Masao Watanabe | Hokkaido University (original) (raw)

Papers by Masao Watanabe

Transactions of the Japan Society of Mechanical Engineers Series B, 2004

Transactions of the Japan Society of Mechanical Engineers Series A, 2004

JAPANESE JOURNAL OF MULTIPHASE FLOW, 2011

Contribution of a toroidal vortex behind a bubble to its steady drag was experimentally investiga... more Contribution of a toroidal vortex behind a bubble to its steady drag was experimentally investigated. Bubble motion in eight different liquids were observed using high-speed photography. Photochromic dye was used to visualize the rear vortex structure. We clarified that the critical aspect ratio of bubble obtained previously in numerical simulations for the onset of the existence of the standing eddy and three-dimensional wake behind an oblate spheroid bubble corresponds well to our experimental results when the front aspect ratio is used. Non-dimensional steady drag on a bubble was found to have a linear relation with the front aspect ratio. It is also confirmed that the existence of standing eddy hardly changes the drag.

Transactions of the Japan Society of Mechanical Engineers Series B, 2007

Journal of Biomechanical Science and Engineering, 2007

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2007

We experimentally evaluate the drag coefficient for spherical and ellipsoidal clean bubbles risin... more We experimentally evaluate the drag coefficient for spherical and ellipsoidal clean bubbles rising steadily in liquids of low Morton number ranging from 10-11 to 10-8. Four different silicone oils and super purified water are used as liquids. The shapes and rising motion of bubbles are captured by using a still camera and a high-speed video camera, respectively. The degree of fore-aft asymmetric bubble shape is quantitatively evaluated using image processing. The experimentally obtained drag coefficients are compared with those for symmetric ellipsoidal bubbles obtained analytically by Moore [J. Fluid Mech. 23, 749 (1965)], and via numerical simulation by Blanco & Magnaudet [Phys. Fluids 7, 1265 (1995)]. The main conclusions are summarized as follows; (1) Moore's drag coefficient overestimates the experimentally obtained drag coefficient especially when bubble aspect ratio increases, (2) Blanco & Magnaudet's prediction of drag coefficients for bubbles with ellipsoidal shape are also valid for those with fore-aft asymmetric shape of corresponding aspect ratio.

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2006

Translational motions of bubbles with volume and shape oscillations were studied using high-speed... more Translational motions of bubbles with volume and shape oscillations were studied using high-speed photography. The volume oscillations of bubbles, which cause hydrodynamic interactions between two bubbles, were captured in detail. Bubbles of around resonant sizes were forced to oscillate in acoustic fields having frequency of 18.0 and 34.5 kHz, and amplitude ranging from 20 to 100 kPa. The recording rate of 125,000, 250,000 and 1000,000 frames per second were used in high-speed photography. Experimental results for the translation are compared to the previous theoretical model derived by Takahira (1992). This model takes into account the diffusion of vorticity from bubble surface, and is valid even for the translation of intermediate Reynolds number. The validity of the model is verified experimentally for bubbles having Reynolds number of the order of 10. The effect of shape deformations on the translation was also examined.

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2006

We have developed micro bubble generator which can control both bubble size and generation freque... more We have developed micro bubble generator which can control both bubble size and generation frequency independently and accurately, by using acoustic gas pressure wave. However, though, the mechanism of this generator has not been fully understood. We further investigated the role of the acoustic gas pressure wave and found the optimal pressure wave for a single micro bubble formation. We succeeded in forming a bubble, whose radius was ranging from 0.3 to 0.8 mm, with extremely small standard deviation of less than 1 micro meter. By analyzing images taken by high-speed photography, detachment of a bubble from a nozzle, especially shrinkage of a capillary bridge connecting a bubble and a nozzle, is investigated in detail. Force balance on a growing bubble is evaluated with the help of experimental data of time rate of both bubble radius and position of the center of mass of a bubble, by applying a spherical bubble formation model. As results, we find that with the decrease in gas pressure, the capillary bridge is sucked down into a nozzle and added mass force is exerted in the upward direction, both of which promote detachment of a bubble from a nozzle.

