A.W. Ott

Al3O3 thin film growth on Si(100) using binary reaction sequence chemistry

Al2O3 films with precisely controlled thicknesses and excellent conformality were grown on Si(100) at low temperatures of 350–650 K using sequential surface chemical reactions. This controlled deposition was achieved by separating a binary reaction for Al2O3 chemical vapor deposition (2Al(CH3)3 + 3H2O → Al 2O3 + 6CH4) into two half-reactions:(A)A1OH*+A1(CH3)3→A1OA1(CH3)2*+CH4(B)A1CH3*+H2O→A1OH*+CH4 In the above reactions, the trimethylaluminum [Al (CH3)3] (TMA) and H2O reactants were employed alternately in an ABAB… binary reaction sequence where the asterisks designate the surface species. At the optimal reaction conditions, a growth rate of 1.1 A per AB cycle was measured on the Si (100) substrate using ellipsometry. These Al 2O3 films had an index of refraction of n= 1.65 and a corresponding density of ρ = 3.50 g cm−3. Additional ellipsometric measurements revealed that the Al2O3 deposition rate per AB cycle decreased at substrate temperatures >450 K. The decrease in the growth rate closely matched the thermal stability of the AlOH*and AlCH3* surface species previously measured with FTIR spectroscopy. This correlation supports a reaction mechanism based on self-limiting surface chemistry. Atomic force microscope images revealed that the deposited Al 2O3 films were exceptionally flat with a surface roughness of only ± 3 A (rms) after 500 AB cycles and the deposition of a film thickness of ∼ 560 A. The power spectra of the surface topography measured by AFM also demonstrated that the surface roughness was nearly identical for the initial Si(100) substrate and the deposited Al2O3 filmsafter 20–500 AB reaction cycles.

Surface chemistry of Al2O3 deposition using Al(CH3)3 and H2O in a binary reaction sequence

Sequential surface chemical reactions for the controlled deposition of Al2O3 were studied using transmission Fourier transform infrared (FTIR) spectroscopy. A binary reaction for Al2O3 chemical vapor deposition (2Al (CH3)3 + 3H2O → Al2O3 + 6CH4) was separated into two half-reactions: (A) AlOH + Al(CH3)3 → Al-O-Al(CH3)2 + CH4; (B) Al-O-Al(CH3)2 + 2H2O → Al-O-Al(OH)2 + 2CH4. The trimethylaluminum [Al(CH3)3] (TMA) and H2O reactants were employed alternately in an ABAB … binary reaction sequence to achieve controlled Akl2O3 deposition. FTIR analysis of these surface reactions was performed in situ in an ultrahigh vacuum (UHV) chamber using high surface area alumina membranes. The AlOH and AlCH3 surface species were monitored by the infrared absorbance of the AlO-H stretching vibrations between 3800 and 2600 cm−1 and the AlC-H3 stretching vibrations between 2942 and 2838 cm−1. The optimal conditions for controlled Al2O3 growth were observed using TMA and H2O exposures at 0.3 Ton on substrates at 500 K. The spectra revealed that both the (A) and (B) reactions were self-limiting and complete. The thermal stabilities of the AlOH and Al(CH3)x surface species on alumina were also measured versus annealing between 300 and 900 K. In addition, the deposition of amorphous Al2O3 thin films was demonstrated on Si (100) using the ABAB … binary reaction sequence.

Atomic layer controlled growth of SiO2 films using binary reaction sequence chemistry

SiO2 thin films were deposited with atomic layer control using binary reaction sequence chemistry. The SiO2 growth was accomplished by separating the binary reaction SiCl4+2H2O→SiO2+4HCl into two half-reactions. Successive application of the half-reactions in an ABAB… sequence produced SiO2 deposition at temperatures between 600 and 800 K and reactant pressures of 1–10 Torr. The SiO2 growth was monitored using ellipsometry versus substrate temperature and reactant exposure time. The maximum SiO2 deposition per AB cycle was 1.1 A/AB cycle at 600 K. The surface topography measured using atomic force microscopy was extremely flat with a roughness nearly identical to the initial substrate.

