrode spacing. We observed that there is a correlation between the film properties (especially stress) and the plasma electrical characteristics. Furthermore, RF probes can be used to detect chamber malfunctions such as lost of RF ground or wafer-out-of-pocket events.

Optical second-harmonic (SH) generation is used to monitor the anodic growth of oxide on a (001) Si surface. The measured SH intensity is dominated by the nonlinear optical response of the space charge region in the Si just below the Si/oxide interface. The interface SH technique can detect the onset of H desorption, identify the flat band potential, and probe the evolution of space charge within the growing oxide layer.

Single wavelength ellipsometry was used to monitor the CVD growth of Si(1-x)Gex alloys onSi and to evaluate the effect of sample irradiation by KrF laser pulses, performed during or afterthe CVD growth. The information obtained was correlated with AFM analysis results in order tooptimize the growth parameters for an improved morphological quality of the alloy layers.

In-situ, real-time, spectroscopic ellipsometry (SE) is utilized to study thermal chlorine etching of GaAs in an all ultra-high-vacuum interconnected growth and etching system. In the low temperature (between ˜40°C and ˜120°C) range, the etch rate is found to exhibit an Arrhenius dependence on substrate temperature with an activation energy of 11.6Kcal/mole and to be proportional to essentially the square root of the chlorine pressure. An SE feedback based real-time etch process control algorithm is developed and successfully implemented on the basis of the above noted input - output relation derived from the experimental data base.

X-ray diffraction, employing a table-top, laser-driven x-ray source, has been used to investigate laser-material interactions with simultaneous picosecond and subatomic range distance resolution. The x-ray source, consisting of a table-top terawatt laser system and a moving Cu wire target apparatus, generates ˜ 5 × 1010 photons (4π steradians s)−1 of Cu Kα radiation. The lattice dynamics of the (111) planes of GaAs single crystals has been studied after the crystal is exposed to intense femtosecond laser pulses. The diffraction results have yielded information about the timescale of the lattice dynamics in the picosecond range and an upper limit for the width of the xray pulses. Initial strain, defined as the percentage of lattice distortion resulted from the laser illumination, is as high as 0.25% and is followed by an exponential decay with a time constant of ˜ 150 ps. Increases in the diffraction intensity after the laser irradiation have also been observed, likely due to a transition from dynamic to kinematic diffraction associated with degradation of the crystal.

Process monitoring and control during semiconductor device fabrication frequently relies on good knowledge of the optical properties of the substrate wafer and the surface coatings. However, these optical data are often unavailable, and as a consequence errors arise in pyrometric temperature measurements, as well as in thermal modelling of heating cycles. In this study, isothermal electron beam heating has been combined with in situ optical measurements to record thermal emission spectra of undoped InP specimens from 347 to 478°C, at wavelengths between I and 9 μm. The absorption coefficient was deduced from the emission spectra and reveals information about the temperature dependence of the infrared absorption mechanisms in InP.

Specular laser reflectance (He-Ne laser) has been used to monitor in-situ and in real time the growth rate and the index of refraction of oxide films during chemical vapor deposition. This technique has been implemented on an inverted vertical stagnation-flow reactor equipped with a solid-source delivery system. Yttria deposited on silicon has been chosen as a starting material to characterize the reactor and the precursor delivery system capabilities. The experimental reflectance curves have been fitted to a simple three-layer (gas/film/substrate) model allowing the determination of the growth rate and of the refractive index. The growth rate has been studied as a function of various key processing parameters: the source feeding rate, the powder packing density, the oxygen partial pressure and the total pressure. The change in reflectivity has also been recorded during pulsed-delivery growth. Nanometer-scale resolution is obtained which demonstrates that this method can be extended to the study of multilayer oxide structures.

The use of in situ sensors to achieve real-time control of molecular beam epitaxy (MBE) is a rapidly evolving technology that promises to revolutionize MBE in terms of process repeatability and first-pass success, and consequently to improve the overall yield and reduce the cost of the process. To achieve robust real-time control of MBE, we have constructed a multiple-sensor control system comprising in situ sensors for substrate temperature, for effusion cell fluxes, and for the epitaxial layer composition and thickness, along with advanced software to manage the sensor information and execute sensor-feedback control algorithms. This system has been used to grow a number of different III-V semiconductor materials and device structures, including heterojunction bipolar transistors, resonant tunneling devices, and mid-IR lasers. In the present paper, we present results demonstrating control and regulation of substrate temperature and epitaxial layer composition during the growth of lattice-matched InGaAs and InA1As on InP. The control algorithms and software used in the system are described, and we discuss how the synergistic application of multiple sensors allows the regime of composition control to be expanded beyond what would be possible with only a single composition sensor.

