Photoresist Mask Research Articles

Effect of Thickness and Sidewall Slope of Photoresist Mask on Etch Profile of Copper Interconnect

We performed high density plasma reactive ion etching of copper thin films using organic gas mixture to define fine patterns less than 10 μm for the application of display devices. However, since redeposition in dry etching of copper thin films frequently occurs due to extremely low reactivity, the etch variables which affect the formation of redeposition were investigated. In this study, the photoresist (PR) masks were employed to etch copper thin films. The effects of the thickness of PR and the sidewall slope of PR on etch profile and redeposition were examined.The thickness of PR mask were in the range of 3 μm ~ 1 μm and the sidewall slopes of the PR mask were in the range of 90° ~ 45°. The etch profile and etch mechanism of dry etching using different masks were evaluated using field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Finally, an etching method to reduce and/or avoid the redeposition in dry etching of copper thin films will be proposed.Acknowledgement : This research was supported by the MOTIE(Ministry of Trade, Industry & Energy (20019504) and KSRC(Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device.

On reactive Ion Etching of Parylene-C with Simple Photoresist Mask for Fabrication of High Porosity Membranes to Capture Circulating and Exfoliated Tumor Cells.

A high porosity micropore arrayed parylene membrane is a promising device that is used to capture circulating and exfoliated tumor cells (CTCs and ETCs) for liquid biopsy applications. However, its fabrication still requires either expensive equipment or an expensive process. Here, we report on the fabrication of high porosity (>40%) micropore arrayed parylene membranes through a simple reactive ion etching (RIE) that uses photoresist as the etching mask. Vertical sidewalls were observed in etched parylene pores despite the sloped photoresist mask sidewalls, which was found to be due to the simultaneous high DC-bias RIE induced photoresist melting and substrate pedestal formation. A theoretical model has been derived to illustrate the dependence of the maximum membrane thickness on the final pore-to-pore spacing, and it is consistent with the experimental data. A simple, yet accurate, low number (<50) cell counting method was demonstrated through counting cells directly inside a pipette tip under phase-contrast microscope. Membranes as thin as 3 μm showed utility for low number tumor cell capture, with an efficiency of 87-92%.

Formation of SiC Mesastructures with Gently Sloping Sidewalls by Dry Selective Etching through a Photoresist Mask

We have demonstrated that SiC mesastructures with gently sloping sidewalls form with the help of selective reactive ion etching (RIE) of silicon carbide through a photoresist mask (slanted walls are formed during simultaneous etching of SiC and the resistive mask with the edge in the shape of a sharp wedge). A simple geometrical model of etching predicts that the resultant slope of the mesastructure wall must be specified by two parameters, i.e., initial angle of the resistive wedge and the selectivity of SiC etching relative to the photoresist (ratio of etching rates of SiC and photoresist). For experiments, we used polished 4H–SiC wafers with the (0001) orientation. Photoresist regions with an edge angle of 22° were deposited using photolithography onto the Si side of the wafers. Then etching of mesastructures was performed in nitrogen trifluoride in a setup with an inductively coupled plasma. We selected RIE parameters ensuring SiC and photoresist etching with rates of 55 and 160 nm/min, respectively (etching selectivity was 1 : 3). The SiC mesastructures formed by etching have a height of 3.2 μm and gently sloping sidewalls with a slope of about 8°. This technology can be used for preparing high-voltage SiC devices with a straight bevel.

Heat Treatment of Carbonized Photoresist Mask with Ammonia for Epitaxial Lateral Overgrowth of a-plane GaN on R-plane Sapphire

