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6194. Anisotropic reactive ion etching technique of GaAs and AlGaAs materials for integrated optical device fabrication
Classified
abstracts
6192-6200
anisotropic material, and the optical constants were compared to infrared spectroscopy values. HREELS spectra as a function of oxide thickness could be obtained from oxidized Si(100) wafers by sputter erosion. Peak positions shifted to lower frequencies and intensities decresed regularly with decreasing oxide thickness. At the interface a transition layer of about 25 A was observed and carbon contamination was identified. The dielectric theory applied to a thin homogeneous supported film cannot account for the observed frequency shift. P A Tbiry et al, J Vuc Sci Technol, B3, 1985, 1118-l 121. 34 6192. Arsenic segregation to silicon/silicon oxide interfaces Arsenic segregation at polycrystalline silicon/silicon and polycrystalline silicon/silicon oxide interfaces was examined directly by transmission electron microscopy (TEM) and scanning transmission electron microscopy(STEM). Segregation occurring precisely at these interfaces was identified. A simple model was proposed based on arsenic segregation to structural units containing dangling bonds and consequent bond saturation. The removal of these dangling bonds will then play an important role in the electrical properties of these interfaces. Furthermore substitutional arsenic segregation at a degenerate level at these interfaces was also proposed. The subsequent dopant ionization and localized charges at the interfaces was discussed. C Y Wong et al, J appl Phys, 58, 1985, 1259-1262.
35. ION AND PLASMA
ETCHING
35 6193. A bilevel resist for ion beam lithography A focused ion beam of gallium was used to implant films of baked photoresist, spin-on glass (SOG) and the bilayer combination of spin-on glass on baked photoresist. Plasma etch conditions were found which gave substantial differences between the implanted and nonimplanted SOG so that the SOG acted as a negative resist. The implanted SOG in the SOGphotoresist bilayer was patterned and then used as an etch mask during 0, reactive ion etching of the photoresist. In this manner, rectangular profile structures of height 2.0 pm and width 0.4 pm were formed where the line width variation along the patterned line is a small fraction of the line width. This bilayer system is shown to be suitable for use in optical trilayer patterning. A new processing sequence for microstructure fabrication is proposed (called dual processing) whereby the bilayer structure is used sequentially in both focused ion beam implantation and trilayer processing (electron beam or optical) to achieve fine features of less than 0.5 pm size within prescribed regions that can be micrometer size. A Milgram and J Puretz, J Vat Sci Technol, B3, 1985, 879-883. 35 6194. Anisotropic reactive ion etching technique of GaAs and AlGaAs materials for integrated optical device fabrication This paper reports a reactive ion etching (RIE) technique using a Cl,-Ar gas mixture for anisotropic microprocessing of GaAs and AlGaAs materials and its fundamental characteristics aimed to applications to monolithic integration of optical devices. This technique allows one to realize very fine as well as deep processing perpendicular to the wafer surface with smooth side walls, independent of the crystallographic orientation of these semiconductor matterials. The etching rate was found to be controllable over a wide range by suitably adjusting the gas composition and the total gas pressure in this gas mixture. We experimentally obtained the optimum condition for smooth and perpendicular etching for both the materials at the total gas pressure of 2 Pa (1.5 x lo-’ torr) with the gas flow ratio of Cl,:Ar=1:5. Under this condition the etching rate ratio of GaAs to SiO, was demonstrated more than 70. The surface damage introduced by this RIE was confirmed to be comparable at least to the case of the wet chemical etching through the measurement of photoluminescence intensities from GaAs samples. Hirobito Yamada et al, J Vat Sci Technol, B3, 1985, 88&888. 35 6195. Ion beam lithography: an investigation of resolution limits and sensitivities of ion-beam exposed PMMA High resolution thin-membrane masks are duplicated in PMMA by contact printing with 250 keV Ga+ ions. Upon development, minimum feature widths on the order of 70 nm are obtained. Broadening of ionexposed lines in PMMA as a function of development time is studied. A microscopic investigation of PMMA irradiated with 50 keV H + ions and 250 keV Ga+ ions at doses near the development threshold reveals peculiar morphological modifications prior to, and following development. The modification of theoretical energy dissipation distributions 736
