JPH10270335A - Apparatus for focusing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus for focusing of simple structure which can be adjusted relatively easily and can precisely focus even on a substrate surface with steps. SOLUTION: An apparatus for focusing including a focus sensor 5 irradiating a substrate 4 with sensor light, a focus detector 6 receiving the reflected light of the sensor light irradiated by the focus sensor 5, a focus calculation unit 7 detecting the height of thickness direction of the substrate 4 with the quantity of the reflected light of the sensor light received by the focus detector 6 and calculating the focal position is provided with one focus sensor 5, one focus detector 6, and even a means for scanning irradiation position scanning the irradiation position of the focus sensor 5 in the irradiated area in a grid pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing apparatus in a lithography process or the like, and more particularly to a focusing apparatus having a high average height detection accuracy.

[0002]

2. Description of the Related Art In a lithography process for forming a resist pattern on a semiconductor substrate, when a circuit pattern is exposed and transferred to a resist layer on the semiconductor substrate, a focus of a transferred image is generally formed accurately on the surface of the semiconductor substrate. The configuration as shown in FIG. 1 is employed. In this configuration, sensor light is emitted from the focus sensor 5 to the semiconductor substrate 4, the reflected sensor light is detected by the focus detection element 6, and a focus detection signal is obtained as positional information in the Z-axis direction (optical axis direction). The best focus is calculated by the focus calculation unit 7, the calculation result is transmitted to the Z-axis stage 3 on which the semiconductor substrate 4 is mounted, and the Z-axis actuator is driven in the optical axis direction to transfer the focus of the transferred image and the semiconductor substrate 4. Match with the surface.

[0003] At this time, the surface of the semiconductor substrate 4 is not a completely flat surface, but the surface of the semiconductor substrate 4 becomes a surface having irregularities as the process proceeds. Therefore, it has been somewhat difficult to obtain the best focus with the conventional fixed focus sensor.

[0004] For example, a problem is raised in the sample shown in FIG. In FIG. 2, the Z-axis is enlarged and deformed so as to be intuitively understandable. This sample shows a structure per shot (a region irradiated by one exposure). A portion having the surface at the highest position with respect to the scribe surface, a scribe surface and this A portion It is composed of a portion B having a surface at an intermediate height from the surface.

Examples of the irradiation position of the sensor when such a semiconductor substrate is focused by a conventional method are shown in Conventional Examples A to C of FIG. The results of the number of detections on the sample in the case of performing the above are shown in Conventional Examples A to C of FIG.

3 and 4, conventional example A detects one point at the center of the shot, conventional example B detects five points on the diagonal of the shot, and conventional example C detects five points at the shot center and four corners. This is the case when detecting.

As shown in FIGS. 3 and 4, the conventional focus sensor detects the focus at a predetermined limited number of points. The average focus height is far from its ideal value. this is,
For example, in the sample shown in FIG. 2, the focus information corresponding to the portion A is not obtained at all in the conventional example A or the conventional example B, and only one point is obtained in the conventional example C. This is because the height is different from the ideal value.

When the circuit pattern is exposed and transferred using the best focus values which are far apart from each other,
As a matter of course, defocus occurs, and the entire surface within the shot cannot be transferred with high dimensional accuracy, resulting in an increase or decrease in dimension.

An increase in the numerical aperture of a lens of a recent exposure apparatus,
Since the focus margin tends to be narrowed due to the complexity of the semiconductor substrate and an increase in the level difference of the semiconductor substrate, it is necessary to obtain a best focus as close as possible to an ideal value in order to obtain a pattern with good dimensional accuracy.

As a method of solving such a problem and performing high-precision focus control, for example, Japanese Patent Laid-Open No.
In step 06, the height at a plurality of fixed autofocus points is determined with the semiconductor substrate fixed, and further the average height of the fixed position is determined by scanning the semiconductor substrate, and the value of the height information obtained from these is determined. Based on this, it is set which step surface should be focused in the exposure process that is currently being performed.

