JP2002169266A - Mask, imaging characteristic measuring method and exposure method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mask capable which is adequately usable for measuring improving characteristics of a projection optical system. SOLUTION: First and third patterns (LS1 and LS3) including line patterns extending in a first direction and second and fourth patterns (LS2 and LS4) including line patterns extending in a second direction are formed on a pattern surface (PA) of a mask substrate (42) constituting the mask (RT). The first and second patterns and the third and fourth patterns which are formed to the same line widths make pairs, respectively. Accordingly, the exposure of the first time by which, for example, the respective patterns are transferred to the substrate and the exposure of the second time by which at least the one patterns are transferred in superposition on the transferred images of the patterns making a pair are carried out, by which the images of the rhombic marks having the same resolution at any of their peripheral edges are formed in the parts overlapping on each and therefore the various imaging characteristics of the projection optical system can be measured by measuring the prescribed lengths of the images.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask, an imaging characteristic measuring method, and an exposure method, and more particularly, to a mask suitable for use in measuring the imaging characteristic of a projection optical system of an exposure apparatus, and the mask. The present invention relates to an imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system using the method, and an exposure method for performing exposure using a projection optical system whose imaging characteristic has been measured by the imaging characteristic measuring method.

[0002]

2. Description of the Related Art Conventionally, in a lithography process for manufacturing a semiconductor device, a liquid crystal display device, or the like, a pattern formed on a mask or a reticle (hereinafter, collectively referred to as a “reticle”) is resisted through a projection optical system. There is used an exposure apparatus that transfers a wafer or a glass plate or the like onto which a substrate or the like is applied (hereinafter, also appropriately referred to as a “wafer”). In recent years, as an apparatus of this kind, from the viewpoint of emphasizing throughput, a step-and-repeat type reduction projection exposure apparatus (so-called “stepper”) or a step-and-scan type scanning type apparatus which is an improvement of this stepper has been used. 2. Description of the Related Art Sequentially moving projection exposure apparatuses such as exposure apparatuses are relatively frequently used.

In this type of exposure apparatus, the accuracy of a projection image greatly changes due to a focus shift during exposure (transfer of a reticle pattern onto a wafer) or aberration of a projection optical system. A technology for accurately measuring the focus position and aberration is required.

As a method of measuring the best focus position of the above-mentioned projection optical system, for example, after performing trial printing on a wafer coated with a resist, the wafer is developed and the line width of a linear pattern is measured, for example. The best focus position and the best exposure dose are measured by using an SEM (scanning electron microscope) and compared with the designed line width value, or by utilizing the fact that the line width becomes the smallest under certain conditions. There are techniques for measuring quantities.

[0005] For example, in the case of a stepper, in trial printing, exposure is performed by changing the exposure dose by a fixed amount while keeping the focus value constant with respect to the arrangement of shot areas on the wafer in the horizontal direction (x direction). In the vertical direction (y direction) of the shot array, exposure is performed while the exposure amount is kept constant and the focus value is changed by a fixed amount (for example, 0.25 μm). Then, the line width of the linear resist pattern in each shot area formed after development is measured immediately, and when the resist pattern is line and space, the line width is the largest among shots of the same exposure amount. The focus position when exposing the reduced shot area and the exposure dose at which the line width becomes a predetermined amount in the shot at the focus position are determined as the best focus position and the best exposure dose, respectively.

As for the aberration of the projection optical system, it is necessary to measure the pattern transferred onto the wafer again at the best focus position and the best exposure dose determined as described above to define the amount of aberration. there were.

However, in the above conventional measuring method,
For example, after transferring a pattern formed on a test reticle to a resist layer such as a wafer, the distance between parallel edges of the resist image of the pattern is measured by SEM, so that SEM focusing must be strictly performed. The measurement time per hit is very long, and it takes several hours to several tens of hours to measure many points.

In addition, there is also a disadvantage that a manufacturing error of a pattern formed on a test reticle, particularly an influence due to an error of a pattern line width, is directly reflected on a measured value of a resist pattern.

[0009] In order to improve such inconvenience, the present applicant has
A linear pattern intersecting at a predetermined angle is sequentially transferred onto a wafer by double exposure, and after developing the wafer, a resist image of a wedge mark is formed on the wafer, and the length of the resist image is measured by an exposure apparatus. (For example, a so-called LSA (Laser Step Alignment) that detects a diffracted light or the like by relatively scanning a laser beam and a resist image.
and a method for determining exposure conditions based on the measurement results (JP-A-2-301).
No. 12, etc.). According to the invention described in this publication,
The processing speed is high, and there is an effect that it is hardly affected by manufacturing errors of a test reticle or the like.

[0010]

However, when a resist image of a wedge mark is formed on a wafer by double exposure using a linear pattern, the linear pattern used for the first exposure and the second pattern are used. When both the linear pattern used for exposure and the isolated pattern are isolated lines, only a single wedge mark resist image can be obtained, and the types of aberrations obtained based on the measurement results of the resist image are limited. It becomes a target. That is, it is difficult to measure coma aberration and the like. In this case, there is also a problem that the S / N ratio is small.

On the other hand, the linear pattern used for the first exposure and the linear pattern used for the second exposure are both line-and-space (hereinafter, referred to as "line and space").
In the case of a pattern (abbreviated as "L / S"), a resist image of a row of wedge marks arranged at predetermined intervals in a predetermined direction is obtained, and coma aberration and the like can be obtained by measuring the resist image. And the S / N ratio is also sufficient.

However, in this case, depending on the setting of the length of each line pattern constituting the original L / S pattern, as shown in FIG. 10, in addition to the target wedge mark MG on the wafer, An extra pattern S such as a part of a wedge mark is often formed. When the resist image as shown in FIG. 10 is measured by the LSA sensor, there is a disadvantage that the above-mentioned extra pattern S becomes a factor of noise and lowers the measurement accuracy.

The present invention has been made under such circumstances, and a first object of the present invention is to provide a mask which can be suitably used for measuring the imaging characteristics of a projection optical system.

It is a second object of the present invention to provide an imaging characteristic measuring method capable of accurately and efficiently measuring the imaging characteristic of a projection optical system.

A third object of the present invention is to provide an exposure method capable of improving the overlay accuracy.

[0016]

According to a first aspect of the present invention, there is provided a first pattern (LS1) including at least one line pattern having a first line width extending in a first direction; A second angle θ (0 ° <θ <180 °)
A second pattern (LS2) paired with the first pattern, the pattern including at least one line pattern having the first line width extending in a first direction, and at least one line pattern having a second line width extending in the first direction; And a fourth pattern (LS4) that includes at least one line pattern of the second line width extending in the second direction and forms a pair with the third pattern. Is a mask provided with a mask substrate (42) formed on the pattern surface (PA) as one of a light transmitting portion and a light shielding portion so as not to overlap with each other.

Here, "angle" means the size of the angle formed by the directions, and is a concept that does not include the angle direction (positive or negative). In this specification, as such a concept,
The vocabulary "angle" is used.

Using this mask, a projection exposure apparatus
Consider the case where exposure is performed twice. For example, by the first exposure, the first to fourth patterns are respectively transferred onto the substrate, and then, by the second exposure, at least one of the first to fourth patterns is transferred to the substrate. The pattern is superimposed and transferred on a transfer image of a pattern forming a pair with the pattern.

Thus, at least one of the overlapping portion between the transferred images of the second pattern and the first pattern and the overlapping portion between the fourth pattern and the third pattern are provided with a pair of rhombic marks having a diagonal angle of θ. Image (including latent image, resist image, etc.)
Is formed.

Here, by the second exposure, the rhombic mark image is formed on both the overlapped portion between the transferred images of the second pattern and the first pattern and the overlapped portion between the fourth pattern and the third pattern. Consider the case where a latent image (such as a latent image) is formed. In this case, since the images of all the rhombic marks formed on the substrate are formed by double exposure of a pair of line patterns, the same resolving power is obtained at any point on the periphery of the rhombus. Therefore, in the image of each rhombic mark, for example, the length of the longer diagonal is measured, and the line width can be calculated by performing a proportional calculation based on the result of the length measurement. Various imaging characteristics of the projection optical system can be measured.

In this case, the measurement of the length of the diamond mark may be performed on the latent image formed on the substrate without developing the substrate, or the image of the diamond mark may be formed. After the developed substrate is developed, the process may be performed on a resist image formed on the substrate or an image (etched image) obtained by etching the substrate on which the resist image is formed. In any case, the measurement is performed on at least two similar rhombic marks formed on the substrate and having an angle θ as a set of diagonals. In this case, for example, the length of the longer diagonal line of each image is determined, for example, by the alignment detection system (LSA) of the exposure apparatus.
System or an image processing type alignment detection system for forming an image of an alignment mark on an image sensor, so-called F
The measurement may be performed using an IA (Field Image Alignment) system or the like. Even in this case, various imaging characteristics of the projection optical system can be measured. Here, particularly when the substrate is developed to obtain a resist image of a rhombic mark, or when the substrate on which the resist image is formed is etched to obtain an etched image, each of these images is a pair of diagonals. Are the same angle θ, and if θ is an angle larger than a certain degree, it is possible to effectively suppress the occurrence of problems such as resist at the sharp tip portion. Further, for example, even if the first and second patterns and the third and fourth patterns have at least different line widths, the diagonal of the rhombic mark such as the resist image is equal. Therefore, for the same reason as described above, even though the line widths of the original line patterns are different, only the same degree of inconvenience such as resist occurs in any image. Therefore, unlike the case where the angle θ is changed in accordance with the change in the line width, any resist image and etching image are similarly affected by the process, so that an image having the intended shape can be obtained.

