Vibration distortion removal for scanning probe microscopes

• US 6,178,813 B1
• Filed: 11/17/1999
• Issued: 01/30/2001
• Est. Priority Date: 11/17/1999
• Status: Expired due to Fees

• Current Assignee: United States Department of the Army (Government of the United States of America), The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Bradshaw, John L., Wortman, Donald E., Gomez, Romel D., Bruno, John D.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): CYGAN, MICHAEL T
• Application Number:
  US09/441,894
• Time in Patent Office: 440 Days
• Field of Search: 73/105, 250/306, 250/307, 356/345, 356/354, 356/356, 356/358, 356/493
• US Class Current: 73/105
• CPC Class Codes: G01Q 30/06 for error compensation
• CPC Class Codes: G01Q 70/04 with compensation for temperature or vibration induced errors
• CPC Class Codes: Y10S 977/868 with optical means

Abstract

A method for improving images of surface features of a sample, constructed by a scanning probe microscope, includes constructing images of surface features of a sample with a scanning probe microscope; measuring a displacement of the sample that occurs during the constructing step; and correcting the images using the measured displacement. An apparatus for improving images of surface features of a sample, constructed by a scanning probe microscope, includes a vacuum chamber; a sample holder disposed in the vacuum chamber; at least one spring connected between the vacuum chamber and the sample holder; at least one magnet disposed in the vacuum chamber for damping vibrations of the sample holder; a probe and piezo tube assembly disposed in the vacuum chamber for scanning surface features of a sample; and an interferometer disposed in the vacuum chamber wherein the interferometer measures a distance between the sample and a point fixed with respect to the sample.

Claims

1. An apparatus comprising;

a vacuum chamber;

a sample holder disposed in the vacuum chamber;

at least one spring connected between the vacuum chamber and the sample holder;

at least one magnet disposed in the vacuum chamber for damping vibrations of the sample holder;

a probe and piezo tube assembly disposed in the vacuum chamber for scanning surface features of a sample;

an interferometer disposed in the vacuum chamber wherein the interferometer measures a distance between the sample and a point fixed with respect to the sample; and

a data processor connected to the probe and piezo tube assembly and the interferometer;

wherein the interferometer comprises a laser, a beam splitter, first and second mirrors and a detector; and

wherein a light beam emitted by the laser is split by the beam splitter into paths 1₁, and 1₃;

a light beam passing along path 1₁ is directed to the first mirror and reflected along path d to the sample where it is reflected off the sample back to the first mirror and back along path 1₁ to the beam splitter where it is split again into a first part and a second part;

the first part follows path 1₂ to a second mirror where the first part is reflected back to the beam splitter and then along path 1₃ to the detector;

the second part is isolated from the laser;

at the beam splitter the first part rejoins a part of the light beam directly emitted by the laser that follows path 1₃ to the detector where the first part and the part of the light beam directly emitted by the laser interfere.

2. The apparatus of claim 1 wherein the second mirror comprises a coating on the beam splitter.

3. The apparatus of claim 1 wherein the first mirror comprises a highly reflecting mirror.

4. An apparatus comprising;

a vacuum chamber;

a support disposed on a bottom of the vacuum chamber;

a sample holder disposed on the support;

a probe and piezo tube assembly disposed in the vacuum chamber for scanning surface features of a sample;

an interferometer disposed in the vacuum chamber wherein the interferometer measures a distance between the sample and a point fixed with respect to the sample; and

a data processor connected to the probe and piezo tube assembly and the interferometer;

wherein the interferometer comprises a laser, a beam splitter, first and second mirrors and a detector; and

wherein a light beam emitted by the laser is split by the beam splitter into paths 1₁ and 1₃;

a light beam passing along path 1₁ is directed to the first mirror and reflected along path d to the sample where it is reflected off the sample back to the first mirror and back along path 1₁ to the beam splitter where it is split into a first part and a second part;

the first part follows path 1₂ to a second mirror where the first part is reflected back to the beam splitter and then along path 1₃ to the detector;

the second part is isolated from the laser;

at the beam splitter the first part rejoins a part of the light beam directly emitted by the laser that follows path 1₃ to the detector where the first part and the part of the light beam directly emitted by the laser interfere.

5. The apparatus of claim 4 wherein the the second mirror comprises a coating on the beam splitter.

6. The apparatus of claim 4 wherein the first mirror comprises a highly reflecting mirror.

7. A method for improving images of surface features of a sample, constructed by a scanning probe microscope, comprising:

constructing images of surface features of a sample with a scanning probe microscope;

measuring a displacement of the sample that occurs during the constructing step; and

correcting the images using the measured displacement;

wherein the displacement is measured using an interferometer; and

wherein the measuring step comprises;

emitting a light beam from a laser;

splitting the light beam into paths 1₁ and 1₃;

passing a portion of the light beam along path 1₁ to a first mirror and reflecting it along a path d to the sample where it is reflected off the sample back to the first mirror and then back along path 1₁ to the beam splitter;

then

splitting the portion of the light beam into a first part and a second part;

the first part following path 1₂ to a second mirror where it is reflected back to the beam splitter and then along path 1₃ to the detector;

isolating the second part of the portion of the light beam from the laser; and

at the beam splitter, combining the first part of the portion of the light beam with another portion of the light beam directly emitted by the laser that follows path 1₃ to the detector where the first part and the another portion of the light beam directly emitted by the laser interfere.