JPH06273344A - Method and equipment for inspecting defect - Google Patents

Abstract

PURPOSE:To make inspection of foreign matter over a wide range of size passibll by setting a plurality of substantially continuous detection sensitivity (detection ability ranges). CONSTITUTION:A scanner control section 131 delivers a control signal 129 for varying the amplification factor each of VCAs 126-128 thus producing signals 132-134 dependent only on the size of dust particle. When a high sensitivity mode is selected, the signals 132-134 are delivered through a switch mechanisms 135 to amplifiers 136-138. Output signals 142-144 therefrom are then compared 145-147 with a reference level 149 set at a relatively high level. Such a decision is made that a foreign matter having the size to be detected is detected when the output signal is higher than the reference voltage 149, otherwise, such a decision is madethat a foreign matter particle or a circuit pattern of smaller size is detected. When a low sensitivity mode is detected, output signals 155-157 from amplifiers 139-141 are compared 158-160 with a reference voltage 162 set at a low level. Such a decision is made that a foreign matter having the size to be detected is detected when the output voltage is higher than the reference voltage 162, otherwise, such a decision is made that a foreign matter or a circuit pattern having lower size is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus and a defect inspection method, and more particularly to a reticle or mask (hereinafter referred to as "reticle") used in a semiconductor exposure process, a pellicle mounted on the reticle, an LSI photomask, and The present invention relates to an apparatus and method for inspecting defects such as foreign matter attached on the surface of a wafer or the like.

[0002]

2. Description of the Related Art In a semiconductor exposure process, foreign matter such as dust may adhere to a reticle and the like, and these adhered foreign matter may be transferred onto a wafer to cause defects in a manufactured wafer. For this reason, an apparatus for optically inspecting foreign matter attached to the surface of the inspection object having a circuit pattern has been proposed (for example, Japanese Patent Publication No. 63-6473).
No. 8, etc.).

In the proposed conventional apparatus, a light beam is obliquely incident on the surface of the object to be inspected, and the surface and the light beam are moved relatively to each other, so that the surface of the object to be inspected is converted into a light beam. It becomes possible to scan in two dimensions. The reflected light from the surface to be inspected is received by a plurality of photoelectric means (photomul, etc.), and the presence or absence and the size of the defect are inspected based on each photoelectric signal from the photoelectric means. More specifically, while the reflected light from the pattern is diffracted light with strong directivity,
Focusing on the fact that the reflected light from a foreign object is scattered light with a weak directivity, it is determined that there is a foreign object when all the photoelectric signals are at or above a certain level, and the size of the foreign object is set to the level of the photoelectric signal. Was sought based on.

Further, in recent years, especially the size of the circuit pattern on the reticle has been miniaturized. With this tendency toward miniaturization, stricter foreign matter management has been required. That is, the scattered signal (photoelectric signal) of the detected foreign matter
The size of the foreign matter is detected as strictly as possible based on the above, and when exposed and transferred to the wafer, the size of the foreign matter is classified based on the size that has no possibility of transferring, the size that has the possibility of transferring, or the size that has reliable transfer. It is necessary to carry out and manage foreign substances.

For example, in a semiconductor device currently in mass production, a foreign substance having a diameter of less than 0.5 μm may not be transferred to a wafer, and a foreign substance having a diameter of 0.5 μm to 1.0 μm may be transferred to a wafer. There is a criterion for reliably transferring foreign matter having a diameter of more than 1.0 μm to the wafer, which is likely to be transferred.

[0006]

In the above-described conventional defect inspection apparatus, the detection sensitivity is calibrated by using reference particles such as polystyrene true spherical beads, and the guaranteed detection sensitivity is set to a diameter of about 0.8 μm. It is set. However, with respect to a foreign matter having a so-called submicron size having a diameter of less than 1.0 μm, the inventor of the present application is aware that the amount Q of scattered light generated from the foreign matter and the size (diameter) D of the foreign matter have the following relationship. I have gained.

