- Email: [email protected]
Electron-beam fabrication of chromium master masks
Classified abstracts 1648-1655
magnetic projection lenses. The limitations imposed by the unavoidable aberrations of the condenser system are also discussed. The performance of the system is illustrated by reference to results by exposing test patterns. M B Heritage, J Vac Sci Technol, 12 (6), 1975, 1135-1140. 34 1648. Synchroton radiation as a new tool within photon-beam technology. (USA) Synchroton radiation is now playing an increasingly important role in recent developments of new light sources. Synchrotron light emitted from a relativistic electron beam has a radiation pattern which makes it a unique source. The advantages with this type of radiation can be summarized as (a) continuous spectrum extending from the ir to the X-ray region, (b) strongly polarized, (c) highly collimated, (d) pulsed structure allowing time-resolution spectroscopy, and (e) high intensity making feasible the use of monochromators with narrow band pass. The Stanford Synchrotorn Radiation Project has been in operation since May 1974 as a U.S. National Facility for uv and X-ray research in many disciplines using the radiation from the storage ring SPEAR at the Stanford Linear Accelerator Center. The radiation spectrum is characterized by the critical energy which varies as E 3 (E = electron-beam energy) and is 11 keV for E = 4 GeV. Useful flux is available out for approximately five times the critical energy. Five monochromators now share the beam run and cover the entire wavelength region from the visible to the hard X-ray region. Several experimenting groups are involved in research programs including (a) uv and X-ray photoelectron spectroscopy, (b) optical reflectance and transmission studies, (c) soft X-ray absorption and extended X-ray absorption fine structure (EXAFS) studies, (d) low-angle scattering studies of certain biological materials, and (e) X-ray diffraction studies of protein crystals and other materials. S Doniach et al, J Vac Sci Technol, 12 (6), 1975, 1123-1127. 34 1649. An atom-probe field ion microscope. (France) An atom-probe field ion microscope (Mueller et al., 1968) combines a time of flight spectrometer and a field ion microscope. The one particule sensitive detector and the 106 magnifying power of the microscope permit the analysis of a sample of I0 ~. diameter through a 1 mm diameter aperture. The atom-probe described here is composed of a field ion microscope with a channel-plate (image intensifier) working in ultra high vacuum and at the temperature of liquid helium. The time of flight measurement that gives the ionised atom weight/ charge ratio is performed either with an oscilloscope or with a 100 MHz time base counter system. J Gallot et al, Vide, 30 (179), 1975, 173-181 (hi French). 34 1650. Mini magnetic lenses for microfocus X-ray applications. (USA) The mini magnetic lens is used to obtain a high-definition X-ray source positioned at the end of a long thin rod. This rod is the magnetic-lens holder which has a useful length of 315 mm and an outer diameter of I0 ram. The X-ray point source has a diameter of 0.1 mm providing a panoramic X-ray pattern with an emergent angle of 45 ° in several elevation angles dependent on the X-ray target configuration selected. Several 80 and 150 kV microfocus X-ray systems based on the mini-magnetic-lens construction are used for high-definition nondestructive X-ray inspection of small-bore large-depth welds as are found in heat exchangers for nuclear power stations. (Netherlands) L A Fontijn, J Vac Sci Technol, 12 (6), 1975, 1359-1362. 34 1651. Optimized source for X-ray lithography of small area devices. (USA) The design and performance of an optimized soft-X-ray source using an aircooled AI target are described in this paper. The technical considerations leading to the choice of mask material, source wavelength, vacuum enclosure, and electron optics arc also described. Although the authors have previously shown the need for large, powerful X-ray sources, the source described here is intended for exposure of small-area surface-acoustic-wave (SAW) devices with submierometer dimensions. Since distortion over large areas need not be controlled, the X-ray source is limited to 1 mm in diameter and the electron beam power to 250 W. A 25 g.m thick Be vacuum window was developed which made it possible to use the AI K= X-ray wavelength with a thin Si mask and yet maintain the exposure
area in He at atmospheric pressure. The custom-designed electron gun, exposure monitor, and thermal control system are also described. Results are reported on the replication of a SAW device pattern in P M M A resist with 0.5 am linewidths. P A Sullivan and J H McCoy, J Vac Sci Technol, 12 (6), 1975, 1325-1328. 35 1652. Composition and detection of alignment marks for electron-beam lithography. (USA) High energy backscattered electron signals have been measured from I, 3, and 10/~m wide gold alignment marks on silicon and gallium arsenide substrates as a function of electron beam energy (5-30 keV) and gold film thicknesses (650--10000 ,~) using an annular silicondiode detector. Thin films of both silicon dioxide (3500 /~) and polymethyl methacrylate (5200 A,) on gold alignment marks (2600 ,~) and polymethyl methacrylate (5200 A) on gold alignment marks (2600 .