Lift-off Resist Research Articles

Fabrication of a New Air-Gap FBAR on an Organic Sacrificial Layer through an Innovative Design Algorithm

Realizing thin-film acoustic wave resonators presents many design and fabrication challenges. Actual material specifications always differ from nominal material properties employed in simulations, as they depend on the deposition technique and parameters used and on equipment type and status. Moreover, each deposition process introduces a degree of uncertainty regarding the thicknesses of the layers. All these factors have a substantial impact on the resonance frequency, which often differs from the designed value. This work details the design and fabrication of an aluminum nitride (AlN)-based thin-Film Bulk Acoustic wave Resonator (FBAR) showing one of the highest products of Q-factor and electromechanical coupling of 6895. The design process is based on an innovative, fast, and scalable design and fabrication approach that considers fabrication tolerances. The algorithm returns very fast results on the order of seconds, and successfully estimates the resonance of a designed stack at 2.55 GHz with a very low error of 0.005 GHz (about 0.2%). The FBAR layer stack is suspended on a polymeric membrane and an innovative rapid dissolving sacrificial layer made of Lift-Off Resist (LOR). This new fabrication protocol obtains resonators with an electromechanical coupling factor of 4.7% and a maximum quality factor of 1467, respectively.

Nanomechanical Analysis of Polydimethylglutarimide Based Lift Off Resist Used for Temporary Bonding and Film Transfers

Temporary bonding has attracted renewed interest for the integration of dissimilar materials in device structures, which cannot be achieved by epitaxial growth techniques alone when the lattice mismatch between the dissimilar materials is too large. In this quest polydimethylglutarimide (PMGI) based lift-off (LOR) resist has been found suitable to serve as a temporary sacrificial adhesive for clean film exfoliation, layer transfer and temporary bonding applications [1]. Furthermore polydimethylglutarimide (PMGI) lends itself easily for temporary bonding purposes, because subsequent complete de-bonding can be readily achieved using an n-methyl-2-pyrrolidone (NMP)-based solvent. In this study we focus on the nanomechanical analysis of PMGI using the Nanoindenter XP by Agilent with continuous stiffness measurement (CSM) attachment. This investigation is aiming to elucidate the relationship between bonding parameters, bond strength and the nanomechanical properties of Young’s modulus and hardness of polydimethylglutarimide (PMGI) as a function of prebake temperature and PMGI resist film thickness. The influence of the spin-on process and the pre-bake treatment on the structure and properties of the PMGI adhesive layers is discussed and correlated to the resulting hardness, modulus and final bond strength and the corresponding Thermal Gravimetric Analysis (TGA) tracking the mass loss of the resist as a function of temperature. . For this experiment Si wafers were first cleaned with standard clean 1 (H2O:NH4OH:H2O2=5:1:1). Afterwards the wafers were spin coated at 2000 rpm with LOR 5A (from MicroChem), which is based on PMGI, and subsequently pre-baked in order to partially evaporate the solvent in the resist. The spin speeds were optimized to achieve 1.00 μm and 500 nm resist thickness for this investigation. Thicker lift-off resist thickness is not practical for a load-depth analysis with a Berkovich tip, because the nanoindenter is depth limited. The solvent, which is used with PMGI lift-off resist is cyclopentanone with a boiling point of 131ºC. With a glass transition point (Tg) of 180-190 ºC, we have chosen to conduct a series of prebakes at 50 °C, 70 °C, 90 °C, 110 °C and 130 °C, 150 °C & 160 °C each for 5 min and to benchmark the results against the hardness and bond strength achieved after thermal compression bonding of Silicon wafer pairs via adhesive PMGI layers at 250 C. This series of different thermal treatments influenced the resist mechanical properties, hardness and modulus. Our nanoindentation experimental results are indicated in Figure 1. As expected, the 500 nm films exhibited high hardness values as compared to the 1 µm thick films. Both PMGI lift-off resist films hardness approach the Si substrate hardness.

