JPH10254123A - Reticle formed with test patterns - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reticle with which an optimum focal position may be obtd. in a short time without variations and a method for detecting the focal position. SOLUTION: Plural staircase surfaces 52A to 52G are formed stepwise on the reticle such that the distances from a sensitive substrate respectively vary when the reticle is placed on a reticle stage SR. Focus masks 53A to 53G constituting the test patterns are formed on the respective step surfaces 52A to 52G. At this point, the test reticle TR is simultaneously exposed on the sensitive substrate and the test patterns exposed on the sensitive substrate are developed. The developed test patterns are measured. Whether which of the mask forming regions 52A to 52G formed with the test patterns is the optimum focal position is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reticle capable of detecting a focal position of an exposure apparatus by projecting and exposing a test pattern on a sensitive substrate, and a method of detecting a focal position.

[0002]

2. Description of the Related Art When exposing a pattern formed on a reticle onto a wafer, it is important to control the focus state of a printed pattern, and various methods have been conventionally proposed and used. For example, a focus mark is printed while moving the wafer at a fine pitch in the Z-axis direction, and the burned focus mark is scanned with a laser beam to measure a focus adjustment state. For example, the focus mark printed on the wafer is observed to determine the best focus position.

[0003]

However, in the above-described conventional best focus position detection method, the stage is moved in the Z direction to obtain the best focus position, and the focus mark is not sequentially exposed. The time it takes to do so is long. Also, the work of determining the best focus position can be relatively easily obtained by a method of automatically detecting the best focus position by scanning with a laser beam, but the work efficiency is poor when the operator performs the work visually, Also, there are many variations among workers.

[0004] It is an object of the present invention to provide a reticle and a focus position detecting method capable of finding the best focus position in a short time without variation.

[0005]

The present invention will be described with reference to the drawings of the embodiments. The invention of claim 1 is applied to a reticle mounted on a reticle stage RS and capable of detecting the focal position of an exposure apparatus by projecting and exposing a test pattern on a sensitive substrate W as shown in FIG. And
A plurality of step surfaces 5 are provided in a step-like manner so that the distance from the sensitive substrate W when mounted on the reticle stage RS is different from each other.
The above-described object is achieved by forming 2A to 52G and forming focus marks 53A to 53G constituting the test pattern 53 on each of the step surfaces 52A to 52G. The focus marks 53A to 53G formed on each of the step surfaces 52A to 52G can be a plurality of diamond marks. The invention of claim 3 is shown in FIGS.
As shown in (1), the present invention is applied to a reticle that is mounted on a reticle stage RS and that can project and expose a test pattern on a sensitive substrate W to detect a focal position of an exposure apparatus.
Then, reticle TR such that the distance from sensitive substrate W changes continuously when mounted on reticle stage RS.
The above-described object is achieved by forming the inclined surface 62 on the inclined surface 62 and forming the test pattern 63 on the inclined surface 62. In the case of the reticle of claim 3, the test pattern 63
Can be manufactured by uniformly arranging pattern elements SL extending in a direction orthogonal to the inclination direction of the inclined surface 62 in the inclination direction. The invention according to claim 5 is applied to a method for detecting a focal position of an exposure apparatus for projecting and exposing a transfer pattern on a sensitive substrate W, as shown in FIGS. 1, 2 and 5,
Then, an exposure step (step S2) of collectively exposing the reticle TR having the test pattern 53 formed in different formation regions in the optical axis direction of the projection optical system onto the sensitive substrate W;
The above-described object is achieved by providing a developing step (Step S3) for developing the test pattern 53W exposed on the sensitive substrate W and a measuring step (Step S4) for measuring the developed test pattern 53W. In this case, based on the result measured in the measuring step, which pattern forming area 52 in which the test pattern 53W is formed is formed.
It is desirable to further include a determination step (step S5) of determining whether A to 52G are the optimum focus positions. The pattern forming surface of the reticle can be formed in a stepped shape 52A to 52G, or can be formed as an inclined surface 62.

