Michael P. Siegal

Formation of epitaxial yttrium silicide on (111) silicon

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...

Growth of pinhole‐free epitaxial yttrium silicide on Si(111)

This paper reports the growth of pinhole‐free epitaxial YSi2−x layers on Si(111) as thin as 30 A. This has been accomplished by depositing both Y and Si at room temperature and then annealing to 500–900 °C. Use of the template method allows for the growth of thicker films also free of pinholes. Deposition of yttrium metal only onto Si(111) requires a temperature ∼300 °C for nucleation of the silicide reaction between the Y overlayer and Si substrate. Such a process creates small pinholes ∼500 A in diameter, randomly distributed throughout the film. These pinholes increase in size with higher annealing temperature, resulting from a raised interface free energy intrinsic to the nucleation controlled growth.

Formation of epitaxial yttrium and erbium silicide on Si(111) in ultra-high vacuum

Abstract The growth of epitaxial yttrium and erbium silicide on Si(111) in ultra-high vacuum is studied. Resistivity, epitaxial quality, and pinhole distributions are studied as a function of annealing temperature. The best films result from the growth of a thin template layer ( 2− x to 900°C and ErSi 2− x to 850°C results in the lowest resistivities (48 μΩ cm for 425 A YSi 2− x and 30 μΩ cm for 200 A ErSi 2− x films). Furthermore, these films have Rutherford backscattering minimum channeling yields χ min ≈ 3% and 2% for Y- and Er-silicides,respectively. YSi 2− x appears to have a sharper interface with Si(111) than does ErSi 2− x from RBS, while pinhole sizes increase with annealing temperature for both silicides, with well-defined hexagonal features prevalent in the ErSi 2− x films only. These are perhaps indicative of the differences in lattice matching with Si(111) of the two silicides.

Epitaxial growth of ErSi2 on (111) Si

The epitaxial growth of ErSi2 is described. In this study, erbium metal is evaporated onto Si(111) and annealed to form erbium silicide, where the pressure during all procedures is maintained below 5 × 10−10 Torr. The interdiffusion of erbium with silicon occurs as low as 300°C, as determined by in situ Auger electron spectroscopy. Low energy electron diffraction shows the 3×3 pattern of the hexagonal silicide, with evidence of surface faceting. Both X-ray and Rutherford backscattering analyses indicate single-crystal growth with a channeling minimum yield of 2%–3% for silicide films of 200–400-A thickness annealed to 800–900°C. The surface morphology of these films is smooth but pitted with an average pinhole size of less than 1 microm. These results support growth models based on nucleation reaction mechanisms and not those based on interfacial contamination effects. Electrical measurements show metallic conduction with a room temperature resistivity of 35micro ohm cm.

The formation of thin‐film tungsten silicide annealed in ultrahigh vacuum

Thin films of tungsten silicide have been formed by sputter depositing 710 A of W metal onto (100)‐oriented, 3–7 Ω cm, p‐type silicon wafers. The samples were annealed in an ultrahigh vacuum ambient (pressure≤1.0×10−9 Torr) at temperatures ranging from 845 to 1100 °C for 30 s. The lack of oxygen contamination in the ambient allows the W‐Si interaction to proceed, first producing both the W‐rich W5 Si3 phase and the tetragonal WSi2 phase near 900 °C, followed by only the tetragonal, low‐resistivity (30–40 μΩ cm) WSi2 phase above 1000 °C. This result is in contrast to previous work where films formed by rapid thermal processing in vacuum showed no significant W‐Si interaction for temperatures below 1100 °C due to the formation of an interfacial oxide diffusion barrier gettered into the films from the 10−6 Torr ambient.

The effects of dopant and impurity redistributions on WSi2 formation by rapid thermal processing

Thin‐film samples of WSi2 were formed by sputter depositing tungsten metal directly onto chemically etched, p‐type, B‐doped, 5 Ω cm Si(100) wafers, followed by rapid thermal processing (RTP) in high vacuum at temperatures over 1100 °C. The resulting dopant and impurity elemental redistributions are studied by secondary ion mass spectroscopy. Boron, initially present both at the W/Si(100) interface as an impurity and in low concentration in the Si substrate, diffuses into the growing WSi2 film, eventually escaping into the vacuum. It is shown that RTP can be used to form high‐quality, low‐resistivity (∼30 μΩ cm) WSi2 films without total dopant out‐diffusion. Oxygen is the major impurity in these samples and is gettered at the metal/Si(100) interface during RTP from the vacuum ambient. Removal of this interfacial oxide is needed for the growth of uniform, low‐resistivity silicide films and can be done with RTP. Trace quantities of F, Cl, Na, K, C, and Cr have also been detected. Their origin and movement th...

Effects of rapid thermal processing on the formation of uniform tetragonal tungsten disilicide films on Si(100) substrates

Thin films of tungsten silicide with resistivities of 30–35 μΩ cm have been formed by sputter depositing 710 A of W metal onto (100)–oriented, 3–7 Ω cm, p‐type silicon wafers. The samples were fast radiatively processed in a rapid thermal processing (RTP) system under high vacuum for time anneals ranging from 15–20 s at two temperatures (∼1100 and ∼1150 °C). The inevitable oxide barrier at the interface is shown to decrease with increasing RTP time and temperature, evidenced by both Auger electron spectroscopy and secondary ion mass spectrometry experiments. The high film stress produced by thermal considerations does not seem to effect the resulting resistivity and, furthermore, appears to relax at higher temperatures when the film surface becomes ‘‘buckled.’’

High Resolution X-Ray Scattering Studies of Strain in Epitaxial Thin Films of Yttrium Silicide Grown on Silicon(111)

We have used high resolution grazing incidence x-ray scattering (GIXS) to study the in-plane and out-of-plane structure of epitaxial YSi 2-x films grown on Si (111), with thicknesses ranging from 85A to 510A. Our results indicate that the films are strained, and that film strain increases as a function of thickness, with lattice parameters varying from a = 3.846A/c = 4.142A for the 85A film to a = 3.877A/c = 4.121A for the 510A film. We correlate these results with an increase in pinhole areal coverage as a function of thickness. In addition, our measurements show no evidence for the existence of ordered silicon vacancies in the films.

Rapid Thermal Annealing of Sputtered Ti-Ni-Si Films

A ternary compound results from the fast radiative processing of Ni/Ti bilayers on Si substrates. In the Ti-Ni-Si system, Ni is the dominant moving specie at low temperatures while Si starts to diffuse at 575°C. For bilayers with Ti in excess, the final product,above 750°C, is a mixture of ternary compound and TiSi 2 whereas excess Ni leads to a layer of NiSi between the substrate and the ternary layer, at tempera-tures below 700° C.