Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2002-04-09
2004-11-09
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S754090, C324S758010
Reexamination Certificate
active
06815959
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to systems and methods for measuring properties of conductive layers. Certain embodiments relate to a pin having a substantially planar contact surface that may be disposed within a probe and a system that may include multiple probes configured to measure a property of a conductive layer.
2. Description of the Related Art
Semiconductor fabrication processes typically involve a number of processing steps to form various features and multiple levels of a semiconductor device. For example, ion implantation may be used to introduce impurity materials such as dopant ions into a region of a semiconductor substrate. An implanted region may form a junction of a semiconductor device such as lightly doped drain (“LDD”) and source/drain (“S/D”) junctions. Rapid thermal annealing may be used to electrically activate the implanted regions of the semiconductor substrate thereby substantially completing the formation of the junctions. Because ion implantation offers several advantages over diffusion doping, it is increasingly becoming an integral processing step of semiconductor fabrication.
Ion implantation systems may be among the most sophisticated and complex systems utilized in semiconductor fabrication. In order to be utilized efficiently, therefore, ion implantation systems may require extensive monitoring to ensure that such systems and ion implantation processes are performing within process constraints. For example, ion implantation processes may be monitored by assessing implant dose, implantation depth profile, uniformity of implant dose across a semiconductor substrate, and uniformity of implant dose across multiple semiconductor substrates. Ideally, extensive monitoring of ion implantation processes takes place during both process development and process control of manufacturing processes. For example, process control of ion implantation manufacturing processes may involve in situ monitoring of implant dose. Accurately monitoring implant dose, however, may be difficult because measurements of implant dose are generally based on integrating the beam current. Error sources may be introduced into measurement of an integrated beam current by interactions between the beam and electrons, neutrals, and negative ions as well as secondary particles which may be emitted as a result of ion bombardment of the target.
An additional process control method that may be used to monitor and assess an ion implantation process may involve determining sheet resistance of implanted regions of a semiconductor substrate using a four-point probe technique. The four-point probe technique may involve using a colinear probe arrangement, which may be positioned to contact implanted regions on the semiconductor wafer. The probe may include four pins that may be disposed in various arrangements. Suitable pins may be commercially available, for example, from Kulicke & Soffa Industries, Inc., Willow Grove, Pa. and Jandel Engineering Limited, England. During operation of the probe, a current may be passed between two outer pins, and a voltage drop may be measured across two inner pins. The measurement may be performed twice to eliminate thermoelectric heating and cooling errors in the measurements. For example, a first measurement may involve passing a current in a first direction, which may be referred to as the forward direction. A second measurement may involve passing a current in a second direction, which may be opposite to the first direction. The second direction may be referred to as the reverse direction. Voltage drop results from the two measurements may be averaged. In addition, a measurement may also be performed at several different current levels because measuring at an improper current may cause the forward and reverse results to differ or may cause the results to drift. Sheet resistance may be determined from the measured voltage drop and current. In addition, sheet resistance may be used to determine characteristics of an implanted region such as implant dose and implantation depth profile. Sheet resistance may also be used to determine characteristics of a conductive layer such as thickness.
Currently available systems that may be configured to determine sheet resistance of implanted semiconductor substrates and conductive layers using a four-point probe technique may include four pins. Each of the four pins may have a contact surface that contacts a conductive layer during measurement. The contact surface of each pin may be rounded or semi-circular. In this manner, a cross-sectional area of each pin, in a plane substantially parallel to the contact surface, may be smallest at the contact surface of the pin and may increase along a length of the pin extending laterally from the contact surface. In addition, the contact surface may be abraded due to contact between the pin and an upper surface of a conductive layer during measurement and a ceramic plate during conditioning. Therefore, since the cross-sectional area of the pin increases along a length of the pin, the surface area of the contact surface may also increase due to such abrasion.
Currently, a pin disposed within a probe may be conditioned until an appropriate surface area may be obtained. For example, a pin may be conditioned to increase a surface area of a contact surface of the pin until the surface area may be large enough to reduce a contact resistance of the pin. A contact resistance of the pin may be reduced such that the contact resistance may not adversely effect measurements. An appropriate surface area may be determined by monitoring improvements in the repeatability of measurements performed with the probe. For example, a surface area at which sufficiently low contact resistance may not be achieved may be determined by an inability to achieve improved probe qualification results after repeated probe conditioning. An appropriate surface area may also be determined by removing the probe from a measurement system and measuring a surface area of a contact surface of each pin within the probe. As such, determining an appropriate surface area may be very time consuming.
Once an appropriate surface area may be obtained, the probe may be used to measure a property of conductive layers. During such measurements, however, a surface area of the contact surface of the probe will continue to increase due to abrasion between the contact surface and a conductive layer. Such continual increases in surface area may also significantly limit the probe life because measurements performed with the probe may change over time. In addition, a pin may be used until the surface area of the contact surface may be larger than a surface area at which sufficiently low contact resistance may not be achieved. If a pin may not achieve a sufficiently low contact resistance, the pin may be replaced with a new pin. Alternatively, a pin which may not be able to achieve a sufficiently low contact resistance may be removed from the probe. A contact surface of the pin may be re-shaped, and the pin may be re-installed in the probe.
Additionally, a surface area of each of the contact surfaces of the four pins may not increase uniformly due to non-uniform abrasion between the contact surfaces of each of the four pins and a conductive layer or a conditioning plate. As such, variations in the results obtained from using such a probe may be more difficult to detect and correct. Furthermore, as the depth of implanted regions of a semiconductor substrate decreases, sheet resistance measurements of the implanted regions may become more dependent on the surface area of the contact surface. In this manner, a range of acceptable surface areas for the contact surfaces of the pins may be reduced. Therefore, pins which have rounded or spherical contact surfaces may have an increased probability of error and a significantly reduced lifetime for accurately measuring sheet resistance such implanted regions.
Currently available four point probe may be configured to accommodate only one probe at
Borchers Torsten
Danet Andrei
Erskine George
Griffing Daniel
Johnson Walter H.
Conley & Rose, P.C.
Deb Anjan K.
KLA-Tencor Technologies Corp.
Mewherler Ann Marie
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