Kunisuke Maki

Formation of uniform nanoscale Si islands on a Si(111)-7×7 substrate

During epitaxial growth on a substrate with a stable surface structure, rearrangement from a superlattice to a normal 1×1 lattice is essential when the substrate is covered with a growing layer. Since rearrangement needs activation energy, lateral growth is prevented at the boundary of the structure unit. In the growth of Si on a stable 7×7 structure composed of a dimer-adatom-stacking- fault layer, lateral growth of islands is prevented at the dimer row. Such a restriction on the lateral growth leads to a discontinuous size distribution of islands, whose size depends on the size of the 7×7 structure unit. In the initial stage of nucleation and growth, we have observed many rounded Si islands with uniform diameters of 3.8 nm when the substrate temperature has been held at 380 °C for 10 min after deposition of Si. From the change in the island size distribution as a function of annealing time after the deposition, we conclude that the rounded island is constructed of atoms created by the dissociation of un...

Stress in Vacuum Deposited Films of Silver

Measurements have been made of the tensile stress in silver films evaporated in a vacuum of 1–2×10-5 torr on to mica strips, electron microscopic observations of the film structure being carried out on the other hand. Films having various thicknesses ranging from about 30 A to 1000 A were under investigation. The tension per unit width of the film, S, increases sigmoidally with the film thickness d: In the initial stages of film growth in which the film is composed of isolated islands, S is very small; S increases rapidly during the late coalescence stage and the channel stage; after the completion of a continuous, hole-free film, S does increase with d, but at a much slower rate. The mean stress per unit cross section of the film, σ (=S/d), increases sharply with d to assume a maximum at a thickness around 200 A where the shoulder of the S-d curve is located, and decreases gradually as d increases further.

Structural control of TiO2 film grown on MgO(001) substrate by Ar-ion beam sputtering

The structure of a 50-nm-thick TiO2 film grown on MgO(001) substrate maintained at 630 °C was studied by x-ray diffraction. Each film was fabricated by varying both the deposition rate of Ti atoms, which are produced by Ar-ion beam sputtering onto a Ti target, and the partial pressure of O2 gas (PO2). When Ti atoms are supplied at a rate of 0.1 nm min−1(4.0×1014 cm−2 min−1) at PO2=1.1×10−2 Pa, the TiO2 film exhibited the anatase structure whose (200) plane was parallel to the MgO(001). The TiO2 film with the rutile structure whose (110) plane was parallel to the MgO(001) was grown at the same deposition rate and PO2=3.1×10−3 Pa. Evidence demonstrating that the structure of TiO2 film is controlled only when Ti atoms and O2 molecules are supplied simultaneously is presented.

Crystallization Thickness of Amorphous Sb Film on GeOx Film Substrate in a Vacuum of 10-5 Torr

Antimony films with thicknesses smaller than a critical value, deposited at room temperature, are composed of amorphous islands. Amorphous Sb film on GeOx film substrate starts to crystallize spontaneously when the fractional area occupied by Sb exceeds 70-80% in the vicinity of the critical thickness, here called the crystallization thickness dc. The value of dc is increased by exposing GeOx to air before evaporating the Sb; it is 60-80 A for as-deposited GeOx but 100-120 A for that exposed to air. This is because the compound islands on as-deposited GeOx cannot contract as easily as those on GeOx exposed to air after the coalescence of islands with neighbouring ones to form a continuous film.

Stress in Vacuum-Deposited Films of Ag, Au, and Cu

The tension per unit width of the film S has been determined for Ag, Au, and Cu films deposited at 10−5 Torr from a few tens of angstroms up to 2000, 1500, and 1000 A in thickness, respectively. S increases rapidly with the film thickness d until the film attains a thickness dI( = 220/320/160 A for Ag/Au/Cu films deposited at 2 A/sec). At dI the mean stress within the film σ ( = S/d) assumes a maximum. With thicker Ag and Cu films S remains nearly constant until at a thickness dII it starts to increase again. With Au films the rapid increase in S below dI is immediately followed by a slower increase with d. The first increase in S below dI is associated with the coalescence of islands. The second increase in S observed at larger thicknesses (d > dII for Ag and Cu, d > dI for Au) is probably due to residual gases. The last view is supported by experiments with Ag films deposited at 10−8 Torr.