Transaction of the Visualization Society of Japan, 2007

... Toshiyuki Sanada Corresponding Author Contact Information , a , E-mail The Corresponding Auth... more ... Toshiyuki Sanada Corresponding Author Contact Information , a , E-mail The Corresponding Author , Minori Shirota a and Masao Watanabe a. ... We present the first experimental support for the existence of the standing eddy at the rear of the clean bubble, as predicted by a ...

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2007

Wake structure of clean bubble rising in quiescent silicone oil solution of photochromic dye is e... more Wake structure of clean bubble rising in quiescent silicone oil solution of photochromic dye is experimentally studied. A single bubble is generated, immediately after UV sheet light illuminates the part of the liquid just above the bubble generation nozzle in order to activate photochromic dye. Once the bubble passes across the colored part of the liquid, the bubble is accompanied by some portion of activated dye tracers; hence the flow structure in the rear of the single rising bubble is visualized. We capture stereo images of both wake structure and bubble motion. We study how wake structure changes with the increase in bubble size. We observe the stable axisymmetric wake structure, which is called `standing eddy' when bubble size is relatively small, and then wake structure becomes unstable and starts to oscillate with the increase in bubble size. With further increase in bubble size, a pair of streamwise vortices, which is called `double thread', is observed. We discuss in detail this transition from the steady wake to unsteady wake structure, especially double thread wake development and hairpin vortices shedding, in relation to the transition from rectilinear to spiral or zigzag bubble motions.

Progress in Multiphase Flow Research, 2006

The growth and collapse of cavitation bubble inside a high-speed droplet, which impacts on the so... more The growth and collapse of cavitation bubble inside a high-speed droplet, which impacts on the solid surface are investigated numerically, using Ghost Fluid Method with TVD-ENO-LLF to solve pressure propagation in two phase compressible flow. Upon the impact on the surface, strong compression wave is generated on the contact surface inside liquid droplet. This wave propagates upward to the free surface and is reflected normal to the surface as an expansion wave, which propagates downward. This expansion wave focuses inside liquid droplet, which results in the generation of low pressure region. We discuss the condition of cavitation bubble growth in this low pressure region, with the effects of thermal environment of liquid droplet taken into account. We evaluate the magnitude of the attainable pressure during bubble collapse, by solving equation of radial motion of single bubble with ambient pressure change, and compare this bubble collapsing pressure to the high-speed liquid droplet impact pressure in order to discuss the contribution of cavitation bubble to the erosion of solid surface.

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2008

A model for a bouncing of a bubble on free surface in super purified water is proposed. The model... more A model for a bouncing of a bubble on free surface in super purified water is proposed. The model is based on mass-spring system and energy conservation system. In order to describing the effect of the bubble and free surface motion in the model, we assume two springs connected in series. We also define that the initial kinetic energy when the bubble contacts with free surface is converted into the increase in surface energy when the rise velocity of the bubble is zero. From the two equations, the contact time which is also the half period of the oscillator is represented by the deformations and the approach velocity. An experiment is also performed to discuss the applicability of the model. Especially, the bubble motion and the free surface deformation are captured. The good agreement is found between the contact time given by images and that derived by the model. However if we consider only the free surface deformation effect, the estimated contact time becomes smaller than that of the model with both of the deformations. We thus conclude that both of the deformation effects are essential for the estimation of the system.

Diffusion and Defect Data Solid State Data Part B Solid State Phenomena, Mar 17, 2009

carbon-like layer "crust", and also that this crust is extremely difficult to d... more carbon-like layer "crust", and also that this crust is extremely difficult to dissolve with wet chemicals. In practice, a combination of dry plasma ashing and wet chemical removal is used to eliminate the photoresist. In this study, a novel photoresist stripping technique is proposed. We have improved wet vapor photoresist stripping technique (1) using the mixture of high-speed steam flow and purified water droplets. Relatively low pressure clean steam is mixed with purified water in the nozzle, and sprayed on a photoresist coated Si wafer. We have also developed a pre-treatment method in a chamber with keeping both temperature and humidity constant, in order to strip post ion-implanted photoresit. The most significant feature of this proposed technique is that we use water only; hence we are able to strip photoresist without chemicals. We first discuss the stripping performance of the proposed technique in the various photoresist coating conditions based on the microscopic observation of the stripped wafer surfaces. And then the effects of pre-treatment in a chamber with keeping both temperature and humidity constant are investigated using SEM observation. Finally, we show examples of stripping of ion-implanted photoresist. Experiments A schematic diagram of experimental setup is shown in Figure 1. In this study, steam and droplet are mixed in a nozzle and then sprayed on a wafer. Using this spray, we successfully strip the photoresist. We first investigate the stripping performance of the proposed technique in the different photoresist coating conditions. Especially the photoresist left on the edge of SiO 2 was carefully observed using a digital microscopy. The conditions are listed in Table I. In this experiment, no ion-implant was used.

