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Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 26 — Dec. 21, 2009
  • pp: 23522–23529

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Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes

D. Elfström, B. Guilhabert, J. McKendry, S. Poland, Z. Gong, D. Massoubre, E. Richardson, B. R. Rae, G. Valentine, G. Blanco-Gomez, E. Gu, J. M. Cooper, R. K. Henderson, and M. D. Dawson  »View Author Affiliations


Optics Express, Vol. 17, Issue 26, pp. 23522-23529 (2009)
http://dx.doi.org/10.1364/OE.17.023522


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Abstract

We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370nm UV light from a demonstrator 8 x 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8W/cm2 per imaged pixel in circular spots of diameter ~8µm. We show example structures written in positive as well as in negative photoresist.

© 2009 OSA

1. Introduction

Photolithography is the preferred method of micro-patterning, not only in electronics manufacturing but also in such emerging areas as micro-electromechanical systems (MEMS), micro-fluidics and ‘digital optical chemistry’ [1

S. P. A. Fodor, J. L. Read, M. C. Pirrung, L. Stryer, A. T. Lu, and D. Solas, “Light-directed, spatially addressable parallel chemical synthesis,” Science 251(4995), 767–773 (1991). [CrossRef] [PubMed]

]. The process normally requires a custom-produced hard photo-mask to be manufactured, which is expensive, time consuming, and often limits flexibility. Much research has therefore gone into developing mask-less photolithographic methods for rapid prototyping, e.g. laser direct writing [2

C. Rensch, S. Hell, M. Schickfus, and S. Hunklinger, “Laser scanner for direct writing lithography,” Appl. Opt. 28(17), 3754 (1989). [CrossRef] [PubMed]

] which is now a commercial technique. Other mask-less approaches also under development include projection writing using a single spatially filtered light emitting diode (LED) [3

R. M. Guijt and M. C. Breadmore, “Maskless photolithography using UV LEDs,” Lab Chip 8(8), 1402–1404 (2008). [CrossRef] [PubMed]

], and various spatial light modulator (SLM) and digital light projector (DLP) based methods [4

T. Naiser, T. Mai, W. Michel, and A. Ott, “Versatile maskless microscope projection photolithography system and its application in light-directed fabrication of DNA microarrays,” Rev. Sci. Instrum. 77(6), 063711 (2006). [CrossRef]

,5

G. P. Watson, V. Aksyuk, M. E. Simon, D. M. Tennant, R. A. Cirelli, W. M. Mansfield, F. Pardo, D. O. Lopez, C. A. Bolle, A. R. Papazian, N. Basavanhally, J. Lee, R. Fullowan, F. Klemens, J. Miner, A. Kornblit, T. Sorsch, L. Fetter, M. Peabody, J. E. Bower, J. S. Weiner, and Y. L. Low, “Spatial light modulator for maskless optical projection lithography,” J. Vac. Sci. Technol. B 24(6), 2852 (2006). [CrossRef]

].

Micro-pixelated gallium nitride LED’s (‘micro-LEDs’), consisting of arrays of individually addressable micrometer-sized light emitting pixels, are being investigated by several groups for applications in areas including micro-displays, bioscience and instrumentation. These devices offer spatio-temporal control of the emission pattern, and also spectrally selective excitation because the emission bandwidth is typically narrow (~15nm full-width at half maximum (FWHM)), with the central wavelength being defined by the semiconductor epitaxy of the light-emitting quantum wells. Indeed, in a preliminary demonstration [6

C. W. Jeon, E. Gu, and M. D. Dawson, “Mask-free photolithographic exposure using a matrix-addressable micropixellated AlInGaN ultraviolet light-emitting diode,” Appl. Phys. Lett. 86(22), 221105 (2005). [CrossRef]

] we were able to show some simple micrometer-sized exposure patterns in photoresist achieved by a ‘first generation’ array designed to operate at an approximately i-line photolithography wavelength (365nm). More recently, the technology has advanced to the point where much higher powers are available per pixel through flip-chip bonding of the devices [7

