The primary measure of process quality in nanoimprint lithography (NIL) is the fidelity of pattern transfer, comparing the dimensions of the imprinted pattern to those of the mold. Routine production of nanoscale patterns will require new metrologies capable of nondestructive dimensional measurements of both the mold and the pattern with subnanometer precision. In this work, a rapid, nondestructive technique termed critical dimension small angle x-ray scattering (CD-SAXS) is used to measure the cross sectional shape of both a pattern master, or mold, and the resulting imprinted films. CD-SAXS data are used to extract periodicity as well as pattern height, width, and sidewall angles. Films of varying materials are molded by thermal embossed NIL at temperatures both near and far from the bulk glass transition (TG). The polymer systems include a photoresist and two homopolymers. Our results indicate that molding at low temperatures (T-TG<40°C) produces small-aspect-ratio patterns that maintain periodicity to within a single nanometer, but feature large sidewall angles. While the observed pattern height does not reach that of the mold until very large imprinting temperatures (T-TG70°C), the pattern width of the mold is accurately transferred for T-TG>30°C.
The primary measure of process quality in nanoimprint lithography (NIL) is the fidelity of pattern transfer, comparing the dimensions of the imprinted pattern to those of the mold. As a potential next generation lithography, NIL is capable of true nanofabrication, producing patterns of sub-10 nm dimensions. Routine production of nanoscale patterns will require new metrologies capable of non-destructive dimensional measurements of both the mold and the pattern with sub-nm precision. In this article, a rapid, non-destructive technique termed Critical Dimension Small Angle X-ray Scattering (CD-SAXS) is used to measure the cross sectional shape of both a pattern master, or mold, and the resulting imprinted films. CD-SAXS data are used to extract periodicity as well as pattern height, width, and sidewall angles. Films of varying materials are molded by thermal embossed NIL at temperatures both near and far from the bulk glass transition (TG). The polymer systems include a photoresist, representing a mixture of a polymer and small molecular components, and two pure homopolymers. Molding at low temperatures (T-TG < 40°C) produces small aspect ratio patterns that maintain periodicity to within a single nanometer, but feature large sidewall angles. While the pattern height does not reach that of the mold until very large imprinting temperatures (T-TG ≈ 70°C), the pattern width of the mold is accurately transferred for T-TG > 30°C. In addition to obtaining basic dimensions, CD-SAXS data are used to assess the origin of loss in pattern fidelity.
We have developed a new method to pattern polymeric materials, including non-thermoplastic polymers, at low
temperature and low pressure. In this method, plasticizers are added to increase the chain mobility of the polymers,
resulting in lower imprinting temperature and/or pressure. Two established imprinting and transfer techniques were
chosen to demonstrate this method, namely, conventional nanoimprint lithography (NIL) and microcontact printing
(μCP). These two techniques were used to pattern poly(3,4-ethylenedioxythiophene) (PEDOT). PEDOT was chosen
because it is a non-thermoplastic polymer and therefore cannot be easily patterned using conventional NIL. Successful
imprint of PEDOT films from the PDMS mold was achieved at a low pressure of 10 kPa and 25°C by controlled
addition of glycerol as a plasticizer using conventional NIL; well-defined arrays of 2μm wide, 185 nm high PEDOT
dots have also been demonstrated by μCP. In contrast, patterning of PEDOT film without plasticizer requires higher
temperature (80°C) and pressure (10 MPa), which could cause severe deformation of the transferred patterns. This
method of plasticizer-assisted imprint lithography (PAIL) broadens the applicapability of NIL to a wide range of
A review of fabrication techniques and testing of single crystal Si resonant devices with high aspect ratio capacitive transduction mechanisms has been presented. Deep trenches have been etched in single crystal Si using a Cl2 plasma generated by an electron cyclotron resonance (ECR) and an inductively coupled plasma (ICP) source. This etching has been extended to the fabrication of resonant devices thicker than 50 micrometer using a frontside-release process and these devices have been electrically tested. The thick devices allow larger capacitance between drive and sense plates, which in turn reduces required driving voltage and increases sensing current. In addition, an etching condition has been developed which can etch trenches as narrow as 0.1 micrometer to depths greater than 3 micrometer. This etch has been used to fabricate comb driven resonators with high aspect ratio gaps (greater than 30) between comb fingers. Finally, a fabrication method to integrate these single crystal Si mechanical devices with a conventional circuit process with only one additional masking step has been developed. Eleven micrometer thick clamped-clamped beam comb driven resonators have been fabricated and tested on the same chip with working CMOS transimpedance amplifiers. The resonator had a resonant frequency of 28.9 kHz and a maximum amplitude of vibration of 4.6 micrometer, while the amplifier had a 3-dB frequency of 150 kHz and a power dissipation of 1.25 (mu) W.
