An apparatus for characterizing multilayer samples is disclosed. An intensity modulated pump beam is focused onto the sample surface to periodically excite the sample. A probe beam is focused onto the sample surface within the periodically excited area. The power of the reflected probe beam is measured by a photodetector. The output of the photodetector is filtered and processed to derive the modulated optical reflectivity of the sample. Measurements are taken at a plurality of pump beam modulation frequencies. In addition, measurements are taken as the lateral separation between the pump and probe beam spots on the sample surface is varied. The measurements at multiple modulation frequencies and at different lateral beam spot spacings are used to help characterize complex multilayer samples. In the preferred embodiment, a spectrometer is also included to provide additional data for characterizing the sample.

Apparatus for evaluating metalized layers on semiconductors

The invention relates to optical microscopy, in particular to methods for photothermal examination of absorbent microinhomogeneities using laser radiation sources and can be widely used in laser engineering, industry and biomedicine for examining relatively transparent objects containing submicron impurities, including the detection of local inclusions and defects in ultrapure optical and semiconductor materials and the non-destructive diagnosis of biological samples on a cellular and subcellular level. The aim of the invention is to increase the sensitivity, spatial resolution and informativity of examination of local absorbent microinhomogeinities in transparent objects and to measure said microinhomogeinities even when they are less than the used emission wavelength. The inventive method consists in radiating a sample with a pumping laser beam. The duration of the radiation is equal to or less than a representative time for cooling the examined microinhomogeinity. The relatively large surface of the sample is radiated, the shape thereof being greater than the wavelength of the used pumping laser. Thermal variations of the refractive index occurring in the sample as a result of absorption produced with the aid of the pumping beam are recorded by measuring parameters of a test laser beam. The diameter of the test beam is chosen in such a way that it is equal to or greater than the diameter of the pumping beam. A diffraction-limited phase distribution along the cross-section of the testing laser beam is transformed into an amplitude image, the microinhomogeinity properties being determined by measuring said amplitude image.

Method and device for photothermal examination of microinhomogeneities

An apparatus measures a property of a layer (such as the sheet resistance or thermal conductivity by the following method: (1) focusing the heating beam on a region of the conductive layer, (2) modulating the power of the heating beam at a predetermined frequency that is selected to be sufficiently low to ensure that at least a majority (preferably all) of the generated heat transfers out of the heated region by diffusion, and (3) measuring the power of another beam that is (a) reflected by the heated region, and (b) modulated in phase with modulation of the heating beam. When the measurement changes by more than a predetermined amount (e.g. by 10 %), a fabrication process parameter is changed to return the measurement to normal.

Apparatus and method for measuring a property of a layer in a multilayered structure

An optical device is provided with first and second inputs. A first coupler coupled is coupled to the first input and produces at least a first and second output. A second coupler is coupled to the second input and produces at least a first and second output. A third coupler is coupled to the first output of the first coupler and to the first output of the second coupler. A fourth coupler is coupled to the second output of the first coupler and to the second output of the second coupler. First and second crossing waveguides are provided with an angle selected to minimize crosstalk and losses between the first and second cross waveguides. The first crossing waveguide connects one of the first or second outputs from the first coupler with an input of the fourth coupler. The second crossing waveguide connects one of the first or second outputs from the second coupler with an input of the third coupler. A first phase shifter is coupled to the first and second waveguides. The first and second waveguides connect one of the outputs of the first or second coupler and one of the inputs of the third or fourth couplers. The first, second, third and fourth couplers, the two crossing waveguides and the phase shifter are each formed as part of a single planar chip made of an electro-optical material.

Coherent optical detector and coherent communication system and method

The surface of a doped semiconductor wafer is heated locally by means of a pump beam whose intensity is modulated at a first frequency. The heated area is sampled by a probe beam whose intensity is modulated at a second frequency. After the probe beam has been modulated (reflected or transmitted) at the first frequency by the wafer, the modulated probe beam is detected at a frequency equal to the difference between the harmonics of the first and second frequencies to determine dose of the dopants in the wafer. Such or similar type of instrument for measuring dose may be combined with an ellipsometer, reflectometer or polarimeter for measuring dose as well as thickness(es) and/or indices of refraction in a combined instrument for measuring the same sample.

System for non-destructive measurement of samples

A process and arrangements for photothermal spectroscopy (thermal wave analysis) by the single-beam method with double modulation technique. A single-beam method is developed making use of the advantages of double modulation technique in detecting the photothermally generated difference frequency without requiring partial beams and while achieving extensive absence of intermodulation, the intensity of the laser beam is modulated before striking the object in such a way that the modulation spectrum substantially contains a carrier frequency (f 1 ) and two sideband frequencies (f 1 ±F 2 ), wherein f 2 is the base clock frequency of the modulation, a regulating detector and a control loop intervening in the modulation process suppress that component of the base clock frequency (f 2 ) in the same phase with the mixed frequency of the carrier frequency and sideband frequencies. After interaction with the object the optical response of the object is measured by means of a measurement detector and frequency-selective and phase-selective device as the amplitude of that component of the base clock frequency (f 2 ) which, as the photothermal mixed product, has the same phase as the mixed frequency of the carrier frequency (f 1 ) and sideband frequency (f 1 ±f 2 ). Use for nondestructive and noncontact analysis of the material parameters of areas of solid bodies close to the surface is described.