Q ∝ D ⁴ Therefore, in a conventional defect inspection apparatus in which the detection sensitivity is calibrated with polystyrene true spherical beads having a diameter of 0.8 μm, the scattered light quantity Q ₀ of the polystyrene true spherical beads having a diameter of 0.8 μm is Q _0.
Where 1 is 1, the scattered light amount Q ₁ of a true spherical bead having a diameter of 0.5 μm and the scattered light amount Q _{2 of} a true spherical bead having a diameter of 1.0 μm
Is given by

Q ₁ = (0.5 / 0.8) ⁴ = 0.15 Q ₂ = (1.0 / 0.8) ⁴ = 2.40 Thus, the true spherical beads of 0.5 μm in diameter are Scattered light quantity Q
₁ and the scattered light amount Q ₂ of the spherical beads having a diameter of 0.5 μm are (2.4 / 0.15) = 16 times different. In other words,
The size of the photoelectric signal differs by 16 times between the foreign matter having a diameter of 0.5 μm and the foreign matter having a diameter of 1.0 μm. The difference between the lower limit and the upper limit (maximum value and minimum value) of the photoelectric signal is as large as 16 times, and the size of the photoelectric signal is determined over a wide range. It was impossible for the reason.

As described above, in the conventional defect inspection apparatus,
There is an inconvenience that it is not possible to discriminate the sizes of foreign matters over a wide range of 0.5 μm to 1.0 μm in diameter.
The present invention has been made in view of the above-mentioned problems, and provides a defect inspection apparatus and method capable of discriminating foreign matters having a wide range of sizes by setting a plurality of detection sensitivities (ranges of detection ability). The purpose is to

[0010]

In order to solve the above problems, in the present invention, in a defect inspection apparatus for optically inspecting a defect on a surface to be inspected, the surface to be inspected is scanned with a light beam. For detecting the reflected light from the surface to be inspected within the first detection capability range defined based on the light beam scanning means and the detection threshold as the lower limit and the saturation level as the upper limit. And the second detecting means for detecting the reflected light from the surface to be inspected in the second detecting ability range which is substantially continuous with the first detecting ability range. Provided is a device characterized by processing photoelectric signals with detection capability.

In the present invention, in a defect inspection method for optically inspecting a defect on a surface to be inspected, the surface to be inspected is scanned with a light beam, and light reflected from the surface to be inspected is photoelectrically detected. Characterized in that the photoelectric signal is processed with a required detection ability selected from a plurality of substantially continuous detection ability ranges respectively defined based on the detection threshold value as the lower limit value and the saturation level as the upper limit value. Provide a way to do.
According to a preferred aspect, the adjacent detection capability ranges are slightly overlapped, the presence or absence of a defect is determined based on each photoelectric signal of reflected light received at a plurality of positions, and based on the magnitude of the photoelectric signal. Detect the size of defects.

[0012]

In the defect inspection apparatus, the discriminable signal range, that is, the detection sensitivity is defined based on the detection threshold value and the saturation level. The detection threshold value is determined based on the noise of the electric circuit or a level at which the circuit pattern is not mistakenly determined to be a foreign substance from the diffracted light from the circuit pattern. On the other hand, the saturation level is determined as a level at which an output signal can maintain a linear relationship with an input signal in an electric circuit (for example, an operational amplifier includes an element such as an A / D converter). Therefore, with the detection threshold as the lower limit and the saturation level as the upper limit, the range in which the signal can be identified by the level based on the lower limit and the upper limit, in other words, the range of the detection capability, that is, the detection sensitivity is defined.

In the present invention, a plurality of detection sensitivities, for example, two detection sensitivities are set. The two detection sensitivities, that is, the detection capability range in the high sensitivity mode and the detection capability range in the low sensitivity mode are set to be substantially continuous. In this way, as described above, the range of the scattered signal is set to 2 so that the difference between the lower limit and the upper limit of the magnitude reaches 16 times.
It is possible to cover the entire area with one sensitivity mode, and reliably and accurately determine the foreign matter size over a wide range in the required sensitivity mode.