~) on silicon reduced the original signal contrast at 30 keV incident-beam energy by only 16% (10% and 6~o, respectively) and degraded the original edge acuity by only about a factor of two. Signal contrast maxima for gold on silicon and gold on gallium arsenide were found to be 1.64 and 0.86, respectively, while silicon and silicon dioxide steps (~4000 A) produced no more than 0.08 and 0.04 contrast, respectively. The gold on silicon results are presented with the full realization of the general processing incompatibility of gold on silicon devices and circuits at high temperatures. These results are applicable to other high-atomic-number materials which can be optimized for a particular electron-beam lithography process. The advantage of efficient high-energy backscattered electron detection and high-atomic-number alignment marks to produce high-contrast video signals which are not significantly degraded by the addition of low-atomic number thin films (e.g., SIP2, resists) will become increasingly important when very accurate alignment is required (+0.05 ~m). E D Wolf et al, J Vac Sci Teehnol, 12 (6), 1975, 1266-1270. 35 1653. Application of moird techniques in scanning-electron-beam lithography and microscopy. (USA) When a grating is viewed by scanning electron microscopy, a moir~ pattern is observed. Applications of the tapir6 phenomenon in scanning-electron-beam lithography and microscopy are discussed, including adjustment of the spatial period and angle of a scan raster, analysis of distortion in a scan raster, analysis of stray-field beam deflection and measurement errors, and registration of a scan field relative to coded patterns on a substrate. H I Smith et al, J Vac Sci Technol, 12 (6), 1975, 1262-1265. 35 1654. Electron-beam fabrication of chromium master masks. (USA) Conventional photolithographic methods of mask manufacture in the semiconductor industry have limitations which can be overcome using electron lithography. This paper describes application of the electron-beam exposure system (EBES) to the fabrication of chromium master masks using the negative electron resist poly(glycidyl methacrylate-co-ethyl acrylate). Lithographic characterization methods developed specifically for this application include the variation of feature size and developed resist thickness with exposure and have led to the choice of correct operating conditions for EBES. Writing time for a typical 2.5-in. (6.35 cm) mask is 30-60 min, and processing time is about 70 min (excluding inspection and handling). Linewidth control is better than -t-0.5 tLm and chip yields typically exceed 90% per mask level for LSI circuits. Masks with chip sizes up to 20 x 16 mm have been processed. One-micrometer feature sizes are obtained routinely. J P Ballantyne, J Vac Sci Technol, 12 (6), 1975, 1257-1260. 35 1655. Control system design and alignment methods for electron lithography. (USA) The electron-beam exposure system (EBES) was designed to economically expose integrated circuit masks on a production basis and to directly pattern semiconductor substrates for special applications where a limited number of devices are required. The machine was designed to assure absolute pattern accuracy over the entire substrate so that masks made by EBES will be interchangeable with those made by our optical mask shop or those made by later electron-beam pattern generators. This has been achieved by a combination of control system design and by automated periodic system alignment. 217
magnetic projection lenses. The limitations imposed by the unavoidable aberrations of the condenser system are also discussed. The performance of the system is illustrated by reference to results by exposing test patterns. M B Heritage, J Vac Sci Technol, 12 (6), 1975, 1135-1140. 34 1648. Synchroton radiation as a new tool within photon-beam technology. (USA) Synchroton radiation is now playing an increasingly important role in recent developments of new light sources. Synchrotron light emitted from a relativistic electron beam has a radiation pattern which makes it a unique source. The advantages with this type of radiation can be summarized as (a) continuous spectrum extending from the ir to the X-ray region, (b) strongly polarized, (c) highly collimated, (d) pulsed structure allowing time-resolution spectroscopy, and (e) high intensity making feasible the use of monochromators with narrow band pass. The Stanford Synchrotorn Radiation Project has been in operation since May 1974 as a U.S. National Facility for uv and X-ray research in many disciplines using the radiation from the storage ring SPEAR at the Stanford Linear Accelerator Center. The radiation spectrum is characterized by the critical energy which varies as E 3 (E = electron-beam energy) and is 11 keV for E = 4 GeV. Useful flux is available out for approximately five times the critical energy. Five monochromators now share the beam run and cover the entire wavelength region from the visible to the hard X-ray region. Several experimenting groups are involved in research programs including (a) uv and X-ray photoelectron spectroscopy, (b) optical reflectance and transmission studies, (c) soft X-ray absorption and extended X-ray absorption fine structure (EXAFS) studies, (d) low-angle scattering studies of certain biological materials, and (e) X-ray diffraction studies of protein crystals and other materials. S Doniach et al, J Vac Sci Technol, 12 (6), 1975, 1123-1127. 34 1649. An atom-probe field ion microscope. (France) An atom-probe field ion microscope (Mueller et al., 1968) combines a time of flight spectrometer and a field ion microscope. The one particule sensitive detector and the 106 magnifying power of the microscope permit the analysis of a sample of I0 ~. diameter through a 1 mm diameter aperture. The atom-probe described here is composed of a field ion microscope with a channel-plate (image intensifier) working in ultra high vacuum and at the temperature of liquid helium. The time of flight measurement that gives the ionised atom weight/ charge ratio is performed either with an oscilloscope or with a 100 MHz time base counter system. J Gallot et al, Vide, 30 (179), 1975, 173-181 (hi French). 