JP2001291658A - Apparatus and method for testing abnormal focus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for testing abnormal focus in reduction projection exposure without having to reduce the throughput, even if foreign matters attach to a semiconductor wafer. SOLUTION: An abnormal focus testing apparatus 3 judges whether a focus value in a shot area is normal or abnormal, before a reduction projection aligner 100 carries out reduction projection exposure. When |reference value Z0-focus value Z1 in a shot area to be exposed| >1.0 μm, the abnormal focus testing apparatus 3 determines that the focus is abnormal. The reference value Z0 is an average value of focus values from a shot area located in the outermost periphery of the semiconductor wafer 100 to a shot area one shot inside the shot area in the outermost periphery of the wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an apparatus and a method for inspecting an abnormal focus in reduced projection exposure.

[0002]

2. Description of the Related Art A reduction projection exposure apparatus is used, for example, in a lithography process in the manufacture of a semiconductor device. The reduced projection exposure will be briefly described. First, the wafer on which the photoresist is applied is fixed to the chuck by vacuum-sucking the wafer to the chuck. Next, the wafer is aligned. Next, by performing a shot, the photoresist in the shot area is exposed. Thus, the reticle pattern projected by the reduction projection lens is printed on the photoresist in the shot area. The alignment of the wafer is performed for each shot. By repeating the shot and the alignment, the photoresist is exposed over the entire surface of the wafer.

When foreign matter (dust or the like) is present between the wafer and the chuck, the shot area above the foreign matter in the photoresist on the wafer is located higher than other shot areas. To position. Therefore, if reduction projection exposure is performed in this state, a poor resolution of the photoresist in the shot area occurs, and as a result, a defect occurs in the pattern of the semiconductor device.

To prevent this, an inspection substrate, which is a substrate having a high degree of flatness, is placed on a chuck, and a displacement in the z-axis direction is inspected using an autofocus mechanism of the reduction projection exposure apparatus. If the deviation is larger than a predetermined reference, it is determined that the focus is abnormal, and a process for removing foreign matter on the chuck is performed.

[0005]

However, conventionally, a reduction projection exposure apparatus cannot be used during inspection. Therefore, there is a problem that the throughput is reduced. Conventionally, even if it is determined that there is no abnormality using the inspection substrate, if foreign matter is attached to the wafer on which the semiconductor device is manufactured,
Poor resolution occurs. In this case, if foreign matter adhered to the wafer on which the semiconductor device is manufactured adheres to the chuck, there is a possibility that all wafers from this wafer to the wafer immediately before the next inspection will have poor resolution.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus and a method capable of inspecting a focus abnormality in reduced projection exposure without lowering the throughput and even when foreign matter is attached to a wafer. It is to be.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an apparatus for inspecting an abnormal focus when a photoresist on a substrate is subjected to a reduced projection exposure, wherein the focus value of a shot area is determined for each shot of the reduced projection exposure apparatus. Means for calculating;
Means for setting, for each shot of the reduction projection exposure apparatus, a reference value for comparison with the focus value, based on a value in the optical axis direction of the projection optical system in an area serving as a reference for alignment of the substrate. And an abnormality determining unit that compares the focus value with the reference value and determines whether the focus value is abnormal.

Further, the present invention is a method for inspecting a focus abnormality when a photoresist on a substrate is subjected to a reduced projection exposure, comprising a step of calculating a focus value of a shot area for each shot of the reduced projection exposure apparatus. A reference value for comparison with the focus value is set for each shot of the reduction projection exposure apparatus, based on a value in the optical axis direction of the projection optical system in an area serving as a reference for alignment of the substrate. And comparing the focus value and the reference value,
An abnormality determining step of determining whether the focus value is abnormal;
Is provided.

