Optical emission and line-of-sight mass spectrometry were used to monitor Cl, Cl2 and SiClx reaction products during etching of Si(100) in a high density (1–2 × 1011 ions/cm3) chlorine plasma. Emission from atomic Cl, and from ion-pair states of C12 at 7.2 – 9.4 eV were monitored, along with emission from a small amount of Xe that was added to the gas to sense changes in the electron energy distribution (i.e. actinometry). In this manner, the normalized emissions provide a measure of relative number densities of C12 and Cl. These measurements were converted into absolute numbers by extending the measurements to extremely low powers, where C12 and Xe number densities are known. These results are compared with those recorded with a differentially pumped, line-of-sight mass spectrometer. At power densities of ˜0.5 W/cm3, the discharge is almost completely dissociated in the plasma source region (˜90%), while above the wafer and downstream of the plasma, the percent consumption of Cl2 drops to 75%. A long term upward drift in the percent dissociation in the source was observed, attributable to a time-dependent decrease in the rate of Cl-atom recombination on the glass walls. These results are compared with recent model predictions and are also discussed in terms of their significance for surface etching reactions, and real-time control.

Advanced diagnostics of high-density inductively coupled plasmas (ICPs) are presented supporting the following three proposals of innovative etching modes: First, pulsed plasma etching mode can suppress charge-up on high-aspect-ratio micro-patterns. In order to understand the mechanism, time-resolved measurements of electrons, chlorine atoms and negative ions in a pulsed chlorine ICP are performed. As a result of electron cooling and negative ion yield in afterglow, electrons are found to be accelerated toward a rf-biased electrode, thus neutralizing positive surface charges on that. Second, downstream etching mode using C4F8 gas enables high etch selectivity of SiO2 to Si. The reason for this is qualitatively discussed using comprehensive measurements of spatial distributions of CF3, CF2, CF and F densities in CF4 and C4F8 plasmas. Third, hot wall etching mode also enables high selectibity etching in fluorocarbon plasmas. Radical diagnostics reveal that wall heating dramatically modifies the radical composition of both CF4 and C4F8 plasmas, and it improves the etch selectivity and reproducibility.

Plasma etching of III-V heterostructures has been monitored using optical emission spectroscopy and mass spectrometry. For the Ga optical emission signal at 417.2 nm, a response time as fast as 0.2 s has been measured. The response time of the mass spectrometer is limited by the transit time of etch products from the wafer surface to the ionizer. A minimum response time of 0.9 s was measured by reducing the signal integration time of the mass spectrometer. Saturation of the optical emission signal has been shown to be related to the residence time of etch gases by varying the flow rate or pressure. Decreasing residence time by reducing the pressure from 6 to 2 mTorr and maintaining a constant flow rate caused the Ga emission signal saturation time to decrease from 7 to 3 min. The 145ASC12+ signal saturated before the Ga emission signal at 417.2 nm. Endpoint detection for etching an AlInAs emitter and stopping on a GaInAs base was studied. By monitoring the changes in the Ga emission intensity, only 2 nm of the GaInAs base layer had been removed when the emitter etch was stopped.

We present evidence of a direct reaction occurring when a hyperthermal fluorine atom beam (4.8 eV) impinges on a fluorinated silicon surface under steady-state etching conditions. When monitoring in-situ and in real time reactive scattering products by means of a quadrupole mass spectrometer, SiF3+ and SiF2+ are detected with bimodal time of flight distributions. The slow component can be described by a Maxwell-Boltzmann distribution at the surface temperature. However, the fast component is leaving the surface with velocities substantially higher than thermal and with a flux which does not obey the cosine law. Its translational energy increases with the angle of incidence of the hyperthermal fluorine beam. Etching in the direct reaction mode should result in highly anisotropic profiles by overcoming product desorption limitations.

Thermal decomposition of SiH4, Si2H6, SiF4 and SiH2F2 used as the reactants in the Si-CVD process was studied by monitoring the gaseous products with a quadrupole mass spectrometcr (QMS). The rates of SiH4 pyrolysis showed a large compensation effect at low pressures, which agreed with the theory of unimolecular reaction. Si2H6 decomposed at relatively low temperatures producing SiH4 as the intermediate products. The decomposition temperatures of the other compounds increased in the order of SiH4, SiH2F2 and SiF4. The pyrolysis rates of SiH2F2 and silanes, i.e., SiH4 or Si2H6, were enhanced synergically when they were mixed together. The results were explained by a reaction mechanism proposed based on analysis of the intermediates produced in the process.

High density plasmas are being increasingly employed in both the deposition of low temperature, high quality passivant films and for highly anisotropic, nanometer-scale pattern transfer. The high degree of control necessary in these processes emphasizes the need for a more complete understanding of the basic physical and chemical mechanisms involved. To this end, a wide range of diagnostic techniques have been employed to characterize electron cyclotron resonance microwave plasmas applied to the etching of semiconductors in both chlorine- and methane-based chemistries. In particular, vacuum ultraviolet spectroscopy has been employed to identify important reactants and, where feasible, measure plasma constituent temperatures (e.g., neutral temperatures range from 0.1–0.3 eV in these plasmas). Langmuir probes, microwave interferometry and microwave electric field probes are used to monitor plasma parameters as a function of process conditions and provide understanding of microwave power deposition. Mass spectroscopy is utilized to characterize the plasma flux incident on the substrate, in terms of mass signature and charge state distribution. This flux is largely ionic with a considerable degree of dissociation, highly appropriate for directional etching. Results from each of these diagnostics are incorporated into an evolving predictive model for highly anisotropic, nanometer-scale etching of semiconductors.

