JP2609638B2 - Foreign matter inspection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a foreign matter suitable for detecting microscopic foreign matter attached on a photomask, a reticle, a semiconductor wafer or the like for manufacturing a semiconductor device with high speed and high sensitivity. It relates to an inspection device.

[Conventional technology]

As described in JP-A-59-65428, a conventional foreign matter inspection apparatus includes a linearly polarized laser, a unit for irradiating the laser beam at a specific incident angle, and a polarizing plate and a lens. When the sample to be inspected is irradiated with linearly polarized light, the scattered light from the photomask substrate and the pattern is different from the scattered light from the foreign material in the direction of polarization. ing. This is shown in the Transactions of the Society of Instrument and Control Engineers Vol.17, No.2, P232-P242, 1981.
Has also been stated. According to this method, the intensity of the scattered light from the pattern is sufficiently smaller than the scattered light from the foreign substance of 2 to 3 μm, and the foreign substance of 2 to 3 μm can be detected separately from the pattern.

As a device having a detection system using a detector having a plurality of visual fields, there is one described in JP-A-59-60343. It detects light.

[Problems to be solved by the invention]

In a conventional foreign matter inspection apparatus, a foreign matter is discriminated from a pattern based on the intensity of scattered light due to oblique illumination. A problem with this method is that, for a minute foreign matter, the scattered light generated by oblique illumination is weakened to the same level as or less than the pattern, and cannot be discriminated from the pattern. On the other hand, the required performance for detecting foreign matter on a photomask is required to be able to detect even finer foreign matter year by year as LSI processing technology becomes finer.

Particularly in the case of a reticle among photomasks, as shown in FIG. 27, the LSI chip pattern 48 on the reticle 71 is
The wafer 59 is repeatedly exposed for each chip. Therefore, the foreign matter 49 existing on the reticle 71 is exposed in common to all chips on the wafer 59, and a defect 72 common to all chips is generated. For this reason, a strict performance is required for the inspection device for the foreign matter on the reticle. Conventional 2μ
In an LSI finely processed by an m-rail, for example, a 256 Kb DRAM, foreign matter detection performance of φ2 μm or more is required for an inspection device for foreign matter on a reticle. However, in LSIs processed by the 1.3 μm rule today and the 0.8 μm rule in the future, for example, 1 μm DRAM and 4 Mb DRAM, φ1 μm and φ1 μm respectively
An inspection apparatus is required to detect a foreign substance having a size of 0.5 μm or more, and there is a great difference from the detection capability φ2 μm according to the related art.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a foreign matter inspection apparatus which solves the above-mentioned problem and can detect a minute foreign matter whose generation of scattered light is so small as to be indistinguishable from a pattern.

[Means for solving the problem]

In the foreign matter inspection device according to the present invention, oblique illumination is performed on a substrate to be inspected having a circuit pattern (hereinafter, abbreviated as a sample),
The scattered light from the sample is detected by a detection system having a new configuration described below. The detection of the scattered light is performed simultaneously by two large and small detectors (the detector's upper field of view is set to be larger than the fine foreign substance and smaller than the circuit pattern). The foreign matter inspection device calculates the difference between the outputs of the two detectors, compares the difference between the outputs with a set threshold value, and determines that the output difference is smaller than the threshold value and the small detector (or the large detector) If the output is not zero, it is determined that "there is a foreign substance". If the output of the small detector (or the large detector) is larger than the set threshold value, it is determined that "large foreign matter exists".

That is, the present invention provides an oblique illumination unit that illuminates a sample such as a substrate having a circuit pattern from an oblique direction, a branching unit that branches scattered light from the sample by the oblique illumination unit, A first scattered light detecting means for detecting scattered light within a desired visual field of the sample for one of the scattered lights branched by the means, and a desired visual field for the other scattered light of the branched scattered lights. Second scattered light detection means for detecting scattered light within a visual field larger than the desired visual field, a first output signal of the first scattered light detection means and a second output of the second scattered light detection means Calculating means for comparing the first output signal or the second output signal with the signal, a calculation result of the calculation means, a preset first threshold value, and a preset second threshold value smaller than the first threshold value; Circuit pattern of the sample based on the threshold of A foreign object determining means for determining to identify the foreign substance on the sample for the presence of this foreign matter, was constructed and an output means for outputting the judgment result of the foreign substance determination unit.

