P. A. Coon

Desorption kinetics of hydrogen and deuterium from Si(111) 7×7 studied using laser‐induced thermal desorption

The desorption of hydrogen and deuterium from Si(111) 7×7 was studied using laser‐induced thermal desorption (LITD) and temperature programmed desorption (TPD) mass spectrometry. Isothermal LITD measurements enabled the surface coverage of hydrogen and deuterium to be monitored as a function of time. These isothermal results were used to obtain accurate desorption kinetics of hydrogen and deuterium from the high‐temperature β1 state on Si(111) 7×7. The desorption of hydrogen displayed second‐order kinetics with an activation barrier of 61±4 kcal/mol and a preexponential factor of 1.2×101±1.3 cm2/s. Likewise, the desorption kinetics of deuterium displayed second‐order kinetics with an activation barrier of 59±3 kcal/mol and a preexponential factor of 2.8×100±1.0 cm2/s. These desorption activation barriers yield upper limits of 82.6 and 81.6 kcal/mol for the Si–H and Si–D chemical bond energies, respectively, on Si(111) 7×7. TPD results obtained as a function of hydrogen coverage were consistent with second...

Adsorption and desorption kinetics for SiCl4 on Si(111)7×7

The adsorption and desorption kinetics for SiCl4 on Si(111)7×7 were studied using laser‐induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. TPD experiments monitored SiCl2 as the desorption product at approximately 950 K using a heating rate of β=9 K/s. SiCl2 was also observed as the desorption product in the LITD yield at all surface coverages. LITD measurements determined the initial reactive sticking coefficient (S0) of SiCl4 on Si(111)7×7 versus surface temperature. The sticking coefficient was observed to decrease with surface temperature from S0≊0.18 at 160 K to S0≊0.03 at 600 K. TPD experiments revealed that the chlorine surface coverage saturated after large SiCl4 exposures and the saturation coverage was independent of surface temperature. Isothermal LITD studies enabled the surface chlorine coverage to be monitored as a function of time during SiCl2 desorption. These studies revealed second‐order desorption kinetics for SiCl2 with a desorption activation bar...

Desorption product yields following Cl2 adsorption on Si(111)7 × 7: Coverage and temperature dependence

Desorption product yields obtained following adsorption of Cl2 on Si(111)7 × 7 were studied using temperature-programmed desorption (TPD) and laser-induced thermal desorption (LITD) techniques. At low chloride coverages of ΘΘs 0.6, a small SiCl4 TPD signal was also monitored at 950 K along with an additional SiCl2 TPD feature at 690 K. LITD experiments detected SiCl2 as the only desorption product in the LITD yield at low chloride coverages of ΘΘs 0.6. In t LITD studies, the SiCl2 LITD signals persisted until 950 K, whereas the SiCl3 LITD signals were only observed up to 700 K. The magnitude of the SiCl3 LITD signal following saturation chlorine exposures also decreased as a function of adsorption temperature. The SiCl2 desorption products were assigned to the recombinative desorption of SiCl + Cl → SiCl2. The SiCl3 LITD signals were attributed to either the direct desorption of SiCl3 surface species or the recombinative desorption of SiCl2 + Cl → SiCl3. Based on photoemission and scanning tunneling microscopy investigations, the SiCl2 and SiCl3 desorption yields were correlated with the existence of mono-, di- and trichloride species on the Si(111)7 × 7 surface. Many similarities were also observed between the chlorides and hydrides on the Si(111)7 × 7 surface.

