Patent Application
20080317208
Several techniques are known for performing measurements on the surface of a semiconductor wafer. In general, these techniques determine properties of a layer by using diffraction, absorption or electron-density related effects. These techniques include but are not limited to X-ray absorption spectroscopy, small-angle X-ray scattering, X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, X-ray reflectometry measurements. While some of these measurement techniques require an X-ray detector, some of them require detecting photo-emitted electrons or photons in an energy range different from the X-ray regime. Suitable detectors include but are not limited to semiconductor detectors or gas detectors. It is desirable to provide a radiation source and a method with improved variability and accuracy during measurements of a layer of an integrated circuit.
A radiation source for a measurement tool is described herein. The radiation source includes an electron source configured to provide an electron beam, an anode configured to emit X-ray radiation under irradiation with the electron beam, and a deflection unit arranged between the electron source and the anode and operable to deflect the electron beam.
The above and still further features and advantages of the present invention will become apparent upon consideration of the following definitions, descriptions and descriptive figures of specific embodiments thereof, wherein like reference numerals in the various figures are utilized to designate like components. While these descriptions go into specific details of the invention, it should be understood that variations may and do exist and would be apparent to those skilled in the art based on the descriptions herein.
The radiation source and method of operation are explained in more detail below with reference to accompanying drawings, where:
Embodiments of a radiation source and methods of using a radiation source are discussed in detail below. It is appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways and do not limit the scope of the invention.
In the following, embodiments of the method and the radiation source are described with respect to improving variability and accuracy during measurements of a layer of an integrated circuit. The embodiments, however, might also be useful in other respects, e.g. reduction in processing time, improvements in measurement system design or improvements in characterization of deposition tools.
Furthermore, it should be noted that the embodiments are described with respect to test patterns but might also be useful in other respects including but not limited to dense patterns, semi dense patterns or patterns with isolated lines and combinations between all them. Lithographic projection can also be applied during manufacturing of different products, e.g. semiconductor circuits, thin film elements. Other products, e.g., liquid crystal panels or the like might be produced as well.
With respect to
The measurement tool 100 comprises a radiation source 104, which is, e.g., an X-ray source emitting X-ray radiation having energy between 1 keV and 250 keV. The radiation source 104 includes an electron source 106 and an anode 108. In one embodiment, the electron source 106 can be a filament comprising a suitable electrically conductive material (e.g., aluminum or tungsten). The filament is connected to a voltage source, (not shown in
The electron beam 120 provided by the electron source 106 hits the anode 108 and thus produces X-ray radiation directing partially towards a semiconductor wafer 130 as depicted by 122 in
For the anode 108, suitable materials can be tungsten, molybdenum, copper, cobalt, iron, chrome, or silver. Other materials including various mixtures or alloys can be used as well. Furthermore, the electron source 106 and the anode 108 can be constructed as separate units which can be connected by a flange.
It should be noted that the measurement tool 100 as depicted in
During operation, the anode is heated up due to the bombardment with electrons from electron beam 120. The intensity of X-ray beam 122 depends on the energy and the intensity of the primary electron beam 120, which can under spot like irradiation only to be increased up to a certain level in order to keep the thermal budget for the anode 108.
Before discussing modes of operation of measurement tool 100 in detail, a top view on semiconductor wafer 130 as a typical measurement object is depicted in
During production of integrated circuits, the semiconductor wafer 130 can for example be coated using an atomic layer deposition procedure which allows covering the surface of the semiconductor wafer with a molecular layer of a predetermined thickness in order to create a specific layer of an integrated circuit.
In order to investigate the properties of the layer coating, an X-ray measurement can be performed on the test structure 134 after, e.g., the atomic layer deposition procedure has been performed. The test structure 134 can be used to determine layer thickness, chemical composition, crystal structure, phase properties or the like.
In order to perform such measurements on the surface of the semiconductor wafer, several techniques are known in the art. In general, these techniques determine properties of a layer by using diffraction, absorption or electron-density related effects. These techniques include but are not limited to X-ray absorption spectroscopy, small-angle X-ray scattering, X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, X-ray reflectometry measurements. While some of these measurement techniques require an X-ray detector 138, some of them require detecting photo-emitted electrons or photons in an energy range different from the X-ray regime. Suitable detectors include but are not limited to semiconductor detectors or gas detectors. Furthermore, reflectivity measurements can be made either successively as a function of the azimuth angle within the surface plane of the semiconductor wafer or perpendicular to the surface plane, for example. It is also conceivable to provide a plurality of detectors in order to perform measurements for different angles or locations at the wafer simultaneously.
Common to all these techniques is that feasibility of the measurement, measurement quality, and measurement time depends on the provided intensity of the X-ray beam within the measurement spot. Furthermore, the thickness of the layer is usually small, which results in a high background signal from scattered X-rays and from material in the volume around the measurement spot. Accordingly, an increased intensity of the X-ray beam within the measurement spot reduces the measurement time and, in some applications even more important, can increase the signal to background ratio.
In order to increase the intensity of radiation source 104 and to obtain a measurable signal, in addition to the elements already explained with respect to
As shown in
Making now reference to
Another mode of operation is depicted with reference to
It should be noted that the above embodiments are only exemplary. It is within the scope of the invention to provide other suitable patterns for a beam spot, e.g., elliptical shaped beam spots or beam spots being shaped as lines having different orientations or being bent.
Furthermore, it is also possible to operate the deflection unit 140 such that it is adapted to widen the electron beam 120. Accordingly, a beam spot 520 results, which has an increasing cross section on the anode 108, as depicted in
A further mode of operation is depicted with reference to
In summary, all above described concepts result in an increased area of the electron beam 120 on the anode 108 thus allowing higher intensities of the generated X-ray beam 122 due to reduced thermal stress at the anode 108. Furthermore, the size of the beam spot can be variably selected which allows for customizing the beam spot size according to the performed measurement. In addition, the tilt angle between the plane perpendicular to the incident undeflected electron beam 120 and the surface plane of anode 108 can be adjusted differently for the above described widened or periodically deflected electron beam in order to minimize losses of X-ray radiation within anode 108.
As a result, the radiation source 104 is capable to provide X-ray radiation for X-ray absorption spectroscopy, small-angle X-ray scattering, X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, X-ray reflectometry measurements which require high intensity X-ray radiation. If lower intensities are sufficient or spot like X-ray beams are required, the deflection unit 140 can be switched in an operating state in which the electron beam 120 is not deflected. Accordingly, the radiation source 104 can be switched between several modes of operation and allows selecting appropriate X-ray intensities, spot sizes and spot cross sections depending on the type of measurement which needs to be performed. However, it is also conceivable that the radiation source 104 is capable to vary spot size and overall intensity of X-ray radiation depending on the measurement task in a continuous mode without discrete switching states.
An embodiment of a method of operating the radiation source 104 is further described making reference to
In step 610, a substrate having a surface is provided and in step 620 a detector is provided.
In step 630, an operating condition for the deflection unit is selected. The operating conditions can include operating the radiation source with a periodically deflected beam (e.g., in a circular or transversal alternating fashion), or with a widened beam.
In step 640 the surface of the substrate is irradiated with the X-ray radiation and in step 650 a measurement of the irradiated substrate is performed with the detector. The measurement can be X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, X-ray reflectometry measurements or measurements, for example, after atomic layer deposition.
While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Accordingly, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