Epitaxial (1120) a-plane GaN films were grown on a (1102) R-plane sapphire substrate with photoresist (PR) masks using metal organic chemical vapor deposition (MOCVD). The PR mask with striped patterns was prepared using an ex-situ lithography process, whereas carbonization and heat treatment of the PR mask were carried out using an in-situ MOCVD. The heat treatment of the PR mask was continuously conducted in ambient H2/NH3 mixture gas at 1140℃ after carbonization by the pyrolysis in ambient H2 at 1100℃. As the time of the heat treatment progressed, the striped patterns of the carbonized PR mask shrank. The heat treatment of the carbonized PR mask facilitated epitaxial lateral overgrowth (ELO) of a-plane GaN films without carbon contamination on the R-plane sapphire substrate. Thhe surface morphology of a-plane GaN films was investigated by scanning electron microscopy and atomic force microscopy. The structural characteristics of a-plane GaN films on an R-plane sapphire substrate were evaluated by ω-2θ high-resolution X-ray diffraction. The a-plane GaN films were characterized by X-ray photoelectron spectroscopy (XPS) to determine carbon contamination from carbonized PR masks in the GaN film bulk. After Ar+ ion etching, XPS spectra indicated that carbon contamination exists only in the surface region. Finally, the heat treatment of carbonized PR masks was used to grow high-quality a-plane GaN films without carbon contamination. This approach showed the promising potential of the ELO process by using a PR mask.

$\hbox{BCl}_{3}/\hbox{Cl}_{2}$-Based Inductively Coupled Plasma Etching of GaN/AlGaN Using Photoresist Mask

Gallium nitride/aluminium gallium nitride (GaN/AlGaN) etching in BCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based inductively coupled plasma (ICP) is investigated for high electron mobility transistor (HEMT) mesa etching using rarely preferred mask-photoresist. The critical issues related to photresist burning/deforming, resist removal, selectivity, mesa edge roughening, and nonuniform etching of GaN and AlGaN layers are discussed in detail using plasma of BCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> / Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gases. The effect of ICP process parameters like ICP power, RF power, pressure, and BCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> flow rate ratio on etch rate of GaN/AlGaN layers and mask is studied systematically for the optimization of a HEMT mesa etching process that results in smooth etched surface with sharp and highly anisotropic mesa edges. The photoresist mask selectivity is found to depend strongly on pressure and RF power, whereas the etched surface morphology changes significantly with the gas flow rate ratio and chamber pressure. The AlGaN etch rate and selectivity with respect to GaN is also characterized for different Al concentrations varying up to 33%. The etch process is finally applied to GaN/AlGaN HEMT mesa etching, where the mesa features with depth of ~ 1500 A° are etched successfully. The resultant process etch uniformity is found to be better than 5% over 2-in wafer.

A Highly Selective Low Pressure Inductively Coupled Plasma Etching Process for GaAs Using Photoresist Mask

A Highly Selective Low Pressure Inductively Coupled Plasma Etching Process for GaAs Using Photoresist Mask

Anodic Etching of InP Substrate through Photoresist Mask Formed by Sphere Photolithography

not Available.

A Simple Photomask with Photoresist Mask Layer for Ultraviolet-Photolithography and Its Application for Selectively Photochemical Surface Modification of Polymers

According to ultraviolet (UV) spectroscopic studies, a positive AZ photoresist film thicker than 10 (m can hardly transmit UV lights of wavelengths 200–285 nm. A simple photomask for UV photolithography was prepared using a quartz glass plate coated with a light-obstructing film of positive AZ photoresist, and the quality of the photomask and fidelity of the pattern transferred by the photomask were evaluated. The developed AZ photoresist photomask was used for fabrication of gold microelectrode on polycarbonate (PC) sheets. PC sheetswere exposed to the UV lights emitted from a low-pressure mercury lamp and passed through the photomask. The PC sheets were subjected to selective surface photolysis in the exposed area. After a series of wet chemical reactions, nano gold particles serving as the catalyst for electroless plating were deposited on the irradiated area. Gold microelectrodes were then generated by immersing the selectively activated PC sheet in an electroless gold plating bath for a specific time. Without need for a clean room, the photomasks can be prepared by a chemist in a common chemical laboratory with low-cost materials and simple procedures.