[0009] The shot area is an area exposed by the shot. One shot area may correspond to one chip or a plurality of chips, or several shot areas may correspond to one chip. Further, the substrate means a wafer on which a semiconductor device is manufactured and a substrate on which a liquid crystal display device is manufactured. Also, the focus abnormality is
Misalignment between the focus value set in the reduction projection exposure apparatus and the actual focus value may occur to the extent that poor resolution of the photoresist occurs due to foreign matter such as dust and unevenness of the photoresist. It is.

According to the focus abnormality inspection apparatus and the focus abnormality inspection method of the present invention, it is determined whether or not the focus value of the shot area is abnormal while performing reduced projection exposure on the photoresist on the substrate. For this reason, it is possible to find an abnormal focus in the shot area without lowering the throughput of the reduction projection exposure apparatus. The reference value is
Since it can be set at the time of substrate alignment,
There is no need to consider variations between substrates. Therefore, it is easy to determine whether the focus value is abnormal. If it is determined that the focus value is abnormal, re-exposure is performed only on the substrate, so that the throughput can be improved.

The determination of the focus value abnormality may be made before or after the shot. In particular, when the focus value is determined to be abnormal before the shot, exposure failure can be prevented in advance.

In the present invention, the calculation of the focus value of the shot area and the setting of the reference value may be performed first or simultaneously.

Note that the focus abnormality inspection apparatus of the present invention may be incorporated in a reduction projection exposure apparatus, or may be independent of the reduction projection exposure apparatus.

In the focus abnormality inspection apparatus and the focus abnormality inspection method according to the present invention, the area includes a plurality of areas.
The values in the optical axis direction of the projection optical system in each case are obtained, and the reference value is set based on the average of those values.

According to this, since the values of the projection optical system in the optical axis direction are obtained at a plurality of locations, it is possible to eliminate the deviation of the values of the projection optical system in the optical axis direction. For this reason, it is possible to average the focus abnormality determination.

According to the focus abnormality inspection apparatus and the focus abnormality inspection method of the present invention, a value in the optical axis direction of the projection optical system in the area is obtained by auto-focusing. The reference value is obtained by averaging values in the optical axis direction of the projection optical system in a shot area one shot inside from a shot area located on the outermost periphery of the substrate. According to this, the variation in the value of the projection optical system in the optical axis direction in the wafer plane can be averaged, so that the focus abnormality can be more accurately determined. In addition, the position information of the shot area inside the above-mentioned one shot is usually used for the alignment of the wafer. Therefore, the value in the optical axis direction of the projection optical system in the area is measured at the same time as the alignment, so that the throughput can be improved.

The focus abnormality inspection apparatus and the focus abnormality inspection method according to the present invention include a unit (step) for stopping exposure based on the abnormality determination by the abnormality determination unit (step). According to this, the damage caused by the poor resolution can be limited to only the substrate.

The focus abnormality inspection apparatus and the focus abnormality inspection method according to the present invention include a unit (step) for generating warning information based on the abnormality determination by the abnormality determination unit (step). According to this, the occurrence of the focus abnormality can be immediately known. The warning information includes, for example, a warning lamp, a warning buzzer, and a warning sound.

The focus abnormality inspection apparatus and the focus abnormality inspection method of the present invention compare the focus value of the shot area with the focus value of a shot area adjacent to the shot area, and determine the focus value of the shot area. Is provided with another abnormality judging means (step) for judging whether or not is abnormal. According to this, in addition to the abnormality determination means (process), further abnormality determination means (process) is provided.
It is possible to more reliably determine the focus value abnormality of the shot area. The number of adjacent shot areas for measuring the focus value may be one, but as the number is larger,
An abnormality in the focus value of the shot area can be accurately determined. Note that the shot area adjacent to the shot area refers to a shot area having a positional relationship in contact with the shot area.

In the focus abnormality inspection apparatus and the focus abnormality inspection method of the present invention, the criterion of the abnormality determining means (step) is different from the criterion of the other abnormality determining means (step). According to this, it is possible to select the optimum criterion for each of the abnormality determining means (step) and the other abnormality determining means (step). Further, there is a mode in which the criterion of the other abnormality determining means (step) is stricter than the criterion of the abnormality determining means (step). According to this, a slight resolution defect can be prevented. That is, the other abnormality determining means (step)
Since the focus value of the shot area is compared with the focus value of a shot area adjacent to the shot area, a slight focus abnormality can be determined.