with the inclusion of recoil atoms in heavy-ion irradiation of resists is investigated with the aid of a Monte Carlo simulation program (RECUL). Using the three-dimensional energy distributions thus obtained, developed-line profiles are simulated. L Karapiperis et al, J Vat Sci Tecbnol, B3, 1985, 353-357. 35 61%. A high-speed, high-precision electron beam lithography system (electron optics) A variably shaped electron beam exposure system HL-600 has been developed for both direct wafer writing and mask making. It was designed as a high-throughput tool to cover lithography requirements down to a 0.5 pm linewidth. To achieve this high-throughput capability, many newly developed techniques were adopted in the electron optics and in the control electronic circuits. The simplified electron beam column consists of only four magnetic lenses. The magnetic deflection for main field scanning was enlarged so as to reach up to 6.5 mm2 in order to reduce the overhead time associated with work stage movement. In addition, the design of an objective lens system with a small aberration, and an algorithm for deflection aberration correction were developed. Automatic measurement of defocusing and astigmatism at a number of sample points were performed by taking through focusing, and the third order polynomial correction function of deflection was determined. As a result, the edge resolution for the 2 pm* beam was less than 0.2 pm over a 6: 5 mm2 field. The column uses a flat-top-type LaB, electron gun with high brightness and large emittance. Although the maximum beam size and current density were limited by Coulomb blurring, the gun realizes a 6.4 pm2 size and 10 A cm-’ density at the same time. It typically has a 5000 h lifetime. This HL-600 is capable of writing more than ten 4 in. wafers per hour on the average. In addition to a summary of the HL-600 system, this paper describes details concerning the novel techniques in optics and some exposure results. N Saitou et al, J Vat Sci Technol, B3, 1985, 98-101. 35 6197. Masked ion beam resist exposure using grid support stencil masks Submicrometer resolution ion beam resist exposure using a new type of stencil mask is described. The mask uses a grid support structure in transmission areas to remove restrictions on pattern geometry and improve stability. The image of the grid is eliminated by rocking the incident angle of the ion beam during exposure, or by special processing of the resist. We describe the mask fabrication sequence and show examples of masks that employ a 320 nm period grid structure. Patterns with a minimum feature size of less than one-half micrometer have been replicated using this type of mask with both single and multilayer resists. In addition, experiments are described which used low energy ion beams to test the ultimate resolution ofstencil masks without grid support. 40 nm wide lines were printed in PMMA at a mask-to-wafer gap of 25 pm. The applicability of such masks in high resolution proximity printing systems is discussed. J N Randall et al, J Vat Sci Technol, B3, 1985, 58-61. 35 6198. Submicron pattern fabrication by focused ion beams A focused ion beam (FIB) technology has many advantages for submicron structure fabrication and other maskless processes. In order to develop 416 M(D) RAM, the FIB technology is strongly desired for its capability of submicron lithography without proximity effects. T Kato et al, J Vat Sci Technol, B3, 1985, 5&53. 35 6199. Pattern profile control of polysilicon plasma etching Profile control in plasma etching of polysilicon is described. Reactive gases are CCl,F,-H, and CCI,F,-C,H,. Undercutting suppression and sloped wall pattern profile without undercutting are realized. Thin film formation on the etched pattern side wall is observed. These characteristics are explained by the plasma polymerization phenomena which occurs competitively with etching reaction. M Kimizuka and K Hirata, _I Vat Sci Technol, 83, 1985, 1619. 35 6200. Aluminum plasma etching process using vacuum systems without cold traps A suitable vacuum pump system used in plasma or RIE-mode dry etching of Al and Al alloys with CCl,/Cl, enables to operate without LN, cold traps. A Roots pump plus rotary vane pump combination, both using inert fluid lubricant, pumps and exhausts all occurring volatile products. Condensing solid AlCl, is quantitatively removed from the backing pump sealing fluid by means of a high speed, main stream oil purification system via an Al,O, deep bed filter. Maintenance of the pump system is limited to just changing the Al,O, filter elements, each time after etching of 4000