Room Temperature Bonding with Lift-Off Resist Using the Surface Activated Bonding Method for a Layer Transfer Platform

This study demonstrates the practicability of surface activated bonding for polymethylglutarimide (PMGI), as a temporary wafer bonding method at room temperature for future material integration. A bonded area covering over 92% of the wafer surface, with a room temperature bond strength of ~2 J/m2 is achieved using the bonding method. To overcome the fundamental transistor-scaling limit, novel material integration methods such as the 3D stacking are being researched. There is a growing interest in temporary bonding as one of the key technologies for 3D stacking. Recently, a wafer bonding method for polymethylglutarimide (PMGI) has been proposed for layer transfer. It has been demonstrated that the PMGI layer can be effectively bonded using thermal compression bonding. Moreover, debonding using N-Methyl-2-pyrrolidone (NMP) results in negligible amounts of the PMGI sacrificial layer as a residue on the debonded wafer surface and is therefore suitable for a transfer process.However, the high temperature annealing process in the bonding process requires a temperature of 250ºC to bond most of the loaded area; this high temperature process may damage the transferred material. Moreover, the high temperature process limits usage in applications such as integration of black phosphorous. For low temperature bonding, a surface activated bonding (SAB) process has been proposed as a room temperature bonding method. It has been proposed that polymer materials could be bonded using this process with thinly deposited layers called nano-adhesion layers at room temperature. In this study, PMGI layer is bonded to a Si substrate using the SAB method at room temperature (around 25 ºC); this method is intended to be used as a layer transfer process. One Si substrate is coated with PMGI layer, and the substrate is bonded to other Si support substrate via a proposed modified method of SAB. The proposed room temperature bonding process consists of five steps: spin-coat and soft-bake, bake in a vacuum, ion beam supper-deposition, surface activation, and bonding. Using the proposed method, a bonded area covering over 92% of the wafer surface, with a room temperature bond strength of ~2 J/m2, is achieved. It is concluded that soft-baking at 120ºC is most suitable for obtaining the strongest bond as well as the largest bonded area. Moreover, even the samples that aren’t baked after spin-coating achieved a bonded area of 81 %. This is because the solvent cyclopentanone is evaporated in the bake-in-vacuum step. The surface profile viewed using an atomic force microscope revealed that the PMGI surface was sufficiently smoothened for bonding at room temperature, after the vacuum baking process. It has been reported that it is difficult to bond a rough surface using room temperature bonding with SAB. The root means square (RMS) values of PMGI surfaces before and after vacuum annealing are 1.5 nm and 0.5 nm, respectively. The results of the AFM indicate that the surface becomes smoother after baking in a vacuum. This smooth surface is one the reasons for a considerable bonded area as well as a strong bonding strength using the proposed bonding technique. To investigate the chemical reaction between the PMGI and the deposited Si layer caused by the bonding process, attenuated total reflectance/Fourier-transform infrared spectroscopy (ATR/FT-IR) was performed on the PMGI layers before and after the deposition of the Si nano-adhesion layer. On comparing these spectra, the following features were observed: The first feature is that the peak height derived from the N-H bond that was at around 1550 cm-1, decreased after the Si deposition procedure. The second is that the peak from the C=O stretch band at around 1700 cm-1also decreased. From these results, it can be assumed that during the Si deposition process, a considerable modification of the N–H and C=O groups of the PMGI occurred after the Si deposition. This chemical modification is the key for the strong bonding of the PMGI at room temperature. In summary, we demonstrated that PMGI bonding at room temperature is capable of providing large and strong bonding interfaces. This process can be applied for 3D integration and material integration, without thermal damage. Thus, the proposed method can provide a platform for a layer transfer process suitable for 3D material integration of thin-layered systems like black phosphorous. Figure 1

Nanomechanical Analysis of Polydimethylglutarimide Based Lift Off Resist Used for Temporary Bonding and Film Transfers

Six samples of polydimethylglutarimide based lift off resist (LOR) were prepared with combinations of two film thicknesses and three prebake temperatures. The LOR thicknesses are 500 nm and 1000 nm and the prebake temperatures are 80ºC, 105ºC, 150ºC. The nanomechanical properties were measured using nanoindentation to determine the modulus and hardness of the six samples. The experiment retained useful information regarding the effects of film thickness and prebake temperatures on the hardness and modulus of the LOR. It was found that the hardness increases as the film thickness decreases and hardness also increases as the prebake temperature increases.