Study of the Roughness in a Photoresist Masked, Isotropic, SF6-Based ICP Silicon Etch

In this paper we study the etching behavior and the resulting roughness in photoresist-masked isotropic silicon plasma etch performed in an inductively coupled plasma (ICP) etcher using . We report detailed observations of the resulting roughness for various etching parameters, covering: pressure from 2.5 to , flow rate from 50 to , platen power from 0 to , and ICP power from 1000 to . Etch processes with a normalized roughness below 0.005 were found at low pressure, , while larger normalized roughness, above 0.02, occurred at higher pressures, . Here the normalized roughness is the ratio of the roughness amplitude to the etch depth. The rough etching processes showed characteristic high-aspect-ratio and crystal-orientation-dependent surface morphology. The temporal evolution of this roughness was studied, and observations suggest a gradual buildup of surface contamination (redeposits) originating from the photoresist mask. A model was used to analyze the etched profiles with respect the internal etching conditions. The almost isotropic etching profiles, obtained in both rough and smooth etching processes, are generally highly radical-dependent; however, the surface roughness itself can be reduced dramatically using an ion energy above a certain threshold value. The roughness causing mechanism is discussed.

Fabrication of Nanoscale PtO[sub x]∕PZT∕PtO[sub x] Capacitors by E-beam Lithography and Plasma Etching with Photoresist Mask

Nanoscaling of PtO x /Pb(Zr x Ti 1-x )O 3 (PZT)/PtO x capacitors in well-ordered arrays down to a cell size of 90 X 90 nm was sucessfully achieved by electron-beam lithography and plasma etching with photoresist mask. Fast etch of PtO x and PZT layers was obtained with a rate of 165 nm/min in plasma of Ar/Cl 2 /10%O 2 and 240 nm/min in Ar/CF 4 /30%O 2 , respectively. The selectivity of PtO x to NEB resist was 5.8 and that for PZT was 4.3. Crystallization of PZT film and reduction of PtO x layer were also observed after post-annealing of the etched specimens. Direct electrical measurement reveals that a good polarization switching characteristic can be retained in the nanoscaled PZT capacitors.

Micro-Scale Metallization of Cu and Au on Flexible Polyimide Substrate by Electroplating Using SU-8 Photoresist Mask

AbstractIn order to fabricate flexible microelectronic devices, fabrication of metallization lines and metal electrodes on the flexible substrate is essential. Cu lines are often used as interconnect lines in electronic devices and Au as microelectrodes in organic transistors and bioelectronics devices due to its good electrochemical stability and biocompatibility. For minimizing the size of device, the realization of metallization lines and microelectrodes with the scale of a few micrometers on the flexible substrate is very important. In this work, micro-scale metallization lines of Cu and Au were fabricated on the flexible polyimide (PI) substrate by electroplating using the patterned mask of a negative-tone SU-8 photoresist. Surface of PI substrate was treated by O2 inductively coupled plasma for improvement in the adhesion between the Cr layer and the PI and in-situ sputter-deposition of 100-nm-thick Cu seed layers on the sputter-deposited 50-nm- thick Cr adhesion layer was followed. Electroplating of Cu and Au lines using a sulfuric acid and a noncyanide solution with the patterned SU-8 mask, respectively, removal of SU-8, and selective wet etch of Cr adhesion and Cu seed layers were carried out. Micro-scale Au electrode lines were successfully fabricated on the PI substrate. Micro-scale gap-filled Cu lines with spin- coated polyimide on the PI substrate with the thickness of 6 ∼ 12 νm and the aspect ratio of 1~3 were successfully fabricated.

Etching Selectivity and Surface Profile of GaN in the Ni, SiO2 and Photoresist Masks Using an Inductively Coupled Plasma

The selectivity and etched surface profile for etching GaN using an inductively coupled plasma (ICP) in Ni, SiO2 and photoresist masks were investigated. The mask etching rates in the Ni, SiO2 and photoresist masks were 26, 70 and 245 nm/min, respectively, for a RF power of 500 W, an ICP power of 600 W and an etching gas ratio of BCl3/Ar/N2=15:5:10 (sccm). A high selectivity of 15 in the Ni mask was found to be higher than that of 5.6 and 1.65 in the SiO2 and photoresist masks, respectively. The best etching surface profile was also obtained in the Ni mask in comparison with the SiO2 or photoresist mask.

Exposure Method Using Photoresist Mask for High-Density Optical Disk Mastering

A high-density digital versatile disk (HD-DVD) is being developed, aiming for high definition television. It is thought that the capacity of HD-DVD would be 15 GB, for example when its track pitch is 0.42 µm, its minimum mark length must be 0.22 µm. To fabricate such a high-density optical disk, we develop an exposure method using a photoresist mask. Super-resolution is also studied in order to make the exposure beam diameter smaller.