H. X. Zhang, D. Massoubre, J. McKendry, Z. Gong, B. Guilhabert, C. Griffin, E. Gu, P. E. Jessop, J. M. Girkin, and M. D. Dawson, “Individually-addressable flip-chip AlInGaN micropixelated light emitting diode arrays with high continuous and nanosecond output power,” Opt. Express 16(13), 9918–9926 (2008). [CrossRef] [PubMed]

] and independent element addressing by custom CMOS control circuitry is possible [8

J. McKendry, B. R. Rae, Z. Gong, K. R. Muir, B. Guilhabert, D. Massoubre, E. Gu, D. Renshaw, M. D. Dawson, and R. K. Henderson, “Individually-Addressable AlInGaN Micro-LED Arrays with CMOS Control and Sub-Nanosecond Output Pulses,” IEEE Photon. Technol. Lett. 21(12), 811–813 (2009). [CrossRef]

].

Here we explore the implications for mask-free photolithography and other forms of optical direct-write patterning engendered by these recent developments. A CMOS-controlled 8 x 8 flip-chip 370nm gallium nitride-based micro-LED array demonstrator is de-magnified through various combinations of back-to-back microscope objectives. The CMOS is shown to be capable not only of controlling the emission pattern, but also the exposure dose. We show example structures written in positive as well as in negative photoresist. The system can be used to directly reproduce the pattern on the micro-LED array and/or lines can be written by moving the sample while one or several LED pixels are turned on. Our system can be considered to bridge the gap between low cost, but low resolution, mask-less prototyping techniques, such as the use of a photocopier [9

A. Tan, K. Rodgers, J. P. Murrihy, C. O?Mathuna, and J. D. Glennon, “Rapid fabrication of microfluidic devices in poly(dimethylsiloxane) by photocopyingPresented at the 14th International Symposium on Microscale Separations and Analysis, Boston, January 13?18, 2001,” Lab Chip 1(1), 7 (2001). [CrossRef] [PubMed]

], toner mediated lithography [10

W. K. T. Coltro, E. Piccin, J. A. Fracassi da Silva, C. Lucio do Lago, and E. Carrilho, “A toner-mediated lithographic technology for rapid prototyping of glass microchannels,” Lab Chip 7(7), 931–934 (2007). [CrossRef] [PubMed]

], or etching through a mask made using a cutter plotter [11

M. H. Sorouraddin, M. Amjadi, and M. Safi-Shalamzari, “Simple and rapid methods for the fabrication of polymeric and glass chips for using in analytical chemistry,” Anal. Chim. Acta 589(1), 84–88 (2007). [CrossRef] [PubMed]

] (feature size limited to over 200µm) and high cost methods competing with traditional optical projection lithography (OPL) in terms of resolution, such as scanning electron-beam lithography (SEBL), focused ion-beam (FIB) lithography [12

G. M. Atkinson, F. P. Stratton, R. L. Kubena, and J. C. Wolfe, “30 nm resolution zero proximity lithography on high-Z substrates,” J. Vac. Sci. Technol. B 10(6), 3104–3108 (1992). [CrossRef]

], interference lithography (IL) [13

T. A. Savas, M. L. Schattenburg, J. M. Carter, and I. Henry, “Smith, “Large-area achromatic interferometric lithography for 100 nm period gratings and grids,” J. Vac. Sci. Technol. B 14(6), 4167–4170 (1996). [CrossRef]

], maskless optical-projection lithography (MOPL) [14

T. Sandstrom, A. Bleeker, J. Hintersteiner, K. Troost, J. Freyer, and K. van der Mast, “OML: optical maskless lithography for economic design prototyping and small-volume production,” Proc. SPIE 5377, 777 (2004). [CrossRef]

,15

N. Choksi, D. S. Pickard, M. McCord, R. F. W. Pease, Y. Shroff, Y. Chen, W. Oldham, and D. Markle, “Maskless extreme ultraviolet lithography,” J. Vac. Sci. Technol. B 17(6), 3047–3051 (1999). [CrossRef]

], and zone-plate-array lithography (ZPAL) [16

D. Gil, R. Menon, and H. I. Smith, “The case for diffractive optics in maskless lithography,” J. Vac. Sci. Technol. B 21(6), 2810–2814 (2003). [CrossRef]

].