In the description of the means for solving the problems described above, the present invention has been described with reference to the drawings of the embodiments. However, the present invention is not limited to the embodiments. .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An exposure apparatus to which a reticle and a focus position detecting method according to the present invention are applied will be described with reference to FIG.

Exposure light from the mercury discharge lamp 1 is condensed by the elliptical mirror 2, passes through a shutter 3 for controlling the amount of exposure, is made uniform in illuminance by an optical integrator 4, and passes through a main condenser lens CL. The reticle R is illuminated. Assuming that the light emission intensity of the discharge lamp 1 is substantially constant, a constant exposure amount can always be obtained by controlling the opening time of the shutter 3 by the shutter controller 6.

The reticle R has an X direction, a Y direction, and θ
It is held on a reticle stage RS that slightly moves in the rotation direction. As the reticle R, a device reticle having a circuit pattern formed thereon, a device reticle having a test pattern formed around the reticle separately from the circuit pattern, a test reticle having a test pattern formed at the center of the reticle, or the like is used. Hereinafter, a case where the best focus position is detected using a test reticle will be mainly described.

The light transmitted through the reticle R is reflected by the projection lens PL.
Is image-formed and projected onto the wafer W. The initial position of reticle R is set by finely moving reticle stage RS based on a mark detection signal from reticle alignment system 5 that photoelectrically detects an alignment mark around reticle R.

Before exposing the circuit pattern, it is necessary to detect the best focus position of the exposure apparatus, and a test reticle to be described later is mounted on the reticle stage RS. In this case, after mounting the wafer W on the wafer stage ST and focusing on one test pattern on the test reticle, a plurality of test patterns are collectively exposed, and a plurality of test patterns are Form. And
The test pattern printed on the wafer W is developed to determine which test pattern is the best focus, and the offset amount of the wafer stage ST in the Z-axis direction is calculated. Here, the offset amount refers to the wafer stage S with respect to the best focus position detected by the AF sensor described later.
This is the amount of movement of T in the Z-axis direction. That is, the true best focus position is set by finely moving the wafer stage ST by this offset amount with respect to the best focus position detected by the AF sensor when the circuit pattern is exposed on the wafer W.

On the other hand, the wafer W
When printing a circuit pattern thereon, the wafer W is placed on the wafer stage ST, and the position of the wafer stage ST in the Z-axis direction is adjusted so as to be at the above-described best focus position. Then, the wafer stage ST is moved by a fixed amount X
The reticle R is moved in such a manner that the circuit pattern of the reticle R is printed for each shot area on the wafer W. The position of wafer stage ST is measured by an interferometer, and the position of wafer stage ST is controlled by driving and controlling a stage drive motor by wafer stage controller 7.

In FIG. 1, a wafer alignment system 11
Is for detecting various patterns such as the alignment mark IR on the wafer W. A laser beam from a laser light source 11a such as He-Ne is applied to a lens system 11b including a cylindrical lens and the like, a beam splitter 1
1c, and is bent by the mirror M via the objective lens 10, and is irradiated as slit light vertically onto the wafer W from outside the axis of the projection lens PL through the center of the entrance pupil of the projection lens PL. The return light from the wafer W travels backward through the projection lens PL, is reflected by the beam splitter 11c via the objective lens 10, passes through the pupil relay system 11d, the spatial filter 11e, and transmits the diffracted light and the scattered light to the photoelectric element 11f. Received.

The photoelectric signal from the photoelectric element 11f is input to a signal processing system 12, and a mark position is detected based on a waveform corresponding to a mark (pattern) profile. At this time, the signal processing system 12 is based on the position measurement pulse from the interferometer in the stage controller 7, and the photoelectric element 11 obtained when the spot light and the wafer W are relatively moved.
The signal waveform from f is sampled. Then, based on the sampling signals obtained by the TTL type wafer alignment system 11 and signal processing system 12, a test pattern on the wafer W, which will be described later, is automatically measured.