34 1650. Mini magnetic lenses for microfocus X-ray applications. (USA) The mini magnetic lens is used to obtain a high-definition X-ray source positioned at the end of a long thin rod. This rod is the magnetic-lens holder which has a useful length of 315 mm and an outer diameter of I0 ram. The X-ray point source has a diameter of 0.1 mm providing a panoramic X-ray pattern with an emergent angle of 45 ° in several elevation angles dependent on the X-ray target configuration selected. Several 80 and 150 kV microfocus X-ray systems based on the mini-magnetic-lens construction are used for high-definition nondestructive X-ray inspection of small-bore large-depth welds as are found in heat exchangers for nuclear power stations. (Netherlands) L A Fontijn, J Vac Sci Technol, 12 (6), 1975, 1359-1362. 34 1651. Optimized source for X-ray lithography of small area devices. (USA) The design and performance of an optimized soft-X-ray source using an aircooled AI target are described in this paper. The technical considerations leading to the choice of mask material, source wavelength, vacuum enclosure, and electron optics arc also described. Although the authors have previously shown the need for large, powerful X-ray sources, the source described here is intended for exposure of small-area surface-acoustic-wave (SAW) devices with submierometer dimensions. Since distortion over large areas need not be controlled, the X-ray source is limited to 1 mm in diameter and the electron beam power to 250 W. A 25 g.m thick Be vacuum window was developed which made it possible to use the AI K= X-ray wavelength with a thin Si mask and yet maintain the exposure
area in He at atmospheric pressure. The custom-designed electron gun, exposure monitor, and thermal control system are also described. Results are reported on the replication of a SAW device pattern in P M M A resist with 0.5 am linewidths. P A Sullivan and J H McCoy, J Vac Sci Technol, 12 (6), 1975, 1325-1328. 35 1652. Composition and detection of alignment marks for electron-beam lithography. (USA) High energy backscattered electron signals have been measured from I, 3, and 10/~m wide gold alignment marks on silicon and gallium arsenide substrates as a function of electron beam energy (5-30 keV) and gold film thicknesses (650--10000 ,~) using an annular silicondiode detector. Thin films of both silicon dioxide (3500 /~) and polymethyl methacrylate (5200 A,) on gold alignment marks (2600 ,~) and polymethyl methacrylate (5200 A) on gold alignment marks (2600 .~) on silicon reduced the original signal contrast at 30 keV incident-beam energy by only 16% (10% and 6~o, respectively) and degraded the original edge acuity by only about a factor of two. Signal contrast maxima for gold on silicon and gold on gallium arsenide were found to be 1.64 and 0.86, respectively, while silicon and silicon dioxide steps (~4000 A) produced no more than 0.08 and 0.04 contrast, respectively. The gold on silicon results are presented with the full realization of the general processing incompatibility of gold on silicon devices and circuits at high temperatures. These results are applicable to other high-atomic-number materials which can be optimized for a particular electron-beam lithography process. The advantage of efficient high-energy backscattered electron detection and high-atomic-number alignment marks to produce high-contrast video signals which are not significantly degraded by the addition of low-atomic number thin films (e.g., SIP2, resists) will become increasingly important when very accurate alignment is required (+0.05 ~m). E D Wolf et al, J Vac Sci Teehnol, 12 (6), 1975, 1266-1270. 35 1653. Application of moird techniques in scanning-electron-beam lithography and microscopy. (USA) When a grating is viewed by scanning electron microscopy, a moir~ pattern is observed. Applications of the tapir6 phenomenon in scanning-electron-beam lithography and microscopy are discussed, including adjustment of the spatial period and angle of a scan raster, analysis of distortion in a scan raster, analysis of stray-field beam deflection and measurement errors, and registration of a scan field relative to coded patterns on a substrate. H I Smith et al, J Vac Sci Technol, 12 (6), 1975, 1262-1265. 35 1654. Electron-beam fabrication of chromium master masks. (USA) Conventional photolithographic methods of mask manufacture in the semiconductor industry have limitations which can be overcome using electron lithography. This paper describes application of the electron-beam exposure system (EBES) to the fabrication of chromium master masks using the negative electron resist poly(glycidyl methacrylate-co-ethyl acrylate). Lithographic characterization methods developed specifically for this application include the variation of feature size and developed resist thickness with exposure and have led to the choice of correct operating conditions for EBES. Writing time for a typical 2.5-in. (6.35 cm) mask is 30-60 min, and processing time is about 70 min (excluding inspection and handling). Linewidth control is better than -t-0.5 tLm and chip yields typically exceed 90% per mask level for LSI circuits. Masks with chip sizes up to 20 x 16 mm have been processed. One-micrometer feature sizes are obtained routinely. J P Ballantyne, J Vac Sci Technol, 12 (6), 1975, 1257-1260. 35 1655. Control system design and alignment methods for electron lithography. (USA) The electron-beam exposure system (EBES) was designed to economically expose integrated circuit masks on a production basis and to directly pattern semiconductor substrates for special applications where a limited number of devices are required. The machine was designed to assure absolute pattern accuracy over the entire substrate so that masks made by EBES will be interchangeable with those made by our optical mask shop or those made by later electron-beam pattern generators. This has been achieved by a combination of control system design and by automated periodic system alignment. 217