Patent Application
20060118718
The invention relates generally to the patterning of layered materials, and more particularly to an enhanced method and system for detection of an endpoint to the patterning of such layered materials.
Accurate and reproducible patterning, e.g. the removal or deposition of a material, is essential for very large scale integration (“VLSI”) devices. Fine line patterning has become increasingly important as devices shrink. Accordingly, endpoint detection is an indispensable tool for the avoidance of undercutting and loss of feature control.
Prior art methods of endpoint detection for the patterning of layered materials include, but are not limited to, interferometry and optical emission spectroscopy. Both interferometry and optical emission spectroscopy determine patterning endpoint.
Interferometry is problematic because as shown in
Optical emission spectroscopy is problematic because some materials do not emit light and optical emission spectroscopy cannot discriminate materials by stoichiometry. For example, silicon nitride is used in both stoichiometric and non-stoichiometric form. When either form of silicon nitride is etched, the emitted light that is monitored by optical emission spectroscopy is the same. Therefore, optical emission spectroscopy cannot discriminate between a layer with stoichiometric versus non-stoichiometric silicon nitride.
These and other deficiencies in the prior art are overcome through the invention.
Therefore, there remains a need in the art for an improved method and system for detection of an endpoint for semiconductors.
The invention is directed to a method and system for detection of an endpoint of a thickness alteration of a topmost layer in a set of layers undergoing patterning. An emission of a plurality of photoelectrons from a layer in the set of layers is received. An endpoint of the thickness alteration of the topmost layer is then detected upon either receipt of the emission or absence of the emission.
The invention detects endpoint of a thickness alteration of a layer in a set of layers undergoing patterning. The invention detects endpoint before destruction of the underlying layers. Accordingly, the invention protects the underlying layers, which in turn can improve production. The invention reliably detects endpoint in a manner independent of topography or stoichiometry. Accordingly, the invention improves upon the versatility of patterning endpoint detection, as new materials are used in layered material fabrication.
For at least the foregoing reasons, the invention improves upon endpoint detection for the patterning of layered materials.
The features and the element characteristics of the invention are set forth with particularity in the appended claims. The figures are for illustrative purposes only and are not drawn to scale. Furthermore, like numbers represent like features in the drawings. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows, taken in conjunction with the accompanying figures, in which:
The invention will now be described with reference to the accompanying figures. In the figures, various aspects of the structures have been shown and schematically represented in a simplified manner to more clearly describe and illustrate the invention.
The invention solves the problems associated with prior art endpoint detection methods. In accordance with the invention, a layered material, e.g. a semiconductor, dielectric, or conductor, is irradiated with an x-ray beam, which comprises photons, and a photoelectron emission is caused in response to this irradiation. Photoelectron emissions have signals with energy levels unique to the material of the layer from which the photoelectrons are emitted. The material can be a compound or a element. Because photoelectrons have a short mean free path, photoelectrons generated from materials >9 nm below the surface are not detectable. Such photoelectrons are collisionally de-energized. When the topmost layer becomes thin, however, e.g. ≦9.0 nm, the underlying layer emits a photoelectron emission. Accordingly, endpoint can be detected upon receipt of the photoelectron emission from the underlying layer.
By way of overview and introduction, polysilicon stack etch (“PC etch”) will be described in accordance with the method of the invention. At the time of PC etch, a semiconductor wafer has ˜2000 A of patterned photoresist, 1000 to 1500 A of underlying polysilicon, and 1000 to 1500 A of further underlying gate oxide. An x-ray beam irradiates the surface of the wafer. A detection system detects a photoelectron signal from the photoresist and polysilicon, but does not detect the photoelectron signal from the gate oxide, which underlies the photoresist and polysilicon. Therefore, the photoelectron signal from the gate oxide is undetectable because of the thickness of the photoresist and polysilicon layers above the gate oxide. As the polysilicon is etched, the thickness of the polysilicon decreases. Once the thickness is ≦9.0 nm, photoelectrons generated from the gate oxide are detectable. Accordingly, at such time a photoelectron emission unique to the gate oxide, such as oxygen, is detectable. A constant photoelectron emission signal of oxygen from the photoresist remains, however that signal becomes a background signal to the photoelectron emission signal of the gate oxide. Accordingly, upon comparison of substantially different signals, patterning endpoint is detected.
While the invention has been particularly described in conjunction with a specific preferred embodiment and other alternative embodiments, it is evident that numerous alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore intended that the appended claims embrace all such alternatives, modifications and variations as falling within the true scope and spirit of the invention.
