The reaction of phosphine PH3 and diborane B2H6 on Si(100) surfaces was studied by surface analytical techniques in relation to the in situ doping process in the chemical vapor deposition of silicon. Phosphine chemisorbs readily either nondissociatively at room temperature or dissociatively with the formation of silicon–hydrogen bonds at higher temperatures. Hydrogen can be desorbed at temperatures above 400 °C to generate a phosphorus layer. Phosphorus is not effective in shifting the Fermi level until the coverage reaches 2×1014/cm2. A maximum shift of 0.45 eV toward the conduction band was observed. In contrast, diborane has a very small sticking coefficient and the way to deposit boron is to decompose diborane directly on the silicon surface at temperatures above 600 °C. Boron at coverages less than 2×1014/cm2 is very effective in shifting the Fermi level toward the valence band and a maximum change of 0.4 eV was observed.

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Secondary ion mass spectrometry (SIMS), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES) have been employed to study the interactions of silane false(SiH4false) and phosphine false(PH3false) with the Si(100) surface. Phosphine adsorption and desorption were investigated at surface temperatures in the range 25°≤T≤700°C . At ambient temperature, phosphine saturated the bare Si(100) surface after 3–5L exposure, and fitting adsorption data to a Langmuir model yields the value s=1.0 for the sticking coefficient. Phosphine adsorption was found to follow the 2×1 pattern of the underlying silicon. Competitive adsorption experiments set an upper bound of s≤0.025 for silane adsorption under like conditions. The silicon surface was observed to be passivated with respect to silane adsorption by prior exposure to phosphine, with a layer of preferentially adsorbed phosphine formed which served to preclude subsequent silane adsorption. The results obtained here are discussed in the context of their bearing upon the phosphorus‐doped low pressure chemical vapor deposition process.

Direct evidence has been obtained for electron tunneling between sputtered Cs + ions and the solid surfaces from which they originate. Strong neutralization of the Cs + ions is observed whenever the tunneling channel is opened by changing the surface work function so that a crossing of the Fermi level by the Cs 6s level occurs. A tunneling model which takes the spatial dependences of the position and the width of the atomic level into account explains the data successfully. PACS numbers: 79.20.Nc, 34.50.Hc, 73.30.+y During the ion-beam bombardment of solid surfaces, an appreciable number of sputtered atoms come out ionized. These ionized species form the basis of secondary-ion mass spectrometry for materials analysis. Mechanisms proposed recently for such inelastic processes involve either electronic excitations by atomic collisions 1 or atom-surface resonant electron tunneling. 2 " 5 There is a conceptual difference between these two approaches. In the electron-tunneling model, the discrete electronic level of the sputtered atom interacts with the continuum of electronic states of the solid. The central feature of this continuum of electronic states is the Fermi level which separates occupied and unoccupied states. On the other hand, the Fermi level plays no explicit role in collisional models. In this paper, we report the first direct observation of the importance of the position of the Fermi level in the ionization of sputtered atoms.We chose to study the sputtering of Cs + in this experiment. It is known that at small coverages, Cs atoms are chemisorbed as Cs + on metal surfaces, with the empty 6s level lying above the metal Fermi level. 6 Hence if the work function cp of the surface is larger than the ionization potential / of Cs (3.9 eV), the 6s level of the sputtered Cs atom will always face empty states of the metal when the Cs atom escapes and little neutralization by electron tunneling can occur. By use of an adatom electric dipole layer to adjust the relative position between the Fermi level and the vacuum level (as measured by a change in cp), the 6s level can be deliberately forced to "cross" the Fermi level (when/xp) as the Cs atom escapes, making electron tunneling energetically possible.We have used three substrates with different work functions to test this concept: Au film {cp = 5.27eV), w-Si(lll) (