In the past, a number of authors have described the advantages of the silylation reaction performed in a novolak resist's latent image. Both the advantages and difficulties were described. A process based on silylation of latent images was shown to improve the working resolution in a novolak resist due to the surface imaging principle. The difficulties included swelling of the resist film during silylation resulting in some loss of dimensional control of critical dimensions. This paper describes a different approach to near surface imaging. The method relies on the use of spin-on, closely planarizing polymeric antireflective coating, such as AZTMBARLiTM coating, followed by imaging thin (less than 0.5 micron) i-line resist. After a conventional lithographic process which includes a wet develop step, a silylation reaction is performed. Swelling of the real resist image due to silylation is controllable within necessary tolerances. Image transfer process of the silylated image is also described.
Optical interferometry has been applied to determine the membrane curvature of p++Si beams. Clamped-clamped Si beams and cantilevered beams were fabricated with an etch- diffusion process and a dissolved wafer process and characterized. This measurement technique allows for very precise measurement of the bending of released Si beams due to stress, thus small height variations due to membrane curvature in clamped-clamped beams can be resolved. Cantilevered beams were found to bend more due to stress as length increased and width decreased. Thicker beams also showed less bending due to stresses due to their increased stiffness. A 6.0 micrometer thick cantilevered beam had a deflection of 12.4 micrometer due to stress, while a 36.7 micrometer thick beam had a deflection of only 0.2 micrometer. Beams fabricated using a dissolved wafer process with a 12 h B diffusion were found to bend the same amount as those fabricated using an etch- diffusion process with a 4 h diffusion. Using the deep etch- shallow diffusion process, resonating elements that are 20 micrometer long, 4 micrometer wide, and 28 micrometer thick were found to be perfectly flat without any bending.
The deep etch-shallow diffusion process has been applied to the fabrication of comb drive resonators and micromirrors successfully. Etch rate of Si with various doping concentrations in a Cl2 plasma generated by an electron cyclotron resonance source and B diffusion in high aspect ratio Si trenches were characterized. It was found that lightly B and P doped Si were etched at similar rates of 0.17 micrometers/min, whereas heavily B doped p++Si had a slower etch rate of 0.16 micrometers/min and heavily P doped n++Si had faster etch rate of 0.31 micrometers/min. Typical etch conditions are 100 W microwave power and 100 W rf power at 3 mTorr, with 20 sccm of Cl2 flow and a source to sample distance of 8 cm. The difference between the p++ and n++Si rate was more significant when etched at higher microwave power, higher rf power, or higher temperature. The depth of a heavily B doped Si layer was measured for different feature sizes, trench openings, and aspect wide trenches to 1.5 micrometers at the bottom of 2 micrometers wide trenches. The diffusion layer on the sides of the trenches for a 30 min B diffusion was 3.25 micrometer thick and it is independent of the trench opening and the trench aspect ratio.
Dry micromachining technology is developed for fabricating high aspect ratio Si structrues for microsensors. Two microsensor structures, including Si resonators and field emitters, will be presented in this ppaer. Released Si resonators up to 30 micrometers deep with 2 micrometers wide gap were fabricated. This is accomplished by a novel deep etch and shallow diffusion technique. High aspect ratio Si microstructures with vertical profile were first etched using an electron cyclotron resonance source, followed by a shallow B diffusion to fully convert the etched microstructures to p++ layer. In addition, dry etching was used to form Si emitters with sharp tips and high packing density. Profile for Si emitters is controlled by erosion of the SiO2 mask during dry etching. The ion flux and energy, controlled through coupled microwave and rf power, were used to obtain the desired etch rate and basewidth of the emitters. By increasing the pressure during etching, more vertical Si emitters were developed. Sharp emitter tips in Si with 2.2 micrometers basewidth and 11 micrometers height were fabricated and packing densities up to 1 X 107 tip/cm2 were achieved.
Photoreflectance (PR) spectroscopy has been used to study the Fermi-level pinning position of chemically modified (100) GaAs surfaces. It is shown that there are two pinning positions for the unmodified 9100) GaAs surface. For n-GaAs the Fermi level pins near midgap, while for p-GaAs the Fermi level pins near the valence band. We used an Ar/Cl2 plasma generated by an electro-cyclotron resonance (ECR) source and P2S5 chemical passivation to change the stoichiometry of the surface. We show that ECR etching makes the surface oxide As rich and that the Fermi-level position for this circumstance is near midgap. The P2S5 passivation produces a thin Ga rich oxide which is observed to in the Fermi-level near the valence band. These results allow us to relate the Fermi-level pinning position to the stoichiometry of the GaAs/oxide interface.
