JPH102863A - Foreign matter detecting method for ic mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foreign matter detecting method having higher detection precision of foreign matters stuck to an IC mask than a conventional method. SOLUTION: Laser beam LT is vertically radiated to an IC mask 1, reflected light RL by he pattern PT, a glass substrate 11, and stuck foreign matters i is focused into an image by a first CCD camera 45a installed in the vertical direction, and the transmitted light TL transmitted through the glass substrate 11 is focused into an image by a second CCD camera 45b. Respective foreign matters i are detected by processing the image signals SR of the first CCD camera 45a and the image signals ST of the second CCD camera 45b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for detecting foreign matter adhering to an IC mask.

[0002]

2. Description of the Related Art In the manufacture of IC devices, a mask (IC mask) on which an IC pattern is formed is superposed on a wafer and exposed, and this pattern is transferred to the wafer. If foreign matter adheres to the IC mask, the foreign matter is transferred to all IC devices and the quality is deteriorated or deteriorated. Therefore, the foreign matter is strictly forbidden. Has been tested for

FIG. 3 is a plan view and a cross-sectional view illustrating a part of the pattern PT formed on the IC mask 1 and the attached foreign matter i. The IC mask 1 is formed on the surface of the glass substrate 11 in a vertical and horizontal direction, and a fine pattern PT made of chromium is used.
Are formed by etching, and there are edges Eg inclined at an angle on both sides of the pattern PT. Foreign matter i
Is attached to an arbitrary place. In the example of the figure, the foreign matter i ₁ is attached to the surface of the pattern PT, and the foreign matter i ₂ is attached to the surface of the glass substrate 11 having no pattern PT.

FIG. 4 shows a schematic structure of a main part of a conventional foreign matter inspection apparatus, which comprises a detection optical system 2 and a foreign matter detection section 3. A foreign matter detection method based on the detection optical system 2 will be described below. The IC mask 1 surface to be inspected, from the laser light source 21 of the detection optical system 2, in an oblique direction, by projecting the laser beam L _T by the projection angle theta _T of example 45 °, substantially symmetrical light thereto the CCD camera 22 is provided in the direction of the angle theta _R, the laser beam reflected light R _L of the projection range of L _T, and received by the imaging lens 221 of the CCD camera 22, pattern PT and the CCD image sensor 222 an image of the foreign matter i Image. The image signal S _R of the image sensor 222 is subjected to processing such as noise removal by the signal processing circuit 31 of the foreign substance detection unit 3 and is input to the foreign substance detection circuit 32. There are various foreign substance detection methods of the foreign substance detection circuit 32,
For example, in the case of the comparison method, data of a normal pattern PT ′ having no foreign matter is set in the foreign matter detection circuit 32 in advance,
By comparing the the pattern PT of the video signal S _R which, whether foreign matter i has been detected with the quality of the pattern PT.

[0005] In order to detect the foreign matter i satisfactorily, it is necessary to clearly form an image of the foreign matter i on the CCD image sensor 222 and to clearly distinguish it from the pattern PT. On the other hand, in the detection optical system 2 described above, the reflected light _RL received by the CCD camera 22 is mainly the reflected light on both the surface of the pattern PT and the surface of the glass substrate 11, and the foreign matter i is usually a laser beam L _T Are scattered in a random direction, and the scattered light is received relatively weakly. Further, the laser beam L _T acceptance angle theta _R of the projection angle theta _T and CCD camera 22 in a diagonal direction to the IC mask 1, since the both edges Eg is inclined, the reflected light projection angle depend vary the relationship of the light receiving angle theta _R and theta _T, since this is the noise is received by the CCD camera 22, but the picture of a certain size or less of the foreign matter i, not necessarily clear, so that its detection It is difficult to say that the accuracy is good. For this reason, the detection accuracy is inevitably reduced, and an inspection is performed on a foreign substance i having a certain size or more.

[0006]

Recently, ICs have been developed.
As the integration density of semiconductor devices increases, the pattern PT becomes finer and more complex, and foreign matter inspection devices are required to inspect even finer foreign matter i. The present invention is superior to conventional foreign matter inspection devices. It is an object to provide a foreign matter detection method having detection accuracy.

[0007]

Means for Solving the Problems] This invention is directed to a foreign substance detecting method of the IC mask, the laser beam L _T projected perpendicular to the above-mentioned IC mask, the IC mask pattern and the glass substrate and these Reflected light R due to extraneous matter
_L is a first imaging device provided in the vertical direction, for example,
And the transmitted light _TL transmitted through the glass substrate is imaged on a second imaging device, for example, a second CCD camera provided in the vertical direction. The video signal S _R of the first CCD camera is compared with a first threshold V _S1 to remove a signal component for the glass substrate and the attached foreign matter, and a signal component S _R ′ for the pattern and the attached foreign matter is removed. Extract. Signal component S _R extracted 'and peak value of the inverted signal of the peak value was adjusted to the same, inverted by adding both the video signal S _T of the second camera CCD camera [- (S _R' + S
_T )], and an edge signal due to each edge of the pattern appearing _therefrom is extracted by comparing with a second threshold value V _S2 .
Remove. The inverted signal [-(S
_R ′ + S _T )] to detect each foreign matter by comparing the foreign matter signal due to the foreign matter attached to the pattern or the glass substrate with the third threshold value V _S3 .

