Rapid heating with an electron beam has been used to react overlayers of rare‐earth (RE) metals with (111) Si, forming epitaxial layers of silicides of Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Under conventional furnace annealing, forming such silicides on Si typically leads to rough, pitted surfaces. The use of fast beam heating not only results in a much smoother surface topology but also helps promote epitaxial growth on (111) Si in both solid and liquid phase reactions. These epitaxial silicides have a hexagonal RESi∼1.7 structure (defected AlB2 type). Their orientation with the Si substrate is (0001)∥(111), with predicted lattice mismatches ranging from +0.83 to −2.55%.

Epitaxial growth of rare-earth silicides on (111) Si

The physiochemical properties of thin layers of rare earth metals and rare earth silicides on Si substrate surfaces are reviewed. The topics discussed include the formation of reactive interfaces at room temperature, the evolution of ordered surface structures at elevated temperature and the oxidation of rare earth interfaces and silicides. Special emphasis is placed on the discussion of the geometrical and electronic structure of ordered overlayer phases.

Rare earth overlayers on silicon

The growth kinetics and surface morphology of erbium silicide formation from Er layers on Si(100) substrates are examined using both fast e‐beam annealing and furnace annealing. Very smooth erbium silicide layers have been grown using a line‐source e beam to heat and react the Er overlayers with the substrate. This contrasts to the severe pitting observed when Er layers are reacted with Si in conventional furnace annealing. The pitting phenomenon can be explained by a thin contaminant layer at the interface between Er and Si. Our results suggest the contamination barrier is not due to oxygen, as usually assumed, but may be related to the presence of carbon. Rapid e‐beam heating to reaction temperatures of ∼1200 K permits dispersion of the barrier layer before substantial silicide growth can occur, allowing smooth silicide growth. Heating to shorter times to just disperse the interface barrier allows uniform layer growth by subsequent furnace annealing and has permitted measurement of the kinetics of erbiu...

Kinetics and morphology of erbium silicide formation

The growth of epitaxial yttrium silicide on Si(111) in ultrahigh vacuum is studied. Resistivity, epitaxial quality, and pinhole coverages are studied as a function of annealing temperature for each growth method used. The best films result from the growth of a thin, 30–40‐A template layer which is annealed to 700 °C, followed by a thicker film growth by depositing additional Y onto the substrate heated high enough to induce silicide formation (∼300 °C). Annealing to 900 °C results in a Rutherford backscattering minimum channeling yield χmin ∼3%, which is the same order of epitaxial quality previously achieved by only Ni‐ and Co‐silicide films on silicon. Films grown without templates have larger pinhole sizes with pronounced features indicative of the hexagonal nature of these structures. The deposition of Y metal onto a substrate held at room temperature, followed by annealing to 900 °C results in the lowest resistivities (48 μΩ cm for 425‐A films), but with a highly dislocated film structure featuring 1...

Formation of epitaxial yttrium silicide on (111) silicon

Etude des composes de terres rares et plus particulierement des variants types d'oxyde interessants comme les materiaux refractaires. On aborde egalement les composes a base de sulfures, oxysulfures, antimoine, bismuthe, silice et bore, en insistant sur le role important joue par les impuretes dans ces materiaux. On propose enfin quelques applications futures en industrie

Rare Earth Compounds (Oxides, Sulfides, Silicides, Boron, …︁) as Thin Films and Thin Crystals Physico‐Chemical Properties and Applications

Rare‐earth silicide layers typically are heavily pitted when formed by furnace reaction of thin metal films with a silicon substrate. We show that this phenomenon can be explained by an inhibiting contamination layer which has a high activation energy for dissolution relative to that for silicide growth. Very smooth erbium silicide growth has been demonstrated by reacting the layers at much higher temperatures (1100–1300 K) for 200–500 μs, using electron beam heating. A novel combination of controlled electron beam heating, ion beam analysis, and computational simulation has been used to determine an activation energy for interface barrier dissolution of 3.7±0.3 eV.

J. A. Knapp

Papers

Erbium silicide formation using a line‐source electron beam