Method for observing cross-sectional structure of sample

#The present invention relates to a method for observing the cross-sectional shape of a sample surface using a focussed ion beam apparatus, and more particularly relates to cross-sectional processing applied to observing grooves occurring with semiconductor elements and thin-film magnetic heads, etc.

#Focussed ion beam apparatus are capable of processing and microscopically observing materials and in recent years have often been used in the processing and observation of the cross-section of samples, down to cross-sectional sizes for the most part from a few μm to a few tens of μm. In a basic procedure shown in FIG. 3A, first, locations of the sample which it is wished to subject to cross-sectional observation are specified (portions surrounded by a dashed line). However, it is necessary to open up the exposed part of the cross-section towards the front in order to monitor the cross-section. It is necessary to perform beam scanning from a severe angle with respect to the cross-section in order to obtain a microscopic image of the cross-section. When the processing regions are specified, the surface of the sample is subjected to rough processing using an ion beam from a vertical direction as shown in FIG. 3B. This processing is to open up a hole required for observation by causing the cross-section to be monitored to be exposed and therefore employs a large current beam to perform rough etching. This means that damage is incurred by the cross-section to be observed, as shown in FIG. 3B. When the hole-opening process finishes, polishing of the cross-section to be observed is carried out by etching with the beam current lowered, so as to expose the clean cross-section shown in FIG. 3C. A supporting table is then tilted and beam scanning is performed by irradiation with an ion beam from a severe angle with respect to the cross-section, and a scanning ion microscope image is obtained for the cross-section it is wished to observe.

#However, an operation is carried out in advance to form a protective film on the material surface in order to prevent damage by the focused ion beam during processing. This operation is referred to as deposition. Typically, a protective layer is formed by spraying W(CO)6 or phenanthrene etc. onto the processing portions from a gas gun. However, when the material for the protective layer is the same as the material of the substance for the surface of the sample, a boundary of the original sample surface and the protective layer cannot be distinguished in an observed microscopic image. In particular, when the cross-sectional image to be observed is the surface shape of a groove, large amounts of protective film material are deposited at the groove so that the groove becomes buried and the original groove shape cannot be distinguished in a microscopic image.

#FIG. 1A is a view illustrating a procedure for processing a cross-section to be observed and a method of taking an observed microscopic image.

#FIG. 1B is a view illustrating a procedure for processing a cross-section to be observed and a method of taking an observed microscopic image.

#FIG. 1C is a view illustrating a procedure for processing a cross-section to be observed and a method of taking an observed microscopic image.

#A characteristic of the present invention is that a covering layer of material different to the material of the sample surface is formed at the sample surface prior to forming a protective layer at a processing portion of the sample.

#Theoretically speaking, a covering layer of a material different to the substance forming the sample surface is formed at the surface of the sample which is as yet un-processed, with it being preferable for the sample to be left in a state that enables identification after cross-sectional processing. However, in this embodiment a method is selected where an appropriate material is affixed by sputtering or vapor deposition, with irradiation of an ion beam then taking place using a gas gun.

#Further, this operation is carried out using a focused ion beam apparatus. It is therefore also possible to form a covering layer in a straightforward manner by opening a hole by irradiating an appropriate region of the sample isolated from the cross-section of the sample to be monitored using irradiation with a focused ion beam, and spraying on a substance different to the surface material such as a metallic material such as iron or nickel other than carbon when, for example, the surface is a resist, so as to cause reattachment to the sample surface.