摘要:

Small structures in high‐mobility semiconductor heterojunctions are expected to show a variety of quantum mechanical phenomena associated with electron interference. At low temperatures in the high‐mobility two‐dimensional electron gas at a GaAs/AlGaAs heterojunction, both the elastic and inelastic electron scattering lengths are several microns, making it possible to fabricate complete devices contained within these dimensions. In ring shaped devices we have observed periodic magnetoconductance oscillations (Aharonov–Bohm effect) caused by electron interference. The magnitude of this effect is as much as 10% of the total conductance, much larger than seen in previously studied metal systems. High‐resolution electron (e)‐beam lithography and reactive ion etching were used to fabricate rings of 1, 2, and 2.5 μm mean diameters with linewidths of 0.5 μm. The electrical channel width is smaller than the physical channel width because of edge depletion. Samples with conducting channels varying from about 0.6 to 0.2 μm have been made. The magnetoconductance of these rings oscillate with a period ofhc/e(±2%) based on the mean diameter, as expected for a single electron interference effect. The Hall resistance of these samples show strong nonlocal effects, demonstrating that the channel acts as a phase preserving electron waveguide. These devices are an excellent test system for studying electron transport in the extreme quantum limit, and exploring the consequences of the limits of microfabrication.

ISSN:1071-1023    

DOI:10.1116/1.584029

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have fabricated GaAs metal–semiconductor field‐effect transistors (MESFET’s) and GaAs/AlGaAs modulation‐doped field‐effect transistors (MODFET’s) with gate lengths of 50 and 100 nm. A JEOL 5DIIU electron‐beam lithography system was used in the fabrication of these nanometer transistors. This system has demonstrated a 30‐nm overlay accuracy and liftoff metal lines as narrow as 25 nm. The electrical measurement results showed a room temperature extrinsic transconductance (gm) of 540 mS/mm for the 100‐nm MESFET’s and over 600 mS/mm for the 100‐nm MODFET’s. The MESFET also exhibited a small signal gain of 16 dB at 18 GHz at the low‐noise bias point which is the highest ever reported for a MESFET. A significant short channel effect, however, has also been observed in these very short gate transistors. In this paper, transistor fabrication will be discussed and electrical results will be presented.

ISSN:1071-1023    

DOI:10.1116/1.584030

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have reported previously on the fabrication, using x‐ray lithography, of Si metal–oxide–semiconductor field‐effect transistors (MOSFET’s) having channel lengths ranging from 60 nm to 5 μm. Devices with channel lengths of 75 nm showed electron velocity overshoot at 4.2 K. We have improved the mobility of the short‐channel MOSFET’s by implanting with B and then growing the gate oxide rapidly such that the concentration in the inversion layer is about 2×1016cm−3rather than the 5×1017cm−3used previously. A peak concentration of 2.2×1017cm−3occurs at a depth of 0.19 μm, where it prevents punchthrough by screening the field lines from the drain. With devices having channel lengths shorter than 100 nm we measured mean electron velocities at 300 and 77 K that exceeded 107and 1.3×107cm/s, the bulk saturation velocities at these two temperatures. The highest mean velocity measured at 77 K was 2.3×107cm/s.

ISSN:1071-1023    

DOI:10.1116/1.584031

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

This paper describes techniques suitable for the fabrication of silicon field effect transistor (FET) circuits with gate lengths as small as 0.07 μm, intended for experiments to assess the feasibility of FET technology in the 0.1‐μm channel length regime. High‐resolution electron‐beam lithography using a vector scan system capable of an 8‐nm Gaussian spot size has been performed successfully for all levels, with various resist systems tailored to the specific processing requirements. Proximity correction has been found to be a critical issue and was performed using parameters derived from measured point exposure distributions. Metal liftoff using double‐layer poly(methyl methacrylate) resist has been performed successfully with complex patterns. Better than 0.1‐μm linewidth and 0.05‐μm alignment accuracy is achieved over a 250‐μm field, using tantalum silicide alignment marks.

ISSN:1071-1023    

DOI:10.1116/1.584032

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

An electron‐beam inspection system with a capability of detecting quarter‐micron defects has been developed and is applied to the inspection of the x‐ray mask itself. The accuracy of this system is measured and discussed. The distortion of the electron‐beam deflection is 0.08 μm (root‐mean‐square error) within 70×90 μm area in the scan field of 100 μm2. A sample x‐ray mask has Au absorption patterns with the thickness of 0.8 μm on a 2.0‐μm‐thick SiN membrane. An accelerating voltage of 3 kV was found to give a stable signal with a minimum of charging effects. The inspection is performed by means of die‐to‐die comparison scheme. Detection of 0.3 μm defects was demonstrated, indicating the potential of electron‐beam technology for x‐ray mask inspection.