In this case, the positional relationship between the first and second patterns may be as follows.
The positional relationship between the third and fourth patterns may be the same.

In each of the masks according to the first and second aspects, as in the invention according to the third aspect, the first pattern and the second pattern each include a plurality of lines having the first line width. The pattern may be a line and space pattern that is periodically arranged. Here, for example, the arrangement direction (the third direction) of the first pattern and the second pattern can be matched. In this case, the third direction may be a direction that intersects the first direction and the second direction at an angle α (0 ° <α <180 °, α ≠ 90 °).

In this case, as in the invention according to claim 4, the third pattern and the fourth pattern are each a line in which a plurality of line patterns having the second line width are periodically arranged. It can be an and space pattern. Here, for example, both the third pattern and the fourth pattern can be arranged in the third direction.

In this case, the arrangement cycle (pitch) of all the line patterns of the first to fourth patterns may be the same, but as in the invention of claim 5, the first line width and the second 2 is the same as the line width, and the first and second patterns and the third and fourth patterns may have different arrangement periods.

In each of the masks according to claims 3 to 5, as in the invention according to claim 6, for removing a pattern corresponding to at least one of the line and space patterns constituting the first to fourth patterns. The pattern (46) may be further provided.

According to a seventh aspect of the present invention, an angle α (0 ° <α <180 °) with respect to the first direction such that a plurality of line patterns having a line width w extending in the first direction has an interval w ′. ,
(α ≠ 90 °), first partial patterns (LS1, LS3, LS5) arranged along a predetermined arrangement direction intersecting with each other;
The angle α () with respect to the second direction is set so that a plurality of line patterns having a line width w extending in the second direction and forming an angle θ (0 ° <θ <180 °) with the first direction have an interval w ′. 0 °
<Α <180 °, α ≠ 90 °) The second partial patterns (LS2, LS) arranged along the array direction intersecting with each other
4, LS6) is provided with a mask substrate formed as one of a light transmitting portion and a light shielding portion so that they do not overlap each other, and the length y of each line pattern is w / tan (θ / 2) ≦ y <{2w ′ / sin θ + w ·
A mask characterized by satisfying tan (θ / 2)｝.

Here, the line width w and the interval w 'may or may not have the same value.

Using this mask, a projection exposure apparatus
Consider the case where exposure is performed twice. For example, by the first exposure, the first and second partial patterns are respectively transferred onto the substrate, and then, by the second exposure, for example, the second partial pattern is superimposed on the transfer image of the first partial pattern. Transfer. As a result, at the overlapping portion between the transferred images of the second partial pattern and the first partial pattern, at least two rhombic mark images (latent image, resist image, etc.) of substantially the same shape having a pair of diagonal angles of θ Is formed on the substrate. In this case, since an unnecessary image other than the rhombic mark image that causes noise is not formed on the substrate, by measuring the length of, for example, the longer diagonal line of each rhombic mark image, S / S Good measurement of N ratio becomes possible,
By using this measurement result, it is possible to accurately measure various imaging characteristics of the projection optical system.

In this case, the measurement of the length of the diamond mark may be performed on the latent image formed on the substrate without developing the substrate, or the image of the diamond mark may be formed. After the developed substrate is developed, the process may be performed on a resist image formed on the substrate or an image (etched image) obtained by etching the substrate on which the resist image is formed. In any case, the measurement is performed on at least two similar rhombic marks formed on the substrate and having an angle θ as a set of diagonals. In this case, for example, the length of the longer diagonal line of each image is determined, for example, by the alignment detection system (LSA) of the exposure apparatus.
System or FIA system). In this case, since an unnecessary image which is a cause of noise other than the image of the rhombic mark is not formed on the substrate, for example, an alignment detection system (LSA system,
In the case of measurement using an FIA system or the like, a decrease in measurement accuracy due to erroneous detection of an unnecessary image can be prevented, and a measurement signal with a good S / N ratio can be obtained.

According to the present invention, an angle α (0 ° <α <180 °) with respect to the first direction so that a plurality of line patterns having a line width w extending in the first direction have an interval w ′. ,
α ≠ 90 °), a first partial pattern disposed along a predetermined array direction intersecting at an angle θ with respect to the first direction.
(0 ° <θ <180 °) line width w extending in the second direction
Are set at an angle α (0 ° <α <180 °, α ≠ 90) with respect to the second direction so that the plurality of line patterns are spaced w ′.
The mask substrate formed as one of a light transmitting part and a light shielding part is provided in a different region so that the second partial pattern disposed along the arrangement direction intersecting at (°) does not overlap with each other. When the length y of each line pattern is equal to or more than {2w ′ / sin θ + w · tan (θ / 2)}, the line patterns constituting the first partial pattern and the second partial pattern, respectively. Any of the following is a shape in which, when the first partial pattern and the second partial pattern are transferred onto a substrate in a superimposed manner, a part thereof is removed so that unnecessary overlapping portions do not occur between the transferred images. Is a mask characterized in that:

Even if exposure is performed twice by a projection exposure apparatus using this mask, similar to the mask according to the fourth aspect, an image other than a target rhombic mark image (a latent image or a resist image) is obtained. Unnecessary images that cause noise in the image are not formed on the substrate. Therefore, unnecessary images may be erroneously generated even when measurement is performed using, for example, an alignment detection system (LSA system, FIA system, etc.) of an exposure apparatus. A decrease in measurement accuracy due to detection can be prevented, and a measurement signal with a good S / N ratio can be obtained.

According to a ninth aspect of the present invention, there is provided an image forming characteristic measuring apparatus for measuring an image forming characteristic of a projection optical system (PL) using the mask ( _RT ) according to any one of the first to sixth aspects. A first exposure step of transferring a plurality of patterns, including first and third patterns on the mask, onto a substrate (W) via the projection optical system; and A second exposure step in which the second pattern and the fourth pattern on the mask are respectively transferred onto the transfer images of the first pattern and the third pattern in a superimposed manner;
Length of at least one of an overlap portion of a transfer image of the pattern and the second pattern and a rhombic mark image (HM) formed on an overlap portion of a transfer image of the third pattern and the fourth pattern, respectively. And a calculation step of calculating the imaging characteristics of the projection optical system based on the measured length of the rhombic mark image.

According to this, in the processing of the first and second exposure steps, in the same manner as described in the first aspect, the overlapping portion between the transferred images of the second pattern and the first pattern, An image (a latent image or the like) of at least two similar rhombic marks having a pair of diagonal angles of θ is formed in the overlapping portion between the transferred images with the third pattern. And in the measurement process,
The length of at least one of the rhombic mark images is measured, and the imaging characteristics of the projection optical system are calculated based on the length of the rhombic mark image measured in the calculation step.

In this case, the images of all rhombic marks have the same resolving power at any point on the periphery of the rhombus. For this reason, the above-described length measurement has sufficiently high reliability, and as a result, the imaging characteristics of the projection optical system are accurately calculated. In particular, when a resist image of a rhombic mark is obtained by developing the substrate, a resist image of at least two rhombic marks having a similar diagonal angle of θ is formed on the substrate after the development. For example, the length of the longer diagonal line of each resist image is measured using, for example, an alignment detection system (LSA system, FIA system) of the exposure apparatus, and various results of the projection optical system are measured based on the measurement results. The image characteristics may be measured. Also in this case, for the same reason as described above, it is possible to effectively suppress the occurrence of a resist failure at the sharp tip portion of the resist image. In addition, despite the fact that the line widths of the original line patterns are different, only the same degree of resist failure occurs in any of the resist images. Therefore, unlike the case where the angle θ is changed, a resist image having the intended shape can be obtained. The same applies to an etched image and the like.

According to a tenth aspect of the present invention, there is provided a projection optical system (PL) using the mask (R _T ) according to the seventh or eighth aspect.
A first exposure step of transferring a first partial pattern on the mask onto a substrate (W) via the projection optical system; and A second exposure step of superimposing and transferring the second partial pattern on the mask on the formed transfer image of the first partial pattern; and transferring the first partial pattern and the second partial pattern on the substrate. A measuring step of measuring at least one of the rhombic mark images formed on the overlapping portions of the images; and forming an image of the projection optical system based on the measured length of the rhombic mark image (HM). Calculating a characteristic.

