Precise stylus control system

Abstract

A system includes a processor configured to excite a pair of torque coils using a force signal to generate a magnetic force between the pair of torque coils and an internal magnet of a control arm disposed between the pair of torque coils. The control arm is connected to a probe arm, and the magnetic force causes the control arm and the probe arm to rotate about a pivot joint and causes a probe tip of the probe arm to contact a surface of a sample. After exciting the sensing subsystem with an excitation signal, the processor receives a sensing signal difference from the sensing subsystem proportional to a rotational position of the control arm that corresponds to a height of the probe tip relative to the surface of the sample.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 460,988, filed Apr. 21, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to stylus profilometry systems for the measurement and testing of surface topography for research, development, and manufacturing. Background Art

[0004] The evolution of manufacturing has placed higher demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions continue to shrink, but the industry needs to reduce the time used to achieve high-yield, high-value production. Minimizing the total time from detecting a yield issue to resolving the issue maximizes the return on investment for the manufacturer.

[0005] As an example of a manufacturing challenge, manufacturing semiconductor devices such as logic and memory devices typically involves processing a sample such as a semiconductor wafer using a large number of manufacturing processes to form various features and multiple levels of the semiconductor device. For example, lithography is a semiconductor manufacturing process that involves transferring a pattern from a photomask to a photoresist disposed on a semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. The arrangement of multiple semiconductor devices fabricated on a single semiconductor wafer can be separated into individual semiconductor devices.

[0006] Metrology processes are used during various steps of semiconductor manufacturing to monitor and control the process. A metrology process differs from an inspection process in that, unlike an inspection process in which defects are detected on a wafer, a metrology process is used to measure one or more properties of a wafer that cannot be determined using existing inspection tools. A metrology process can be used to measure one or more properties of a wafer such that the performance of the process can be determined from the one or more properties. For example, a metrology process can measure the dimensions (e.g., line width, thickness, etc.) of features formed on a wafer during a process. Additionally, if one or more properties of a wafer are unacceptable (e.g., outside a predetermined range of the property), then the measurement of the one or more properties of the wafer can be used to change one or more parameters of the process such that additional wafers fabricated by the process have acceptable properties.

[0007] Some metrology processes utilize styli or probes to measure the surface of a sample. For example, a stylus can be placed in contact with the surface of the sample and scanned across the sample to measure its topography and the dimensions of surface features, or indentation and scratch tests can be performed by applying a force to the surface of the sample using the stylus. However, a stylus profilometry system that is an open loop lacks feedback from a mechanism that senses the position of the stylus, which feedback can be applied to a mechanism that controls the force and positioning of the stylus. Accordingly, the measurement sensitivity and force control depend on system calibration, and the open loop system has low adaptability to different operating modes, measurements of different samples, or real-time changes in the measurement environment. Additionally, separate system configurations and calibrations are required to perform force and position measurements. The separate configurations and calibrations are decoupled from any subsequent changes to the stylus or the environment. For example, open loop force control systems are challenged by their insensitivity to temperature-induced drifts in the applied force.

[0008] Accordingly, there is a need for a closed loop stylus profilometry system with integrated force and position control. SUMMARY

[0009] Embodiments of the present disclosure provide a system. The system can include a probe arm having a probe tip. The probe tip can be configured to contact the surface of a sample.

[0010] The system can further include a control arm connected to the probe arm. The control arm can include an internal magnet.

[0011] The system can further include one or more torque coils disposed on opposite sides of the control arm. The one or more torque coils can be configured to cause rotation of the control arm about a pivot joint based on an interaction with the internal magnet.

[0012] The system can further include a sensing subsystem. The sensing subsystem can be configured to measure the rotational position of the control arm.

[0013] The system can further include a processor in electronic communication with the one or more torque coils and the sensing subsystem. The processor can be configured to excite at least one of the one or more torque coils with a force signal to generate a magnetic force between the one or more torque coils and the internal magnet, which causes the control arm to rotate about the pivot joint, thereby causing the probe arm connected to the control arm to rotate about the pivot joint and causing the probe tip to contact the surface of the sample. The processor can be further configured to excite the sensing subsystem with an excitation signal. The processor can be further configured to receive from the sensing subsystem a sensed signal difference proportional to the rotational position of the control arm, which corresponds to the height of the probe tip relative to the surface of the sample. The sensed signal difference can be a voltage difference or a current difference.

[0014] In some embodiments, the processor may include a servo loop integrator. The servo loop integrator may be configured to apply the rotational position of the control arm determined from the sensing subsystem as feedback to control the force signal.

[0015] In some embodiments, the processor may be further configured to determine an adjusted force signal based on feedback from the rotational position or force of the control arm to generate a preset force; and use the adjusted force signal to excite at least one of the one or more torque coils, thereby causing the probe tip to contact the surface of the sample using the preset force.

[0016] In some embodiments, the processor may be further configured to determine an adjusted force signal based on the feedback from the rotational position or force of the control arm to position the probe tip at a preset height; use the adjusted force signal to excite at least one of the one or more torque coils, thereby causing the probe tip to be positioned at the preset height relative to the surface of the sample; and confirm that the probe tip is positioned at the preset height based on the sensed signal difference received from the sensing subsystem.

[0017] In some embodiments, the processor may be further configured to generate a modulated force signal; and use the modulated force signal to excite at least one of the one or more torque coils, thereby causing the height of the probe tip to oscillate relative to the surface of the sample.

[0018] In some embodiments, the sensing subsystem may include a main coil and a pair of secondary coils disposed on opposite sides of the main coil. The core of the pivot joint may be surrounded by the main coil and the pair of secondary coils such that a change in the rotational position of the control arm may cause the core to move within the main coil and the pair of secondary coils, and the sensed signal difference measured from the pair of secondary coils may be proportional to the position of the core.

[0019] In some embodiments, the main coil and the pair of secondary coils may be coaxial, and the core may move linearly within the main coil and the pair of secondary coils.

[0020] In some embodiments, the main coil and the pair of secondary coils may be co-planar, and the core may move angularly within the main coil and the pair of secondary coils.

