Literature review : Direct Laser Writer for Maskless Lithography System
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Direct Laser Mask Writer / Maskless lithography
Wikipedia:[1]
- Maskless lithography utilizes methods that directly transfer the information onto the substrate, without utilizing an intermediate static mask, i.e. photomask that is directly replicated. In microlithography typically radiation transfer casts an image of a time constant mask onto a photosensitive emulsion (or photoresist).
- The concept takes advantage of high speed or parallel manipulation technologies that have been enabled by large and cheap available computing capacity, which is not an issue with the standard approach that decouples a slow, but precise structuring process for writing a mask from a fast and highly parallel copy process to achieve high replication throughputs as demanded for in industrial microstructuring.
Market Survey
- Traditional photolithography calls for the fabrication or purchase of a photomask and the use of a stepper or mask aligner to transfer the CAD-pattern onto the resist-covered wafer or plate. At this point in time, the well-established photomask process is indeed the only feasible way for high volume manufacturing of sub-micron sized design features.
- Another photolithography technique available which constitutes the perfect tool for many other applications: Maskless photolithography. In maskless photolithography the pattern is exposed directly onto the substrate surface with the help of a spatial light modulator (SLM) – which serves essentially as a programmable mask. The system takes your design file and simply “writes” the pattern onto the resist-covered substrate.
- Direct-write process puts you in a position to skip the entire time-consuming and expensive photomask process and all it involves: Instead, you can redesign your CAD-drawing (again and again, if necessary) and immediately re-expose the pattern.
Reference :
List of References
Cost effective maskless lithography: Direct UV laser writing of microstructures for microfluidics applications
Mohammed Ziauddin ; Abdel-Hamid I. Mourad ; Saud A. Khashan
- In this study, cost effective measures are taken in selecting each component in building the system.
- Main components that took larger share of the cost are the XY linear stage, software, stepper motors and drivers, and power supply.
- In this study, the maskless lithography system is developed based on UV laser writing tool and simultaneously moving XY linear stage
A programmable mask for direct write lithography
Kunal Pharas 1979-University of Louisville
- This project aims at designing and fabricating a programmable mask for a direct write lithography system which can achieve higher throughput at a reasonable cost for the semiconductor industry in the future.
- The device has apertures of different sizes that can be used as programmable masks by opening and closing the shutters over them.
- The optical image of the developed photoresist that was exposed through the apertures resembles almost identical feature size and linewidth measurement of the pattern exposed
Laser writing techniques for photomask fabrication using a femtosecond laser
K. Venkatakrishnan, B.K.A. Ngoi, P. Stanley, L.E.N. Lim, B. Tan & N.R. Sivakumar
- Currently they are fabricated by a lithographic process, which is very expensive and time-consuming since it is a multi-step process. These issues can be addressed by fabricating photomasks by direct femtosecond laser writing, which is a single-step process and comparatively cheaper and faster than lithography.
- In this paper they discuss our investigations on the effect of two types of laser writing techniques, namely front- and rear-side laser writing, with regard to the feature size and the edge quality of a feature.
Augmenting mask-based lithography with direct laser writing to increase resolution and speed
MILES P. LIM, XIAOFEI GUO, EVA L. GRUNBLATT, GARRETT M. CLIFTON, AYDA N. GONZALEZ, AND CHRISTOPHER N. LAFRATTA
- A new method of hybrid photolithography, Laser Augmented Microlithographic Patterning (LAMP), is described in which direct laser writing is used to define additional features to those made with an inexpensive transparency mask.
- This combination of direct laser writing and conventional UV lithography compensates for the drawbacks of each method, and enables high-resolution prototypes to be created, tested, and modified quickly.
The next generation of maskless lithography
Steffen Diez, Heidelberg Instruments Mikrotechnik GmbH (Germany)
- The essential goal for fast prototyping of microstructures is to reduce the cycle time. Conventional methods up to now consist of creating designs with CAD software, then fabricating or purchasing a Photomask, and finally using a mask aligner to transfer the pattern to the photoresist.
