Photoresist Removal Research Articles

Influence of Photoresist and BARC Selection on the Efficiency of a Post-Etch Wet Strip in BEOL Applications

All-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) and Bottom AntiReflective Coating (BARC) in the back-end-of-line (BEOL) semiconductor manufacturing, as plasma ash, traditionally used to remove the PR and BARC layer after etch, cause damage to the low-k dielectric. This study investigates the modification of 193 nm post-etch PR and BARC layer by UV irradiation, that can be used as an intermediate step to enhance PR and BARC wet strip by O3/H2O.

Study of Controlled Oxygen Diffusion Approaches for Advanced Photoresist Strip

Two alternative plasma strip processes were developed to meet the photoresist (PR) removal requirements of future technology nodes. Compared to traditional oxidizing chemistries, the new plasma strip approaches showed significantly lower silicon oxidation and substrate loss, while achieving good residue removal capabilities. Plasma strip-induced dopant loss and profile changes were also evaluated for gate-first and gate-last high-k/metal gate applications.

High-dose ion-implanted photoresist stripping in environmentally benign supercritical CO2 nonfluorous surfactant microemulsions

The stripping behavior of high-dose ion-implanted (HDIM) photoresist was investigated in a scCO2 microemulsion with 3wt.% surfactant of 2-ethyl hexanol polyoxyethylene-polyoxypropylene and 2vol.% co-solvent of dimethylsulfoxide. The removal efficiency was studied under the pressure of 10-25MPa at 40-60^oC. The results of surface characterization and composition analysis for the cleaned samples by SEM, FTIR, and XPS revealed that the removal rate increased with time with a sharp increase during the first 10min. Temperature and pressure are favorable to the stripping within 20min. The photoresist removal efficiency at 50^oC improved from 40% to 85% as the pressure range of 10-25MPa due to the higher scCO2 density at higher pressure which enhances the photoresist solubility in scCO2. The magnetic agitation and pressure pulsation generated a higher fluid velocity to provide a larger physical force. This new environment-friendly photoresist stripping method allows dramatic reduction in water and chemicals consumption and overcomes the obstacle in the conventional microelectronics processing due to the shrinkage in the feature size.

Proven Cleaning Technology Solutions for Lead-Free Micro-Bumping Processes

Opportunities for developing new and enabling packaging schemes are being pursued as part of device improvement strategies for electronic products. Processes such as embedded technologies in wafer level packaging and 3-D chip architecture schemes open up opportunities for realization of a variety of package configurations. As a result, there are many opportunities to impact both device performance and the processes used to create them. In the area of electroplated solder application, one area of growing interest is cleaning technology. There is a need for an integrated process to fabricate defect-free copper pillars with lead-free caps and lead-free solder plated bumps compatible with advanced packaging schemes and with improved yields and reliability. Photoresist removal and surface preparation have been identified as critical to the success. In familiar and widespread technology using 150 micropitch solder bumping, the introduction of RoHS rules for lead-free solder bump compositions, (SnAg, SnAgCu), proceeded in the absence of an integrated and tailored process capable of defect-free surface preparation. It was relatively simple for solder bump compositions in many devices to be converted to lead-free alloys. However, new challenges continue to arise in higher volume fabrication of SnAg micro-pillars (micro-pillars) or copper micro-pillars with lead-free solder caps as the bump pitch approaches 25 microm with aspect ratios of 1:1 or 1.5:1. Individual processes that are involved in the total integration, including (1) dielectric cleaning steps, (2) PVD seed Ti and Cu deposition, (3) electroplating, (4) thick photoresist application and patterning, (5) photoresist removal, (6) associated descum processes, and (7) copper seed metal etch steps, have been challenged to meet the demands. New geometries, higher aspect ratios and very dense solder bump arrays have created further challenges for these processes, stretching the older 150 microm technology beyond its capability. The focus of this paper is to identify a reliable route to defect-free copper micro-pillars with lead-free caps and lead-free solder plated micro-bumps after photoresist removal in applications compatible with advanced packaging schemes and with improved yields and reliability.

Removal of Ion-implanted Resists using High Concentration Wet Ozone

This paper discusses the relationship between ozone concentration and photoresist removal rate, and the removal of ion-implanted photoresists using high concentration wet ozone. The photoresist removal rates increased linearly with increasing ozone concentration. We achieved 3.84μm/min in ozone concentration of 30vol%. This value is four times as fast as the photoresist removal rate which is expected in a semiconductor manufacturing process. In ozone concentrations of 10vol% and 30vol%, the photoresist into which B ions were implanted with a dose of 5×1014 atoms/cm2 at acceleration energy of 70keV was removed. In ozone concentration of 30vol%, the ion-implanted photoresist removal rate was twice as fast as that of ozone concentration of 10vol%.