Further, according to the present invention, a foreign matter inspection apparatus, oblique illumination means for illuminating a sample such as a substrate having a circuit pattern from an oblique direction, and scattered light detection means for detecting scattered light from the sample by the oblique illumination means Image signal output means for receiving an output signal of the scattered light detection means and outputting an image signal of a desired visual range on the substrate and an image signal of a visual range including the desired visual range and larger than the desired visual range. Calculating means for comparing the image signal of the desired visual field range on the substrate from the image signal output means with the image signal of the large visual field range; and calculating the image signal of the desired visual field range or the image signal of the large visual field range The circuit pattern of the sample and the foreign matter on the sample are identified based on the calculation result of the means, a first preset threshold value, and a second preset threshold value smaller than the first threshold value. Existence And the foreign matter determination unit determines, was constructed and an output means for outputting the judgment result of the foreign substance determination unit.

[Action]

Hereinafter, the operation of the present invention will be described assuming a photomask (reticle) for a 1-4 Mb DRAM as a sample. In this case, the minimum size of the circuit pattern on the sample is about several μm, and the minimum size of the foreign matter to be detected is about 0.5 μm.

When oblique illumination is performed on the sample and scattered light from the sample is detected, the detector output has the following difference depending on the visual field size of the detector. The detector has a field of view on the sample of 2 μm ^□ , 3
As the size is sequentially increased to μm ^□ and 4 μm ^□ , the magnitude of the scattered light from the detected circuit pattern increases sequentially.
On the other hand, the magnitude of the scattered light from the minute foreign matter is constant. This is for the following reason.

Since the circuit pattern on the sample is larger than a 2 μm ^square detector (this is tentatively called a small detector), only a part of the scattered light from the circuit pattern is incident on the small detector. Therefore, when the detection field of view is enlarged, the amount of scattered light incident on the small detector increases.

On the other hand, the size of the minute foreign matter is smaller than the field of view of the small detector, and all the scattered light from the minute foreign matter enters the small detector. Even if the size of the field of view is increased, the amount of incident scattered light does not increase. Because. From the above, the output of 4 [mu] m ^□ detector (referred Suppose large detectors this), when obtaining the difference between the outputs of the small detector, the fine foreign matter, becomes substantially zero, not zero in the circuit pattern. However, even when no foreign matter or circuit pattern exists, the output difference between the large and small detectors becomes zero (because both the output of the large detector and the output of the small detector become zero). If the output of ()) is not zero and the output difference between the large and small detectors is zero or almost zero, it is determined that "there is a foreign substance".

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an overall configuration diagram of a foreign matter inspection apparatus according to one embodiment of the present invention. The present foreign matter inspection apparatus includes a sample stage 4 including an XY stage 1, a stage driving system 2, and a clamp 3 on which a photomask 14 as a sample is mounted, a polarizing laser 5, a beam expander 6, a condenser lens 7, And incident angle setting means 8
An oblique illumination unit 9 composed of a half mirror 11, magnification correction lenses 38 and 39, photoelectric conversion elements 15 and 16, and signal amplifiers 40 and 41.
Photoelectric conversion unit 12, consisting of an objective lens 10a and a relay lens
10b, the analyzer 17, the scattered light detection unit 13 including the photoelectric conversion unit 12 and the difference circuit 42, and the control unit 35 including the foreign substance determination circuit 24, the stage controller 25, the CRT display 32, the printer 33, and the microcomputer 34. Consists of

In the sample stage 4, a photomask 14 is fixed on the XY stage 1 by the clamp 3. The XY stage 1 moves the surface to be inspected on the photomask 14 and also on the pellicle film 37 (this is a transparent thin film for preventing foreign substances from approaching the photomask 14) in the Z direction. With a positioning mechanism.

The X stage has a half-period of constant acceleration movement of about 0.1 second, constant velocity movement of 0.1 second, and constant deceleration movement of 0.1 second, and performs periodic movement with a maximum velocity of about 1 m / second and an amplitude of 200 mm. .

