Optics: measuring and testing – Dimension – Thickness
Reexamination Certificate
2002-06-19
2004-07-13
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Dimension
Thickness
C356S503000
Reexamination Certificate
active
06762849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the fields of semiconductor, optical component and electro-optic component processing and manufacturing, and in particular, to a method and apparatus for in-situ monitoring and controlling deposited film thicknesses in real-time.
2. Description of Related Art
In semiconductor manufacturing, the fabrication processes that are used to date must be very accurately controlled due to the constant increase in integration density of the resultant integrated circuit. One of the important process steps in semiconductor processing, as well as in other types of device processing, is the deposition of films, such as those formed into interconnect lines, bus structures, Schottky barriers, ohmic contacts or other device structures.
Appropriate thickness of the deposited metal film is imperative to the performance of the resultant device. The thickness of the film must be precisely controlled because variations in thickness may affect the electrical properties of the layers and adjacent device patterns, particularly in the interconnections between different layers of microelectronic devices. For example, if too thin a metal film is deposited, an interconnect line formed from that film may be unacceptably resistive or may have a greater likelihood of becoming an open circuit either during subsequent processing steps or during the normal operation of the device. A thick metal film is also undesirable as the film deposition process takes too long and the film thickness may be in excess of the tolerances of later processing steps. Accordingly, it is desirable to maintain film thicknesses near their optimal levels.
In so stating, tools used for such semiconductor manufacture processing have becoming more and more complex over the years. For example, typical processing tools may include a plurality of chambers, whereby each chamber runs a number of varying processing steps. A wafer is sequentially introduced within each of the plurality of chambers and processed sequentially therein, generally under the control of a computer. Typically, the deposition monitoring techniques within such chambers are often performed using repetitive techniques and generally require test wafers. The film thickness is generally measured on one or more of the test wafers, after the film has been deposited thereon, to determine if the film thickness is near an optimal level and if the process is within normal operating parameters. If the measured film thickness and parameters are not within the desired tolerances, the process parameters are adjusted and more test wafers are measured to assure optimal film thickness and process compliance. These processes have a number of disadvantages including, for example, being costly as one or more test wafers must be utilized, time consuming as the film thickness must be measured after the film is deposited thereon, unreliable from wafer-to-wafer and inefficient compared to current deposition monitoring techniques.
Accordingly, as variations of certain process variables cannot be accurately predicted over the course of many process runs using the above systems, new methods for tool and process characterization such as gas analysis, in-situ monitoring and the like, are now of common use in the semiconductor industry. Further, external film thickness metrology, located outside of the wafer processing tool, typically is used as a film thickness monitor. However, as it is advantageous to monitor the progress of critical wafer processing steps to ensure that the steps are properly completed, it is desirable to utilize in-situ process monitoring systems. In-situ monitoring systems improve both process monitoring as well as control of the processing steps based on such process monitoring.
In-situ monitoring systems have been developed to monitor and control the deposition of a film onto a wafer surface, as well as for film removal systems such as those for detecting an endpoint of a process. The endpoint determination is used to monitor the progress of the process and/or to control the process, such as by automatically terminating the specific processing operation being monitored. In film removal systems and processes, it must be accurately determined when enough of the film has been removed; i.e., to detect the endpoint of the removal operation. If an etch step exceeds the predetermined endpoint, the substrate, insulating layer and/or resultant circuit pattern may be damaged. As such, these systems typically rely on in-situ measurements to determine the progressive depth of the etch process as these systems provide greater control of the etch process and improve uniformity over a batch of processed wafers.
There has been some success in the art of developing in-situ film thickness deposition and etch depth measuring systems that utilize optical emission spectroscopy to monitor light emissions from the plasma as the etch process progresses. Such a system may monitor the optical emission intensity of the plasma in a narrow band as well as a wide band and generates signals indicative of the spectral intensity of the plasma by collecting the optical emissions using an optical fiber. When the signals diverge, a termination signal is generated thereby terminating the etch process. However, such systems typically require a separate light source, the measurement is done on spots on the wafer, and in the case where multiple spots need to be measured at least part of the measurement equipment needs to be duplicated for such measurement as well as the computation time increasing. As such, these methods and technologies for film thickness determinations are slow, costly, inefficient, unreliable and negatively impact production yield. Other techniques include the use of laser interferometry, beamsplitters and diffraction gratings to measure the phase shift of a laser beam reflected from two closely spaced surfaces. For example, the phase shift between a first beam reflected off the mask pattern and the beam reflected off an etched portion of the wafer is measured and compared to a predetermined phase shift that corresponds to the desired etch depth. Unfortunately, the above discussed optical emission spectroscopy and other monitoring and measuring systems are plagued by inadequate signal to noise ratios to achieve in-situ or real time data processing, as well as the minimum etch depth being limited by the wavelength of the light source used in the monitor. Also, the film thickness or film thickness change is typically measured at a fixed spot, such as a fixed spot on a wafer. Disadvantageously, the overall film thickness across the wafer is unknown as only the thickness at that measured spot is determined, thus leading to an increased risk of detecting film thickness from the incorrect location where features of the film thickness may not be representative for the entire wafer. Furthermore, these systems often have the disadvantage of requiring substantial modification of the conventional equipment and processes thereby making them undesirable, expensive, time consuming, difficult to integrate, inefficient and impracticable.
Accordingly, a need continues to exist in the art for low cost improved systems and methods for accurately and directly measuring, monitoring and controlling film deposition thickness across the entire wafer surface within a deposition tool whereby the deposited material is uniform from wafer to wafer.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved low-cost method and system for direct, real-time measurement of thickness of deposited film during the deposition process.
Another object of the present invention is to provide a method and a system for real-time, in-situ wafer fabrication processes that prevents misprocessing errors, corrects for process drifts and detection of incorrect tool operation by real-time detection of deposited film thickness during wafer processing by detecting unusual signal behaviors of
Connolly Patrick
DeLio & Peterson LLC
Font Frank G.
Novellus Systems Inc.
Reynolds, Esq. Kelly M.
LandOfFree
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