Quantum optical lithography from 1nm resolution to pattern transfer on silicon wafer

A major problem in the optical lithography was the diffraction limit. Here, we report and demonstrate a lithography method, Quantum Optical Lithography [1,2], able to attain 1 nm resolution by optical means using new materials (fluorescent photosensitive glass-ceramics and QMC-5 resist). The performance is several times better than that described for any optical or Electron Beam Lithography (EBL) methods. In Fig. 1 we present TEM images of 1 nm lines recorded at 9.6 m/s. a) b) Fig. 1 TEM images of: a) multiple 1 nm lines written in a fluorescent photosensitive glass-ceramics sample; b) single 1 nm line written in QMC-5 resist.

Optical lithography is the unrivalled mainstream patterning method that allows for costefficient, high-volume fabrication of microand nanoelectronic devices. Current optical photolithography allows for structures with a reproducible resolution below 32 nm. Nevertheless, alternative lithography methods coexist and excel in all cases where the requirement for a photomask is a disadvantage. Especially for low-volume fabrication of microdevices, the need for a photomask is inefficient and restricts a fast structuring, such as required for prototype device development and for the modification and repair of devices. The necessity of high-resolution masks with a price well above €10k is too cost intensive for the fabrication of single test devices. For this reason ‘direct-write’ approaches have emerged that are popular for several niche applications, such as mask repair and chip repair. Optical direct-write lithography and electron beam lithography are among the most prominent techniques of direct-write lithography. Less known, but highly versatile and powerful, is the ion beam lithography (IBL) method. Optical direct-write lithography uses laser beam writers with a programmable spatial light modulator (SLM). With 500 mm2/minute write speed and advanced 3D lithography capabilities, optical direct-write lithography is also suitable for commercial microchip fabrication. However, with a resolution of 0.6-μm minimum feature size of the photoresist pattern, optical direct-write lithography cannot be considered a nanopatterning method. Electron beam lithography uses a focused electron beam to expose an electron beam resist. Gaussian beam tools operate with electron beams with a diameter below 1 nm so that true nanofabrication of structures is feasible. A resolution of 10 nm minimum feature size of the e-beam resist pattern has been successfully demonstrated with this method. However, special resists are required for e-beam lithography, that are compatible with the high energy of forward scattered, back-scattered and secondary electrons. A common resist for sub-50nm resolution is polymethylmetacrylate (PMMA) requiring an exposure dose above 0.2 μC/μm2. For highest resolution (below 20 nm) inorganic resists such as hydrogen silsesquioxane (HSQ) or aluminium fluoride (AlF3) are used, which unfortunately require a high electron exposure dose. Hence, high-resolution electron beam lithography (EBL) is linked to long exposure times which, in combination with a single scanning beam, results in slow processing times. Therefore, this high-resolution method is only used for writing photomasks for optical projection lithography and for a limited number of high-end applications. A resolution to this dilemma may be the use of multi-beam electron tools, as are currently under development. Also electron projection lithography has been under

T-Gate fabrication processes for InP-based High electron mobility transistors (HEMTs) are described using PMMA/Al/UVIII. The single-step and two-step Electron beam lithography (EBL) methods are proposed contrastively without dielectric support layer. The opti- mal gate-foot length is 196nm for 50nm geometry path by single-step EBL technique. Since the gate-foot and gate-head are defined independently, the two-step EBL process minimizes forward scattering and enables smaller gate-foot length, which improves to be 141nm for 50nm geometry path and also 88nm for 30nm geometry path. Both EBL methods have been incorporated into InP- based HEMTs fabrication. With the gate-foot length de- creases from 196nm to 141nm, the current-gain cutoff fre- quency (fT) is improved from 125GHz to 164GHz, and also the maximum oscillation frequency (fmax )i ncreases from 305GHz to 375GHz.

Since the photoelectric response and charge carriers transport can be influenced greatly by the density and spacing of the ZnO nanorod arrays, controlling of these geometric parameters precisely is highly desirable but rather challenging in practice. Here, we fabricated patterned ZnO nanorod arrays with different densities and spacing distances on silicon (Si) substrate by electron beam lithography (EBL) method combined with the subsequent hydrothermal reaction process. By using the EBL method, patterned ZnO seed layers with different areas and spacing distances were obtained firstly. ZnO nanorod arrays with different densities and various morphologies were obtained by the subsequent hydrothermal growth process. The combination of EBL and hydrothermal growth process was very attractive and could make us control the geometric parameters of ZnO nanorod arrays expediently. Finally, the vertical transport properties of the patterned ZnO nanorod arrays were investigated through the microprobe station equipment, and the I-V measurement results indicated that the back-to-back Schottky contacts with different barrier heights were formed in dark conditions. Under UV light illumination, the patterned ZnO nanorod arrays showed a high UV light sensitivity, and the response ratio was about 104. The controllable fabrication of patterned ZnO nanorod arrays and understanding their photoelectric transport properties were helpful to improve the performance of nanodevices based on them.

