idonus UV-LED exposure system for photolithography

illustration UV EXP series

idonus proposes an innovative UV illumination system based on the use of high-power LEDs and high-grade microlens arrays. This product finds application in photoresist exposure and is suitable for a wide variety of substrates. Our complete line of UV illumination products addresses photolithography needs for masks and wafers up to 300 mm wide (11.8 inches). Customized solutions can be designed to suit your specific requirements (e.g., retrofit of mask aligners, OEM for your future products).

LED BENEFITS

Until recently, mercury arc lamps were the only sources capable of providing high intensity light suitable for UV photolithography exposure. Thanks to the advances in LED technology, UV-LEDs have become a very attractive alternative to the hazardous and energy-consuming mercury lamps.

Along with the ecological and security aspects, the technical advantages of UV-LEDs as compared with traditional mercury lamps are numerous and significant for photolithography. A foremost advantage of UV-LEDs is that they operate with consistent emission for very long lifetimes. As a result, daily calibration and maintenance are not required. Furthermore, by being more energy efficient, LEDs have reduced heating, which greatly simplifies system cooling.

 

Benefits of UV-LED technology
  • long lifespan of LEDs, meaning no more consumable required
  • no daily calibration required, instantly stable illumination
  • instant-on, light is ON only during exposure, no mechanical shutter needed
  • low power consumption
  • limited heating, implying very low air cooling costs
  • no maintenance costs

UV-LED EXPOSURE SYSTEM

idonus has introduced a complete line of UV-LED exposure products. Our systems integrate the most effective UV-LEDs available on the market together with high-grade microlens arrays. They are fully assembled and controlled in-house. Our design features a fully telecentric optics that provides reproducible and uniform illumination conditions over the whole exposure area – i.e., highly homogeneous and stable intensity with very small divergence angles. This cutting edge optics ensures perfectly uniform exposure of the entire substrate, producing cured photoresists with straight sidewalls and enabling precise microstructuring of patterns with micrometer critical dimensions.

optical system
Figure A: Optical system (simplified) • High uniformity of the illumination is achieved thanks to the use of a microlens array homogenizer.

 

PERFORMANCES

Our UV-LED exposure system is available in several standard configurations that can be customized with a multitude of variations (e.g., single or  mixed wavelengths). As a manufacturer of special machines, idonus can also develop fully customized equipments according to client's specifications (e.g., different exposure area, adapted equipment housing). The main characteristics of our products are given in Table "Standard UV-LED exposure systems". A typical measurement performed during the calibration process is shown in Figure B. In the usable exposure area, irradiance inhomogeneity, ±(max-min)/(max+min), is lower than ±3%. The maximum collimation angle α which is illustrated in Figure A is another important parameter that we systematically characterize. Data shown in Figure C are typical results extracted from measurements performed on one of our models. To evaluate α, irradiance is measured as a function of the collimation angle: α corresponds to the FWHM (full width at half maximum). This threshold is commonly used to consider light energy effectively contributing to photoresist irradiation. Given the performance of our exposure system, about 95% of the energy is enclosed within the collimation angle.

  

Table: Standard UV-LED exposure systems • Typical specifications of our standard products that are optimized for different exposure areas.

Characteristics \ System type UV-EXP150R UV-EXP150S UV-EXP200S UV-EXP300S UV-EXP600S
Useful exposure area Ø 150 mm 150 × 150 mm² 200 × 200 mm² 300 × 300 mm² 600 × 600 mm²
Wavelength
(single or mixed)
365 nm and/or 385 nm / 395 nm / 405 nm
all models can be configured with UV-LEDs with multiple wavelength peaks
Irradiance
(@385/395/405 nm)
50 mW/cm² 50 mW/cm² 30 mW/cm² 17 mW/cm² 30 mW/cm²
multiple LEDs
Irradiance
(@365 nm)
40 mW/cm² 40 mW/cm² 25 mW/cm² 12 mW/cm² 20 mW/cm²
multiple LEDs
Irradiance inhomogeneity
±(max-min)/ (max+min)
±3% ±3% ±3% ±3% ±3%
Max. collimation angle
(±α, FWHM)
±1.8° ±1.8° ±1.4° ±1.0° ±2.0°
Working Distance (WD) * 350 mm 300 mm 400 mm 300 mm 300 mm
Ext. dim.
H × W × D
(lamphouse only)
610 × 302 × 244 mm
607 × 352 × 294 mm 728 × 412 × 354 mm 936 × 560 × 504 mm 1500 × 1100 × 900 mm
Ext. dim.
H × W × D
(complete system)
1000 × 480 × 330 mm 960 × 500 × 420 mm 1170 × 530 × 520 mm 1270 × 670 × 670 mm **

* Note that for all models, other WD can be designed to address your specific needs.
** To be defined, as it depends on user application.