When the circuit pattern of the reticle R is printed on the wafer W, the best image forming surface of the projection lens PL, that is, the surface on which the pattern image of the reticle R is formed with the highest contrast, and the resist surface of the wafer W are accurately aligned. Must match. Therefore, in this embodiment, an oblique incident light type focus detection system (AF sensor) is provided. The AF sensor makes the light from the non-photosensitive light source 14 insensitive to the resist layer into an image forming light flux by the projection optical system 15 and projects it obliquely onto the wafer W, and the reflected light passes through the light receiving optical system 16 and the slit 17. The light is received by the photoelectric detector 18. And the projection lens PL
When the best image forming surface coincides with the resist surface, the detector 18 outputs a focusing signal. When the wafer surface is displaced in the optical axis direction with respect to the best image surface, the amount corresponding to the amount of the displacement is determined. Output a signal. These signals (AF signals) representing the focus and the defocus are processed by a focus control unit (AF unit) 9. The main control system 8 totally controls various operations of the main body of the projection exposure apparatus.

FIG. 2 is a plan view of a test reticle showing an embodiment of the reticle according to the present invention. The region 51 of the test reticle TR is a region where a circuit pattern is formed in the device reticle, and has a stepped surface 52A-52 provided with a step in the Z-axis direction as shown in FIG.
52G are formed. Focus marks 53A to 53G are formed on each of the step surfaces 52A to 52G. The seven focus marks 53A to 53G are collectively called a test pattern. This focus mark 53
Each of A to 53G is formed by arranging five diamond marks elongated in the Y-axis direction in the X-axis direction. The step surface 52D is flush with the surface SR of the test reticle TR. When one of the focus marks 53A to 53G is focused and the other is exposed on the wafer W in a defocused state, the length of the mark 53W exposed on the wafer W in the Y-axis direction as shown in FIG. Changes greatly.

A method for obtaining the best focus position using such a test reticle will be described. The test reticle TR shown in FIG. 2 is placed on the reticle stage RS, and the reticle stage RS is finely moved based on the mark detection signal from the reticle alignment system 5 to initialize the reticle R. The wafer W is placed on the wafer stage ST, and the wafer W is initialized by a photoelectric signal from the photoelectric element 11f of the wafer alignment system 11. In this state, the wafer stage ST is moved to direct the optical axis of the projection lens PL to an arbitrary shot area on the wafer W. further,
The AF sensor performs focus detection so that the surface of the reticle R, that is, the pattern surface of the step surface 52D is focused on the wafer W. As a result, the amount of deviation between the best imaging plane of the projection lens PL and the resist plane on the wafer W is detected and input to the AF controller 9, and the Z-axis position of the wafer stage ST is adjusted. And the shutter controller 6
To open the shutter 3 and print the test patterns of the step surfaces 52A to 52G on an arbitrary shot area at a time.
The test pattern is visualized by developing the wafer W. The developed wafer W is placed on the wafer stage ST, and the length of the focus mark in the Y-axis direction is measured to detect the step surface at which the best focus is obtained.

FIG. 3 is a view showing a focus mark 53W formed in an arbitrary shot area SH on the wafer W after developing the wafer W. 52WA to 52WG correspond to the step marks 52A to 52G on the wafer W. Represents the region to be used. As shown in FIG. 3, the stair surface 52D which is the best focus
Is the longest in the Y-axis direction. The positions of the focus marks 53A to 53G on the reticle in the Z axis direction are the mark forming surfaces 52A to 52G.
Since it changes on the Z-axis due to the step due to 2G, the wafer W
In the above, the images are printed as if the focus was changed one by one. As a result, the focus marks on the step surface located on the left and right of the step surface 52D are in a front focus state and a rear focus state,
The image shift amount increases and the length of the focus mark 53W on the wafer W in the Y-axis direction decreases as shown in FIG.