abstracts
6192-6200
anisotropic material, and the optical constants were compared to infrared spectroscopy values. HREELS spectra as a function of oxide thickness could be obtained from oxidized Si(100) wafers by sputter erosion. Peak positions shifted to lower frequencies and intensities decresed regularly with decreasing oxide thickness. At the interface a transition layer of about 25 A was observed and carbon contamination was identified. The dielectric theory applied to a thin homogeneous supported film cannot account for the observed frequency shift. P A Tbiry et al, J Vuc Sci Technol, B3, 1985, 1118-l 121. 34 6192. Arsenic segregation to silicon/silicon oxide interfaces Arsenic segregation at polycrystalline silicon/silicon and polycrystalline silicon/silicon oxide interfaces was examined directly by transmission electron microscopy (TEM) and scanning transmission electron microscopy(STEM). Segregation occurring precisely at these interfaces was identified. A simple model was proposed based on arsenic segregation to structural units containing dangling bonds and consequent bond saturation. The removal of these dangling bonds will then play an important role in the electrical properties of these interfaces. Furthermore substitutional arsenic segregation at a degenerate level at these interfaces was also proposed. The subsequent dopant ionization and localized charges at the interfaces was discussed. C Y Wong et al, J appl Phys, 58, 1985, 1259-1262.
35. ION AND PLASMA
ETCHING
35 6193. A bilevel resist for ion beam lithography A focused ion beam of gallium was used to implant films of baked photoresist, spin-on glass (SOG) and the bilayer combination of spin-on glass on baked photoresist. Plasma etch conditions were found which gave substantial differences between the implanted and nonimplanted SOG so that the SOG acted as a negative resist. The implanted SOG in the SOGphotoresist bilayer was patterned and then used as an etch mask during 0, reactive ion etching of the photoresist. In this manner, rectangular profile structures of height 2.0 pm and width 0.4 pm were formed where the line width variation along the patterned line is a small fraction of the line width. This bilayer system is shown to be suitable for use in optical trilayer patterning. A new processing sequence for microstructure fabrication is proposed (called dual processing) whereby the bilayer structure is used sequentially in both focused ion beam implantation and trilayer processing (electron beam or optical) to achieve fine features of less than 0.5 pm size within prescribed regions that can be micrometer size. A Milgram and J Puretz, J Vat Sci Technol, B3, 1985, 879-883. 35 6194. Anisotropic reactive ion etching technique of GaAs and AlGaAs materials for integrated optical device fabrication This paper reports a reactive ion etching (RIE) technique using a Cl,-Ar gas mixture for anisotropic microprocessing of GaAs and AlGaAs materials and its fundamental characteristics aimed to applications to monolithic integration of optical devices. This technique allows one to realize very fine as well as deep processing perpendicular to the wafer surface with smooth side walls, independent of the crystallographic orientation of these semiconductor matterials. The etching rate was found to be controllable over a wide range by suitably adjusting the gas composition and the total gas pressure in this gas mixture. We experimentally obtained the optimum condition for smooth and perpendicular etching for both the materials at the total gas pressure of 2 Pa (1.5 x lo-’ torr) with the gas flow ratio of Cl,:Ar=1:5. Under this condition the etching rate ratio of GaAs to SiO, was demonstrated more than 70. The surface damage introduced by this RIE was confirmed to be comparable at least to the case of the wet chemical etching through the measurement of photoluminescence intensities from GaAs samples. Hirobito Yamada et al, J Vat Sci Technol, B3, 1985, 88&888. 35 6195. Ion beam lithography: an investigation of resolution limits and sensitivities of ion-beam exposed PMMA High resolution thin-membrane masks are duplicated in PMMA by contact printing with 250 keV Ga+ ions. Upon development, minimum feature widths on the order of 70 nm are obtained. Broadening of ionexposed lines in PMMA as a function of development time is studied. A microscopic investigation of PMMA irradiated with 50 keV H + ions and 250 keV Ga+ ions at doses near the development threshold reveals peculiar morphological modifications prior to, and following development. The modification of theoretical energy dissipation distributions 736
