Plasma Chemical Vaporization Machining Research Articles

High-precision finishing method for narrow-groove channel-cut crystal x-ray monochromator using plasma chemical vaporization machining with wire electrode.

A channel-cut crystal monochromator (CCM) is a popular and powerful device for producing monochromatic x-ray beams with extreme angular stability at a nano-radian level. Narrowing the groove width of CCMs has various benefits; for example, it is made possible to design more compact CCMs with an equivalent working energy range and to reduce the optical delay and the amount of beam shift, enhancing compatibility with various experimental techniques. An obstacle to the use of narrow-groove CCMs is the lack of a high-precision finishing method for the inner-wall reflecting surfaces, which imposes the distortion of x-ray wavefronts and spectral purity. We propose a new, damage-free surface-finishing method for silicon CCMs with a narrow groove of 1mm or less with a localized etching technique using plasma generated with a wire electrode of 50 µm diameter under atmospheric pressure. Repeating plasma-on and plasma-off periods with a pulsed power supply, we reduce the concentration of reaction products through self-diffusion during the plasma-off periods and minimize the redeposition of the products on the processed surface that deteriorates the surface roughness. Under optimized conditions, we processed a CCM with a groove width of 1.2mm, which has uniform reflection profiles and a nearly ideal reflectivity behavior for coherent monochromatic x rays.

(Invited) High-Speed Plasma Etching of SiC Wafer Toward Backside Thinning

Semiconductor power devices are necessary to convert electric voltage, current, and frequency for efficient electrical energy use. Although most of them are now fabricated using silicon (Si) semiconductors, wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN), which have a larger bandgap than Si, are attracting attention for efficient conversion improvement. Continuous research and development of crystal growth, crystal evaluation, and device improvement technologies over many years have led to the commercialization of SiC transistors and inverters. One of the issues of SiC power devices is their comparatively higher cost than Si power devices; therefore, reducing the cost is essential for their wide application. Not only high quality and low-cost crystal growth technology is essential for SiC power devices but also a low-cost processing technique. Most power transistors have a vertical structure. Device wafer substrate thickness must be thin to minimize onstate resistance; however, there is a limiting thickness necessary for handling a wafer during device processing. Therefore, wafer thickness must be reduced from a backside after devices are fabricated on it. Although a mechanical process such as grinding is suitable for the backside thinning of silicon, it is costly for SiC because of extended processing time due to its hardness and the high wear rate of an expensive diamond grinding wheel. Additionally, the process leaves subsurface damage on a processed surface, decreasing device chip strength and reliability.We investigated the applications of plasma chemical vaporization machining (PCVM), a plasma etching method using high-pressure plasma, to the SiC backside thinning process. In conventional plasma etching for device fabrication, reactive ion etching (RIE) is employed to ensure anisotropy, an important requirement for pattern transferability. In the RIE process, applied pressure cannot be increased because the mean-free path of the gas molecules must be long enough for ion acceleration. Owing to the limited amount of gas molecules contributing to the reaction, the processing rate is limited to approximately 1 μm/min. PCVM is a chemical etching process in which neutral radicals are employed as the active species. Although it lacks anisotropy, an etching rate that is difficult to achieve with RIE can be attained by increasing working pressure. We developed a wafer-sized electrode, i.e., an electrode with the same surface geometry as a wafer, with many gas supply holes fabricated for wafer-level thinning. It was found that the SF6 plasma generated over the entire wafer surface by reducing the working pressure from atmospheric pressure to a few tenths of the atmospheric pressure without helium dilution. The results of the experiments showed that the thickness of the entire 2-inch 4H-SiC (0001) wafer could be reduced at a high removal rate of 15 μm/min by increasing rf power. The removal rate mainly depended on power density and was relatively insensitive to the processing parameters such as processing gap and gas flow rate. In addition, it was discovered that almost the same removal rate could be achieved with rf power being proportional to the area of the wafer even if the wafer diameter was increased. It was demonstrated that the thickness of the commercially available two-inch wafer could be thinned to approximately 100 μm by 20-min plasma etching. Furthermore, a commercially available SiC MOSFET chip was used for a backside thinning experiment to evaluate the influence of plasma irradiation on the MOS interface using the C–V characteristic measurements. Although the deterioration of the SiO2/SiC interfacial properties due to ultraviolet (UV) irradiation was reported, there was no change in the C–V characteristic before and after exposure to SF6 plasma. The constant C–V characteristic might be because the amount of UV light reaching from the backside to frontside surface is small owing to the thin penetration depth.PCVM for the backside thinning of a SiC wafer contributes to cost reduction owing to reduction in processing time and the nonuse of an expensive diamond grinding wheel. It also improves the reliability of fabricated devices because it leaves no subsurface damage on the backside of a wafer, resulting in the wide-spread utilization of low-power consumption SiC power devices for a sustainable society.

