Patent Application
20060043071
The present invention relates to process control and particularly to adjusting process parameters for Chemical-Mechanical Polishing (CMP) and plating processes using in-situ thickness measurement.
A continued emphasis on semiconductor device miniaturization, leading to the technological evolution of Large Scale Integration (LSI), Very Large Scale Integration (VLSI) and Ultra Large Scale Integration (ULSI), has resulted in shorter inter-linear device distances. As a result of this ever shallower image depth, target surfaces must be created with enhanced flatness. Increased semiconductor device density is frequently implemented using multi-layered configurations, further leading to demands of increased planarity of the surface over which additional semiconductor device features are created.
A polishing system that uses chemical slurry is commonly known as a chemical mechanical polishing (CMP) system. Currently, CMP is widely used for planarizing inter-level dielectrics and metal layers. A CMP process is performed by sliding a wafer surface on a relatively soft polymeric porous pad flooded with chemically active slurry containing abrasive particles of sub-micron diameter. The mechanical properties of the polishing pad and its surface morphology control the quality and efficiency of CMP process. The pad surface morphology controls the partition of down pressure between the abrasive particles and direct wafer/pad contact. In addition, the polishing pad behaves in an elastic and/or viscoelastic manner under the applied pressure, which is thought to affect the WIWNU (within wafer non-uniformity) or planarity. In practice, it is not clear what pad property should be measured to characterize the polishing results.
Hence, there is a need for a process control system that addresses within wafer non-uniformity arising from the existing CMP technology.
It is therefore an object of the invention to provide a system and method for real time process control to improve process accuracy for film plating and removal. To achieve this and other objects, embodiments of the present invention provide a system and method employing an eddy current testing to monitor surface characteristics of a substrate during a polishing process, and using the surface characteristics to adjust process parameters of plating and polishing tools performing plating and polishing processes.
According to an embodiment of the invention, a fabrication system comprising a plating tool, a polishing tool, a metrology tool, and a controller is provided. The plating tool generates a layer of conductive material on a substrate. The polishing tool uses a mechanical mechanism to remove the conductive material from the substrate. The metrology tool measures an electromagnetic signal induced in the conductive material using a non-destructive testing mechanism. The controller, coupled to the polishing and metrology tools, determines residue thickness and removal rate of the conductive material during the polishing process according to the measured electromagnetic signal, and adjusts a process parameter for the polishing tool accordingly.
Another embodiment of the invention provides a processing method executed in a fabrication system. First, a substrate covered with a layer of conductive material is provided. Second, a first polishing run, defined by a first process parameter, is performed to remove the conductive material using a mechanical mechanism. An electromagnetic signal induced in the conductive material is measured using a non-destructive testing mechanism. A residue thickness and removal rate of the conductive material during the first polishing run are then determined according to the measured electromagnetic signal. The first process parameter for the polishing tool is then adjusted accordingly. Next, a second polishing run defined by the adjusted process parameter is performed. Additionally, a second process parameter for a plating tool is determined, and a plating process is performed as defined by the second process parameter.
The above-mentioned method may take the form of program code embodied in a tangible media. When the program code is loaded into and executed by a machine, the machine becomes an apparatus for practicing embodiments of the invention.
A detailed description is given in the following embodiments with reference to the accompanying drawings.
Embodiments of the present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
Embodiments of the present invention will now be described with reference to FIGS. 2 to 6, which in general relate to a process control system within a fabrication system. While the embodiments disclosed operate with a Cu-removal CMP process, it is understood that any metal-film removal process polishing a face-down substrate may operate with the present invention.
The fabrication system 200 comprises a polishing tool 21, a plating tool 22, a metrology tool 23, and a controller 25. The plating tool 22 generates a layer of conductive material on a substrate The polishing tool 21 uses a mechanical mechanism to remove the layer of conductive material, such as copper (Cu), from the substrate. According to this embodiment, the polishing tool 21 is a chemical-mechanical polishing (CMP) tool, applying variable downward pressure on different polishing zones, resulting in different removal rates for different polishing zones. The metrology tool 23 measures an electromagnetic signal generated from the Cu layer using a non-destructive testing method. According to this embodiment, the metrology tool 23 is an eddy current testing device comprising two testing probes 231 and 233 measuring Cu film thickness in different polishing zones. The testing probe 231 is disposed on the central area of the polished surface, while the testing probe 233 is disposed on an edge area thereof. Polishing tool 21, plating tool 22, and metrology tool 23 are connected to controller 25. Polishing tool 21 and metrology tool 23 cooperate but may not be connected directly. The controller 25 determines residue thickness and removal rate of Cu during the polishing process according to the measured electromagnetic signal and a preset regression model specifying correlation therebetween, and adjusts process parameters for polishing tool 21 and plating tool 22 accordingly. The preset regression model is stored in a database 27, connected to controller 25.