Laser-induced fluorescence(LIF) spectroscopy has been applied to the detection of excited nitrogen molecules coming out of a plasma source used for p-type doping of ZnSe. With the use of a fluorescence-photon-counting system, the fluorescence of nitrogen molecules in the A3 Σ u+ (v=0) state was observed even in a high vacuum condition ˜ 10−4 Pa. The correlation between LIF intensity of nitrogen molecules in the A3 Σ u+(v=0) state and the net acceptor concentration of nitrogen doped ZnSe epitaxial layers was investigated.

We show that in the RPECVD process the addition of a small upstream flow of H2 gas, combined with the He injected into the plasma region of the reactor, promotes chemical exchange between H and D when the material was deposited from deuterated Silane and ammonia and densifies the a- Si:N:H network. We have deposited hydrogenated stoichiometric nitrides with and without H2 injected into the plasma region. For small H2 flows, the deuterated samples show Fourier transform infrared (FTIR) N-D and N-H stretching and bending modes that interchange their populations, as the total bonded hydrogen content in the films remain constant. The hydrogen assisted grown films show, for small H2 flows, a constant amount of bonded-H, an optical index of refraction n=1.85, and reduced etch rate.

Hydrogenated silicon nitride films were deposited in a remote plasma reactor using a plasmaexcited NH3/He mixture, and with downstream injection of SiH4. An electrically biased grid placed between the plasma tube and the deposition region was used to control the extent of the plasma afterglow into the deposition region. In situ monitoring by mass spectrometry (MS) indicated that the Si content of the film was increased when charged species were transported from the plasma region to the deposition region of the chamber, and that the properties of the resulting films could be understood in terms of two different deposition pathways, driven respectively by neutral, and a combination of neutral and charged precursor species.

We demonstrate the use of diffuse reflectance spectroscopy as a non-invasive probe for measurement of temperature in real time on Si and GaAs substrates during semiconductor processing. Our results show that the standard deviation of the non-invasive optical technique is less than 0.7 °C for GaAs over the temperature range 50 °C < T< 600 °C with 5-second updates. These results support the notion that non-invasive optical temperature measurement can be used in semiconductor processing with a precision exceeding that of a thermocouple.

The increase in wafer temperature due to plasma heating during etching has been studied. Si and InP were etched using a high ion density discharge generated by an electron cyclotron resonance source. The wafer temperature was measured in-situ using fiberoptic thermometry as microwave power, rf power, chamber pressure, and gas flow were varied. Wafer temperatures increased with both microwave and rf power, and decreased with chamber pressure. For rf power of 50 W, chamber pressure of 1 mTorr, a source distance of 13 cm, and 10 sccm Ar flow, an increase in microwave power from 50 to 500 W caused the temperature to increase from 62 to 186 °C. Additionally, the use of He flowing at the backside of the wafer for temperature control was analyzed. By setting the backside He pressure at 3 Torr, the temperature increased from 20 °C at the beginning of the etch to only 29 °C after 12 min. Time dependent etch characteristics of InP were studied and related to the wafer temperature measurements. At 100 W microwave power, the InP etch rate increased from 100 to 400 nm/min as the wafer temperature rose from 20 to 150 °C. As the temperature increased above 150 °C, the profile became more undercut and the surface morphology improved. By setting the stage temperature to -100 °C and using 3 Torr He pressure at the backside of the wafer, the InP etch rate remained constant during etching and undercutting was suppressed. For 500 W microwave power, a fast InP etch rate of 2 μm/min was obtained when the wafer temperature was <110 °C, and it increased to over 4 μm/min when the temperature was >150 °C.

An optical spectroscopy system was configured to monitor several plasma positions at the same time. The system allows monitoring of several points within a single plasma. Magnetron sputtering of YBa2Cu3O7 (YBCO) in a reduction-oxidation (redox) environment provided a process in which both cation and gas species are vital in determining the quality of the product film. Spatial sampling of the sputter plasma defined a disparity in the manner in which Ba and Cu emissions respond to changes in chamber gas composition. Oxygen emissions were found to respond quickly to inlet gas composition while Cu emissions were notably sluggish.

The goal of this paper is the presentation of a new algorithm for determining etch rate from single or multiple wavelength reflectometry data. This algorithm is based on techniques from recursive nonlinear estimation theory — Extended Kalman Filtering. A major advantage of our algorithm is extremely high speed. Consequently, it can be used in real-time feedback control applications. The speed advantage also makes it a suitable candidate for full wafer high speed etch rate measurement.