[0014]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view schematically illustrating the configuration of the defect inspection apparatus according to the embodiment of the present invention. In the illustrated apparatus, the reticle 100 is placed on the stage 101. It is assumed that the surface to be inspected of the reticle 100, which is the object to be inspected, extends in parallel with the XY plane in the figure. Stage 1
01 is reciprocally movable in the Y direction in the figure by the drive unit 102, and the amount of movement can be measured by a length measuring device 103 such as a linear encoder.
On the other hand, a light beam 104 emitted from a light source 200 such as a laser light source is deflected and scanned in the X direction in the drawing by a scanner 105 such as a galvano scanner or a polygon mirror, and is scanned on the reticle 100 by a scanning lens 106 such as an fθ lens. Becomes a light beam that converges to
A scan line 107 that is substantially parallel to the direction is formed.

As described above, the scanning of the light beam in the X direction and the movement of the reticle 100 by the driving unit 102 in the Y direction cause
A two-dimensional light beam can be scanned over the entire surface of the reticle 100, which is the surface to be inspected. Incidentally, the moving speed of the reticle 100 in the Y direction is set to be extremely smaller than the scanning speed of the light beam 104 in the X direction.

As shown in the figure, when there is a defect such as a foreign substance 108 on the surface of the reticle 100, scattered light 110 is generated from the foreign substance 108 irradiated with the light beam 109.
The scattered light 110 is provided with light-receiving lenses 111 and 11 which are appropriately arranged at three positions so that the scanning line 107 is seen from different directions.
Photodetectors 114, 115 such as photomultipliers (hereinafter abbreviated as “photomul”) disposed behind each light receiving lens via 2 and 113.
And 116 are photoelectrically detected. On the other hand, a circuit pattern 117 for transfer onto a wafer is formed on the surface of the reticle 100, and diffracted light 118 is generated from the circuit pattern 117 irradiated with the light beam 109.

The scattered light 110 from the foreign matter 108 described above has a weak directivity and is scattered isotropically, whereas the diffracted light 118 from the circuit pattern 117 has a very high scattering directivity. Therefore, when all the photoelectric detectors among the three photoelectric detectors 114, 115, and 116 appropriately arranged in multiple directions receive a light amount of a predetermined level or more, it is determined that a foreign substance having a size to be detected exists. . Further, if any one of the three photoelectric detectors 114, 115, and 116 receives only a light amount that does not reach a predetermined level, whether there is a foreign substance having a size smaller than the size to be detected or a circuit pattern. Is determined to exist or none exists.

FIG. 2 is a block diagram showing the configuration of the detection circuit of the defect inspection apparatus of FIG. The processing of the received light signal will be described with reference to FIG. Photoelectric detectors 114, 115 and 1
16 is an electrical signal 120, 1 which is almost proportional to the amount of received light
21 and 122 are output, respectively. Electrical signal 12
0, 121 and 122 are preamplifiers 123 and
VCA126, 1 after amplified with 124 and 125
27 and 128. VCA is Voltage Co
It is an abbreviation for ntrolAmplifier, and is a circuit that can change the amplification factor according to the input voltage 129. Scanner 10
5 also has a swing angle variable according to the input voltage 130. In this way, based on the voltages 129 and 130 output from the scanner controller 131, it is possible to control the scanner 105 and the amplification degree of the VCAs 126, 127, and 128.