According to this, in the first exposure step, the first partial patterns are transferred onto the substrate, and transferred images of those patterns are formed on the resist layer on the substrate. Next, in a second exposure step, the second partial pattern is transferred while being superimposed on the transfer image of the first partial pattern. As a result, in the overlapping portion between the transferred images of the second partial pattern and the first partial pattern,
At least two of substantially the same shape whose set of diagonals is an angle θ
An image (such as a latent image) of two rhombic marks is formed on the substrate. Then, in a measuring step, at least one of the rhombic mark images formed on the overlapping portion of the transferred image of the first partial pattern and the second partial pattern on the substrate is measured, and in the calculating step, the length is measured. The imaging characteristics of the projection optical system are calculated based on the length of the obtained rhombic mark image. In this case, since an unnecessary image other than the rhombic mark image that causes noise is not formed on the substrate, the unnecessary diagonal line of each rhombic mark image is measured, for example, by measuring the length of the longer diagonal line. A decrease in measurement accuracy due to erroneous image detection can be prevented, and a good measurement of the S / N ratio can be performed. By using the measurement results, it is possible to accurately measure various imaging characteristics of the projection optical system. Becomes

In this case, the measurement of the length of the rhombic mark may be performed on the latent image formed on the substrate without developing the substrate, or the image of the rhombic mark may be formed. After the developed substrate is developed, the process may be performed on a resist image formed on the substrate or an image (etched image) obtained by etching the substrate on which the resist image is formed. In any case, the measurement is performed on at least two similar rhombic marks formed on the substrate and having an angle θ as a set of diagonals. In this case, for example, the length of the longer diagonal line of each image is determined, for example, by the alignment detection system (LSA) of the exposure apparatus.
System, FIA system, etc.). In this case, since an unnecessary image which causes noise other than the image of the rhombic mark is not formed on the substrate, it is possible to prevent a decrease in measurement accuracy due to erroneous detection of the unnecessary image, and
A good measurement signal with an N ratio can be obtained.

According to the eleventh aspect of the present invention, at least one
An imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system (PL) using a mask ( _RT ) on which two line-and-space patterns are formed, wherein a substrate is provided via the mask and the projection optical system Exposing (W) to form a transfer image of a first line-and-space pattern formed of a line pattern extending in a first direction on the substrate; and a substrate through the mask and the projection optical system. And a second line-and-space consisting of a line pattern extending in a second direction intersecting the first direction at a predetermined angle so as to overlap a transfer image of the first line-and-space pattern formed on the substrate. A second exposure step of forming a transfer image of the pattern; and the first and second exposure steps
A parallelogram mark row (4) formed on each of the overlapping portions of the transferred images of the first line and space pattern and the second line and space pattern on the substrate.
4A, 44B), a third exposure step of further exposing the substrate so that only the image of the desired parallelogram mark remains; and measuring the length of the parallelogram mark image formed on the substrate. Measuring the imaging characteristics of the projection optical system based on the measurement result.

According to this, in the first exposure step, the substrate is exposed through the mask and the projection optical system, and a transfer image of the first line and space pattern composed of the line pattern extending in the first direction is formed on the substrate. It is formed. Then the second
In the exposing step, a second line pattern extending in a second direction that intersects the first direction at a predetermined angle and overlaps with a transfer image of the first line and space pattern formed on the substrate.
A transfer image of the line and space pattern is formed. As a result, an image (a latent image or the like) of a parallelogram mark array arranged at a predetermined interval in a predetermined direction is formed at an overlapping portion between the transferred images of the first line and space pattern and the second line and space pattern. It is formed on a substrate.
Next, in a third exposure step, a parallelogram mark formed at an overlapping portion of a transfer image of the first line and space pattern and the second line and space pattern on the substrate by the first and second exposure steps The substrate is further exposed so that only the desired parallelogram mark image of the rows remains.

In the measuring step, the length of the parallelogram mark image formed on the substrate is measured, and the imaging characteristics of the projection optical system are calculated based on the measurement result. In this case, the length of the parallelogram mark is measured after the third exposure is performed so that only the image of the desired parallelogram mark in the parallelogram mark row remains, so that the necessary mark Can be measured simultaneously or individually, and it is possible to prevent a decrease in measurement performance due to the presence of a mark irrelevant to the measurement.

In this case, as in the twelfth aspect of the present invention, in the third exposure step, the exposure is performed such that only the parallelogram marks located at positions other than both ends of the parallelogram mark row remain. Alternatively, as in the invention according to claim 13, in the third exposure step, the exposure may be performed such that only the parallelogram mark on at least one end of the parallelogram mark row remains. .

According to a fourteenth aspect of the present invention, the mask (R)
14. An exposure method for transferring the pattern (1) onto a substrate (W) via a projection optical system (PL), wherein the projection optical system uses the imaging characteristic measurement method according to any one of claims 9 to 13. A step of measuring imaging characteristics; and adjusting various conditions at the time of exposure in consideration of the measured imaging characteristics to transfer the pattern of the mask onto the substrate. is there.

According to this, the imaging characteristics of the projection optical system can be accurately measured by the respective imaging characteristic measuring methods according to the ninth to thirteenth aspects. Then, various conditions at the time of exposure are adjusted in consideration of the measured imaging characteristics, and the pattern of the mask is transferred onto the substrate. The adjustment of the exposure conditions typically includes, for example, adjustment of the imaging characteristics of the projection optical system based on the measured imaging characteristics, adjustment of the alignment error between the mask and the substrate caused by the imaging characteristics, and the like. In any case, since various conditions at the time of exposure are adjusted, highly accurate exposure can be performed.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG.

FIG. 1 shows an exposure apparatus 100 according to an embodiment suitable for carrying out the imaging characteristic measuring method and the exposure method according to the present invention. The exposure apparatus 100 is a step-and-repeat type reduction projection exposure apparatus (so-called stepper).

The projection exposure apparatus 100 includes an illumination system IO
P, a reticle stage RST for holding a reticle R as a mask, a projection optical system PL for projecting an image of a pattern formed on the reticle R onto a wafer W as a substrate coated with a photosensitive agent (photoresist), and a wafer. XY stage 2 that moves on a two-dimensional plane (within the XY plane) while holding W
0, a drive system 22 for driving the XY stage 20, and a control system for these components. The control system is CPU, RO
Workstation (or microcomputer) including M, RAM, I / O interface, etc.
And a main control device 28 for centrally controlling the entire apparatus.

The illumination system IOP includes a light source such as a KrF excimer laser, an ArF excimer laser, an ultra-high pressure mercury lamp, a fly-eye lens or a rod-type (internal reflection type) integrator as an optical integrator or a homogenizer, a relay lens, and a condenser. An illumination optical system including a lens, a reticle blind, and the like (both not shown). This lighting system IOP
Is a reticle R by an illumination light IL for exposure from a light source.
Is illuminated with a uniform illuminance distribution on the pattern on the lower surface (pattern forming surface). Here, as the illumination light for exposure IL, for example, KrF excimer laser light (wavelength 248 nm), ArF
Ultraviolet pulse light such as excimer laser light (wavelength 193 nm) and ultraviolet emission lines (g-line, i-line) from an ultra-high pressure mercury lamp
Are used.

The reticle stage RST includes an illumination system I
It is located below the OP in FIG. A reticle R is fixed on the reticle stage RST via fixing means such as a vacuum chuck (not shown), and the reticle stage RST is driven by a driving system (not shown).
The axial direction (the horizontal direction in FIG. 1) and the Y-axis direction (FIG. 1)
In the direction perpendicular to the plane of the drawing) and in the θz direction (the rotation direction in the XY plane). Thus, reticle stage RST can position reticle R (reticle alignment) in a state where the center of the pattern of reticle R (reticle center) substantially matches optical axis AXp of projection optical system PL. FIG. 1 shows a state in which this reticle alignment has been performed.

The projection optical system PL has an optical axis AXp of XY
The direction is a Z-axis direction orthogonal to the plane, and here is bilateral telecentric, and a predetermined reduction magnification β (β is, for example, ４, 1 /
5 etc.) are used. For this reason, if the reticle R is illuminated with uniform illuminance by the illumination light IL in a state where the pattern of the reticle R and the shot area on the wafer W are aligned (aligned), the pattern on the pattern forming surface is changed. The image is reduced by the projection optical system PL at the reduction magnification β, projected onto the wafer W coated with the photoresist, and a reduced image of the pattern is formed in each shot area on the wafer W.

The XY stage 20 is actually a Y stage that moves on a base (not shown) in the Y axis direction.
An X stage is configured to move on the stage in the X axis direction. In FIG.
Shown as zero. A wafer table 18 is mounted on the XY stage 20, and a wafer W is held on the wafer table 18 by vacuum suction or the like via a wafer holder (not shown).

The wafer table 18 minutely drives the wafer holder for holding the wafer W in the Z-axis direction and the tilt direction with respect to the XY plane, and is also called a Z-tilt stage. A movable mirror 24 is provided on the upper surface of one end of the wafer table 18, and a laser beam is projected on the movable mirror 24 and the reflected light is received. Is provided to face the reflecting surface of the movable mirror 24. Actually, the moving mirror is provided with an X moving mirror having a reflecting surface orthogonal to the X axis and a Y moving mirror having a reflecting surface orthogonal to the Y axis. X laser interferometer for directional position measurement and Y for Y direction position measurement
Although a laser interferometer is provided, these are representatively shown as a moving mirror 24 and a laser interferometer 26 in FIG. The X laser interferometer and the Y laser interferometer are multi-axis interferometers having a plurality of measurement axes, and the wafer table 1
In addition to the X and Y positions of 8, the rotation (yawing, pitching,
Rolling) can also be measured. Therefore, in the following description, the wafer interferometer 26
It is assumed that the positions of eight X, Y, θz, θy, and θx in five degrees of freedom are measured.

The measured value of the laser interferometer 26 is
The main controller 28 controls the laser interferometer 2
By driving the XY stage 20 via the drive system 22 while monitoring the measurement value of the
Is positioned. In addition, the position in the Z direction of the surface of the wafer W is determined by, for example, a focus sensor AFS including a light incident type multipoint focal position detection system having a light transmission system 50a and a light reception system 50b disclosed in Japanese Patent Application Laid-Open No. 6-283403. The output of the focus sensor AFS is also supplied to the main controller 28. The main controller 28 controls the wafer table 18 via the drive system 22 based on the output of the focus sensor AFS. The control is performed so-called focus leveling control. That is, the wafer table 18
, The position and orientation of the wafer W in the directions of five degrees of freedom of X, Y, Z, θx, and θy are controlled.
The remaining error of θz (yaw) is corrected by rotating reticle stage RST based on yaw information of wafer table 18 measured by laser interferometer 26.