However, in this method, since a plurality of sets of focus sensors and focus detection elements are used, the device configuration is complicated, adjustment is not easy, and it cannot be said that focus detection for one shot is reliably performed. There are problems such as.

[0012]

As described above, the conventional focusing apparatus cannot detect an accurate focus on a substrate having a step, and the apparatus configuration is complicated and adjustment is complicated. was there.

It is an object of the present invention to improve this point and to realize a focusing apparatus which is a simple apparatus which is relatively easy to adjust and which can perform accurate focusing even on a substrate surface having a step.

[0014]

In order to achieve the above object, the present invention provides a sensor light irradiating means for irradiating a sensor light onto a substrate, and receiving a reflected light of the sensor light irradiated by the sensor light irradiating means. A focusing light detecting means for detecting a height in the thickness direction of the substrate from a reflected light amount of the sensor light received by the light receiving means and calculating a focal position, wherein the sensor light irradiating means is provided. And the reflected light receiving means are each provided one by one, and are provided with irradiation position scanning means for scanning the irradiation position of the sensor light irradiation means in a grid pattern within the irradiation target area.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a focusing apparatus according to the present invention will be described in detail with reference to the accompanying drawings. FIG.
FIG. 1 is a block diagram showing a schematic configuration of a projection exposure apparatus to which an embodiment of the present invention is applied.

In FIG. 1, reference numeral 1 denotes a reticle which is a unit photomask which is illuminated with illumination light from an illumination light source and transmits the illumination light to form a transmission image. And Z which is the direction of the optical axis
A Z-axis stage that moves in the axial direction; 4 a target semiconductor substrate fixed to the Z-axis stage 3; 5 a focus sensor serving as a light source for focus detection for inputting light onto the semiconductor substrate from the side of the reduction projection lens; 6 is a focus detection element that receives reflected light from the semiconductor substrate and detects the amount of the reflected light;
Reference numeral 7 denotes a focus calculation unit including a CPU for taking in an output from the focus detection element 6, calculating a focus position, and moving the Z-axis stage 3 to adjust the focus.

In the first embodiment of the present invention, first, an irradiation spot having a diameter of 1 mm is step-and-repeat on a semiconductor substrate 4 at intervals of 1 mm using a focus sensor 5 having an irradiation spot of 1 mm. Therefore, 400 points are scanned in a grid in one shot (the area irradiated by one exposure) to detect the focus of the entire surface in the shot. The position of the sensor in this case is shown in FIG.
FIG. 4 shows Example A of the present invention in FIG. 4 showing the number of detections and the distribution when focus detection was performed on the sample in FIG.

The scanning method of the focus sensor 5 may be a method of moving the semiconductor substrate 4 by step-moving an XY stage (not shown) provided further below the Z-axis stage on which the semiconductor substrate 4 is mounted at intervals of 1 mm. A method is adopted in which the irradiation angle of the light from the focus sensor 5 is sequentially changed, and thereby the sensor light is moved on the semiconductor substrate 4 at intervals of 1 mm. By such a method, the focus information is the sample of FIG.
96 points out of 0 points and 304 points out of 400 points in the B portion are obtained, and a calculated average height close to the ideal value is obtained.

According to this embodiment, the target area is scanned in a grid pattern using one set of the focus sensor 5 and the focus detecting element 6, so that the element can be easily adjusted with a relatively simple configuration. In addition, it is possible to realize a focusing device capable of performing accurate focusing even on a substrate surface having a step.

Further, since the spot diameter of the focus sensor 5 is set to be equal to the grid interval for scanning by the XY stage, the scanning becomes congested, an error occurs in the detection value, and the focusing accuracy deteriorates. Accurate focusing is possible without taking longer than necessary.

