Quantitative two-dimensional dopant profile measurement and inverse modeling by scanning capacitance microscopy
AssigneeUniversity of Utah Research Foundation
InventorsClayton C. Williams, Yunji Huang
Life of this patent
Estimating the term…
Abstract
Quantitative dopant profile measurements are performed on a nanometer scale by using a scanning capacitance microsope. A nanometer scale tip of the microscope is positioned at a semiconductor surface, and local capacitance change is measured as a function of sample bias. The method incorporates a feedback system and procedure in which the magnitude of the AC bias voltage applied to the sample is adjusted to maintain a constant capacitance change as the tip is scanned across the sample surface. A one dimensional model is used to extract dopant density profiles from the measurements made by the scanning capacitance microscope.
Claims4
In a method for determining dopant density of a semiconductor material with respect to a least two dimensions, wherein said method comprises the steps of (a) scanning a fine tip in close proximity to a surface of said material within a predetermined scan area, (b) applying an AC voltage to said tip with respect to said material, (c) measuring a parameter corresponding to the capacitance in a region of said material near said tip at a plurality of locations within said scan area, and (d) relating the parameter values and the AC voltage levels applied to said tip with respect to said material according to a predetermined relationship to derive said dopant density at each of the locations, the improvement comprising
- measuring an AC parameter corresponding to the capacitance in a region of said material near said tip;
- feeding the AC parameter corresponding to the capacitance to a lock in amplifier;
- comparing the output of the lock in amplifier to a set value;
- generating a feedback signal that corresponds to the comparison of the output of the lock in amplifier to said set value;
- using the feedback signal to control the AC voltage applied to said tip with respect to said material in accordance with the comparison of the output of the lock in amplifier to said value so that the output of the lock in amplifier is maintained at a substantially constant value determined by said set value to which it is compared, whereby capacitance change due to depletion depth of majority carriers at the tip resulting from the AC bias voltage remains substantially constant as the tip scans the surface of said material;
- and
- utilizing the feedback signal to determine dopant density for each of the locations.
Dependencies are inferred from the claim text.