The measurement of the length of the focus mark in the Y-axis direction can be performed by using the wafer alignment system 11 and the signal processing system 12 and relatively scanning the slit-shaped laser beam and the wafer W. That is, as shown in FIG. 4, the slit-shaped laser beam LB is applied to each region 52W in the X-axis direction.
A is extended by the width of A to 52WG, and the wafer stage ST is moved in the Y-axis direction to move each of the regions 52WA to 52WG.
Is relatively scanned for each focus mark 53W. In this case, scattered light is generated from the edge of the focus mark 53W extending in the Y-axis direction. Also, the focus mark 53
If the diamond-shaped mark of W has a periodic structure similar to the diffraction grating mark, diffracted light corresponding to the period is also generated, and these are received by the photoelectric element 11f, and are signaled as a photoelectric signal corresponding to the amount of received light. It is input to the processing system 12. The photoelectric signal has, for example, a waveform as shown in FIG. 4B. Therefore, if the threshold is appropriately determined and binarization processing is performed to calculate the interval between high-level signals, the length L of the diamond-shaped mark is obtained. Can be detected.

The operation of detecting the best focus position will be described with reference to the flowchart of FIG. After placing the test reticle TR on the reticle stage RS and positioning it as described above, the Z-axis position of the wafer stage ST is adjusted so as to focus on the step surface 52D (step S1). Focus marks 53A to 53G are
A batch exposure is performed on the upper surface (step S2). Then, the wafer W
Is carried out from the projection exposure apparatus and developed (step S
3). The developed wafer W is carried into the projection exposure apparatus again, set on the wafer stage ST, and the focus marks 53W on the step surfaces 52A to 52G are respectively set by the wafer alignment system as described above.
The length L in the axial direction is measured (step S4), and these signals are sent from the signal processing system 12 to the main control system 8. The main control system 8 selects an area in which the mark having the longest signal is formed from the measured values, and determines which staircase surface has the best focus (step S5).

If the focus mark on the step surface 52D is the best focus, the wafer W is focused on the front surface SR of the test reticle TR. Therefore, it is necessary to adjust the position of the wafer W in the Z-axis direction with respect to the focus position detected by the AF sensor. There is no. When it is determined that the focus mark 53W other than the step surface 52D is in the best focus, the step surface and the step surface 52D are determined.
The wafer W is moved to Z in accordance with the height deviation from D (reticle surface).
In order to adjust the position in the axial direction, the deviation is stored as an offset amount (step S6). At the time of actual exposure, an in-focus state of an arbitrary shot area on the wafer W is measured by the AF sensor, and an offset amount is added to the measured value to adjust the height position of the wafer W in the Z-axis to perform exposure.

FIG. 6 is a view showing an example of a method of manufacturing the test reticle TR of FIG. In FIG. 6, the test reticle TR includes three divided reticles TRa, TRb, TRc, and stepped surfaces 52A to 52G as shown in FIG. 2A are formed in the central divided reticle TRb. Split reticle TRb from above and below
The test reticle TR is created by being sandwiched between the layers c and by an adhesive. In this way, a stepped surface 52A to 52G can be formed by a normal grinding operation on the surface of a rectangular prismatic material prepared as the divided reticle TRb, and the stepped surface is formed at the center of the flat plate. The manufacturing process is simplified and the cost is reduced.

FIG. 7 is a diagram showing an example of another embodiment of the test reticle according to the present invention. The inclined surface 6 as shown in FIG.
Form 2 The central surface of the region 62D at the center of the inclined surface is made to coincide with the reticle surface SR, and the regions 62A, 62B, 62C, 6 are equally inclined to the left and right of the region 62D.
2E, 62F and 62G are formed. Then, the test pattern 63 is formed by forming linear pattern element wires SL extending in a direction orthogonal to the inclination direction of the inclined surface 62 at uniform intervals in the inclination direction.

Using such a test reticle TR and the test reticle TR and the wafer W in the same manner as described above.
To any shot area SH on the wafer W
Coincide with the optical axis of the projection lens PL, and the test reticle T
The test pattern is collectively exposed by adjusting the focus on the surface of R, that is, the center of the region 62D, and further developed.