ISSN:1071-1023    

DOI:10.1116/1.584033

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

In x‐ray lithography at deep submicron and sub‐100‐nm linewidths, the effects of diffraction are not negligible. We have investigated the possibility of improving the slope of the irradiance profile at feature edges by using an absorber that produces a pi‐phase shift in addition to about 10 dB attenuation. Both numerical simulation and experimental modeling at a longer wavelength (365 nm) were used. These show that the irradiance profile at the edge of features is steeper when using a pi‐phase shifting mask. For gold, the condition of pi‐phase shift and 10 dB attenuation occurs when the wavelength is 1.15 nm and the thickness is 290 nm; and for tungsten at a wavelength of 1.3 nm and a thickness of 275 nm. X‐ray masks made with the proper phase‐shift and attenuation yield an increased slope at feature edges which should result in improved process latitude. The phase‐shifting scheme introduced here differs from those previously described, and applies to patterns of arbitrary geometry, including isolated lines and spaces.

ISSN:1071-1023    

DOI:10.1116/1.584034

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

This study investigates the effects of hydrogen removal on the properties of nonstoichiometric B3NH films. Total removal of the hydrogen from such films is shown to result in the production of x‐ray mask membranes that are mechanically stable under synchrotron radiation. However, the phase separation that accompanies the high temperature annealing (∼1100 °C), essential for removal of all of the hydrogen, is seen to result in undesirable darkening of the film. This problem is shown to be resolved by the preparation of stoichiometric BN films under optimized deposition conditions. Although BN films are seen not to degrade optically after high temperature annealing and x‐ray irradiation, their characteristic compressive stress makes them undesirable for single membrane x‐ray masks. A hybrid x‐ray mask structure is proposed which combines the favorable properties of stoichiometric and nonstoichiometric boron nitride films. This radiation‐hard x‐ray mask structure is shown to meet the mechanical stability and optical transmission requirements.

ISSN:1071-1023    

DOI:10.1116/1.584035

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The optical and mechanical properties of boron nitride vapor deposited at 400 °C are shown to degrade when exposed to synchrotron radiation. The extent of the damage and the rate at which the damage occurs are similar to that first reported by Johnsonetal. Transmission through membranes of boron nitride was measuredinsituduring exposure to x rays. Membranes darkened considerably with the transmission through a typical membrane falling from 50% to 20% after absorbing ∼250 kJ/cm3of x rays. Changes in local film stress were measured with a simple cantilever technique. Films originally in tension (∼5E8 dyne/cm2) were found to become compressive after absorbing 300 kJ/cm3of x rays. Both forms of damage responded well to annealing. Fourier transform infrared (FTIR) and near‐edge x‐ray absorption measurements were made to discern the structural differences between degraded and unexposed films. No significant structural changes were observed. Boron nitride films deposited at higher temperatures (600 °C) proved to be much less susceptible to radiation damage. In a related development, films produced through the pyrolysis of borazine appeared to be completely immune to radiation damage as were silicon and silicon nitride membranes. FTIR spectra indicate that less hydrogen is present in the 600 °C chemical‐vapor deposition (CVD) and the pyrolytic boron nitride films than in the 400 °C CVD films. As proposed by Johnsonetal., hydrogen is implicated as an intermediary in the boron nitride damage mechanism.

ISSN:1071-1023    

DOI:10.1116/1.584036

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Statistical variations in the local energy deposition in resist can result in defect generation and unacceptable linewidth variation. The lower limit of exposure dose at which these variations limit pattern integrity is termed the shot noise limit. Several analyses of the shot noise limit have been published. We find that refinements in the underlying assumptions on which these analyses are based have led to a substantial reduction in the shot noise limit. The refined assumptions include optimization of the resist absorption, use of a binary exposure‐dissolution model with a sharp, percolation threshold, consideration of multipath dissolution effects, and separation of bias and linewidth variation in algebraic models. The infrequent occurrence of large defects is shown to dominate over the 3σ linewidth variation. While typically 30 exposure events per defect volume is still required, a factor of 30 reduction in the shot noise exposure limit is established primarily by showing that defect sizes up to (1)/(3) of the linewidth are tolerable. For lithography at 0.37‐μm‐feature size, consistent with 64 Mbit dynamic random access memories, the refined shot noise limit is below 1 mJ/cm2for 1.0 μm‐resist coating thickness. Thus the shot noise limit does not appear to be a fundamental road block to the use of high sensitivity resists with nonsynchrotron x‐ray sources.

ISSN:1071-1023    

DOI:10.1116/1.584037

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

In order to reduce distortion and to obtain good pattern‐placement accuracy in x‐ray masks, a stress‐compensation technique in x‐ray absorber layers has been developed using ion bombardment. The absorber material selected is amorphous WNx(x=0.1) deposited with rf sputtering because its compressive stress of 1010dyn/cm2can be completely compensated with the present technique, although it is effective in all the metals attempted with both compressive and tensile stresses. It is shown that ion bombardment at an elevated temperature enables precise stress control together with excellent thermal stability in stress. In‐plane distortion caused by opening of 3×3‐mm2patterns in the WNxabsorber was measured in masks with 2‐μm‐thick SiNxsupporting membranes. The 0.4‐μm‐thick WNxlayers used were stress compensated by bombardment with 400‐keV N+ions at 300 °C to a dose of 4 to 6×1014ions/cm2. The distortion has been reduced to less than 5×10−6relative to the pattern size. The mechanism of the stress compensation is also discussed.

ISSN:1071-1023    

DOI:10.1116/1.584038

出版商:American Vacuum Society    

年代:1988

数据来源: AIP