The Y stage synchronizes with the constant acceleration and constant deceleration movements of the X stage, and feeds it in one direction stepwise by 0.15 mm. Assuming that 670 steps are sent for one inspection, 100 mm can be sent in about 130 seconds.

With this configuration, an area of 100 × 100 mm can be inspected in about 130 seconds.

In the oblique illumination unit 90, the light emitted from the linearly polarized laser 5 is incident on the photomask 14 through the beam expander 6 and the condenser lens 7. The incident angle at this time is set by the incident angle setting means 8. The light scattered on the photomask 14 passes through the objective lens 10a, the relay lens 10b, and the analyzer 17. The use of the analyzer 17 and the linearly polarized laser 6 enables more stable and highly sensitive detection of foreign substances. The scattered light that has passed through the analyzer 17 is divided into two by the half mirror 11, and magnification correction lenses 38 and 39 each having a magnification set to constitute two types of detectors having different visual field dimensions on the sample. And form an image on the photoelectric conversion elements 15 and 16. The photoelectric conversion result is amplified by the signal amplifiers 40 and 41, and the difference between the two signal amplifiers 40 and 41 is obtained by the difference circuit 42.

In the foreign matter determination circuit 24, the output of the difference circuit 24 and the signal amplifier
The presence / absence of a foreign substance is determined from the output of 40 and the result is sent to a microcomputer system 34 which controls the entire apparatus.
The transmitted information is output to an output device such as a CRT display 32 or a printer 33 after performing necessary processing such as matching with the stage coordinate information by the microcomputer system 34.

FIG. 6A is a graph showing the magnitude of scattered light from the edge of a circuit pattern (hereinafter referred to as a pattern) on the sample 14 with respect to the pattern angle θ. Here, the pattern angle θ is the sixth angle when the photomask is viewed from above.
As shown in FIG. 8B, the angle θ of the pattern edge 48 when the direction of the oblique illumination is set to the arrow 5 (the direction of the laser beam).

FIG. 6 also shows the scattered light detection outputs V _0.5 , V _1.0 , V _2. from the φ0.5 μm, 1.0 μm, and 2.0 μm standard particles in addition to the scattered light output from the pattern edge. According to this, φ
Considering the detection up to 0.5 μm standard particles, it can be seen that it is not possible to discriminate a foreign substance from a pattern with a pattern angle of 10 ° to 30 ° (hereinafter referred to as a specific pattern) only by detecting the size of the scattered light. .

FIG. 7 shows the scattered light detection outputs of the large foreign matter, φ0.5 μm small foreign matter, φ0.5 μm small foreign matter in contact with the specific pattern, the non-specific pattern, and the S-polarized laser irradiation from the specific pattern. V _α and V _β shown in FIG. 7 are thresholds used in the detection method according to the present embodiment. As described above (FIG. 6), it is necessary to discriminate the specific pattern from the small foreign matter of φ0.5 μm. Therefore, if the scattered light detection output exceeds V _alpha is obtained a large foreign body or, since foreign matter in contact with a particular pattern, it is determined that "there is foreign matter". If the scattered light detection output does not exceed V _beta is obtained is determined as "no foreign matter". When a scattered light detection output intermediate between V _α and V _β is obtained, the determination is made as follows.

FIG. 2 shows that a detector having two different visual field dimensions a (here, 2 μm ^□ , 3 μm ^□ , 4 μm ^□ ) within a range larger than a 0.5 μm foreign substance and smaller than a circuit pattern is used.
It is a result of detecting scattered light from a 5 μm particle (V _0.5 ) and a specific pattern (Vp). The detected scattered light V _0.5 from the 0.5 μm particles is substantially constant even when the field size a changes, whereas the scattered light from the specific pattern increases as the field size a increases.

This is for the following reason. As shown in FIG.
Since the pattern 48 has a visual field dimension a larger than the detector 18 (hereinafter, small detector) having a size of 2 μm, only a part of the scattered light from the pattern is incident on the small detector 18. Therefore, when the detector field of view is enlarged (FIG. 9B), the amount of scattered light incident on the detector 19 increases. On the other hand, as shown in FIG. 4A, since the size of the minute foreign matter 50 (for example, 0.5 μm particle) is smaller than the pixel of the small detector 18, all the scattered light from the minute foreign matter is transmitted to the small detector 18. Incident. Therefore, the detector 19 (fourth
This is because the amount of incident scattered light does not increase even if the visual field size is increased as shown in FIG.