Diethylsilane on silicon surfaces: Adsorption and decomposition kinetics

The adsorption and decomposition kinetics of diethylsilane (DES), (CH3CH2)2SiH2, on silicon surfaces were studied using laser‐induced thermal desorption (LITD), temperature programmed desorption, and Fourier transform infrared (FTIR) spectroscopic techniques. LITD measurements determined that the initial reactive sticking coefficient of DES on Si(111) 7×7 decreased versus surface temperature from S0≊1.7×10−3 at 200 K to S0≊4×10−5 at 440 K. The temperature‐dependent sticking coefficients suggested a precursor‐mediated adsorption mechanism. FTIR studies on high surface area porous silicon surfaces indicated that DES adsorbs dissociatively at 300 K and produces SiH and SiC2H5 surface species. Annealing studies also revealed that the hydrogen coverage on porous silicon increased as the SiC2H5 surface species decomposed. CH2=CH2 and H2 were the observed desorption products at 700 and 810 K, respectively, following DES adsorption on Si(111) 7×7. The ethylene desorption and growth of hydrogen coverage during eth...

Decomposition of NH3 on Si(111) 7×7 studied using laser‐induced thermal desorption

The decomposition of ammonia on Si(111) 7×7 was studied using laser‐induced thermal desorption (LITD), temperature‐programmed desorption (TPD), and Auger electron spectroscopy (AES). Product yields versus NH3 exposure were determined using TPD and LITD measurements. Besides the NH3 multilayer desorption, the only TPD products were H2 and Si2 N, which desorbed at ∼800 and 1350 K, respectively. H2 was also observed in the LITD yield from NH3 on Si(111) 7×7. In addition, NH3 , SiNH2, and SiNH were detected in the LITD yield at temperatures above the NH3 multilayer desorption. After saturation NH3 exposures, the LITD desorption yield for NH3 and SiNH2 persisted until 700 K, and the SiNH LITD signals were observed up to 800 K. These SiNH2 and SiNH LITD signals were assigned to reaction intermediates on the Si(111) 7×7 surface because neither SiNH2 nor SiNH was observed in the TPD yield. The effect of preadsorbed deuterium on the reactive adsorption of NH3 was also investigated. Deuterium was observed to decrea...

FTIR studies reveal that silicon-containing laser-induced desorption products are surface reaction intermediates

Abstract Silicon-containing laser-induced desorption (LID) products such as SiOH and SiNH 2 have been observed from Si(111) 7 × 7 surfaces exposed to H 2 O and NH 3 . Assuming that the LID species were derived from surface reaction intermediates, these LID products were employed to examine the thermal stability of the SiOH and SiNH 2 surface species. Fourier transform infrared (FTIR) transmission spectroscopy was recently utilized to monitor the decomposition of SiOH and SiNH 2 surface species following the dissociative adsorption of H 2 O and NH 3 on porous silicon surfaces. The FTIR results on porous silicon surfaces were in excellent agreement with the previous LID studies on Si(111) 7 × 7. The correspondence between the FTIR and LID investigations indicates that silicon-containing LID products are derived from silicon surface reaction intermediates.

Adsorption and Desorption Kinetics for Chlorosilanes on Si(111) 7×7

The adsorption and desorption kinetics for SiCl 4 and SiCl 2 H 2 on Si(111) 7×7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Both LITD and TPD experiments monitored SiCl 2 as the main desorption product at 950 K at all coverages of SiCl 4 and SiCl 2 H 2 on Si(111) 7×7.HC1 desorption at 850 K and H 2 desorption at 810 K were also observed following SiCl 2 H 2 adsorption. Isothermal LITD measurements of SiCl 4 and SiCl 2 H 2 ) adsorption on Si(111) 7×7 revealed that the initial reactive sticking coefficient decreased with increasing surface temperature for both molecules. The temperature-dependent sticking coefficients were consistent with precursor-mediated adsorption kinetics. Isothermal LITD studies of SiC1 2 desorption revealed second-order SiCl 2 desorption kinetics. The desorption kinetics were characterizedby a desorption activation energy of E d = 67 kcal/mol and a preexponential of vd = 3.2 cm 2 /s. TPD studies observed that the HCI desorption yield decreased relative to H 2 and SiCl 2 desorption as a function of surface coverage following SiCl 2 H 2 exposure. These results indicate that when more hydrogen desorbs as H 2 at higher coverages, The remaining chlorine is forced to desorb as SiCl 2 .