On the wafer table 18, a reference plate FP whose surface is the same as the surface of the wafer W is set.
Has been fixed. On the surface of the reference plate FP, various reference marks including a reference mark used for so-called baseline measurement or the like are formed.

Further, in this embodiment, an off-axis type alignment detection system AS as a mark detection system for detecting an alignment mark formed on the wafer W is provided on a side surface of the projection optical system PL. This alignment detection system AS is an LSA (Laser Step Alignment) system,
FIA (Filed Image Alignment) system, LIA (Laser
It has three types of alignment sensors of an interferometric alignment (Alignment) type, and can measure the position of the reference mark on the reference plate FP and the alignment mark on the wafer in the X and Y two-dimensional directions.

Here, the LSA system is the most versatile sensor that irradiates a laser beam onto a mark and measures the position of the mark by using diffracted and scattered light. Is done. The FIA system is a sensor that illuminates a mark with broadband (broadband) light such as a halogen lamp and measures the mark position by processing the mark image, and is used effectively for an asymmetric mark on an aluminum layer or a wafer surface. You. In addition, LIA system
A sensor that irradiates a diffraction grating mark with laser light whose frequency is slightly changed from two directions, interferes the two generated diffraction lights, and detects mark position information from its phase. Used effectively for rough wafers.

In the present embodiment, these three types of alignment sensors are properly used depending on the purpose, and so-called baseline measurement and fine alignment for accurately measuring the position of each shot area on the wafer are performed. ing.

Information DS from each alignment sensor constituting the alignment detection system AS is A / D-converted by the alignment controller 16 and arithmetically processes a digitized waveform signal to detect a mark position. The result is sent to the main controller 28.

Further, in the exposure apparatus 100 of the present embodiment, although not shown, a reticle is provided above the reticle R via a projection optical system PL disclosed in, for example, Japanese Patent Application Laid-Open No. 7-176468. TTR (Through The Reticl) using an exposure wavelength for simultaneously observing a reticle mark (not shown) on the R and a mark on the reference plate FP.
e) A pair of reticle alignment microscopes comprising an alignment optical system are provided. The detection signals of these reticle alignment microscopes are transmitted to the alignment control device 1
6 to a main controller 28.

Next, an example of a reticle used in the method for measuring an imaging characteristic according to the present invention will be described.

FIG. 2 shows an example of the reticle _RT used for measuring the imaging characteristics. FIG. 2 is a plan view of reticle _RT viewed from the pattern surface side (the lower surface side in FIG. 1). In the reticle R _T , a pattern area PA is provided at the center of a glass substrate 42 as a substantially square mask substrate, and a plurality of patterns described later are arranged in the pattern area PA. Further, a pair of reticle alignment marks RM1, R is provided on both sides in the X-axis direction of the pattern area PA passing through the center of the pattern area PA, that is, the center of the reticle _RT (reticle center).
M2 is formed.

In the pattern area PA, for example, four types of line and space (hereinafter abbreviated as “L / S”) patterns LS1 to LS as shown in FIG.
S4 is arranged.

L / S pattern LS1 and L / S pattern L
S2 matches the arrangement direction (the X-axis direction in the figure),
These patterns form a pair with each other, and have a pitch (arrangement cycle of line patterns) and a ratio of the width (w) of the line portion to the width (w ′) of the space portion (hereinafter, referred to as “duty ratio”).
And all the line widths w of the line patterns are the same pattern. Here, the duty ratio of these L / S patterns LS1 and LS2 is 5: 8. Furthermore, L
The / S pattern LS1 is composed of a plurality of line patterns extending in a first direction forming an angle θ / 2 clockwise with respect to the Y axis in the plane of the paper, and the L / S pattern LS2 is counterclockwise in the plane with respect to the Y axis. It is composed of a plurality of line patterns extending in the second direction around the angle θ / 2. Therefore,
An extension of each line pattern forming the L / S pattern LS1 and an extension of each line pattern forming the L / S pattern LS2 intersect at an angle θ. In addition, these L
/ S patterns LS1 and LS2 have the same angle α (0 ° <α <180 °, α ≠ 90) with respect to the first direction and the second direction.
The line patterns are arranged at equal intervals along a third direction (X-axis direction in the figure) intersecting at (°). That is,
In FIG. 3A, in the L / S pattern LS1, the third direction rotates clockwise in the plane of the drawing with respect to the first direction by an angle α.
In the S pattern LS2, the third direction is rotated by an angle α counterclockwise in the drawing with respect to the second direction.

The L / S pattern LS3 and the L / S pattern LS4 are patterns forming a pair with each other, and have the same pitch, duty ratio, and line width of each line pattern. These L / S patterns LS
3, LS4 has a duty ratio of 1: 1 here. Further, the L / S pattern LS3 is composed of a plurality of line patterns extending in a first direction forming an angle θ / 2 clockwise in the plane of the drawing with respect to the Y axis.
Reference numeral 4 denotes a plurality of line patterns extending in the second direction at an angle θ / 2 counterclockwise in the drawing with respect to the Y axis. Therefore, an extension of each line pattern forming the L / S pattern LS3 and an extension of each line pattern forming the L / S pattern LS4 intersect at an angle θ.
In these L / S patterns LS3 and LS4, the same angle α (0 ° <α <1) with respect to the first direction and the second direction.
Line patterns are arranged at equal intervals along a third direction (X-axis direction in the figure) intersecting at 80 ° and α ≠ 90 °). That is, in FIG. 3A, the L / S pattern LS3
In this case, the third direction is an angle α clockwise in the plane of the paper with respect to the first direction.
And the third direction is the second direction in the L / S pattern LS4.
That is, it is rotated by α in the counterclockwise direction on the paper with respect to the direction.

In this case, the L / S patterns LS1 and L / S
The pattern LS2 has a symmetric relationship with respect to an axis X1 parallel to the X axis, and the L / S pattern LS3 and the L / S pattern LS4 have a symmetric relationship with respect to the axis X1. Also,
The distance between the L / S pattern LS1 and the L / S pattern LS2 in the Y-axis direction is the same as the distance between the L / S pattern LS3 and the L / S pattern LS4 in the Y-axis direction.

The L / S patterns LS1, LS2,
The pitches of the L / S patterns LS3 and LS4 may be the same or different.

In the pattern area PA, for example, two types of L / S patterns LS5 and LS6 as shown in FIG. 3B may be repeatedly arranged at predetermined intervals. Here, the patterns LS5 and LS6 correspond to the L /
The patterns are exactly the same as the S patterns LS3 and LS4, respectively, and are arranged in the same positional relationship.

For example, under almost ideal exposure conditions (assuming that the imaging characteristics of the projection optical system are also ideal), FIG.
Exposure is performed using a reticle having a pattern arrangement as shown in (B) to transfer the L / S patterns LS5 and LS6 to a positive resist layer on the substrate, and then to the L / S transferred to the resist layer. L / S is applied to the transfer image of the pattern LS5.
When double exposure is performed to transfer the pattern LS6 in an overlapping manner, three rhombic marks HM (FIG. 4) as shown in FIG.
A transfer image (latent image) of a region surrounded by a thick solid line in the middle is formed on the resist layer.

One set of diagonals (small diagonal) of each diamond mark HM is the L / S pattern LS5 (transferred image) and L / S pattern LS5.
It should be the same as the intersection angle θ with (the transfer image of) the S pattern LS6 (see FIG. 4).

However, when the length of each line pattern becomes longer than a certain length, an unnecessary transfer image of the overlapping portion S is formed as shown by oblique lines in FIG. In such a case, if the development processing of this substrate is performed, the diamond-shaped mark HM
In addition to the resist image, the resist image of the overlapping portion S is also formed on the substrate.

Here, it is assumed that the lengths of the resist images of the three rhombic marks HM are measured using, for example, an alignment detection system AS. In this case, detection laser light (slit-like light elongated in the X-axis direction) is scanned in the Y-axis direction on the surface of the substrate. At this time, not only the resist image of the diamond mark HM but also the resist of the overlapping portion S is scanned. The image is relatively scanned. Therefore, the detection signal of the LSA-based sensor includes a considerably large noise caused by the overlapping portion S, and the S / N ratio is reduced.

Therefore, in the present embodiment, in order to prevent the above-described inconvenience from occurring, the L / S
Pattern configuration conditions (length, etc.) of patterns LS5, LS6
Is determined in advance. In the following description of the pattern configuration conditions, for convenience, the projection magnification is assumed to be the same, and the description will be made without distinguishing the size of the pattern on the reticle _{RT from} the size of the transferred image.

As shown in FIG. 4, each L / S
The width of each line pattern forming the pattern is w, and the length of the diamond mark HM (the length of the longer diagonal) is L.
Also, let P be the length of each line pattern when the diamond mark HM is just formed.

From FIG. 4, the following relationship holds geometrically. L = w / sin (θ / 2) (1) P = w / tan (θ / 2) (2) Both L / S patterns LS5 and LS6 are L / S
Same as S pattern LS3, LS4, duty ratio is 1:
Therefore, if the width of the space portion is w ′, then w ′ =
w.