2 nm Quantum Optical Lithography

Micromechanical milling has been shown to be a rapid and direct method for the fabrication of structures with the geometry and size suitable for use as x-ray mask absorbers. While the micromilling process can not duplicate the size and resolution of absorber patterns created by high energy electron beam or optical lithography methods, micromilling can repeatedly create absorber line widths down to 10 micrometers, or less, with a one-sigma tolerance of 0.5 micrometers. A method for easily characterizing milling tool run out has been adapted so tool change out can be more routine. The milling process leaves some absorber burrs and the absorber is apparently tapered at the machined wall which introduce process biases, both of which add to exposure degradation. Nevertheless, based on work to date, it appears both of these effects can be reduced to acceptable limits.

Waveguide (WG) structures are patterned on polymeric thin films and on three-dimensional colloidal photonic crystals (PhC). Different techniques such as direct laser writing, electron beam lithography (EBL), optical lithography and femto-second laser writing are used to pattern the WG structures on PPR, polymethyl methacrylate (PMMA) and SU-8 photoresists. All these techniques are found to be successful in writing the WG structures on thin films. Air channel WGs are formed by EBL and direct laser writing techniques on PMMA and PPR, respectively. The air channel is further infiltrated with a higher index zinc oxide by sol-gel chemistry for guidance of light by total internal reflection. The structure written on SU-8 by optical lithography and on PMMA thin film by femto second laser writing resulted in the ridged WG structures where the guidance is possible by total internal reflection. The WG writing is also successfully carried out by electron beam lithography and femto second laser writing on PhCs fabricated from PMMA and polystyrene colloidal particles using inward growing self-assembly method. Unlike the earlier WG structures, the light guidance is possible due to photonic band gap effect in PhC WG, only for the wavelengths that lie within the stop band of the PhC. The quality of the written structures is characterized using images from scanning electron microscope, atomic force microscope and optical microscope. For optical characterization, a diode laser beam is successfully guided through the WG structure fabricated on PMMA PhC by EBL and on SU-8 thin film by optical lithography method.

The “top‐down” approach is used to fabricate Silicon Nanowires using Scanning Electron Microscope (SEM) based Electron Beam Lithography (EBL) method. Silicon Nanowires or one dimensional nanowires are widely recognized as important elements in development of certain advance nanoscale devices. The Silicon Nanowires with line‐width of 50 nm are successfully fabricated at our clean room using this approach. The approach used includes SEM based EBL method, followed by size reduction using Inductively Coupled Plasma—Reactive Ion Etching (ICP—RIE). In addition, the diameter and the length of the Silicon Nanowires can be precisely controlled. In this paper, the Silicon Nanowires formation which includes the EBL system and fabrication processes have been reviewed and discussed. High Power Microscope (HPM), SEM and Atomic Force Microscopy (AFM) were used to characterize the Silicon Nanowires.

An electron beam (EB) lithography method using inedible cellulose-based resist material derived from woody biomass has been successfully developed. This method allows the use of pure water in the development process instead of the conventionally used tetramethylammonium hydroxide and anisole. The inedible cellulose-based biomass resist material, as an alternative to alpha-linked disaccharides in sugar derivatives that compete with food supplies, was developed by replacing the hydroxyl groups in the beta-linked disaccharides with EB-sensitive 2-methacryloyloxyethyl groups. A 75 nm line and space pattern at an exposure dose of 19 μC/cm2, a resist thickness uniformity of less than 0.4 nm on a 200 mm wafer, and low film thickness shrinkage under EB irradiation were achieved with this inedible cellulose-based biomass resist material using a water-based development process.

A three-dimensional (3D) seamless roll mold is difficult to fabricate because of its cylindrical shape. However, seamless 3D nanoscale patterns are in great demand for optical film applications and printed electronics. The authors have therefore developed a method for producing a 3D seamless roll mold by direct electron-beam (EB) writing onto a layer of resist material coated on a cylindrical substrate that is rotating in a vacuum. In addition, the 3D shape is produced by using the EB dose change method and the controlled-acceleration-voltage electron beam lithography (CAV-EBL) method developed by the authors. In the case of the EB dose change method, hydrogen silsesquioxane (HSQ), which is a negative-type EB resist, was used for the 3D roll mold. In the case of CAV-EBL, spin on glass, which is a positive-type EB resist, was used for the 3D roll mold. As a result, the developed HSQ height can be controlled by changing the EB dose; however, the dose change also causes a line width change. On the other hand, in the CAV-EBL method, the EB dose and acceleration voltage can be used to control the line width and depth independently; therefore, this method can successfully fabricate the coveted 3D roll mold.

