JPH0760251B2 - Automatic focusing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing method applied to a projection printing apparatus for manufacturing semiconductor circuit elements such as IC, LSI, VLSI, etc. The image and the whole image are formed on the wafer, and the mask and the wafer are set at predetermined positions with respect to the imaging optical system.
The present invention relates to an automatic focusing method for performing accurate positioning.

[Description of Prior Art] The minimum dimension of the constituent pattern of a semiconductor circuit element is miniaturized, and therefore, high resolution is required also in a projection printing apparatus. In order to obtain high resolution, the mask and the wafer must be accurately aligned with the optical reference plane positions of the imaging optical system that are conjugate with each other.

For this alignment, an air microsensor (hereinafter referred to as an air sensor) or the like is used as a measuring system for the distance to the wafer, and a motor, a piezo (piezoelectric element) or the like is used as a driving system. In particular, the drive system may include a coarse drive system having a large drive amount and a fine drive system having a small drive amount but high drive accuracy.

FIG. 1 is a cross-sectional view of a main part of a projection printing apparatus which is a conventional example and is also an application example of the present invention. In the figure, 1 is a reduction projection lens, 2 is a nozzle of an air sensor, 3 is a pulse motor, 4 is a driving force transmission mechanism for converting and transmitting the driving force of the pulse motor 3 to the driving force in the moving direction of the Z stage 6, and 5 is a driving force transmission mechanism. It is a piezo. The pulse motor 3 is a coarse movement system, and a piezo 5
Is used as a fine movement system, and the Z stage 6 and the wafer 7 can be moved in the optical axis direction of the reduction projection lens 1 by driving them. The air sensor nozzle 2 is located on the wafer 7 and measures the distance between the wafer 7 and the reduction projection lens 1. Based on this measurement value, the drive amount in the lens optical axis direction is calculated so that the mask and the wafer are at the mutually conjugate optical reference plane positions of the imaging optical system. The amount is distributed to the pulse motor 3 as a coarse movement system and the piezo 5 as a fine movement system to drive them respectively, and the Z stage 6 is moved.

[Problems to be Solved by the Invention] Here, in order to accurately align the wafer with the image plane of the projection optical system, the nozzle mounting error of each air sensor and the relative displacement amount between each air sensor ( Offset) must be measured in advance and their relative offsets must be reflected in the measured value of the air sensor.

However, in the past, the wafer was actually baked,
As a result, these offsets were measured. For this reason, it takes time and labor, and an error in offset measurement is caused, so that there is a drawback that accurate alignment cannot be performed as a whole focusing system.

In view of the above-mentioned conventional problems, the present invention eliminates the need to actually print and evaluate a wafer when measuring a relative displacement amount, that is, an offset of a position detection means such as the air sensor. It is an object of the present invention to provide an automatic focusing method that automatically calculates these offsets only from the measurement values of the detection means and enables highly accurate positioning.

[Means and Actions for Solving Problems] In order to achieve the above object, the automatic focusing method of the present invention is such that a flat plate-like object such as a wafer is stepwise moved in the horizontal direction, and after each step movement, the object plane In the automatic focusing method in which each region is sequentially matched with the image plane of the projection optical system, the relative displacement of a plurality of position detection means for measuring the distance between the image plane of the projection optical system and the flat object surface in advance. It is characterized in that the amounts are automatically taken in and the amounts of these deviations are reflected in the alignment operation.

As a result, it is possible to automatically calculate the relative displacement amount between the position detecting means, which has been conventionally measured by printing the wafer, and to improve the alignment accuracy.

This relative shift amount can be calculated, for example, by sequentially measuring the distance by each position detecting means for an appropriate point on the flat object surface and taking the difference between the measurement results.

Description of Embodiments Embodiments of the present invention will be described below with reference to the drawings. The present invention can be applied to the projection printing apparatus as shown in FIG.

FIG. 2 shows a top view of the reduction projection lens 1, the nozzle of the air sensor, and the wafer 7. 12-15 is a reduction projection lens 1
The nozzles of the four air sensors attached to the wafer measure the distance to the surface of the wafer 7. If the distances from the end surface of the reduction projection lens 1 measured by the nozzles 12 to 15 to the surface of the wafer 7 are d1, d2, d3 and d4, respectively, the average distance is (d1 + d2 + d3 + d4) / 4. Assuming that the distance between the predetermined image plane position of the reduction projection lens 1 and the end face of the reduction projection lens 1 is d0, the amount Δd of Δd = d0− (d1 + d2 + d3 + d4) / 4 is required to move the wafer to the image plane position. Only the wafer 7 needs to be moved. As a result, the average plane of the wafer becomes the image plane position.

