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Multi electron beam lithography: Fabrication of a control unit
Microelectronic North-Holland
Engineering
205
9 (1989) 205-208
MlJLTl ELECTRON U. Schnakenberg,
BEAM LITHOGRAPHY:
FABRICATION
OF A CONTROL
W. Benecke, V. Wallendszus, K.P. Muller, A. Heuberger
UNlT
and B. Lischke*
Fraunhofer-lnstitut fur Mikrostrukturtechnik (IMT), Dillenburger Str. 53, D-1000 Berlin 33, Germany Otto-Hahn-Ring
* Siemens AG, ZT ZFE FKE 24, 6, D-8000 Munchen 83, Federal Republic of Germany
Electron beam lithography is limited by the extremely low throughput machines. This paper describes a multiple beam forming unit for a lithography system called High Speed, High Resolution Electron (HISEL). The simultaneous Ze of a multiple number of individually beams allows an essential reduction of the pattern transfer time. total number of 1024 electron beams is used.
of currently working new line printer type Lithography System Controllable electron In a first version, a
The control unit consists of two independent elements: the aperture plate (illuminated by an electron line pe source) which forms a line of 1024 square-shaped (IO x IO) pm* electron beams and tx e deflection plate with a corresponding set of 1024 microcapacitors. The capacitors allow an individual beam deflection, e.g. on-off switching of the beams. The fabrication is based on silicon micromechanics and X-ray lithography. 1.
2.
INTBODUCTION
The throughput of conventional electron-beam lithography systems is extremely low if the critical dimensions of the patterns fall down to the sub-Nrn range. To increase the pixel transfer rate, one can use variable shaped beams, image projection systems or a parallel writing system. A new concept for a High Speed, High Resolution Electron Lithography Syste?n (HISEL) has been proposedby Lischke /1,2/. The basic element of this parallel writing machine is a line printer type pattern transfer system using a multiple number of individually controllable electron beams. This new generation of lithography systems will be designed for direct wafer writing and mask fabrication in the I:1 scale, e.g. for the use in X-ray lithography. The specifications are determined by the requirements of future IC-generations. In the late nineties, the critical dimensions on the wafer will be below 0.5 rrn and will reach the 0.2 pm range in the For applications like GaAs IC’s and year 2000. integrated optics linewidths down to 0.1 Km might be necessary much earlier. Therefore, the first generation designed for 100 nm smallest
HISEL has linewidth.
been
This pa er describes the fabrication of a control P which is one of the essential elements if”‘:he/3ejectron beam column /I ,2,4,5/. The key technologies for the fabrication of the control unit are silicon micromechanics and X-ray lithography using synchrotron radiation.
0167.9317/89/$3.50
0 1989, Elsevier Science Publishers
B.V. (North-Holland)
DESIGN CONSIDERATIONS
aperture
deflection
Fig. 1:
plate
Plate
Schematic
drawing
of the control
unit
A schematic drawing of the control unit is shown in Fig. 1. The assembly has been divided into two independent elements. These elements are called aperture plate for sub-beam formation and beam shape definition and de%ction plate for individual beam deflection. These two parts have to be well aligned to each other, which can be done by fineomechanics or byet;;E$hire spheres inserted anlsotroprc pyramidal cavities. The aperture plate consists of a silicon substrate locally thinned to form a rectangular membrane. This membrane bears a linear array of 1024 physical holes with a 10 rm square shaped geometry and a periodicity of 20 pm. The thickness of the membrane has been adjusted between 1 and 2 pm to achieve the contrast ratio required. To minimize the scattering of
U. Schnakenberg
206
et al. /Multi electron beam lithography
* Deposition
of a thin Si,N,-layer using LPCVD-techniques to protect the wafer from the etch solution. * Boron implantation (dose: 1 x 1015 cms2, energy: 200 keV) to reduce the tensile stress of the nitride layer.
electrons in order to achieve a well defined beam geometry, vertical sidewalls of .the holes are required. Using a. 1OO:l demagnrfytng projection system, a spot srze of 100 x 100 nm can be achieved. The deflection plate bears a slot shaped opening with a set of 1024 microcaoacitors for beam deflection corresponding to the geometries of the aperture plate. The capacitor gap is approximately 14 am and the width of the plates measured in the direction of line array is approximately 12 pm. To achieve a beam deflection of 0.1 mrad using electrons with 50 keV and a capacitor voltage of * 10 V, a capacitor height of 25 clrn is required /4/. 3. 3.1
b) *
Lithography and etching of the Si3N,-layer at the front and anisotropic dry etching of the epitaxial layer using a SF process In a MERIE reactor (Magnet&y Enhanced Reactive Ion Etching).
c) * *
Lithography and etching of the Si3N,-layer on the back to define the etch-groove. Anisotropic wet etching of the substrate from the back using EPW which stops at the epitaxial layer. _ Deposition of a thin metal layer (gold) to minimize distortions during operation due to charging of insulators.