2. CMOS-bonded flip-chip micro-LED array

The AlInGaN quantum well micro-LED devices are based on 370nm-emitting epitaxial wafers and are designed for flip-chip bonding. They consist of a 16 x 16 array of individually-addressable micro-disk pixels, each 72μm in diameter on a 100μm center-to-center pitch. The sapphire (epitaxial substrate) side was polished and the substrate was diced into individual device chips of approximately 3x3mm2, of which the active area is 1.6x1.6mm2. A bump bonding process was used to electrically and physically contact these chips to a custom-designed CMOS control device in the manner reported recently [8

J. McKendry, B. R. Rae, Z. Gong, K. R. Muir, B. Guilhabert, D. Massoubre, E. Gu, D. Renshaw, M. D. Dawson, and R. K. Henderson, “Individually-Addressable AlInGaN Micro-LED Arrays with CMOS Control and Sub-Nanosecond Output Pulses,” IEEE Photon. Technol. Lett. 21(12), 811–813 (2009). [CrossRef]

], such that alternate pixels were operable, thus giving a light-emitting 8 x 8 array [Fig. 1(a) ]. This was done due to the bump bonding process, which currently limits the pixel to pixel pitch to ~200µm.

Fig. 1 (a) CMOS driven micro-LED device with pixels turned on to show a representative double square pattern, and (b) the computer control interface as the pattern in (a) is addressed.

The CMOS device permits continuous wave (CW) operation of the individual micro-pixels, square wave and pulsed operation [8

J. McKendry, B. R. Rae, Z. Gong, K. R. Muir, B. Guilhabert, D. Massoubre, E. Gu, D. Renshaw, M. D. Dawson, and R. K. Henderson, “Individually-Addressable AlInGaN Micro-LED Arrays with CMOS Control and Sub-Nanosecond Output Pulses,” IEEE Photon. Technol. Lett. 21(12), 811–813 (2009). [CrossRef]

]. In CW operation, we measured a single bare pixel to deliver an optical power of up to 604µW at a driving current of 80.0mA (340µW at 20mA) at 370nm. The frequency of the square wave (the repetition rate in pulsed mode) can be set by the on-chip voltage-controlled oscillator (VCO) from 6MHz to 800MHz. With the external clock facility any frequency can be chosen. In pulsed mode the duration of the pulses can be controlled, ranging from 300ps to 40ns.

The spectral characteristic in CW operation at 27mA, measured after the imaging, confirms that it is close to Hg i-line operation (peak at 370nm with a FWHM of 15nm).

The CMOS control device was attached to a printed circuit board (PCB), which is computer controlled via a field programmable gate array (FPGA) board (XEM3010-1000 from Opal Kelly). In the custom-made software interface, shown in Fig. 1(b), the mode of operation of the CMOS chip can be set to linear feedback shift register (LFSR, not used in this work), DC/External (if no external clock is present this is CW operation), or VCO. The LED mode can be set to either DC/Square (CW operation or a square wave clocked to the external or VCO frequency) or Pulse (pulse at a controllable duration with the repetition rate set by external or VCO frequency). The VCO divider sets a value (1, 4, 16, or 64) with which the VCO frequency is divided before it is used. A pixel or a pattern consisting of a set of pixels can be chosen either by setting the row and column [upper right corner in Fig. 1 (b)] or by highlighting the desired pixels in the grid pattern of the software interface. With the timing control the LED on-time can be set accurately down to ~100ms

3. The setup

A photographic image and a corresponding schematic of the setup for mask-less photolithography can be seen in Fig. 2 . The setup consists of the CMOS driven computer controlled micro-LED device mounted vertically on a manual XYZ stage, a horizontally-mounted infinity-corrected microscope objective (Nikon CFI Plan Fluor Series) for light collection (collection objective), a mirror to direct the light downwards, a 50-50 UV beam-splitter cube, and a second (vertical) infinity-corrected microscope objective (projection objective), mounted on a Z-translation stage, to project the LED array image onto the sample. A CCD camera (Prosilica EC650C) with zoom lens attachment (Navitar, 11-110mm) adjusted to focus at infinity is used to monitor the position of the sample or the LED array depending on the orientation of the beam-splitter. Infinity-corrected objectives give collimated (or parallel) output beams of the object in the focal plane, hence when the camera objective is set to focus at infinity, the image displayed on the camera is optically conjugate to the focal plane of each objective.