We study experimentally the motion and the wake of a pair of non-spherical bubbles rising side by... more We study experimentally the motion and the wake of a pair of non-spherical bubbles rising side by side at high Reynolds number. The motions of bubbles were recorded by a high-speed video camera. The wakes of bubbles were visualized by using photochromic dye that is colored with UV light irradiation. We observed vortex separation from bubbles' rear surface at their collision, resulting in a great decrease in rising velocity of bubbles. Applying an existing model for spherical bubble-wall interaction by taking into account non-spherical effects on translational velocities and characteristics at the collision, we found that the revised model accurately describes the trajectory of a pair of bouncing-approaching bubbles. On the contrary, in the case of bubbles bouncing repeatedly, the effect of wake instability of a pair of bubbles on the motion of bubbles rather than the effect of bubble-bubble interaction dominates. We clarify that the vortex separation is strongly related with vertical velocity fluctuation.

Diffusion and Defect Data Solid State Data Part B Solid State Phenomena, 2009

A novel cleaning technique using steam-water mixed spray is proposed. Relatively low-pressure sup... more A novel cleaning technique using steam-water mixed spray is proposed. Relatively low-pressure super-purified steam (0.1 MPa -0.2 MPa) is mixed with super-purified water in a nozzle, and then sprayed on a silicon wafer surface, which is located at approximately 10 mm from the nozzle. The most striking result of this proposed technique is that we are able to clean a wafer surface, i.e., to eliminate fine particles, without using any chemicals. We investigated the cleaning performance of the proposed technique, and confirm the validity and usefulness. We arrived at the idea that water droplet impact in steam is enormously larger than that in air since the droplet kinetic energy reduction in steam is much less than that in air, mainly due to condensation. For this reason, we numerically studied the dynamics of a water droplet impact on a water thin film on a solid surface. We discuss both generation and propagation of the shock wave, which plays a significant role in cleaning, inside both water droplet and water thin film upon the impact.

We experimentally observed the wake structure behind a rising clean bubble by using silicon oil s... more We experimentally observed the wake structure behind a rising clean bubble by using silicon oil solution of photochromic dye. Clean bubble condition was realized since both the dye and the silicon oil are non-polar. A single bubble was generated just below a colored region where the dye was activated by UV sheet light illumination. Once the bubble passed the colored part of the liquid, the bubble was accompanied by some portion of activated dye. Hence the flow structure in the rear of the single rising bubble was visualized. In this visualization method, we are able to distinguish the liquid portion trapped behind the bubble from the non-colored surrounding liquid that flows in the colored trapped portion. We precisely controlled the size of the bubble in order to observe how the size of the toroidal vortex behind a bubble evolves and the axial symmetry breaks. The relation between the in-flow of the surrounding liquid into the toroidal vortex and the bubble motion was studied in detail.

九州大学工学紀要, Dec 1, 1999

Abstract; The behavior of millimeter and submillirneter sized bubbles generated by a single nozzl... more Abstract; The behavior of millimeter and submillirneter sized bubbles generated by a single nozzle in the stagnant water, and the flow fields around bubbles are investigated experimentally. The ranges of bubble diameters and Reynolds numbers used are ...

Solid State Phenomena, May 22, 2012

ABSTRACT We performed two experiments on resist-coated wafers. In the measurement of the resist-w... more ABSTRACT We performed two experiments on resist-coated wafers. In the measurement of the resist-wafer adhesivity, we confirmed that it is significantly increased by an HMDS layer in between. In the resist-removal experiment using steam-water mixed spray, we found that the area of resist removal is limited within the area of spray application if HMDS is used, otherwise the former can be larger than the latter. These results suggest that the resist removal from a wafer surface by steam-water mixed spray is essentially a peel-off process.