Process and arrangement for photothermal spectroscopy

A method and apparatus for thermowave analysis employs a single laser beam, which has an additive, two-frequency, intensity modulation, and is directed onto the object. The amplitude of the mixed frequency of the discrete modulation frequencies, which is not contained in the exciting beam, is analyzed as response signal. By obtaining a reference signal from the exciting beam and forming the difference between this exciting beam and the measurement signal, noise suppression and a lowering of the limit of sensitivity are achieved in an advantageous manner.

Method and apparatus for thermowave analysis

A method for optical stress analysis comprises the steps of directing an incident beam of polarized light to the sample to be analyzed and analyzing a light bundle exiting the sample in two detection channels extending perpendicular to one another with respect to the polarization direction, providing that the incident beam is elliptically polarized, carrying out the elliptical polarization with an elliptic shape having a comparatively large ratio of the large principal axis to the small principal axis, the direction of rotation of the elliptical polarization of the incident beam changing periodically and using two alternative states of the direction of rotation for each measurement process, adjusting the detection channels which extend perpendicular to one another corresponding to the position of the principal axes of the ellipse and carrying out the difference between two measurements consecutively with the same beam intensity of the incident beam and the same ratio of principal axes, but with opposite direction of rotations of the elliptical polarization, being given by the two detection channels An arrangement in accordance with the method is also disclosed

Method and arrangement for optical stress analysis of solids

Two noncontact laser-based heterodyne techniques, photo- thermal heterodyne (PTH) and photoluminescence heterodyne (PLH), are introduced and applied to processing and quality control in silicon wafer manufacturing. The crystallographic characteristics of process- induced defects in silicon wafers are suitable for the application of PTH and PLH techniques, which are demonstrated on selected examples from different steps of silicon wafer production. Both PLH and PTH tech- niques meet the demand for nondestructive and on-line-suitable mea- surement in the semiconductor industry. © 1997 Society of Photo-Optical Instru- mentation Engineers. Subject terms: photoacoustic and photothermal science and engineering; photo- luminescence heterodyne; photothermal heterodyne; silicon wafer manufacturing; ultra-large-scale integration; subsurface damage.

Selected applications of photothermal and photoluminescence heterodyne techniques for process control in silicon wafer manufacturing

Die Erfindung betrifft ein Verfahren und Anordnungen zur photothermischen Spektroskopie (Thermowellenanalyse) nach dem Typ des Einstrahlverfahrens mit Doppelmodulationstechnik. Die Aufgabe, ein Einstrahlverfahren zu entwickeln, das die Vorzuge der Doppelmodulationstechnik beim Detektieren der photothermisch generierten Differenzfrequenz nutzt, ohne Partialstrahlen zu benotigen, und das eine hohe Intermodulationsfreiheit erreicht, wird erfindungsgemas dadurch gelost, das die Intensitat des Laserstrahles vor dem Auftreffen auf dem Objekt derart moduliert wird, das im Modulationsspektrum im wesentlichen eine Tragerfrequenz (f1) und zwei Seitenbandfrequenzen (f1-f2) enthalten sind, wobei f2 die Grundtaktfrequenz der Modulation ist, mittels eines Regeldetektors und einer in den Modulationsvorgang eingreifenden Regelschleife diejenige Komponente der Grundtaktfrequenz (f2) unterdruckt wird, die zu der Mischfrequenz aus Trager- und Seitenbandfrequenzen phasengleich ist, und nach Wechselwirkung mit dem Objekt mittels Mesdetektor und frequenz- und phasenselektiver Einrichtung die optische Response des Objekts als Amplitude derjenigen Komponente der Grundtaktfrequenz (f2) gemessen wird, die als photothermisches Mischprodukt zur Mischfrequenz aus Tragerfrequenz (f1) und Seitenbandfrequenz (f1-f2) phasengleich ist. Die Erfindung findet Anwendung zur zerstorungsfreien und beruhrungslosen Analyse der Materialparameter oberflachennaher Bereiche von Festkorpern.

Hans-Dieter Geiler

Papers

Process and arrangement for photothermal spectroscopy

Method and apparatus for thermowave analysis

Method and arrangement for optical stress analysis of solids

Selected applications of photothermal and photoluminescence heterodyne techniques for process control in silicon wafer manufacturing

Verfahren und anordnung zur photothermischen spektroskopie