Method and system for thickness measurements of thin...

Details Method and system for thickness measurements of thin... Method and system for thickness measurements of thin...

2003-06-12

2004-11-09

Nguyen, Vincent Q. (Department: 2858)

Electricity: measuring and testing

Magnetic

With means to create magnetic field to test material

C324S229000

Reexamination Certificate

active

06815947

ABSTRACT:

FIELD OF THE INVENTION
This invention is generally in the field of electrical measurements and relates to a method and system for measuring a thickness of a conductive film. The present invention is particularly useful for measuring conductive layer bearing structures for contactless electrical testing. The technique of the present invention can be used for controlling a certain process of the sample manufacture, for example manufacture of semiconductor wafers.
BACKGROUND OF THE INVENTION
The manufacture of semiconductor devices typically includes a process of depositing a metal layer onto a semiconductor wafer in order to define interconnects. The quality of this process, as well as that of a process of removing metal from selected regions (e.g., polishing) that follows the deposition process, should be controlled.
FIG. 1
illustrates a cross section of a copper-based wafer structure
10
(utilizing copper interconnects patterned with a known dual Damascene process) prior to the application of a CMP process to the structure. The structure
10
includes a substrate
11
with an inter layer dielectric (ILD)
12
thereon, optional “etch stop” layer
14
(e.g., SiN), ILD layer portions
16
and
18
, and a copper layer
20
. These stack layers define a dense structure
22
, which is composed of the ILD layer portions
18
and copper layer
20
, and is surrounded by the ILD field layer portions
16
.
Copper is deposited by one of the known techniques, such as CVD, PVD electroplating or electroless plating. Depending on the deposition process, the uppermost copper layer
20
has certain topology, namely, has the topology within the dense structure
22
repeating that of the underlying pattern.
It should be noted that, if electroplating is used, a thin copper seed layer
24
(with the thickness of about 1000-5000 A) should be deposited onto the structure prior to the deposition of the layer
20
as a prerequisite for electroplating. The thickness of this layer could be measured by optical- or electrical-based techniques. Additionally, although not specifically shown, a barrier layer (TaN or Ta) is typically provided above the ILD layer portions
16
and
18
to prevent copper migration therein.
After deposition, a chemical-mechanical polishing (CMP) is applied in order to remove copper from the top ILD surface and thus to leave copper only within the ILD trenches.
Copper CMP is a complex process because of the need to completely remove the barrier layers and copper, without the overpolishing of any feature. This is difficult because current copper deposition processes are not as uniform as the oxide deposition process. To this end, the quality of the copper deposition process should be controlled.
Contact electrical-based measurement techniques have been developed and are disclosed, for example, in the scientific article “
An Overview of Thickness Measurement Techniques for Metallic Thin Films
”, S. C. P. Lim and D. Ridley, Solid State Technology, February 1983, pp. 99-103.
It is also known to use an eddy current passage through a conductive film for contactless measurement of the film properties, such as conductance/resistance and thickness. Such a technique is disclosed, for example, in. U.S. Pat. No. 4,849,694. This technique utilizes an eddy current apparatus including an alternating frequency driving coil, a detector coil mounted in a housing adjacent one surface of the thin film, and circuitry for measuring the signal across the detector coil which senses the field after it is subjected to the eddy currents generated within the conductive film. Precise adjustment of a fixed distance between coils and film surface is important and achievable by positioning the film surface at the focal point of an optical microscope objective lens to which the eddy current apparatus is coupled.
Another techniques of the kind specified are disclosed in the following patent publications:
WO 01/46684 discloses in-situ metallization monitoring using eddy current measurements and optical measurements that can be integrated in a CMP machine. According to this technique, an eddy-current sensor (ESC) and an optical reflectivity sensor are embedded in the polishing table. The eddy-current sensor (ECS) operates with relativity low frequency (up to 100 MHz). A measuring scheme utilizes two coils in balanced bridge, a differential amplifier, a synchronous detection (in-phase and in-quadrature). The optical sensor simply measures the reflection from the wafer under measurements: polishing end point corresponds with a dip in reflectivity graph (vs. time).
U.S. Pat. No. 6,433,541 discloses a method and apparatus of obtaining information in-situ regarding a film of a sample using an eddy probe during a process for removing the film. The eddy probe has at least one sensing coil. An AC voltage is applied to the sensing coil(s), and one or more first signals are measured when the sensing coil(s) are positioned proximate the film of the sample, and one or more second signals are measured when the sensing coil(s) are positioned proximate to a reference material having a fixed composition and/or distance from the sensing coil. The first signals are calibrated based on the second signals so that undesired gain and/or phase changes within the first signals are corrected. A property value of the film is determined based on the calibrated first signals.
U.S. Pat. No. 6,407,546 discloses a non-contact technique for using an eddy current probe for measuring the thickness of metal layers disposed on semi-conductor wafer products. This technique utilizes a probe housing, comprising an eddy current sense coil and a linear motion controller, and a computer that controls the linear motion controller and the eddy current sense coil. The computer identifies a thickness of the inspection sample by a method comprising the generation of a natural intercepting curve based on resistance and reactance measurements of at least two data points. Then, a plurality of corresponding resistance and reactance measurements of a location on the inspection sample is obtained with the eddy current sensor, where the eddy current sensor makes a first measurement at a first distance from the inspection sample, and makes each of the remaining plurality of measurements at a distance that is incrementally further away from the inspection surface. Next an inspection sample curve is generated based on the plurality of corresponding resistance and reactance measurements obtained from the inspection sample. An intersection point between the natural intercepting curve and the inspection sample curve is also generated. A vector impedance for each of the at least two data points, and the intersection point, is calculated to identify a closest two data points that the intersection point is positioned. Then, the thickness of the identified location of the inspection sample is calculated by performing an interpolation between the closest two data points.
U.S. Pat. No. 5,552,704 discloses an eddy current test method and apparatus for measuring conductance. According to this method, an eddy current probe is used, without the need for measurement or knowledge of the separation between probe and sample. The probe comprises sense and drive coils mounted in close proximity to each other (or a single coil which functions as both a sense and drive coil), circuitry for producing AC voltage in the drive coil, and a meter for measuring in-phase and quadrature components of induced voltage in the sense coil. Look-up table data can be generated for use in subsequent measurements on samples of unknown conductance by performing eddy current measurements on samples having different known conductances to generate reference lift-off curves, processing the reference lift-off curves to determine a conductance function relating each known conductance to a location along a selected curve, and storing conductance values determined by the conductance function for different points on the selected curve as the look-up table data. An unknown sample conductance can then be determined by g

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