Transactions of the Japan Society of Mechanical Engineers Series B, 2004

Transactions of the Japan Society of Mechanical Engineers Series A, 2004

JAPANESE JOURNAL OF MULTIPHASE FLOW, 2011

Contribution of a toroidal vortex behind a bubble to its steady drag was experimentally investiga... more Contribution of a toroidal vortex behind a bubble to its steady drag was experimentally investigated. Bubble motion in eight different liquids were observed using high-speed photography. Photochromic dye was used to visualize the rear vortex structure. We clarified that the critical aspect ratio of bubble obtained previously in numerical simulations for the onset of the existence of the standing eddy and three-dimensional wake behind an oblate spheroid bubble corresponds well to our experimental results when the front aspect ratio is used. Non-dimensional steady drag on a bubble was found to have a linear relation with the front aspect ratio. It is also confirmed that the existence of standing eddy hardly changes the drag.

Transactions of the Japan Society of Mechanical Engineers Series B, 2007

Journal of Biomechanical Science and Engineering, 2007

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2007

We experimentally evaluate the drag coefficient for spherical and ellipsoidal clean bubbles risin... more We experimentally evaluate the drag coefficient for spherical and ellipsoidal clean bubbles rising steadily in liquids of low Morton number ranging from 10-11 to 10-8. Four different silicone oils and super purified water are used as liquids. The shapes and rising motion of bubbles are captured by using a still camera and a high-speed video camera, respectively. The degree of fore-aft asymmetric bubble shape is quantitatively evaluated using image processing. The experimentally obtained drag coefficients are compared with those for symmetric ellipsoidal bubbles obtained analytically by Moore [J. Fluid Mech. 23, 749 (1965)], and via numerical simulation by Blanco & Magnaudet [Phys. Fluids 7, 1265 (1995)]. The main conclusions are summarized as follows; (1) Moore's drag coefficient overestimates the experimentally obtained drag coefficient especially when bubble aspect ratio increases, (2) Blanco & Magnaudet's prediction of drag coefficients for bubbles with ellipsoidal shape are also valid for those with fore-aft asymmetric shape of corresponding aspect ratio.

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2006

Translational motions of bubbles with volume and shape oscillations were studied using high-speed... more Translational motions of bubbles with volume and shape oscillations were studied using high-speed photography. The volume oscillations of bubbles, which cause hydrodynamic interactions between two bubbles, were captured in detail. Bubbles of around resonant sizes were forced to oscillate in acoustic fields having frequency of 18.0 and 34.5 kHz, and amplitude ranging from 20 to 100 kPa. The recording rate of 125,000, 250,000 and 1000,000 frames per second were used in high-speed photography. Experimental results for the translation are compared to the previous theoretical model derived by Takahira (1992). This model takes into account the diffusion of vorticity from bubble surface, and is valid even for the translation of intermediate Reynolds number. The validity of the model is verified experimentally for bubbles having Reynolds number of the order of 10. The effect of shape deformations on the translation was also examined.

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2006

We have developed micro bubble generator which can control both bubble size and generation freque... more We have developed micro bubble generator which can control both bubble size and generation frequency independently and accurately, by using acoustic gas pressure wave. However, though, the mechanism of this generator has not been fully understood. We further investigated the role of the acoustic gas pressure wave and found the optimal pressure wave for a single micro bubble formation. We succeeded in forming a bubble, whose radius was ranging from 0.3 to 0.8 mm, with extremely small standard deviation of less than 1 micro meter. By analyzing images taken by high-speed photography, detachment of a bubble from a nozzle, especially shrinkage of a capillary bridge connecting a bubble and a nozzle, is investigated in detail. Force balance on a growing bubble is evaluated with the help of experimental data of time rate of both bubble radius and position of the center of mass of a bubble, by applying a spherical bubble formation model. As results, we find that with the decrease in gas pressure, the capillary bridge is sucked down into a nozzle and added mass force is exerted in the upward direction, both of which promote detachment of a bubble from a nozzle.