Towards Fully Aqueous Ozone Wet Strip of 193 nm Photoresist Stack Using UV Pre-Treatments in Low-k Patterning Applications

All-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) and Bottom Anti Reflective Coating (BARC) in the Back-End-Of-Line (BEOL) semiconductor manufacturing, as an alternative to plasma strip, which may cause damage to advanced porous low-k materials. However, degradation of DUV PR by etch plasmas results in a modified top layer that is cross-linked (so-called crust) and therefore not soluble anymore using pure organic solvents. This study investigates the combination of UV with ozonated processes to remove PR and BARC in BEOL applications. Treatment of PR and BARC by UV irradiation was proved to be an interesting process to increase the concentration of reactive C=C bonds in the post-etch PR and BARC layer. Another effect of UV irradiation is that it can cause scissioning of C–C bonds in the PR main chain, thereby improving the dissolution of the PR in solvents. This UV pre-treatment was used as a preliminary step to enhance PR and BARC removal by ozonated wet strips. Different pathways were studied in detail, leading to the development of a fully aqueous ozonated wet strip process.

PR and BARC Wet Strip in BEOL Patterning Using a UV-Enabled Aqueous Process

Conventional plasma strip processes are prone to cause damage to advanced porous low-k materials. Therefore, all-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) and Bottom Anti Reflective Coating (BARC) in Back-End-of-Line (BEOL) semiconductor manufacturing. A two step process with a UV pre-treatment and an ozonated strip process is considered. The UV pre-treatment under O2 at high temperature enhances PR and BARC removal. With a subsequent fully aqueous ozone wet strip, complete removal is feasible.

Influence of thermal cycles on the silylation process for recovering k-value and chemical structure of plasma damaged ultra-low-k materials

The integration of porous ultra low-k (ULK) materials within the interconnect system of integrated circuits is one of the most promising approaches to reduce RC-delay or crosstalk. The application of plasma processes for patterning, cleaning and photoresist removal is known to degrade the electrical parameters of the ULK by carbon depletion, densification and introduction of silanol species. In this study we investigate the influence of different thermally assisted immersion processes on the effectiveness of a silylation based k-restore process of plasma damaged porous low-k dielectrics. The results show that network recovery effects like methyl incorporation are different at the surface and in the depth of the damaged area addicted to precursor temperature and curing conditions. The most promising process sequence was shown to consist of an immersion at temperatures of 100-150^oC with subsequent UV anneal depending on the precursor used for recovery process.

Properties of Surface Metal Micromachined Rectangular Waveguide Operating Near 3 THz

Single-mode TE10 rectangular waveguides operating near 3 THz have been demonstrated. The waveguides have internal dimensions of 75 μm × 37 μm (WR-0.3) and are fabricated using an additive gold electroplating process on a silicon substrate. The impact of photoresist removal holes was minimized by full-wave design of the hole and matching structures. Waveguides were measured at three frequencies from 2.56 to 3.11 THz and demonstrated loss as low as 1.3 dB/mm at 3.11 THz, corresponding to a loss per wavelength of 0.12 dB/λ. This paper summarizes the design, fabrication, and measurement of these micromachined waveguides operating near 3 THz.

Study of Alternative Plasma Strip Techniques for Advanced Photoresist Removal

This paper reports on the investigation and development of two alternative plasma strip processes to meet the photoresist (PR) removal requirements of future technology nodes. Experimental results show that new plasma strip approaches have comparable crust breakthrough and removal capabilities as O2/N2:H2 and fluorine-containing strip processes, but achieve significantly lower silicon oxidation, which is comparable to, or even lower than that of an N2:H2-only plasma process. Improved residue removal capability and very low metal (TiN and TaN) oxidation values have also been achieved. SIMS analyses of implanted silicon wafers processed with the new strip approaches have shown minimal dopant loss and profile changes. This work demonstrates that these novel plasma strip approaches are viable candidates for meeting the demanding wafer cleaning requirements of the 32nm technology node and beyond.

UV-LIGA microfabrication of 220 GHz sheet beam amplifier gratings with SU-8 photoresists

Microfabrication techniques have been developed using ultraviolet photolithography (UV-LIGA) with SU-8 photoresists to create advanced sheet beam amplifier circuits for the next generation of vacuum electron traveling wave amplifiers in the 210–220 GHz (G-band) frequency regime. We describe methods that have led to successfully fabricated millimeter wave circuits, including applying ultra-thick SU-8 photoresist layers on copper, copper electroforming solutions, and the challenging removal of the SU-8 photoresists. A table of experimental liquid SU-8 removal chemistries and results is also presented.

