Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2002-01-04
2004-03-02
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S310000, C250S492200, C324S071300, C324S765010
Reexamination Certificate
active
06700122
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a wafer inspection technique using a charged particle beam and, more particularly, to an inspection technique using a charged particle beam such as an electron beam for detecting a foreign matter or a defect on a wafer such as a semiconductor wafer having a fine circuit pattern.
As a method of evaluating a semiconductor waver having a fine circuit pattern with an electron beam, a technique of conducting a higher-precision inspection of higher throughput adapted to the larger diameter of a wafer and a finer circuit pattern is being practically used. For example, as disclosed in Japanese Patent Application Laid-Open No. H06-139985, a method of conducting an inspection for a defect by using contrast of a secondary electron beam generated due to surface potential variations is known.
In a method of detecting an electric defect from voltage contrast, an electron beam is emitted before an inspection to preliminarily positively or negatively charge the surface of a wafer, and a secondary electron image is acquired, thereby enabling voltage contrast to be increased. An example of a method of positively charging the surface of a wafer is disclosed in Japanese Patent Application Laid-Open No. 2000-208085, where a pattern such as a contact hole in which a plug is buried is inspected by irradiating the surface of a wafer with an electron beam to positively charge the surface and, after that, voltage contrast is obtained.
Although the method of conducting an inspection on a circuit in which a plug is buried is described in the above publications, a method of conducting an inspection on the bottom of a pattern having very a large step such as a hole after dry etching is not described.
On the other hand, a technique of observing the bottom of a hole pattern from an image of secondary electrons discharged when the hole pattern is irradiated with an electron beam is known. By conventional scanning electron microscopes, however, it takes time to observe an object in a limited field of view at a high scaling factor. It is therefore impossible to observe the entire surface of a wafer and detect a defect.
An example of an inspection method of negatively charging the surface of a wafer and detecting a contact hole with an open contact failure is disclosed in the above-described Japanese Patent Application Laid-open No. H06-139985 in which the surface of a wafer is negatively charged by being irradiated with an electron beam with low energy and, after that, a secondary electron image is obtained. In the method, by using the fact that when a residual film exists on the bottom of a hole, the potential of the opening is changed by the residual film, and the diameter of the hole becomes seemingly small, a hole with an open contact failure is detected.
According to the method, however, an object in a limited field of view is observed at a high scaling factor over long time, and it is impossible to observe the entire surface of a wafer to detect a defect. Since an electron beam is preliminarily emitted to negatively charge the surface of a wafer and, after that, a secondary electron image is captured and further, since irradiation electron energy used to negatively charge the surface of a wafer and that used to acquire a secondary electron image are largely different from each other, it is difficult to set an electron beam optics unit and an inspection cannot be efficiently conducted on the entire surface of a wafer. Since the wafer has to be irradiated with an electron beam twice or more, the whole surface of a wafer cannot be efficiently inspected.
A conventional inspection system using an electron beam has problems as described below.
In a conventional inspection system using an electron beam, a defect is detected from contrast obtained due to potential variations which occur on a wafer having a circuit pattern. However, it is difficult to detect the state of the bottom of a pattern having a large step, such as a contact hole with an open contact failure, with high sensitivity by detecting a secondary electron signal from the bottom portion of the pattern. Particularly, most of secondary electrons from the bottom of a hole pattern having a high aspect ratio are hindered by side walls and cannot be detected. It is therefore difficult to detect a hole pattern with an open contact failure.
By a conventional scanning electron microscope, although the shape of the bottom of a hole pattern and a foreign matter can be detected, it is difficult to detect, for example, a hole having an open contact failure. By the conventional scanning electron microscope, observation is made at high a scaling factor with high spatial resolution. Consequently, scan speed is low, the scan range is narrow, and it is impossible to scan a large area such as a wafer required for a defect detector at high speed.
In the method of negatively charging the surface of a wafer and detecting a contact hole with an open contact failure, the electron beam accelerated to low speed is emitted to negatively charge the surface of the wafer and, after that, a secondary electron image is captured. However, in the method, due to a large difference between the energy of the electron beam emitted to negatively charge the surface of the wafer and that of the electron beam emitted to obtain a secondary electron image, it is difficult to emit the electron beams by using the same electron source. Further, the electron beam is emitted once to negatively charge the surface of the wafer and, after that, the secondary electron image is observed at a high scaling factor with high spatial resolution. Consequently, the scan speed is low, the scan range is narrow, and it is impossible to scan a large area such as a wafer at high speed required for the defect detector. Thus, the entire surface of a wafer cannot be efficiently inspected.
Further, in the conventional apparatuses, the surface of a wafer is negatively charged and the opening is evaluated. Consequently, according to the kind and material of a semiconductor circuit pattern, the kind of a semiconductor device which can be evaluated is limited. There is a problem such that sensitivity of detection of a hole with a contact hole failure varies according to the kind of a circuit pattern.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide, as a technique solving the problems, of conducting an inspection of a wafer being subjected to a semiconductor manufacturing process, a wafer inspection system and a wafer inspection process for inspecting a pattern having a large step such as a hole pattern for a defect at high speed and with high precision. Another object of the invention is to provide a technique contributing optimization of a semiconductor manufacturing process by using defect information such as an open contact failure of a hole. Further another object of the invention is to provide a technique contributing to increase reliability of a semiconductor device by detecting an abnormal process at an early stage and taking a measure in the control of a semiconductor manufacturing process.
First, the method of carrying out an inspection by positively charging the surface of a wafer will be described. The principle of the invention in which a secondary electron emitted from the bottom of a hole is detected will be described by referring to
FIGS. 2A and 2B
.
An image of a hole pattern is captured by a conventional inspection system using an electron beam. For example, when the irradiation energy of the electron beam is 500 eV (electron volts) and the aspect ratio is 4 or less, secondary electrons
34
exhausted from the bottom of a hole are easily detected. An open hole is observed light and a hole with an open contact failure is observed dark. However, when the aspect ratio is high, as shown in
FIG. 2A
, most of the secondary electrons
34
from the bottom of the hole are interrupted by side walls
35
. Consequently, the open hole is also observed dark, so that a hole with an open contact failure cannot be detected.
To
Matsui Miyako
Nozoe Mari
Takafuji Atsuko
Lee John R.
Leybourne James J.
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