We present a technique to produce isolated lines and trenches with arbitrary widths in the range of 12 nm to 500 nm, arbitrary heights and depths in the range of 100 nm to 2 μm, 90-degree sidewall angle, and top corner radii as small as 5 nm. These structures are ideal candidates as Critical Dimension (CD) absolute standards. The sidewall angle can further be varied to create an arbitrary sidewall angle that can be accurately measured.

In semiconductor manufacturing, the performance of metrology equipment directly impacts yield. Fabs and equipment suppliers depend on calibration standards to ensure that their metrology results are within tolerances and to maintain their ISO and QS quality certifications. This task becomes more challenging as the device features shrink and tolerances become tighter, to the extent of their physical limits in many cases. As the industry keeps finding ways to meet the demanding metrology requirements, calibration standards have been developed and enhanced for all essential measurements, i.e. critical dimensions, thin films, surface topography, overlay, doping, and defect inspections. This paper provides an overview of such standards and demonstrates how they are certified and tested to be traceable to the International System (SI) unit of length in order to ensure reliable and transferable calibrations for fabs. The latest results on 50 nm critical dimension (CD) standards. 2 nm film thickness standards, and 50 nm particle sizing standards, along with their certification strategies, are also presented.

This paper is a practical guide to the calibration of magnification of a CD-SEM using a pitch standard. It answers two fundamental metrology questions: 1) how many individual pitch measurements should one take in order to estimate the average pitch of the sample with a specified uncertainty and with a specified confidence level?, and 2) when is it appropriate to recalibrate the instrument following the measurement of the standard? In answering these questions, this paper identifies Cost of Ownership (CoO) elements of the calibration process and outlines best engineering practices for the calibration procedure. The discussion is then extended to the case of tool matching and calibration of not just a single measurement tool, but an entire measurement system comprised of several measurement tools all matched to each. other. Finally, this paper discusses the problem of hydrocarbon contamination in a CD-SEM, which limits the number of times that a certain location on the standard can be used for calibration, and presents a methodology to determine how often the measurement location should be changed.

An atomic force microscope (AFM) is an instrument which measures the topography of a surface by bringing a cantilever beam into contact with a sample and measuring the deflection of the cantilever as it is scanned across the surface. The complexity of an AFM is predominantly governed by the detector used for measuring the deflection of the cantilever probe. The authors describe the fabrication of a silicon cantilever beam with an integrated piezoresistor for sensing its deflection. A silicon-on-insulator material is used for the fabrication. A p-type resistor is fabricated at the surface of the cantilever along a <110> direction so that the piezoresistive effect of silicon causes its resistance to vary linearly with its deflection. The cantilevers considered typically have spring constants from 1 to 10 N/m and minimum detectable deflections from 1 to 10 AA over a 10-Hz-1-kHz frequency range. The cantilevers were successfully used in an AFM, and an image of a grating was obtained with this technique.<>

In this paper we present and characterize a NIST-traceable, all-silicon, 100 nm pitch structure with the necessary quality attributes to calibrate CD-SEM tools used for metrology of sub-0.25 micron semiconductor process technology.

Frequency modulation atomic force microscopy (FM-AFM) has made imaging of surfaces in ultrahigh vacuum with atomic resolution possible. Here, we demonstrate a new approach which simplifies the implementation of FM-AFM considerably and enhances force sensitivity by directly exciting the cantilever with the thermal effects involved in the deflection measurement process. This approach reduces the mechanically oscillating mass by 6 to 8 orders of magnitude as compared to conventional FM-AFM, because external actuators and oscillating cantilever mounts are not needed. Avoiding external actuators allows the use of cantilevers with very high oscillation frequencies, which results in improved force sensitivity. Further, the implementation and operation of this new technique is significantly simplified, because external actuator, bandpass filter, and phase shifter are eliminated.

The key component of the atomic force microscope (AFM) is a cantilever with a tip. The tip must be sharp enough to record with high lateral resolution the topography. The cantilever must also have the appropriate compliance and resonant frequency for the type of operation selected, which can be either a contact or a noncontact mode of operation. The requirement for a low spring constant (less than 1 N/m) and a high resonant frequency (greater than 10 kHz) led to silicon micromachining techniques early on in the development of the AFM. Silicon micromachining is a technology by which a silicon wafer is processed through a series of deposition, photolithography, and etching steps to produce a mechanical structure with dimensional tolerances in the order of 1 μm. The use of silicon micromachining techniques has benefited the AFM in several aspects: (1) sharper tips can be manufactured with micromachining techniques than with alternative electrochemical etching techniques, as used for scanning tunneling microscopy tips; (2) batch fabrication simultaneously of thousands of cantilevers guarantees a high degree of reproducibility in the mechanical properties of the cantilevers; and (3) micromachined cantilevers are inexpensive.

Piezoresistive cantilevers offer a novel detection scheme for Atomic Force Microscopy (AFM) in which no optics and no alignments are required to measure the deflection of the cantilever. The cantilever deflection is measured through the resistance of a stress sensitive resistor-a piezoresistor-integrated in the silicon cantilever. The use of piezoresistive cantilevers simplifies the operation of the microscope, especially for applications in ultrahigh vacuum (UHV) and at low temperature, where other detection schemes are difficult to implement. This paper reviews the principle of operation of piezoresistive cantilevers and presents recent results obtained using piezoresistive cantilevers for imaging in air, in water, in ultra high vacuum, at low temperature, on magnetic samples, for lateral force microscopy, in contact and noncontact modes.

This paper addresses the problem of determining the absolute force constant of Atomic Force Microscope cantilevers. In the method presented, the cantilever under test is deflected against a reference cantilever of known spring constant. The relative deflection of the two cantilevers is related to their spring constants. The novelty of our approach is in the use of a micromachined reference cantilever of a precisely controlled force constant. Preliminary results show that our method is capable of measuring the force constant of cantilevers in the range of 0.1 to 10 N/m with an accuracy of better than 20%. The error is dominated by the non-linear effects in the force versus distance curves used for the measurement.

We have imaged vortices in superconducting thin films with a low-temperature magnetic force microscope that utilizes microfabricated piezoresistive cantilevers with built-in tips. The films of YBa2Cu3O7−x and Bi2Sr2Ca1Cu2O8+x, are made by laser ablation and molecular beam epitaxy, respectively. The vortices usually appear as round features in the noncontact image with a diameter of about 1 μm or slightly less. In some cases the position of the vortices is correlated to defects observed in the topographic image of the same area. The vortices move sometimes, especially after taking a topographic (contact mode) scan.

We demonstrate the use of piezoresistive cantilevers with an atomic force microscope that operates in conjunction with a scanning electron microscope. This is a very attractive combination because the two microscopes complement each other in terms of depth and lateral resolution, field of view, speed, and ability to image insulating surfaces. Images of a grating and an integrated circuit are shown as examples. Simultaneous operation in real time was achieved.

We have developed a low temperature magnetic force microscope capable of operation down to 6 K in vacuum by using piezoresistive cantilevers. We use the non-contact frequency modulation technique to detect the magnetic force gradient between an iron-coated tip and the sample. We demonstrate the operation of this new instrument by obtaining images of magnetic domains in VHS tape at room temperature, 77 and 6 K. This microscope is ideally suited for the characterization of thin films of high temperature superconductors.