Atomic layer controlled deposition of SiO2 and Al2O3 using ABAB… binary reaction sequence chemistry

Abstract Sequential ABAB… surface chemical reactions can be employed for atomic layer controlled deposition. We have examined the binary reactions SiCl 4 +2H 2 O⋌SiO 2 +4HCl for SiO 2 deposition and 2Al(CH 3 ) 3 +3H 2 O ⋌ Al 2 O 3 + 6CH 4 for Al 2 O 3 deposition. Each binary reaction (A + B ⋌ products) was performed sequentially by individual exposures to the A reactant and then the B reactant. If each surface reaction is self-limiting, repetitive ABAB… cycling may produce layer-by-layer controlled growth. For example, the individual “A” and “B” surface reactions for SiO 2 deposition can be described by (A) Si–OH + SiCl 4 ⋌ Si–O–SiCl 3 + HCl, (B) Si–Cl + H 2 O ⋌ Si-OH + HCl. We have studied ABAB… binary reaction sequences for SiO 2 and Al 2 O 3 deposition using laser-induced thermal desorption, temperature-programmed desorption and Auger electron spectroscopy techniques on single-crystal Si(100) surfaces. Fourier transform infrared spectroscopy techniques were also employed to examine these binary reaction schemes on high surface area SiO 2 and Al 2 O 3 samples. Controlled deposition of SiO 2 and Al 2 O 3 was demonstrated and optimized utilizing the above techniques. Under the appropriate conditions, each surface reaction was self-terminating and atomic layer controlled growth was a direct consequence of the binary reaction sequence chemistry.

Atomic layer controlled deposition of Al2O3 films using binary reaction sequence chemistry

Al2O3 films with precise thicknesses and high conformality were deposited using sequential surface chemical reactions. To achieve this controlled deposition, a binary reaction for Al2O3 chemical vapor deposition (2Al(CH3)3 + 3H2O → Al2O3 + 6CH4) was separated into two half-reactions: (A) AlOH∗ + Al(CH3)3 → AlOAl(CH3)2∗ + CH4, (B) AlCH3∗ + H2O → AlOH∗ + CH4, where the asterisks designate the surface species. Trimethylaluminum (Al(CH3)3) (TMA) and H2O reactants were employed alternately in an ABAB … binary reaction sequence to deposit Al2O3 films on single-crystal Si(100) and porous alumina membranes with pore diameters of ∼ 220 A. Ellipsometric measurements obtained a growth rate of 1.1 A/AB cycle on the Si(100) substrate at the optimal reaction conditions. The Al2O3 films had an index of refraction of n = 1.65 that is consistent with a film density of ϱ = 3.50 g/cm3. Atomic force microscope images revealed that the Al2O3 films were exceptionally flat with a surface roughness of only ±3 A (rms) after the deposition of ∼ 270 A using 250 AB reaction cycles. Al2O3 films were also deposited inside the pores of Anodisc alumina membranes. Gas flux measurements for H2 and N2 were consistent with a progressive pore reduction versus number of AB reaction cycles. Porosimetry measurements also showed that the original pore diameter of ∼ 220 A was reduced to ∼ 130 A after 120 AB reaction cycles.

Atomic layer growth of SiO2 on Si(100) using SiCl4 and H2O in a binary reaction sequence