*
EXPERIMENTAL RESULTS AND DISCUSSION Aperture Plate
The aperture plate is fabricated using nologies of silicon micromechanics.
the tech-
The membranes are made of epitaxially-grown highly boron-doped silicon. Codoping with germanium is used for stress compensation 161. It is well-known that the etch rate of highly boron doped silicon (o+-Si) is drasticallv reduced in anisotrooic wet etchanis like poiasium hydroxide or EPW (EthylenediaminePyrocatechol-Water) /7/. The holes are generated by lithography and reactive ion etching. An outline of the fabrication process is given in Fig. 2.
An SEM of a single hole in the membrane of the aperture plate is shown in Fig. 3. The deviations from the square geometry of the hole are due to the limited resolution of the printer used at this stage. The hole geometry can be determinated to (6.6 x 6.6) ,m2. The SEM in Fig. 4 shows a cross section of a hole in a 2 pm thick membrane. The edge characteristic at the top is due to the fact that the photoresist, which serves as masking material, does not show vertical sidewalls. Due to an incomplete sidewall passivation, a slight undercut occurs.
_LPCVD-Si3N, Lp+-Si
a)
-(loo)-Si
b)
-Au C)
Fig. 2:
a) **
Fabrication
process
of the aperture
Fig. 3:
SEM-micrograph of a single hole in the highly boron doped Si-membrane, top view
Fig. 4:
Cross-section of the hole shown 3. The membrane is 2 pm thick.
plate
Substrate: (100) Si-wafer, 100 mm diameter Epitaxial deposition of a p+-Si layer (boron concentration: 1.3 x 1020 cms3). The mechanical tensile stress due to the high boron concentration is reduced by co-doping with germanium (germanium concentration: 1 x 102’ cme3).
3.2
Deflection
in Fig.
Plate
For the fabrication of the deflection plate, anisotropic wet etching of silicon is combined with the technique of depth lithography using UV-light as
U Schnakenberg
201
et al. /Multi electron beam lithography
well as synchrotron radiation. Anisotropic wet etching of silicon is used to produce a slot shaped opening for the 1024 electron beams created by the aperture plate. The fabrication of microcapacitors is done by depth lithography and local electroplating.
Additionally, its high sensitivity to X-rays could be For elaboratron of the complete demonstrated. fabrication process, the experiments have been started with UV-lithography.
The fabrication process is shown schematically in Fig. 5 and can be summarized by the following steps:
Adhesion of the resist was increased b treatment in a promoter atmosphere (SELECTIPLA 8 T HTR AP-3, E. MERCK Comp.). After removal of surplus resist at the edge of the wafer, the spin coating process results in a resist thickness of 30 pm * 5%. The wafer was prebaked at 100°C for 60 minutes on a hot plate.
LPCVD-Si,N, (lOO)-Si
3.2.1
UV-Lithography
Exposure experiments were carried out applying a usual mask aligner (MA 25 by K. Suss Comp., FRG) at an exposure dose of 336 mJ/cm2. -Au
The resist was developed using a spray process with the developer SELECTIPIAST HTR D-2. The following development procedure was carried out:
“)
20 10 10 30
c)
s s s s
spray with developer lingering period rinse with 2-propanol spin dry
at at at at
500 500 500 3000
rpm, rpm, rpm, rpm.
The capacitors were formed by goldplating (LEA RONAL (AURALL 2.92). The total plating process took about 4 hours. No significant change in the geometry of the resist could be observed after the electroplating step.
d) Fig. 5:
6 shows Fig. capacitors. Fabrication plate
orocess
of
the
an SEM
of electroplated
micro-
deflection
’
a) ** *
Substrate: (100) Si-wafer, 100 mm diameter. Deposition of a Si,N,-layer (LPCVD). Lithography and etching of the SisN,-layer.
b) * *
Cr/Au-metallization serving as a plating base. Lithography and local electroplating of gold to form the interconnection lines.
c) *
Depth lithography using a photoresist with a thickness of aooroximatelv 30 urn and electroplating of gold’up to a thickness of approximately 25 Wm.
d) * *
Anisotropic wet etching of the material. Etching of the plating base.
silicon
bulk
The most important and critical process step is the deoth lithoaraohv. Exoeriments were carried out with the comfier&airy available negative photoresist SELECTILUX HTR 3-200. IE. MERCK Como.. FRGI. The resist can be deposited up to a thickness of 8b pm using spin-on techniques. It is well-known that this resist is sensitive to UV radiation (350 - 450 nm).