High-resolution micro channel-cut crystal monochromator processed by plasma chemical vaporization machining for a reflection self-seeded X-ray free-electron laser.

A high-resolution micro channel-cut crystal monochromator (µCCM) composed of an Si(220) crystal is developed for the purpose of narrowing the bandwidth of a reflection self-seeded X-ray free-electron laser. Subsurface damage on the monochromator, which distorts the wavefront and broadens the bandwidth of the monochromatic seed beam, was removed by using a plasma etching technique. High diffraction performance of the monochromator was confirmed through evaluation with coherent X-rays. Reflection self-seeding operation was tested with the Si(220) µCCM at SPring-8 Angstrom Compact free-electron laser. A narrow average bandwidth of 0.6 eV, which is five times narrower than the value previously reported [I. Inoue et al., Nat. Photonics13, 319 (2019)10.1038/s41566-019-0365-y], was successfully obtained at 9 keV. The narrow-band X-ray beams with high intensity realized in this study will further expand the capabilities of X-ray free-electron lasers.

Cause of Etch Pits during the High Speed Plasma Etching of Silicon Carbide and an Approach to Reduce their Size

To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin silicon carbide (SiC) wafers with a high removal rate by conventional mechanical processing because their hardness and brittleness cause cracks and chips during thinning. Therefore, the authors have attempted to thin SiC wafers using plasma chemical vaporization machining (PCVM), which is plasma etching using high-pressure plasma. PCVM has a high removal rate because of the high radical density in the high-pressure plasma, and it does not form a damaged layer on the processed surface because of the low ion energy. The authors have already achieved a very high removal rate of 15.6 μm/min by PCVM. However, many etch pits were generated on the wafer during PCVM in these high-speed machining conditions. Therefore, this study, using molten potassium hydroxide (KOH) etching, investigated the cause of such etch pits and found that they may stem from threading screw dislocation in the wafers. In addition, this research considered a process for reducing an etch pit size and succeeded in doing so by controlling wafer temperature.

Etching Characteristics of Quartz Crystal Wafers Using Argon-Based Atmospheric Pressure CF4 Plasma Stabilized by Ethanol Addition

Atmospheric-pressure plasma chemical vaporization machining (AP-PCVM) using helium as a carrier gas to achieve uniform thickness of quartz crystal wafers has been practically applied to the mass production of high-performance crystal units. However, because of the high cost and limited supply of helium, the proposed use of argon instead of helium has garnered interest. Argon plasma at atmospheric pressure tends to become unstable, but it has been reported that the addition of a small amount of ethanol makes it possible to generate a stable and uniformly spread glow discharge atmospheric-pressure argon plasma. In this study, an AP-PCVM experiment was conducted on quartz crystal wafers using an argon-ethanol mixture gas as the carrier gas and CF4 and O2 as process gases. A uniform, stable glow discharge plasma was generated by applying the ethanol-containing process gas, and satisfactory removal characteristics for correcting the thickness deviation of a quartz crystal wafer were obtained.

Surface Finishing Method Using Plasma Chemical Vaporization Machining for Narrow Channel Walls of X-Ray Crystal Monochromators

Channel-cut Si crystals are useful optical devices for providing monochromatic X-ray beams with extreme angular stability. Owing to difficulties in the high-precision surface finishing of narrow-channel inner walls of the crystals, typical channel-cut crystals have considerable residual subsurface crystal damage and/or roughness on their channel-wall reflection surfaces that decrease intensity and distort the wavefronts of the reflected X-rays. This paper proposes a high-precision surface finishing method for the narrow-channel inner walls based on plasma chemical vaporization machining, which is a local etching technique using atmospheric-pressure plasma. Cylinder- and nozzle-shaped electrodes were designed for channel widths of more than 5 and 3 mm, respectively. We optimized process conditions for each electrode using commercial Si wafers, and obtained a removal depth of 10 μm with a surface flatness and roughness of less than 1 μm and 1 nmRMS, respectively, which should allow the damaged layers to be fully removed while maintaining the wavefront of coherent X-rays.