FIG. 3 shows the shot layout on the wafer 7 and the arrangement of the reduction projection lens 1 and the air sensor nozzles 12 to 15 when printing with a step-and-repeat type projection exposure machine. In the figure, 16 indicates a shot layout represented by a matrix, and a hatched portion S in the figure indicates a shot to be printed at present.

In this embodiment, the relative offsets to be reflected on the measured values d1, d2, d3 and d4 of the air sensor nozzles 12 to 15 are automatically calculated.

Next, the flow of processing for automatic offset calculation will be described with reference to the flowchart in FIG. 4 and the diagram showing the movement of the stage in FIG.

When the offset automatic capture is started (step 301), the stage first moves so that the optical axis is located at P1 in FIG. 5 (step 302). Then, the air sensor 15 measures at that position, and the measured value S _U is stored in a memory (not shown) (step 303). This measured value S _U becomes the measured value at the position T in FIG.

Next, the stage is moved so that the optical axis is located at P2 (step 304). The position of P2 is such that the air sensor nozzle 12 now coincides with the position T where the air sensor nozzle 15 was located when the optical axis was previously located at P1. At the position T, the air sensor nozzle 12
And measure the measured value S _L in the memory (step
305).

Similarly, the stage is moved to the position P3 so that the air sensor nozzle 13 coincides with the position T (step 306). And this time, measure with the air sensor nozzle 13 at that position,
The measured value _SD at the position T is stored in the memory (step 307). Further, the stage is moved to the position P4 so that the air sensor nozzle 14 coincides with the position T (step
308). The air sensor nozzle 14 measures at that position, and the measured value S _R at that position T is stored in a memory (step
309).

The measured values S _U , S _L , S _D , S _R are measured values when the air sensor nozzles are located at T, and the difference between these measured values is a relative offset between the nozzles. Therefore, the offset of each nozzle based on S _U is calculated as follows.

O _LU = S _L -S _U O _DU = S _D -S _U O _RU = S _R -S _U (step 310) With the above, the automatic calculation of the offset is completed (step 31).
1). These offsets are reflected in the following manner when aligning each shot area with the image plane of the projection optical system.

That is, in FIG. 2, the average distance is {d1 + (d2 + O _LU ) + (d3 + O _DU ) + (d4 + O _RU )} / 4 for the measured values d1, d2, d3, d4 measured by the nozzles 12 to 15. It is calculated.

According to this embodiment, since the relative offset between the air sensors is accurately calculated automatically and reflected in the subsequent alignment, it is not necessary to actually print the wafer to measure the offset, and the projection printing apparatus can be used. It is also possible to avoid a decrease in throughput.

Although the air sensor is used as the position detecting means in the embodiment of FIG. 1, the position detecting means is not limited to this, and any means for measuring the distance to the wafer can be used instead. Further, a DC motor or a piezo having a long stroke may be used in place of the pulse motor 3, and a pulse motor having a higher driving accuracy may be used in place of the piezo.

[Effects of the Invention] As described above, according to the present invention, the relative displacement of the plurality of detection units is based on the measurement values obtained by moving the wafer and measuring the same position on the wafer with the plurality of position detection units. Since the amount (offset) is calculated, this offset is not affected by the state of the wafer (unevenness, inclination). Therefore, by using this offset, high alignment accuracy can be always ensured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reduction projection lens and an air sensor portion of a projection printing apparatus which is a conventional example and is also an application example of the present invention, and FIG. 2 is a top view of a reduction projection lens, a nozzle of the air sensor, and a wafer. FIG. 3 is a diagram showing a shot layout on a wafer and arrangement of reduction projection lenses and air sensor nozzles. FIG. 4 is a flowchart showing a processing procedure of offset automatic capture. FIG. 5 is a stage at the time of offset automatic capture. It is a figure which shows the movement of. 1 ... Reduction projection lens, 2, 12 to 15 ... Air sensor nozzle, 3 ... Pulse motor, 4 ... Driving force transmission mechanism, 5 ... Piezo, 6 ... Z stage, 7 ... Wafer.

Claims (2)

[Claims] 1. An imaging plane and an object using a plurality of position detecting means for measuring predetermined positions different from each other on the object plane to measure a distance between the imaging plane of the projection optical system and the object plane. In an automatic focusing method for matching surfaces, by moving the object surface in a direction orthogonal to the optical axis of the projection optical system, each of the plurality of position detection means measures the same position on the object surface. A first measuring step; a step of calculating a relative deviation amount of a plurality of position detecting means from the measurement result of the first measuring step; and a second step of measuring the predetermined location by the plurality of position detecting means. A measuring step, and a step of causing the image forming surface and the object surface to coincide with each other, based on position information calculated by reflecting the relative deviation amount on the measurement result of the second measuring step. Automatic focusing characterized by having Combined method. 2. The automatic focusing according to claim 1, wherein the step of calculating the relative positional deviation amount includes a step of calculating a difference between the measurement results of the first measuring step. Method.