Al Etching Research Articles

Fabrication of sub-half μm patterns for MOS devices by means of X-ray lithography and plasma etching

The definition and transfer of patterns with minimal structures below 0.5 μm into poly-Si, BPSG and aluminum layers by means of X-ray lithography and subsequent dry etching will be described. A new X-ray resist developed by Hoechst, with a sensitivity of better than 30 J/cm 3, serves as an etch mask and shows sufficient process stability even in the very aggressive Cl 2/BCL 3/CCl 4/N 2 plasma environment of Al etching. The processes employed for etching gate structures into poly-Si and contact holes into BPSG are based on Cl 2/He and CHF 3/O 2 chemistry, respectively. All dry etch processes lead to highly anisotropic profiles with total linewidth losses of less than 0.05 μm. They will serve as basic tools for the realization of 0.5 μm MOS devices patterned completely by X-ray lithography.

Surface passivation by adding fluorocarbons and chlorofluorocarbons into an Al dry etch reactor

Adding fluorocarbon or chlorofluorocarbon compounds into an Al etch reactor can alter the induction time, change the Al etch rate, and inhibit the Al etching from the grounded electrode and chamber wall. These phenomena are explained by a surface passivation mechanism. During an etching process, the aluminum can react with chlorine-containing radicals and fluorine-containing radicals simultaneously to form either a volatile aluminum chloride or a stable passivation layer. The important parameters which control the etch and passivation rates, for a given system geometry, are the gas flow rate, the fluorine atomic concentration, and the bias voltage of the bottom electrode.

Dry Patterning of Al and Al Alloys

AbstractPlasmachemical etching of Aluminium in chlorine containing discharges is discussed from a thermochemical point of view. A model of Al etching is proposed, in which diffusion of reaction products through the carbon‐rich deposite layer is considered to be rate‐limiting. The model quantitatively describes the dependence of the etch reaction on different process parameters of the CCl4‐plasma.

Anisotropic etching of Al by a directed Cl2 flux

A new Al etching technique is described that uses an ion beam from a Kaufman ion source and a directed Cl2 flux. The ion beam is used primarily to remove the native oxide to allow the Cl2 to spontaneously react with the Al film forming volatile Al2Cl6. By controlling both the flux equivalent pressure of Cl2 and the ion beam current, this etching technique makes possible the anisotropic etching of Al with etch rates from 100 nm min−1 to nearly 10 μm min−1 with a high degree of selectivity.

Microfabrication Technologies for Advanced VLSI Devices

ABSTRACTRecent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10−3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.

Microfabrication Technologies for Advanced VLSI Devices

AbstractRecent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10-3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.

Plasma beam studies of Si and Al etching mechanisms: Donald L Smith and Paul G Saviano, J Vac Sci Technol, 21 (3), 1982, 768–773

Plasma beam studies of Si and Al etching mechanisms: Donald L Smith and Paul G Saviano, J Vac Sci Technol, 21 (3), 1982, 768–773

Etching Characteristics of n+ Poly-Si and Al Employing a Magnetron Plasma

Phosphorous doped Poly-Si and Al etching characteristics in and outside a magnetron plasma have been investigated. Although the ion accelerating voltage is very low in a magnetron plasma, both materials with resist mask are etched anisotropically owing to the side wall Protection film which arises from resist sputtered by intense ion bombardments. Outside the plasma, though, some undercutting occurs due to poor protection film caused by an insufficient amount of ions, despite the higher ion energy. Thus, anisotropic etching of the whole wafer is achieved by scanning the magnetron plasma. Magnetic field dependencies for Al and n+ Poly-Si etch rates reveal that Al etch rate due to plasma scanning is not enhanced by the magnetic field, in contrast to the case for n+ Poly-Si.

Laser microchemical techniques for reversible restructuring of gate-array prototype circuits

Laser direct-write Al etching and poly-Si deposition have been adapted to the mask-free alteration of simple gate-array test circuits. Simple test structures on commercial CMOS chips have been reconfigured with no degradation in device or circuit performance. These new methods may be useful for rapid evaluation and optimization of integrated-circuit prototypes.

Poly(chloromethylstyrene): A high performance x-ray resist

X-ray lithographic performance of poly(chloromethylstyrene) (PCMS), a high performance negative e-beam resist, was investigated. Superior resolution, i.e., resist profile and linewidth control, was obtained by x-ray exposure due to the essentially square x-ray exposure profile and the significantly reduced amount of backscattered electrons from the substrate. Sensitivity and resolution were evaluated as a function of polymer molecular parameters. Dry etching characteristics were evaluated under polysilicon, SiO2 and Al etching conditions. Excellent resolution, sensitivity and dry process compatibility were obtained and attributed to the high absorption of chlorine to Pd Lα radiation, the high chemical reactivity of the benzyl chloride moiety and the high plasma stability of the aromatic styrene moiety. Sensitivity of 300 000 molecular weight PCMS is 25–30 mJ/cm2 (D0.5g) to Pd Lα radiation; resolution is 1 μm in 1 μm final thickness resist with vertical walls at D0.9g (70 mJ/cm2), and submicron in thinner layers. Dry etch resistance is comparable to that of AZ-type photoresist. Postexposure deep UV hardening minimizes thermally induced flow and profile distortion even at temperatures greater than 300 °C. Lithographic performance of PCMS compares very favorably with other leading x-ray resists including the mixture of poly(2,3-dichloropropyl acrylate) and poly(glycidyl methacrylate-co-ethyl acrylate) (DCOPA), poly(allyl methacrylate-co-hydroxyethyl methacrylate) (EK88) and chloromethylated polystyrene (CMS).

