Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2000-11-30
2002-09-17
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C382S145000, C382S149000, C382S151000
Reexamination Certificate
active
06451492
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P11-345466 filed Dec. 3, 1999, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
The present invention relates to an inspection apparatus and an inspection method suitable for inspecting the state of a resist pattern formed on a semiconductor wafer in a lithography step in semiconductor process.
In recent years, the integration rate of semiconductor integrated circuit has been improved as digitalization has been developed in the electric industrial field. How this highly integrated semiconductor circuit can be efficiently supplied at low costs is a significant problem that will decide future progress in the digital electronic industrial field.
To produce efficiently semiconductor integrated circuits at low costs, it is important to detect rapidly and correctly problems which occur during the manufacturing process. Therefore, there is a greater demand for an inspection apparatus capable of inspecting a micro pattern.
Known as inspection apparatuses having a high resolution are those using a scanning electron microscope (SEM), an atomic force microscope (AFM), and the like. However, these scanning electron microscopes and atomic force microscopes require vacuum in inspection, and are therefore inconvenient for handling. In addition, it takes much time to inspection entirely a semiconductor device.
In contrast, an inspection apparatus using an optical microscope is advantageous in that inspection can be carried out undestructively without necessitating vacuum or contact. In recent years, developments have been made in a ultraviolet solid laser apparatus which performs wave-conversion on a YAG laser or the like with use of non-linear optical crystal thereby to emit laser light having a wavelength of a ultraviolet range. If this ultraviolet solid laser apparatus is used as an illumination light source and if an optical system is constructed by using an objective lens having a high NA, even an optical microscope can attain a resolution close to that of a scanning electronic microscope. Hence, expectation is much devoted to the optical microscope.
Meanwhile, it is desired that inspection of a pattern of a semiconductor integrated circuit should be carried out with a resist pattern formed on a semiconductor wafer. This resist pattern is formed in a manner that resist material coated on a semiconductor wafer is exposed by an exposure apparatus and developed, in accordance with a pattern to be formed.
Suppose a case that a resist pattern as described above is inspected by an inspection apparatus which inspects an inspection target by picking up an image of the inspection target by an image pickup element such as a CCD (charge-coupled device) camera or the like, with an ultraviolet solid laser apparatus used as an illumination light source. In this case, the wavelength of illumination light is close to the wavelength of a light source of an exposure apparatus. Therefore, the resist pattern to be detected may contract in response to the illumination light if the irradiation light amount of the illumination light is large. Although an anti-reflection film is normally provided in the vicinity of the resist pattern in order to prevent abnormal exposure due to reflection during exposure, the absorption rate of this anti-reflection film changes thereby influencing harmfully the inspection of the resist pattern, if the irradiation light amount of the illumination light is large.
On the other side, if the irradiation light amount of the illumination light is too small when a resist pattern is inspected by the above-described inspection apparatus, the noise component of the image pickup element is large relatively to the obtained signal component, so that the resist pattern cannot be inspected with good accuracy in some cases.
Consequently, it is important to control the irradiation light amount of the illumination light to a proper value, in order to inspect the resist pattern by the above-described inspection apparatus.
BRIEF SUMMARY OF THE INVENTION
The present invention has been proposed in view of the situation described above and has an object of providing an inspection apparatus and an inspection method capable of inspect a resist pattern accurately and properly by irradiating illumination light at a proper irradiation light amount on a resist pattern to be inspected.
An inspection apparatus according to the present invention comprises: illumination means for irradiating a resist pattern as an inspection target with illumination light having a wavelength of 355 nm or less within an ultraviolet range; image pickup means for picking up an image of the resist pattern illuminated by the illumination means; an imaging optical system for forming an image of the resist pattern illuminated by the illumination means; and image processing means for processing the image of the resist pattern picked up by the image pickup means.
In this inspection apparatus, the imaging magnification of the imaging optical system is set such that the image resolution of the image pickup means falls in a range from 10 nm to 30 nm on the resist pattern. The “image resolution” means a value expressing how large area on the resist pattern as an inspection target one minimum image pickup unit (one pixel) of the image pickup means corresponds to. In this inspection apparatus, the imaging magnification is set such that the image resolution of the image pickup means falls in a range from 10 nm to 30 nm.
Also, in this inspection apparatus, the illumination means irradiates the resist pattern with the illumination light at an irradiation light amount within a range from 0.5 mJ/cm
2
to an irradiation threshold value at which the resist pattern is not caused to contract or an irradiation threshold value at which an absorption rate of an anti-reflection film provided near the resist pattern is not caused to change, every time when the image pickup means picks up an image.
According to this inspection apparatus, a resist pattern as an inspection target is illuminated with illumination light having a wavelength of 355 nm within an ultraviolet range. Further, an image of the resist pattern illuminated with the illumination light having a wavelength within the ultraviolet range is guided to and formed by the image pickup means. At this time, the image resolution of the image pickup means corresponds to an area ranging from 10 nm to 30 nm.
The image of the resist pattern picked up by the image pickup means is taken in and processed by the image processing means. The image of the resist pattern thus processed by the image processing means is an image of the resist pattern illuminated with the illumination light having a wavelength within an ultraviolet range, which is light having a very short wavelength. Therefore, the state of the resist pattern can be inspected very accurately by analyzing the image of the resist pattern processed by the image processing means.
Also, in the inspection apparatus according to the present invention, the illumination means irradiates illumination light on the resist pattern at an irradiation light amount within the range described above, every time when the image pickup means picks up one image. Therefore, the noise component of the image pickup element can be reduced relatively to the signal component, so that the inspection accuracy can be improved. In addition, contraction of the resist pattern and change of characteristics of the anti-reflection film can be prevented effectively so that inspection of the resist pattern can be carried out properly.
That is, if the resist pattern is not irradiated with an irradiation light amount equal to or higher than 0.5 mJ/cm
2
every time when the image pickup means picks up an image, the ratio of the noise component to the signal component becomes too high to inspect accurately the resist pattern, in an inspection apparatus in which the image resolution of the image pickup means on the resist pattern is set
Imai Yutaka
Taguchi Ayumu
Tamada Hitoshi
Wada Hiroyuki
Sonnenschein Nath & Rosenthal
Young Christopher G.
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