X-ray optics for advanced ultrafast pump-probe X-ray experiments at SACLA.

X-ray optics were implemented for advanced ultrafast X-ray experiments with different techniques at the hard X-ray beamline BL3 of SPring-8 Ångstrom Compact free-electron LAser. A double channel-cut crystal monochromator (DCCM) and compound refractive lenses (CRLs) were installed to tailor the beam conditions. These X-ray optics can work simultaneously with an arrival-timing monitor that compensates for timing jitter and drift. Inner-walls of channel-cut crystals (CCs) in the DCCM were processed by plasma chemical vaporization machining to remove crystallographic damage. Four-bounced reflection profiles of the CCs were investigated and excellent diffraction qualities were achieved. The use of CRLs enabled two-dimensional X-ray focusing with a spot size of ∼1.5 µm × 1.5 µm full width at half-maximum, while keeping reasonable throughputs for a wide photon energy range of 5-15 keV.

Review of several precision finishing processes for optics manufacturing

The ultrasmooth optical components with atomic-order surface roughness and nanometre-level shape accuracy are in immense demand with the rapid advancement of modern optical technology. In recent years, aspherical and free-form surfaces are gaining more interest for its favorable properties. Moreover, the new optical materials with immensely enhanced mechanical properties are being developed to meet the stringent requirements of modern optics. Fabrication of complex-shaped ultrasmooth optical components becomes a significant challenge as conventional finishing techniques are unable to machine aspherical or free-form surfaces precisely. This situation demands some highly deterministic finishing processes. Mostly, the optical components are fabricated by shaping or pre-finishing methods followed by final finishing processes. In the shaping or pre-finishing methods, the rigid abrasive tools are used to remove the material at an enhanced rate and near net shape of the elements can be attained. Surface finish and shape accuracy can also be improved to some extent. Owing to the presence of residual finishing marks generated by shaping methods, the application of the components is limited to the infrared (IR) optics. Final finishing processes include more deterministic and flexible polishing techniques that can achieve desired surface finish, figure accuracy and surface integrity to make it suitable for shorter wavelength applications. In recent years, single point diamond turning, precision grinding, plasma chemical vaporization machining and magnetorheological fluid-based finishing are widely used for fabricating ultrasmooth optics. In this article, principle, mechanism of material removal and applicability of the aforementioned precision finishing processes to different materials are discussed.

Next-Generation, Super-Hard-to-Process Substrates and Their High-Efficiency Machining Process Technologies Used to Create Innovative Devices

SiC, GaN, and diamond are known as super-hard-to-process substrate for next-generation green devices. In this paper, we report on some breakthrough in developing highly efficient processing for such hard-to-process materials, for which we propose improvements in conventional processing, and innovative processing. As part of our project, we developed a “dilatancy pad®” that can efficiently produce high-quality surfaces as well as a high-rigidity, high-speed and high-pressure processing machine. We also designed and prototyped “plasma fusion CMP®,” which is an innovative processing technology fusing CMP (Chemical Mechanical Polishing) with P-CVM (Plasma Chemical Vaporization Machining) to machine super-hard diamond substrates that are considered indispensable for future devices. Before the advent of “singularities” by 2045, super-hard-to-process substrates and ultra-precision polishing technology will become more and more essential.

Optimization of Gas Composition Used in Plasma Chemical Vaporization Machining for Figuring of Reaction-Sintered Silicon Carbide with Low Surface Roughness

In recent years, reaction-sintered silicon carbide (RS-SiC) has been of interest in many engineering fields because of its excellent properties, such as its light weight, high rigidity, high heat conductance and low coefficient of thermal expansion. However, RS-SiC is difficult to machine owing to its high hardness and chemical inertness and because it contains multiple components. To overcome the problem of the poor machinability of RS-SiC in conventional machining, the application of atmospheric-pressure plasma chemical vaporization machining (AP-PCVM) to RS-SiC was proposed. As a highly efficient and damage-free figuring technique, AP-PCVM has been widely applied for the figuring of single-component materials, such as Si, SiC, quartz crystal wafers, and so forth. However, it has not been applied to RS-SiC since it is composed of multiple components. In this study, we investigated the AP-PCVM etching characteristics for RS-SiC by optimizing the gas composition. It was found that the different etching rates of the different components led to a large surface roughness. A smooth surface was obtained by applying the optimum gas composition, for which the etching rate of the Si component was equal to that of the SiC component.