[0021] In some embodiments, the sensing subsystem may include a primary coil and a secondary coil disposed opposite the primary coil. The core of the control arm may be disposed between the primary coil and the secondary coil such that a change in the rotational position of the control arm may cause the core to move between the primary coil and the secondary coil, and the sensed signal difference measured from the secondary coil may be proportional to the position of the core.

[0022] In some embodiments, the system may further include an external magnet. The external magnet may be configured to attract the internal magnet of the control arm, which may cause the control arm to rotate to a retracted position where the probe tip may be spaced apart from the surface of the sample. The one or more torque coils may be configured to cause the control arm to rotate against the attraction of the external magnet.

[0023] In some embodiments, the external magnet may be movable between a first position and a second position. In the first position, the external magnet may be close to the internal magnet to attract the internal magnet of the control arm, and in the second position, the external magnet may be away from the internal magnet to allow free rotation of the control arm.

[0024] In some embodiments, the pivot joint may include a torsion bar configured to bias the control arm toward a neutral position. In the neutral position, the probe tip may be spaced apart from the surface of the sample, and the one or more torque coils may be configured to cause the control arm to rotate against the bias of the torsion bar.

[0025] In some embodiments, the processor may be further configured to use the force signal to energize one of the one or more torque coils to control the direction of rotation of the control arm about the pivot joint based on the magnetic force.

[0026] Another embodiment of the present disclosure provides a method. The method may include using a force signal to energize a pair of torque coils to generate a magnetic force between the pair of torque coils and an internal magnet of a control arm disposed between the pair of torque coils. The control arm may be connected to a probe arm, and the magnetic force may cause the control arm and the probe arm to rotate about a pivot joint and may cause the probe tip of the probe arm to contact the surface of the sample. Energizing one of the pair of torque coils of the pair of torque coils using the force signal may control the direction of rotation of the control arm about the pivot joint based on the magnetic force.

[0027] The method may further include exciting the sensing subsystem with an excitation signal; measuring a sensed signal difference from the sensing subsystem that is proportional to the rotational position of the control arm, where the sensed signal difference is a voltage difference or a current difference; and determining the height of the probe tip relative to the surface of the sample based on the rotational position of the control arm.

[0028] In some embodiments, the method may further include applying the rotational position of the control arm determined from the sensing subsystem as feedback in a servo loop to control the force signal.

[0029] In some embodiments, the method may further include determining an adjusted force signal based on feedback from the rotational position or force of the control arm to produce a preset force; and exciting the pair of torque coils with the adjusted force signal, thereby causing the probe tip to contact the surface of the sample using the preset force.

[0030] In some embodiments, the method may further include determining an adjusted force signal based on feedback from the rotational position or force of the control arm to position the probe tip at a preset height; exciting the pair of torque coils with the adjusted force signal, thereby causing the probe tip to be positioned at the preset height relative to the surface of the sample; and confirming that the probe tip is positioned at the preset height based on the sensed signal difference from the sensing subsystem.

[0031] In some embodiments, the method may further include generating a modulated force signal; and exciting the pair of torque coils with the modulated force signal, thereby causing the height of the probe tip to oscillate relative to the surface of the sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more fully understand the nature and objects of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0033] Figure 1 is a diagram of a system according to an embodiment of the present disclosure;

[0034] Figure 2 is a schematic communication diagram of a processor according to an embodiment of the present disclosure;

[0035] Figure 3 is a diagram of a system according to another embodiment of the present disclosure;

[0036] Figure 4 is a diagram of a system according to another embodiment of the present disclosure;

[0037] Figure 5A is a longitudinal cross-section of a pivot joint of a system according to an embodiment of the present disclosure;

[0038] Figure 5B is Figure 5A a cross-sectional view of a pivot joint of

[0039] Figure 6A a longitudinal cross-section of a pivot joint of a system according to another embodiment of the present disclosure;

[0040] Figure 6B is Figure 6A a cross-sectional view of a pivot joint of

[0041] Figure 7 a flowchart of a method according to an embodiment of the present disclosure;

[0042] Figure 8 is Figure 7 a flowchart of a method step of a force command in the method of

[0043] Figure 9 is Figure 7 a flowchart of a method step of a position command in the method of

[0044] Figure 10 is Figure 7 a flowchart of a method step of a modulation command in the method of; and

[0045] Figure 11 a block diagram of a control system according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0046] Although the claimed subject matter will be described with respect to certain embodiments, other embodiments (including embodiments that do not provide all of the benefits and features set forth herein) are also within the scope of the present disclosure. Various structural, logical, process step, and electronic changes can be made without departing from the scope of the present disclosure. Accordingly, the scope of the present disclosure is defined only by reference to the appended claims.

[0047] Embodiments of the present disclosure provide a system 100, as Figures 1 - 4As shown in. System 100 can be a stylus profilometry system configured to measure the topography of a sample 101. The sample 101 can be planar or substantially planar and can have a slope or features within the dynamic range of the system 100. Such features can include, for example, machined metal parts, polished glass, lenses, mirrors, or the like. The sample 101 can be a semiconductor wafer containing silicon, GaAs, GaN, SiN, SiC, ceramics, substrates, display panels, test pieces, metals, inorganic, conductive, insulating, non-patterned, patterned, relatively smooth, relatively rough, or having a topographical surface and other samples or workpieces encountered in industries including but not limited to semiconductor, power device, MEMS device, LED device, automotive industry, and general process development across many material and device types. The system 100 can include a probe arm 110 having a probe tip 111 disposed at one end. The probe tip 111 can include diamond, sapphire, tungsten, layered, coated, or other materials or alloys that can maintain their shape when scanned and can be fabricated into a probe shape. The probe tip 111 can be configured to contact the surface of the sample 101 to measure a series of individual points (e.g., point cloud) within the dynamic range of the system 100, step heights and feature sizes on the surface of the sample 101, or perform a measurement of the topography of the surface. The probe tip 111 can have a conical shape (e.g., conical, pyramidal, spherical, or other shape, steep wall or shallow) that can provide an upward force on the probe tip 111 when laterally contacting features or point-to-point contacting to contact the surface of the sample 101 between narrow features and particles or fabricated features during scanning. The included cone angle of the probe tip 111 can vary from greater than 90° to less than 20°. The radius of the probe tip 111 can be in the range of greater than 50 microns to less than 40 nm, where a smaller radius enables the measurement of smaller geometries. A probe tip 111 with a smaller diameter can be more susceptible to damage and wear, which can benefit from the sensitive closed-loop servo system 100 of the present disclosure to reduce the chance of wear and breakage. For example, the system 100 can allow the use of a probe tip 111 of a smaller size, which can improve the resolution of the stylus that otherwise would not be achievable. Improving the resolution can enable smaller feature sizes to be characterized, which can be beneficial for many industries.