Room Temperature Bonding with Lift-Off Resist Using the Surface Activated Bonding Method for a Layer Transfer Platform

A room temperature bonding of polymethylglutarimide (PMGI) is performed as a temporary bonding process. The previous study showed that temporary bonding process with PMGI achieves extremely small residues on a debonded surface, but bonding temperature reaches to 250 oC. In this study, the surface activated bonding (SAB) method is applied for bonding the PMGI to the Si wafer at room temperature for heat-sensitive materials. Using SAB, a bonded area covering over 92% of the wafer surface, with a room temperature bond strength of ~2 J/m2, is achieved. For debonding, PMGI dissolve into N-methylpyrrolidone based solvent. Surface profile revealed that extremely small amount PMGI residues remains on the debonded surface. This process can be applied for 3D integration of 2D materials.

(Invited) Temporary Bonding with Polydimethylglutarimide for Residue-Free Layer Transfer and 3-D Integration

Bonding of lift off resist (LOR) was performed to realize temporary wafer bonding without residue. Bonding process conditions such as spin speed, pre-bake temperature, and bonding temperature were optimized to obtain a large bonded area with high bond strength. Under optimized process conditions, a bonded area covering over 98% of the wafer surface, with a room temperature bond strength of nearly 5 J/m2 is achieved. During razor blade testing, fracture often occurs at the Si wafer. Moreover, debonding using an N-Methyl-2-pyrrolidone (NMP)-based solvent left the wafer surface extremely small amount of residue. Thus, the optimized bonding processed developed in this research is suitable for a clean temporary bonding process.

(Invited) Temporary Bonding with Polydimethylglutarimide for Residue-Free Layer Transfer and 3-D Integration

Residue free temporary bonding with Polydimethylglutarimide (PMGI) was studied for a Layer Transfer Platform. Temporary wafer bonding is one of promising technologies for 3D integration, in particular transferring 2D materials such as graphene. PMGI was traditionally applied for lift off resist (LOR) and used as sacrificial layer for undercutting during lift-off processing. However, it has recently been reported that a sacrificial layer of LOR based PMGI (MicroChem) realized a clean graphene surface and free of residue after protolithic-graphic processing1. The practicability of LOR as a temporary wafer bond adhesive is investigated by varying bonding parameters and monitoring the size of the bonded area as well as the bond strength. Bonding of Si wafers using PMGI as a temporary adhesive was performed. Before bonding, Si wafers were cleaned using Standard Clean 1 (H2O:NH4OH:H2O2 = 5:1:1). After surface cleaning, Si wafers are spin coated with LOR 5A (MicroChem), which is based on PMGI, and pre-baked to evaporate the solvent in the resist. Finally, the two PMGI surfaces are brought into contact and the wafer pair was introduced into a bonding machine (EV-501 from EVGroup Inc.). In the bonding machine, the two PMGI layers are compressed face to face with a force of 150 N, under vacuum condition of around 10-3 Pa, and heated to 200-250 ºC. To evaluate these bonded samples, the size of bonded area was observed using an Infrared camera, and the bond strength was evaluated by blade crack test 2. Under optimized process conditions, the wafers are bonded with a few small voids. The size of bonded area covers over 98% of the wafer surface. Also, the wafers are bonded strongly. The bond strength of the sample under optimized conditions is 4.86 J/m2. The surface energy of two Si wafers is 5 J/m2. This means the strength of bonded samples is almost as same as the bulk of Si under the optimized conditions. For an optimization of spinning speed at coating stage, samples are bonded with the spin speed ranging from 2000 to 5000 rpm. This result shows bonded area is large enough (>98%) at spinning speed is between 2000–4000 rpm. However, some voids appear after bonding when spinning speed is higher than 5000 rpm and the bond strength gradually deceased with higher spin speed. From these results, the strongest bonding as well as largest bonded area is obtained when spin speed is 2000 rpm. For an optimization of pre-bake temperature after spinning, samples are bonded with pre-bake temperature from 120 to 220◦C. Bonding quality of the samples baked at 120 ºC was poor in both bond strength and bonded area. However, when the pre-bake temperature is higher than 160◦C, most of the loaded area was bonded and the bond strength is high. One reason for this is that the boiling point of cyclopentanone, the solvent of LOR, is 131◦C. Thus, samples baked at 120 or 140ºC still have residual solvent left in the LOR layer. Therefore, cyclopentanone vapor during bonding prevents successful bonding at the interfaces. Bonding with pre-baking over 160◦C can achieve high quality bonding. Lower process temperature is preferable to reduce thermal damage to bonding materials, so an optimized pre-baking temperature is concluded to be 160◦C. For an optimization of bonding temperature samples are bonded under bonding temperature ranging from 200 to 250 ºC under a 750 KPa load for 30 minutes at a vacuum of around 10−3 Pa. With increasing bonding temperature, the bonding across the LOR surfaces improves. When the bonding temperature was at least 250◦C, most of the loaded area was bonded and bond strength was high. Moreover, contamination after debonding was studied using atomic force microscopy (AFM). Si wafers bonded with PMGI were debonded using N-Methyl-2-pyrrolidone (NMP)-based solvent called Remover PG (MicroChem). Comparison of the Si wafer surface before processes and after bonding-debonding processes shows RMS of surfaces are 0.75 ± 0.06 nm and 0.87 ± 0.36 nm, respectively. Any residue remaining on the Si wafer surface after LOR removal is negligibly small and any resist residue can be 100% removed with a subsequent oxygen plasma ashing process. In conclusion wafer bonding with polydimethylglutarimide (PMGI) has been demonstrated to be suitable for 3-D integration with a temporary bonding process enabling a layer transfer technology. Reference 1. A.Nath,A.D.Koehler,G.G.Jernigan,V.D.Wheeler,J.K.Hite,S.C.Herna andez, Z. R. Robinson, N. Y. Garces, R. L. Myers-Ward, C. R. Eddy, D. K. Gaskill, and M. V. Rao, Appl. Phys. Lett., 104 (2014). 2. W. P. Maszara, G. Goetz, A. Caviglia, and J. B. McKitterick, J. Appl. Phys., 64,4943 (1988).