Fig. 2 A photograph of the micro-projection setup (a) and schematic of the same (b).

A piezo-driven stage (PI P-725.4CD) for the Z-translation of the projection microscope objective gives a very accurate (100nm resolution with current driver and feedback measuring system) control of the focus on the sample. The sample is placed on an XY stage (2 x PI M-112.1DG) allowing for large areas (up to 25x25mm2) to be patterned. The computer control allows for movement of the sample in any pre-defined pattern at a maximum velocity of 1.5mm/s and with a repeatability of ~1µm.

The two objectives can be changed to give the capability of magnifying or de-magnifying the projected spots from the LED pixels. A range of microscope objectives with magnifications from 4X to 40X gives theoretical spot-sizes from 7.2µm (4X collection objective and 40X projection objective) to 720µm (40X collection objective and 4X projection objective) when projecting the 72µm diameter pixels of the micro-LED device. In Fig. 3 , four pixels can be seen through the 4X collection objective [Fig. 3(a)] and reflected off a mirror placed at the sample position through the 40X collection objective [Fig. 3(b)], showing how the system can demagnify the illuminated spot.

Fig. 3 Four LED pixels turned on., (a) on the device itself and (b) reflection off a mirror at the sample position, showing the focal spot size at the applications plane. The dashed line corresponds to the trace of the intensity profile plotted in (c).

4. Characterization of the system

To characterize the performance of the system, the optical power per pixel delivered at the sample was measured by placing a calibrated UV optical power meter (Coherent FieldMax Top) at the sample position. The total projected power was measured to be 140µW with the 40X collection objective and 4.4µW with the 4X collection objective, all obtained at a CMOS drive current of ~27mA. The projected powers are independent of the projection objective as the transmission losses are low and very similar for this type of objective. The measurements also indicate that there are only small transmission losses in the overall system (approximately less than 4%), except for the beam-splitter where ~50% of the power is lost.

Projected spot-sizes are determined by imaging a reflection off a mirror placed at the sample position. By using the high precision Z-translation stage the projection objective was translated to match the focal plane to the reflective surface of the mirror. From the thus acquired images, intensity profiles were taken of the projected spots and the FWHM values were measured of the profiles. An example image, of the reflection from a mirror at the sample position, is shown in Fig. 3(b). The intensity profile through the centre of the two top spots in Fig. 3(b), is shown in Fig. 3(c). In this particular case, the 4X collection objective and the 40X projection objective were used, giving spot sizes of approximately 8µm FWHM. The form of the intensity profile is determined by the emission pattern from the light emitting pixel and typically has brighter edges, attributed to sidewall scatter in the emitting pixels. This feature, although unintended, is actually beneficial when exposing photoresist as it gives better defined feature edges compared to the case with a Gaussian intensity profile.

By combining the spot-size measurements with the power measurements for various combinations of objectives, the intensity values presented in Table 1 were obtained. The maximum power density value of 8.8W/cm2 permits the required exposure dose for most photoresist types to be reached in fractions of a second (e.g. 46ms for an exposure dose of 400mJ/cm2).

Table 1  Intensities delivered by different collection and projection objectives. Image plane spot sizes measured in FWHM are in parentheses. Spot sizes have also been established by measurements in exposed photoresist and the errors in the measurements below are determined to be less than ± 10% throughout.
Collection objective\ Projection objective4X10X20X40X
4X88mW/cm2 (80µm)0.51W/cm2 (33µm)1.7W/cm2 (18µm)8.8W/cm2 (8.0µm)
40X25mW/cm2 (850µm)0.16W/cm2 (330µm)0.61W/cm2 (170µm)3.3W/cm2 (73µm)

The 4X collection objective has a larger field of view (~4mm), but it also has a lower N.A. which means it has a lower collection angle. This allows for the whole micro-LED device (1.6x1.6mm2) to be imaged at once, but with the trade-off of lower light collection. Despite this, the highest optical power density is achieved using the 4X collection/40X projection objective combination. When calculating the power densities, all power was assumed to be uniformly distributed within the spot diameter [c.f. ‘flat top’ beam profiles in Fig. 3(c)]. Dosage energy is given by multiplying the optical power by the exposure time. When the sample is moving the dosage curve is given by
E= 2P π R2v R2− y2,
where P is the total power, R the pixel radius, v the velocity, and y (≤R) the coordinate perpendicular to the velocity, i.e. a half-circular dosage curve.