Transaction of the Visualization Society of Japan, 2007

... Toshiyuki Sanada Corresponding Author Contact Information , a , E-mail The Corresponding Auth... more ... Toshiyuki Sanada Corresponding Author Contact Information , a , E-mail The Corresponding Author , Minori Shirota a and Masao Watanabe a. ... We present the first experimental support for the existence of the standing eddy at the rear of the clean bubble, as predicted by a ...

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2007

Wake structure of clean bubble rising in quiescent silicone oil solution of photochromic dye is e... more Wake structure of clean bubble rising in quiescent silicone oil solution of photochromic dye is experimentally studied. A single bubble is generated, immediately after UV sheet light illuminates the part of the liquid just above the bubble generation nozzle in order to activate photochromic dye. Once the bubble passes across the colored part of the liquid, the bubble is accompanied by some portion of activated dye tracers; hence the flow structure in the rear of the single rising bubble is visualized. We capture stereo images of both wake structure and bubble motion. We study how wake structure changes with the increase in bubble size. We observe the stable axisymmetric wake structure, which is called `standing eddy' when bubble size is relatively small, and then wake structure becomes unstable and starts to oscillate with the increase in bubble size. With further increase in bubble size, a pair of streamwise vortices, which is called `double thread', is observed. We discuss in detail this transition from the steady wake to unsteady wake structure, especially double thread wake development and hairpin vortices shedding, in relation to the transition from rectilinear to spiral or zigzag bubble motions.

Progress in Multiphase Flow Research, 2006

The growth and collapse of cavitation bubble inside a high-speed droplet, which impacts on the so... more The growth and collapse of cavitation bubble inside a high-speed droplet, which impacts on the solid surface are investigated numerically, using Ghost Fluid Method with TVD-ENO-LLF to solve pressure propagation in two phase compressible flow. Upon the impact on the surface, strong compression wave is generated on the contact surface inside liquid droplet. This wave propagates upward to the free surface and is reflected normal to the surface as an expansion wave, which propagates downward. This expansion wave focuses inside liquid droplet, which results in the generation of low pressure region. We discuss the condition of cavitation bubble growth in this low pressure region, with the effects of thermal environment of liquid droplet taken into account. We evaluate the magnitude of the attainable pressure during bubble collapse, by solving equation of radial motion of single bubble with ambient pressure change, and compare this bubble collapsing pressure to the high-speed liquid droplet impact pressure in order to discuss the contribution of cavitation bubble to the erosion of solid surface.

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2008

A model for a bouncing of a bubble on free surface in super purified water is proposed. The model... more A model for a bouncing of a bubble on free surface in super purified water is proposed. The model is based on mass-spring system and energy conservation system. In order to describing the effect of the bubble and free surface motion in the model, we assume two springs connected in series. We also define that the initial kinetic energy when the bubble contacts with free surface is converted into the increase in surface energy when the rise velocity of the bubble is zero. From the two equations, the contact time which is also the half period of the oscillator is represented by the deformations and the approach velocity. An experiment is also performed to discuss the applicability of the model. Especially, the bubble motion and the free surface deformation are captured. The good agreement is found between the contact time given by images and that derived by the model. However if we consider only the free surface deformation effect, the estimated contact time becomes smaller than that of the model with both of the deformations. We thus conclude that both of the deformation effects are essential for the estimation of the system.

Diffusion and Defect Data Solid State Data Part B Solid State Phenomena, Mar 17, 2009

carbon-like layer "crust", and also that this crust is extremely difficult to d... more carbon-like layer "crust", and also that this crust is extremely difficult to dissolve with wet chemicals. In practice, a combination of dry plasma ashing and wet chemical removal is used to eliminate the photoresist. In this study, a novel photoresist stripping technique is proposed. We have improved wet vapor photoresist stripping technique (1) using the mixture of high-speed steam flow and purified water droplets. Relatively low pressure clean steam is mixed with purified water in the nozzle, and sprayed on a photoresist coated Si wafer. We have also developed a pre-treatment method in a chamber with keeping both temperature and humidity constant, in order to strip post ion-implanted photoresit. The most significant feature of this proposed technique is that we use water only; hence we are able to strip photoresist without chemicals. We first discuss the stripping performance of the proposed technique in the various photoresist coating conditions based on the microscopic observation of the stripped wafer surfaces. And then the effects of pre-treatment in a chamber with keeping both temperature and humidity constant are investigated using SEM observation. Finally, we show examples of stripping of ion-implanted photoresist. Experiments A schematic diagram of experimental setup is shown in Figure 1. In this study, steam and droplet are mixed in a nozzle and then sprayed on a wafer. Using this spray, we successfully strip the photoresist. We first investigate the stripping performance of the proposed technique in the different photoresist coating conditions. Especially the photoresist left on the edge of SiO 2 was carefully observed using a digital microscopy. The conditions are listed in Table I. In this experiment, no ion-implant was used.

