Yousuke Goto

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 5 × 10 12 -5 × 10 15 atoms/cm 2 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 5 × 10 15 atoms/cm 2 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 B → P → As, 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 B → P → As, 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 0 1s and the increase in C=C, C 1s, and π-conjugated systems.

Removal Characteristics of Resists Having Different Chemical Structures by Using Ozone and Water

We investigated an environmentally friendly resist removal method using ozone and water (wet ozone). The resist removal rate was optimum when the temperature of the wet ozone was 83 °C and that of the substrate was 78 °C. Novolak resin of a positive type of novolak resist base polymer has a carbon–carbon double bond in the main chain, so Novolak resin reacted easily with ozone. The resulting removal rate of the novolak resist was about 1.1 µm/min, which was the highest removal rate among novolak, KrF and ArF resists. For all implanted ion species (B, P, and As), all the resist with ions of 5×1013 atoms/cm2 could be removed. Resist with 5×1014 atoms/cm2 As and P ions could not be removed at al, but resist with B ion could be removed. The energy to harden the resist of B ion was less than that to harden P and As ions, because B ion is lighter than the other ions. All the resist with ions of 5×1015 atoms/cm2 could not be removed.

Removal of Ion-Implanted Photoresists Using Wet Ozone

Using environmentally friendly wet ozone instead of chemicals, we removed B-, P-, and As-ion-implanted positive-tone novolak photoresists with an implantation dose of 5 × 10 12 ―1 × 10 16 atoms/cm 2 at an acceleration energy of 70 keV. Ion-implanted photoresists with an implantation dose exceeding 5 × 10 15 atoms/cm 2 could not be removed, but photoresists implanted at doses below 5 × 10 13 atoms/cm 2 could be removed. Photoresist implanted with B ions at 5 × 10 14 atoms/cm 2 was removed slowly, but photoresists implanted with P and As ions were not removed at all. The hardness of the photoresist with B ions implanted at 5 × 10 14 atoms/cm 2 was 1.8 times greater than that of the nonimplanted photoresist (AZ6112), that of the P-ion-implanted photoresist was eight times greater, and that of the As-ion-implanted photoresist was five times greater. The B-ion-implanted photoresist was softer than the P- and As-ion-implanted photoresists. We also obtained the calculation results in which the energy supplied from the B ions to the photoresist was lower than that from P and As ions. We assumed that the ion-implanted photoresists were hardened by cross-linkage due to the energies supplied to the photoresists from the ions. Therefore, we determined that the hardness threshold of the photoresist that could be removed by using wet ozone was twice the hardness of AZ6112.

A high-speed photoresist removal process using multibubble microwave plasma under a mixture of multiphase plasma environment

This paper proposes a photoresist removal process that uses multibubble microwave plasma produced in ultrapure water. A non-implanted photoresist and various kinds of ion-implanted photoresists such as B, P, and As were treated with a high ion dose of 5 × 1015 atoms/cm2 at an acceleration energy of 70 keV; this resulted in fast removal rates of more than 1 μm/min. When the distance between multibubble microwave plasma and the photoresist film was increased by a few millimeters, the photoresist removal rates drastically decreased; this suggests that short-lived radicals such as OH affect high-speed photoresist removal.

Study of the Removal of Ion-Implanted Resists Using Wet Ozone

We have investigated the removal of novolac resists into which B and P ions had been implanted with a dose of 5×1014 atoms/cm2 at acceleration energies of 10, 70, and 150 keV (ion-implanted resists), using wet ozone. Also, we confirmed the presence of the surface hardened layer of ion-implanted resists by cross-sectional observation using scanning electron microscopy (SEM), the stripping of the hardened layer using chemicals, and the measurement of the plastic-deformation hardness of the resists by nanoindentation. The removal rate for a resist using wet ozone decreased with increasing acceleration energy because the hardness of the resist increased with increasing acceleration energy. Moreover, we clarified by time-of-flight secondary ion mass spectrometry (TOF-SIMS), that the ion intensity of C10H- (m/z 121.01) for the hydrocarbon component, which has the unsaturated bonds as a component of the surface hardened layer increased with increasing acceleration energy. Cresol novolac resin was destroyed and carbonized by ion implantation. Therefore, the removal of ion-implanted resists became difficult with increasing acceleration energy.

Removal of SU-8 resists using hydrogen radicals generated by tungsten hot-wire catalyzer

We investigated removal of chemically amplified negative-tone i-line resist SU-8 using hydrogen radicals, which was generated by the catalytic decomposition of H2/N2 mixed gas (H2:N2 = 10:90vol.%) using tungsten hot-wire catalyzer. SU-8 with exposure dose from 7 (Dg100×0.5) to 280mJ/cm2 (Dg100×20) were removed by hydrogen radicals without a residual layer. When the distance between the catalyzer and the substrate was 100mm, the catalyzer temperature was 2400°C, and the initial substrate temperature was 50°C, removal rate of SU-8 was 0.17μm/min independent of exposure dose to the SU-8. Finally, we obtained high removal rate for SU-8 (exposure dose = 14mJ/cm2 (Dg100)) of approximately 4μm/min when the distance between the catalyzer and the substrate was 20mm, the catalyzer temperature was 2400°C, and the initial substrate temperature was 165°C.

Reaction mechanism of polymer removal using wet ozone

We evaluated the removal of polymers with various chemical structures using wet ozone, and investigated the reaction mechanism between wet ozone and polymers using fourier-transform infrared (FT-IR) and in situ FT-IR. The removal rate of poly(vinyl phenol) (PVP), which has a carbon–carbon double bond (C=C) in the side chain was lower than that of the novolak resin, which has C=C in the main chain. Poly(methyl methacrylate) (PMMA), which has no C=C, was not removed. It was considered that the ozone reaction is an electrophilic reaction, and the wet ozone should react with C=C with ease. The removal rate of PVP with rinsing was higher than that without rinsing. This result indicates that the reaction products remain on the Si wafer. However, in the novolak resin, there was no difference between with and without rinsing. It was considered that the main chain of the novolak resin was decomposed to gas by the reaction with wet ozone. In the FT-IR measurement of PVP, the peak intensity of C=O stretching of carboxylic acid increased with increasing wet ozone processing time. However, in the novolak resin, there was no difference between with and without rinsing. Moreover, the peak intensity of the C=O stretching of carboxylic acid did not increase with increasing wet ozone processing time after 10 s of wet ozone processing time. From the result of in situ FT-IR, in the removal of the novolak resin using wet ozone, the main chain of the novolak resin was decomposed, and the reaction products of the wet ozone and novolak resin (low-molecular-weight carboxylic acid) should change to CO2.

Development of an Environmentally Friendly Resist-Removal Process Using Wet Ozone

We investigated the removal of polymers with various chemical structures and the removal of ion-implanted resists using wet ozone. The removal rates of polymers that have carbon-carbon (C–C) double bonds in the main chain were high. The main chain of these polymers may be decomposed. The removal rates of polymers that have C–C double bonds in the side chain were low. The benzene ring in the side chain changes into carboxylic acid, so their ability to dissolve in water increased. The polymers without C–C double bonds were not removed. Removal of B and P ion-implanted resists became difficult with increasing acceleration energy of ions at implantation. The resist with plastic-deformation hardness that was twice as hard as that of nonimplanted resist should be removed similarly to nonimplanted resist. Using TOF-SIMS, we clarified that the molecule of cresol novolak resin was destroyed and carbonized by ion implantation.