Or field size on the sample because of 4μm detector (hereinafter, the large detector) when determining the difference between the output V _S of the output V _L and the small detector 18 19, becomes substantially zero in the fine foreign matter (the 4
Figure) It does not become zero in the circuit pattern. However, foreign matter output difference V _L -V _S of large and small detector even when not present pattern (Figure 5) becomes zero. (Because both V _L and V _S become zero). Therefore, when V _S (or V _L ) is not zero and thus a foreign substance or a pattern exists, it is determined that “a foreign substance is present” when the output difference between the large and small detectors is zero or almost zero.

Here, as an example of the visual field size of the large detector, 4 μm is used.
m ^□ , 2 μm ^□ as an example of the visual field size of the small detector, which should be selected appropriately according to the size of the foreign matter to be detected and the size of the circuit pattern.

Also, as shown in FIG. 8, by using outputs Va, Vb, Vc, Vd of a plurality of (four kinds in FIG. 8) detectors 20, 21, 22, 23 having different pixel sizes, foreign matters having different sizes are obtained. (3 in FIG. 8)
Species) 26, 27 and 27 can be detected by discriminating them from the pattern 48. The detection conditions Pa, Pb, and Pc for the three types of foreign substances are as follows: Pa = (Vb−Va0) ∩ (Vc−Vb0) ∩ (Vd−Vc0) And when pattern 48 is detected, Becomes

The method using a plurality of detectors is an extension of the method using two types of detectors, large and small, and the following description will be made for the case of using two types of detectors, large and small.

From the description so far, the foreign matter detection formula P
The output V _L of the large detector, the output V _S of small detectors, the threshold V _alpha,
V _beta, and, V _L the states of -V _S 0 using the V _L -V _S ≦ ε small set value for representing the _{ε, P = (V S ≧} V α) ∪ {(V α> V _S ≧ V _β ) ∩ (V _L −V _S ≦
ε)｝.

FIG. 9 shows the configuration of the foreign matter determination circuit 24 that realizes this equation.

Foreign matter determination circuit 24 includes a comparator circuit 29 of V _S and V _alpha, a comparison circuit 30 of V _S and V _beta, a comparison circuit 31 with the V _L -V _S and epsilon,
It comprises an OR circuit 31a.

Next, a method for obtaining the detection output V _L by the large detector and the detection output V _S by the small detector will be described.

In FIG. 1, two types of magnification correcting lenses are provided on two photoelectric conversion elements 15 and 16 having the same shape and size.
The images on the sample 14 are imaged at different magnifications using 38 and 39, and V _L and V
_S is gaining. Here, the object is achieved if images can be formed on the two photoelectric conversion elements 15 and 16 at different magnifications. Therefore, by appropriately selecting the magnification of the relay lens 1b and the dimensions of the photoelectric conversion element 16, the photoelectric conversion unit 12 can make one magnification correction lens 39 unnecessary as shown in FIG.

Also, since the purpose of correcting the magnification is to provide two different sizes of detector fields of view on the sample 14, if two types of photoelectric conversion elements 15 and 16 with different dimensions can be prepared, the eleventh type can be prepared. As shown in the figure, both magnification correction lenses 38 and 39 can be omitted.

Figure 12 shows the small detector field of view 18 and the large detector field 1 on the sample.
The state of 9 is shown. As shown in FIG.
18 - 19, if you set shifting, it is necessary to use such a structure of the memory circuit or a delay circuit for adjusting the detection position of the detector output V _L, V _S. Therefore, as shown in FIG. 12 (b), a configuration in which the fields of view 18, 19 of the large and small detectors are set so as to overlap is practical.

FIG. 12 (b) shows a case where a single type of photoelectric conversion element is used for the photoelectric conversion elements 15 and 16. However, in order to perform a foreign substance inspection at a high speed, it is more advantageous to use a parallel detection type photoelectric conversion element such as a one-dimensional solid-state image sensor array than a single type element.

Hereinafter, a method for obtaining V _L and V _S using a parallel detection type photoelectric conversion element (detector) will be described.