with the inclusion of recoil atoms in heavy-ion irradiation of resists is investigated with the aid of a Monte Carlo simulation program (RECUL). Using the three-dimensional energy distributions thus obtained, developed-line profiles are simulated. L Karapiperis et al, J Vat Sci Tecbnol, B3, 1985, 353-357. 35 61%. A high-speed, high-precision electron beam lithography system (electron optics) A variably shaped electron beam exposure system HL-600 has been developed for both direct wafer writing and mask making. It was designed as a high-throughput tool to cover lithography requirements down to a 0.5 pm linewidth. To achieve this high-throughput capability, many newly developed techniques were adopted in the electron optics and in the control electronic circuits. The simplified electron beam column consists of only four magnetic lenses. The magnetic deflection for main field scanning was enlarged so as to reach up to 6.5 mm2 in order to reduce the overhead time associated with work stage movement. In addition, the design of an objective lens system with a small aberration, and an algorithm for deflection aberration correction were developed. Automatic measurement of defocusing and astigmatism at a number of sample points were performed by taking through focusing, and the third order polynomial correction function of deflection was determined. As a result, the edge resolution for the 2 pm* beam was less than 0.2 pm over a 6: 5 mm2 field. The column uses a flat-top-type LaB, electron gun with high brightness and large emittance. Although the maximum beam size and current density were limited by Coulomb blurring, the gun realizes a 6.4 pm2 size and 10 A cm-’ density at the same time. It typically has a 5000 h lifetime. This HL-600 is capable of writing more than ten 4 in. wafers per hour on the average. In addition to a summary of the HL-600 system, this paper describes details concerning the novel techniques in optics and some exposure results. N Saitou et al, J Vat Sci Technol, B3, 1985, 98-101. 35 6197. Masked ion beam resist exposure using grid support stencil masks Submicrometer resolution ion beam resist exposure using a new type of stencil mask is described. The mask uses a grid support structure in transmission areas to remove restrictions on pattern geometry and improve stability. The image of the grid is eliminated by rocking the incident angle of the ion beam during exposure, or by special processing of the resist. We describe the mask fabrication sequence and show examples of masks that employ a 320 nm period grid structure. Patterns with a minimum feature size of less than one-half micrometer have been replicated using this type of mask with both single and multilayer resists. In addition, experiments are described which used low energy ion beams to test the ultimate resolution ofstencil masks without grid support. 40 nm wide lines were printed in PMMA at a mask-to-wafer gap of 25 pm. The applicability of such masks in high resolution proximity printing systems is discussed. J N Randall et al, J Vat Sci Technol, B3, 1985, 58-61. 35 6198. Submicron pattern fabrication by focused ion beams A focused ion beam (FIB) technology has many advantages for submicron structure fabrication and other maskless processes. In order to develop 416 M(D) RAM, the FIB technology is strongly desired for its capability of submicron lithography without proximity effects. T Kato et al, J Vat Sci Technol, B3, 1985, 5&53. 35 6199. Pattern profile control of polysilicon plasma etching Profile control in plasma etching of polysilicon is described. Reactive gases are CCl,F,-H, and CCI,F,-C,H,. Undercutting suppression and sloped wall pattern profile without undercutting are realized. Thin film formation on the etched pattern side wall is observed. These characteristics are explained by the plasma polymerization phenomena which occurs competitively with etching reaction. M Kimizuka and K Hirata, _I Vat Sci Technol, 83, 1985, 1619. 35 6200. Aluminum plasma etching process using vacuum systems without cold traps A suitable vacuum pump system used in plasma or RIE-mode dry etching of Al and Al alloys with CCl,/Cl, enables to operate without LN, cold traps. A Roots pump plus rotary vane pump combination, both using inert fluid lubricant, pumps and exhausts all occurring volatile products. Condensing solid AlCl, is quantitatively removed from the backing pump sealing fluid by means of a high speed, main stream oil purification system via an Al,O, deep bed filter. Maintenance of the pump system is limited to just changing the Al,O, filter elements, each time after etching of 4000