[0048] The system 100 can further include a control arm 120. The control arm 120 can be connected to the probe arm 110. For example, the probe arm 110 can cantilever out from the control arm 120. The control arm 120 can be configured to pivot about a pivot joint 115. Based on the connection between the probe arm 110 and the control arm 120, the rotation of the control arm 120 about the pivot joint 115 can cause a corresponding rotation of the probe arm 110 and the probe tip 111 connected thereto. The control arm 120 can include an internal magnet 125. The internal magnet 125 can be a permanent magnet disposed within or connected to the control arm 120.

[0049] System 100 may further include a pair of torque coils 130. The pair of torque coils 130 may be disposed on opposite sides of the internal magnet 125 of the control arm 120. For example, the pair of torque coils 130 may include a first torque coil 131 and a second torque coil 132 each disposed on opposite sides of the internal magnet 125 of the control arm 120. The pair of torque coils 130 may be configured to cause rotation of the control arm 120 about the pivot joint 115 based on interaction with the internal magnet 125, as further described below. Each torque coil of the pair of torque coils 130 may include one or more coils. In some embodiments, the pair of torque coils 130 may include a single torque coil.

[0050] System 100 may further include a processor 140. The processor 140 may include a microprocessor, a microcontroller, an FPGA, or other device.

[0051] The processor 140 may be coupled to the components of the system 100 in any suitable manner (e.g., via one or more transmission media, which may include wired and / or wireless transmission media) such that the processor 140 can receive the output. The processor 140 may be configured to perform several functions using the output. The inspection tool may receive instructions or other information from the processor 140. The processor 140 may optionally communicate electronically with another inspection tool, metrology tool, repair tool, or re-inspection tool (not shown in the figure) to receive additional information or send instructions.

[0052] The processor 140 may be part of various systems, including a personal computer system, an image computer, a host computer system, a workstation, a network device, an Internet device, or other devices. The subsystem or system may also include any suitable processor known in the art, such as a parallel processor. Additionally, the subsystem or system may include a platform with high-speed processing and software as a stand-alone or network tool.

[0053] The processor 140 may be disposed in the system 100 or another device or otherwise be part of the system 100 or another device. In an example, the processor 140 may be part of an independent control unit or may be part of a centralized quality control unit. Multiple processors 140 may be used to define multiple subsystems of the system 100.

[0054] In practice, the processor 140 may be implemented by any combination of hardware, software, and firmware. Additionally, its functions as described herein may be performed by one unit or divided among different components, each of which may be implemented by any combination of hardware, software, and firmware. Program codes, instructions, configuration data, look-up tables, calibration data, algorithms, etc. for the processor 140 to implement various methods and functions may be stored in a readable storage medium (e.g., a memory).

[0055] If system 100 includes more than one subsystem, different processors 140 may be coupled to each other such that images, data, information, instructions, etc. may be sent between the subsystems. For example, one subsystem may be coupled to an additional subsystem by any suitable transmission medium, which may include any suitable wired and / or wireless transmission medium known in the art. Two or more of such subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown in the figures).

[0056] Processor 140 may be configured to perform several functions using the output of system 100 or other outputs. For example, processor 140 may be configured to send the output to an electronic data storage unit or another storage medium. Processor 140 may be further configured as described herein.

[0057] Processor 140 may be configured according to any of the embodiments described herein. Processor 140 may also be configured to perform other functions or additional steps using the output of system 100 or using images or data from other sources.

[0058] Processor 140 may be communicatively coupled to any of the various components or subsystems of system 100 in any manner known in the art. Additionally, processor 140 may be configured to receive and / or obtain data or information (e.g., inspection results originating from an inspection system (such as a re-inspection tool, a remote database containing design data, and the like)) from other systems by a transmission medium that may include wired and / or wireless portions. In this way, the transmission medium may act as a data link between processor 140 and other subsystems of system 100 or systems external to system 100. The various steps, functions, and / or operations of system 100 and the methods disclosed herein are performed by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, FPGAs, analog or digital control / switches, microcontrollers, or computing systems. Program instructions implementing the methods described herein may be transmitted via a carrier medium or stored on a carrier medium. The carrier medium may include storage media such as read-only memory, random access memory, magnetic disks or optical disks, non-volatile memory, solid-state memory, magnetic tape, and the like. The carrier medium may include transmission media such as metal wires, cables, PCB traces, or wireless transmission links. For example, the various steps described throughout this disclosure may be performed by a single processor 140 (or computer subsystem), or alternatively, by multiple processors 140 (or multiple computer subsystems). Additionally, different subsystems of system 100 may include one or more computing or logic systems. Accordingly, the above description should not be construed as a limitation on this disclosure but merely as illustrative.

[0059] As Figure 2As shown, the processor 140 can be in electronic communication with the pair of torque coils 130 and other elements of the system 100. The processor 140 can be configured to use the force signal 141 to excite at least one torque coil of the pair of torque coils 130 to generate a magnetic force between the pair of torque coils 130 and the internal magnet 125. In other words, when the force signal 141 is applied to at least one of the first torque coil 131 and the second torque coil 132, an electromagnetic field that can repel or attract the internal magnet 125 can be generated based on the magnitude and direction of the magnetic force applied to the internal magnet 125 from the electromagnetic field. The magnetic force can cause the control arm 120 to rotate about the pivot joint 115, thereby causing the probe arm 110 connected to the control arm 120 to rotate. Depending on the direction of rotation, the magnetic force can cause the probe tip 111 to descend to contact the surface of the sample 101 or to lift from the surface of the sample 101. The processor 140 can be configured to use the force signal 141 to excite at least one of the first coil 131 and the second coil 132 to control the direction of rotation of the control arm 120 about the pivot joint 115. In some embodiments, the processor 140 can be configured to use the force signal 141 to excite both the first coil 131 and the second coil 132. The processor 140 can include a force signal generator 142 configured to generate the force signal 141. The magnetic force can be modulated by the control input circuit to adjust the downward pressure applied to the probe tip 111 when the probe tip 111 contacts the surface of the sample 101 and when the probe tip contacts the surface of the sample 101. In some embodiments, the first coil 131 and the second coil 132 can be connected in series such that both the first coil 131 and the second coil 132 experience the same current, and each coil can generate a magnetic field in the same direction to generate a greater resultant force from the pair of torque coils 130. In some embodiments, the system 100 can include only one torque coil (e.g., one of the first coil 131 or the second coil 132), which can reduce the manufacturing cost of the system 100 by reducing the number of components, and a single torque coil can be used to generate the magnetic force.