In practice, it is desirable that each line pattern has a certain margin in the pattern length in consideration of an overlay error and the like. As shown in FIG.
When the S pattern LS5 and the L / S pattern LS6 are ideally overlapped with each other, by setting this margin shorter than ΔP at one end in the longitudinal direction of the line pattern, an unintended unnecessary overlapping portion S Can be prevented from occurring.

The length ΔP shown in FIG. 4 is expressed by the following equation (3), as is apparent from FIG. ΔP = w · tan (θ / 2) (3)

Therefore, the line width w and the space width w '= w
In the case of the L / S pattern described above, the allowable length of each line pattern (hereinafter, appropriately referred to as “line length”) y can be represented by the following equation (4). w / tan (θ / 2) ≦ y <w / tan (θ / 2) + 2w · tan (θ / 2) (4) Further, this equation (4) is transformed using the double angle theorem. For example, w / tan (θ / 2) ≦ y <2w / sin θ + w · tan (θ / 2) (5)

In practice, in consideration of the positional accuracy after completion of the opposing pattern and the positioning accuracy of the device to be used, the line length y is larger than P within a range satisfying the above equation (4) or (5). It is desirable to make it longer.

For example, the line length y is defined as the central length within the range defined by the equation (4), that is, w / tan (θ / 2) + w · t
When set to an (θ / 2), the maximum allowable overlay error is as follows. W · tan (θ / 2) · sin (θ / 2) in the left-right direction (X-axis direction) (6) w · tan (θ / 2) · sin (θ / 2) (7) If there is a shift in both the X and Y axes, the permissible error is further reduced.

When the length of each line pattern is longer than the length defined by the equation (4) or (5), the overlap is determined based on the geometrical relationship shown in FIG. The respective dimensions of the portion S are obtained, and the corners of at least one of the L / S patterns are removed so as to include the entire overlapping portion S and not overlap the rhombic mark HM. Good. Even in this case, by performing the double exposure as described above, only the latent image of the rhombic mark can be formed, and the occurrence of the overlapping portion S can be prevented.

It should be noted that the duty ratios of a pair of L / S patterns that are opposed to each other (intersect at an angle θ) are the same and are 1: 1.
If it is larger, that is, if the line width w> the width w ′ of the space portion, the line length y is set so as to satisfy the above equation (4) or (5), or (4)
Alternatively, in the case where the length is equal to or longer than the range defined by the expression (5), the corner portion of at least one of the line patterns may be removed in the same manner as described above. Thus, by performing the double exposure as described above, only the latent image of the rhombic mark is formed, and the occurrence of the overlapping portion S can be prevented.

Next, the pattern configuration conditions (length and the like) of the L / S patterns LS1 and LS2 employed in this embodiment will be described.

In the case of the L / S patterns LS1 and LS2, the duty ratio is smaller than 1: 1 and 5: 8.
The width of the line portion is smaller than the width of the space portion w ′.

In this case, as shown in FIG. 6, if the length of the diamond-shaped region formed by the overlap of the space portions of the opposing line patterns is L ′, the occurrence of unnecessary overlap portions is prevented. The line length y that is allowable is given by w / tan (θ / 2) ≦ y <L ′ / 2 / cos (θ / 2) + w · tan (θ / 2) where w is the line width. Becomes

According to the geometric relationship shown in FIG. 6, the width of the space portion is defined as w ′, and L ′ = w ′ / sin (θ / 2) (9) By substituting equation (9) into equation (8) above and transforming, equation (8) can be expressed as the following equation (10). w / tan (θ / 2) ≦ y <2w ′ / sin θ + w · tan (θ / 2) (10) The L / S patterns LS1 and LS2 are given by the above equation (1
The line length y of each line pattern is defined so as to satisfy 0).

Here, when the equation (10) is compared with the above-described equation (5), it can be seen that the first term on the right side has been changed. Comparing these two equations shows that equation (5) is a special case of equation (10) (w '= w).

Therefore, when the rhombic mark is formed in a state where the L / S patterns having the same pitch and the same duty ratio intersect at the intersection angle θ, the expression (10) is satisfied regardless of the duty ratio. That is, the length of each line pattern may be set as described above.

In the case of FIG. 6 as well, if the length is longer than the range defined by the equation (10), corner portions of at least one of the line patterns are removed in the same manner as described above. Good. Thus, by performing the double exposure as described above, only the latent image of the rhombic mark is formed, and the occurrence of the overlapping portion S can be prevented.

In the above description, the case where the exposure conditions (including the imaging characteristics of the projection optical system) are ideal has been described. However, even if the projection optical system PL has an aberration and is defocused, , A set of opposing L / S of symmetric shape
Diamond-shaped marks (rows) formed by overlapping patterns
May be changed, but as long as the above expression (10) is satisfied, formation of a diamond-shaped mark row and prevention of generation of unnecessary overlapping portions can be similarly performed.

Next, a brief description will be given of a flow of an operation at the time of measurement for measuring the imaging characteristics of the projection optical system PL by the exposure apparatus of the present embodiment.

As a premise, mark area M of reticle _{RT is} assumed.
It is assumed that L / S patterns LS1 to LS4 are formed in _{i, j} (see FIG. 2) in an arrangement as shown in FIG.

First, wafer W is loaded onto wafer table 18 by a wafer loader (not shown), and reticle _RT is loaded onto reticle stage RST by a reticle loader (not shown).

The reference plate FP provided on the wafer table 18 is moved to the projection image position of the reticle alignment marks RM1 and RM2 via the projection optical system PL. This movement is performed by the main controller 28 while monitoring the measurement result of the laser interferometer 26 while driving the XY stage 20 via the drive system 22.
This is done by moving. As described above, the reference plate F
The surface of P is almost the same height as the surface of wafer W (optical axis direction)
A reference mark (not shown) is formed on the surface. At this time, for example, a reticle microscope (not shown) detects the relative positions of the reticle alignment marks RM1 and RM2 and the corresponding pair of reference marks via the projection optical system PL. Then, main controller 28 operates a drive system (not shown) based on the detection result of the relative position detected by the reticle microscope so that the relative position error between RM1 and RM2 and a pair of corresponding reference marks is minimized. The position of the reticle stage RST in the XY plane is adjusted through the XY plane. Thereby, the center (reticle center) of reticle _RT substantially coincides with the optical axis of projection optical system PL.

Next, the main controller 28 controls the illumination system IO
By adjusting the size and position of the opening of the reticle blind (not shown) in P, the irradiation area of the illumination light IL is adjusted to the reticle _RT.
The size and the position of the opening of the reticle blind (not shown) in the illumination system IOP are adjusted so as to match the pattern area of (1). At the same time, main controller 28 moves wafer XY to a position below projection optical system PL by moving XY stage 20 via drive system 22 while monitoring the measurement result of laser interferometer 26. .

Exposure is performed in this state, and the pattern of reticle _RT is transferred to wafer W via projection optical system PL.
At this time, the exposure is performed with an exposure dose amount that is approximately half that of the normal exposure. As a result, the resist layer on the wafer W is
L / S patterns LS1 to LS as indicated by dotted lines inside
4 are transferred.

Next, main controller 28 moves XY stage 20 by a predetermined amount in the + Y direction in the same manner as described above, and then performs exposure again, and projects the pattern of reticle _RT onto wafer W via projection optical system PL. Transcribe. At this time, the exposure is performed with an exposure dose that is almost half that of the normal exposure. Thereby, part of the images of the L / S patterns LS1 to LS4 as indicated by solid lines in FIG. 7 are transferred to be superimposed on the latent images of LS1 to LS4 transferred to the resist layer on the wafer W. .

Next, the main controller 28 moves the XY stage 20 in the same manner as described above, for example, by one shot in the + X direction, and moves the Z position of the wafer table 18 by a predetermined pitch ΔZ using the focus sensor AFS.
Move in the Z direction. Exposure is performed in this state, and the pattern of the reticle _RT is transferred onto the wafer W via the projection optical system PL at an exposure dose that is almost half that of normal exposure. Next, the main controller 28 moves the XY stage 20 by a predetermined amount in the −Y direction in the same manner as described above,
Exposure is performed again, and the pattern of the reticle _RT is transferred to the wafer W via the projection optical system PL. At this time, the exposure is performed with an exposure dose that is almost half that of the normal exposure.

Thereafter, the wafer table 1
The double exposure is repeated by the step-and-repeat method while changing the Z position of No. 8 by a predetermined pitch ΔZ.

When the double exposure for a plurality of adjacent shot areas on the wafer W is completed, the main controller 28
After the exposure of the exposed wafer W is unloaded from above the wafer table 18 by a wafer loader (not shown), the wafer W is connected inline to the exposure apparatus 100 by a wafer transfer system (not shown). It is transported to a coater / developer not shown (hereinafter abbreviated as “C / D”).

The wafer W is developed in the C / D. Upon completion of the development, a plurality of partitioned areas are formed on the wafer W, and two types of similar rhombic marks H having different sizes as shown in FIG.
M1 and HM2 resist images are alternately formed at predetermined intervals in the X-axis direction. In the Y-axis direction, rows of rhombic marks HM1 or HM2 of the same type are formed at predetermined intervals.

Next, in response to the notification of the completion of the development from the C / D, the wafer W is transferred into the exposure apparatus by a wafer transfer system (not shown), and the transferred wafer W is loaded on the wafer table 18 again by the wafer loader. Is done.