 

uvlight result web graph 1
Figure B: Irradiance inhomogeneity • Measurements show inhomogeneity lower than ±3%. Typical values extracted from one of our models UV-EXP100S (square illumination area of 100×100 mm²).

 

Figure UV EXP Angular spectrum

Figure C: Angular spectrum • UV light is enclosed within the max. collimation angle (intensity threshold at FWHM, corresponding to 95% of light energy). Typical values extracted from our UV-EXP150S (max. collimation angle α of ±1.8°).

 

 close up view UV EXP idonus
Detail view of model UV-EXP300S. Anti-reflective coating gives this distintive color to the front lens

         

photo 2
Highly homogenous exposure area of 300 × 300 mm² is obtained with model UV-EXP300S.

VPE - TCRC

Reaction chamber temperature control

The etch rate of silicon dioxide varies slightly with the temperature of the liquid HF in the reaction chamber. The temperature of the HF depends on the ambient temperature of the clean room. Additionally, the HF heats during long etching processes, which results in an increasing etch rate from wafer to wafer until the system has stabilized. To stabilize the etch rate we have developed a reaction chamber with temperature controlled HF in the container. The temperature of the HF can be adjusted with an additional controller. A Peltier element heats or cools the acid depending on the desired process parameters.





VPE - Publications

Publications

COMBINED AL-PROTECTION AND HF-VAPOR RELEASE PROCESS FOR ULTRATHIN SINGLE CRYSTAL SILICON CANTILEVERS
S. Mouaziz; Microsystems Laboratory, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland

ETCH STOP MATERIALS FOR RELEASE BY VAPOR HF ETCHING
Thor Bakke; Fraunhofer IPMS, Dresden, Germany
16th MME Workshop 2005, Goeteborg, Sweden

QUASI-DRY RELEASE FOR MICRO ELECTRO-MECHANICAL SYSTEMS
M. Zickar; SAMLAB, Institute of Microtechnology (IMT), University of Neuchatel, Switzerland

A CLEAN WAFER-SCALE CHIP-RELEASE PROCESS WITHOUT DICING BASED ON VAPOR PHASE ETCHING
T. Overstolz; SAMLAB, Institute of Microtechnology (IMT), University of Neuchatel, Switzerland

VPE - Release service

HF vapor phase release service for MEMS

We offer a release service for MEMS wafers as well as single chips.
All the manipulations are carried out in a clean room. As every application is different we are pleased to discuss the release of your MEMS with you.

VPE - Technology

Technology: vapor phase etching

First experiments on vapor phase etching were carried out by Holmes & Snell in 1966 [1]. They observed that silicon dioxide on a wafer is etched with a comparable etch rate even when the wafer is not in the etch bath but close to. Helms & Deal established that the role of water is to provide a condensed solvent medium for the HF on the surface. Offenberg et al. [2] proposed a two step reaction where first the oxide surface is opened by formation of silanol groups by adsorbed water (H2O ) . Subsequently silanol groups are attacked by the HF:

SiO2 + 2H2O -> Si(OH)4

Si(OH)4 + 4HF -> SiF4 + 4H2O

The above formula shows that water acts as initiator of the etching process as well as reactant. This fact suggests that the etching process can be temperature controlled in order to maintain in equilibrium the amount of water needed to initiate the process and the amount of reactant water . In idonus' Vapor Phase Etcher this equilibrium is achieved by heating the wafer. The water film on the wafer is evaporated at moderate temperatures. The etch rate decreases with increasing temperature and stops completely at temperatures above 50°C.
Sticking free MEMS release is achieved at etch rates around 5 µm/h.

For further information ask our skilled team for assistance!


[1] P. J. Holmes and J. E. Snell, Microelectronics and Reliability (Pergamon, New York 1966), Vol. 5, p. 337.

[2] M. Offenberg, B. Elsner, and F. Lärmer, "Vapour HF etching for sacrificial oxide removal in surface micromachining", Extended Abstracts: Electrochem. Soc. Fall Meeting (Miami Beach) vol 94-2, pp 1056-7, 1994.