The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Lithography is widely used in various industrial applications, including the manufacture of integrated circuits, flat panel displays, micro-electro-mechanical systems, micro-optical systems etc. Generally speaking, the lithography process is used for producing a patterned structure. During the manufacture of integrated circuits, a semiconductor wafer undergoes a sequence of lithography-etching steps to produce a plurality of spaced-apart stacks, each formed by a plurality of different layers having different optical properties. Each lithography procedure applied to the wafer results in the pattern on the uppermost layer formed by a plurality of spaced-apart photoresist regions.
"To assure the performance of the manufactured products, the applications of the kind specified above require accurate control of the dimensions of the sub-micron features of the obtained pattern. When dealing, with wafers, the most frequently used dimensions are the layer thickness and the so-called 'critical dimension' (CD). CD is the smallest transverse dimension of the developed photoresist, usually the width of the finest lines and spaces between these lines. Since the topography of the measured features is rarely an ideal square, additional information found in the height profile, such as slopes, curves etc., may also be valuable in order to improve the control of the fabrication process.
"Generally, an ordinary optical microscope can be used for measuring features' dimensions. A microscope is practically capable of measuring line width with a resolution of no less than 0.1 .mu.m. The current high-performance semiconductor devices, however, have features' dimensions of 0.18 .mu.m, and require CD measurement with the resolution of a few nanometers.
"Several Optical CD (OCD) measurement techniques recently developed rely on imaging a certain test pattern which is placed in a special test area of the wafer. These techniques utilize various methods aimed at amplifying tiny differences in the line-width to obtain macroscopic effects that could be resolved by visible light, although the original differences are more than two orders of magnitude below the wavelength used. However, some of these techniques do not rely on fundamental physical effects, and thus could be more effective in some cases and less effective in others.
"Another kind of technique utilizes scatterometric measurements, i.e., measurements of the characteristics of light scattered by the sample. To this end, a test pattern in the form of a grating is usually placed in the scribe line between the dies. The measurement includes the illumination of the grating with a beam of incident light and determining the diffraction efficiency of the grating under various conditions. The diffraction efficiency is a complicated function of the grating line profile and of the measurement conditions, such as the wavelength, the angle of incidence, the polarization and the diffraction order. Thus, it is possible to gather a wealth of data thereby allowing the extraction of information about the line profile.
"Techniques that utilize the principles of scatterometry and are aimed at the characterization of three-dimensional grating structures and the determination of line profiles have been disclosed in numerous publications. Publications, in which diffraction efficiency was measured versus wavelength, include, for example the following: (1) A. Roger and
"According to another group of publications, a monochromatic light source (e.g. laser) is utilized, and grating profile parameters are extracted from the measurement of the diffraction efficiency versus incidence angle. Such publications include, for example the following: (A) S. S.
"In a third group of publications, the diffraction efficiency is measured when both wavelength and incidence angle are constant. In this case, information is extracted from the comparison of diffraction efficiency of several orders. This group of publications includes, for example, the following documents: (I) U.S. Pat. No. 4,330,213 discloses a line-width measurement system using a diffraction grating. In this system, the intensities of first and second order light components are obtained to determine the line-width using empirical formulae. (II) U.S. Pat. No. 5,361,137 discloses another example of the use of a conventional scatterometry technique. Here, a set of intensities of the '1' or '2' diffraction order image of the set of 'fixed-line width and variable-pitch-width' test gratings is recorded. From this set of intensities, line-width can be calculated.
"Generally speaking, the conventional techniques use the following methodology in order to analyze the measured results:
"First, a model is assumed for the grating profile having a number of parameters that uniquely define the profile. The user defines the required model (type of model) and sets the limits and the required resolution for each of the desired parameters.
"Second, a spectral library is prepared using an optical model. The spectral library contains the calculated spectra for all possible profiles as defined by the user.
"Third, given a measured spectrum, a fitting procedure finds the profile whose calculated spectrum included in the spectral library best matches the measured spectrum."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "There is accordingly a need in the art to facilitate the control of the manufacture of patterned structures by providing a novel method and system for measurements in a patterned structure to determine a line profile of the structure, utilizing the principles of scatterometry.
"The term 'patterned structure' signifies a structure comprising a plurality of spaced-apart stacks (elements) each including different layers, the pattern being formed by patterned regions and un-patterned regions. The term 'pattern region' used herein signifies is a region including elements (stacks) having different optical properties, and the term 'unpatterned region' signifies a region with substantially uniform optical properties, as compared to the patterned region. Such an un-patterned region is comprised of a single stack including different layers having different optical properties.
"The main idea of the present invention is based on obtaining measured data from at least two measurements applied to the same patterned structure (e.g., wafer) in order to achieve both high accuracy and high reliability measurements. The entire measurement procedure is carried out is several steps, taking a different measurement at each step. Analysis, likewise, is performed in several steps, wherein each analysis step utilizes the information obtained in the previous steps. The two measurements could be applied at two different measurement sites located, respectively, in patterned and un-patterned regions. The two measurements may be carried out so as to detect light returned from the structure with different solid angles of propagation, or with different states of polarization.
