Patent Application
20120242985
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-068507, filed on Mar. 25, 2011, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a pattern inspection apparatus and a pattern inspection method.
In the fields of semiconductor devices, flat panel displays, MEMS (micro electro mechanical systems) and others, a structure having a fine pattern formed on a surface thereof (which will be referred to as a “fine structure” hereinafter) is manufactured using a lithography technology or another.
For Inspection of such a fine structure, an optical inspection apparatus is used. Heretofore, in the optical inspection apparatus, a defect inspection is carried out by fixing a focus plane onto the surface of the pattern with the aid of an autofocus function, scanning the surface of a substrate such as a wafer with light in a horizontal direction to form an image of reflected light from the wafer surface onto a detector, and evaluating an obtained pattern image, or detecting a difference in reflectance between a defect-free position and a defective position.
In recent years, however, with the progress of miniaturization or high integration in the fine structure, a pattern having a high aspect ratio is formed. For example, in the case of a trench pattern having a high aspect ratio, defects may be possibly produced at various positions in a depth direction, and when a focus plane is fixed on the surface of the pattern, a focus does not match with a defect, and hence there is a problem that it is hard to obtain reflected light which reflects an accurate shape from a wafer surface.
In accordance with an embodiment, a pattern inspection apparatus includes a stage, a stage drive unit, a light source, a detection unit, an optical system, a focus position change unit, a control unit, and a determination unit. The stage is configured to support a substrate with a pattern thereon as an inspection target. The stage drive unit is configured to move the stage in a direction horizontal to the surface of the substrate. The light source is configured to Irradiate the substrate with light. The detection unit is configured to detect reflected light from the substrate irradiated with the light and output a signal. The optical system is configured to lead the light emitted from the light source to the substrate and lead the reflected light from the substrate to the detection unit. The focus position change unit is configured to change a focus position of the light to the substrate in a direction vertical to the surface of the substrate. The control unit is configured to associate the movement of the stage with the light irradiation to the pattern and control the stage drive unit and the focus position change unit in a manner that the focus position changes. The determination unit is configured to determine presence/absence of a defect of the pattern based on the signal from the determination unit.
Embodiments will now be explained with reference to the accompanying drawings. It is to be noted that like reference numerals denote like constituent elements in the respective drawings to appropriately omit repeated description.
First of all, a comparative example examined by the present inventor in a process for developing the present invention will be described.
In a pattern inspection apparatus 400 according to the comparative example depicted in
Furthermore, when the wafer stage 300 on which the wafer W is placed is moved in a direction horizontal to the wafer surface in a state that the focal position is fixed, the wafer W is scanned with the light L100 in the direction horizontal to the wafer surface. Light L200 reflected from the wafer by the emission of the light L100 is transmitted through the half mirror HM to form an image on a detection plane of the detector 200, and an image of the pattern as the inspection target is formed from the resultant signal. On the basis of this image, presence/absence of defects is determined.
However, in recent years, with the further progress of miniaturization or high integration of fine structures, an aspect ratio of the pattern which is the inspection target is heightened.
In the example of
In such a trench pattern having a high aspect ratio, defects at different depths may be possibly formed, as indicated by reference characters DF1 and DF2 in
When performing a defect inspection for such an inspection target pattern by use of the pattern inspection apparatus 400 depicted in
Again referring to
In a pattern inspection apparatus 1 depicted in
The objective lens 22 is formed of an electric-optical (EO) element that electrically changes a refractive index, and it changes a focus position of the light L1 according to a control signal supplied from the control unit 30. A piezo element 24 is provided on the column 20 to vibrate the column 20 in a direction vertical to the surface of the wafer W according to the control signal supplied from the control unit 30. In this embodiment, the control unit 30 and at least one of the objective lens 22 and the piezo element 24 correspond to, e.g., a focus position varying unit.
A single layer film or a laminated layer film 500 is formed on the wafer W, and in the single layer film or the laminated layer film 500, trench patterns TR as inspection targets are formed. The wafer W corresponds to, e.g., a substrate in this embodiment.
Light L is reflected on the wafer W, and reflected light L2 enters the column 20. In the column 20, the reflected light L2 is led to the detector 60 through the half mirror HM to form an optical image on a detection plane of the detector 60.
The wafer W is placed on the stage 40, and the stage 40 moves the wafer W in a direction horizontal to a wafer plane according to a control signal supplied from the stage controller 50. As a result, the wafer W Is scanned with the light L1 in the direction horizontal to the wafer plane. The stage controller 50 generates a control signal, which is used for driving the stage 40, according to an instruction signal from the control unit 30. The stage 40, the stage controller 50, and the control unit 30 correspond to, e.g., a stage drive unit in this embodiment.
The detector 60 photoelectrically converts the light L2 that forms image on the detection plane thereof and outputs a detection signal. The detector 60 is constituted of, e.g., an infrared charge coupled device (CCD) or a photo-multiplier. However, the detector 60 is not restricted thereto, and it is possible to appropriately select any detector that can photoelectrically convert the light for image formation.
The signal processing unit 70 processes the detection signal supplied from the detector 60 to generate an image on the surface of the single layer film or the laminated film 500 including the trench patterns TR. The defect determination unit 80 processes the image supplied from the signal processing unit 70 to determine presence/absence of defects and others in the trench patterns TR based on, e.g., a die-to-die comparison or a cell-to-cell comparison. In this embodiment, the defect determination unit 80 corresponds to, e.g., a determination unit.