Atmospheric, Non-Contact and High Speed Electro Chemical Machining Processes for X-Ray Optics

High resolution X-ray focusing optics is critical component in many spatially resolved techniques at many synchrotron facilities, such as micro X-ray fluorescence, micro-diffraction, and micro-spectroscopy. In order for these optics to achieve modern capability goals, they must embody various key performance attributes such as a minimum in spatial resolution, a maximum in focusing efficiency, a practical working distance (no more than a few meters), and ideally robust achromaticity (negligible photon energy dependence). The state of the art in X-ray optics encompasses, among others, diffractive zone plate optics, Kirkpatrick-Baez (K-B) mirrors, and compound refractive lenses (CRLs). Among these, only K-B mirrors provide highly efficient collection of X-ray photons and essentially perfect achromaticity, but require elliptical mirrors of exceptionally precise figure and placement, as well as sub-nanometer smoothness1. In attempting to identify potential advances in X-ray optics beyond this state of the art, one promising solution is the design of single-bounce, axially symmetric mirror optics with parabolic inner profiles capable of focusing x-rays simultaneously in two orthogonal directions, which may overcome the long focal length limitation of KB mirrors. Manufacture of such precise optics as these novel one-bounce mirrors or the traditional K-B mirrors requires highly advanced surface finishing techniques. Silicon is mostly used in this application due to its low CTE, low thermal deformation, low z, high reflectivity, and low radiation adsorption. The conventional manufacturing approaches used to prepare aspherical, low roughness, and high-z coated silicon mirrors, included Ion Beam Figuring, Elastic Emission Machining (EEM), Plasma Machining, Lapping/Polishing2,3. Of these techniques the Plasma and Ion Beam approaches require vacuum atmosphere for processing limiting the size of the components that can be produced. Meanwhile, EEM can achieve better final finishes (up to 1 A) under atmospheric, non-contact conditions, however it is several orders of magnitude slower (0.1 to 0.001 µm/min) than these approaches. Furthermore, contact machining techniques like Lapping/Polishing tend to lead to surface defects that must be removed prior to mirror usage. Therefore, the design of low cost/high speed machining and polishing systems that can form high resolution x-ray focusing optics over large mirror areas is critical for the formation of next generation of x-ray optics. This paper will discuss ongoing efforts by Faraday to design an atmospheric, non-contact, low cost/high speed electrochemical machining process to produce next-generation ellipsoidal x-ray optics via a scalable pulse-reverse electrochemical manufacturing approach. Unlike conventional electrochemical surface finishing processes, the pulse-reverse process does not require low conductivity/high viscosity electrolytes or the addition of hazardous chemical species (like HF) to remove the oxide film associated with electropolishing of passive and strongly passive materials like Si. This paper will focus on the potential of pulse/pulse reverse electrofinishing process to produce optics such as Kirkpatrick-Baez mirrors and compound refractive lenses for X-ray optic technologies being used at synchrotron facilities. In particular, this talk will discuss fundamental processing techniques and the performance observed in ongoing studies. Initial trials of atmospheric, non-contact process demonstrated a material removal rate of 40 µm/h which is 100 times faster than currently used EEM technique. Acknowledgement This material is based upon ‎work supported by the Department of Energy under ‎Award No‎. ‎DE‎-‎ SC0015201. References S. Matsuyama., et.al., “Textbook for hard X-ray focusing with Kirkpatrick-Baez optics.” Online resource: http://cheiron2009.spring8.or.jp/images/PDF/Practicals?16_29XLU.pdf. Accessed 15 Oct 2015. H. Takino., et.al., “ Ultraprecision Machining of Optical Surfaces.” Nikon Corporation.Y. Mori., et.al., “Development of plasma chemical vaporization machining and elastic emission machining systems for coherent X-ray optics.” SPIE 4501, 2001.