Further, the scanning can be performed by moving the stage on which the substrate is placed in a plane in the X and Y directions or by changing the irradiation angle of the sensor light, so that selection according to the situation is possible. When the stage is available, the XY stage is used, and when the XY stage is not available, high-speed scanning can be performed relatively easily by changing the irradiation angle.

As described above, this embodiment has an advantage that high-accuracy detection can be realized by a relatively simple device, but since scanning must always be performed, it takes a longer time to detect as compared with the conventional example. There are drawbacks.

In the second embodiment of the present invention, an irradiation spot having a diameter of 2 mm is step-and-repeated at 4.5 mm intervals on a semiconductor substrate 4 using a focus sensor 5 having an irradiation spot diameter of 2 mm. 2 in one shot
5 points are scanned in a grid and this 25
Detects point focus. Further, the position of the irradiation point of the sensor in this case is shown in Example B of the present invention in FIG. 3, and the number of detections and the result of the distribution when the focus detection of the sample in FIG. This is shown in Invention Example B. FIG. 5 shows an arrangement state of sensor irradiation spots performed on the sample of FIG. 2 in the present embodiment.

As a method of scanning the focus sensor 5, a method is used in which the XY stage (not shown) provided further below the Z-axis stage on which the semiconductor substrate 4 is mounted is moved stepwise at intervals of 4.5 mm to move the semiconductor substrate 4. Alternatively, the irradiation angle of the light from the focus sensor 5 is sequentially changed, so that the sensor light is transmitted on the semiconductor substrate 4.
There is a method of moving at intervals of 5 mm.

As shown in the present invention example B of FIG. 4 and FIG. 5, in this method, the focus information of 6 points out of 25 points in the part A is changed to 19 points out of the 25 points in the part B.
Since the focus information of the point is obtained and this ratio is equal to that of the example A of the present invention, the calculated average height can be obtained close to the ideal value.

This method uses a set of focus sensors 5
The average height close to the ideal can be calculated using the focus detection element 6 and the focus detection element 6, and highly accurate detection can be realized by a relatively simple device. Further, since the spot diameter of the focus sensor 5 is set smaller than the grid interval for scanning by the XY stage, the scanning is congested, an error occurs in the detection value, and the focusing accuracy is deteriorated. It does not take much time as described above, and the number of scanning points is smaller than in the case of Example A of the present invention, so that the time required for scanning can be shortened.

In the above description, the sample shown in FIG. 2 has been described as a sample of the semiconductor substrate 4, but it is needless to say that the target substrate is not limited to this. Since not only the average height but also the height distribution can be accurately obtained, the height of the plane to be processed can be accurately calculated from the distribution ratio.

In the present invention, since the height of the processed surface can be accurately measured by improving the detection accuracy of focusing, it is not necessary to measure the height of each shot, and the focus information of adjacent shots is referred to. Exposure transfer is possible. Therefore, since it is not necessary to focus all shots in the wafer, the processing can be performed at a correspondingly high speed, and the throughput can be improved.

The present embodiment is described with reference to FIGS.
Compared with Conventional Example B (hereinafter referred to as Conventional Example), the following points are different.

1) Number of Used Focus Sensors In the present embodiment, only one set of a focus sensor and a focus detection element is used. Since scanning is performed, a plurality of sets of focus sensors and focus detection elements are required. As described above, since a plurality of sets of the focus sensor and the focus detection element are used, it is complicated to adjust the sensor sensitivities of the plurality of sensors to the same value in the conventional example, but in the present embodiment, the focus sensor and the focus detection Since only one set of elements is used, there is no need to adjust the sensor sensitivity.

2) Scanning area As shown in the conventional example B of FIGS. 3 and 4, when sampling is performed using a five-point focus sensor arranged diagonally, the sensor is arranged diagonally, and as shown in FIG. As shown in (2), the focus sensor extends to the left and right shots, and the scan area to be sampled is not strictly per shot. Further, when focusing the outermost shot, one side scans an unprocessed wafer edge, so that a focus error may occur, and as a result, a focus value of a shot to be exposed may not be obtained. In this regard, since the present invention can uniformly scan one shot, the sampled focus information is accurately standardized within one shot, and an accurate focus value can be obtained.