At this time, the wafer W is loaded on the wafer table 18 again in a state where the center position deviation and the rotation correction of the wafer W have been corrected by a pre-alignment device (not shown). Therefore, only by controlling the movement of the XY stage 20 in accordance with the measurement result of the laser interferometer 26 based on the designed arrangement coordinate information of the shot area and the arrangement information of the L / S pattern on the reticle R _T , An alignment detection system AS without misidentifying one of a large number of rhombic mark images formed in a region as another rhombic mark.
To obtain position information (such as coordinate values).

Next, in main controller 28, any diamond mark HM formed in each shot area on wafer W
The rows of 1, HM2 are moved directly below the alignment detection system AS, and the length of each rhombic mark is measured using, for example, the alignment detection system AS, for example, the LSA system. Note that a method of measuring the line length of a wedge mark (a kind of diamond mark) using an LSA-based sensor is widely known as an SMP measurement technique, and thus the details of the measurement method are omitted.

For example, it is formed by an overlapping portion of a pair of vertically symmetric L / S pattern transferred images arranged at or near the optical axis position of the projection optical system PL during the above-described double exposure. The length of the diamond-shaped mark is measured for each shot area on the wafer W, the longest diamond-shaped mark (or row of diamond-shaped marks) is detected, and the wafer for exposure to form the mark is exposed. Z of table 18
Let the position be the best focus position.

This is a case where a positive type reticle (a reticle in which a light-shielding pattern is formed in a light transmitting portion) and a positive type resist are used when an image of a rhombic mark is formed on the wafer W by double exposure. This is because, when the exposure is performed in the best focus state, the length of the formed diamond mark becomes the maximum.

Note that the length of the diamond mark may be longer in the defocused state than in the focused state depending on the type of resist or reticle used, or a combination thereof. An example is given in which the line length becomes shorter in the focus state.

Further, for example, the above-mentioned best focus position is measured for rhombic marks corresponding to different image height positions, so that the image plane (field curvature) of the projection optical system PL is measured.
Can be requested. Also, on the reticle, mutually paired L / S patterns (extending lines of the line patterns constituting the respective lines intersect) so that the rhombic marks to be formed have various directions. (Intersecting at an angle θ). When an image of a rhombic mark is formed by double exposure using such a reticle, astigmatism can also be measured based on the measurement result of the length of each rhombic mark.

Next, the measurement of coma will be described in detail.

For example, when a normal L / S pattern is transferred onto a wafer using a projection optical system (projection lens) in which coma aberration occurs, transfer of line patterns located at both ends of the transferred image is performed. It is known that a phenomenon in which the line width of an image greatly differs occurs. In order to express the coma aberration caused by this phenomenon, the line widths of the transferred images of the line patterns located at both ends in the best focus state are defined as D1 and D2, and are defined as | D1−D2 | / (D1 + D2) (11) , An abnormal line width (a change in line width due to coma) is used.

Therefore, in the measurement method according to the present embodiment in which the line width of the original L / S pattern is converted into the line length of the rhombic mark (transferred image of the rhombic mark) by a proportional operation based on a geometrical relationship, With the line lengths of the transfer images of the rhombic marks located at both ends of the rhombic mark array formed by double exposure using a pair of L / S patterns having the same duty ratio and pitch, L1 and L2, the coma aberration As an index of, an amount represented by the following equation may be defined as an abnormal line width value. Line width abnormal value = | L1-L2 | / (L1 + L2) (12)

As a specific example, as shown in FIG. 3B, a reticle on which a plurality of pairs of L / S patterns having the same pitch and the same duty ratio are formed (a reticle for convenience of discrimination from reticle _RT). When a rhombic mark array is formed by double exposure in the same manner as described above using R _T ′), a latent image (or resist image) of the rhombic mark array as shown in FIG. 9A is obtained. Will be.

Here, in order to determine the coma aberration of the projection optical system PL, consider the case where the resist image of the mark row in FIG. 9A is measured by the LSA system sensor. The detection signal of the central diamond mark that is not related to the calculation may cause an error in the calculation of the abnormal line width value. This is because in a measurement method using an LSA-based sensor, a wedge mark formed on a substrate (a diamond-shaped mark is one type)
This is because the laser light is scanned with respect to the resist image and the diffracted light generated from the resist image is obtained as an electric signal, so that the diffracted light generated in the mark portion that is not the measurement target becomes a kind of noise. That is, for each mark row, it is desirable to obtain diffracted light from only the rhombic marks at both ends.

Therefore, in the present embodiment, after forming a plurality of sets of rhombic mark latent images on the resist layer as shown in FIG. 9A, a third exposure exposes the latent images other than the target mark (pattern). The mark is to be deleted.

More specifically, as shown in FIG. 9B, in the first diamond mark row group 44A, only one (right end) diamond mark is left for each mark row, and the second diamond mark row is left. In the group 44B, exposure is performed such that only the diamond mark at the other end (left end) is left for each mark row. Such third exposure is performed, for example, as shown in FIG.
Is mounted on the reticle stage RST immediately after the above-described double exposure, another reticle having a plurality of rectangular opening patterns 46 as shown in FIG.
By performing exposure at the exposure dose during normal exposure,
Can be easily realized. The third exposure is performed by main controller 28 in the same manner as described above.

That is, by performing the triple exposure as described above, the resist layer on the wafer W is added to the resist layer shown in FIG.
Is formed, and a resist image of the rhombic mark group is formed on the wafer W by developing the wafer W.

Then, the main controller 28 uses the LSA type sensor of the alignment detection system AS to execute the rhombic marks M _1,1 , M _{1,2 ,. 2,1} , M _2,2 ..., And each length is measured simultaneously. In the main controller 28, the diamond mark M
Let L1 be the average value of the length of _{1, i} (i = 1, 2,..., M) and L2 be the average value of the diamond marks M _{2, i} (i = 1, 2,..., M). Substituting into the above equation (12), an abnormal line width value is obtained, and the coma aberration of the projection optical system PL is calculated.

In the above description, although not particularly described for the sake of simplicity, it is necessary to perform triple exposure in a state where the wafer table 18 is set at the best focus position when measuring the coma aberration. There is. The reason is that at the defocus position, even if a pattern is formed, the difference or sum of the line lengths (or line widths) changes, and the actual amount of coma aberration and the calculated line width abnormal value are different. This is because they will no longer respond. That is, the above formula for calculating the abnormal line width value is based on the line width difference in the best focus state, and the calculated abnormal line width value is different in a state out of the best focus state.

For this reason, the best focus position for the mark pattern of reticle R _T ′ may be obtained in advance. Alternatively, the triple exposure is performed in a step-and-repeat manner while changing the Z position of the wafer table 18 in the same manner as in the above-described best focus measurement. It is possible to calculate the best focus position by utilizing the change in the length of the line, and to calculate the abnormal line width value (coma aberration) based on the line length of the rhombic mark in the corresponding shot area. .

In the above description, unnecessary marks (or patterns) are removed by the third exposure. However, the present invention is not limited to this. , And the remaining unnecessary marks (or patterns) may be removed by the fourth and subsequent exposures. In such a case, the opening of the reticle blind in the illumination system may be set in accordance with the mark portion to be deleted, even if the reticle is not necessarily replaced after the double exposure.

In this embodiment, a reticle dedicated to pattern erasure is used. However, for example, at least one erasing aperture pattern 46 is provided in a part of the reticle R _T or R _T ′ used for double exposure. The third exposure may be performed by any method as long as it can irradiate only unnecessary transfer images with illumination light. In this way, only triple exposure using one reticle is performed,
Coma can be accurately measured using an LSA-based sensor.

When measuring aberrations of the projection optical system other than the coma aberration, the marks located at both ends of the rhombic mark row are set to the third in order to remove the influence of the coma aberration.
The target aberration measurement may be performed by using only the resist image of the diamond-shaped mark in the central portion after removing by the subsequent exposure.

In the processing of the exposure sequence at the time of device manufacture in the exposure apparatus 100 of the present embodiment, the main controller 28 executes the projection optical system PL before the exposure by the method of measuring the imaging characteristics described above. The exposure processing operation is the same as that of a normal stepper, except that the imaging characteristics of the stepper are measured and various conditions at the time of exposure are adjusted in consideration of the measured imaging characteristics. Detailed description is omitted.

As described in detail above, the reticle R _T used for measuring the imaging characteristics in the present embodiment.
Is an L / S pattern LS1 including a plurality of line patterns having a first line width (w) extending in a first direction (a direction forming an angle θ / 2 with respect to the Y axis), and an angle θ with respect to the first direction. (0 °
<Θ <180 °), an L / S pattern LS2 paired with the L / S pattern LS1 including a plurality of line patterns having a line width w extending in the second direction, and a second line extending in the first direction. An L / S pattern LS3 including a plurality of line patterns having a line width (a line width different from the first line width) and a plurality of line patterns having a second line width extending in the second direction, and L
This is a reticle provided with a glass substrate (mask substrate) formed on its pattern surface as a light shielding portion so that the / S pattern LS3 and the paired L / S pattern LS4 do not overlap each other.

By performing double exposure using the reticle _RT in the above-described procedure, the transfer images of the paired patterns (LS1 and LS2, LS3 and LS4) are transferred onto the wafer W in a superimposed manner. (See FIG. 7). As a result, in the resist layer on the wafer W, an image (latent image) of the pair of rhombic marks HM1 and HM2 having a diagonal angle of θ is formed at the overlapping portion between the transfer images of the pattern forming a pair. You. In this case, the diamond mark H formed on the wafer W
Since the images of M1 and HM2 are formed by double exposure using the paired L / S patterns, the same resolving power is obtained at any point on the periphery of the diamond.