Amorphous carbon films have been deposited by plasma enhanced chemical vapor deposition which provide a high degree of planarization over large distances. These films can be deposited at room temperature with low ion bombardment energy (10 V) and high deposition rate (300 nm/min). The planar films have low viscosity and molecular weight, and their molecular structure is similar to that of the source gases. A post-deposition hardening step was utilized to improve the compatibility of the films with subsequent processing steps by heating the samples and/or exposing them to a low power plasma. Submicrometer patterns have been defined using excimer laser projection lithography in bilayer resist. In addition, a multipolar electron cyclotron resonance source was used to generate an oxygen plasma for Si oxidation. Oxidation rate was found to increase with microwave power but decrease with source distance and rf power. Maximum oxidation rate was found at 0.25 mTorr. This low pressure is desirable for forming conformal insulator. The oxide films were found to have O to Si ratio of 2 and refractive index of 1.47. Breakdown field was >12 MV/cm and fixed charge density was 3 X 1010 cm-2.
This paper describes a coherent detection receiver (CDR) with adaptive image rejection capability which is also compatible with existing monolithic integrated optics and MMIC technology. It details the component selection and circuit layout tradeoffs that were considered for the design and fabrication of the CDR in monolithic IC format. An optical `half receiver' IC with waveguides, phase shifter, 3 dB coupler, and balanced mixer diodes has been constructed and tested. Measurements and results for this chip are given and discussed. An initial design and simulated results for the microwave (intermediate frequency) IC are also given and discussed.
A new etch technique which oscillates between sputter etching and RIE modes of etching was investigated. Extensive studies for InP using BCl/Ar and Cl/BCl/Ar gas systems were performed with standard RIE equipment. The etching sequence was performed with a programmable controller which automates the cycling sequence. The time period and sputter duty cycle or percent sputter time are two important factors that were studied in these experiments. Using this cyclic technique an etch rate of 300 A/mm was obtained which is an order of magnitude higher than our standard RIE etch rate for InP. Standard optical photoresists can be used as masks for this technique although metal masks are more feasible. The resulting wall shape is vertical with smooth morphology. Etch enhancements may be explained by the removal of an indium chloride layer. Surface analysis was performed to verify that chlorine is forming on the surface.
New double-barrier resonant-tunneling diodes have been fabricated in the pseudomorphic In0.53Ga0.47As/AlAs material system that have peak current densities exceeding 1x105 A cm-2 and peak-to-valley current ratios of approximately 10 at room temperature. One of these diodes yielded oscillations up to 125 GHz, but did not oscillate at higher frequencies because of a large device capacitance. A device with a much lower capacitance is estimated to have a maximum oscillation frequency of 932 GHz and a voltage rise time of 1.5 ps in switching from the peak bias point to the valley bias point. Other reported In0.53Ga0.47As/AlAs diodes are analyzed and yield theoretical maximum oscillation frequencies over 1 THz and rise times as low as 0.3 ps.
3 August 2003 | San Diego, California, United States
Micromachining and Microfabrication Process Technology VIII
27 January 2003 | San Jose, CA, United States
Micromachining and Microfabrication Process Technology III
29 September 1997 | Austin, TX, United States
Micromachining and Microfabrication Process Technology II
14 October 1996 | Austin, TX, United States
SC305: Microfabrication Technology for Micro-electromechanical Systems
In this short course, various microfabrication technologies for MEMS are introduced. Process design, precise dimension control, integrating mechanical and electrical components are covered. Current technology trends for MEMS with examples in mechanical, optical, and chemical sensing and actuation are given. New development of MEMS technology in the future is addressed.
SC535: Microfabrication Technology for Micro-ElectroMechanical Systems
In this short course, various microfabrication technologies for MEMS will be introduced. Process design and factors for precise dimension control for MEMS will be covered. Issues related to integrating mechanical and electrical components will be discussed. Current technology trends for MEMS with examples in mechanical, optical and chemical sensing and actuation will be given. New development of MEMS technology in the future will be addressed. The specific topics covered are: patterning by optical, x-ray and focused ion beam lithography; selective wet-etching processes; directional dry-etching processes; thin-film deposition by evaporation, sputtering, electroplating, chemical vapor deposition and laser-assisted deposition; new materials for MEMS; bonding and release of mechanical structures; packaging and circuit integration; MEMS technology for mechanical, optical, and chemical sensors.