Aluminum Reactive Ion Etching Employing CCl4+Cl2 Mixture

Alumintun reactive ion etching has been investigated employing a CCl4+Cl2 mixture. Anisotropic etching was achieved at a self-bias voltage of –150V, a flowrate concentration of 50% Cl2 in CCl4 and 13.56 MHz rf power at 200 W. The photo-resist swelling, which is closely related to undercutting of the isotropic etching condition is attributed to the heat of reaction between neutral reactive species and Al. A mass analysis makes it clear that a CCl4+Cl2 plasma generates more CCl+3 species while suppressing unsaturated monomers, and also reduces the water vapor. Decreasing the final pressure in the reactor shortens the initiation period, then it disappears for the anisotropic etching condition with CCl4+Cl2. A “load-lock” type reactor is confirmed to offer reproducible Al etching. Blowing hot air (\\doteqdot200°C) over the wafers after etching was found to be an effective measure against rapid Al corrosion.

Plasma beam studies of Si and Al etching mechanisms

The study of plasma etching mechanisms is made difficult by the presence of the plasma at the etching surface. However, etching in a plasma beam extracted from such a plasma allows: (1) mass analysis of beam species and of directly desorbing etching product, (2) simultaneous XPS analysis of the etching surface, and (3) ion acceleration or retardation without changing neutral species composition. The present beam was extracted from the unpowered electrode of a source operating under typical plasma etching conditions of 50 Pa and 27 MHz. Appearance potential mass spectroscopy was used to distinguish spectrometer fragmentation products from plasma radicals. Cl2 plasma beam reaction with undoped Si and with oxidized Al occurs only with ion bombardment, whereas with clean Al it occurs without ions, leading to isotropic (undercut) etching. Surface oxygen depletion and the onset of Al2Cl6 desorption were simultaneously monitored during the ’’initiation’’ phase of Al etching. Anisotropic Al etching in chlorocarbon plasmas is believed to be dependent on sidewall etching inhibition by chlorocarbon deposits. Mass analysis of beams from Cl2 plasmas containing 20% CCl4, CHCl3, or CH3Cl showed a similar product distribution of CmCln species in all three cases and, in the latter two cases, almost complete abstraction of H by Cl atoms to form HCl. The HCl neither enhances nor inhibits the reaction of Al with Cl2 plasma, nor does it react with clean Al in the absence of ion bombardment.

Si and Al Etching and Product Detection in a Plasma Beam under Ultrahigh Vacuum

The study of plasma etching mechanisms is made difficult by the inaccessability of the wafer surface to analysis during etching. In the present work, a “plasma beam” is extracted from a miniaturized plasma etching chamber through an array of molecular‐flow orifices in an Mg‐foil electrode. The beam effuses into ultrahigh vacuum and onto either a mass spectrometer for ionic and neutral plasma species analysis or onto an Si or Al film on a quartz crystal thickness monitor for etching studies. Desorbing etch product can be mass‐analyzed before encountering gas or wall collisions. The plasma beam source and its rf power supply can be d‐c biased relative to the mass spectrometer and the etching film to accelerate or retard the ionic component without affecting neutral plasma species, thus allowing energy analysis of effusing ions and measurement of ion energy effect on etching. For plasma maximum ion energy was ≅100 eV at 27 MHz and ≅400V at 100 kHz. Beam etching of Si using and plasma (27 MHz) and of Al using plasma has been carried out, and , ,, and desorption has been observed. Ion bombardment is required to initiate etching in all cases. Subsequently, the effect of ion energy variation from zero (ions reflected) to 500 eV on etching rate and product desorption rate is large (≅x18 enhancement) for Si in , much less (x4) for Si in and zero for Al in . These results correlate with the degree of anisotropy obtained for these etching systems in conventional plasma etching, assuming that the anisotropy is produced by vertical etching rate enhancement by the normally incident ions. They also explain the much higher etching rate observed for Si and at the lower frequency, where ion energy is higher.

Fabrication process for surface acoustic wave filters having 0.5 μm finger period electrodes

A new fabrication process using ion milling has been developed for 0.5-μm finger period SAW filters, Electron-resist (PMMA) patterns are transferred to a 200-Å-thick Ti film using liftoff, followed by oxygen ion-beam etching, in order to transfer the Ti patterns to a 1900-Å-thick AZ 1350 film. The two-step mask transfer process yields high-durability masks. Using argon ion-beam etching, 700-Å-thick Al electrodes are delineated. The etching masks are easily removed by oxygen plasma, because the Ti film is etched away during the Al etching. A desirable shape for delineated electrodes is obtained by adjusting the AZ 1350 film thickness. A 0.5-μm finger period SAW filter, fabricated using the process, shows 7dB insertion loss at 1.89 GHz.

Electron beam direct writing technology applied to 512 kbit ROM with 1 µm geometry

A 512 kbit read-only memory (ROM) to store Chinese ideographs has been fabricated using variable-shaped electron beam and dry-etching lithography. 1.0-µm minimum line width was used to delineate device area spacings smaller than those obtained with conventional design rules using photoimaging techniques. SiO 2 , Si 3 N 4 , and polysilicon etchings were accomplished by reactive sputter techniques with CF 4 + H 2 and CCl 3 F gases using negative electron beam resist PGMA and positive resist AZ-2400. Al etching was carried out by plasma with CCl 4 gas using negative electron beam resist NER-1. The alignment marks detectability and their locating accuracy were improved by properly using the basis arithmetic operations, subtraction and summation, in backscatter signal processings. 6.6 mm × 8.9 mm chip-by-chip alignment yielded about 0.2-µm level-to-level registration accuracy. Memory cell size and chip size are 5.2 µm × 8.4 µm and 6.6 mm × 8.9 mm, respectively; access time and power dissipation are 400 ns and 800 mW, respectively.