Fig. 6:
SEM-micrograph of electroplated microcapacitors using depth lithography with UV-radiation. Dimensions (I * w * t) = (53 * 14 * 20) .um3
The dimensions can be evaluated to (I*w*t) = (53*14*20) pm3 with a spacing of 6 pm. The capacitors are laterally slightly cone formed and show nearly vertical side-walls. Compared to the
U, Schnukenberg
208
et al. /Multi electron beam lithography
lateral geometries defined on the mask level, they show an enlargement of about 2 rrn in the width. 3.2.2 X-ray Lithography To increase the lateral geometrical accuracy, the critical lithoaraohv steo will be replaced bv X-rav lithography,- especially’ with synchrotron radiation /8/. Exposure experiments were made at the Elektronenspeicherring-Gesellschaft fur Berliner Svnchrotronstrahlung mbH (BESSY) in Berlin, FRG (electron energy 805 MeV, maximum spectral wavelenath 3 nm). Durina exposure, the wafer was mounted vertically into v&urn chamber filled with 40 mbar He and was mechanically scanned through the horizontal beam. Fig. 7 shows an SEM-picture of some bar type structures transferred into a 24 rm resist using a dose of 64 mJ/cm*. The following development parameter set for the spray developer was evaluated: 35 s spray developer at 500 rpm, IO s lingering time at 500 rpm, 10 s rinse with P-propanol at 500 rpm, 30 s spin dry at 3000 rpm. The width at the top of the bars can be determinated to 1 rm and is slightly reduced to 0.9 pm near the bottom. The ratio of height to width - the aspect ratio - is 24:l. At the bottom a little enlargement can be seen but cannot be explained. The edges show well defined geometries. The inclination and touch of the bars will probably be generated by capillary forces during the process siep of development.
tron beam lithography system, HISEL, has been described. The control unit illuminated by an electron line source consists of an aperture plate, which forms 1024 square shaped electron beams and a deflection plate for individual on-off switching of the beams using a set of microcapacitors. Both plates are fabricated using the technology of silicon micromechanics and depth lithography by applying UV and synchrotron radiation, respectively. The holes in the Si-membrane of the aperture plate show rounded edges which are due to the limited resolution of the proximity lithography system. High resolution X-ray lithography will be used to fabricate the final devices. Depth lithography was carried out using SELECTILUX HTR 3-200 as photoresist with a thickness of 30 pm to form the microcapacitors. First examples of capacitors were fabricated using UV-radiation for patterning. The sidewalls of the electroplated microcapacitors are almost vertical. The aspect ratio (height to width of the space) can be evaluated to 5:l. To increase the lateral geometrical accuracy, the use of high resolution X-ray lithography WIII be necessary. First experiments demonstrate the patterning of the resist down to the sub-km range with large aspect ratios. 4.
ACKNOWLEDGEMENT
The authors would like to thank S. Vogelsang and B. Schroth for their valuable assistance during the device fabrication. 5.
Fig
4.
7:
SEM-micrograph of 24 pm thick polyimide exposed by synchrotron radiation of BESSY witha dose of 64 mJ/cm*.