According to the focus abnormality inspection apparatus and the focus abnormality inspection method of the present invention, the exposure is stopped based on the abnormality determination by the abnormality determination means (step) or based on the abnormality determination by the another abnormality determination means (step). Means for performing According to this, the damage caused by the poor resolution can be limited to only the substrate.

The focus abnormality inspection apparatus and the focus abnormality inspection method according to the present invention provide warning information based on abnormality determination by the abnormality determination means (step) or abnormality determination by the another abnormality determination means (step). It is characterized by having means (step) for generating. According to this, the occurrence of the focus abnormality can be immediately known. Note that the warning information is as described above.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 schematically shows a reduction projection exposure apparatus 100. The reduction projection exposure apparatus 100 includes a reduction projection exposure mechanism 1 and a first projection
And a focus abnormality inspection device 3 of the embodiment. In addition,
The focus abnormality inspection device 3 of the present invention may be provided separately and independently of the reduced projection exposure device 100.

The reduction projection exposure mechanism 1 includes an illumination system 11 including a mercury lamp and the like, and a reticle 13 serving as a mask pattern.
A reduction projection lens system 15 for projecting an image from the reticle 13 onto a semiconductor wafer, an autofocus mechanism 17,
A stage 19 including a chuck 21. The reduction projection exposure mechanism 1 performs exposure of the semiconductor wafer fixed to the chuck 21 for each shot area by vacuum suction.

The focus abnormality inspection device 3 includes an auto-focus mechanism 17 and a reference value setting unit 2 for setting a reference value to be used as a reference for comparison with a focus value in a shot area.
3, an abnormality determination unit 25 that determines whether the focus value of the shot area is abnormal by comparing the focus value of the shot area with the reference value, and an abnormal lamp 27.

The auto focus mechanism 17 is a component of the reduction projection exposure mechanism 1 and a component of the focus abnormality inspection device 3. The auto-focus mechanism 17 as a component of the reduction projection exposure mechanism 1 calculates a focus value in the z-axis direction (ie, the optical axis direction of the projection optical system) of a shot area to be exposed for each shot of the reduction projection exposure mechanism 1. I do. After adjusting in the z-axis direction based on the focus value, a shot is performed. The focus value is an average value of the focus positions in the z-axis direction of the shot area to be exposed. Therefore, if there is a foreign substance or the like under the semiconductor wafer, even if the shot is performed after the adjustment in the z-axis direction, a focus abnormality occurs. Thus, the present invention is effective.

The autofocus mechanism 17 as a component of the focus abnormality inspection device 3 is used for calculating data for setting a reference value which is a reference for comparing with the focus value of the shot area in addition to the above. . The details will be described later.

Next, the operation of the focus abnormality inspection apparatus 3 will be described with reference to FIGS. FIG. 5 is a flowchart for explaining the operation of the focus abnormality inspection device 3. First, as shown in step S1, a reference value Z ₀ is set. The reference value Z ₀ is set as follows. FIG. 3 is a plan view of a semiconductor wafer to which a photoresist has been applied. The shot area to be exposed is referred to as a shot area A. Before exposing the shot area A, x of the shot areas B1 to B8 is adjusted by a positioning mechanism (not shown) to align the semiconductor wafer.
On-axis and y-axis alignment is performed. The shot areas B1 to B8 are shot areas one shot inside the shot area located on the outermost periphery of the semiconductor wafer.

At the time of this alignment, the focus values of these areas are calculated by the auto focus mechanism 17. As shown in FIG. 2, the focus value detects the position of the table in the z-axis direction when the light from the light emitting element is received by the light receiving element and the light receiving amount of the light receiving element is the maximum in the auto focus mechanism 17. It is obtained by doing.

