REBL: A novel approach to high speed maskless electron beam direct write lithography

Abstract

The system concepts used in a novel approach for a high throughput maskless lithography system called reflective electron beam lithography (REBL) are described. The system is specifically targeting five to seven wafer levels per hour throughput on average at the 45nm node, with extendibility to the 32nm node and beyond. REBL incorporates a number of novel technologies to generate and expose lithographic patterns at estimated throughputs considerably higher than electron beam lithography has been able to achieve as yet. A patented reflective electron optic concept enables the unique approach utilized for the digital pattern generator (DPG). The DPG is a complementary metal oxide semiconductor application specific integrated circuit chip with an array of small, independently controllable metallic cells or pixels, which act as an array of electron mirrors. In this way, the system is capable of generating the pattern to be written using massively parallel exposure by ∼1×106 beams at extremely high data rates (∼1Tbit∕s compressed data). A rotary stage concept using a rotating platen carrying multiple wafers optimizes the writing strategy of the DPG.

Electron caustic lithography

“…In REBL, the role of the mask is played by the digital pattern generator (DPG) developed by Petric et al, 12,13 which is a sophisticated array of electrostatic mirrors that create the pixels of the image projected onto the resist. As a logical extension, the flexibility of ECL could be improved by adopting a DPG with every individually controllable pixel 'on,' i.e.…”

“…Caustics are commonly produced when focusing an optical beam, and they are typically stable to perturbations 19 such as imperfections on the mirror surface, and aberrations in the optical system including an electron energy spread. 3,8,12 Thus a variety of caustics should be readily formed from a vast range of mirror surfaces, including curved lines and junctions, with contributions from both surface topography and potential variations, such as differences in material work function. Caustic features can typically be focused to finer dimensions than the surface structures or variations producing them, improving resolution of lithographic patterns.…”

“…2,8,9,11 In addition there has been a development of maskless approaches, including the use of multiple beams, 14,15 low energy electron microscopy, 10 and reflective electron beam lithography (REBL) wherein the electron beam is reflected by an array of electrostatic mirrors. 12,13 In this letter we describe a complementary approach to REBL and electron projection lithography which is based on the formation of intense electron caustics which can be subsequently projected onto a resist by suitable electron optics. The caustics are formed within the cathode lens of a mirror electron microscope (MEM) in which electrons turn around in the vicinity of a negatively biased specimen surface.…”

Lossless compression algorithm for REBL direct-write e-beam lithography system

“…3(a), and detailed in [5][6]. REBL's goal is to produce the high resolution of electron-beam lithography while maintaining throughputs comparable to those of today's optical lithography systems.…”

“…A new writing system, called Reflective Electron Beam Lithography (REBL), is currently under development at KLATencor [5]. In this system, the layout patterns are written on a rotary writing stage, resulting in layout data which is rotated at arbitrary angles with respect to the pixel grid.…”