Optimized High-Voltage Power Supply for Electron Beam Direct Write Resist Sensitivity

Electron beam direct write (EBDW) lithography remains a critical tool for mask writing, prototyping, and low-volume manufacturing of specialized devices. A key determinant of throughput and resolution in EBDW is the sensitivity of the electron beam resist. Resist sensitivity, defined as the required dose (charge per unit area) to achieve a specific development outcome, is not solely a material property; it is intimately influenced by the characteristics of the high-voltage power supply that accelerates the electrons. This article details how power supply performance parameters directly affect resist exposure kinetics and how optimization can lead to significant process benefits. The primary function of the high-voltage supply in an electron column is to establish the accelerating voltage (typically ranging from 1 kV to 100 kV). This voltage determines the landing energy of the electrons, which in turn controls their penetration depth (proximity function), scattering behavior, and the energy deposition profile within the resist layer. A supply optimized for resist sensitivity goes beyond merely providing a stable high voltage. It must provide exceptional long-term stability and low noise. Fluctuations in the accelerating voltage, even as small as tens of ppm, alter the electron's landing energy. This changes the electron scattering range (the interaction volume), effectively blurring the point spread function. For a chemically amplified resist, this energy deposition variation leads to inconsistent acid generation during exposure, causing line edge roughness (LER) and critical dimension (CD) errors. A power supply with ultra-low output ripple and high stability ensures that the energy of every electron is virtually identical, leading to a sharper, more predictable exposure latent image. Furthermore, modern EBDW systems employing variable shape beam or character projection techniques require rapid beam blanking and modulation. The blanking plates are driven by high-voltage amplifiers. The slew rate, settling time, and overshoot characteristics of these blanking amplifiers are crucial. Poor settling behavior can lead to dose errors at the beginning of a shot, affecting the exposure of small features. An optimized supply for blanking ensures crisp, precise beam turn-on/off, translating directly into accurate dose control at the resist level. Another advanced consideration is the use of beam acceleration techniques that influence resist chemistry. For instance, at very low accelerating voltages (below 5 kV), electrons interact primarily with the resist surface. The power supply must deliver extremely stable low currents at these lower high-voltage settings, as resist sensitivity is often highest here, making the process more susceptible to dose errors from current instabilities. The power supply's current regulation loop must be exceptionally tight. The beam current, controlled by the gun supply or through apertures, defines the dose rate. Any drift or noise in the beam current directly translates into a dose error across the written pattern. A supply with precision current feedback and control, often integrating low-noise sensing resistors and high-stability reference components, is essential for maintaining the intended dose, thereby ensuring consistent resist development rates and pattern profiles. In practice, optimizing for resist sensitivity involves a co-engineering effort between the exposure tool's column design and the power supply's capabilities. It enables lithography engineers to push resists to their theoretical sensitivity limits, reducing the required dose. This has a direct, multiplicative effect on throughput, as lower dose requirements allow for higher beam currents or faster stage speeds without sacrificing resolution or increasing proximity effect complications. Consequently, the high-voltage power supply transforms from a simple energizing component into a critical enabler for resolution, LER control, and throughput in advanced EBDW lithography.