Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2002-06-12
2004-06-22
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S311000, C250S548000, C250S566000, C250S576000, C324S754120, C324S754120, C356S394000, C356S237100, C356S237500
Reexamination Certificate
active
06753524
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to technology for inspecting a wafer with a circuit using a charged-particle beam such as an electron beam and more particularly to technology for detecting foreign bodies and defects on the substrates of wafers with minute circuit patterns.
2. Description of Related Art
With the ever heightening integration of integrated circuits, the number of wiring layers of each integrated circuit is increasing and its wiring pattern is becoming more complex. At the same time, the dielectric constants of materials of insulators are being reduced and the materials of insulators are being diversified. Hoped for under the circumstances is technology for inspecting integrated circuits for electric defects speedily, stably in their manufacturing processes. It is necessary for the production of system LSI's and the like to develop many circuit-forming processes in a short time period, which requires technology for inspecting many kinds of circuits. Available at present is technology to detect electric defects of wafers in their manufacturing processes by applying a charged-particle beam to each inspection area on the surface of a wafer and finding defects by, or based on, their distinctive contrasts in a secondary-electron image of the inspection area, the distinctive contrasts caused by the changed electric potential of the defects.
Japanese Patent Laid-Open No. 121561/1999 discloses a process for detecting discontinuity of contact holes containing transistors such as CMOS's. According to the method, contact holes opened on n-type diffusion layers are inspected by electrifying the surface of the wafer negatively and contact holes opened on p-type diffusion layers are inspected by electrifying the surface of the wafer positively. When contact holes opened on n-type diffusion layers are inspected, the surfaces of non-defective contact holes are not electrified negatively, but the surfaces of defective ones are electrified negatively; accordingly, defective contact holes can be distinguished from non-defective ones based on their differential contrasts in a secondary-electron image of the inspection area. When contact holes opened on p-type diffusion layers are inspected, the surfaces of non-defective contact holes are not electrified positively, but the surfaces of defective ones are electrified positively; accordingly, the defective contact holes can be distinguished from the non-defective ones based on their differential contrasts in a secondary-electron image of the inspection area. Japanese Patent Laid-Open No. 87451/1999 discloses an inspection method. According to the method, while a charged-particle beam is applied to a wafer to feed it with an electric charge, a laser beam is applied to the wafer to generate carriers at p-n junctions. The currents induced by the laser beam are taken out from the substrate and measured to detect defective contacts. Thus, this method makes possible non-contact supply of currents at any spots; accordingly, it is unnecessary to form pads for electrodes on integrated circuits and integrated circuits can be inspected and analyzed with OBIC in their manufacturing processes.
Conventional methods of inspecting integrated circuits by using an electron beam have the following problems. To detect the discontinuity of a circuit pattern including contacts with various types of junctions such as CMOS's, it is necessary to electrify the surface of each wafer positively for inspection and then electrify the surface of the wafer negatively for inspection; i.e., each wafer requires inspection twice. When the surface of a wafer shown in
FIG. 2
, for example, is electrified negatively for inspection, contact holes
38
opened on n-type diffusion layers
40
are electrified negatively, whereas non-defective contact holes
38
opened on the n-type diffusion layers
40
are not. When the surface of the wafer is electrified positively for inspection, defective contact holes
39
opened on p-type diffusion layers
41
are electrified positively, whereas non-defective contact holes
39
opened on the p-type diffusion layers
41
are not. In this way, each wafer, having a number of inspection areas, has to be inspected by electrifying it positively and negatively alternately. Thus, such inspection takes a considerable time, such electrification is liable to be uneven, and the sensitivity of such inspection is liable to be low. If the resistance of junctions of, for example, n-type diffusion layers of the wafer of
FIG. 2
is uneven, the contact holes
38
opened on the n-type diffusion layers are electrified unevenly when the surface of the wafer is electrified positively; accordingly, some non-defective contact holes may be detected as defective based on their differential contrasts in a secondary-electron image.
In the case of the process for inspecting wafers by applying a laser beam and a charged-particle beam simultaneously and measuring the currents of the substrate, the laser beam produces electron-hole pairs, generating noises in the currents of the substrate; accordingly, it is difficult to detect differences in the faint OBIC currents. Besides, in the case of the process for measuring the currents of the substrate by applying a laser beam to generate carriers, the spatial resolution of inspection is limited by that of the laser beam applied; accordingly, it is difficult to inspect minute circuit patterns. Moreover, because dope layers are usually formed below p-n junctions under contacts, OBIC currents are influenced by the junctions between the dope layers and, hence, the sensitivity of inspection is liable to be low. Furthermore, if the circuit patterns and the Si substrate of an integrated circuit are insulated from each other by an insulator, the integrated circuit cannot be inspected by the inspection process.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a process for controlling the electrification of (i) the surfaces of wafers with various circuit patterns and (ii) the circuit patterns speedily, stably and inspecting the wafers for defects speedily, accurately. It is another object of the invention to provide technology for contributing toward the optimization of the manufacturing processes of integrated circuits based on data on their defects. It is yet another object of the invention to provide technology for contributing toward improving the reliability of integrated circuits by founding trouble early in their manufacturing processes and taking measures.
First of all, a process for inspecting circuit patterns including contacts with various types of junctions such as CMOS's for defects of discontinuity will be described. According to conventional methods, each wafer with a circuit is electrified positively and negatively alternately for inspection, taking a considerable time, uneven electrification being liable to occur, the sensitivity of inspection being liable to be low. In order to solve such problems, this invention provides a means for (i) capturing a secondary-electron image of an inspection area of a wafer by applying an optical beam to the front surface of a wafer while an electron beam is being applied to the front surface and (ii) thereby reducing the influence of junctions upon the contrasts of objects being inspected in the image. With this means, a wafer can be inspected by a single inspection. An optical beam to be applied to wafers for inspection is of wavelength such that the optical beam penetrates the insulators of circuit patterns, but does not penetrate junctions of silicon. If insulators formed on circuit patterns are of SiO
2
and Si
3
N
4
, an optical beam of wavelength of 200 nm or longer is used. The optical beam penetrates SiO
2
and Si
3
N
4
on the circuit patterns and is absorbed by the Si substrate to produce electron-hole pairs. Because the optical beam does not penetrates plugs on junctions, a means is provided for applying an optical beam at a slight angle from each stra
Matsui Miyako
Nozoe Mari
A. Marquez, Esq. Juan Carlos
Fisher Esq. Stanley P.
Hashmi Zia R.
Hitachi , Ltd.
Lee John R.
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