- The new Maskless Aligner (MLA) enables to expose the pattern directly without fabricating a mask, which results in a significantly shorter prototyping cycle. To achieve this short prototyping cycle, the MLA has been improved in many aspects compared to other direct-write lithography solutions: exposure speed, user interface, ease of operation, and flexibility.
Maskless Photolithography System
The conventional photolithography process is used to create patterns in the micro scale by implementing the energy of light to expose a photo-restive material on a silicon wafer. The conventional process is neither time nor cost-efficient. In addition; new machines designed for rapid prototyping are still expensive. Therefore; the author of this paper has developed a cost-efficient mask-less photolithography system for rapid prototyping in laboratory environments. The purpose of this report is to discuss engineering specifications, existing technologies, engineering analysis, final prototype, and manufacturing plans. The paper also includes a validation plan, which is included as future work, to verify the performance of the system and determine that all specifications have been met.
Maskless Lithography
The form of lithography used in the Si semiconductor industry is optical projection lithography (OPL). In this technique, a pattern is first created on a reticle or mask at four times the desired final size, and the image of the mask is projected onto a Si wafer by a large and very expensive reduction lens. The rapid advances in the semiconductor industry have been enabled by advances in OPL technology and in the quality of the photoresist that records the projected image. Today, in semiconductor manufacturing, the operating wavelength in advanced OPL systems (so-called ‘steppers’ or ‘scanners’) is 193 nm, the throughput is 60 or more Si wafers per hour, the field size is about 20 mm × 30 mm, and the minimum feature size is ∼90 nm. To achieve such results, a variety of resolution-enhancement techniques (RETs) are employed, including phase-shift masks off-axis illumination, and optical proximity-effect correction (OPC)1, 2. In the near future, water-immersion optics will be used to further improve the resolution and depth-of-focus achievable with 193 nm OPL.
A maskless photolithographic prototyping system
Photolithography is a key step in the fabrication of the modern integrated circuit. Multiple levels of aligned photolithography, combined with thin-film deposition and etching, allow a three-dimensional circuit to be built upon a two-dimensional surface. Because it is such an important part of the semiconductor manufacturing industry, much research has been performed in this area.1,2 However, this research is largely directed toward high-volume industrial purposes rather than low-volume academic research needs. Mask costs are a serious issue even in industrial applications, and maskless lithography tools are being developed for next-generation lithography systems such as extreme ultraviolet lithography, where mask costs are expected to be a major problem.
Maskless Photolithography using UV LEDs
A UV light-emitting diode (LED) with a maximum output of 372 nm was collimated using a pinhole and a small plastic tube and focused using a microscope objective onto a substrate for direct lithographic patterning of the photoresist. Movement of the substrate with a motorized linear stage (syringe pump) allowed lines in SU-8 to be pattered with a width down to 35 μm at a linear velocity of 80 μm s−1, while in the dry film resist Ordyl SY 330, features as narrow as 17 μm were made at a linear velocity of 245 μm s−1. At this linear velocity, a 75 mm long feature could be patterned in 5 min. Functional microfluidic devices were made by casting PDMS on a master made by LED lithography. The results show that UV LEDs are a suitable light source for direct writing lithography, offering a budget-friendly, and high-resolution alternative for rapid prototyping of features smaller than 20 μm.
A maskless exposure device for photolithography prototyping
A cost-effective maskless exposure device(MED) for the fast lithographic prototyping of various layouts is presented in this paper. The device is assembled using a digital light processing projector (DLP), an optical microscope, alignment stages and a web camera. Layouts created on the computer can be easily transferred to the substrate without an expensive photomask and the process can be improvised for different layouts. Components are tuned for a constant area of exposure and a resolution of 20 micrometres is possible at the moment without using reduction lenses. Different materials such as silicon, glass, metal etc. have been successfully used as substrate materials in this paper successfully.
