Patent Application
20090107399
Embodiments of the invention relate to systems of film height measurements and methods of measuring film height on a substrate.
In the accompanying drawings:
Embodiments of methods and systems measuring film height on a substrate 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 system are described with respect to measuring film height on a substrate during manufacturing of an integrated circuit. The embodiments, however, might also be useful in other respects, e.g., improvements in process control, improvements in identifying lot to lot variations of a layout pattern, yield enhancement techniques or the like.
Furthermore, it should be noted that the embodiments are described with respect to film height measurements during production of integrated circuits but might also be useful in other respects and can be applied during manufacturing of other products, e.g., semiconductor circuits, thin film elements. Other products, e.g., liquid crystal panels or the like might be produced as well.
According to an embodiment of the invention the photometric measurement system 100 includes a radiation source 120 which is configured to emit a beam of radiation 110 onto a substrate 140. The light source 120 can be a lamp or a laser emitting radiation having a plurality of wavelengths in the visible range, i.e., serving as a polychromatic light source. The term “visible range” includes wavelength starting at about 300 nm up to approximately about 800 nm.
The emitted beam 110 is focused on the substrate 140. Focusing can be performed by employing a lens 130 together with an aperture stop 135 which are arranged between the radiation source 120 and the substrate 140. Furthermore, other optical devices like a polarizer for providing a linear, elliptical or radial polarized beam can be employed as well.
Substrate 140 reflects the incoming beam 110 from the surface as reflected beam 150. The reflected beam 150 shows an interfering behavior which results in a characteristic interference color depending on various properties of the surface of the substrate 140 as generally known with respect to interference colors of thin films on a substrate. It should be noted that the term “interference color” refers to a spectral color described by monochromatic light as well as a color value described by a composition of several wavelengths.
When a substrate 140 is coated with a layer on top of an optically reflecting surface, the color depends upon other properties of the film thickness of the layer, optical properties of the layer, the angle of incidence and the material properties of the layer.
Accordingly, a measurement of the color value is related to the film height of the layer on substrate 140. Furthermore, during manufacturing of integrated circuits the layer on top of substrate 140 can be manufactured such that the optical and material properties of the layer do not significantly vary. Accordingly, measurement of the color can be directly related to film thicknesses.
In order to perform measurements of color values, the reflected beam 150 is sampled on a detector 160. As shown in
For manufacturing of integrated circuits, the surface of substrate 140 is typically patterned in different illumination areas which can be structured using a lithographic projection apparatus having an Excimer laser as a light source, for example. Light coming from the light source is projected through a photomask, which comprises a mask pattern, i.e., being composed of light absorptive or light attenuating elements.
The mask pattern is derived from a layout pattern which can be provided by a computer aided design system, in which structural elements of the layout pattern is generated and stored. The different illumination areas can be successively projected onto substrate 140. Typically, different illumination areas are surrounded by a cutting frame in which test structures or other elements not required for a functional circuit are arranged.
As shown in
In order to evaluate the signals, a measurement tool is provided which allows for absolute film height thickness measurements. For example, an ellipsometer or scatterometer can be used to determine the absolute film height thickness for one or more specific sample points while in regions between the sample points the color or color differences are used to determine thickness values of the layer.
It should be noted that the interference color determined during a photometric measurement can change its value for different film heights according to characteristic rainbow color spectrum, i.e., starting from violet, blue, yellow, green, red and then violet again, which repeats for different orders of interferences. Depending on coherency or light emitting area of radiation source 120, it is also possible to achieve non-spectral colors, i.e., a superposition of several wavelengths which are described by color values.
By comparing different color values at neighboring positions on substrate 140, a color map can be measured. By calibrating the color map with one absolute measurement, e.g., using scatterometry or the like, the film height differences between adjacent positions on the substrate can be translated into absolute film height values by observing the interference color sequence of the layer under investigation.
This is now further illustrated making reference to
Furthermore, it is possible to move the substrate 140 underneath the illumination area 200 so as to arrive at many color values for the whole substrate. This can be achieved by either moving the substrate 140 on a holder together with a rigidly installed measurement system 100. Other options, including proper light guides or moving the measurement system 100 instead of the substrate 140 or moving both the measurement system 100 and the substrate 140 are conceivable as well.
Accordingly, it is possible to calculate a set of film height values which are stored in a memory and can be compared to actual measurements, so as to arrive at a complete map of film height values for a plurality of sample points. It should be noted, however, that many other possible approaches can be used in order to arrive at a sample parameter. For example, the measurements can be performed iteratively or subsequently for different sample points on the substrate 140.
For an unstructured substrate 140, i.e., a substrate having a planar surface, the color values can be translated into film height values by providing at least one absolute measurement. As indicated in
In
For the partially structured substrate 140, i.e., a substrate having a planar surface, the color values can only be derived in regions within the cutting frame. Furthermore, at least one absolute measurement is necessary in order to translate color values into film height values.
As indicated in
As shown in
In order to arrive at film height differences the color value can be further investigated by providing a characteristic of film height differences versus interference color for several orders of interference.
As shown in
Here, color values according to characteristic interference colors, i.e., starting from and successively repeating violet, blue, yellow, green, red and then violet again are shown together with the associated film height differences derived by absolute calibration using, for example, a suitable spectroscopic measurement tool for one color value 510. It should be noted that the characterization of curve 500 can also be derived from theoretical model calculations.
In
In step 610 a substrate is provided being coated with a layer having a nominal film height.
In step 620 a radiation source is provided configured to emit a beam of radiation having a wavelength in the optical range.
In step 630 the substrate is illuminated with the beam of radiation for at least two positions.
In step 640 a signal for at least two positions is detected which corresponds to radiation being reflected from the substrate.
In step 650 a film height difference of the layer is calculated.
As an example, semiconductor products usually require coating of a layer. According to an embodiment of the invention it is now possible to measure layer thicknesses even without employing other technologies like ellipsometry, reflectometry or scanning electron microscopy of a wafer cutted along the surface axis which is either time-consuming or may destroy the substrate 140.
As systems of measuring film height values on a substrate can be readily implemented into a fabrication unit of semiconductor manufacturing equipment, it is possible to achieve in situ measurements of layers having either structured or unstructured surfaces.
As shown in
The signals are forwarded via lines 706 to processor 720 which is capable of calculating a film height difference of the layer based on layer reflected beam signals for the at least two positions. The substrate 140 is forwarded to the absolute measurement system 710 which provides a film height for a specific point, as explained with respect to
Having described embodiments of the invention, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as defined by the appended claims.
Having thus described the invention with the details and the particularity required by the patent laws, what is claimed and desired to be protected by Letters Patent is set forth in the appended claims.