[0060] The system 100 can further include a sensing subsystem 150. The sensing subsystem 150 can be configured to measure the rotational position of the control arm 120. For example, the processor 140 can be configured to use the excitation signal 143 to excite the sensing subsystem 150, and the sensing subsystem 150 can be configured to measure the sensing signal difference 145 based on the excitation signal 143. The processor 140 can include an excitation signal generator 144 configured to generate the excitation signal 143. The sensing signal difference 145 can correspond to the rotational position of the control arm 120, and more specifically, can correspond to the height of the probe tip 111 relative to the sample 101. The sensing signal difference 145 can be a voltage difference or a current difference.

[0061] In some embodiments, the sensing subsystem 150 can include a main coil 151 and a pair of secondary coils 152, asFigure 1 and Figure 3 as shown in Figure 3 . For example, the sensing subsystem 150 can be a linear displacement sensor or an angular displacement sensor. The pair of secondary coils 152 can be disposed on opposite sides of the primary coil 151. The processor 140 can be configured to excite the primary coil 151 with an excitation signal 143, and the sensing subsystem 150 can be configured to measure the sensed signal difference 145 between the pair of secondary coils 152. The system 100 can further include a core 155 surrounded by the primary coil 151 and the pair of secondary coils 152. The core 155 can be made of a highly permeable and low hysteresis magnetic material (such as, for example, a NiFe alloy, iron, or an iron alloy or the like) or other materials. The core 155 can be an extension of the probe arm 110, the pivot joint 115, or the control arm 120. A change in the rotational position of the control arm 120 can cause the core 155 to move within the primary coil 151 and the pair of secondary coils 152. The position of the core 155 relative to the pair of secondary coils 152 can affect the sensed signal difference 145 measured by the sensing subsystem 150. For example, a sensed signal difference 145 of zero can indicate that the core 155 is equidistant between the pair of secondary coils 152 because their relative voltages cancel each other out. However, when the core 155 moves in a direction closer to one of the secondary coils 152, the sensed signal difference 145 becomes non-zero, where the positive or negative value of the sensed signal difference 145 indicates the rotational direction of the control arm and the magnitude of the sensed signal difference 145 is proportional to the rotational position of the control arm 120 and the displacement of the probe tip 111.

[0062] In some embodiments, the sensing subsystem 150 can be configured as an angular displacement sensor, as Figure 1 shown in Figure 1 , which can measure the rotational displacement of the core 155. For example, the primary coil 151 and the pair of secondary coils 152 can be co-circular along an arc 154, and the core 155 can move along the same arc 154 within the primary coil 151 and the pair of secondary coils 152. The position of the core 155 along the arc 154 relative to the pair of secondary coils 152 can be proportional to the rotational position of the control arm 120. Thus, the sensed signal difference 145 measured by the sensing subsystem 150 can correspond to the displacement of the probe tip 111. In an example, both the primary coil 151 and the pair of secondary coils 152 can each have more than 1000 turns in their respective coils, which can increase the gain and sensitivity of the sensing subsystem 150.

[0063] In some embodiments, the sensing subsystem 150 can be configured as, as Figure 3The linear displacement sensor shown therein can measure the linear displacement of the core 155. For example, the primary coil 151 and the pair of secondary coils 152 can be coaxial along the axis 153, and the core 155 can linearly move within the primary coil 151 and the pair of secondary coils 152 along the same axis 153. The linear position of the core 155 along the axis 153 relative to the pair of secondary coils 152 can be proportional to the rotational position of the control arm 120. Therefore, the sensed signal difference 145 measured by the sensing subsystem 150 can correspond to the displacement of the probe tip 111.

[0064] In some embodiments, the sensing subsystem 150 can include a primary coil 151 and a single secondary coil 156, as Figure 4 shown therein. The secondary coil 156 can be disposed opposite to the primary coil 151. The core 155 of the control arm 120 can be disposed between the primary coil 151 and the secondary coil 152. The processor 140 can be configured to excite the primary coil 151 using the excitation signal 143, and the sensing subsystem 150 can be configured to measure the sensed signal difference 145 from the secondary coil 152. A change in the rotational position of the control arm 120 can cause the core 155 to move relative to the primary coil 151 and the secondary coil 152. The position of the core 155 relative to the secondary coil 152 can affect the sensed signal difference 145 measured by the sensing subsystem 150. For example, when the core 155 moves in a direction closer to the primary coil 151 or the secondary coil 152, the magnitude of the sensed signal difference 145 can be proportional to the rotational position of the control arm 120 and the displacement of the probe tip 111.

[0065] In some embodiments, the system 100 can further include an additional magnet that can cause the control arm 120 to retract to a reference or rest position. This function of the system 100 can be useful during a power-off condition. Although the additional magnet can introduce a biasing force, the system 100 can compensate for these forces. For example, as Figure 4 shown therein, the system 100 can further include an external magnet 160. The external magnet 160 can be a permanent magnet configured to attract the internal magnet 125 of the control arm 120, which can cause the control arm 120 to rotate to the retracted position. In the retracted position, the probe tip 111 can be spaced apart from the surface of the sample 101 to prevent damage to the probe tip 111 when the system 100 is not in use. It should be understood that the pair of torque coils 130 can be configured to cause the control arm 120 to rotate against the attraction of the external magnet 160. In other words, since the external magnet 160 attracts the internal magnet 125, the magnetic force generated by the pair of torque coils 130 can be greater than the force from the external magnet 160 to rotate the control arm 120 in a direction to bring the probe tip 111 into contact with the surface of the sample 101.

