The invention relates to the printing of patterns with high precision, in particular to printing of microlithographic pattern such as patterns on photomasks and wafers. The invention may also be applied to other printing, such as for the formation of optical devices, electronic interconnects and even to decorative printing and security printing.
The invention is particularly suited to but not limited to optical printing using partially coherent light, such as from excimer and atomic lasers and from EUV light sources. In a preferred embodiment it is applied to a maskless scanner for exposure of patterns onto semiconductor wafers without the need for reticles or masks.
In the past, integrated circuits have been manufactured more or less solely by using a number of masks or reticles comprising a pattern of a layer in said integrated circuit. In today""s integrated circuits the number of layers could be larger than 30. Said Masks or reticles may be prepared in lithographical manner by using for example electron beams or laser beams for exposing a layer of material sensitive for the type of beam chosen. The mask material is most commonly transmissive on top of one of its sides a thin layer of opaque material is attached. In said thin material the pattern of one layer of said integrated circuit is created. The mask has typically N times larger pattern than the pattern to be printed on the semiconducting substrate for forming said integrated circuit. The reduction in size is performed in a stepper, which uses the mask(s) for forming said integrated circuit.
More recently, the need to manufacture integrated circuits by means other than using a conventional mask has developed for a number of reasons, for example the price of manufacturing mask(s) has increased due to its complexity to manufacture, small-scale development which needs very small series of integrated circuits, etc.
Unfortunately, all of the present known techniques for forming integrated circuits without using conventional masks or reticles have drawbacks and limitations.
For example, most direct-writers known in the art are based on electron beams, typically so called shaped beams, where, the pattern is assembled from flashes, each defining a simple geometrical figure. Other systems are known which use raster scanning of Gaussian beams. By using a conventional mask writer, which uses beams of electrons or laser beams for forming the pattern on a workpiece, is limited to relatively low scanning speeds, and, perhaps worst of all, can only scan a single dimension.
SLM writers disclosed in other patent applications, such as WO 01/18606 and U.S. patent application Ser. No. 09/954,721 by the same assignees as the present invention and hereby incorporated by reference is related to raster scanning in the sense that it permits a bitmap pattern, but distinct by printing an entire frame of pattern in one flash instead of building the pattern from individual pixels.
A spatial light modulator (SLM) comprises a number of modulator elements, which can be set in a desired way for forming a desired pattern. Reflective SLMs may be exposed to any kind of electromagnetic radiation, for example DUV or EUV for forming the desired pattern on the mask.
The same assignee has in a number of previous patent applications, for instance WO 99/45440 and WO 99/45441, disclosed pattern generator technology for precision printing of submicron patterns. Typically the embodiments taught in said applications use SLMs with analog modulation. The modulating elements are micromechanical mirrors that are capable of gradually move from a resting to a fully actuated state in response to an electronic drive signal, and the elements form one or two-dimensional arrays of modulating elements. A pattern defined in an input database is rasterized to a bitmap were each pixel can have several states between a lightest and a darkest state.
What is needed is a method and apparatus, which creates pattern on a workpiece using a programmable reticle or mask, such as a spatial light modulator, capable to create patterns with high feature edge acuity. What is also needed is a method and apparatus capable to pattern feature boundaries with high accuracy of placement.
Accordingly, it is an object of the present invention to provide a method of patterning a workpiece, which overcomes or at least reduces the above-mentioned problem of creating fine patterns with huh acuity and high accuracy of placement of feature boundaries.
This object, among others, is according to a first aspect of the invention attained by a method for printing fine patterns with high precision Said method comprising the actions of providing an SLM having an array of modulator elements, providing an electromagnetic radiation source, collimating radiation from said radiation source to create partially coherent illumination of said SLM with a coherence length that is larger than half the pitch of the modulating elements in the SLM, creating a negative complex amplitude with at least one modulator element.
Other aspects of the present invention are reflected in the detailed description, figures and claims.