The focus values of the shot areas B1 to B8 are sent to the reference value setting section 23. The reference value setting unit 23 calculates an average value of these focus values. This average value becomes the reference value Z ₀ . The reference value Z ₀ is sent to the abnormality determination unit 25.

The shot area B1 to shot area B8
The average value of the focus value is calculated as the reference value Z.₀And so the criteria
Value Z₀Eliminates bias in the focus value that is the basis of the calculation
be able to. For this reason, the average
Can be achieved. The reference value Z ₀Minimum required to seek
The limited shot area is shot area B1, shot area
B3, shot area B5 and shot area B7.
You.

[0032] Next, as shown in step S2, the auto-focus mechanism 17, and calculates the focus value Z ₁ of the shot region A to be exposed. Then, the focus value Z ₁
, The position of the semiconductor wafer in the z-axis direction is adjusted. The focus value Z ₁ is sent to the abnormality judging section 25. Step S2 may be performed before step S1.

Next, as shown in step S3, when M = | Z ₀ -Z ₁ |> 1.0 μm, the abnormality judging section 25 judges that the focus is abnormal. Note that this condition (M>
The value of 1.0 μm can be increased (for example, M> 1.5 μm) under conditions that are milder than 1.0 μm if no resolution failure occurs in the photoresist. Also, if a resolution failure occurs in the photoresist under this condition (M> 1.0 μm), the value of 1.0 μm can be reduced (for example, M> 0.5 μm).

If the focus is abnormal, a warning such as turning on the abnormal lamp 27 is issued as shown in step S4 to notify the operator of the abnormality. If not abnormal, return to start.

FIG. 4 shows the semiconductor wafer in a state where it has been exposed up to the shot area A. The numerical value in each shot area is the M value of each shot area. In the shot area A, since M = | Z ₀ −Z ₁ | = 1.5 μm, it is determined that the focus is abnormal. In a shot area exposed before the shot area A is exposed, M = | reference value Z ₀ −z-axis focus value of each shot area | = 0.1 μ
m, 0.2 μm, 0.3 μm or 0.4 μm,
It is not determined that the focus is abnormal.

The focus abnormality inspection device 3 of the first embodiment
Determines whether the focus value of the shot area is abnormal while performing reduced projection exposure on the photoresist on the semiconductor wafer. For this reason, it is possible to find an abnormal focus in the shot area without reducing the throughput of the reduced projection exposure apparatus 100.

[Second Embodiment] FIG. 6 is a view schematically showing a reduction projection exposure apparatus 200. Reduction projection exposure device 2
Reference numeral 00 includes a reduction projection exposure mechanism 5 and a focus abnormality inspection device 7 according to the second embodiment of the present invention. The reduction projection exposure mechanism 5 has the same configuration as the reduction projection exposure mechanism 1 of the first embodiment. Therefore, the same components are denoted by the same reference numerals and description thereof will be omitted.

The difference between the focus abnormality inspection device 7 and the focus abnormality inspection device 3 shown in FIG.
It is to have. The memory 29 stores the M value of the shot area that has already been exposed. Except for the memory 29, the focus abnormality inspection device 7 has the same configuration as the focus abnormality inspection device 3 shown in FIG. Therefore, the same components are denoted by the same reference numerals and description thereof will be omitted.

In the second embodiment, in addition to the focus abnormality determination step (step 3) of the first embodiment, another focus abnormality determination step is added to determine a focus abnormality. FIG. 7 is a flowchart of the second embodiment.

The operation of the second embodiment will be described with reference to FIGS. Steps T1, T2, and T3 are the same as steps S1, S2, and S3 of the first embodiment shown in FIG. 5, respectively. Therefore, description is omitted.

When it is determined in step T3 that the focus is abnormal, as shown in step T6, the abnormal lamp 27
A warning such as lighting of is issued to notify the operator of the abnormality.
When the focus abnormality is not determined in step T3,
Proceed to step T4. In step T4, the M value of the adjacent shot area that has been exposed is read from the memory 29.