[0066] In some embodiments, the external magnet 160 can move between a first position and a second position within the housing 165 of the system 100, as Figure 4As shown. In the first position, the external magnet 160 can approach the internal magnet 125 to attract the internal magnet 125 and control the rotation of the arm 120 to the retracted position. In the second position, the external magnet 160 can move away from the internal magnet 125 so as not to attract the internal magnet 125 and allow the control arm 120 to rotate freely. When the external magnet 160 is in the second position, the smaller magnetic force generated by the pair of torque coils 130 can cause the control arm 120 to rotate in the direction in which the probe tip 111 contacts the surface of the sample 101. The position of the external magnet 160 can be manually adjusted (e.g., by screws, sliding, or other moving mechanisms) and can be set to the first position or the second position during the calibration of the system 100.

[0067] In some embodiments, the pivot joint 115 can include a torsion bar 116 (as shown in FIGS. 5 - 6), a leaf spring, a jewel, or a regular bearing or other type of biasing member for small - angle pivoting. The torsion bar 116 can be connected to the housing 165 at both ends, with the control arm 120 disposed therebetween. The torsion bar 116 can be configured to bias the control arm 120 towards a neutral position. In the neutral position, the probe tip 111 can be spaced from the surface of the sample 101 to allow the sample 101 to be loaded and unloaded from the system 100 without damaging the probe tip 111 between processing steps. The angular range of the control arm 120 can depend on the length of the torsion bar 116, the length of the control arm 120, and the manufacturing tolerances of the components of the system 100, which can enable the probe tip 111 to move to the neutral position and contact the surface of the sample 101. It should be understood that the pair of torque coils 130 can be configured to cause the control arm 120 to rotate against the bias of the torsion bar 116. In other words, since the torsion bar 116 is configured to bias the control arm towards the neutral position, the magnetic force generated by the pair of torque coils 130 can be greater than the force from the torsion bar 116 to cause the control arm 120 to rotate away from the neutral position so that the probe tip 111 contacts the surface of the sample 101. In some embodiments, the torsion bar 116 can have a circular cross - section, as Figure 5A and Figure 5B shown. Alternatively, the torsion bar 116 can have a cross - shaped cross - section, as Figure 6A and Figure 6B shown. Compared with the torsion bar 116 having a circular cross - section, the torsion bar 116 having a cross - shaped cross - section can have better stiffness on non - rotational axes, can minimize the lateral movement of the control arm 120, and allows for accurate positioning. Increasing the length of the torsion bar 116 can also increase stiffness while still allowing sufficient angular freedom. The height and thickness of the cross - sectional shape can also be tuned, as the height controls stiffness and the thickness prevents buckling and unwanted modal shape responses.

[0068] In some embodiments, the processor 140 can include a servo loop integrator 146, as Figure 2As shown. The servo loop integrator 146 can be configured to apply the rotational position of the control arm 120 determined from the sensing subsystem 150 as feedback to control the force signal 141. For example, the servo loop integrator 146 can receive the sensed signal difference 145 measured by the sensing subsystem 150 and can apply the feedback of the rotational position of the control arm 120 to the force signal generator 142 to adjust the force signal 141. In other words, the servo loop integrator 146 can provide a closed-loop operation of the system 100 for precise positioning and force control of the probe tip 111. The servo loop integrator 146 can be configured to control the mechanical resonance frequency. The servo loop integrator 146 can be further configured to control the settling time of the position of the probe tip 111. For example, if the probe tip 111 rapidly traverses the surface of the sample 101, then the servo loop integrator 146 can provide feedback to the system 100 to actively damp the mechanical resonances of the control arm 120 and the torsion bar 116 so as not to limit the control arm 120 from moving up and down at a given frequency.

[0069] In an example, the processor 140 can be configured to determine an adjusted force signal 141 based on feedback from the rotational position or force of the control arm 120 to generate a preset force. The feedback can indicate that the control arm 120 is at a position where the probe tip 111 is in contact with the surface of the sample 101 such that further rotation of the control arm 120 will apply a force to the surface of the sample 101 using the probe tip 111. Thus, the processor 140 can determine the adjusted force signal 141 that will generate the preset force. The processor 140 can be further configured to excite at least one of the pair of torque coils 130 using the adjusted force signal 141, thereby causing the probe tip 111 to contact the surface of the sample 101 using the preset force. The preset force can be adjusted based on the material of the sample 101 to (for example) bring the sample 101 into contact with the probe tip 111 for measuring soft and hard materials using an appropriate force. The preset force can help minimize wear of the probe tip 111, make it easier to scan soft samples, and can also protect the sample 101 being measured.

[0070] In another example, the processor 140 may be configured to determine an adjusted force signal 141 based on feedback from the rotational position or force of the control arm 120 to position the probe tip 111 at a preset height. The feedback may indicate that the control arm 120 is at a position where the probe tip 111 is at a height different from the preset height, such that further rotation of the control arm 120 will move the probe tip 111 to be positioned at the preset height. Accordingly, the processor 140 may determine the adjusted force signal 141 for positioning the probe tip 111 at the preset height based on the currently measured position. The processor 140 may be further configured to use the adjusted force signal 141 to energize at least one of the pair of torque coils 130, thereby causing the control arm 120 to rotate and positioning the probe tip 111 at the preset height. The processor 140 may be further configured to confirm that the probe tip 111 is positioned at the preset height based on the sensed signal difference 145 received from the sensing subsystem 150. Accordingly, the feedback information may allow for precise positioning of the probe tip 111 and constant adjustment of the force signal 141 during measurement. The precise position may enable measurement of fragile samples or samples with small feature heights or roughnesses.

[0071] In some embodiments, the processor 140 may be configured to generate a modulated force signal 147. For example, the force signal generator 142 may be configured to generate the modulated force signal 147. Alternatively, the processor 140 may further include a filter configured to modulate the force signal 141 generated by the force signal generator 142 to generate the modulated force signal 147. The modulated force signal 147 may be applied to the main coil 151. The modulated force signal 147 may be an oscillating signal. The processor 140 may be further configured to use the modulated force signal 147 to energize at least one of the pair of torque coils 130, which may cause the internal magnet 125 to oscillate between the pair of torque coils 130 and may cause the probe tip 111 to oscillate relative to the surface of the sample 101. By oscillating up and down, the probe tip 111 may have a reduced chance of getting stuck in a highly viscous sample 101. This may also reduce wear on the probe tip 111 and allow for scanning of smaller and more fragile samples.