In the above, a test IC mask having a pattern and each foreign substance is used in advance, and the video signals S of the first and second CCD cameras for the IC mask are used.
_R, determine the S _T. This video signal S _R, 'first defines a threshold V _S1 of, and these signal components S _R to extract' inverted signal of the video signal S _T signal component S _R with respect to the pattern and its attached foreign substance [- (S _R '+ S _T )]
A second threshold V _S2 for extracting an edge signal and a third threshold V _S3 for detecting a foreign substance signal are determined.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a description of a hint of the present invention will be described.
The dimension measurement is performed by an optical dimension measuring instrument. The dimension measuring instrument vertically projects a laser beam onto the IC mask, receives the reflected light in a vertical direction on a CCD camera, and forms a pattern PT. An image is formed on a CCD image sensor and its dimensions are measured. In this case, if a foreign substance is present on the IC mask, a clear image of the foreign substance and the pattern PT can be obtained. It is expected that the pattern PT and the foreign matter can be more clearly distinguished from the conventional method of projecting a laser beam in the oblique direction and receiving the reflected light, which is a hint of the present invention. .

[0010] That is, in the foreign substance detecting method of the present invention, the laser beam L _T is projected perpendicularly to the IC mask, the pattern and the glass substrate and the reflected light R _L by these adhesion foreign matter, vertically disposed The first CC
A good image signal S _R is obtained by clearly forming an image on the D camera, and the transmitted light _TL transmitted through the glass substrate is imaged on a second CCD camera provided in the vertical direction, which also provides a good image. A signal _ST is obtained.

The video signal S _R is compared with a first threshold value V _S1 to remove a signal component for the glass substrate and the attached foreign matter, and a signal component S for the pattern and the attached foreign matter is removed.
_R 'is extracted. The signal component S _R 'and peak value of the peak value of the video signal S _T is adjusted to the same, the inverted signal inverted by adding them [- (S _R' when + S _T)] to synthesize,
In this case, an edge signal due to each edge of the pattern and a foreign substance signal for each foreign substance attached to the pattern or the glass substrate appear. The edge signal is extracted after being compared with the second threshold value V _S2 , and is removed. The foreign matter signal is compared with the third threshold value V _S3 to detect each foreign matter.

In the above, a test IC mask having a pattern and each foreign substance is used, and a signal component S is obtained by a video signal S _R of the first CCD camera with respect to this IC mask.
_R 'first threshold V _S1 of extracting is properly determined, and these signal components S _R' inverted signal of the video signal S _T - by _{[(S R '+ S T} )], extracted edge signal a second threshold value V _S2 to the third threshold value V _S3 for detecting a foreign object signal is properly determined, respectively.

[0013]

FIG. 1 is a schematic block diagram of a foreign matter inspection apparatus according to one embodiment of the present invention, and FIG. 2 is a waveform diagram showing signal waveforms of various parts in FIG. In FIG. 1, the foreign matter inspection device includes a detection optical system 4 and a foreign matter detection unit 5. The detection optical system 4 includes a laser light source 41, a prism mirror 42, a half mirror
43, a prism mirror 44, a first CCD camera 45a, and a second CCD camera 45b.
a.45b has an imaging lens 451 and a CCD image sensor 452. The foreign object detection unit 5 includes a signal processing circuit 51 and an addition circuit.
52, an inversion circuit 53, an edge extraction and removal circuit 54, and a foreign matter detection circuit 55.

The laser beam L _T output from the laser light source 41
Is reflected by the prism mirror 42 and the half mirror 43
And is projected perpendicularly to the IC mask 1 to illuminate a certain area. Since the pattern PT is chrome,
The laser beam L _T favorably reflected, the glass substrate 11 is at most reflective few percent. Further, the foreign matter i present in this illumination range scatters scattered lights in random directions, and the reflected light _RL obtained by combining these scattered lights is transmitted through the half mirror 43 to the first CCD.
The light enters the camera 45a and is imaged on the CCD image sensor 452 by the imaging lens 451. On the other hand, the projected laser beam L _T is not transmitted pattern PT chrome, glass substrate 11 is transmitted through 90%, the foreign matter i adhering thereto
Is largely shut off the laser beam L _T A part of the scattered light is transmitted. The transmitted light _TL enters the second CCD camera 45b via the prism mirror 44,
1 forms an image on the CCD image sensor 452.