Damage-free finishing of CVD-SiC by a combination of dry plasma etching and plasma-assisted polishing

To realize the damage-free finishing of CVD-SiC substrates, which are used as materials for space telescope mirrors and glass lens molds, plasma chemical vaporization machining (PCVM) and plasma-assisted polishing (PAP) were combined. In this study, the properties of such CVD-SiC substrates, including their surface morphology, composition and crystalline orientation, were investigated. Lapping using diamond abrasives and conventional chemical mechanical polishing (CMP) using CeO2 slurry were conducted for comparison with the proposed atmospheric-pressure-plasma-based finishing process. Many scratches and a subsurface damage (SSD) layer were formed by the diamond lapping of CVD-SiC. Conventional CMP using CeO2 slurry was conducted for the damage-free finishing of CVD-SiC. However, the polishing efficiency was very low. In the proposed process, PCVM, which is a noncontact dry etching process, was performed to remove the SSD layer while PAP, which combines plasma modification and soft abrasive polishing, was performed for damage-free surface finishing. PCVM was conducted on a diamond-lapped CVD-SiC surface. After PCVM for a short duration of 5min, the scratches and SSD layer formed by lapping were completely removed, although the surface roughness was slightly increased. PAP using a resin-bonded CeO2 grindstone was conducted to decrease the surface roughness of CVD-SiC processed by diamond lapping and PCVM for 5min, for which a loose-held-type grindstone was demonstrated to be very useful. A flat and scratch-free surface with an rms roughness of 0.6nm was obtained after PAP finishing.

Preliminary study on atmospheric-pressure plasma-based chemical dry figuring and finishing of reaction-sintered silicon carbide

Reaction-sintered silicon carbide (RS-SiC) is a research focus in the field of optical manufacturing. Atmospheric-pressure plasma-based chemical dry figuring and finishing, which consist of plasma chemical vaporization machining (PCVM) and plasma-assisted polishing (PAP), were applied to improve material removal rate (MRR) in rapid figuring and ameliorate surface quality in fine finishing. Through observing the processed RS-SiC sample in PCVM by scanning white-light interferometer (SWLI), the calculated peak-MRR and volume-MRR were 0.533 μm/min and 2.78×10−3 mm3/min, respectively. The comparisons of surface roughness and morphology of the RS-SiC samples before and after PCVM were obtained by the scanning electron microscope and atomic force microscope. It could be found that the processed RS-SiC surface was deteriorated with surface roughness rms 382.116 nm. The evaluations of surface quality of the processed RS-SiC sample in PAP corresponding to different collocations of autorotation speed and revolution speed were obtained by SWLI measurement. The optimal surface roughness rms of the processed RS-SiC sample in PAP was 2.186 nm. There were no subsurface damages, scratches, or residual stresses on the processed sample in PAP. The results indicate that parameters in PAP should be strictly selected, and the optimal parameters can simultaneously obtain high MRR and smooth surface.

Development of speckle-free channel-cut crystal optics using plasma chemical vaporization machining for coherent x-ray applications.

We have developed a method of fabricating speckle-free channel-cut crystal optics with plasma chemical vaporization machining, an etching method using atmospheric-pressure plasma, for coherent X-ray applications. We investigated the etching characteristics to silicon crystals and achieved a small surface roughness of less than 1 nm rms at a removal depth of >10 μm, which satisfies the requirements for eliminating subsurface damage while suppressing diffuse scattering from rough surfaces. We applied this method for fabricating channel-cut Si(220) crystals for a hard X-ray split-and-delay optical system and confirmed that the crystals provided speckle-free reflection profiles under coherent X-ray illumination.

Wavelength-tunable split-and-delay optical system for hard X-ray free-electron lasers.

We developed a hard X-ray split-and-delay optical (SDO) system based on Bragg diffraction in crystal optics for generating two split pulses with a variable temporal separation. To achieve both high stability and operational flexibility, the SDO system was designed to include variable-delay and fixed-delay branches. As key optical elements, we fabricated high quality thin crystals and channel-cut crystals by applying the plasma chemical vaporization machining technique. The SDO system using Si(220) crystals covered a photon energy range of 6.5-11.5keV and a delay time range from a negative value to > 45 ps over the photon energy range (up to 220 ps at 6.5 keV). A simple alignment method for realizing a spatial overlap between the split pulses was developed. The SDO system was tested at a SPring-8 beamline in combination with a focusing system. We achieved an excellent overlap with an accuracy of 30 nm for ∼ 200 nm focused beams in both the horizontal and vertical directions. This achievement is an important progress towards the realization of time-resolved studies using multiple X-ray pulses with a time range from femtosecond to subnanosecond scales at X-ray free-electron laser facilities.

