Introduction to Photolithography Systems

Over two decades ago, Oriel Instruments developed a sophisticated design mercury source with unprecedented high intensity, collimation, and homogeneity to address the requirement for high resolution exposure sources for photolithography. Since then, Oriel Instruments has designed a host of mask alignment fixtures as well as the building blocks of current mask alignment systems.

At present, Oriel Instruments provides a comprehensive portfolio of instruments, ranging from photoresist photospeed testing systems to full mask alignment systems and flood exposure sources, to address the ever-changing requirements of the broad photolithography market. The company keeps on updating its advanced designs with the launch of new products.

Flood Exposure Sources

Early requirements demanded Oriel Instruments’ NUV Mercury source (350-450 nm), which gradually expanded to include its DUV sources (220-260 nm or 260-320 nm). These sources are offered in 350, 500 and 1000 Watt ratings and are in use all across the globe. Oriel Flood Exposure Sources exhibit unprecedented output stability, thanks to Oriel’s Digital Exposure Controller that gets rid of the factors causing both short and long term instability.

Mask Alignment Fixtures

Oriel Instruments offers user friendly fixtures that secure many different sizes of substrates, masks and wafers. These fixtures are both versatile and cost effective, making them suitable for use in today's dynamic environment, in both research and industry. Two basic models are offered by Oriel Instruments. One model can hold up to 152 x 152mm substrates in vacuum contact and another can hold substrates up to 229 x 229mm in proximity. A rapid, three step alignment technique facilitates operation and higher throughput, saving time significantly when used in Oriel mask aligner systems. Figure 1 shows Mask Alignment Fixture and Flood Exposure Source.

Mask Alignment Fixture and Flood Exposure Source.

Figure 1. Mask Alignment Fixture and Flood Exposure Source.

Mask Alignment Systems

Oriel modular mask alignment systems consist of mask alignment fixtures, very stable sources, vibration isolated tables, and viewing systems. With these features, they are the robust equipment for high resolution imaging. Oriel Instruments can design bespoke systems to meet specific customer requirements.

ACCUDOSE 9000™

Accudose 9000™ uses a light source like Oriel standard flood exposure source to yield a high intensity beam of NUV or DUV radiation to customers’ photoresist. Wafers are moved through a cycle of high resolution, incremental exposures by an automated stage. The task of photospeed determination is completed with accuracy through the development of the wafer.

Custom Requirements

Oriel Instruments has the capability to meet the requirements of customers whether it is a one piece prototype or a large quantity OEM requirement. The company offers 350, 500 and 1000W Flood Exposure Sources for the NUV (350-450nm) and DUV (220-260nm and 260-320nm). The use of a collimated output beam up to 254 x 254mm facilitates irradiating large samples or multiple samples concurrently.

It is possible to rotate the output of the 1000 W model to 90° for generation of a horizontal beam. Oriel Instruments offers many different filters and dichroics, including both standard and bespoke, for these illuminators.

Superior Collimation and Beam Uniformity

Oriel sources are recognized for their superior collimation and beam uniformity. The divergence at the work plane relies on the focal length of the collimating lens and the illuminated integrator size. The divergence ranges from ±1.4 to ±6.6°. A mercury or mercury(xenon) lamp is used in Oriel sources. The dichroic mirror adjusts the output to identify the source spectra. The three wavelength ranges offered by Oriel Instruments are as follows:

  • 220 - 260nm - for deep ultraviolet studies
  • 260 - 320nm - for polymer cross linking and novel resist materials
  • 350 - 450nm - designed to expose the majority of the available photosensitive materials

Components of a Flood Exposure Source

Each source is composed of three components: the illuminator housing, lamp and a power supply. The beam path of the housing is illustrated in Figure 2, wherein up to 70% of the lamp output is collected and directed towards a NUV or DUV dichroic reflector by an ellipsoidal reflector for spectral selection. The light is scrambled by the optical integrator, producing several diverging beams, which overlap at the collimating lens to yield a homogenous, collimated beam at the work plane. An electronic splitblade shutter allows control over exposure times.

Optical configuration of Flood Exposure Source.

Figure 2. Optical configuration of Flood Exposure Source.

The selection of the lamp relies on the type of the source selected. The lamp to be used is a 350 W Hg, 500 W Hg, 500 W Hg(Xe) or 1000 W Hg(Xe) short arc lamp. Typical output of 6285 500W Hg Lamp is illustrated in Figure 3. The modified output of the 6285 500W Hg Lamp using a 350-450nm dichroic is delineated in Figure 4. The use of the dichroic significantly reduces the out of band radiation.

Typical output of 6285 500 W Hg Lamp.

Figure 3. Typical output of 6285 500 W Hg Lamp.

Output of 6285 Lamp, modified by a 350 - 450nm dichroic

Figure 4. Output of 6285 Lamp, modified by a 350 - 450nm dichroic.

An ignitor, needed to generate the high voltage ignition pulses for the arc lamp, is placed near the lamp to shorten the pathlength to be travelled by the pulse, thereby facilitating ignition and lowering EMI. An interlock system in the housing ensures the operator safety. Optimum lamp, optics and housing temperature is maintained by the air cooling provided by a temperature controlled fan.

The low level pulses are sent to the ignitor by the ultrastable power supply. After the establishment of the arc, the lamp can be controlled directly by the power supply. The lamp can be operated under extremely tight current control, thanks to its efficient switching circuitry. This causes low ripple and high line voltage regulation.

This information has been sourced, reviewed and adapted from materials provided by Oriel Instruments.

For more information on this source, please visit Oriel Instruments.

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