Hereinafter, the foreign matter detector 5 will be described with reference to FIG.
The operation of detecting foreign matter will be described. As shown in FIG. 2, the video signal S _R of the first CCD camera 45a has a waveform of a high peak value h _P due to the pattern PT having good reflection performance, on which the weak scattered light of the attached foreign matter i ₁ is superimposed. And it is concave. In addition, the low peak value h _GR of the glass substrate 11 having a relatively small reflectivity
The waveform is recessed by a weak scattered light of the attached foreign matter i _1. However, since both sides of the edge E _g of the pattern PT reflects little, between the waveform pattern PT and the glass substrate 11, there is a deep gap for the edge E _g.
This video signal S _R is input to the signal processing circuit 51 and compared with a first threshold value V _S1 which is slightly larger than the _peak value h _GR set therein, and is integrated with the glass substrate 11 and the attached foreign matter i ₂ . Is removed, and the pattern PT and its attached foreign matter i ₂
, A signal component S _R ′ of a peak value h _P ′ is extracted.

[0016] On the other hand, the video signal S _T of the CCD image sensor 452 of the second CCD camera 45b, there is a waveform of a high peak value h _GT by the glass substrate 11 of good permeability, which is blocked by the adhered foreign matter i ₂ It is concave. Signal component S _R 'is extracted by the peak value is adjusted in the signal processing circuit 51, a video signal S _T identical to the peak value h
_C , which are added by the adder circuit 52, and then the polarity is inverted by the inverting circuit 53, and the inverted signal [− (S
_{When R} ′ + S _T ) is synthesized, an edge signal S _Eg and a foreign matter signal S _i appear as shown in FIG. The inverted signal [-(S
_R ′ + S _T ) is input to an edge extraction and removal circuit 54, which is compared with a second threshold value V _S2 set therein to extract and remove the edge signal S _Eg and remove only the foreign matter signal _Si from the foreign matter. The third threshold value V is input to the detection circuit 55 and is set to this.
The data is detected by comparison with _S3, and the data of the foreign substance i is output.

The first, second, and third thresholds V _S1 , V _S2 , and V _{S2 described above} are based on the pattern PT and the two foreign substances i ₁ ,
Each is determined by the method described above, using a test IC mask having i ₂ .

[0018]

As described above, according to the foreign matter detection method of the present invention, a clear image of the foreign matter and the pattern PT can be obtained, and both the projection direction of the conventional laser beam and the reception direction of the reflected light are oblique. Compared to the method with the direction, the two are more clearly distinguished, and it is possible to detect fine foreign matter. Conventionally, the detection accuracy of the foreign matter inspection device is There are significant effects that can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a foreign matter inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing signal waveforms at various parts in FIG. 1;

FIG. 3 is a plan view and a cross-sectional view illustrating a part of a pattern of an IC mask and an attached foreign matter;

FIG. 4 is a schematic configuration diagram of a main part of a conventional foreign matter inspection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... IC mask, 11 ... Glass substrate, 4 ... Detection optical system of this invention, 43 ... Half mirror, 45a ... 1st CCD camera, 45b ... 2nd CCD camera, 451 ... Imaging lens, 45
2 ... CCD image sensor, 5 ... foreign object detection unit of the present invention, 51 ... signal processing circuit, 52 ... addition circuit, 53 ... inversion circuit 54
... edge extraction removal circuit, 55 ... foreign matter detection circuit, PT ... pattern, i ... adhered foreign matter, S _R .S _T ... video signal, V _S1 ... first
, V _S2 ... second threshold, V _S3 ... third threshold.

Claims (2)

[Claims] 1. A targeting IC mask pattern is formed of chromium on the surface of the glass substrate, the laser beam L _T projecting perpendicularly to said IC mask, the pattern and the glass substrate and these attached foreign substance Of the reflected light _RL by the first imaging device provided in the vertical direction, and forming the transmitted light _TL transmitted through the glass substrate on the second imaging device provided in the vertical direction, The video signal S _R of the first imaging device is compared with a first threshold value V _S1 to remove a signal component for the glass substrate and the attached foreign matter, and a signal component S for the pattern and the attached foreign matter is removed. 'extracts, the extracted signal component S _{R' R} and the wave height value of the inverted signal of the peak value of the video signal S _T of the second imaging device was adjusted to the same, inverted by adding both _{[- (S R '+ S} T)] were synthesized, the inverted signal _{[- (S R' + S} T)] The edge signal from each edge of the pattern appearing on, after extraction compared to the second threshold value V _S2, removed, inverted signals respective edge signal is removed _{[- (S R '+ S} T)] in The remaining foreign matter signal due to the remaining foreign matter attached to the pattern or the glass substrate is converted to a third threshold value V
Detecting each of the foreign substances as compared with _S3.
Method for detecting foreign matter on C mask. 2. The image pickup apparatus according to claim 1, wherein said first and second image pickup apparatuses are cameras using a CCD light receiving element.
Video signal S _R of the first and second CCD cameras with respect to the mask, seek S _T, the video signal S _R, the first threshold value V for extracting a signal component S _R 'with respect to the pattern and its attachment foreign matter defines _S1, 'inverted signal and the video signal S _T [- (S _R' the signal component S _R by + S _T)],
The two threshold V _S2, the third, characterized in that defining the threshold value V _S3 respectively, in the foreign substance detecting method of the IC mask as claimed in claim 1, wherein for detecting the foreign object signal for extracting the edge signal.