[0072] In some embodiments, the processor 140 may be configured to cause the probe tip 111 to contact the surface of the sample 101 at a single point, and then use the pair of torque coils 130 to lift the surface of the sample 101 to a safe height, and translate the probe tip 111 to a second position, and cause the probe tip to contact the surface of the sample 101 with a constant force, and continue point contact at several other positions on the surface of the sample 101 to generate a point cloud, which can be used to generate an absolute height map. This can reduce wear on the probe tip 111, increase the measurement throughput, particularly for large samples 101, allow measurement of larger and smaller samples 101 when scanning is not required for the measurement, and allow scanning of fragile samples 101 or adhesive samples 101 when constant contact scanning is not feasible.

[0073] In some embodiments, the processor 140 may be configured to dynamically compensate in real time the spring constant of the sensing subsystem 150 through the full dynamic range of the height sensor. This can also reduce wear on the probe tip 111 and allow scanning of smaller and more fragile samples 101 and reduce errors in the measured surface height.

[0074] In some embodiments, the sample 101 may be placed on the stage 105. The stage 105 may be moved in one or more directions in the plane (i.e., the x and y directions) or out of the plane (i.e., the z direction) by one or more actuators. The processor 140 may be configured to send instructions 148 to the stage 105 via the transceiver 149 to position the sample 101 by moving one or more actuators. For example, the processor 140 may be configured to send instructions 148 to move the stage 105 to scan the probe tip 111 across the surface of the sample 101, and the rotational position of the control arm 120 measured by the sensing subsystem 150 may indicate the topography of the sample 101 in the scanning direction. The processor 140 may be configured to control the speed of movement of the stage 105, where a faster scanning speed may increase the throughput while a slower scanning speed may increase the measurement accuracy. The processor 140 may be further configured to set a preset force and / or a preset height of the probe tip 111 during scanning, as described above.

[0075] For the system 100, the rotational position of the control arm 120 may be controlled via a force signal 141 applied to the pair of torque coils 130, and the sensing subsystem 150 may determine the rotational position of the control arm 120 to provide feedback for closed-loop control. Thus, the system 100 may provide precise position and force control in an integrated system.

[0076] Another embodiment of the present disclosure provides a method 200. As Figure 7 shown, the method 200 may include the following steps.

[0077] At step 210, a force signal is used to excite a pair of torque coils to generate a magnetic force between the pair of torque coils and an internal magnet of a control arm disposed between the pair of torque coils. The control arm may be connected to a probe arm, and the magnetic force may cause the control arm and the probe arm to rotate about a pivot joint and may cause the probe tip of the probe arm to contact the surface of a sample.

[0078] In an embodiment, step 210 may include using the force signal to excite one of the pair of torque coils to control the direction of rotation of the control arm about the pivot joint based on the magnetic force. For example, one of the torque coils may be excited to attract or repel the internal magnet of the control arm to rotate the control arm in a controlled direction. Alternatively, step 210 may include using different force signals to excite the two torque coils to control the direction of rotation of the control arm about the pivot joint based on the magnetic force. For example, each torque coil may be excited such that it attracts / repels the internal magnet of the control arm to rotate the control arm in a controlled direction. Each torque coil may be excited such that the resulting magnetic forces from the two torque coils control the direction of rotation of the control arm.

[0079] At step 220, a sensing subsystem is excited using an excitation signal. The sensing subsystem may be configured according to any of the embodiments of the system 100 described above, for example, configured as an angular displacement sensor, a linear displacement sensor, a dual-coil structure, or other sensor configurations.

[0080] At step 230, a sensed signal difference from the sensing subsystem is measured. The sensed signal difference may be proportional to the rotational position of the control arm. The sensed signal difference may be a voltage difference or a current difference. Specifically, a change in the rotational position of the control arm may cause the iron core of the control arm to move relative to a main coil and a pair of secondary coils. By measuring the sensed signal difference at the pair of secondary coils, the direction and magnitude of the rotation of the control arm can be determined.

[0081] At step 240, the height of the probe tip relative to the surface of the sample is determined based on the rotational position of the control arm. For example, based on the rotation of the control arm, the corresponding rotational position of the probe arm may indicate the height of the probe tip. Based on contact with the sample, the height of the probe tip relative to the surface of the sample and the height of the surface features of the sample can be determined.

[0082] At step 250, the rotational position of the control arm determined from the sensing subsystem is applied as feedback in a servo loop to control the force signal. In other words, the rotational position of the control arm can be used to provide a closed-loop operation for precise positioning and force control of the probe tip, as further described below.

[0083] In some embodiments, method 200 may further include a force command 260. The force command 260 may cause the probe tip to apply a controlled force to the surface of the sample, e.g., for a scratch test or an indentation test of the sample. After receiving the force command 260, method 200 may include Figure 8 the following additional steps as shown in

[0084] At step 261, an adjusted force signal is determined based on the feedback of the rotational position or force from the control arm to generate a preset force. For example, based on the position information of the control arm, it can be determined when the probe tip contacts the surface of the sample and which additional rotation of the control arm will cause the probe tip to apply the preset force to the sample. Thus, the adjusted force signal may be an adjustment (e.g., increase or decrease) to the force signal applied to at least one of the pair of torque coils, which will cause the control arm to rotate to generate the preset force.

[0085] In step 262, the pair of torque coils is excited using the adjusted force signal, thereby causing the probe tip to contact the surface of the sample using the preset force. The force applied to the sample can be confirmed as the preset force based on the sensed signal difference from the sensing subsystem. The closed-loop feedback of method 200 may allow precise control of the force applied to the surface of the sample by the probe tip for scratch and indentation tests.

[0086] In some embodiments, method 200 may further include a position command 270. The position command 270 may be configured to position the probe tip at a preset height relative to the surface of the sample for precise positioning and measurement. After receiving the position command 270, method 200 may include Figure 9 the following additional steps as shown in

[0087] At step 271, an adjusted force signal is determined based on the feedback of the rotational position or force from the control arm to position the probe tip at the preset height. For example, based on the position information of the control arm, it can be determined where the current position of the probe tip is and which additional rotation of the control arm will cause the probe tip to be positioned at the preset height. Thus, the adjusted force signal may be an adjustment (e.g., increase or decrease) to the force signal applied to at least one of the pair of torque coils, which will cause the control arm to rotate to position the probe tip at the preset height.

