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The chemisorption and reaction of dichlorosilane (SiH2Cl2) with Si(111) and Si(100) surfaces is investigated with core-level soft x-ray photoelectron spectroscopy employing synchrotron radiation, in order to ascertain the surface chemistry involved in atomic layer epitaxy (ALE). Exposures to 8 kL of SiH2Cl2 were performed as a function of sample temperature in the range from room temperature to 800 °C. At all temperatures, SiH2Cl2 chemisorbs dissociatively forming silicon monochloride surface species. The coverage of monochloride displays a maximum for exposures at ∼600 °C. Under all conditions studied, larger chlorine coverages are observed on Si(100) than on Si(111). A Si surface that was first saturated with SiH2Cl2 at 600 °C was subsequently exposed to H2 at 600 °C, and no reaction occurred. These results indicate that recent models for silicon ALE are incorrect. An alternative method for low-temperature ALE of Si is proposed, in which SiH2Cl2 is adsorbed onto Si at 600 °C and Cl is removed via reaction with atomic H.

The growth of GaF3 films on GaAs(110) wafers via exposure to XeF2 is studied as a function of substrate temperature with soft x-ray photoelectron spectroscopy. For temperatures between 300 and 550 K, a GaF3 film forms with an interface to the substrate consisting of GaF, elemental As and possibly some AsF. In this temperature range, the films thicken with exposure up to a limit of ∼15 Å. The initial F uptake rate increases with elevated substrate temperature without altering the limiting thickness. In addition, there is little variation in the thickness or composition of the film–substrate interface over this temperature range. Above 550 K, XeF2 etches GaAs, leaving a GaAs surface covered with ∼1 monolayer of elemental As. A film growth mechanism is discussed to explain these results.