Removal of Ion-Implanted Photoresists Using Atomic Hydrogen

In this paper, we investigated the removal characteristic of positive-tone novolak photoresists into which B, P, and As ions were implanted with doses of at an acceleration energy of 70 keV using atomic hydrogen, and the hardening mechanisms for the photoresists. All of the ion-implanted photoresists with doses up to were removed without regard for ion species. The removal rates of the photoresists decreased with increasing ion-implantation dose due to hardening of the photoresist surfaces with implantation. The thickness of the surface-hardened layer of the photoresists decreased in the order of , and the removal rate increased with decreasing thickness. The energy supplied from the ions to the photoresist concentrated on the surface side in the order of , and the impact of the heavier ion on the photoresist was greater than that of the lighter ion. We deduced that the photoresists exhibited carbonization and cross-linkage attributable to the decrease in OH, CH, and O 1s and the increase in , C 1s, and π-conjugated systems.

Solution processable micron- to nanoscale conducting polymer patterning utilizing selective surface energy engineering

We developed a new conducting polymer microscale and nanoscale patterning method; a bottom-up approach for applying a conducting polymer solution on a substrate with locally varied surface energies. Selective surface energy engineering was achieved by combining conventional photolithography and local hydrophobic treatments with a self-assembled monolayer (SAM) at the exposed surface. The regions under the photoresist patterns remained hydrophilic after the photoresist removal. Here, a poly(3,4-ethylene-dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) conducting polymer solution was dispensed with a razor blade on the substrate, wetting only the hydrophilic regions. Next, conducting source/drain polymer electrodes were fabricated (channel length: 5 μm) and utilized for poly(3-hexylthiophene) (P3HT) organic field-effect transistors. For nanoscale conducting polymer line patterns, a photoresist template with nanoscale features was fabricated using holographic lithography. Finally, multi-step spin coating method reliably produced polymer lines having a linewidth of 292 nm at 1 μm spacing.

Substrate Temperature Dependence of the Photoresist Removal Rate Using Atomic Hydrogen Generated by a Hot-Wire Tungsten Catalyst

Instead of photoresist removal methods using chemicals, we investigated an environmentally friendly removal method using atomic hydrogen generated by decomposing hydrogen molecules by contact with a hot-wire tungsten catalyst. We set the distance between the catalyst and the photoresist substrate (DCS) at 20, 60, 100 and 120 mm and evaluated the apparent activation energy (EAP) for the reaction between photoresist and atomic hydrogen at each DCS. The EAP was determined from Arrhenius plots of the photoresist removal rate against the average substrate temperature. When DCS was 20 and 60 mm, EAP decreased with increasing catalyst temperature (WT=2040–2420 °C) and was not constant. However, when DCS was 100 and 120 mm, EAP was nearly constant at 19 ±1 kJ/mol without depending on WT. We might obtain the activation energy of about 19 kJ/mol in the reaction of photoresist with atomic hydrogen.

Removal of post-etch 193 nm photoresist in porous low- k dielectric patterning using UV irradiation and ozonated water

All-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) in the back-end-of-line (BEOL) semiconductor manufacturing. However, degradation of DUV–PR by etch plasmas results in a modified top layer of the PR that is cross-linked (so-called crust) and therefore not soluble anymore using pure organic solvents. This study investigates the modification of 193 nm post-etch PR by UV irradiation with different wavelengths. UV irradiation showed to be an interesting process to increase C C bond concentration in post-etch PR, which was used as an intermediate step to enhance PR wet strip using ozonated DI water. Treatment of post-etch PR by 222 or 283 nm led to the largest increase in C C bonds. The combination of UV with ozonated DI water is a promising process sequence for PR and BARC strip in BEOL applications.

Photoresist removal using an O2∕N2 medium pressure plasma jet with high speed wafer scanning: Unimplanted resist studies

The authors describe a plasma ashing system where a stationary jet of hot, activated gases removes photoresist from a scanning wafer. The jet is created by a reactant stream flowing through a 2.45GHz surface wave discharge in a 6mm quartz tube. For O2∕N2 plasmas in the medium pressure range from 20to100Torr, a luminous plasma jet emerges from the end of the discharge tube that transports both heat and reactive species to the wafer. A single scan results in a Gaussian track profile with a standard deviation of 7mm for the source-to-substrate distance of 9mm. A simple model of the ashing process, which assumes a thermally activated ash rate and Gaussian distributions for both power density and reactant flux, unifies the dependence of effective ash rate on the substrate temperature and scan speed at a constant power. The best fit activation energy at 2.5kW is 0.23eV, about half of the value found in conventional downstream ashing, implying that diffusion plays a significant role in limiting the ash rate. The peak thermal power density in a 2.5kW jet at 80Torr is 160W∕cm2, resulting in an effective instantaneous ash rate of 2.5mm∕min for a scan speed of 70cm∕s and 200°C chuck temperature. This implies that the time to clear a 1.2μm thick resist coating from a 300mm wafer is 18s.