3) Scanning Method In the present invention, as a method for scanning the focus sensor, in addition to the method of moving the stage on which the semiconductor substrate is mounted to scan, the irradiation angle of the focus sensor is different from the conventional example. Since a variable method is also proposed, it is possible to select according to the situation.

As described above, in the present invention, the one-shot irradiation target area on the semiconductor substrate is scanned in a grid pattern using one set of the focus sensor 5 and the focus detection element 6, so that the configuration of the apparatus is comparatively small. It is simple and easy to adjust the element, and accurate focus information can be obtained even on a substrate surface having a step. Therefore, by using the focusing apparatus of the present invention, highly accurate processing of an integrated circuit or the like can be performed on a semiconductor substrate.

[0034]

As described above, in the present invention, the target area is scanned in a grid pattern by one set of sensor light irradiating means and reflected light receiving means, so that the element can be adjusted with a relatively simple structure. It is possible to realize a focusing device that is easy and can perform accurate focusing even on a substrate surface having a step.

Further, since the spot diameter of the sensor light irradiating means is equal to or smaller than the lattice spacing scanned by the irradiation position scanning means, the scanning becomes congested and the focusing accuracy deteriorates. It does not take longer than necessary.

Furthermore, since the accuracy of focusing detection is improved, it is possible to perform exposure transfer with reference to focus information of adjacent shots. Therefore, since it is not necessary to perform focusing for all shots in the wafer, processing can be performed at a correspondingly high speed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a projection exposure apparatus to which the present invention is applied.

FIG. 2 is a configuration diagram of an example of a sample for acquiring focus information.

FIG. 3 is an explanatory chart showing irradiation positions of sensors, the number of sensors, and the like in the embodiment of the present invention and a conventional example.

FIG. 4 is an explanatory chart showing the number of detections on the sample shown in FIG. 2 in the embodiment of the present invention and the conventional example.

FIG. 5 is a diagram showing an arrangement state of sensor irradiation spots with respect to the sample of FIG. 2 in the second embodiment of the present invention.

FIG. 6 is a diagram showing a sampling position for a shot when a conventional five-point focus sensor arranged obliquely is used.

[Explanation of symbols]

1 reticle, 2 projection lens, 3 Z-axis stage, 4 semiconductor substrate, 5 focus sensor, 6
... Focus detection element, 7... Focus calculation unit.

Claims (5)

[Claims] 1. A sensor light irradiating means for irradiating a sensor light onto a substrate, a reflected light receiving means for receiving a reflected light of the sensor light irradiated by the sensor light irradiating means, and the sensor receiving the reflected light by the light receiving means A focusing device having a calculating means for detecting a height in the thickness direction of the substrate from a reflected light amount of light and calculating a focal position, wherein the sensor light irradiating means and the reflected light receiving means are each constituted by one each. A focusing apparatus comprising: an irradiation position scanning unit that scans an irradiation position of the sensor light irradiation unit in a lattice shape in an irradiation target area. 2. The method according to claim 1, wherein a spot diameter of the sensor light irradiating means is equal to a grid interval scanned by the irradiation position scanning means.
2. The focusing device according to claim 1, wherein the distance is set smaller than the lattice spacing. 3. The focusing apparatus according to claim 1, wherein said irradiation position scanning means performs scanning by moving a stage on which said substrate is mounted in a plane in XY directions. 4. The focusing apparatus according to claim 1, wherein the irradiation position scanning unit performs scanning by changing an irradiation angle of the sensor light of the sensor light irradiation unit. 5. The focusing device according to claim 1, wherein a plurality of unit elements arranged in a plane are dealt with by using a focusing value for an adjacent unit element. apparatus.