Measurements of the ion species generated in the planar type neutral loop discharge of tetrafluoroethyl trifluoromethyl ether (CF3–O–CHF–CF3;HFE 227) demonstrate the presence of CFx+ species and CFx radicals, in a comparable manner to plasmas of more established gases such as C4F8, C2F6 or CHF3. However, as the etch selectivity of boron phosphorus silica glass (BPSG) to resist is quite poor in HFE 227 plasmas, organosilane Si(CH3)xH4−x additive gases are investigated as a source of Si to improve the BPSG/resist selectivity. The addition of 10% trimethylsilane to HFE 227 is capable of providing selectivity close to 5, which is desirable for the fabrication of deep holes. It is shown that the HFE 227/trimethylsilane plasma chemistry also preserves the resist hole pattern and does not cause hole expansion during the etching process. These latter observations are attributed to the deposition of polymer precursors induced by the trimethylsilane addition which reduces the top resist surface etch rate and balances the removal rate of the resist sidewalls. As a result, 0.15 μm diam holes with an aspect ratio of 15 are successfully fabricated. Mass spectrometry measurements of fluorocarbon radicals and ionic species imply that the high aspect ratio feature can be fabricated by having mostly CF3+ ions and lower density of fluorocarbon radicals. Furthermore, the microloading-free etching of contact holes is achieved at a bias voltage of −500 V for diameters down to 0.15 μm holes. The limit of the etching performance of the HFE 227/10% trimethylsilane plasma etch chemistry is investigated using very fine patterns defined by electron beam lithography. Trenches of 20 nm in width and mesh holes of 70 nm can be fabricated.

The selective etching of SiO2 on Si employing C4F8/H2 inductively coupled plasma (ICP) was studied based on measurements of radical and ion densities, flow rate and wall temperature. Since polymer films were not deposited when the reacter wall was heated to temperatures above 200° C, CF1 radical density at 200° C was one order higher than that at the wall temperature of 30° C. Thus both Si and SiO2 etch rates decreased rapidly with increasing H2 concentration in C4F8, and Si etching stopped at 15% H2. The etch stop was attributed to insufficient removal of polymer with a reduced amount of ions and was suppressed considerably by increasing the RF power to generate a large amount of ions. The use of poly-Si masks reduced the microloading effect in comparison to resist masks and a contact hole feature with 0.2 µ m size and aspect ratio of 6 was successfully obtained.

In this paper we describe all the Voronoi and Delone tiles arising in tilings of point sets ( ) ('quasicrystals') built by the standard projection of the root lattice of type A 4 onto a two-dimensional plane spanned by the roots of the Coxeter group H 2 (dihedral group of order 10). The acceptance window for ( ) is a disc of any radius 0 < r < ∞. There are 22 distinct sets V T j (j = 1, . . . , 22) of Voronoi tiles and eight sets DT k (k = 1, . . . , 8) of Delone tiles, up to a uniform scaling by a factor τ n where τ = 1 2 (1 + √ 5) is the golden ratio and n ∈ Z.

Articles you may be interested inSurface kinetics modeling of silicon and silicon oxide plasma etching. I. Effect of neutral and ion fluxes on etching yield of silicon oxide in fluorocarbon plasmas Effect of nonsinusoidal bias waveforms on ion energy distributions and fluorocarbon plasma etch selectivityThe residence time effects on SiO 2 etching characteristics using inductively coupled plasma of C 4 F 8 alone were first studied in the range from 6 to 300 ms. It was then found that SiO 2 and Si etch rates were minimum at a residence time of 25 ms, at which the CF 1 ϩ ion density and the fluorocarbon polymer deposition rate measured at 130°C became maximum. From this good correspondence, the SiO 2 etching was considered to follow a reaction model where the CF 1 ϩ ions might contribute to the polymer deposition, thus suppressing the SiO 2 etching, and where the dominantly observed CF 3 ϩ ions could etch SiO 2 on the assumption of elevated SiO 2 surface temperature due to the ion bombardment. Next, in the condition of short residence times ͑Ͻ25 ms͒, Ar was added to C 4 F 8 in order to allow Ar ϩ ions to remove the fluorocarbon polymer film that is responsible for the reduction of the SiO 2 etch rate. For a residence time of 10 ms the SiO 2 etch rate continuously increased with the Ar concentration up to a maximum etch rate of 0.4 m/min for 90% Ar addition. Various plasma diagnostics demonstrated that the 90% Ar addition resulted in an increase of the CF x ϩ (xϭ1 -3), C ϩ , and Ar ϩ ion densities, in contrast to a decrease of the CF 3 radical density. Metastable Ar atoms as well as highly elevated electron temperature are considered to be responsible for the increasing ion species. Consequently SiO 2 /Si contact hole features with 0.18 m opening and 2 m depth were successfully fabricated employing the 90% Ar/C 4 F 8 mixture at a residence time of 10 ms. The He addition has also been investigated and showed similar changes in plasma characteristics to those observed for Ar addition, but the ''etch stop'' occurred. This probably resulted from the poor sputtering effect of He ϩ ions due to their light mass.

Residence time effects on high aspect ratio SiO2 hole etching with a 90% Ar addition to C4F8 have been studied using a planar type neutral loop discharge. An adopted wide-type antenna instead of the original narrow one enabled us to improve uniformity of ion currents, electron densities, and plasma generation over a wide range of pressure. Thus, the residence time (τ) dependence of radical and ion densities, and etched features were investigated for various pressures (P). It was found that the conditions which achieved high aspect ratio features followed a straight line passing an origin in the τ-P diagram. This demonstrated that the high aspect ratio feature etching was determined unequivocally by the adequate flow rate, because the gradient of the line resulted in the reciprocal of the flow rate. On the other hand, at short τ, a large amount of radicals generated due to suppressed recombination produced the excess polymer deposition, causing the “etch stop.” At longer τ, ions and radical densities decreased due to recombination and thus dominated Ar+ ion sputtered the mask resist, forming the tapered feature.