Abstract:
A method of manufacturing a semiconductor device includes depositing a layer over a substrate and etching the layer to form a grating structure, a cross bridge test structure and a line width measurement structure. The grating structure includes a plurality of parallel lines and one of the multiple parallel lines is connected to the line width measurement structure and the cross bridge test structure. A scatterometry test is performed on the grating structure to obtain a line width and this width is compared to a line width calculated using the line width measurement structure. A semiconductor device is also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the manufacturing of semiconductor devices, and more particularly, to forming strained-silicon devices having improved characteristics. 
     BACKGROUND OF THE INVENTION 
     Over the last few decades, the semiconductor industry has undergone a revolution by the use of semiconductor technology to fabricate small, highly integrated electronic devices, and the most common semiconductor technology presently used is silicon-based. A large variety of semiconductor devices have been manufactured having various applications in numerous disciplines. One silicon-based semiconductor device is a metal-oxide-semiconductor(MOS) transistor. The MOS transistor is one of the basic building blocks of most modern electronic circuits. Importantly, these electronic circuits realize improved performance and lower costs, as the performance of the MOS transistor is increased and as manufacturing costs are reduced. 
     A typical MOS device includes a bulk semiconductor substrate on which a gate electrode is disposed. The gate electrode, which acts as a conductor, receives an input signal to control operation of the device. Source and drain regions are typically formed in regions of the substrate adjacent the gate electrodes by doping the regions with a dopant of a desired conductivity. The conductivity of the doped region depends on the type of impurity used to dope the region. The typical MOS device is symmetrical, in that the source and drain are interchangeable. Whether a region acts as a source or drain typically depends on the respective applied voltages and the type of device being made. The collective term source/drain region is used herein to generally describe an active region used for the formation of either a source or drain. 
     During the manufacturing process, a semiconductor device undergoes many types of metrology tests to ensure the quality of the semiconductor device. For example, processes, such as lithography, are controlled, in part, by taking dimensional measurements of certain features of the semiconductor device formed by the lithography process. One type of measurement technique used to measure the dimensions of a structure in a semiconductor device is scatterometry. Scatterometry is a non-destructive optical technique that records and analyzes changes in the intensity of light reflected from a periodic scattering surface. By measuring and analyzing the light diffracted from a patterned periodic sample, the dimensions of the sample structure can be measured. Other types of measurement techniques used to measure the dimension of a structure are electrical tests, known as I-force and V-measure. These tests use known parameters, such as length of a line, and calculated parameters, such as sheet resistance, to calculate line width based on voltage drop across electrodes connected to the line. These different types of metrology tests, however, use different structures on the semiconductor device. As such, cross-correlating the results of these metrology tests has not been possible. Furthermore, the width of the lines in two different test structures can vary as a result of process used to form the lines. As the size of structures are becoming increasingly smaller, the variation in line width introduced by the manufacturing process becomes increasingly significant to the accuracy of the testing. Accordingly, a need exists for an improved semiconductor device and method of forming the same that allows for cross-correlation of results from different types of metrology tests and eliminates line width disparity between two different test structures. 
     SUMMARY OF THE INVENTION 
     This and other needs are met by embodiments of the present invention which provide a method of manufacturing a semiconductor device that allows for a direct comparison of a line width calculated by optical scatterometry metrology and a line width calculated by an electrical line width measurement test. The method includes depositing a layer over a substrate and etching the layer to form a grating structure, a cross bridge test structure and a line width measurement structure. The grating structure includes a plurality of parallel lines and one of the multiple parallel lines is connected to the line width measurement structure and the cross bridge test structure. A scatterometry test is performed on the grating structure to obtain a line width and this width is compared to a line width calculated using the line width measurement structure. 