By developing the wafer W on which the above-mentioned rhombic mark image is formed, a resist image of a mark row composed of a similar rhombic mark having a pair of diagonal angles θ is formed on the wafer W. You. Therefore, for example, the length of the longer diagonal line of each resist image is measured using an LSA sensor constituting the alignment detection system AS, and SMP measurement is performed. The width can be calculated, and as a result, various imaging characteristics of the projection optical system PL can be measured.

In this case, the resist images of the rhombic marks HM1 and HM2 each have a pair of diagonals having the same angle θ. It is possible to effectively suppress occurrence of a failure of the resist. Also, for similar reasons,
Despite the line widths of the underlying line patterns being different, only the same degree of resist failure occurs in any of the resist images. Therefore, unlike the case where the angle θ is changed in accordance with the change in the line width, all the resist images are similarly affected by the process, so that a resist image having the intended shape can be obtained.

Therefore, it is possible to accurately measure the length of the resist image of these rhombic marks, and thus, the image forming characteristics of the projection optical system PL with high accuracy.

Here, as described above, the L / S pattern LS
1 and the L / S pattern LS2 and the L / S pattern LS3 and the L / S pattern LS4 have the same positional relationship. Therefore, prior to the second exposure in the double exposure, the XY stage 20
Are moved in the same direction by the same distance, the paired L / S patterns (LS1 and LS2, LS3 and L
The transferred images in S4) can be overlaid.

In the above-described reticle R _T and reticle R _T ′, the L / S patterns LS1, LS2, LS3,
In all of the LS4, since the length y of each line pattern constituting each satisfies the relationship of the above-described expression (10), after the double exposure described above, L
The latent images of the rhombic marks HM1 and HM2 described above are formed in the overlapping portions of the transferred images of the / S pattern LS1 and the L / S pattern LS2 and in the overlapping portions of the transferred images of the L / S patterns LS3 and LS4. Is formed, and no unnecessary image other than the rhombic mark image that causes noise is formed on the wafer W. Therefore, even after development of the wafer W, unnecessary images other than the resist images of the rhombic marks HM1 and HM2 are not formed. Therefore, for example, the length of the longer diagonal line of each resist image is set to, for example, L
Even when measurement is performed using an SA-based sensor, since an unnecessary resist image that causes noise is not formed on the wafer, the S / N ratio is also required when performing LSA measurement using an LSA-based sensor. A measurement signal with a good ratio can be obtained.

Therefore, even when the imaging characteristics such as the best focus, the curvature of field, the spherical aberration, and the astigmatism of the projection optical system PL are calculated based on the measurement result of the line length by the LSA measurement, the accuracy is high. It is possible to calculate those imaging characteristics.

In measuring coma aberration of the projection optical system PL, a latent image of a diamond-shaped mark array is formed on the wafer W by double exposure in the same procedure as in the case of measuring other imaging characteristics. The third (or third and subsequent) exposure is performed such that the latent image of the diamond-shaped mark at the center other than both ends of each mark row irrelevant to the measurement of the coma aberration is removed. Therefore, when the wafer W after the triple exposure is developed, a resist image of only the rhombic marks at both ends of each mark row necessary for measuring the coma aberration is formed on the wafer W.
Therefore, by measuring the wafer W using an LSA-based sensor, the obtained signal does not include a noise component due to the presence of an unnecessary mark, and the S / N ratio can be improved. . For this reason, based on the obtained signals, the measurement results of the line lengths of the marks located at both ends of each mark row are averaged based on the number of mark rows, and the above-mentioned equation (12) is calculated using the average value. By calculating the line width abnormal value by using this, the coma aberration can be accurately obtained.

In the present embodiment, the rhombic mark is used to convert the line width of the line pattern into the length of the rhombic mark (the conversion ratio is determined by setting the above-described intersection angle θ), and this is measured. Therefore, a pattern as small as the resolution limit can be measured at a very high magnification. Further, the measurement time can be reduced as compared with the conventional line width measurement using an SEM.

In this embodiment, as described above,
Since the C / D is connected in-line to automatically perform a series of measurement operations, great advantages such as reduction in human load are expected.

Further, since a rhombic mark is formed by double exposure and is measured, which means that one exposure measures two exposure patterns, there is also an effect of producing data averaging. In addition, in LSA measurement, information on the diamond mark length is obtained from diffracted light from a large number of patterns, so that the effect of averaging the measurement data is further enhanced.
The effect of enabling such multiple measurements with one measurement is
When viewed from the reticle side, it is regarded as averaging of pattern accuracy, and the effect of reducing performance variation due to reticle accuracy variation can be obtained.

Note that the third and subsequent exposures described above
The technique of removing unnecessary marks is also suitable for application to measurement of aberrations other than coma, for example, distortion. In such a case, contrary to the above, the third and subsequent exposures may be performed to remove the rhombic mark rows at both ends of each mark row. By doing so, it is possible to measure the imaging characteristics such as distortion with high accuracy while reducing the influence of coma aberration.

In the exposure apparatus 100 of the present embodiment,
Main controller 28 controls each unit of the apparatus, and measures the imaging characteristics of projection optical system PL by the above-described imaging characteristic measuring method before the start of exposure. Then, main controller 28 adjusts various conditions at the time of exposure in consideration of the measured imaging characteristics, and transfers the pattern of reticle R to each shot area on wafer W in a step-and-repeat manner. Transfer sequentially. As the adjustment of the exposure condition, for example, the image forming characteristic of the projection optical system PL based on the measured image forming characteristic is adjusted by an image forming characteristic correction device (not shown)
Or a device that drives the plurality of lens groups constituting the lens in the optical axis direction and a tilt direction with respect to a plane orthogonal to the optical axis, and a device that shifts the wavelength of the exposure light. Typically, adjusting the alignment error between the reticle and the wafer due to the imaging characteristics is exemplified. In any case, since various conditions at the time of exposure are adjusted, highly accurate exposure can be performed.

In the exposure apparatus of the present embodiment, the projection optical system P
It is also possible to detect the best focus of L and accurately perform calibration of the focus sensor AFS based on the detection result.

In the above embodiment, when measuring the imaging characteristics of the projection optical system, the LSA of the alignment detection system AS is used.
The case of measuring the length of the resist image of the rhombic mark using the sensor of the rhombic mark has been described. However, the present invention is not limited to this. Of course, the length of the rhombic mark may be measured by image processing based on the image signal. In this manner, similarly to the above embodiment, the imaging characteristics of the projection optical system PL can be obtained with the same or higher accuracy as in the above embodiment.

When measuring the length of a rhombic mark using this FIA sensor, the third exposure is not required for measuring coma aberration. This is because, in the case of image processing, it is sufficient to capture an image of only necessary marks. Further, instead of using the alignment detection system AS of the exposure apparatus, for example, a rhombic mark image may be detected using a measurement apparatus (for example, an overlay measurement apparatus) different from the exposure apparatus.

In the above-described embodiment, the L / S patterns are superimposed and transferred to form the rhombic mark. However, the present invention is not limited to this. The L / S pattern and the isolated line may be superimposed and transferred. In short, it suffices that at least one line pattern and at least one line pattern that can cross the line pattern at an angle θ are formed on the reticle. In this case, only one type of line pattern or L / S pattern on the reticle may be used. That is, if a mechanism capable of rotating the reticle _RT is provided on the reticle stage RST, the same line patterns can intersect at an angle θ during double exposure. In such a case, if LSA measurement is performed, the above equation (1) is used if the L / S pattern is used.
It is desirable to satisfy the condition 0).

When a negative resist is used,
What is necessary is just to use a negative reticle formed in the light-shielding part using a pattern such as LS1 to LS6 as the light-transmitting part. Further, in each of the above-described embodiments, the resist image of the rhombic mark is detected. However, for example, a latent image of the rhombic mark or an image obtained by etching the wafer on which the resist image is formed is detected. May be.

In the above embodiment, the pattern LS1
LS6 is tilted by θ / 2 with respect to the Y axis. However, the direction of the paired pattern may be in any direction as long as the intersection angle between the two is θ.

In the above embodiment, the case where the present invention is applied to the step-and-repeat type reduction projection exposure apparatus has been described. However, the scope of the present invention is not limited to this. That is, step
The present invention can be suitably applied to an exposure apparatus such as an AND-scan type scanning exposure apparatus. The illumination light for exposure is not limited to ultraviolet light, but may be X-rays (including EUV light) or the like.

Of course, the present invention relates to an exposure apparatus for transferring a device pattern onto a glass plate, which is used not only for an exposure apparatus used for manufacturing a semiconductor element but also for a display including a liquid crystal display element and a plasma display. The present invention can also be applied to an exposure apparatus used for manufacturing a thin-film magnetic head, which transfers a device pattern onto a ceramic wafer, and an exposure apparatus used for manufacturing an imaging device (such as a CCD).