As shown in step T5, the abnormality judging unit 2
5, N = | M value of shot area to be exposed−M value of adjacent shot area already exposed |> 0.5
μm is determined to be a focus error. Note that this condition (N
> 0.5 μm), it is possible to increase the value of 0.5 μm (for example, N> 0.7 μm) if resolution failure does not occur in the photoresist even under mild conditions. Further, if a resolution failure occurs in the photoresist under this condition (N> 0.5 μm), the value of 0.5 μm can be reduced (for example, N> 0.3 μm).

When the focus is abnormal, as shown in step T6, a warning such as turning on the abnormal lamp 27 is issued to notify the operator of the abnormality. If not abnormal, return to start.

FIG. 8 shows the semiconductor wafer in a state where it has been exposed up to the shot area A. The numerical value in each shot area is the M value of each shot area. In the shot area A of the semiconductor wafer, since M = 0.9 μm, step T3
Then, no focus abnormality determination is made. However, in relation to the shot area C1, the N value of the shot area A is | M value of shot area A−M value of shot area C1 | = | 0.9 μm−0.2 μm | = 0.7 μm.
Further, in relation to the shot area C2, the N value of the shot area A is | M value of the shot area A−M value of the shot area C2 | = | 0.9 μm−0.3 μm | = 0.6 μ.
m. Therefore, in step T5, a focus abnormality is determined.

According to the second embodiment, even a slight resolution defect can be prevented. That is, step T5 shown in FIG.
, The M value of the shot area to be exposed (this M value is
Is calculated based on the focus value of the shot area to be exposed) and M of the shot area adjacent to this shot area.
Since the value (the M value is calculated based on the focus value of the shot area and the focus value of the adjacent shot area) is compared, a slight focus abnormality can be determined.

The focus value of the shot area to be exposed and the focus value of the shot area adjacent to the shot area may be directly compared to determine the focus abnormality.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a reduced projection exposure apparatus 100 including a focus abnormality inspection apparatus 3 according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of an autofocus mechanism included in the focus abnormality inspection device 3 according to the first embodiment of the present invention.

FIG. 3 is a plan view of a semiconductor wafer including shot areas B1 to B8.

FIG. 4 is a plan view of a semiconductor wafer including a shot area A having an abnormal focus.

FIG. 5 is a flowchart illustrating an operation of the focus abnormality inspection device 3 according to the first embodiment of the present invention.

FIG. 6 is a schematic diagram of a reduced projection exposure apparatus 200 including a focus abnormality inspection apparatus 7 according to a second embodiment of the present invention.

FIG. 7 is a flowchart illustrating an operation of the focus abnormality inspection device 7 according to the second embodiment of the present invention.

FIG. 8 is a plan view of a semiconductor wafer including a shot area A having an abnormal focus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reduction projection exposure mechanism 3 Focus abnormality inspection apparatus 5 Reduction projection exposure mechanism 7 Focus abnormality inspection apparatus 11 Illumination system 13 Reticle 15 Reduction projection lens system 17 Autofocus mechanism 19 Stage 21 Chuck 23 Reference value setting section 25 Abnormality judgment section 27 Abnormal lamp 29 memory 100 reduction projection exposure apparatus 200 reduction projection exposure apparatus

Claims (22)