"According to the present invention, at least one parameter of the profile considered in an optical model used for measurements is determined by analyzing at least one preliminary measurement applied to a predetermined site on the structure (wafer). The preliminary measurement is inherently different from further measurements by either the type of site under measurements or the measurement conditions (angle, polarization, wavelength range, diffraction order, etc.). For example, the preliminary measurement utilizes normal incidence of an illuminating beam, while the further measurement utilizes oblique illumination. Data (parameters) obtained through this preliminary measurement is used for optimizing the fitting procedure, thereby improving further measurements applied to other locations on the structure.
"Preferably, the parameters obtained through the preliminary measurement include the reflectivity and thickness of at least one layer underneath the uppermost layer. Additionally, the at least one preliminary measurement allows for determining optical constants (i.e., refraction and absorption coefficients n and k) and thickness of the regions of the uppermost layer.
"There is thus provided according to one aspect of the present invention, a method of determining a line profile in a patterned structure for controlling a process of manufacture thereof, wherein the patterned structure comprises a plurality of different layers, the pattern in the structure being formed by patterned regions and un-patterned regions, the method comprising the steps of: carrying out at least first and second measurements, each of the measurements utilizing illumination of the structure with a broad wavelengths band of incident light which is directed on the structure at a certain angle of incidence, detection of spectral characteristics of light returned from the structure, and generation of measured data representative thereof; analyzing the measured data obtained with the first measurement and determining least one parameter of the structure; and analyzing the measured data obtained with the second measurement and utilizing at least one parameter for determining the profile of the structure.
"According to another aspect of the present invention, there is provided a measurement system for determining a line profile in a patterned structure comprising a plurality of different layers, the pattern in the structure being formed by patterned regions and un-patterned regions, the system comprising a measuring unit including an illumination assembly and a collection-detection assembly, and a control unit coupled to output of the measuring unit, wherein: the illumination assembly produces incident light of substantially broad wavelengths band directed onto the structure at a certain angle of incidence, and the collection-detection assembly detects spectral characteristics of light returned from the structure and generates measured data representative thereof; the measuring unit is operable for carrying out at least first and second measurements and generating measured data representative of the detected returned light; and said control unit is operable to be responsive to the generated measured data for analyzing the measured data obtained with the first measurement to determine at least one parameter of the structure, and utilizing the at least one determined parameter while analyzing the measured data obtained with the second measurement for determining the line profile of the structure.
"The scatterometry based measurement technique provides the collection of a large amount of data from each measured profile, e.g., the diffraction efficiency in a large number of different angles or a large number of wavelengths. This richness of data may allow the fitting of the measurements to the results of a multi-parameter model describing the measured profile, thus providing more information than merely stating the CD. This additional information also provides confidence in the results, particularly if the effective number of independent measured values is significantly larger than the number of free parameters in the model. Since exact models describing diffraction from general profiles and in general situations have been developed for years and are known to be of high accuracy, these methods have a good chance of obtaining accurate results.
"The system according to the invention can be applied as an integrated metrology tool. In contrast to all conventionally used off-line measurement tools, occupying a large footprint and requiring additional manual operations that slow down the entire fabrication process and allow only the measurement of samples from each production lot, the system of the present invention may be integrated as part of the production machine, thus allowing full automation of the manufacturing process. For this integration to be possible, the system should be very economical in space.
"Additionally, the operation of the system is fast enough, so that every semiconductor wafer in the production line can be measured, allowing closer control over the process. The system of the present invention enables a multi-stage measurement procedure, thereby improving the quality of the entire measurement. The measurement technique according to the invention requires only a small measurement site in accordance with the area constraints, which characterize current lithography.
"More specifically, the present invention is used for process control in the manufacture of semiconductor devices (wafers), e.g., the control of a lithography process, and is therefore described below with respect to this application.
BRIEF DESCRIPTION OF THE DRAWINGS
"in order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
"FIG. 1 is a schematic illustration of a wafer structure;
"FIGS. 2A and 2B are schematic illustrations of two possible examples, respectively of the line profile showing some parameters thereof to be measured;
"FIG. 3 is a schematic illustration of the main components of a measurement system constructed according to one embodiment of the invention;
"FIG. 4 is a schematic illustration of the main components of a measurement system constructed according to another embodiment of the invention;
"FIG. 5 is a schematic illustration of the main components of a measurement system constructed according to yet another embodiment of the invention;
"FIG. 6 is a schematic illustration of one more embodiment of the invention;
"FIG. 7 is an example of a part of a production line utilizing the system of either of FIGS. 3, 4, 5 and 6;
"FIG. 8 illustrates another example of a production line utilizing the system of either of FIGS. 3, 4, 5 and 6; and
"FIG. 9 is a schematic illustration of a system utilizing several measurement systems according to the invention using a common server utility.
"FIG. 10 is a flowchart illustrating the method according to the present invention."
For additional information on this patent application, see: FINAROV, Moshe; BRILL, Boaz. Method and System for Measuring Patterned Structures. Filed
Keywords for this news article include: Electronics, Semiconductor,
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