The measurements presented above are all made under CW (DC driven) operation, however the CMOS driver provides the capability to use pulses for exposure. By adjusting the length of each pulse at a given repetition rate, effectively changing the duty cycle to the LED pixel, the projected optical output can be accurately controlled. Figure 4 shows how the average projected optical power varies with pulse duration from 0.5ns to 40ns at an example fixed repetition rate of 9.75MHz. The power scales linearly, but the pulsed driving of the LED allows us to explore the intermittent curing behaviour of photoresists [17

X. Sun, D. Yin, H. Dai, J. Liu, R. Lu, and S. T. Wu, “Intermittent curing and its effect on pulsed laser-induced photopolymerization,” Appl. Phys. B 92(1), 93–98 (2008). [CrossRef]

]. This feature of the CMOS driver can also, in principle, be used to correct differences in output power between pixels and to compensate for collection efficiency variations over the field of view.

Fig. 4 The relationship between average projected power and pulse width is linear for long enough pulses. Repetition rate = 9.75 MHz throughout. The insets are optical micrographs of exposed dots in NOA81 negative photoresist on glass substrates exposed for 40s at 5ns, 20ns and 40ns pulse width. The spot diameters are 11µm, 17µm and 24µm, respectively.

5. Patterning experiments

To test the micro-lithography system, a number of different ‘demonstrator’ patterns were produced in positive as well as in negative photoresist. An optical adhesive from Norland (NOA81) was chosen for the negative type photoresist because of its excellent adhesion to glass and relatively low viscosity, allowing thin films to be spun on substrates and hence offering the possibility of feature a few µm in size. The optical adhesive has a spectral peak sensitivity at 365nm and the manufacturer’s recommended dose for full cure is 2J/cm2. In preparation, substrates of borosilicate glass were cleaned thoroughly in an ultrasonic bath with acetone and subsequently methanol. They were then rinsed in deionised (DI) water and dried on a hotplate at 110°C for at least 20 minutes. NOA81 was then spin-coated at 8000 rpm for 40s, resulting in a film thickness of 1.7µm as measured by a stylus (DekTak) profilometer on cured structures. The substrate with the Norland film was placed on the XY stage and then exposed by the UV light from the micro-LED device projected through the setup. Directly after the exposure, the development was done by immersing the substrate in acetone for 1 minute. The substrate was cleaned of acetone and polymer residue in running methanol and subsequently in running DI water. The ‘IoP’ logo in Fig. 6(a) is used as a demonstrator pattern. The ‘I’ and the ‘P’ were exposed with square wave addressing for 8s while the ‘o’ was exposed for 4s, giving an average exposure dose of 10J/cm2 for each dot. This variation is due to the collection efficiency decreasing as the distance from the centre of the imaging area increases, which we note can be corrected for directly by the CMOS control. Small variations in exposure dose exist because pixel to pixel uniformity is not perfect. These issues can also, however, in principle be compensated for by adjusting the CMOS control duty cycle for each individual pixel.

Fig. 6 (a)‘IoP’ (Institute of Photonics) pattern in NOA81. The exposed dots are 8-9µm in diameter. (b) Four parallel channels written in Microposit S1805 photoresist at a velocity of 100µm/s. Lines are 9-11µm wide. The two different patterns were chosen to show the static and dynamic writing capability of the system.