FIG. 13 is a diagram showing a state of a detection visual field on a sample in a case where the single-type photoelectric conversion element in FIGS. 1, 10 and 11 is directly replaced with a parallel detection type element. This is shown in the same manner as in FIG. In general, since the field of view of the large detector 19 and the field of view of the small detector 18 have different periods, a phase shift occurs, and the entire field of view of the detector is brought into a state as shown in FIG. 12 (b). Is not possible with this configuration. Therefore,
As shown in FIG. 15, the configuration is such that the field of view of the large detector 19 is a rectangular field of view and the period is equal to the field of view of the small detector 18. This is because the specific pattern is a vertical pattern 47 in FIG. 14 from the direction of the oblique illumination 5. In this direction, the detection output _VL is the same whether the shape of the field of view of the large detector 19 is square as shown in FIG. 14 (a) or rectangular as shown in FIG. 14 (b). For this reason, even if the shape of the large detector is as shown in FIG. 15, there is no problem of discrimination from the specific pattern. FIGS. 16 and 17 show the configuration of the photoelectric conversion unit in this case.

FIG. 16 shows a large / small detector constructed by changing the shapes of the photoelectric conversion elements 15 and 16 as in FIG. FIG. 17 shows a cylindrical lens 51 in front of a photoelectric conversion element for a large detector using photoelectric conversion elements 15 and 16 having the same shape.
Is provided so that a rectangular visual field can be obtained on the sample.

In order to improve the stability of discriminating patterns and foreign objects,
A configuration in which the field of view of the large detector can be made square by devising will be described below.

FIG. 18 shows the length of one side of the field of view of the large detector 19 as a small detector.
The relationship of the visual field when the value is doubled to 18 is shown. Thus, the visual field of the small detector 18 has a correct positional relationship (as shown in FIG. 12 (b)) with one visual field of the large detector 19 every other visual field.
Therefore, two large pixel detectors 54 whose phases are shifted by 1/2
The use of-55, can be obtained V _L, V _S for each field of small detectors 18 (Figure 19). The configuration in this case is
Shown in the figure. The detected scattered light separated by the half mirror 11 is further separated by the second half mirror 56 and is incident on the large detectors 54 and 55 which are arranged shifted from each other by 1/2 field of view. One of the detection outputs is selected by the multiplexer 43 in accordance with the position of the field of view of the small detector 15, and is output as _VL .

By adding the detection outputs of the two fields of view A and B as shown in FIG. 22, an output equivalent to a field of view in which the two fields of view A and B are combined can be obtained. Therefore, as shown in Fig. 21,
Place a small detector. In this case, the V _L corresponding to the output V _S of small detectors a, can be obtained as the sum of the outputs of a large detector AB. Hereinafter, the small detectors b, c, d,... Are combined with the large detectors B, C, C, D, D, E,. In this configuration, one large detector 19 may be used, and it is not necessary to divide the optical path into three parts as shown in FIG. 20, which is advantageous in terms of light quantity.

FIG. 23 is a further development of the above idea. In this method, different visual fields are equivalently formed by adding the outputs of the respective pixels of the two-dimensional photoelectric conversion array while changing the number of pixels.
It is configured to determine the V _L and V _S as a set of photoelectric conversion elements. FIG. 24 shows the configuration of the photoelectric conversion unit in this case. Since the photoelectric conversion element is one set of the two-dimensional photoelectric conversion array 44, the separation of the optical path by the half mirror is unnecessary. Therefore, the configuration of the optical system is simple, and is most rational in terms of light quantity. The photoelectric conversion unit 12 includes a two-dimensional photoelectric conversion array driving circuit 52 and a pixel cutout addition circuit 53 that performs output addition of each pixel.

Scan the one-dimensional photoelectric conversion array 45 as shown in FIG.
In the method of obtaining the two-dimensional image by storing the result obtained in the memory in the memory, as shown in FIG.
And a result equivalent to the above is obtained. FIG. 26 shows the configuration in that case. The difference from FIG. 24 is that the one-dimensional photoelectric conversion array 45, the driving circuit 57 for the primary photoelectric conversion element, the image memory 58
It is.