We study experimentally the motion and the wake of a pair of non-spherical bubbles rising side by... more We study experimentally the motion and the wake of a pair of non-spherical bubbles rising side by side at high Reynolds number. The motions of bubbles were recorded by a high-speed video camera. The wakes of bubbles were visualized by using photochromic dye that is colored with UV light irradiation. We observed vortex separation from bubbles' rear surface at their collision, resulting in a great decrease in rising velocity of bubbles. Applying an existing model for spherical bubble-wall interaction by taking into account non-spherical effects on translational velocities and characteristics at the collision, we found that the revised model accurately describes the trajectory of a pair of bouncing-approaching bubbles. On the contrary, in the case of bubbles bouncing repeatedly, the effect of wake instability of a pair of bubbles on the motion of bubbles rather than the effect of bubble-bubble interaction dominates. We clarify that the vortex separation is strongly related with vertical velocity fluctuation.

Diffusion and Defect Data Solid State Data Part B Solid State Phenomena, 2009

A novel cleaning technique using steam-water mixed spray is proposed. Relatively low-pressure sup... more A novel cleaning technique using steam-water mixed spray is proposed. Relatively low-pressure super-purified steam (0.1 MPa -0.2 MPa) is mixed with super-purified water in a nozzle, and then sprayed on a silicon wafer surface, which is located at approximately 10 mm from the nozzle. The most striking result of this proposed technique is that we are able to clean a wafer surface, i.e., to eliminate fine particles, without using any chemicals. We investigated the cleaning performance of the proposed technique, and confirm the validity and usefulness. We arrived at the idea that water droplet impact in steam is enormously larger than that in air since the droplet kinetic energy reduction in steam is much less than that in air, mainly due to condensation. For this reason, we numerically studied the dynamics of a water droplet impact on a water thin film on a solid surface. We discuss both generation and propagation of the shock wave, which plays a significant role in cleaning, inside both water droplet and water thin film upon the impact.

We experimentally observed the wake structure behind a rising clean bubble by using silicon oil s... more We experimentally observed the wake structure behind a rising clean bubble by using silicon oil solution of photochromic dye. Clean bubble condition was realized since both the dye and the silicon oil are non-polar. A single bubble was generated just below a colored region where the dye was activated by UV sheet light illumination. Once the bubble passed the colored part of the liquid, the bubble was accompanied by some portion of activated dye. Hence the flow structure in the rear of the single rising bubble was visualized. In this visualization method, we are able to distinguish the liquid portion trapped behind the bubble from the non-colored surrounding liquid that flows in the colored trapped portion. We precisely controlled the size of the bubble in order to observe how the size of the toroidal vortex behind a bubble evolves and the axial symmetry breaks. The relation between the in-flow of the surrounding liquid into the toroidal vortex and the bubble motion was studied in detail.

九州大学工学紀要, Dec 1, 1999

Abstract; The behavior of millimeter and submillirneter sized bubbles generated by a single nozzl... more Abstract; The behavior of millimeter and submillirneter sized bubbles generated by a single nozzle in the stagnant water, and the flow fields around bubbles are investigated experimentally. The ranges of bubble diameters and Reynolds numbers used are ...

Solid State Phenomena, May 22, 2012

ABSTRACT We performed two experiments on resist-coated wafers. In the measurement of the resist-w... more ABSTRACT We performed two experiments on resist-coated wafers. In the measurement of the resist-wafer adhesivity, we confirmed that it is significantly increased by an HMDS layer in between. In the resist-removal experiment using steam-water mixed spray, we found that the area of resist removal is limited within the area of spray application if HMDS is used, otherwise the former can be larger than the latter. These results suggest that the resist removal from a wafer surface by steam-water mixed spray is essentially a peel-off process.