Further curing experiments in NOA81 were performed under pulsed operation of the LED device. By varying the pulse width from 5ns to 40ns, and hence the exposure dose from 16.4J/cm2 to 120J/cm2, spot-sizes ranging from 11µm to 24µm diameter were written with an exposure time of 40s. A selection of these written dots is shown as insets in Fig. 4. Lines in NOA81 were also written under pulsed operation, as well as in CW. The lines shown in Fig. 5(a) were exposed with a maximum dose, in the middle of the line, of 14.7J/cm2, 6.0J/cm2, and 5.4J/cm2 going from right to left, corresponding to line widths of 11µm, 8µm, and 8µm respectively. The height of the lines was determined to be 1.7µm (i.e. curing the full thickness of the film), 0.9µm, and 0.9µm, by a stylus (Dektak) profilometer. The uniformity of the cured lines is good and shows no bulging or other variations.

Fig. 5 (a) Three lines in NOA81 written in, respectively, CW mode, with 50ns pulses and with 40ns pulses at a velocity of 5µm/s. Widths are 11µm, 8µm and 8µm respectively. (b) Close up on the middle line showing good uniformity of the line width.

For the positive photoresist features as shown in Fig. 6(b), a standard photoresist, Microposit S1805 from Shipley, was used. It is optimized for g-line (436nm) exposure, but works well for exposure wavelengths down to 350nm. Recommended exposure dose at the g-line is 150mJ/cm2. Silicon substrates were cleaned thoroughly in an ultrasonic bath with acetone and subsequently methanol. They were then rinsed in DI water and dried on a hotplate at 110°C for at least 20 minutes. The photoresist was spun at 2000 rpm for 30s. The substrate with the 0.7µm thick film was then placed on a hotplate at 120°C for 1 minute to soft-bake the photoresist prior to being exposed. After the exposure, development was completed using a micro-developer solution (Microposit 1:1 volume ratio with deionised water). The substrate was immersed and gently moved around in the solution for a duration of 1 minute. Residue developer was washed off with DI water. The four “channels” seen in Fig. 6(b) are written by turning on four individual pixels (each delivering an optical power of ~2.5µW to the sample) in one column of the micro-LED array while moving the sample at a velocity of 100µm/s. This corresponds to a maximum exposure dose, in the middle of each channel, of ~400mJ/cm2.

As a further demonstration patterns were written in a thicker positive type photoresist, Microposit S1818 from Shipley. Glass substrates were cleaned in a similar manner to previous samples and were subsequently covered with a ~2.0µm thick layer photoresist by spincoating. The samples were then exposed simultaneously by four pixels for the duration of 2s in pulsed mode, giving an exposure dose of 1.1J/cm2. The sample was then translated 40µm and an other exposure was performed. This was repeated four times and followed by a development step as described above. The resulting pattern is shown in Fig. 7 . The scanning electron microscope (SEM) image in Fig. 7(b) was taken by a Hitachi S4700 in ultra high resolution mode and confirms that we have well defined patterns with close to vertical sidewalls.

Fig. 7 (a) Micrograph showing an array of exposed dots in S1818, each with a diameter of ~9µm. (b) Oblique SEM image of the same array, showing well defined sidewalls and good dot to dot uniformity.

6. Conclusion

By combining novel CMOS driven micro-LED arrays with a projection system, we have built a versatile computer-controlled micro-photolithography tool capable of writing features down to ~8μm in positive and negative photoresist. It is capable of simultaneously exposing multiple spots and has, through the CMOS driving mechanism, facility to precisely control the dose delivered during a determined period of time as well as capability to correct for non-uniform exposure across the field of view. This type of system offers attractive prospects for many areas of direct write photo-patterning and patterned photo-stimulation, including polymer microstructuring, mask-less photolithography, digital optical chemistry, microfluidic systems and optogenetics [18

H. Xu, J. Zhang, K. M. Davitt, Y.-K. Song, and A. V. Nurmikko, “Applications of blue-green and ultraviolet micro-LEDs to biological imaging and detection,” J. Phys. D Appl. Phys. 41(9), 094013 (2008). [CrossRef]

]. Our demonstrator establishes a baseline capability, but offers considerable scope for further scaling and refinement. Wavelengths from deep ultraviolet to violet can readily be chosen for spectrally selective excitation and we have developed flip-chip devices of pixel diameter 5-10µm, where there is a separate bond-pad for each pixel for “off-pixel” bump bonding to CMOS. When incorporated into the system at 10:1 de-magnification, we anticipate being able to create 8 x 8 arrays capable of writing features down to ~1um. There is the prospect of further scaling of the number of CMOS controlled pixels.