     In another embodiment of the present invention, a semiconductor device is provided. The semiconductor device includes a grating structure with a plurality of parallel lines. One of the parallel lines is connected to a line width measurement structure. The line is also connected to a sheet resistance test structure. The line width measurement structure is formed from first and second pairs of electrodes, and the sheet resistance test structure is a cross bridge test structure formed from the second pair of electrodes and a third pair of electrodes. 
     Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout, and wherein: 
     FIGS. 1-4 schematically illustrate sequential phases of a method of forming a semiconductor device with embedded test structures according to one embodiment of the present invention. 
     FIG. 5 is a top plan view of a combination test structure according to an embodiment of the present invention. 
     FIG. 6 schematically illustrates an optical scatterometry test using the test structure of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention allows for cross-correlation of the same measured dimension using two different types of metrology testing techniques. This is achieved, in part, by providing a semiconductor device having a grating structure connected to a line width test structure. A line width can then be measured both optically, using a technique such as scatterometry with the grating structure, and electrically, using a technique with the line width test structure. 
     An exemplary method of manufacturing a semiconductor device having two combined test structures is illustrated in FIGS. 1-4. Although FIGS. 1-4 describe that the combined test structures are formed using the same layers as a gate electrode of a transistor, the invention is not limited in this manner, as the combined test structures can be formed separately or formed from the layer(s) used to form other structures in the semiconductor device, such as metal lines in inter-level dielectrics. 
     In FIG. 1, a layer, such as a gate dielectric 16, is formed on a top surface of the substrate  10 , and the gate dielectric  16  is not limited as to a particular material. For example, the gate dielectric  16  can be formed from a high-K material or from a material such as silicon dioxide. The formation of a silicon dioxide gate dielectric  16 , for example, can be accomplished using thermal oxidation at temperatures between about 700 and about 1000° C. in an oxygen-steam ambient. Although not limited in this manner, the gate dielectric  16  can have a thickness between about 3 and about 20 nanometers. The substrate  10  can be formed from such materials as silicon, strained silicon, and silicon-on-insulator(SOI). 
     After formation of the gate dielectric  16 , a gate electrode is formed over the gate dielectric  16 . Although not limited in this manner, an exemplary method of forming a gate electrode is illustrated in FIGS. 2-4. In FIG. 2, a layer of undoped polysilicon  18  is blanket deposited, for example by low pressure chemical vapor deposition (LPCVD) at temperatures between about 600 and about 800° C., on the top surface of gate dielectric  16 . Although not limited in this manner, the polysilicon layer  18  can have a thickness between about 50 and about 500 nanometers. The polysilicon layer 18 can then he implanted with nitrogen ions. The implanted nitrogen ions, for example, can be used to retard the diffusion of boron atoms. The implantation of the nitrogen ions can be at a dosage between about 5×10 14  and about 5×10 15  dopants/cm 2  and at an energy level between about 20 and about 200 keV. 
     The polysilicon layer  18  is then etched to form the gate electrode. As illustrated in FIG. 3, the etching involves forming a photoresist  22  on the polysilicon layer  18 , and selectively irradiating the photoresist  22  using a photolithographic system, such as a step and repeat optical projection system, in which ultraviolet light from a mercury-vapor lamp is projected through a first reticle and a focusing lens to obtain a first image pattern. The photoresist  22  is then developed, and the irradiated portions of the photoresist  22  are removed to provide openings in the photoresist  22 . The openings expose portions of the polysilicon layer  18 , which when removed, will define the gate electrode. 
     In FIG. 4, an etch, typically anisotropic, is applied to remove the exposed portions of the polysilicon layer  18  and the underlying portions of the gate dielectric  16 . After etching, the remaining portion of the polysilicon layer  18  provides a gate electrode  24 . Although not limited in this manner, the width of the gate electrode  24  can be from about 20 to 250 nanometers. 
