US 5,473,408 A · High-efficiency, energy-recycling exposure system

Abstract

A system is described for recycling radiation reflected by an illuminated patterning mask in a via-hole drilling or exposure tool. The mask is illuminated by high-energy laser radiation, and the illuminated region is imaged onto a substrate by a projection, proximity, or contact method. The source radiation is suitably shaped by a lens assembly and focused into an optical intensity homogenizer with the desired numerical aperture. The homogenizer has the base function of converting the focused beam to self-luminous light required for drilling of via-holes or other processes accomplished by the tool, while maintaining the numerical aperture of the beam. The homogenizer also participates in the radiation-recycling function. An apertured reflector allows radiation from the source to enter the homogenizer. The radiation passing through and exiting the homogenizer is image by a lens to illuminate a portion of the mask. Radiation incident on transparent areas of the mask coming propagates to the substrate, but radiation incident upon reflective regions of the mask coating is reflected back into the homogenizer. The apertured reflector at the entry port of the homogenizer has a reflective back surface which returns the majority of the light re-entering the homogenizer to the patterning mask. The effective illumination intensity is greatly increased by the recycling of the back-reflected radiation, allowing for a reduction in source power or decrease in exposure time for the drilling of via-holes or other exposure processes.

Claims30

Dependent claims

An energy-efficient exposure system for producing a pattern on a target substrate, comprising:

a) a radiation source (22);
b) optical imaging means for operatively presenting an image of a selected portion of the pattern on a target substrate (12/72), having an optical imaging path between said radiation source and the target substrate (12/72);
c) an optical intensity homogenizer (34) in said optical imaging path, comprising a cylinder with an entry port, a highly reflective interior surface, and an exit port, for enhancing the uniformity of radiation entering the homogenizer, by multiple reflections from said interior reflective surface;
d) reflective mask means (10/70) mounted optically downstream from said homogenizer exit port, having transmitting areas and reflective areas defining the pattern, which selectively passes radiation through the transmitting areas to selected areas of said target substrate (12/72), and reflects radiation from said reflecting areas, whereby a significant portion of such reflected radiation re-enters said homogenizer through its exit port and re-traverses the cylinder of said homogenizer to its entry port;
and
e) means for recycling homogenizer radiation, comprising an apertured reflector (30) having a source side and a mask side, having a radiation-transmitting entry aperture (31) for accepting radiation from said radiation source (22) in a forward direction, and having a reflective surface (32) on the mask side to reflect in a forward direction the radiation which is incident upon said reflective surface (32) after being reflected by said mask and re-traversing said homogenizer (34) in a backward direction.

3 more elements

Dependencies are inferred from the claim text.

High-efficiency, energy-recycling exposure system

Life of this patent

High-efficiency, energy-recycling exposure system

Life of this patent

Abstract

Claims30