In addition to a micro device such as a semiconductor element, a light exposure apparatus, an EUV (Extreme Ultra
t) The present invention can be applied to an exposure apparatus that transfers a circuit pattern onto a glass substrate or a silicon wafer in order to manufacture a reticle or mask used in an exposure apparatus, an X-ray exposure apparatus, an electron beam exposure apparatus, and the like. . Where DUV
In an exposure apparatus that uses (far ultraviolet) light or VUV (vacuum ultraviolet) light, a transmission reticle is generally used. As the reticle substrate, quartz glass, fluorine-doped quartz glass, fluorite, magnesium fluoride, Alternatively, quartz or the like is used. In addition, a transmission type mask (stencil mask, membrane mask) is used in a proximity type X-ray exposure apparatus or an electron beam exposure apparatus, and a reflection type mask is used in an EUV exposure apparatus, and a silicon wafer is used as a mask substrate. Is used.

In the semiconductor device, a step of designing the function and performance of the device, a step of manufacturing a reticle based on the design step, a step of manufacturing a wafer from a silicon material, and a step of forming a reticle pattern by the exposure apparatus of the above-described embodiment. It is manufactured through a step of transferring to a wafer, a step of assembling a device (including a dicing step, a bonding step, and a package step), an inspection step, and the like.

[0147]

As described above in detail, according to the present invention, it is possible to provide a mask which can be suitably used for measuring the imaging characteristics of a projection optical system.

Further, according to the imaging characteristic measuring method according to the present invention, there is an effect that the imaging characteristic of the projection optical system can be measured accurately and efficiently.

According to the exposure method of the present invention,
There is an effect that the overlay accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a configuration of an exposure apparatus according to one embodiment.

FIG. 2 is a diagram illustrating an example of a reticle used for measuring an imaging characteristic.

FIGS. 3A and 3B are enlarged views of a mark area on the reticle shown in FIG. 2;

FIG. 4 is a view showing a transferred image (latent image) formed on a resist layer when double exposure is performed using the reticle on which the L / S mark shown in FIG. 3B is formed. .

FIG. 5 is an enlarged view showing a part of FIG. 4;

FIG. 6 is a view showing a transfer image (latent image) formed on a resist layer when double exposure is performed using the reticle having the L / S mark shown in FIG. 3A. .

FIG. 7 is a view for explaining double exposure using the reticle shown in FIG. 2;

FIG. 8 is a diagram showing a diamond mark formed in a partitioned area on a wafer.

FIGS. 9A to 9C are views for explaining an exposure method including a third exposure step.

FIG. 10 is a view showing a resist image formed on a wafer by double exposure using a conventional pattern.

[Explanation of symbols]

Reference numeral 42: glass substrate (mask substrate), 44A: first rhombic mark row group (parallelogram mark row), 44B: second rhombic mark row group (parallelogram mark row), 46: aperture pattern (pattern removal) , HM: diamond-shaped mark image, LS1: L / S pattern (first pattern, first partial pattern), LS2: L / S pattern (second pattern,
L / S pattern (third pattern, first partial pattern), LS4 ... L / S pattern (fourth pattern, second partial pattern), LS5 ... L / S
Pattern (first partial pattern), LS6 L / S pattern (second partial pattern), PA pattern area (pattern surface), PL projection optical system, R _T reticle (mask), R reticle (mask) , W: wafer (substrate).

Continued on front page F term (reference) 2F065 AA03 AA39 BB02 BB29 CC20 DD03 FF01 FF42 FF48 FF55 GG04 HH01 JJ01 MM02 PP12 PP24 QQ03 QQ17 QQ42 2H095 BD03 BD06 BE03 BE05 BE08 BE09 5F046 AA25 DA13 DA14 DB05

Claims (14)

[Claims] 1. A first pattern including at least one line pattern having a first line width extending in a first direction and a second pattern forming an angle θ (0 ° <θ <180 °) with the first direction.
A second pattern that includes at least one line pattern having the first line width extending in a first direction, and a second pattern forming a pair with the first pattern, and at least one line pattern having a second line width extending in the first direction; A third pattern comprising:
Any one of a light transmitting portion and a light shielding portion so as to include at least one line pattern having the second line width extending in a direction, and so that the third pattern and the fourth pattern forming a pair do not overlap with each other. A mask comprising a mask substrate formed on the pattern surface. 2. The positional relationship between the first and second patterns and the positional relationship between the third and fourth patterns,
2. The mask according to claim 1, wherein the mask is the same. 3. The method according to claim 1, wherein the first pattern and the second pattern are line-and-space patterns in which a plurality of line patterns having the first line width are periodically arranged. 3. The mask according to 1 or 2. 4. The line pattern according to claim 3, wherein the third pattern and the fourth pattern are line and space patterns in which a plurality of line patterns each having the second line width are periodically arranged. 3. The mask according to 3. 5. The method according to claim 1, wherein the first line width and the second line width are the same, and the first and second patterns are different in arrangement period from the third and fourth patterns. The mask according to claim 4, wherein 6. The method according to claim 3, further comprising a pattern for pattern removal corresponding to at least one of the line and space patterns constituting the first to fourth patterns. The mask as described. 7. An angle α (0 ° <α <180 °, α ≠ 90 °) with respect to the first direction so that a plurality of line patterns having a line width w extending in the first direction have an interval w ′. A first partial pattern disposed along a predetermined intersecting arrangement direction, and an angle θ (0 ° <θ <180 °) with respect to the first direction
The angle α with respect to the second direction is set such that a plurality of line patterns having a line width w extending in the second direction are spaced from each other by w ′.
(0 ° <α <180 °, α ≠ 90 °) any one of the light transmitting portion and the light shielding portion so that the second partial patterns disposed along the arrangement direction intersecting with each other do not overlap each other. And the length y of each line pattern is w / tan (θ / 2) ≦ y <{2w ′ / sin θ + w ·
A mask satisfying tan (θ / 2)｝. 8. An angle α (0 ° <α <180 °, α ≠ 90 °) with respect to the first direction so that a plurality of line patterns having a line width w extending in the first direction have an interval w ′. A first partial pattern disposed along a predetermined intersecting arrangement direction, and an angle θ (0 ° <θ <180 °) with respect to the first direction
Angle α with respect to the second direction so that a plurality of line patterns having a line width w extending in the second direction, which forms
(0 ° <α <180 °, α ≠ 90 °) any one of the light transmitting portion and the light shielding portion so that the second partial patterns disposed along the arrangement direction intersecting with each other do not overlap each other. And a length y of each line pattern is {2w '/ sin θ +
When the length is not less than w · tan (θ / 2)｝, one of the line patterns constituting the first partial pattern and the second partial pattern is one of the first partial pattern and the second partial pattern. A mask characterized in that, when a partial pattern and a partial pattern are transferred onto a substrate, a part of the transferred image is removed so that an unnecessary overlapping portion does not occur between the transferred images. 9. An imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system using the mask according to claim 1, wherein the first and third masks are arranged on the mask. A first exposure step of transferring a plurality of patterns including a pattern onto a substrate via the projection optical system; and a transfer image of the first pattern and the third pattern formed on the substrate to the transfer pattern on the mask. Second
A second exposure step of overlapping and transferring the pattern and the fourth pattern, respectively; an overlapping portion of a transfer image of the first pattern and the second pattern on the substrate, and the third pattern and the fourth pattern; Measuring the length of at least one of the rhombic mark images respectively formed on the overlapped portions of the transferred images, and the imaging characteristics of the projection optical system based on the measured length of the rhombic mark image And a calculating step of calculating the following. 10. An imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system using the mask according to claim 7 or 8, wherein the first partial pattern on the mask is formed by using the projection optical system. A first exposure step of transferring the second partial pattern on the mask onto a transfer image of the first partial pattern formed on the substrate, and a second exposure step of transferring the second partial pattern on the mask; A measuring step of measuring at least one length of a rhombic mark image formed on an overlapping portion of a transfer image of the first partial pattern and the second partial pattern on a substrate; and the measured rhombic mark A calculating step of calculating the imaging characteristics of the projection optical system based on the length of the image. 11. An imaging characteristic measuring method for measuring an imaging characteristic of a projection optical system using a mask on which at least one line and space pattern is formed, wherein a substrate is provided via the mask and the projection optical system. Expose,
A first exposure step of forming a transfer image of a first line-and-space pattern formed of a line pattern extending in a first direction on the substrate; exposing the substrate via the mask and the projection optical system; A transfer image of a second line-and-space pattern formed of a line pattern extending in a second direction intersecting the first direction at a predetermined angle is formed on the transfer image of the first line-and-space pattern formed on the substrate. A second exposure step; four parallel sides formed in the overlapped portions of the transferred images of the first line and space pattern and the second line and space pattern on the substrate by the first and second exposure steps, respectively. A third exposure step of further exposing the substrate so that only an image of a desired parallelogram mark remains in the shape mark row;
A measuring step of measuring a length of a parallelogram mark image formed on the substrate and calculating an imaging characteristic of the projection optical system based on the measurement result. 12. The imaging characteristic according to claim 11, wherein, in the third exposure step, exposure is performed such that only parallelogram marks located at positions other than both ends of the parallelogram mark row remain. Measurement method. 13. The method according to claim 1, wherein in the third exposure step, exposure is performed such that only at least one of the parallelogram marks at both ends of the parallelogram mark row remains.
2. The imaging characteristic measuring method according to 1. 14. An exposure method for transferring a pattern of a mask onto a substrate via a projection optical system, wherein the projection optical system is provided with the imaging characteristic measurement method according to claim 9. An exposure method including: measuring an imaging characteristic; and adjusting various conditions at the time of exposure in consideration of the measured imaging characteristic, and transferring the pattern of the mask onto the substrate.