Abstract The atomic layer control of SiO2 growth can be accomplished using binary reaction sequence chemistry. To achieve this atomic layer growth, the binary reaction SiCl4 + 2H2O → SiO2 + 4 HCl can be divided into separate half-reactions: (A) SiOH ∗ +SiCl 4 →SiOSiCl ∗ 3 +HCl , SiCl ∗ +H 2 O→SiOH ∗ +HCl , where the asterisks designate the surface species. Under the appropriate conditions, each half-reaction is complete and self-limiting and repetitive ABAB... cycles should produce layer-by-layer-controlled SiO2 deposition. The atomic layer growth of SiO2 thin films on Si(100) was achieved at temperatures from 600–680 K with reactant pressures from 1–50 Torr. These experiments were performed in a small high pressure chamber situated in an ultrahigh vacuum (UHV) apparatus. This design couples high pressure conditions for film growth with an UHV environment for surface analysis using laser-induced thermal desorption (LITD), temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). The controlled growth of a stoichiometric and chlorine-free SiO2 film on Si(100) was demonstrated using these techniques. SiO2 growth rates of approximately 0.73 ML of oxygen (1.1 A of SiO2) per AB cycle were obtained at 600–680 K. Additional vibrational spectroscopic studies performed in a second vacuum chamber utilized transmission Fourier transform infrared (FTIR) experiments on high surface area, oxidized porous silicon to monitor the surface species during the binary reaction sequence chemistry. These FTIR measurements observed the SiCl stretching vibration at 625 cm−1 and the SioH vibration at 3740 cm−1 and confirmed that each half-reaction was complete and self-limiting. These studies illustrate the feasibility of atomic-layer-controlled SiO2 growth and have determined the reactant pressures and substrate temperatures required for the SiO2 binary reaction sequence chemistry.

Surface chemistry of In2O3 deposition using In(CH3)3 and H2O in a binary reaction sequence

Abstract Sequential surface chemical reactions for the controlled deposition of In2O3 were examined using transmission Fourier transform infrared (FTIR) spectroscopy. In this study, the binary reaction (2In(CH3)3+3H2O→In2O3+6CH4) was separated into two half-reactions: (A) InOH ∗ +In(CH 3 ) 3 →In–O–In(CH 3 ) ∗ 2 +CH 4 ; (B) InCH ∗ 3 +H 2 O→InOH ∗ +CH 4 , where the asterisks designate the surface species. The InOH* and InCH3* surface species were monitored by the infrared absorbances of the InO–H and InC–H3 stretching vibrations. The reactions were thermally activated and the maximum reaction temperature was limited to 525 K because of trimethylindium (TMIn) pyrolysis. At 525 K, the (A) reaction saturated after depletion of ∼60% of the InOH* coverage. In contrast, the (B) reaction went to completion and was self-limiting. Despite these observed surface reactions, the growth of conformal In2O3 films was not achieved on Si(100) at 525 K. Very rough In2O3 films with low growth rates were also observed at 675–775 K in previous studies using InCl3 and H2O in a binary reaction sequence. The thermal stabilities of the InOH* and InCH3* surface species were measured from 300–900 K. The low coverage of surface species at the various reaction temperatures may explain the rough In2O3 films and low In2O3 growth rates.

Atomic Layer Growth of SiO 2 on Si(100) Using the Sequential Deposition of SiCl 4 and H 2 O

This study explored the surface chemistry and the promise of the binary reaction scheme: (A) Si-OH+SiCl 4 → Si-Cl + HCl (B) Si-Cl + H 2 O → Si-OH + HCl for controlled SiO 2 film deposition. In this binary ABAB… sequence, each surface reaction may be self-terminating and ABAB… repetitive cycles may produce layer-by-layer controlled deposition. Using this approach, the growth of SiO 2 thin films on Si(100) with atomic layer control was achieved at 600 K with pressures in the 1 to 50 Torr range. The experiments were performed in a small high pressure cell situated in a UHV chamber. This design couples CVD conditions for film growth with a UHV environment for surface analysis using laser-induced thermal desorption (LITD), temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). The controlled layer-by-layer deposition of SiO 2 on Si(100) was demonstrated and optimized using these techniques. A stoichiometric and chlorine-free SiO 2 film was also produced as revealed by TPD and AES analysis. SiO 2 growth rates of approximately 1 ML of oxygen per AB cycle were obtained at 600 K. These studies demonstrate the methodology of using the combined UHV/high pressure experimental apparatus for optimizing a binary reaction CVD process.