J. A. Mackenzie

Semiconductor substrate temperature measurement by diffuse reflectance spectroscopy in molecular beam epitaxy

The temperature of semiconductor substrates used in molecular beam epitaxy is determined from the diffuse reflection spectrum (DRS) of the substrates, measured with an external light source. The relative sensitivity of the technique is better than 1 °C. The absolute calibration of the DRS technique for substrates of different thickness, conductivity and back surface texture, is described. The DRS technique is also sensitive to changes in front surface roughness as demonstrated by the increase in the diffuse reflectance at short wavelengths when the oxide desorbs.

Oxide thickness effect and surface roughening in the desorption of the oxide from GaAs

The temperature for thermal desorption of the gallium oxide from GaAs is shown to increase linearly with oxide thickness. In addition, we show by diffuse light scattering that highly polished GaAs substrates roughen during the oxide desorption. These results are interpreted in terms of a model in which the oxide evaporates inhomogeneously.

Diffuse optical reflectivity measurements on GaAs during molecular-beam epitaxy processing

In situ measurements of the diffuse and specular reflectivity of GaAs substrates in molecular‐beam epitaxy show that the GaAs surface roughens during thermal desorption of the oxide and smooths during the growth of a buffer layer. The diffuse reflectivity increases abruptly over a temperature interval smaller than 0.4 °C as the oxide desorbs. This provides a convenient optical signature for determining when the substrate is clean. The oxide desorption temperature and the amount of surface roughening both increase with the thickness of the oxide. The decrease in the diffuse reflectivity during the growth of the buffer layer is not monotonic, showing instead an oscillatory behavior.

Semiconductor substrate cleaning and surface morphology in molecular beam epitaxy

Abstract In-situ laser light scattering shows that the surface morphology of GaAs substrates during the initial stages of homoepitaxial growth is a sensitive indicator of substrate cleanliness. Oxide removal by atomic-hydrogen etching has no effect on the morphology of polished (100) GaAs substrates, while thermal oxide desorption roughens the surface. Carbon contamination of the surface causes roughening during subsequent film growth. Secondary ion mass spectrometry and photoemission spectroscopy show that atomichydrogen etching reduces the carbon contamination on the substrate but does not remove silicon oxide. Synchrotron radiation photoemission measurements show that some as-received substrates are contaminated with a thin uniform layer of SiO 2 .

Film thickness and composition monitoring during growth by molecular beam epitaxy using alpha particle energy loss

The α-particle energy loss method (AEL) has been implemented in situ to monitor film thickness during growth by molecular beam epitaxy. For InP and GaAs substrates recoil implanted with α-particle emitters, we have been able to measure thickness and composition of deposited GaAs, AlGaAs and InGaAs in real time. The AEL method yields in situ real time results comparable in accuracy to those obtained by ex situ scanning electron microscope and high-resolution x-ray diffraction measurements.The α-particle energy loss method (AEL) has been implemented in situ to monitor film thickness during growth by molecular beam epitaxy. For InP and GaAs substrates recoil implanted with α-particle emitters, we have been able to measure thickness and composition of deposited GaAs, AlGaAs and InGaAs in real time. The AEL method yields in situ real time results comparable in accuracy to those obtained by ex situ scanning electron microscope and high-resolution x-ray diffraction measurements.

Factors affecting the temperature uniformity of semiconductor substrates in molecular‐beam epitaxy

The temperature of GaAs substrates is profiled in a molecular‐beam epitaxy system with a spatial resolution of 3 mm and a thermal resolution of 0.4 °C, respectively. The effects of substrate doping, back surface textures, thermal contact to the holder, and a pyrolytic boron nitride diffuser plate, on the temperature uniformity, are explored for indium‐free mounted substrates. Both positive and negative curvature temperature profiles are observed.

In situ thickness measurements in molecular beam epitaxy using alpha particle energy loss

Abstract The α-particle energy loss method has been implemented in situ to monitor film thickness during growth by molecular beam epitaxy. For InP and GaAs substrates dosed with 500–1500 Bq of α-particle emitters, we have been able to measure thickness in situ of deposited GaAs and InP, to an accuracy of 6 nm in 180 s of counting time. The corresponding growth rate accuracy for growth rates on the order of 0.3 nm/s was ±0.01 nm/s. The accuracy and counting time improvements expected with the use of a stronger marking source are also discussed.

In situ real time monitoring of thickness and composition in MBE using alpha particle energy loss

The α-particle energy loss method (AEL) has been implemented in situ to monitor film thickness and composition during growth of GaAs, InP and LaF 3 based materials by molecular beam epitaxy (MBE). In the AEL method, a 228 Th source is used to recoil implant a 5 mm diameter region of the surface of the wafers with the α-emitter daughter isotope 224 Ra prior to growth. The implanted nuclei decay with a half life of 3.7 days through a sequence of daughters which emit alpha particles at different energies. Deposition on the surface causes the emission lines to be shifted to lower energies due to energy loss in the film. For substrates marked with a low activity (∼ 30 kBq; similar to activity of smoke detectors) we are able to measure film thickness with ± 6 nm uncertainty and growth rate with ± 0.01 nm/s uncertainty in real time. By measuring the relative growth rates of the different materials, AEL also allows us to infer the composition of a ternary laver film as well as the sticking coefficients rates directly at different growth temperatures.