[Claims] 1. An apparatus for inspecting a focus abnormality when a photoresist on a substrate is subjected to reduced projection exposure, comprising: means for calculating a focus value of a shot area for each shot of the reduced projection exposure apparatus; Means for setting, for each shot of the reduced projection exposure apparatus, a reference value for comparison with the focus value, based on a value in the optical axis direction of the projection optical system in an area serving as a reference for alignment. An abnormality determination unit that compares a focus value with the reference value to determine whether the focus value is abnormal. 2. The focus according to claim 1, wherein the plurality of areas are provided at a plurality of positions, values in an optical axis direction of the projection optical system in each of the areas are obtained, and the reference value is set based on an average of those values. Abnormal inspection device. 3. The focus abnormality inspection device according to claim 1, wherein a value of the projection optical system in the optical axis direction in the area is obtained by autofocusing. 4. The focus according to claim 3, wherein the reference value is obtained by averaging values in the optical axis direction of the projection optical system in a shot area one shot inside from a shot area located on the outermost periphery of the substrate. Abnormal inspection device. 5. The focus abnormality inspection device according to claim 1, further comprising: a unit that stops exposure based on the abnormality determination of the abnormality determination unit. 6. The focus abnormality inspection device according to claim 1, further comprising a unit that generates warning information based on the abnormality determination of the abnormality determination unit. 7. The method according to claim 1, wherein the focus value of the shot area is compared with a focus value of a shot area adjacent to the shot area, and the focus value of the shot area is abnormal. A focus abnormality inspection device including another abnormality determination unit for determining whether the focus is abnormal. 8. The focus abnormality inspection device according to claim 7, wherein a criterion of the abnormality determination unit is different from a criterion of the another abnormality determination unit. 9. The focus abnormality inspection device according to claim 8, wherein a criterion of the other abnormality determining means is stricter than a criterion of the abnormality determining means. 10. The focus abnormality test according to claim 7, further comprising: means for stopping exposure based on an abnormality judgment of the abnormality judgment means or an abnormality judgment of the another abnormality judgment means. apparatus. 11. The focus abnormality according to claim 7, further comprising: a unit that generates warning information based on an abnormality determination of the abnormality determination unit or based on an abnormality determination of the another abnormality determination unit. Inspection equipment. 12. A method for inspecting a focus abnormality when a photoresist on a substrate is subjected to reduction projection exposure, comprising: calculating a focus value of a shot area for each shot of the reduction projection exposure apparatus; In a region serving as a reference for positioning, based on a value in the optical axis direction of the projection optical system, a reference value for comparison with the focus value,
A focus abnormality inspection method, comprising: a setting step for each shot of the reduction projection exposure apparatus; and an abnormality determining step of comparing the focus value with the reference value to determine whether the focus value is abnormal. 13. The focus according to claim 12, wherein there are a plurality of areas, a value in a direction of an optical axis of the projection optical system is determined for each of the areas, and the reference value is set based on an average value of the values. Abnormal inspection method. 14. The focus error inspection method according to claim 12, wherein a value of the projection optical system in the optical axis direction in the area is obtained by autofocusing. 15. The focus according to claim 14, wherein the reference value is obtained by averaging values in a direction of an optical axis of the projection optical system in a shot area one shot inside from a shot area located on the outermost periphery of the substrate. Abnormal inspection method. 16. The focus abnormality inspection method according to claim 12, further comprising a step of stopping exposure based on the abnormality determination in the abnormality determination step. 17. The focus abnormality inspection method according to claim 12, further comprising a step of generating warning information based on the abnormality determination in the abnormality determination step. 18. The method according to claim 12, wherein the focus value of the shot area is compared with a focus value of a shot area adjacent to the shot area, and the focus value of the shot area is abnormal. A focus abnormality inspection method including another abnormality determination step of determining whether the focus is abnormal. 19. The focus abnormality inspection method according to claim 18, wherein a criterion of the abnormality determination step is different from a criterion of the another abnormality determination step. 20. The focus abnormality inspection method according to claim 19, wherein a criterion in the another abnormality determination step is stricter than a criterion in the abnormality determination step. 21. The focus abnormality inspection according to claim 18, further comprising a step of stopping exposure based on an abnormality determination in the abnormality determination step or an abnormality determination in the another abnormality determination step. Method. 22. The focus abnormality according to claim 18, further comprising a step of generating warning information based on the abnormality determination in the abnormality determination step or based on the abnormality determination in the another abnormality determination step. Inspection methods.