Thermal processing in silicon integrated circuit fabrication steps for dopant activation, metal silicides, annealing, and oxidation commonly uses single-wafer furnaces that rapidly heat wafers with incandescent infrared lamps. Radiation pyrometers and thermocouple probes are the principle methods of measuring wafer temperature for closed-loop control of rapid thermal processes. The challenge with thermocouples is in dealing with heat from the lamps and non-ideal thermally resistive wafer contact. The challenge with pyrometry is in compensating for the variable emissivity of wafer surfaces and suppressing interference from the lamps. Typical deposited or grown layers of silicon nitride, silicon dioxide, and polycrystalline silicon can produce dramatic changes in emissivity. Layer thicknesses and composition are generally not known with sufficient accuracy, so a method for real time in situ emissivity compensation is required. Accufiber introduced a “ripple technique” to address this issue. The idea is to use two probes, separately sensing radiation from the wafer and the lamps, and extracting AC and quasi-DC parts from each. The AC signals provide a measure of the reflectivity of the wafer, and thence emissivity, as well as the fraction of reflected lamp radiation present in the DC signals. Lucent Technologies introduced a method of using AC lamp ripple to measure wafer temperatures with two radiation probes at a wall in the furnace. One probe views radiation emanating from the wafer through a gap in the lamp array. The other probe has a wide field of view to include lamp radiation. The accuracy of Lucent devices, determined from process results on wafers with various emissivities, is typically in the range of 12°C to 18°C at three standard deviations.

Monitoring and control in epitaxy based on chemical vapor deposition is a challenge created by growth conditions that often preclude more common sensors like thermocouples and mass spectrometry. We report results of experiments to measure and control temperature and flux by non-invasive optical sensing. We have developed a temperature control system with precision and accuracy better that 5°C. Satisfactory control of flux poses difficulties that will require innovative solutions before a useful control system can be developed.

In addition to being an established technique for ex-situ structural studies, x-ray absorption spectroscopy (XAS) has recently been realized to be a powerful tool for in-situ time-resolved investigations in materials science. This paper describes two complementary techniques: quick-scanning EXAFS (QEXAFS) and energy-dispersive XAS (DXAS) which offer time resolution in the seconds and milliseconds range, respectively. Formation of a heterogeneous catalyst from a solid-state reaction of a precursor is presented as an example of a time-resolved XAS application.

Polycapillary optics, shaped arrays consisting of hundreds of thousands of hollow glass capillary tubes, are used to redirect, collimate, or focus x-ray beams from conventional laboratory-based sources. Focused spot sizes as small as 20μm have been measured, with flux densities two orders of magnitude larger than that produced by pinhole or crossed slit collimation. Such flux increases have made possible faster and more sensitive x-ray fluorescence (XRF) and diffraction measurements to the extent that in situ measurements become possible. XRF data taken with a 12 W source were comparable to data taken with a 1.5 kW source. Ex situ diffraction and texture measurements on thin multilayered films and single crystal silicon demonstrate the tremendous experimental and analytical improvements made possible by polycapillary optics.

With 0.5° and 2° focusing polycapillary x-ray optics, diffraction intensity gains of more than two orders of magnitude were measured on small Lysozyme protein crystals with exposure times an order of magnitude less than required by traditional measurement techniques

In addition, the optics greatly reduce the background high energy Bremsstrahlung, permitting more accurate analysis of thin complex multilayer diffraction peaks. Rapid measurement times resulting from the application of these polycapillary optics, indicate tremendous possibilities for in situ process monitoring

Fe/Ag multilayers, prepared by pulsed laser deposition (PLD) using KrF radiation, were characterized in-situ by RHEED (diffraction of high energetic electrons) and resistance measurements during deposition, and by X-ray diffraction after deposition. While the x-ray diffraction experiments give indications for sharp interfaces, the in-situ investigations clearly show an asymmetry of the structural behaviors at the interfaces and mixing effects on a nm scale, especially as soon as Fe is deposited on Ag. Time-of-flight (TOF) measurements performed with a Faraday cup show that during PLD in ultrahigh vacuum ions are deposited with kinetic energies of more than 100 eV. The results are modeled and discussed with respect to implantation and mixing effects due to the high kinetic energy of the deposited particles during PLD.

Spatially nonuniform electrodeposition can cause discrepancies between predicted and experimentally measured mass loadings on an electrochemical quartz crystal microbalance (EQCM) since the sensitivity of the quartz crystal varies significantly from point to point. These discrepancies can be significant even if the current distribution is nearly uniform. These effects were examined experimentally by varying the conductivity of the electrolyte and the current density during the electrodeposition of copper on an EQCM, effecting changes in the spatial, deposited-mass distribution in a controlled manner. The resulting frequency shifts are in agreement with results predicted by current distribution simulations, validated a posteriori with profilometry measurements. Our results permit determination of the spatial variation of the quartz crystal sensitivity factor or of the current distribution on the EQCM.