Method and apparatus for micromachining a sample using a focused ion beam

A method for inspecting a sample in an apparatus for micromachining samples, the apparatus including an integral combination of a sample holder for holding the sample, a focused ion beam exposure system comprising an assembly for projecting a focused ion beam onto a first position where, in use, the focused ion beam impinges on the sample held by the sample holder, and a light optical system, wherein the light optical system comprises a light source for projecting light towards the sample holder, light collecting optics for collecting at least part of the light from the sample on the sample holder, and a detector for detecting at least a part said collected light, wherein the light optical system comprises an imaging detector and/or a wavelength selective element,

• the method comprising the steps of:
• providing a sample that has at least partially been micromachined by the focused ion beam exposure system;
• projecting light towards the sample and collecting at least part of the light from said sample;
• analyzing the light collected by the light collecting optics and establishing a measure for the modulation of an intensity of said collected light due to an optical interference of said light from a first surface of the sample and light from a second surface of the sample, wherein the first surface of said sample is facing towards the light collecting optics of the light optical system and wherein the first surface is arranged in between the second surface of sample and the light collecting optics of the light optical system, and wherein said measure is established for one or more positions on the sample and/or for one or more wavelengths of the projected light;
• and
• using the measure for the modulation of said collected light due to the optical interference for establishing a measure for the distance between said first surface and said second surface,
• wherein the light source is configured for projecting light with at least three different wavelengths towards the sample on the sample holder,
• wherein the step of analyzing the light collected by the light collecting optics further comprises:
• measuring the intensity of the collected light from the sample for each one of the at least three different wavelengths in order to establish the measure for the modulation of the intensity of said collected light due to an optical interference of the light from the first surface of the sample and light from the second surface of the sample, for each one of the at least three different wavelengths of the projected light, and using the wavelength dependence of the modulation of the intensity of said collected light for establishing a measure for the distance between said first surface and said second surface.

A method for inspecting a sample in an apparatus for micromachining samples, the apparatus including an integral combination of a sample holder for holding the sample, a focused ion beam exposure system comprising an assembly for projecting a focused ion beam onto a first position where, in use, the focused ion beam impinges on the sample held by the sample holder, and a light optical system, wherein the light optical system comprises a light source for projecting light towards the sample holder, light collecting optics for collecting at least part of the light from the sample on the sample holder, and a detector for detecting at least a part said collected light, wherein the light optical system comprises an imaging detector and/or a wavelength selective element,

• the method comprising the steps of:
• providing a sample that has at least partially been micromachined by the focused ion beam exposure system;
• projecting light towards the sample and collecting at least part of the light from said sample;
• analyzing the light collected by the light collecting optics and establishing a measure for the modulation of an intensity of said collected light due to an optical interference of said light from a first surface of the sample and light from a second surface of the sample, wherein the first surface of said sample is facing towards the light collecting optics of the light optical system and wherein the first surface is arranged in between the second surface of sample and the light collecting optics of the light optical system, and wherein said measure is established for one or more positions on the sample and/or for one or more wavelengths of the projected light;
• and
• using the measure for the modulation of said collected light due to the optical interference for establishing a measure for the distance between said first surface and said second surface,
• wherein the sample comprises a part with a substantially continuous increasing or decreasing thickness,
• wherein the step of analyzing the light collected by the light collecting optics further comprises:
• measuring the intensity of the collected light from the sample as a function of the position on the sample on the part with a substantially continuous increasing or decreasing thickness and substantially in a direction in which the thickness of the sample increases or decreases, in order to establish the measure for the modulation of the intensity of said collected light due to the optical interference of said light from the first surface of the sample and light from the second surface of the sample, and using the position dependence of the modulation of the intensity of said collected light for establishing a measure for the change in distance between said first surface and said second surface in said part with the substantially continuous increasing or decreasing thickness.

A method for inspecting a sample in an apparatus for micromachining samples, the apparatus including an integral combination of a sample holder for holding the sample, a focused ion beam exposure system comprising an assembly for projecting a focused ion beam onto a first position where, in use, the focused ion beam impinges on the sample held by the sample holder, and a light optical system, wherein the light optical system comprises a light source for projecting light towards the sample holder, light collecting optics for collecting at least part of the light from the sample on the sample holder, and a detector for detecting at least a part said collected light, wherein the light optical system comprises an imaging detector and/or a wavelength selective element,

• the method comprising the steps of:
• providing a sample that has at least partially been micromachined by the focused ion beam exposure system;
• projecting light towards the sample and collecting at least part of the light from said sample;
• analyzing the light collected by the light collecting optics and establishing a measure for the modulation of an intensity of said collected light due to an optical interference of said light from a first surface of the sample and light from a second surface of the sample, wherein the first surface of said sample is facing towards the light collecting optics of the light optical system and wherein the first surface is arranged in between the second surface of sample and the light collecting optics of the light optical system, and wherein said measure is established for one or more positions on the sample and/or for one or more wavelengths of the projected light;
• and
• using the measure for the modulation of said collected light due to the optical interference for establishing a measure for the distance between said first surface and said second surface,
• wherein the sample comprises a part with a substantially continuous increasing or decreasing thickness,
• wherein the method further comprises the steps of:
• configuring the light source for projecting light with a coherence length substantially equal or larger than the sample thickness, towards the sample on the sample holder, wherein the modulation of the intensity of said collected light due to the optical interference of said light from the first surface of the sample and light from the second surface of the sample results in one or more fringes,
• establishing a distance in which said one or more fringes extends over said part in the direction in which the thickness of the sample increases or decreases, and
• using the number of said one or more fringes, a value of a refractive index of the sample material, and the wavelength of the projected light for establishing a measure for the change in distance between said first surface and said second surface between the outermost fringes of the number of said one or more fringes,
• or
• using said distance and an angle between the FIB beam and the surface of the sample for establishing a measure for the change in distance between said first surface and said second surface between the outermost fringes of the number of said one or more fringes.