[0088] At step 272, the pair of torque coils are excited using the adjusted force signal, thereby causing the probe tip to be positioned at the preset height relative to the surface of the sample.

[0089] At step 273, based on the sensed signal difference from the sensing subsystem, it is confirmed that the position of the probe tip is at the preset height. The closed-loop feedback of method 200 can allow precise control of the position of the probe tip for precise positioning and measurement of features on the surface of the sample.

[0090] In some embodiments, method 200 may further include modulation command 280. Modulation command 280 may be configured to oscillate the probe tip relative to the surface of the sample. After receiving modulation command 280, method 200 may include Figure 10 the following additional steps shown in

[0091] At step 281, a modulated force signal is generated. The modulated force signal may reverse or interrupt the force signal applied to the pair of torque coils in a periodic manner. Thus, the modulated force signal may be a signal separate from the force signal or may be generated by passing the force signal through a filter to produce the modulated force signal.

[0092] At step 282, the pair of torque coils are excited using the adjusted force signal, thereby causing the probe tip to oscillate relative to the surface of the sample. By oscillating up and down, the probe tip may have a reduced chance of getting stuck in a highly viscous sample.

[0093] Using method 200, the rotational position of the control arm can be controlled via the force signal applied to the pair of torque coils, and the sensing subsystem can determine the rotational position of the control arm to provide feedback for closed-loop control. Thus, method 200 can provide precise position and force control in an integrated system.

[0094] Figure 11 shows a block diagram of a control system for a precision stylus. The control system may be a closed-loop system and may be applied to any of the embodiments of system 100 and method 200 described herein. The elements of the control system shown in Figure 11 are further described below.

[0095] The control system may include a probe sensing tip. The probe sensing tip may correspond to probe tip 111 of system 100 described above.

[0096] The control system may further include a position sensor excitation synthesizer. The position sensor excitation signal synthesizer may generate a pure sine wave to drive the main coil. The position sensor excitation signal synthesizer may correspond to the excitation signal generator 144 configured to generate the excitation signal 143 of the above system 100.

[0097] The control system may further include a position sensor main coil and a position sensor secondary coil. The position sensor main coil may be driven using a sinusoidal current driver that induces an alternating magnetic flux in the movable core traveling with the profiler probe tip. The sensor core may travel between the secondary coils. The alternating magnetic flux in the core induced by the primary winding is differentially coupled into the secondary winding. The position sensor main coil may correspond to the main coil 151 of the above system 100, and the position sensor secondary coil may correspond to the pair of secondary coils 152 of the above system 100.

[0098] The control system may further include a position sensor buffer amplifier. The position sensor buffer amplifier may extract a combined signal from the sensor coil that is proportional to the magnitude of the position and has a phase indicating the sign of the position relative to the center of the sensor travel.

[0099] The control system may further include a pusher coil. The pusher coil may induce a bi-directional force on the magnet mounted in the probe shaft to allow closed-loop damping of the probe tip movement. The pusher coil may be used to induce a precise pressure on the probe tip in contact with the test sample. The pusher coil may correspond to the pair of torque coils 130 of the above system 100.

[0100] The control system may further include a retractor magnet. The retractor magnet may be positioned above the probe shaft magnet that generates a slight attractive force on the shaft when the unit is not powered. In the event of a power loss in the system, the retractor function may protect the test sample and the probe tip. The retractor magnet may correspond to the external magnet 160 of the above system 100.

[0101] The control system may further include a position sensor signal demodulator and a low-pass filter. The demodulator may convert the probe tip position signal from a sinusoidal waveform to a DC voltage waveform. The demodulator may be coupled to the low-pass filter, which may remove residual ripple from the probe position signal.

[0102] The control system may further include a servo loop integrator. The servo loop integrator may drive the probe tip to the zero position. The control system may further include a servo loop lead / lag filter compensator. The lead-lag filter may be used to correct the phase and gain of the probe position servo loop. The control system may further include a servo loop indenter drive power amplifier. The servo loop power amplifier may drive the indenter coil to force the sensor shaft to the desired position. The loop power amplifier may have an input for enabling the downforce drive current.

[0103] The control system may further include a profilometer tip position command and feedback buffer. The command buffer may interface with the host system to initiate the downforce function, the modulation function, and the retraction function and provide an output path for the current feedback signal. The current feedback signal may be proportional to the force driving the probe downforce. The servo loop modulation signal may allow driving the probe tip with a variable signal to achieve a tapping motion.

[0104] The control system may further include a probe position output buffer. The probe position output buffer may perform the final compensation of the position output, perform any linear compensation as needed, and provide multiple gain amplifiers to allow the sensitivity to be user-selectable. Higher gain levels may further utilize an offset circuitry to shift the data into the output voltage aperture. The unity gain output may be proportional to the probe position. For example, 10 volts may be proportional to a 2 mm range of the probe tip. The gain of 10 position outputs may provide a position output with 10 times the sensitivity. For example, 10 volts may be proportional to a 200 micron probe deflection. The zeroing circuit may allow the 10 volt output window to be shifted along a virtual 100 volt range. The gain of 100 position outputs may provide a position output with 100 times the sensitivity. For example, 10 volts is proportional to a 20 micron probe deflection. The zeroing circuit allows the 10 volt output window to be shifted along a virtual 1000 volt range. The probe position signal may be the filtered output of the demodulator, which is proportional to the position of the probe tip.

[0105] The control system may further include a probe position buffer aperture reset. The aperture reset may allow the user to shift the aperture window into a range that can be displayed by the test system.

[0106] The downforce enables a signal to connect the downforce signal into the control loop. The downforce loop enable may control the integral gain of the control loop. In the low gain mode, the integrator may be disabled. The indenter drive current sense signal may be fed back into the control loop to allow regulation of a constant downforce. The demodulator reference signal may be synchronized with the excitation signal to allow precise control of the phase of the demodulator process.