FIG. 8A shows an area 62D by the AF sensor.
Focus mark 63 printed with focus on
W, and the length of the center focus mark 63W in the Y-axis direction is the maximum. FIG. 8B shows a focus mark 63W printed when the best focus is performed on an area on the left side of the central area 62D.

In the case of the test reticle TR shown in FIG.
Since it is difficult to know which of the regions 62A to 62G on the inclined surface is in focus, it is preferable to form the index 64 along the focus mark 63 as shown in FIG. FIGS. 10A and 10B respectively show FIGS.
The index 64W printed on the wafer W in (b)
FIG.

The test reticle TR shown in FIG. 7 can be formed by bonding three divided reticles TRa, TRb and TRc to each other as shown in FIG. 11, similarly to the test reticle of FIG. In this case, the center divided reticle TRb remains a quadratic prism, and the rotation axis AX is erected on the upper and lower surfaces thereof, and the shaft hole HL in which the rotation axis fits on the lower surface of the upper divided reticle TRa and the upper surface of the lower divided reticle TRc. May be provided, and the center divided reticle TRb may be rotated by a predetermined angle and bonded as shown by the two-dot chain line in FIG.

FIG. 12 is a view showing an example of another embodiment of the test reticle according to the present invention. As shown in FIG. 12B, the central part of the circuit pattern formation region 71 is
Step surfaces 72A to 72G (generally referred to as step surfaces 72) having steps in the Z-axis direction as shown in FIG. 2A are formed. Each of the steps 72 has a focus mark 7
3AA, 73AB, 73AC and 73AD are formed.

In FIG. 12 (c), the focus mark 73AA is obtained by arranging a plurality of straight lines extending in the X direction in the Y axis direction. The focus mark 73AB is obtained by arranging a plurality of straight lines extending in the Y direction in the X axis direction. The focus mark 73AC is obtained by arranging a plurality of straight lines inclined at +45 degrees with respect to the X axis in the direction of -45 degrees with respect to the X axis. The focus mark 73AC is obtained by arranging a plurality of straight lines inclined at -45 degrees with respect to the X axis in the direction of +45 degrees with respect to the X axis. That is, the focus mark 73 moves in the X-axis direction,
It is composed of four marks extending in the Y axis direction, in the +45 degree direction with respect to the X axis, and in the -45 degree direction with respect to the X axis.

Such focus marks 73AA, 7AA
If 3AB, 73AC, and 73AD are formed on each step surface 72, aberrations (field curvature aberration, spherical aberration, astigmatism, etc.) of the projection lens PL can also be confirmed. Therefore, it is possible to obtain the focal position (step surface) having the least aberration. The focus mark 73 is not limited to a straight line but may be a diamond mark.

FIG. 13 is a diagram showing an example of still another embodiment of the test reticle according to the present invention. FIG.
As shown in FIG. 13B, inclined surfaces 82X and 82Y (generally referred to as inclined surfaces 82) which are inclined in the Z-axis direction as shown in FIG. A diamond mark is formed on each of the inclined surfaces 82. By forming such focus marks 82X and 82Y, the optimum focal position of the projection lens PL in the X and Y axis directions can also be confirmed. For example,
If an optimum image is obtained at the mark 82C in the X-axis direction and an optimum image is obtained at the position of the mark 82D (the Y-axis direction is not shown) in the Y-axis direction, the marks 82C and 82C
An average position in the Z-axis direction with respect to D may be determined as the optimum focus position. The focus mark 82 may be a linear mark instead of a diamond mark.

Although the case where a plurality of test patterns are formed on the test reticle has been described above, the present invention can be similarly applied to a device reticle in which a circuit pattern is formed in a central portion and a test pattern is formed in a peripheral portion. Further, although the shape of the focus mark is diamond-shaped, it is not limited to this. Further, in the case of a test reticle having a stepped surface, the case where the heights of the formation surfaces of the seven focus marks are changed has been described. However, the number of the stepped surfaces is not limited to seven. A surface can be formed. Furthermore, although it has been described that the inclined surface has seven regions, the region may be divided more finely. Furthermore, the sensitive substrate is not limited to a wafer, and may be a glass substrate or the like.