CONCLUSIONS
The fabrication
of a control
unit for a multi elec-
REFERENCES B. Lischke et al: Proceedings ME ‘88 B. Lischke et al: 32nd International Symposium on Electron, Ion and Photon Beams 1988, May 31 -June 2, 1988, Fort Lauderdale, Florida U. Schnakenberg et al: 32nd International Symposium on Electron, Ion and Photon Beams 1988, May 31 - June 2, 1988, Fort Lauderdale, Florida P. Schaffer et al: Proc. ME ‘88 G. Schcnecker et al: Proc. ME ‘88 H.-J. Herzog et al: Electrochem. Sot.: Solid-State Science and Technology, Vol. 131, 2969-2974, December 1984 H. Seidel: Proc. of the 4th Int. Conf. on -. Solid-State Sensors and Actuators, Transducers ‘87, June 2-5, Tokyo, Japan, 120 A. Heuberger: Microelectronic Engineering 3, 535 (1985)
Engineering
205
9 (1989) 205-208
MlJLTl ELECTRON U. Schnakenberg,
BEAM LITHOGRAPHY:
FABRICATION
OF A CONTROL
W. Benecke, V. Wallendszus, K.P. Muller, A. Heuberger
UNlT
and B. Lischke*
Fraunhofer-lnstitut fur Mikrostrukturtechnik (IMT), Dillenburger Str. 53, D-1000 Berlin 33, Germany Otto-Hahn-Ring
* Siemens AG, ZT ZFE FKE 24, 6, D-8000 Munchen 83, Federal Republic of Germany
Electron beam lithography is limited by the extremely low throughput machines. This paper describes a multiple beam forming unit for a lithography system called High Speed, High Resolution Electron (HISEL). The simultaneous Ze of a multiple number of individually beams allows an essential reduction of the pattern transfer time. total number of 1024 electron beams is used.
of currently working new line printer type Lithography System Controllable electron In a first version, a
The control unit consists of two independent elements: the aperture plate (illuminated by an electron line pe source) which forms a line of 1024 square-shaped (IO x IO) pm* electron beams and tx e deflection plate with a corresponding set of 1024 microcapacitors. The capacitors allow an individual beam deflection, e.g. on-off switching of the beams. The fabrication is based on silicon micromechanics and X-ray lithography. 1.
2.
INTBODUCTION
The throughput of conventional electron-beam lithography systems is extremely low if the critical dimensions of the patterns fall down to the sub-Nrn range. To increase the pixel transfer rate, one can use variable shaped beams, image projection systems or a parallel writing system. A new concept for a High Speed, High Resolution Electron Lithography Syste?n (HISEL) has been proposedby Lischke /1,2/. The basic element of this parallel writing machine is a line printer type pattern transfer system using a multiple number of individually controllable electron beams. This new generation of lithography systems will be designed for direct wafer writing and mask fabrication in the I:1 scale, e.g. for the use in X-ray lithography. The specifications are determined by the requirements of future IC-generations. In the late nineties, the critical dimensions on the wafer will be below 0.5 rrn and will reach the 0.2 pm range in the For applications like GaAs IC’s and year 2000. integrated optics linewidths down to 0.1 Km might be necessary much earlier. Therefore, the first generation designed for 100 nm smallest
HISEL has linewidth.
been
This pa er describes the fabrication of a control P which is one of the essential elements if”‘:he/3ejectron beam column /I ,2,4,5/. The key technologies for the fabrication of the control unit are silicon micromechanics and X-ray lithography using synchrotron radiation.
0167.9317/89/$3.50
0 1989, Elsevier Science Publishers
B.V. (North-Holland)
DESIGN CONSIDERATIONS
aperture
deflection
Fig. 1:
plate
Plate
Schematic
drawing
of the control
unit
A schematic drawing of the control unit is shown in Fig. 1. The assembly has been divided into two independent elements. These elements are called aperture plate for sub-beam formation and beam shape definition and de%ction plate for individual beam deflection. These two parts have to be well aligned to each other, which can be done by fineomechanics or byet;;E$hire spheres inserted anlsotroprc pyramidal cavities. The aperture plate consists of a silicon substrate locally thinned to form a rectangular membrane. This membrane bears a linear array of 1024 physical holes with a 10 rm square shaped geometry and a periodicity of 20 pm. The thickness of the membrane has been adjusted between 1 and 2 pm to achieve the contrast ratio required. To minimize the scattering of
U. Schnakenberg
206
et al. /Multi electron beam lithography
* Deposition
of a thin Si,N,-layer using LPCVD-techniques to protect the wafer from the etch solution. * Boron implantation (dose: 1 x 1015 cms2, energy: 200 keV) to reduce the tensile stress of the nitride layer.
electrons in order to achieve a well defined beam geometry, vertical sidewalls of .the holes are required. Using a. 1OO:l demagnrfytng projection system, a spot srze of 100 x 100 nm can be achieved. The deflection plate bears a slot shaped opening with a set of 1024 microcaoacitors for beam deflection corresponding to the geometries of the aperture plate. The capacitor gap is approximately 14 am and the width of the plates measured in the direction of line array is approximately 12 pm. To achieve a beam deflection of 0.1 mrad using electrons with 50 keV and a capacitor voltage of * 10 V, a capacitor height of 25 clrn is required /4/. 3. 3.1
b) *
Lithography and etching of the Si3N,-layer at the front and anisotropic dry etching of the epitaxial layer using a SF process In a MERIE reactor (Magnet&y Enhanced Reactive Ion Etching).
c) * *
Lithography and etching of the Si3N,-layer on the back to define the etch-groove. Anisotropic wet etching of the substrate from the back using EPW which stops at the epitaxial layer. _ Deposition of a thin metal layer (gold) to minimize distortions during operation due to charging of insulators.
