T. H. P. Chang

Micromachining applications of a high resolution ultrathick photoresist

This article describes a new negative‐tone photoresist, SU‐8, for ultrathick layer applications. An aspect ratio of 10:1 has been achieved using near‐ultraviolet lithography in a 200‐μm‐thick layer. The use of this resist for building tall micromechanical structures by deep silicon reactive‐ion etching and electroplating is demonstrated. Using SU‐8 stencils, etched depths of ≳200 μm in Si and electroplated 130‐μm‐thick Au structures with near‐vertical sidewalls have been achieved.

Electron‐beam microcolumns for lithography and related applications

Lithography with an array of miniaturized scanning electron‐beam columns presents one of the most promising high‐throughput possibilities for fabrication of devices with feature sizes less than 100 nm. With scanning electron beams no mask is required and the necessary resolution and alignment of overlay structures are realizable. With arrays of microcolumns, the lithography throughput of a single column can be multiplied. The approach can also be used for a number of lithography related applications such as metrology, inspection, testing, etc. We review the status of the microcolumn program and discuss opportunities and challenges of this approach to high‐throughput nanolithography and related applications. Special emphasis is given to lithography in the 100 nm regime.

Arrayed miniature electron beam columns for high throughput sub‐100 nm lithography

In recent years, considerable progress has been made on an approach based on a novel concept which combines scanning tunneling microscope, microfabricated lenses, and field emission technologies to achieve microminiaturized low‐voltage electron beam columns with performance surpassing the conventional column. High throughput lithography is a potentially very important application for these microfabricated columns which measure only millimeters in dimensions. This is to be achieved using an array of these minicolumns in parallel in a multibeam mode with one or more columns per chip. The low‐voltage operation is attractive because proximity effect corrections may not need to be applied. In addition, an arrayed microcolumn system also has the potential of reducing the cost of the overall system through the compaction of the mechanical system. The throughout advantages for such an arrayed system based on different beam forming optics and pattern generation approaches will be discussed. In addition to lithogra...

Electron beam technology-SEM to microcolumn

As a continued effort to improve the performance of low energy scanning electron probe systems for application in microscopy, lithography, metrology, etc., miniaturized electron beam columns, approximately 3 mm in length, demonstrating a probe size of 10 nm with a beam current of >=1 nA at 1 keV, have been successfully developed. This paper presents current status, future directions and potential applications of these microcolumns.

Advances in arrayed microcolumn lithography

A microcolumn array has been designed, fabricated, and tested. The 2×2 array has a 2 cm pitch and operates at 1 keV. Key components include vertical interconnects, silicon low-distortion octupole deflectors, miniature long-range flexure-based tip positioners, and low-power thermal field emitters. Initial results show no observable crosstalk between columns during simultaneous operation at a 50 MHz beam blanking rate. Preliminary lithography results are presented.

Experimental evaluation of a 20×20 mm footprint microcolumn

A miniaturized 1 kV electron beam column with a 20×20 mm square footprint for application in arrayed lithography was developed. The actual beam forming optics measured from the electron emitter to the last electrode in the beam focusing Einzel lens is only 3.5 mm in length. The electron source is a miniaturized, high brightness (120 μA/sr), low heating power (<1.5 W) Zr/O/W Schottky field emitter that provides a stable beam current with <1%/h current fluctuations. A custom designed, ultralow profile (0.8 mm high) annular microchannel plate (MCP) detector is fitted into the working distance, which can be varied between 1 and 5 mm, between the Einzel lens and the sample. The MCP provides a high gain, up to 3×104, detector for secondary and backscattered electron detection from solid samples. The beam is scanned over the sample using a prelens double octupole deflector for large field size, ≥100 μm, at low distortions and low deflection aberrations. Using a computer controlled digital pattern generator, patt...

Microminiaturization of electron optical systems

The performance of miniaturized electron optical systems comprising a field emission microsource and a microlens for probe forming has been studied. A complete system measuring millimeters in length and diameter with performance exceeding that of a conventional system over a wide range of potentials (100 V–10 kV) and working distances (up to 10 mm) appears to be feasible. A scanning tunneling microscope aligned field emission microsource offers performance well suited for this application and a selective scaling approach has been developed to allow a wide range of potentials to be applied. Such miniaturized systems can be of significant importance to many areas of electron‐beam applications.

An electron-beam microcolumn with improved resolution, beam current, and stability

We have built and tested a 1 keV electron‐beam microcolumn that focuses 1 nA of beam current into a 10 nm full width half‐maximum beam diameter at a working distance of 1 mm. The electron source is a miniaturized Zr/O/W Schottky field emitter with 150 μA/sr angular emission current density operating at about 1800 K at a distance of only 100 μm from a silicon membrane extractor electrode. The actual microcolumn is 3.5 mm long assembled mainly from silicon membrane electrodes. Improved einzel lens design and fabrication allowed the operation of this beam focusing element in the accelerating mode. Spherical and chromatic aberrations were reduced by factors of about 2–3, respectively, as compared to the retarding lens mode. Excellent beam current stability with less than 1% variation over several hours has been observed.

1 &#181;m MOSFET VLSI technology: Part VI&#8212;Electron-beam lithography

This paper discusses the fabrication of 1 µm minimum linewidth FET polysilicon-gate devices and circuits. These were designed for the tight dimensional ground rules (resolution, linewidth control, and overlay) achievable using direct wafer write scanning electron-beam lithography with individual chip registration. The present work focuses on vector-scan electron-beam technology and processing, while other papers in this series discuss other aspects of the work. Different types of 1 µm MOSFET chips were written on 57 mm Si wafers using a totally automated electron-beam system which performs table stepping, registration to fiducial marks, and pattern writing in a vector scan mode (on an individual shape basis) with control of exposure dose for individual shapes. The pattern data were prepared by batch processing which includes proximity correction as well as sorting of shapes to achieve data compaction and minimal distance between shapes. A novel two-layer positive resist system has been developed to achieve reproducible liftoff profiles over topography and better linewidth control. The final results presented here demonstrate that there are no fundamental barriers to the extension of this work to small dimensions.

High aspect ratio aligned multilayer microstructure fabrication

This paper presents a technique for fabricating precisely aligned high aspect ratio multilayer microstructures based on anodic bonding of silicon and PyrexTM glass. The process involves stacking alternate silicon substrates containing patterns in two dimensions with thin Pyrex glass spacers to form tall three‐dimensional structures. The methods used for accurately aligning the layers by optical microscopy and for bonding the layers anodically are described. The application of this technique for building fully functional microlenses for electron‐beam microcolumns is presented.