Multiscale analysis of silicon low-pressure chemical vapor deposition

We consistently performed computer fluid dynamics (CFD) analysis in a reactor (macroscale analysis) and deposition profile analysis on a submicron hole (microscale analysis) for Si low-pressure chemical vapor deposition (LPCVD). For the gaseous phase and the surface reaction of the SiH4 source gas, we adopted the dominant reaction model, which involved two intermediates, SiH2 and Si2H6, and was based on the Kleijn Model. We analyzed the fluid flow, heat transfer and chemical reactions throughout the entire batch-type reactor, and estimated the Si growth rate, gaseous species concentration, and relative contributions of SiH4, SiH2 and Si2H6 to Si growth. Moreover, the Si-filling profile on a submicron hole was predicted by topography simulation in which the parameters were the growth rate, the relative contribution and the sticking coefficient of each species. The relationship between the relative contribution of SiH2, which has a high sticking coefficient, to Si growth and the hole-filling capability was quantitatively clarified from the results of a combination of the two analyses. The hole-filling capability at the wafer edge was deteriorated by the influence of SiH2 gas produced in the decomposition of Si2H6 gas, which was diffused from outside the wafer. This effect became considerable with increasing temperature. Reducing the wafer pitch will be effective in improving the hole-filling capability because both the SiH2 generation reaction in the region between wafers and SiH2 gas diffusion from outside the wafer will be inhibited.

Formation of some hierarchy in amorphous structure during the crystallization of vacuum‐deposited amorphous semiconductor films

A view that some hierarchy in the structure of the amorphous phase surrounding the crystallized phase is formed, is proposed from the investigation of the kinetics in the crystallization process of amorphous semiconductor films. The view is discussed from some results in the study of solid‐phase epitaxial growth of the amorphous Si film deposited on the Si(111) surface by low‐energy electron diffraction. Some comment on the formation of the amorphous structure is also given from a viewpoint of thin‐film growth.

A characteristic feature of crystalline thin-film growth of Si on a 7 × 7 superlattice surface of Si(111)

Abstract A Si film has been grown on a 7 × 7 superlattice surface of a Si(111) substrate at 250 and 380°C. Reflection high-energy electron diffraction patterns of the Si film at 250°C consist of a diffuse 2 × 2 structure and a weak 7 × 7 structure at 380°C. The experimental results indicate that the initial growth of crystalline nuclei is caused by the crystallization of amorphous-like islands at 250°C and by the formation of an island composed of three 5 × 5 structural units with a corner hole at their center at 380°C. The formation of crystalline nuclei is discussed.

Observation of Initial Growth Stage of Amorphous Si Film Deposited on 7×7 Superlattice Surface of Si(111) by Low-Energy Electron Diffraction

The intensities of low-energy electron diffraction (LEED) were measured from Si films with various thicknesses (d) which had been deposited on a 7×7 reconstructed surface of Si(111) substrates maintained at 170°C. The intensity profile from Si films at d>60 A gives a feature showing the formation of an amorphous phase. From ultrathin Si films with 5 A<d<60 A, two peaks were observed clearly at positions which correspond to the (0, 0) and (1, 0) rods in the Si(111) surface. This suggests that the Si film in the vicinity of the Si(111) substrate comprises interface layers with the some ordered structure. Some discussion is given on the interface layers, which are composed of two epitaxially grown grains. A normal stacking sequence of the diamond structure is formed in one grain and the reversed stacking sequence grows at the stacking fault layer on the preserved 7×7 structure in another grain.

Change in surface roughness with the thickness of TiO2 film grown on MgO(001) by Ar-ion beam sputtering

The surface roughness, Ra, and the crystallinity are studied for the rutile-type TiO2 films at their thickness, d, above 10 nm deposited on the air-cleaved MgO(001) held at 630 °C at 3.1×10−3 Pa in the partial pressure of O2 by sputtering the Ti target by Ar-ion beam accelerated with 1.2 kV. The amount of Ra estimated by observing the surface morphology with an AFM is the order of nanometers and changes with d according to d1/2. The linear relationship between the intensity ratio of the (110) peak for the TiO2 to the (004) peak for the MgO in x-ray diffraction pattern and d2 is also confirmed which is evidence of little change in the film crystallinity during growth. These mean that the surface morphology of the TiO2 films at d>10 nm keeping their crystallinity is determined from the statistical fluctuation in the impinging vapor flux.