Self-masking FIB milling

A method of depassivating conductors within a selected region of an integrated circuit specimen, comprising the steps of:

• a. scanning a focused ion beam over a surface of an integrated circuit specimen to mill material from the surface;
• b. preparing a set of data representing an image of the surface, the image having a first image portion representing an area of dielectric material and a second image portion representing at least one conductor;
• c. scanning the focused ion beam over the surface while controlling the focused particle beam to selectively mill the area represented in the first image portion and to minimize milling of the area represented in the second image portion;
• and
• d. repeating steps b. and c. a plurality of times so that the focused ion beam preferentially mills dielectric material to thereby expose conductors of the specimen.

A method of modifying a specimen, comprising the steps of:

• a. scanning a focused particle beam over a surface of a specimen to mill material from the surface;
• b. preparing a set of data representing an image of the surface, the image having a first image portion representing an area to be milled further and a second image portion representing an area over which further milling is to be minimized, by
• i. acquiring a first set of pixel data defining a contrast image of the surface, the pixel data comprising a respective intensity value for each X-Y location of the image, and
• ii. thresholding the intensity values to produce a set of data defining a mask image having a gray-level value for each X-Y location of the image;
• and
• c. scanning the focused particle beam over the surface while controlling the focused particle beam to selectively mill further the area represented in the first image portion and to minimize further milling of the area represented in the second image portion, wherein controlling the focused particle beam comprises controlling the effective milling rate of the beam at each X-Y location of the surface in dependence on the set of data defining a mask image.

A method of depassivating conductors within a selected region of an integrated circuit specimen having multiple metal layers separated by dielectric layers, comprising the steps of:

• a. scanning a focused ion beam over a surface of an integrated circuit specimen to mill material from the surface, to thereby expose a conductor (1902) of a first metal layer;
• b. preparing a set of data representing an image of the surface, the image having a first image portion (1922) representing dielectric material and a second image portion (1920) representing the exposed conductor of the first metal layer;
• c. scanning the focused ion beam over the surface while controlling the focused particle beam to selectively mill the area of dielectric material represented in the first image portion and to minimize milling of the conductor of the first metal layer represented in the second image portion, to thereby expose a conductor (1904, 1908) of a second metal layer;
• d. preparing a set of data representing an updated image of the surface, the updated image having a first image portion (1932) representing dielectric material and second image portions (1930) representing the conductor of the first metal layer and the conductor of the second metal layer;
• and
• e. scanning the focused ion beam over the surface while controlling the focused particle beam to selectively mill the dielectric material represented in the first image portion of the updated image and to minimize milling of the conductors of the first and second metal layers represented in the second image portion of the updated image, to thereby expose a conductor (1910) of a third metal layer.

A method of removing non-metallic material overlying metal layers of an integrated circuit specimen to expose selected areas of the metal layers, comprising the steps of:

• a. scanning a focused ion beam over a surface of an integrated circuit specimen to remove non-metallic material until a first area (1902) of at least one of the metal layers is exposed;
• b. preparing an image of the surface having a first image portion (1922) representing non-metallic material and a second image portion (1920) representing the exposed first area of at least one of the metal layers;
• c. scanning the focused ion beam over the surface while controlling the focused particle beam to selectively mill the area of non-metallic material represented in the first image portion and to minimize milling of the exposed first area of at least one of the metal layers, until a second area (1904, 1908) of the metal layers is exposed;
• and
• d. preparing an updated image of the surface having a first image portion (1932) representing non-metallic material and second image portions (1930) representing the exposed first area (1902) and the exposed second area (1904, 1908) of the metal layers.