Adsorption and Decomposition of Diethylsilane on Silicon Surfaces

Diethylsilane (DES), Si(C 2 H 5 ) 2 H 2 , is a promising candidate for the atomic layer epitaxy of silicon. The adsorption and decomposition kinetics of DES on silicon surfaces were studied using laser-induced thermal desorption (LITD), temperature programmed desorption (TPD), and Fourier transform infrared (FTIR) spectroscopy. FTIR studies on porous silicon surfaces indicated that DES dissociatively adsorbs below 600 K and produces Si-H and Si-C 2 H 5 surface species. The desorption products following DES adsorption on Si(111) 7×7 were C 2 H 4 and H 2 for all surface coverages using both LITD and TPD techniques. Ethylene and H 2 desorption occurred at 700 and 810 K, respectively, during TPD experiments with a heating rate of β = 9 K/s. Ethylene desorption was consistent with a β-hydrogen elimination mechanism from the Si-C 2 H 2 surface species. Isothermal LITD studies monitored the desorption kinetics of C 2 H 4 from Sl (111) 7×7 as a function of time following DES exposures. The first-order ethylene desorption kinetics were E d = 36 kcal/mol and v d = 2.7 × 10 9 s −1 . Additional LITD measurements determined that le initial reactive sticking coefficient of DES on Si(111) 7×7 decreased versus surface temperature. The temperature-dependent sticking coefficients suggested a precursormediated adsorption mechanism.

Growth of SiO 2 on Si(111)7×7 Using SiCl 4 and H 2 O

The controlled atomic layer growth of SiO 2 insulating layers on silicon surfaces might be achieved through the sequential reaction of SiCl 4 and H2 O : (A) Si-Cl + H 2 O → Si-OH + HCl (B) Si-OH + SiCl 4 → Si-O-SiCl 3 + HCl. To explore this ABAB… binary reaction scheme, laser-induced thermal desorption, temperature-programmed desorption, and Auger electron spectroscopy techniques were utilized to measure the kinetics of H 2 O oxidation of a Si(111)7×7 surface that had been previously subjected to a saturation SiCl 4 exposure. Reaction kinetics studies for the oxidation of the chlorinated surface revealed that the rate of oxygen gain and the rate of chlorine loss were equal at reaction temperatures between 200 K and 700 K. These results were consistent with a direct substitution reaction according to: (A) Si-Cl + H2O → Si-OH + HCl. Above 700 K, the amount of oxygen gain became progressively greater than the amount of chlorine loss. This behavior was associated with the thermal desorption of H 2 and the resultant formation of new dangling bond sites for H 2 O adsorption. For all temperatures, the oxidation kinetics of the chlorinated surface were nearly equivalent to the kinetics for the oxidation of clean silicon. This surprising result indicates that chlorine sites and free dangling bond sites react with equal probability to H 2 O. The kinetics of SiCl 4 deposition were also measured on a Si(111)7×7 surface previously exposed to a saturation H 2 O dose. This chlorination reaction occurred at a much slower rate and was not as amenable to UHV studies.

Laser-induced thermal desorption studies of surface reaction kinetics

Laser induced thermal desorption (LITD) has proven to be an effective probe of reaction kinetics on single-crystal surfaces. The ability of LITD techniques to measure adsorption, decomposition and desorption kinetics will be illustrated by studies of SiCl4 and (CH3CH2)2 SiH2 on Si(111)7X7. Silicon tetrachloride, SiCl4, is important in silicon epitaxial growth and diethylsilane, (CH3CH2)2 SiH2, is a promising candidate for silicon atomic layer epitaxy. The desorption products, sticking coefficients and decomposition and desorption kinetics measured by these LITD investigations are important for an understanding of silicon epitaxy by chemical vapor deposition.