The memory MR stores a recipe file in which an inspection algorithm for executing a later-described defect inspection method is written, and it also stores a design database of the trench patterns TR as the inspection target including three-dimensional positional information.
The control unit 30 reads the recipe file from the memory MR, generates the above-described various kinds of control signals according to the written inspection algorithm, and supplies the generated control signals to the stage controller 50, the objective lens 22, and the piezo element 24 of the column 20.
Next, description will be given as to an example of a method of performing a defect inspection by use of the pattern inspection apparatus depicted in
First, a non-illustrated alignment pattern or the like is used to associate an X-Y coordination system of the stage 40 with pattern positional information in the design database stored in the memory MR.
Next, the control unit 30 generates the control signal while irradiating the wafer W with the light L1 from the light source 10, and the stage 40 is moved so that the trench patterns TR in an inspection target region can be sequentially scanned with the light L1 by the stage controller 50. Furthermore, when the light L1 is placed immediately above the trench pattern TR, the control unit 30 generates the control signal and supplies it to the objective lens 22 or the piezo element 24, whereby a focus position of the light L1 changes in a direction vertical to the surface of the wafer W.
Moreover, the light L1 is condensed by the objective lens 22 at each focus position so that the light L1 can be applied to the wafer W and reflected thereon, so that optical images at different depths in the trench patterns TR are formed on the detection plane of the detector 60. Then, the signal processing unit 70 generates a plurality of pattern images regarding the same trench pattern TR, and the defect determination unit 80 determines presence/absence of defects.
An example of a method of determining the defects based on the die-to-die comparison will be explained with reference to
For example, a comparison will now be made between a die having a defect DF in which etching has been performed only to a depth D2 in a trench pattern TR3 due to an influence of, e.g. an impurity as a die 80 shown on the left side of
When a focus position is changed so that just focusing can be achieved at each position of, e.g., depths D1, D2 and D3 at timing that irradiation light reaches a position of each trench pattern by the movement of the stage 40, three pattern images can be obtained for each trench pattern, and eventually six pattern Images can be obtained from the die 80 and the die 90.
In the example of
Additionally, when a pattern image 801 obtained from the trench pattern TR3 at the depth D1 is compared with a pattern image 901 obtained from the trench pattern TR13 at the depth D1, both the pattern images are defocus images, but between these images, a difference is scarcely present, and a defect cannot be detected.
However, comparing a pattern image 802 obtained from the trench pattern TR3 at the depth D2 with a pattern image 902 obtained from the trench pattern TR13 at the depth D2, although the pattern image 902 is a defocus image, line patterns vertically extending in the image are shorted to each other at a middle point in the pattern image 802 and, on the other hand, such a short is not present in the pattern image 902. Therefore, it is determined that a defect DF3 is present in the trench pattern TR3 of the die 80.
Additionally, comparing a pattern image 803 obtained from the trench pattern TR3 at the depth D3 with a pattern image 903 obtained from the trench pattern TR13 at the depth D3, the pattern image 803 is a defocus image but is considerably different from the pattern image 903, and it is determined that the defect DF3 is present after all. In this embodiment, the pattern images 801 to 803 correspond to, e.g., a first image, respectively, and the pattern images 901 to 903 correspond to, e.g., a second image, respectively.
It is to be noted that reference has been made to the defect-free die 90 in the above determination but, if presence of a defect is unclear in the die 90, the defect determination is carried out based on double comparisons including a comparison with another die like a general die-to-die comparison.
As described above, in accordance with this embodiment, since the focus position is changed in not only the direction horizontal to the surface of a substrate but also a direction vertical to the same to scan an inspection target pattern, a defect which is present in the pattern of a high aspect ratio can be detected with high sensitivity.
Although the embodiment has been described, the present invention is not restricted thereto, and it can be modified in many ways and applied within its technical scope as a matter of course.
For example, the three pattern images are obtained with respect to each trench pattern in the foregoing embodiment, but a different quantity of pattern images may be obtained and compared with each other as long as the quantity is above one.
Further, although the description has been given as to the example where the pattern image is obtained from the detection signal of the detector 60 and presence/absence of a defect is determined based on the obtained pattern image in the foregoing embodiment, but the presence/absence of a defect can be likewise determined by comparing, e.g., intensity levels of the detection signals without obtaining the pattern image.
In this case, for example, the detection signal from the detector 60 is directly supplied to the defect determination unit 80 without using the signal processing unit 70 in the constituent elements of the pattern inspection apparatus 1 in
In a pattern inspection in which a pattern of a thin film is an inspection target, interference of light caused due to film thickness unevenness of the thin film results in noise. To avoid such a situation, it is desirable for a light source of the pattern inspection apparatus to have a wavelength width that can cancel the film thickness unevenness. More specifically, a light source having a wavelength width of ±several nm or above is desirable and, for example, a Ti:sapphire triple harmonic femto(10-15)second-order pulse laser having a wavelength of 260 nm±40 nm or below can be used to realize this light source.
Moreover, a broadband light source constituted by coupling a plurality of lasers of different wavelengths with each other can be used in place of the pulse laser equipment.
A basic light source unit 620 depicted in
The deep ultraviolet light output from the SHG element 624b has a wavelength width of approximately 266 nm±10 pm since a relationship between the wavelength and the wavelength width is as follows:
Δλ=Δλ266 nm×(λ266 nm×/λ1064 nm)2
A broadband light source 600 depicted in
Furthermore, a broadband light source 700 shown in
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-068507 | Mar 2011 | JP | national |