A sacrificial process for fabrication of biodegradable polymer membranes with submicron thickness.

A new sacrificial molding process using a single mask has been developed to fabricate ultrathin 2-dimensional membranes from several biocompatible polymeric materials. The fabrication process is similar to a sacrificial microelectromechanical systems (MEMS) process flow, where a mold is created from a material that can be coated with a biodegradable polymer and subsequently etched away, leaving behind a very thin polymer membrane. In this work, two different sacrificial mold materials, silicon dioxide (SiO2 ) and Liftoff Resist (LOR) were used. Three different biodegradable materials; polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and polyglycidyl methacrylate (PGMA), were chosen as model polymers. We demonstrate that this process is capable of fabricating 200-500 nm thin, through-hole polymer membranes with various geometries, pore-sizes and spatial features approaching 2.5 µm using a mold fabricated via a single contact photolithography exposure. In addition, the membranes can be mounted to support rings made from either SU8 or PCL for easy handling after release. Cell culture compatibility of the fabricated membranes was evaluated with human dermal microvascular endothelial cells (HDMECs) seeded onto the ultrathin porous membranes, where the cells grew and formed confluent layers with well-established cell-cell contacts. Furthermore, human trabecular meshwork cells (HTMCs) cultured on these scaffolds showed similar proliferation as on flat PCL substrates, further validating its compatibility. All together, these results demonstrated the feasibility of our sacrificial fabrication process to produce biocompatible, ultra-thin membranes with defined microstructures (i.e., pores) with the potential to be used as substrates for tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1192-1201, 2016.

Bilayer lift-off process for aluminum metallization

Recently published reports in the literature for bilayer lift-off processes have described recipes for the patterning of metals that have recommended metal-ion-free developers, which do etch aluminum. We report the first measurement of the dissolution rate of a commercial lift-off resist (LOR) in a sodium-based buffered commercial developer that does not etch aluminum. We describe a reliable lift-off recipe that is safe for multiple process steps in patterning thin (<100 nm) and thick aluminum devices with micron-feature sizes. Our patterning recipe consists of an acid cleaning of the substrate, the bilayer (positive photoresist/LOR) deposition and development, the sputtering of the aluminum film along with a palladium capping layer and finally, the lift-off of the metal film by immersion in the LOR solvent. The insertion into the recipe of postexposure and sequential develop-bake-develop process steps are necessary for an acceptable undercut. Our recipe also eliminates any need for accompanying sonication during lift-off that could lead to delamination of the metal pattern from the substrate. Fine patterns were achieved for both 100-nm-thick granular aluminum/palladium bilayer bolometers and 500-nm-thick aluminum gratings with 6-μm lines and 4-μm spaces.