[0107] Although the present disclosure has been described with respect to one or more particular embodiments, it should be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure. Accordingly, the present disclosure is considered to be limited only by the appended claims and their reasonable interpretation.

Claims

1. A system, comprising: A probe arm, comprising a probe tip, wherein the probe tip is configured to contact a surface of a sample; A control arm, connected to the probe arm, wherein the control arm includes an internal magnet; One or more torque coils, disposed on opposite sides of the internal magnet of the control arm, wherein the one or more torque coils are configured to cause rotation of the control arm about a pivot joint based on interaction with the internal magnet; A sensing subsystem, configured to measure a rotational position of the control arm; And A processor, in electronic communication with the one or more torque coils and the sensing subsystem, wherein the processor is configured to: Excite at least one of the one or more torque coils with a force signal to generate a magnetic force between the one or more torque coils and the internal magnet, which causes the control arm to rotate about the pivot joint, thereby causing the probe arm connected to the control arm to rotate about the pivot joint and causing the probe tip to contact the surface of the sample; Excite the sensing subsystem with an excitation signal; And Receive from the sensing subsystem a sensed signal difference proportional to the rotational position of the control arm, which corresponds to a height of the probe tip relative to the surface of the sample, wherein the sensed signal difference is a voltage difference or a current difference.

2. The system according to claim 1, wherein the processor includes a servo loop integrator configured to apply the rotational position of the control arm determined from the sensing subsystem as feedback to control the force signal.

3. The system according to claim 1, wherein the processor is further configured to: Determine an adjusted force signal based on feedback from the rotational position or force of the control arm to generate a preset force; and Excite at least one of the one or more torque coils with the adjusted force signal, thereby causing the probe tip to contact the surface of the sample with the preset force.

4. The system according to claim 1, wherein the processor is further configured to: Determine an adjusted force signal based on feedback from the rotational position or force of the control arm to position the probe tip at a preset height; Excite at least one of the one or more torque coils with the adjusted force signal, thereby causing the probe tip to be positioned at the preset height relative to the surface of the sample; and Confirm that the probe tip is positioned at the preset height based on the sensed signal difference received from the sensing subsystem.

5. The system according to claim 1, wherein the processor is further configured to: Generate a modulated force signal; and Excite at least one of the one or more torque coils with the modulated force signal, thereby causing the height of the probe tip to oscillate relative to the surface of the sample.

6. The system according to claim 1, wherein the sensing subsystem includes: A main coil; And A pair of secondary coils, disposed on opposite sides of the main coil; The core of the pivot joint is surrounded by the main coil and the pair of secondary coils such that a change in the rotational position of the control arm causes the core to move within the main coil and the pair of secondary coils, and the sensed signal difference measured from the pair of secondary coils is proportional to the position of the core.

7. The system according to claim 6, wherein the main coil and the pair of secondary coils are coaxial, and the core moves linearly within the main coil and the pair of secondary coils.

8. The system according to claim 6, wherein the main coil and the pair of secondary coils are co-planar, and the core moves angularly within the main coil and the pair of secondary coils.

9. The system according to claim 1, wherein the sensing subsystem comprises: a main coil; and a secondary coil, which is disposed opposite to the main coil; wherein the core of the control arm is disposed between the main coil and the secondary coil such that a change in the rotational position of the control arm causes the core to move between the main coil and the secondary coil, and the sensed signal difference measured from the secondary coil is proportional to the position of the core.

10. The system according to claim 1, further comprising an external magnet configured to attract the internal magnet of the control arm, which causes the control arm to rotate to a retracted position, wherein the probe tip is spaced apart from the surface of the sample.

11. The system according to claim 10, wherein the one or more torque coils are configured to cause the control arm to rotate against the attraction of the external magnet.

12. The system according to claim 10, wherein the external magnet is movable between a first position and a second position, wherein in the first position, the external magnet is close to the internal magnet to attract the internal magnet of the control arm, and in the second position, the external magnet is away from the internal magnet to allow free rotation of the control arm.

13. The system according to claim 1, wherein the pivot joint includes a torsion bar configured to bias the control arm towards a neutral position, wherein in the neutral position, the probe tip is spaced apart from the surface of the sample, and the one or more torque coils are configured to cause the control arm to rotate against the bias of the torsion bar.

14. The system according to claim 1, wherein the processor is further configured to: excite one of the one or more torque coils using the force signal to control the direction of rotation of the control arm about the pivot joint based on the magnetic force.

15. A method, comprising: exciting a pair of torque coils using a force signal to generate a magnetic force between the pair of torque coils and an internal magnet of a control arm disposed between the pair of torque coils, wherein the control arm is connected to a probe arm, and the magnetic force causes the control arm and the probe arm to rotate about a pivot joint and causes the probe tip of the probe arm to contact the surface of a sample; exciting a sensing subsystem using an excitation signal; Measuring a sensed signal difference proportional to the rotational position of the control arm from the sensing subsystem, wherein the sensed signal difference is a voltage difference or a current difference; and Determining the height of the probe tip relative to the surface of the sample based on the rotational position of the control arm.

16. The method according to claim 15, further comprising: Applying the rotational position of the control arm determined from the sensing subsystem as feedback in a servo loop to control the force signal.

17. The method according to claim 15, further comprising: Determining an adjusted force signal based on feedback from the rotational position or force of the control arm to generate a preset force; and Using the adjusted force signal to excite the pair of torque coils, thereby causing the probe tip to contact the surface of the sample with the preset force.

18. The method according to claim 15, further comprising: Determining an adjusted force signal based on feedback from the rotational position or force of the control arm to position the probe tip at a preset height; Using the adjusted force signal to excite the pair of torque coils, thereby causing the probe tip to be positioned at the preset height relative to the surface of the sample; and Confirming that the probe tip is positioned at the preset height based on the sensed signal difference from the sensing subsystem.

19. The method according to claim 15, further comprising: Generating a modulated force signal; and Using the modulated force signal to excite the pair of torque coils, thereby causing the height of the probe tip to oscillate relative to the surface of the sample.

20. The method according to claim 15, wherein using the force signal to excite the pair of torque coils comprises: Using the force signal to excite one of the pair of torque coils to control the direction of rotation of the control arm about the pivot joint based on the magnetic force.

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