Nano-patterns fabricated with extreme ultraviolet (EUV) or electron-beam (E-beam) lithography exhibit unexpected variations in size. This variation has been attributed to statistical fluctuations in the number of photons/electrons arriving at a given nano-region arising from shot-noise (SN). The SN varies inversely to the square root of a number of photons/electrons. For a fixed dosage, the SN is larger in EUV and E-beam lithographies than for traditional (193 nm) optical lithography. Bottom-up and top-down patterning approaches are combined to minimize the effects of shot noise in nano-hole patterning. Specifically, an amino-silane surfactant self-assembles on a silicon wafer that is subsequently spin-coated with a 100 nm film of a PMMA-based E-beam photoresist. Exposure to the E-beam and the subsequent development uncover the underlying surfactant film at the bottoms of the holes. Dipping the wafer in a suspension of negatively charged, citrate-capped, 20 nm gold nanoparticles (GNP) deposits one particle per hole. The exposed positively charged surfactant film in the hole electrostatically funnels the negatively charged nanoparticle to the center of an exposed hole, which permanently fixes the positional registry. Next, by heating near the glass transition temperature of the photoresist polymer, the photoresist film reflows and engulfs the nanoparticles. This process erases the holes affected by SN but leaves the deposited GNPs locked in place by strong electrostatic binding. Treatment with oxygen plasma exposes the GNPs by etching a thin layer of the photoresist. Wet-etching the exposed GNPs with a solution of I2/KI yields uniform holes located at the center of indentations patterned by E-beam lithography. The experiments presented show that the approach reduces the variation in the size of the holes caused by SN from 35% to below 10%. The method extends the patterning limits of transistor contact holes to below 20 nm.

The suppression of wave-particle duality in multiple-slit experiments indicated the presence of type I diffracted photons with particle behavior. Overcoming the diffraction limit is possible with type I diffracted photons and will be applied in optical lithography. In this paper, we present results on a diffraction-free optical lithography, projection quantum optical lithography (projection QOL), with different NA projection lenses and ∼14nm resolution. A potential application for realizing complex 1nm patterns is analyzed. Projection QOL could support the research and development efforts of the semiconductor chip industry.

The ability to fabricate materials and structures with sub-micrometer scale features is interesting in many areas of science and technology [l]. Of importance for many applications in nanotechnology is the ability to arrange nanocrystals into larger-scale patterns with precise lateral control, such as photonic crystal, data storage, and biosensors. Recently, great efforts have also been made on position-controllable assembling of colloidal nanoparticles on solid substrates [2]. Despite the increasing efforts in the past few years, it is still a great challenge to develop an effective way to fabricate well-controllable nanostructures using colloidal as the structural elements.

Reports on a hybrid method of AFM lithography and optical lithography that increases the drawing speed and decreases the drawing length. Advanced devices, such as quantum ones, have both nanometer-scale structures and large area structures, such as contact pads. It takes a long time to fabricate all the patterns using AFM lithography alone. It is preferable to combine AFM lithography with optical lithography. In this way, AFM lithography is used for nanometer structures only. When this hybrid process is used, the most significant problem is aligning the patterns produced by optical lithography and AFM lithography. To solve this problem, we use small step structures fabricated by slight development on the resist surface, fabricated by optical-lithography exposure. The positional information of the pattern structure in the resist film, fabricated by using optical lithography, is obtained by observing the steps with AFM. The additional patterning is performed by using AFM lithography. Patterns can be observed without exposure, since the force needed to observe the surface and that for the exposure are different.

An alignment technique for electron-beam (EB) lithography that corrects the writing pattern to match the pattern-dependent lens distortion of an optical stepper is proposed. In mix-and-match EB and optical lithography, precise measurement of positional distortion caused by the stepper lens is necessary. However, recent research in optical lithography has shown that the lens distortion differs depending on the pattern features. Thus, we have enhanced the measurement method to reflect the pattern-feature dependence of positional distortion in optical lithography. To measure the various types of distortions more effectively, we modified the marks used for distortion and overlay measurement. The measured pattern dependence of the lens distortion was in good agreement with our simulation results and the overlay accuracy in mix-and-match lithography was improved with this method.