Non-linear optical second harmonic generation (SHG) from bulk silicon is very weak because of the inversion symmetry of the silicon lattice structure. However, when silicon material is subjected to the ion implantation and thermal annealing processes, the inversion symmetry will be broken. As a result, the optical second harmonic generation from the material will increase, and the characteristics of the second harmonic signal are related to the material conditions. In this study, we compare SHG results with Transmission Electron Microscope (TEM) observations for silicon material that has been treated with phosphorous ion implantation and rapid thermal annealing, and suggest that the SHG method may be used for the detection and monitoring of impurities and defects during ion implantation and thermal annealing processes.

Single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) is used in situ to monitor desorbing species and surface reactions during molecular beam epitaxy (MBE) of GaAs. In this method, the 1064 nm fundamental output of a Nd:YAG laser is tripled twice to produce 118 nm (10.5 eV) photons. The pulsed light is passed in front of a growing substrate, giving gaseous scattered molecules sufficient energy to ionize, but not fragment, them. Ionized species are detected with time-of-flight mass spectrometry. Arrangement of the experiment also allows for simultaneous real time monitoring with reflection high-energy electron diffraction (RHEED).

Mass spectra are examined and analyzed to quantify fluxes and relative ionization cross sections of growth species. The real time behavior of arsenic and gallium mass signals during epitaxy is presented as a function of substrate temperature and incident gallium flux. Surface reactions are proposed to elucidate mechanisms of arsenic incorporation and compared to measured RHEED results.

In this paper we discuss the use of optical-based flux monitoring (OFM) for real-time control of atomic antimony fluxes for applications in molecular beam epitaxy. Atomic antimony beams were generated using a two-zone cracking effusion cell. The product distribution of the source was characterized using a time-of-flight mass spectrometer employing resonance-enhanced laser ionization. A double-pass OFM system has been developed to monitor the atomic antimony beam that is capable of precise flux measurement during MBE growth.

We report application of in-situ laser reflectometry in monitoring InAl1−xAs (0 ≤ x ≤1) epitaxial layers grown on a GaAs substrate by low pressure metal-organic chemical vapor deposition. Two different lasers were used simultaneously: One was a He-Ne laser operating at 0.6328 μm and the other was a diode laser operating at 1.53 μm. The two laser beams were incident on the growing layer at an angle of 71° from the surface normal, and the reflected beams were detected by Si and Ge photovoltaic detectors, respectively. Since the epitaxial layer of InxAl1−xAs (0 ≤ x ≤1) has a wide range of index of refraction, the reflected signals showed a variety of patterns. The optical constants of the InxAl1−xAs epitaxial layers were obtained for the entire range of composition.

We present a detailed study of the influence of growth parameters on the broadening of CdTe-CdMnTe interfaces using a new magneto-optical technique [1,2] in MBE-grown quantum wells and superlattices. For growth temperatures up to about 300°C the Mn content decreases exponentially at the CdTe on CdMnTe interface and conversely the Cd one decreases exponentially at the CdMnTe on CdTe interface. At temperatures exceeding 300°C an additional broadening takes place which acts equally on both interfaces. Growth interruptions and modified flux stoechiometry do not exhibit significant influence on the broadening.

In this paper we report the combined application of p-polarized reflectance spectroscopy (PRS), reflectance difference spectroscopy (RDS), and laser light scattering (LLS) to investigate the heteroepitaxy of GaxIn 1−xP/GaP on Si by pulsed chemical beam epitaxy (PCBE) with tertiarybutylphosphine (TBP), triethylgallium (TEG), and trimethylindium (TMI) precursors. Both, PRS and RDS follow the growth process with submonolayer resolution utilizing a periodic fine structure signal, which is caused by a periodic alteration of thickness and composition of an ultra-thin surface reaction layer during the periodic TEG and TBP exposure of the surface. After the transition from GaP growth to GaxIn 1−xP growth, the RDS oscillations are reoriented after about five precursor cycles in a new oscillation periodicity, where the response to the TBP pulse has the opposite direction. The ratio of the changes in the amplitudes of RDS signals as a response to TEG and TMI surface exposure is used to estimate the composition fo GaxIn 1−xP. The PRS fine structure is maintained after switching to GaxIn 1−xP growth with a separate feature for each TEG and TMI surface exposure. The amplitude ratio of these features changes during growth.

Metalorganic chemical vapor deposition (MOCVD) is a process used to manufacture electronic and optoelectronic devices that has traditionally lacked real-time growth monitoring and control. We have developed control strategies that incorporate monitors as real-time control sensors to improve MOCVD growth. An analog control system with an ultrasonic concentration monitor was used to reject bubbler concentration disturbances which exist under normal operation, during the growth of a four-period GaInAs/InP superlattice. Using X-ray diffraction, it was determined that the normally occurring concentration variations led to a wider GaInAs peak in the uncompensated growths as compared to the compensated growths, indicating that closed loop control improved GaInAs composition regulation. In further analysis of the X-ray diffraction curves, superlattice peaks were used as a measure of high crystalline quality. The compensated curve clearly displayed eight orders of satellite peaks, whereas the uncompensated curve shows little evidence of satellite peaks.