Temporary Bonding with Polydimethylglutarimide Based Lift Off Resist as a Layer Transfer Platform

Bonding of lift off resist (LOR) was performed to realize temporary wafer bonding without residue. Bonding process conditions such as spin speed, pre-bake temperature, and bonding temperature were optimized to obtain a large bonded area with high bond strength. Under optimized process conditions, a bonded area covering over 98% of the wafer surface, with a room temperature bond strength of nearly 5 J/m2 is achieved. During razor blade testing, fracture often occurs at the Si wafer. Moreover, debonding using an N-Methyl-2-pyrrolidone (NMP)-based solvent left the wafer surface extremely small amount of residue. Thus, the optimized bonding processed developed in this research is suitable for a clean temporary bonding process.

Optimisation of bi-layer resist overhang structure formation and SiO2 sputter-deposition process for fabrication of gold multi-electrode array

In this paper we report the results on the optimization of the bi-layer lift-off resist (LOR) SiO2 sputter-deposition technique which is ideal for obtaining damage-free multi-electrode array (MEA).

Fabrication of multi-electrode array platforms for neuronal interfacing with bi-layer lift-off resist sputter deposition

We report a bi-layer lift-off resist (LOR) technique in combination with sputter deposition of silicon dioxide (SiO2) as a new passivation method in the fabrication of a multi-electrode array (MEA). Using the photo-insensitive LOR as a sacrificial bottom layer and the negative photoresist as a patterning top layer, and performing low-temperature sputter deposition of SiO2 followed by lift-off, we could successfully fabricate damage-free indium-tin oxide (ITO) and Au MEA. The bi-layer LOR sputter deposition processed Au MEA showed an impedance value of 6 × 105 Ω (at 1 kHz), with good consistency over 60 electrodes. The passivation performance of the bi-layer LOR sputter-deposited SiO2 was tested by electrodepositing Au nanoparticles (NPs) on the Au electrode, resulting in the well-confined and uniformly coated Au NPs. The bi-layer LOR sputter deposition processed ITO, Au, and Au NP-modified MEAs were evaluated and found to have a neuronal spike recording capability at a single unit level, confirming the validity of the bi-layer LOR sputter deposition as an effective passivation technique in fabrication of a MEA. These results suggest that the damage-free Au MEA fabricated with bi-layer LOR sputter deposition would be a viable platform for screening surface modification techniques that are available in neuronal interfacing.

Magnetic and meniscus-effect control of catalytic rolled-up micromotors

Rolled-up catalytic micromotors with tubular structures are fabricated by rolling up strained Pt/Co/Ti metallic nanomembranes through selectively etching of the sacrificial lift off resist (LOR). The rolled-up micromotors present distinct motion behaviors in an organic/aqueous mixture fuel compared to those in a pure aqueous fuel. These self-propelled micromotors can move in pure aqueous fuel with a speed up to several millimeters per second. However, when placed into an organic/aqueous mixture fuel, the micromotors walk on the liquid surface. An intermediate Co layer facilitates a magnetically guided motion of these microtubular motors. The motion at the air–liquid interface can be regulated and suspended by the meniscus-climbing effect. Such meniscus-navigated motion represents a novel approach for regulation of micromotors at the air–liquid interface and opens the door to new and exciting operations of these micro-scale machines.

Double layer resist process scheme for metal lift-off with application in inductive heating of microstructures

We present a new method to define metal electrodes on top of high-aspect-ratio microstructures using standard photolithography equipment and a single chromium mask. A lift-off resist (LOR) layer is implemented in an SU-8 photolithography process to selectively remove metal at the end of the processing. In this way, we have successfully defined metal electrodes on top of 75 μm high SU-8 microstructures to be used as test structures for the measurement of temperature increase due to inductive heating.

Electrically isolated nanostructures fabricated using self-assembled multilayers and a novel negative-tone bi-layer resist stack

We create metal nanoelectrode structures with precise proximal placement by blending traditional top-down and bottom-up lithography. Multiple levels of conventional lithography are used in combination with self-assembled multilayer resists (molecular rulers) to generate metallic electrode structures with nanoscale spacings. These multilayers are deposited on initial lithographic gold electrode structures forming a type of lift-off resist used to fabricate proximally placed secondary metal structures with nanometer-scale resolution. By controlling the thicknesses of these multilayers, selective self-assembly is exploited to generate molecular ruler resists, enabling the creation of tailored nanogaps in the 10–50 nm regime. The ability to fabricate electrically isolated nanoelectrodes would enable reliable measurement of the conducting properties of single molecules, nanoparticles and other low-dimensional materials. This paper outlines a new process using a lift-off resist (LOR)/SU-8 negative-tone bi-layer stack to improve the yield of nanoelectrodes. SU-8 finds application in a variety of fabrication techniques, but is difficult to release from the substrate. The LOR/SU-8 process that we have developed possesses the following additional advantages: easy chemical removal of the resist stack with the LOR acting as a release layer, creation of metal lift-off patterns with near-vertical sidewalls, and the ability to withstand chemical processing.