〔The invention's effect〕

According to the present invention, in a foreign substance inspection of a substrate having a circuit pattern such as a photomask, it is possible to detect a submicron foreign substance, which is impossible with the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram of a foreign matter inspection apparatus according to one embodiment of the present invention, FIG. 2 is a graph showing the relationship between the output of scattered light from a minute foreign matter and a specific pattern and the size of a detection visual field, and FIG. FIGS. 4 (a) and 4 (b) are diagrams for explaining the relationship between the scattered light detection output from a specific pattern and the size of the detection visual field, and FIGS. 5 (a), a diagram for explaining the relationship with the size of
FIG. 6B is a view for explaining the relationship between the scattered light detection output when there is nothing on the sample and the size of the detection visual field.
(B) is a graph showing the relationship between the scattered light detection output from the pattern edge and the angle of the pattern edge to the oblique illumination light, and FIG. 7 is a large foreign matter, a minute foreign matter, a minute foreign matter in contact with a specific pattern, a non-specific pattern, a specific pattern. FIG. 8 (a), (b), (c), (d) Comparison of scattered light detection output from pattern
FIG. 9 is an explanatory diagram of the scattered light detection output when the size of the foreign matter and the size of the detection visual field are changed. FIG. 9 is a configuration diagram of the foreign matter determination circuit shown in FIG. 1, FIG. 10, FIG. , Fig. 17, Fig. 20
FIG. 24, FIG. 24, and FIG. 26 are configuration diagrams of a photoelectric conversion unit (scattered light detection unit) shown in FIG. 1 according to another embodiment, respectively, and FIGS. 12 (a), (b) and FIG. Fig. 14, Fig. 15, Fig. 18,
FIG. 19, FIG. 21, FIG. 22, FIG. 23, and FIG. 25 are plan views of a detection pixel according to another embodiment, and FIG. 27 is an explanatory view of a chip manufactured with a reticle having a defect. . 4 sample base unit, 9 oblique illumination unit, 12 photoelectric conversion unit, 13 scattered light detection unit, 14 sample (photomask),
18: Field of view on sample of small detector, 19: Field of view on sample of large detector, 24: Foreign matter determination circuit, 26, 27, 28 ... Foreign matter, 48
... Circuit pattern.

Claims (4)

(57) [Claims] An oblique illumination means for illuminating a sample such as a substrate having a circuit pattern from an oblique direction, a branching means for branching scattered light from the sample by the oblique illumination means, and a branching means for branching the light. A first scattered light detection unit that detects scattered light within a desired field of view of the sample for one of the scattered lights, and includes the desired field of view for the other scattered light of the branched scattered lights. Second scattered light detection means for detecting scattered light within a visual field larger than the desired visual field, a first output signal of the first scattered light detection means, and a second output signal of the second scattered light detection means. Calculating means for comparing the first output signal or the second output signal, the calculation result of the calculating means, a first threshold value set in advance, and a smaller value than the first threshold value. The test is performed based on the set second threshold value. A foreign matter determining means for distinguishing between the circuit pattern and the foreign matter on the sample to determine the presence of the foreign matter, and an output means for outputting a determination result of the foreign matter determining means. . 2. An oblique illumination means for illuminating a sample such as a substrate having a circuit pattern in an oblique direction, scattered light detection means for detecting scattered light from the sample by the oblique illumination means, and detecting the scattered light. Image signal output means for receiving an output signal of the means and outputting an image signal of a desired field of view on the substrate and an image signal of a field of view larger than the desired field of view including the desired field of view; Calculating means for comparing the image signal of the desired visual field range and the image signal of the large visual field range on the substrate from the image signal output means, and the image signal of the desired visual field range or the image signal of the large visual field range; Discriminating a circuit pattern of the sample and a foreign substance on the sample based on a calculation result of the calculation means, a first threshold set in advance, and a second threshold smaller than the first threshold. Then the difference And the foreign matter determination unit for the presence of determining, foreign substance inspection apparatus characterized by comprising an output means for outputting the judgment result of the foreign matter determination unit. 3. The foreign matter inspection device according to claim 2, wherein said scattered light detecting means includes a one-dimensional photoelectric conversion element and a storage section for storing an output of said photoelectric conversion element. apparatus. 4. The foreign matter inspection apparatus according to claim 2, wherein said scattered light detection means includes a two-dimensional photoelectric conversion element.