*
EXPERIMENTAL RESULTS AND DISCUSSION Aperture Plate
The aperture plate is fabricated using nologies of silicon micromechanics.
the tech-
The membranes are made of epitaxially-grown highly boron-doped silicon. Codoping with germanium is used for stress compensation 161. It is well-known that the etch rate of highly boron doped silicon (o+-Si) is drasticallv reduced in anisotrooic wet etchanis like poiasium hydroxide or EPW (EthylenediaminePyrocatechol-Water) /7/. The holes are generated by lithography and reactive ion etching. An outline of the fabrication process is given in Fig. 2.
An SEM of a single hole in the membrane of the aperture plate is shown in Fig. 3. The deviations from the square geometry of the hole are due to the limited resolution of the printer used at this stage. The hole geometry can be determinated to (6.6 x 6.6) ,m2. The SEM in Fig. 4 shows a cross section of a hole in a 2 pm thick membrane. The edge characteristic at the top is due to the fact that the photoresist, which serves as masking material, does not show vertical sidewalls. Due to an incomplete sidewall passivation, a slight undercut occurs.
_LPCVD-Si3N, Lp+-Si
a)
-(loo)-Si
b)
-Au C)
Fig. 2:
a) **
Fabrication
process
of the aperture
Fig. 3:
SEM-micrograph of a single hole in the highly boron doped Si-membrane, top view
Fig. 4:
Cross-section of the hole shown 3. The membrane is 2 pm thick.
plate
Substrate: (100) Si-wafer, 100 mm diameter Epitaxial deposition of a p+-Si layer (boron concentration: 1.3 x 1020 cms3). The mechanical tensile stress due to the high boron concentration is reduced by co-doping with germanium (germanium concentration: 1 x 102’ cme3).
3.2
Deflection
in Fig.
Plate
For the fabrication of the deflection plate, anisotropic wet etching of silicon is combined with the technique of depth lithography using UV-light as
U Schnakenberg
201
et al. /Multi electron beam lithography
well as synchrotron radiation. Anisotropic wet etching of silicon is used to produce a slot shaped opening for the 1024 electron beams created by the aperture plate. The fabrication of microcapacitors is done by depth lithography and local electroplating.
Additionally, its high sensitivity to X-rays could be For elaboratron of the complete demonstrated. fabrication process, the experiments have been started with UV-lithography.
The fabrication process is shown schematically in Fig. 5 and can be summarized by the following steps:
Adhesion of the resist was increased b treatment in a promoter atmosphere (SELECTIPLA 8 T HTR AP-3, E. MERCK Comp.). After removal of surplus resist at the edge of the wafer, the spin coating process results in a resist thickness of 30 pm * 5%. The wafer was prebaked at 100°C for 60 minutes on a hot plate.
LPCVD-Si,N, (lOO)-Si
3.2.1
UV-Lithography
Exposure experiments were carried out applying a usual mask aligner (MA 25 by K. Suss Comp., FRG) at an exposure dose of 336 mJ/cm2. -Au
The resist was developed using a spray process with the developer SELECTIPIAST HTR D-2. The following development procedure was carried out:
“)
20 10 10 30
c)
s s s s
spray with developer lingering period rinse with 2-propanol spin dry
at at at at
500 500 500 3000
rpm, rpm, rpm, rpm.
The capacitors were formed by goldplating (LEA RONAL (AURALL 2.92). The total plating process took about 4 hours. No significant change in the geometry of the resist could be observed after the electroplating step.
d) Fig. 5:
6 shows Fig. capacitors. Fabrication plate
orocess
of
the
an SEM
of electroplated
micro-
deflection
’
a) ** *
Substrate: (100) Si-wafer, 100 mm diameter. Deposition of a Si,N,-layer (LPCVD). Lithography and etching of the SisN,-layer.
b) * *
Cr/Au-metallization serving as a plating base. Lithography and local electroplating of gold to form the interconnection lines.
c) *
Depth lithography using a photoresist with a thickness of aooroximatelv 30 urn and electroplating of gold’up to a thickness of approximately 25 Wm.
d) * *
Anisotropic wet etching of the material. Etching of the plating base.
silicon
bulk
The most important and critical process step is the deoth lithoaraohv. Exoeriments were carried out with the comfier&airy available negative photoresist SELECTILUX HTR 3-200. IE. MERCK Como.. FRGI. The resist can be deposited up to a thickness of 8b pm using spin-on techniques. It is well-known that this resist is sensitive to UV radiation (350 - 450 nm).
