Constant-force profilometer with stylus-stabilizing sensor assembly, dual-view optics, and temperature drift compensation

A profilometer for microstructures comprising,

• an elongated stylus arm having a stylus mounted thereon for contact with a specimen, the stylus arm associated with a stylus displacement measuring means,
• a magnetic stylus force biasing means operably connected to the stylus arm for urging the stylus tip into contact with the specimen,
• feedback means in electrical communication with the stylus displacement measuring means for electrically controlling the magnetic stylus force biasing means to apply a constant desired level of force to the specimen, and a magnetic shield surrounding the stylus force biasing means, the magnetic shield comprising,
• a primary shield of low hysteresis, high permeability material shaped to closely house the coil, and
• a secondary shield of low hysteresis, high permeability material shaped to substantially enclose the primary shield, the coil, and a portion of the lever having the ferromagnetic tip.

A constant-force profilometer for microstructures comprising,

• a stylus arm for step-height measurements of a specimen, said arm being substantially rigid when it is in contact with and moved over the specimen,
• a displacement transducer rigidly connected to the stylus arm, said transducer having means for providing a signal to indicate a current position of the stylus arm when the stylus arm moves over the specimen,
• a stylus force biasing means operably connected to the stylus arm for urging the stylus tip into contact with the specimen, and
• feedback means responsive to the signal from the transducer for controlling the stylus force biasing means to apply a desired level of force to the specimen, said force being a function of the current position of the stylus tip, said feedback means including a digital circuit.

A constant-force profilometer comprising,

• an elongated stylus arm having a stylus tip mounted for contact with a specimen in accord with desired force signals,
• a magnetic stylus force biasing means having a current-carrying solenoidal coil, the stylus force biasing means operably connected to the stylus arm for urging the stylus tip into contact with the specimen,
• a stylus displacement measuring means associated with the stylus arm, the displacement measuring means producing a displacement analog signal,
• a signal conditioning circuit for selecting and storing first analog signals corresponding to vertical positions to form data points,
• an analog-to-digital converter for converting the first analog signals to digital signals,
• a digital signal processor means for converting displacement signals to force signals and comparing with desired force signals and for generating a polynomial curve for data points collected while the stylus tip is not engaged, the curve being adjusted by a steady signal offset to establish the desired force signals, the processor providing modulation of the force signals for the positions on the specimen to conform to the adjusted curve,
• a digital-to-analog converter for converting the modulated signals to second analog signals, and
• a coil drive circuit for using the second analog signals to modulate current in the solenoidal coil for the positions on the specimen.

A method for controlling the stylus force in a profilometer having a magnetic stylus force biasing mechanism with a current-carrying force coil, the method comprising,

• moving a nonengaged stylus to a plurality of specified vertical positions, the stylus generating an electrical signal corresponding to step heights,
• reading and storing a first electrical signal corresponding to each position to form a first set of data points,
• generating a polynomial curve for the first set of data points,
• adjusting the polynomial curve by steady signal offsets to form a second set of data points comprising a second electrical signal for each position,
• engaging the stylus with a specimen to be profiled at a desired force level,
• profiling the specimen while modulating the force coil current so that the force coil current conforms to the adjusted polynomial curve for achieving the desired force levels.

A method for controlling the stylus force in a profilometer, the method comprising the steps of:

• moving a nonengaged stylus to a plurality of specified vertical positions, the stylus generating an electrical signal corresponding to step heights;
• providing an electrical signal corresponding to each of said vertical positions to form a first set of data points;
• generating from said first set of data points a second set of data points;
• engaging the stylus with a specimen to be profiled at a desired force level,
• profiling the specimen while modulating a biasing force by the stylus on the specimen as a function of the second set of data points for achieving the desired force levels.