Generally, the light receiving lenses 111, 112 and 11 to which the photoelectric detectors 114, 115 and 116 correspond.
The optical information (light quantity) obtained via 3 depends on the irradiation position of the light beam. That is, even if the size of the foreign matter is the same, the amount of light obtained by each photoelectric detector differs depending on the position of the foreign matter. For example, when the light beam 109 irradiates the one end 107A on the scanning line 107 and the other end 107B, from the light receiving lenses 111, 112 and 113 to the irradiation position of the light beam 109. Each distance changes. Therefore, at the above-mentioned two irradiation positions, the solid angle that can be received by each light receiving lens changes, and the amount of light that can be received also changes naturally. Further, the angle formed by each light receiving lens and the light beam 109 also changes. Therefore, even if exactly the same scattering objects, for example, polystyrene true spherical beads having the same particle size are arranged on the scanning line 107, the photoelectric outputs 120, 121 and 122 change depending on the position in the X direction. This VCA 126, 127 and 128 is corrected by the voltage 129 corresponding to the position in the X direction output from the scanner controller 131 so that the amount of change is corrected and the output signal is always constant without depending on the position in the X direction.
The amplification degree of is changed appropriately. In other words, a signal that depends only on the size of the foreign matter is independent of each V regardless of the position of the foreign matter.
It can be obtained through CA.

Next, VCAs 126, 127 and 12
8 output signals 132, 133 and 134 are transmitted via a switch mechanism 135 to a first set of amplifiers 136, 136, respectively.
137 and 138 or the second set of amplifiers 1 respectively
39, 140 and 141. Where the first
The amplification degree of the amplifiers 136, 137 and 138 of the set is constant, and is set relatively high so that the smallest foreign matter to be detected can be detected, and the amplifiers 139, 140 and 14 of the second set are detected.
The amplification factor of 1 is also constant and is set lower than the amplification factors of the amplifiers 136, 137 and 138 of the first set. As will be described in more detail below, it is possible to select the high sensitivity mode by connecting to the first set of amplifiers 136, 137 and 138 and the low sensitivity mode by connecting to the second set of amplifiers 139, 140 and 141. it can. In the initial state, the high sensitivity mode is usually selected.

When the high sensitivity mode is selected, the first
Output signal 14 of the pair of amplifiers 136, 137 and 138
2, 143 and 144 are respectively the first set of comparators 1
45, 146 and 147, and are compared with the reference voltage 149 output from the reference voltage generator 148. In each comparator, the input signal is the reference voltage 149
In the above case, the digital signal "1" is output, and in the case where the input signal is less than the reference voltage 149, the digital signal "0" is output. Digital output signals 150, 151 and 1 of the first set of comparators 145, 146 and 147.
52 is input to the AND circuit 153 and the logical product is taken. That is, all digital output signals 150, 1
AND circuit 153 only when 51 and 152 are "1"
Output signal 154 becomes "1", and in other cases, output signal 154 becomes "0".

As already described above, even if the diffracted light 118 of the pattern 117 is received, at least one of the photoelectric detectors 114, 115 and 116 has a small amount of received light, and any one of the comparators 145, 146 and 147. In one of them, the magnitude of the reference voltage 149 is set so as to output a digital signal "0". Therefore, AND
When the output signal 154 of the circuit 153 becomes "1", it indicates that the foreign matter of the size to be detected is detected.
When the output signal 154 of the AND circuit 153 becomes "0", it indicates that the foreign matter or the circuit pattern that is smaller than the size to be detected is detected.

On the other hand, when the low sensitivity mode is selected, the output signals 155, 156 and 157 of the second set of amplifiers 139, 140 and 141 are input to the second set of comparators 158, 159 and 160, respectively. , The reference voltage 16 output from the reference voltage generator 161 respectively.
Compared to 2. In each comparator, when the input signal is equal to or higher than the reference voltage 162, the digital signal "1"
When the input signal is less than the reference voltage 162, the digital signal "0" is output. The second set of comparators 158, 15
The digital output signals 163, 164, and 165 of 9 and 160 are input to the AND circuit 166 to be ANDed. That is, all digital output signals 16
The output signal 167 of the AND circuit 166 becomes "1" only when 3, 164 and 165 are "1", and the output signal 167 becomes "0" otherwise.