Acknowledgements

We acknowledge support under an EPSRC Science and Innovation programme on “Molecular Nanometrology”, the EPSRC “HYPIX” programme, from the EU (PHOTOLYSIS - LSHM-CT-2007-037765) and the Scottish Consortium in Integrated Microphotonic Systems.

References and links

1.

S. P. A. Fodor, J. L. Read, M. C. Pirrung, L. Stryer, A. T. Lu, and D. Solas, “Light-directed, spatially addressable parallel chemical synthesis,” Science 251(4995), 767–773 (1991). [CrossRef] [PubMed]

2.

C. Rensch, S. Hell, M. Schickfus, and S. Hunklinger, “Laser scanner for direct writing lithography,” Appl. Opt. 28(17), 3754 (1989). [CrossRef] [PubMed]

3.

R. M. Guijt and M. C. Breadmore, “Maskless photolithography using UV LEDs,” Lab Chip 8(8), 1402–1404 (2008). [CrossRef] [PubMed]

4.

T. Naiser, T. Mai, W. Michel, and A. Ott, “Versatile maskless microscope projection photolithography system and its application in light-directed fabrication of DNA microarrays,” Rev. Sci. Instrum. 77(6), 063711 (2006). [CrossRef]

5.

G. P. Watson, V. Aksyuk, M. E. Simon, D. M. Tennant, R. A. Cirelli, W. M. Mansfield, F. Pardo, D. O. Lopez, C. A. Bolle, A. R. Papazian, N. Basavanhally, J. Lee, R. Fullowan, F. Klemens, J. Miner, A. Kornblit, T. Sorsch, L. Fetter, M. Peabody, J. E. Bower, J. S. Weiner, and Y. L. Low, “Spatial light modulator for maskless optical projection lithography,” J. Vac. Sci. Technol. B 24(6), 2852 (2006). [CrossRef]

6.

C. W. Jeon, E. Gu, and M. D. Dawson, “Mask-free photolithographic exposure using a matrix-addressable micropixellated AlInGaN ultraviolet light-emitting diode,” Appl. Phys. Lett. 86(22), 221105 (2005). [CrossRef]

7.

H. X. Zhang, D. Massoubre, J. McKendry, Z. Gong, B. Guilhabert, C. Griffin, E. Gu, P. E. Jessop, J. M. Girkin, and M. D. Dawson, “Individually-addressable flip-chip AlInGaN micropixelated light emitting diode arrays with high continuous and nanosecond output power,” Opt. Express 16(13), 9918–9926 (2008). [CrossRef] [PubMed]

8.

J. McKendry, B. R. Rae, Z. Gong, K. R. Muir, B. Guilhabert, D. Massoubre, E. Gu, D. Renshaw, M. D. Dawson, and R. K. Henderson, “Individually-Addressable AlInGaN Micro-LED Arrays with CMOS Control and Sub-Nanosecond Output Pulses,” IEEE Photon. Technol. Lett. 21(12), 811–813 (2009). [CrossRef]

9.

A. Tan, K. Rodgers, J. P. Murrihy, C. O?Mathuna, and J. D. Glennon, “Rapid fabrication of microfluidic devices in poly(dimethylsiloxane) by photocopyingPresented at the 14th International Symposium on Microscale Separations and Analysis, Boston, January 13?18, 2001,” Lab Chip 1(1), 7 (2001). [CrossRef] [PubMed]

10.

W. K. T. Coltro, E. Piccin, J. A. Fracassi da Silva, C. Lucio do Lago, and E. Carrilho, “A toner-mediated lithographic technology for rapid prototyping of glass microchannels,” Lab Chip 7(7), 931–934 (2007). [CrossRef] [PubMed]

11.