First, a substrate covered with a layer of conductive material is provided (step S31). The conductive material can be any metal deposited on a substrate during semiconductor manufacture, such as copper (Cu).
Before a polishing process is performed, a first regression model is provided, specifying correlation between residue Cu thickness and a measured electromagnetic signal (step S321). Additionally, a second regression model is provided, specifying correlation of the Cu removal rate and a change rate of the measured electromagnetic signal (step S323). According to this embodiment, the electromagnetic signal is a voltage measurement obtained by a voltmeter, and the first and second regression models are linear regression models. The first and second regression models are determined experimentally using a blank wafer.
y=0.4638x−175.17 (Equation 1.1)
R2=0.7411
The regression equation for a testing probe disposed on the central area of the polished surface is as follows:
y=0.436x−76.99 (Equation 1.2)
R2=0.8434
According to the regression equations 1.1 and 1.2, y is voltage measurement (mV) and x is residue Cu thickness (Å).
y=−0.0063x+16.303 (Equation 2.1)
R2=0.6926
The regression equation for a testing probe disposed on the center of the polished surface is as follows:
y=−0.0087x+2.851 (Equation 2.2)
R2=0.7724
According to the regression equations 2.1 and 2.2, y is change rate of measured voltage (mV/sec) and x is Cu removal rate (Å/min).
A first polishing run is then performed (step S33). The first polishing run performs a CMP process as defined by a first process parameter to remove a layer of Cu and to planarize the surface of the substrate. The first polishing run removes bulk of Cu from the substrate, leaving a slightly concave surface as shown in
The Cu film thickness measurements on the central and edge areas are then obtained using an eddy current testing device. The central and edge areas of the polished surface are inspected using central and edge testing probes, respectively.
Electromagnetic signals induced from the Cu layer on the central and edge areas are then measured by the central and edge testing probes, respectively (step S35). According to this embodiment, a voltage measurement of the induced eddy current is obtained by a voltmeter.
Residue Cu thickness is then determined according to the voltage measurement and the first regression model (step S37). The voltage measurement is then used to determine a corresponding residue Cu thickness according to the first regression model. Y in Equation 1.1 is substituted by a voltage measurement obtained by the edge testing probe, and a corresponding residue Cu thickness is then determined accordingly. Similarly, y in Equation 1.2 is substituted by a voltage measurement obtained by the central testing probe, and a corresponding residue Cu thickness is then determined accordingly.
Cu removal rate is then determined according to a change rate of the voltage measurement and the second regression model (step S39). The change rate of the voltage measurement is then determined and used to estimate a corresponding Cu removal rate according to the second regression model described above. Y in Equation 2.1 is substituted by a change rate of voltage measurement obtained by the edge testing probe, and a corresponding Cu removal rate is then determined accordingly. Similarly, Y in Equation 2.2 is substituted by a change rate of voltage measurement obtained by the central testing probe, and a corresponding Cu removal rate is then determined accordingly.
After the residue Cu thickness and the Cu removal rate for the edge and central areas are determined, a process parameter of the first process run is then adjusted accordingly (step S391).
Downward pressure applied at the edge and central areas of the polished surface are adjusted to modify Cu removal rates thereof (step S395). The polishing tool applies the adjusted downward pressure on the edge and center of the polished surface to remove Cu, and leaves a planarized Cu film without a concave appearance, as shown in
The method of the present invention, or certain aspects or portions thereof, may take the form of program code (i.e. instructions) embodied in a tangible media, such as floppy diskettes, CD-ROMS, hard drives, or any other machine-readable storage medium, wherein, when the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. The methods and apparatus of the present invention may also be embodied in the form of program code transmitted over some transmission medium, such as electrical wiring or cabling, through fiber optics, or via any other form of transmission, wherein, when the program code is received and loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code combines with the processor to provide a unique apparatus that operates analogously to specific logic circuits.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