When the output signal 167 of the AND circuit 166 becomes "1", it indicates that the foreign matter of the size to be detected is detected, and when the output signal 167 of the AND circuit 166 becomes "0". As in the case of the high-sensitivity mode, the fact that foreign matter or a circuit pattern smaller than the size to be detected is detected is detected.

Further, when the high sensitivity mode is selected, the output signals 142, 143 and 144 of the amplifiers 136, 137 and 138 of the first set are output to the first arithmetic unit 168.
Entered in. The first calculation unit 168 uses the three detection signals 1
The averaging processing of 42, 143 and 144 is executed and the detection signal 169 is output. On the other hand, when the low sensitivity mode is selected, the second set of amplifiers 139, 140 and 14
The output signals 155, 156 and 157 of 1 are input to the second arithmetic unit 170. The second calculation unit 170 executes the averaging process of the three detection signals 155, 156 and 157, and outputs the detection signal 171.

As already mentioned above, the detection signal 16
There is a correlation between the sizes of 9 and 171 and the size of the detected foreign matter, and it is possible to determine and manage the size of the foreign matter using this correlation.

FIG. 3 is a diagram showing the relationship between the size of the detected foreign matter and the detection signal. In the figure, the horizontal axis represents the diameter φ of the polystyrene true spherical beads that are the reference particles modeling the foreign matter, and the vertical axis represents the detection signal S of each reference particle (corresponding to the detection signals 169 and 171 described above). Are shown on a logarithmic scale. Thus, the diameter of the foreign substance φ
A linear relationship is established between and the logarithm of the magnitude of the detection signal S.

In the figure, L1 is a detection threshold value in the high sensitivity mode, and in the present embodiment, the diameter of the corresponding foreign matter is 0.47 μm.
And U1 has a saturation level in the high-sensitivity mode (saturation level of the circuit of FIG. 2 depending on the amplification degree of the amplifiers 136, 137, and 138 of the first set), and the diameter of the corresponding foreign matter is 0.68 μm. Is set. Also,
L2 is the detection threshold of the low sensitivity mode and is the saturation level of the high sensitivity mode (the second set of amplifiers 139, 140 and 1).
The saturation level of the circuit of FIG. 2 depending on the amplification degree of 41) is set to be almost the same, and U2 is set to the saturation level of the low sensitivity mode so that the diameter of the corresponding foreign matter is 1.2 μm. There is. Note that the second set of amplifiers 139, 1
The amplification degrees of 40 and 141 are set so that the magnitude of the detection signal S of the foreign matter having a diameter of 0.68 μm becomes substantially equal to the saturation level U1.

In general, the detection capability range of each sensitivity mode, that is, the detection sensitivity, is defined based on the detection threshold value as the lower limit and the saturation level as the upper limit. Therefore,
In this embodiment, the detection sensitivity in the high sensitivity mode is 0.47μ.
m to 0.68 μm, and the detection sensitivity in the low sensitivity mode is 0.68 μm to 1.2 μm. In this way, the detection capability ranges of the two sensitivity modes, that is, the detection sensitivities are continuous, and it is configured to be able to detect a foreign substance having a size of 0.47 μm to 1.2 μm as a whole.

As already mentioned above, there is no possibility that foreign matter having a diameter of less than 0.5 μm will be transferred, and a diameter of 0.
When performing foreign matter management according to the criteria that foreign matter having a size of 5 μm to 1.0 μm may be transferred, and foreign matter having a diameter of more than 1.0 μm is reliably transferred,
It suffices to determine which of the following three ranks the obtained detection signal S corresponds to.

A rank L1 ≦ S <S1 B rank S1 ≦ S ≦ S2 C rank S2 <S ≦ U2 Here, S1 and S2 are detection signal levels corresponding to the diameters of the foreign matter of 0.5 μm and 1.0 μm, respectively. is there. Therefore, when the detection signal S is displayed in the A rank via the display means such as a CRT, the size of the foreign matter is not likely to be transferred, and when the detection signal S is displayed in the B rank, the size of the foreign matter is likely to be transferred. That is, when the C rank is displayed, it means that the size of the foreign matter is the size that can be reliably transferred.