High-spatial Resolution Figuring by Pulse Width Modulation Controlled Plasma Chemical Vaporization Machining

Numerically controlled plasma chemical vaporization machining (NC-PCVM) is an ultra-precision figuring technique using chemical reactions between radicals generated in atmospheric pressure plasma and surface of the workpiece. Figure error consists of waviness which has long spatial wavelength and roughness which has short spatial wavelength. In the case of NC-PCVM using the cylindrical electrode with a diameter of 3-6mm, it is difficult to remove the small wavelength components (several millimetres in wavelength). Therefore, improvement of spatial resolution in figuring is required for NC-PCVM. To resolve this issue, pulse width modulation (PWM) control unit was developed to control the removal volume distribution instead of scanning speed control of the worktable. Removal error at the position where the set removal depth steeply change drastically decreased to less than 4% by applying PWM controlled figuring, while the maximum removal error of figuring which applied the scanning speed control of the worktable to control the removal depth distribution was 20%. And a new electrode, which limits the irradiation area of plasma by installing of a alumina ceramics cover having a small orifice with a diameter of 1.0mm, was also developed. By applying this electrode, the full width at half maximum (FWHM) of the removal spot was reduced from 4.68mm to 1.10mm. Small spatial wavelength components of 4mm were successfully corrected by NC-PCVM which was combined PWM control and orifice electrode.

大気開放型プラズマCVMにおける高精度・高効率化に関する研究（第3報）

大気開放型プラズマCVMにおける高精度・高効率化に関する研究（第3報）

Basic Study on Etching Selectivity of Plasma Chemical Vaporization Machining by Introducing Crystallographic Damage into Work Surface

Plasma chemical vaporization machining (PCVM) is a high-speed plasma etching method using atmospheric-pressure plasma. Although it does not leave an affected layer on the processed surface because of the small ion energy owing to the small mean free path of gas molecules, it is not suitable for planarization because of its isotropic etching. Thus, a combination of PCVM and a mechanical machining process is proposed. The convex parts of a substrate surface are considered to be affected by mechanical machining and are removed preferentially by PCVM. In this report, it is investigated whether etching rate of the affected layer becomes larger or not. As a result, it was found that the etching rate increased in the first 100 nm depth of the mechanically polished substrate, which corresponds to the thickness of the heavily damaged layer observed by cross-sectional transmission electron microscopy.

Material Removal Rate Control in Open-Air Type Plasma Chemical Vaporization Machining by Pulse Width Modulation of Applied Power

Plasma chemical vaporization machining (PCVM) is an ultraprecise figuring technique for optical components without introducing the subsurface damage. In our previous study, the material removal volume was controlled by changing the scanning speed of the worktable. However, because of inertia of the worktable, a discrepancy between the theoretical scanning speed and the actual scanning speed will occur if the spatial change rate of speed is rapid. Therefore, we proposed the application of the pulse width modulation (PWM) control and the amplitude modulation (AM) control of the applied RF power to control the material removal rate (MRR). Experimental results showed that the relationship between the MRR and the average RF power had high linearity, the control range of the PWM control mode was from 0.19 x 10-2 mm3/min to 3.90 x 10-2 mm3/min (from 5% to 100%), which was much wider than that of the AM control mode.

Open-air type plasma chemical vaporization machining by applying pulse-width modulation control

Photolithography techniques have been used to enable the low-cost and high-speed transfer of a pattern onto a silicon wafer. However, owing to the high integration of semiconductors, extreme ultraviolet will be increasingly used as the exposure light source and all optics must be reflective to focus light because the wavelength of the light will be so short that it cannot pass through a lens. The form accuracy of reflective optics affects the accuracy of transfer, and a flatness of less than 32 nm on a 6 inch photomask substrate is required according to the International Technology Roadmap for Semiconductors roadmap. Plasma chemical vaporization machining is an ultraprecise figuring technique that enables a form accuracy of nanometre order to be obtained. In our previous study, the removal volume was controlled by changing the scanning speed of the worktable. However, a discrepancy between the theoretical scanning speed and the actual scanning speed occurred owing to the inertia of the worktable when the change in speed was rapid. As an attempt to resolve this issue, we controlled the removal volume by controlling the electric power applied during plasma generation while maintaining a constant scanning speed. The methods that we adapted to control the applied electric power were amplitude-modulation (AM) control and pulse-width modulation (PWM) control. In this work, we evaluate the controllability of the material removal rate in the AM and PWM control modes.