     FIG. 5 illustrates a top view of a grating structure  100  after the photoresist  22  is stripped. The grating structure  100  comprises dummy gate electrodes or dummy lines  24 D. The grating structure  100  is not limited as to a particular line width W or pitch P of the lines  24 . However, in at least one aspect of the grating structure  100 , the line width W is 60 nanometers or less and the pitch P is about three times the line width W. Attached to one of the lines  30  of the grating structure  100  is a line width test structure that can be used to measure the line width W of the line  30 . Although not limited in this manner, the line  30  to which the line width test structure is attached can be positioned at the center of the grating structure  100 , as viewed from above. 
     Although any line width test structure capable of measuring line width W is acceptable for use in the semiconductor device, in least one aspect of the invention the line width test structure is a linear bridge formed from a first pair of electrodes E 1 , E 3  and a second pair of electrodes E 2 , E 4  that are interconnected via the line  30 . Although not required, the semiconductor device can include a sheet resistance testing structure, and any sheet resistance testing structure capable of measuring sheet resistance is acceptable for use in the semiconductor device. In least one aspect of the invention the sheet resistance testing structure is a cross bridge formed from the second pair of electrodes E 2 , E 4  that are interconnected to a third pair of electrodes E 5 , E 6 . Using the structures described above, the line width W of the line  30  is electrically calculated as follows using a probing device commonly known to those skilled in the art: 
     The resistance R L  of the linear bridge is given by:          R   L     =       V   43       I   21                              
     Where V 43 =V 4 −V 3  (voltage drop measured between electrodes E 4  and E 3 ) and I 21  is a current between electrodes E 2  and E 1 . The sheet resistance R S  of the cross bridge is given by:          R   S     =       π     LN                 2            (       (       (         V   2     -     V     4                      I   56       )     +     (         V   5     -     V     2                      I   64       )       )     /   2     )                              
     Resistance R L  of the linear bridge relates to sheet resistance R S  of the cross bridge as follows:          R   S     =         W   L          R   L       =       W   L                       V   43       I   21                                  
     Where L is a length of the line  30  being measured. By rearranging this equation to solve for line width W:        W   =       R   s        L                     I   21       V   43                                
     The line width W of the line  30  can then be calculated using sheet resistance R S , length L of the line  30 , drive current I 21  between electrodes E 2  and E 1 , and voltage drop V 43  measured between electrodes E 4  and E 3 . 
     After the grating structure  100  has been formed, the dimensional characteristics of the lines  24 ,  30  in the grating structure  100  can be measured using an optical technique, such as scatterometry, as illustrated in FIG.  6 . The method of determining dimensional characteristics of the lines  24 ,  30  by scatterometry is not limited as to the type of scatterometry tool used, and examples of scatterometry tools include 2 Theta-type systems and lens-type systems. The scatterometry tool may use white light, or other wavelength or combination of wavelengths, depending on the specific implementation. 
     Typically, the scatterometry tool  60  generates an incident beam  66  from emitter  62  that has a wide spectral composition, and the intensity of the light  66  changes relative to changes in wavelength. The light  66  reflected from the grating structure  100  is measured by a receiver  64 . The angle of incidence of the light  66  onto the grating structure  100  may also vary, depending on the specific implementation. Also, the profile traces generated by the scatterometry tool  60  may be based upon a comparison of light intensity to wavelength (for white light, fixed angle type scatterometry tools) or a comparison of intensity to incident angle (for angle resolved systems that use a single light source). For example, a spectroscopic ellipsometer (single angle, many wavelengths), or a laser (single wavelength, many angles) may be used. In addition, the intensity of the reflected light may be measured as s- and p-polarization over either multiple angles or at multiple wavelengths. 
     From the data obtained by the scatterometry tool, a line width W of the lines can be obtained. The line width obtained from the scatterometry tool can than be compared to the line width calculated using the line width measuring structure. In this manner, the results of the two tests can be double checked with one another to thereby provide a more robust testing of the semiconductor device. 
     The present invention can be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention can be practiced without resorting to the details specifically set forth. In other instances, well-known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention. 
     Only the preferred embodiment of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concepts as expressed herein.