Switching of the sensitivity mode and ranking of the foreign matter size in this embodiment will be described with reference to the following table.

[0033]

[Table 1]

As shown in the attached table, when the detection signal S is in the range of L1≤S <S1 in the high sensitivity mode, it is not necessary to switch to the low sensitivity mode and the size of the detected foreign matter is A rank, that is, It is determined that there is no possibility of transfer. Further, when the detection signal S is in the range of S1 ≦ S <U1 in the high sensitivity mode, it is not necessary to switch to the low sensitivity mode, and the size of the detected foreign matter is B rank, that is, the size that may be transferred. To be judged.

On the other hand, when the detection signal S reaches the saturation level and S = U1 in the high sensitivity mode, the size of the foreign matter cannot be discriminated unless the mode is switched to the low sensitivity mode. That is, when the detection signal S reaches the saturation level in the high sensitivity mode and the detection signal S is in the range of L2 ≦ S ≦ S2 in the switched low sensitivity mode, the size of the detected foreign matter is B rank, that is, It is determined that there is a possibility of transfer. Further, the detection signal S reaches the saturation level in the high sensitivity mode and the detection signal S is S2 <S2 in the switched low sensitivity mode.
In the case of S, the size of the detected foreign matter is C
The rank, that is, the size for sure transfer is determined.

In this embodiment, two sensitivity modes are set, but three or more sensitivity modes may be set depending on the size range of the foreign matter to be detected. Further, in this embodiment, the detection sensitivities of the adjacent sensitivity modes are set to be substantially continuous, but two adjacent detection sensitivities may be slightly overlapped. Further, in the present embodiment, the present invention has been described by taking the defect inspection of the reticle as an example. However, foreign matter adheres to other inspected objects such as a photomask, a wafer or a photomask without departing from the scope of the present invention. It is obvious that the present invention can also be applied to the inspection of defects of foreign matter such as fine dust adhered on the surface of a thin film (pellicle) or the like for preventing the above.

[0037]

As described above, since the defect inspection apparatus and method of the present invention are provided with a plurality of sensitivity modes having substantially continuous detection sensitivities, foreign matter that covers a wide range of foreign substances reliably and accurately in the required sensitivity mode. The size can be determined.

[Brief description of drawings]

FIG. 1 is a perspective view schematically illustrating a configuration of a defect inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a detection circuit of the device of the present invention.

FIG. 3 is a diagram showing a relationship between a size of a detected foreign matter and a detection signal.

[Explanation of symbols]

 100 reticle 104 light beam 105 scanner 107 circuit pattern 108 foreign matter 111 light receiving lens 114 photoelectric detector

Claims (4)

[Claims] 1. A defect inspection apparatus for optically inspecting a defect on a surface to be inspected, a light beam scanning means for scanning the surface to be inspected with a light beam, and a detection threshold and an upper limit as lower limit values. First detection means for detecting reflected light from the surface to be inspected within a first detection capability range defined based on the saturation level as a value, and substantially continuous with the first detection capability range. A second detection means for detecting the reflected light from the surface to be inspected within the second detection capability range, and processing the photoelectric signal with a selected required detection capability. 2. A defect inspection method for optically inspecting a defect on a surface to be inspected, wherein the surface to be inspected is scanned with a light beam,
The reflected light from the surface to be inspected is photoelectrically detected, and the required level selected from a plurality of substantially continuous detection capability ranges respectively defined based on the detection threshold value as the lower limit value and the saturation level as the upper limit value. A method characterized by processing photoelectric signals with detectability. 3. The method of claim 2, wherein the adjacent detection capability ranges overlap slightly. 4. The presence or absence of a defect is determined based on each photoelectric signal of reflected light received at a plurality of positions, and the size of the defect is detected based on the magnitude of the photoelectric signal. Or the method described in 3.