M. H. Sorouraddin, M. Amjadi, and M. Safi-Shalamzari, “Simple and rapid methods for the fabrication of polymeric and glass chips for using in analytical chemistry,” Anal. Chim. Acta 589(1), 84–88 (2007). [CrossRef] [PubMed]

12.

G. M. Atkinson, F. P. Stratton, R. L. Kubena, and J. C. Wolfe, “30 nm resolution zero proximity lithography on high-Z substrates,” J. Vac. Sci. Technol. B 10(6), 3104–3108 (1992). [CrossRef]

13.

T. A. Savas, M. L. Schattenburg, J. M. Carter, and I. Henry, “Smith, “Large-area achromatic interferometric lithography for 100 nm period gratings and grids,” J. Vac. Sci. Technol. B 14(6), 4167–4170 (1996). [CrossRef]

14.

T. Sandstrom, A. Bleeker, J. Hintersteiner, K. Troost, J. Freyer, and K. van der Mast, “OML: optical maskless lithography for economic design prototyping and small-volume production,” Proc. SPIE 5377, 777 (2004). [CrossRef]

15.

N. Choksi, D. S. Pickard, M. McCord, R. F. W. Pease, Y. Shroff, Y. Chen, W. Oldham, and D. Markle, “Maskless extreme ultraviolet lithography,” J. Vac. Sci. Technol. B 17(6), 3047–3051 (1999). [CrossRef]

16.

D. Gil, R. Menon, and H. I. Smith, “The case for diffractive optics in maskless lithography,” J. Vac. Sci. Technol. B 21(6), 2810–2814 (2003). [CrossRef]

17.

X. Sun, D. Yin, H. Dai, J. Liu, R. Lu, and S. T. Wu, “Intermittent curing and its effect on pulsed laser-induced photopolymerization,” Appl. Phys. B 92(1), 93–98 (2008). [CrossRef]

18.

H. Xu, J. Zhang, K. M. Davitt, Y.-K. Song, and A. V. Nurmikko, “Applications of blue-green and ultraviolet micro-LEDs to biological imaging and detection,” J. Phys. D Appl. Phys. 41(9), 094013 (2008). [CrossRef]

OCIS Codes
(110.3960) Imaging systems : Microlithography
(220.4000) Optical design and fabrication : Microstructure fabrication
(230.3670) Optical devices : Light-emitting diodes

ToC Category:
Imaging Systems

History
Original Manuscript: September 30, 2009
Manuscript Accepted: October 31, 2009
Published: December 8, 2009

Citation
D. Elfström, B. Guilhabert, J. McKendry, S. Poland, Z. Gong, D. Massoubre, E. Richardson, B. R. Rae, G. Valentine, G. Blanco-Gomez, E. Gu, J. M. Cooper, R. K. Henderson, and M. D. Dawson, "Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes," Opt. Express 17, 23522-23529 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-26-23522


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References

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  14. T. Sandstrom, A. Bleeker, J. Hintersteiner, K. Troost, J. Freyer, and K. van der Mast, “OML: optical maskless lithography for economic design prototyping and small-volume production,” Proc. SPIE 5377, 777 (2004). [CrossRef]
  15. N. Choksi, D. S. Pickard, M. McCord, R. F. W. Pease, Y. Shroff, Y. Chen, W. Oldham, and D. Markle, “Maskless extreme ultraviolet lithography,” J. Vac. Sci. Technol. B 17(6), 3047–3051 (1999). [CrossRef]
  16. D. Gil, R. Menon, and H. I. Smith, “The case for diffractive optics in maskless lithography,” J. Vac. Sci. Technol. B 21(6), 2810–2814 (2003). [CrossRef]
  17. X. Sun, D. Yin, H. Dai, J. Liu, R. Lu, and S. T. Wu, “Intermittent curing and its effect on pulsed laser-induced photopolymerization,” Appl. Phys. B 92(1), 93–98 (2008). [CrossRef]
  18. H. Xu, J. Zhang, K. M. Davitt, Y.-K. Song, and A. V. Nurmikko, “Applications of blue-green and ultraviolet micro-LEDs to biological imaging and detection,” J. Phys. D Appl. Phys. 41(9), 094013 (2008). [CrossRef]

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