Fig. 6:
SEM-micrograph of electroplated microcapacitors using depth lithography with UV-radiation. Dimensions (I * w * t) = (53 * 14 * 20) .um3
The dimensions can be evaluated to (I*w*t) = (53*14*20) pm3 with a spacing of 6 pm. The capacitors are laterally slightly cone formed and show nearly vertical side-walls. Compared to the
U, Schnukenberg
208
et al. /Multi electron beam lithography
lateral geometries defined on the mask level, they show an enlargement of about 2 rrn in the width. 3.2.2 X-ray Lithography To increase the lateral geometrical accuracy, the critical lithoaraohv steo will be replaced bv X-rav lithography,- especially’ with synchrotron radiation /8/. Exposure experiments were made at the Elektronenspeicherring-Gesellschaft fur Berliner Svnchrotronstrahlung mbH (BESSY) in Berlin, FRG (electron energy 805 MeV, maximum spectral wavelenath 3 nm). Durina exposure, the wafer was mounted vertically into v&urn chamber filled with 40 mbar He and was mechanically scanned through the horizontal beam. Fig. 7 shows an SEM-picture of some bar type structures transferred into a 24 rm resist using a dose of 64 mJ/cm*. The following development parameter set for the spray developer was evaluated: 35 s spray developer at 500 rpm, IO s lingering time at 500 rpm, 10 s rinse with P-propanol at 500 rpm, 30 s spin dry at 3000 rpm. The width at the top of the bars can be determinated to 1 rm and is slightly reduced to 0.9 pm near the bottom. The ratio of height to width - the aspect ratio - is 24:l. At the bottom a little enlargement can be seen but cannot be explained. The edges show well defined geometries. The inclination and touch of the bars will probably be generated by capillary forces during the process siep of development.
tron beam lithography system, HISEL, has been described. The control unit illuminated by an electron line source consists of an aperture plate, which forms 1024 square shaped electron beams and a deflection plate for individual on-off switching of the beams using a set of microcapacitors. Both plates are fabricated using the technology of silicon micromechanics and depth lithography by applying UV and synchrotron radiation, respectively. The holes in the Si-membrane of the aperture plate show rounded edges which are due to the limited resolution of the proximity lithography system. High resolution X-ray lithography will be used to fabricate the final devices. Depth lithography was carried out using SELECTILUX HTR 3-200 as photoresist with a thickness of 30 pm to form the microcapacitors. First examples of capacitors were fabricated using UV-radiation for patterning. The sidewalls of the electroplated microcapacitors are almost vertical. The aspect ratio (height to width of the space) can be evaluated to 5:l. To increase the lateral geometrical accuracy, the use of high resolution X-ray lithography WIII be necessary. First experiments demonstrate the patterning of the resist down to the sub-km range with large aspect ratios. 4.
ACKNOWLEDGEMENT
The authors would like to thank S. Vogelsang and B. Schroth for their valuable assistance during the device fabrication. 5.
Fig
4.
7:
SEM-micrograph of 24 pm thick polyimide exposed by synchrotron radiation of BESSY witha dose of 64 mJ/cm*.
CONCLUSIONS
The fabrication
of a control
unit for a multi elec-
REFERENCES B. Lischke et al: Proceedings ME ‘88 B. Lischke et al: 32nd International Symposium on Electron, Ion and Photon Beams 1988, May 31 -June 2, 1988, Fort Lauderdale, Florida U. Schnakenberg et al: 32nd International Symposium on Electron, Ion and Photon Beams 1988, May 31 - June 2, 1988, Fort Lauderdale, Florida P. Schaffer et al: Proc. ME ‘88 G. Schcnecker et al: Proc. ME ‘88 H.-J. Herzog et al: Electrochem. Sot.: Solid-State Science and Technology, Vol. 131, 2969-2974, December 1984 H. Seidel: Proc. of the 4th Int. Conf. on -. Solid-State Sensors and Actuators, Transducers ‘87, June 2-5, Tokyo, Japan, 120 A. Heuberger: Microelectronic Engineering 3, 535 (1985)