Fabrication of cantilever based mass sensors integrated with CMOS using direct write laserlithography on resist

A CMOS compatible direct write laser lithography technique has been developed forcantilever fabrication on pre-fabricated standard CMOS. We have developed cantileverbased sensors for mass measurements in vacuum and air. The cantilever is actuated intolateral vibration by electrostatic excitation and the resonant frequency is detected bycapacitive readout. The device is integrated on standard CMOS circuitry. In the work anew direct write laser lithography (DWL) technique is introduced. This laser lithographytechnique is based on direct laser writing on substrates coated with a resist bi-layerconsisting of poly(methyl methacrylate) (PMMA) on lift-off resist (LOR). Laser writingevaporates the PMMA, exposing the LOR. A resist solvent is used to transfer the patterndown to the substrate. Metal lift-off followed by reactive ion etching is used for patterningthe structural poly-Si layer in the CMOS. The developed laser lithography technique iscompatible with resist exposure techniques such as electron beam lithography.We demonstrate the fabrication of sub-micrometre wide suspended cantileversas well as metal lift-off with feature line widths down to approximately 500 nm.

Laser lithography on resist bi-layer for nanoelectromechanical systems prototyping

We present a laser lithography technique based on lift-off, for fast and flexible prototyping of micro and nanoelectromechanical systems (MEMS/NEMS). The technique is based on direct laser writing on substrates coated with a resist bi-layer consisting of polymethyl methacrylate (PMMA) on lift-off resist (LOR). Laser writing melts and evaporates the PMMA exposing the LOR. Oxygen ashing removes PMMA residues within the lithography pattern. A resist solvent is used to transfer the pattern down to the substrate. The LOR is dissolved isotropically while the PMMA is unaffected by the solvent, hence creating an undercut profile. After metal evaporation a two-step lift-off process prevents metal flakes from adhering to the surface. First, warm acetone dissolves the PMMA and lifts off the metal layer, then warm Remover PG removes the LOR and any remaining metal. Metal structures with line widths down to 600 nm and dots with 600 nm diameters are presented.

A lift-off process for high resolution patterns using PMMA/LOR resist stack

A lift-off process using a bi-layer resist stack with PMMA on top and lift-off resist (LOR) below was investigated. The dissolution rates of LOR underneath the PMMA layer in alkali solvent, CD26, were measured under various processing conditions. Our results indicate that the undercut length can be well controlled so that pattern transfer by lift-off using this bi-layer structure can be carried out reliably for feature sizes from sub micron down to sub 100 nm.

Fabrication of ultra-short T gates by a two-step electron beam lithography process

This paper proposes a two-step electron beam lithography process, i.e., exposing feet and heads in two separate steps for ultra-short T gates, using a PMMA/UNIII resist stack separated by a thin lift off resist (LOR) layer. Results from both experiments and Monte Carlo simulations show that the two-step lithography process has advantages over the traditional one-step process of being able to pattern shorter feet with a much thicker top layer. The optimum thickness of the LOR for patterning T shape profiles in the PMMA/UVIII resist stack has been found to be about 20 nm.

Laser lithography on resist bi-layer for nanoelectromechanical systems prototyping

We present a laser lithography technique based on lift-off, for fast and flexible prototyping of micro and nanoelectromechanical systems (MEMS/NEMS). The technique is based on direct laser writing on substrates coated with a resist bi-layer consisting of polymethyl methacrylate (PMMA) on lift-off resist (LOR). Laser writing melts and evaporates the PMMA exposing the LOR. Oxygen ashing removes PMMA residues within the lithography pattern. A resist solvent is used to transfer the pattern down to the substrate. The LOR is dissolved isotropically while the PMMA is unaffected by the solvent, hence creating an undercut profile. After metal evaporation a two-step lift-off process prevents metal flakes from adhering to the surface. First, warm acetone dissolves the PMMA and lifts off the metal layer, then warm Remover PG removes the LOR and any remaining metal. Metal structures with line widths down to 600 nm and dots with 600 nm diameters are presented.