Influence of Reaction Products on Si Gate Etching with a Photoresist Mask in HBr/O2 and Cl2/O2 Electron Cyclotron Resonance Plasma

Highly directional and highly selective (Si/SiO2 and Si/photoresist) dry etching of Si metal-oxide-semiconductor (MOS) gates with a photoresist mask is achieved using electron cyclotron resonance (ECR) HBr/O2 etching reactions. In this process, the photoresist mask is coated with SiO2 in HBr/O2 plasma, and highly selective etching in Cl2/O2 plasma is combined with this SiO2 coating process. In the Cl2/O2 plasma, oxygen reacts with Si etching products such as SiClx on the surface of both the Si and the coated SiO2, generating SiO2 which is deposited as a film on the coated SiO2. However, no deposition occurs on the etching surface of Si, and the Si etching rate increases. This result proves that the SiO2 coating protects the photoresist during Cl2/O2 plasma etching.

Surface Modification of Positive Photoresist Mask during Reactive Ion Etching of Si and W in SF 6 Plasma

This paper reports the results of a preliminary study concerning the surface modification of a diazoquinone‐novolak photoresist (HPR 204)1 during reactive ion etching of Si and W in plasmas. X‐ray photoelectron spectroscopy analyses provide the following information: the spectrum reveals various bonding states of carbon with fluorine such as , , and which proves the fluorination of the carbon network. The existence of and species is also most probable. A loss in the oxygen content is the main degradation observed. Sulfur residues are present and discussed in relation to the nature of the cathode material. In the case of a W cathode, the identification of tungsten fluorides on the photoresist surface is correlated with the etching of the cathode. Ion bombardment‐induced effects are investigated, in particular concerning the presence of metallic tungsten sputtered from the cathode.

Preferential Etching of InP Through Photoresist Masks

Photoresist etch mask undercutting problems have been studied for the etching of v‐grooves in (100) substrates for channelled substrate laser growth. The relationship between the photoresist mask undercutting and the impurity contents (, , and ) in the etchant were studied. The fluoride anion in the etchant causes the separation of the photoresist from the oxidized surface and results in excessive undercutting.

Mask Dependent Etch Rates II: The Effect of Aluminum vs. Photoresist Masking on the Etch Rates of Silicon and Silicon Dioxide in Fluorine Containing Plasmas

Plasma etch rates of silicon and silicon dioxide when masked with photoresist and aluminum are compared. It was observed that the aluminum masked silicon had an enhanced etch rate relative to photoresist masking with a variety of fluorocarbon (, , and ) and nonfluorocarbon ( and ) containing etch gases. It is also shown that the aluminum masked silicon dioxide etch rate is depressed relative to that of photoresist masked but that this effect is limited to the fluorocarbon etch gases. It is shown that the aluminum mask is responsible for affecting the etch rates and not the photoresist mask. Evidence is presented that favors a mechanism by which excess fluorine radicals are catalytically produced at the aluminum mask surface. The relative amount of silicon etch rate enhancement is strongly linked to the oxygen concentration present in the etch gas mixture. This is consistent with a competition between fluorine and oxygen for reaction with and attachment to the aluminum surface. It is postulated that is a catalyst for fluorine production and is not.

Ion-Bombardment-Induced Improvement of Photoresist Mask Properties for RF Sputter-Etching

Ion-bombarded photoresists were found to have improved mask properties for sputter-etching. The photoresist bombarded with Ar ions with an intensity of the order of 1015 ions cm-2 has a smaller etching rate than the unbombarded photoresist and shows no traces of thermoplastic flow and no surface morphology degradation, even when it is sputter-etched without any intentional thermal contact, which is often made for preventing the photoresist mask degradation. Although reduction in the photoresist pattern dimensions and in the photoresist removal rate by the oxygen plasma ashing technique occurs when the photoresist is ion-bombarded, it is confirmed that these drawbacks do not impede the application of the improved photoresist. Delineation of fine gold patterns for an absorber for an X-ray lithography mask is demostrated as an example of the application of the improved photoresist mask for sputter-etching.