Novel Single-Wafer Single-Chamber Dry and Wet Hybrid System for Stripping and In Situ Cleaning of High-Dose Ion-Implanted Photoresists

There is increasing demand for moving from batch immersion tools to single-wafer spin tools for silicon wafer cleaning, etching, and photoresist/residue removal in advanced semiconductor manufacturing. However, high-dose ion-implanted photoresist removal using a conventional single-wafer spin tool is very difficult. We have developed a novel single-wafer single-chamber dry and wet hybrid system in combination with dry ashing and moderate-temperature wet-cleaning treatments by implementing an atmospheric-pressure plasma unit into a conventional single-wafer spin cleaning tool. This compact single-wafer single-chamber system can completely remove the hardened photoresist due to high-dose ion-implantation by an atmospheric-pressure plasma ashing process followed by an in situ wet chemical process in the same single chamber within 2 min. This single-wafer single-chamber dry/wet hybrid system offers less than 1/3 smaller footprint, less than 1/4 shorter cycle time (for 50 wafer processing), and potentially better process control and less contamination risk, as well as lower equipment cost, compared to the conventional combination of two separate dry- and wet-processing systems.

The fabrication of diversiform nanostructure forests based on residue nanomaskssynthesized by oxygen plasma removal of photoresist

A simple lithography-free approach for fabricating diversiform nanostructure forestsis presented. The key technique of the approach is that randomly distributednanoscale residues can be synthesized on substrates simply by removing photoresistwith oxygen plasma bombardment. These nanoresidues can function as masks inthe subsequent etching process for nanopillars. By further spacer and then deepetching processes, a variety of forests composed of regular, tulip-like or hollow-headnanopillars as well as nanoneedles are successfully achieved in different etchingconditions. The pillars have diameters of 30–200 nm and heights of 400 nm–3 µm. The needles reach several microns in height, with their tips less than 10 nm in diameter.Moreover, microstructures containing these nanostructure forests, such as surfacemicrochannels, have also been fabricated. This approach is compatible with conventionalmicro/nano-electromechanical system (MEMS/NEMS) fabrication.

Effect of Radical Scavenger and UV Irradiation on Removal of Photoresist and BARC using Water/Ozone in Cu/Low-k Interconnect

This study focused on the removal of post-etch photoresist (PR) and bottom anti-reflection coating (BARC) layers using O3 dissolved in H2O at 60 {degree sign}C. A complete removal of the PR layer was achieved with a short rinse in propylene carbonate (PC). However, the k-value of the film as determined using Hg-probe showed an increase of about 0.3 due to the wet process at 60 {degree sign}C for 5 min, and the BARC layer remained on the substrate. Using acetic acid (HAc) 0.5 M, a radical scavenger, as additive resulted in a small reduction in k-value of about 0.2 with respect to the sample processed in the same solution without HAc. Within the range of HAc concentration of 0.01-0.5 M, there was no clear trend and no significant effect in terms of PR removal as a function of HAc concentration, indicating a direct O3 attack of PR. The issue of BARC removal was addressed using UV treatment at 222 nm wavelength.

Removal of Photoresist and BARC in Cu BEOL using an All-wet Process

Wet removal of post-etch photoresist (PR) and bottom anti-reflective coating (BARC) was studied using "multi functional" cleaning solutions based on BASFs tool box. For blanket wafer, Fourier-transform infrared (FTIR) data showed that both PR and BARC layers were completely removed at a megasonic power of 10 W for 2 min. For patterned structure, the plasma used for opening of the BARC layer and metal hard mask resulted in the formation of fluorine- and titanium-containing species in the PR crust. Cross-sectional secondary electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS) data indicated that complete removal of post-etch PR can be achieved under experimental conditions typical for single wafer processing. Subsequent patterning of porous low-k layer showed good low-k profile. Wet processes using solvent-based chemistry followed by a bake at 350 {degree sign}C for 1 min at low pressure was found to have no detrimental impact on k-value degradation.