Convergent charged particle beam apparatus and inspection method using same

#The present invention relates to a convergent charged particle beam apparatus using a charged particle beam such as an electron beam or ion beam for microstructure fabrication or observation and an inspection method using the same, and more particularly to an automatic focusing system and arrangement in the convergent charged particle beam apparatus.

#As an example of an apparatus using a charged particle beam, there is an automatic inspection system intended for inspecting and measuring a microcircuit pattern formed on a substrate such as a semiconductor wafer. In defect inspection of a microcircuit pattern formed on a semiconductor wafer or the like, the microcircuit pattern under test is compared with a verified non-defective pattern or any corresponding pattern on the wafer under inspection. A variety of optical micrograph imaging instruments have been put to practical use for this purpose, and also electron micrograph imaging has found progressive applications to defect inspection by pattern image comparison. In a scanning electron microscope instrument which is specifically designed for critical-dimension measurement of line widths and hole diameters on microcircuit patterns used for setting and monitoring process conditions of semiconductor device fabrication equipment, automatic critical-dimension measurement is implemented through use of image processing.

#In comparison inspection where electron beam images of corresponding microcircuit patterns are compared for detecting a possible defect or in critical-dimension measurement where electron beam images are processed for measuring such dimensions as pattern line widths, reliability of results of inspection or measurement largely depends on the quality of electron beam images. Deterioration in electron beam image quality occurs due to image distortion caused by deflection or aberration in electron optics, decreased resolution caused by defocusing, etc., resulting in degradation of performance in comparison inspection or critical-dimension measurement.

#FIGS. 1(a)-1(d) show inspection of a wafer at different regions and electron beam images of the different regions;

#FIG. 2 is a schematic sectional view showing an exemplary structure of an automatic inspection system according to the present invention;

#FIG. 3 is a schematic sectional view of a height detection optical system for illustrating a principle of height detection;

#Referring now to the accompanying drawings wherein like reference numerals are utilized to designate like parts throughout the views, there is shown in FIG. 2 an overview of an automatic semiconductor device inspection system using electron beam images as an exemplary preferred embodiment of the present invention. In an electron optical system shown in FIG. 2, an electron beam emitted from an electron gun 1 is converged through an objective lens 2, and the electron beam thus converged can be scanned over a surface of a specimen in an arbitrary sequence. A signal of secondary electrons 4 produced on a surface of a specimen wafer 3 in irradiation with the electron beam is detected by a secondary electron detector 5, and then the secondary electron signal is fed to an image input part 6 as an image signal.

#The specimen wafer under inspection can be moved by an X-Y stage 7 and a Z stage 8. By moving each stage, an arbitrary point on the surface of the specimen wafer is observable through the electron optical system. Electron beam irradiation and image input can be performed in synchronization with stage movement, which is controlled under direction of a control computer 10. A height detector 11 is of an optical non-contact type which does not cause interference with the electron optical system, and it can speedily detect a height of the specimen surface at or around an observation position in the electron optical system by a height calculator 11a. Resultant data of height detection is input to the control computer 10.

#According to the height of the specimen surface, the control computer 10 adjusts a focal point of the electron optical system, i.e., a position of the Z stage, and it receives input of the image signal. Using the image signal input in a focused state and inspection position data detected by a position monitoring measurement device, defect judgment is carried out through comparison with a pattern pre-stored by an image processing circuit 9, a corresponding pattern at a location on the specimen wafer under inspection, or a corresponding pattern on a different wafer with a defect being detected by defect detector 100. While the automatic semiconductor device inspection system using secondary electron images is exemplified in FIG. 2, back scattered electron images or transmitted electron images may also be used for specimen surface observation instead of secondary electron images.