[0033]

The reticle according to the first to fourth aspects of the present invention has a plurality of stepped surfaces formed in steps so as to have different distances from the sensitive substrate when mounted on the reticle stage, or an inclined surface. To form focus marks on each of these stairs, and to form a uniform test pattern on the inclined surface along the direction of inclination. Then, compared to the case where the height of the sensitive substrate is moved little by little using one focus mark (test pattern) and printed,
The efficiency of the operation for detecting the best focus position is improved. According to the focus position detecting method of the present invention, test patterns formed in different formation regions in the optical axis direction of the projection optical system are collectively exposed on the sensitive substrate, the test patterns are developed, and further developed. Since the best focus position can be detected by measuring the performed test pattern,
Compared with the case where the height of the sensitive substrate is moved little by little using one focus mark (test pattern) and printing is performed, the efficiency of the pre-operation for detecting the best focus position is improved. As in the method according to claim 6, if it is determined which pattern forming area is the optimum focus position based on the measurement result of the developed test pattern, it is not necessary to visually detect the test pattern having the best focus. In addition, high-precision detection can be performed without variation.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a configuration example of a projection exposure apparatus using a reticle according to the present invention.

2A is a sectional view taken along line aa of FIG. 2B, showing an example of a test reticle, and FIG.

FIG. 3 is a view showing a focus mark printed on a wafer.

FIG. 4 is a view for explaining a method of measuring the length of a focus mark in the Y-axis direction.

FIG. 5 is a flowchart illustrating a process of detecting a staircase having the best focus from among focus marks.

FIG. 6 is a perspective view illustrating a method for manufacturing the test reticle shown in FIG. 2;

FIGS. 7A and 7B are diagrams showing another embodiment of the test reticle, wherein FIG. 7A is a cross-sectional view taken along line aa of FIG.

8 is a diagram showing a case where the focus mark of FIG. 7 is printed on a wafer.

FIG. 9 is a plan view showing a test reticle obtained by adding an index to the test reticle of FIG. 7;

FIG. 10 is a diagram showing a case where the focus mark of FIG. 9 is printed on a wafer.

FIG. 11 is a perspective view illustrating a method for manufacturing the test reticle shown in FIG. 7;

FIGS. 12A and 12B are diagrams showing still another embodiment of the test reticle, wherein FIG. 12A is a cross section taken along line aa of FIG. 12B, FIG. 12B is a plan view, and FIG.

13A and 13B are diagrams showing still another embodiment of the test reticle, wherein FIG. 13A is a cross-sectional view taken along line aa of FIG. 13B, and FIG.

[Explanation of symbols]

51 Circuit pattern area 52A to 52G Stepped surface 53, 63 Focus mark on test reticle 53W, 63W Focus mark 71, 81 Circuit pattern area 72A to 72G Stepped surface 73AA to 73AD Mark 82X, 82Y Slope R Reticle RS Reticle stage TR Test reticle W Wafer ST Wafer stage

Claims (8)

[Claims] 1. A reticle mounted on a reticle stage and capable of detecting a focal position of an exposure apparatus by projecting and exposing a test pattern on a sensitive substrate. A reticle, wherein a plurality of steps are formed stepwise so that the distances are different from each other, and a focus mark constituting the test pattern is formed on each of the steps. 2. A reticle according to claim 1, wherein said focus mark formed on each of said step surfaces comprises a plurality of diamond marks. 3. A reticle mounted on a reticle stage and capable of detecting a focal position of an exposure apparatus by projecting and exposing a test pattern on a sensitive substrate, wherein the sensitive substrate is placed on the reticle stage when the reticle is mounted on the reticle stage. A reticle, wherein an inclined surface is formed such that a distance of the test pattern continuously changes, and the test pattern is formed on the inclined surface. 4. The reticle according to claim 3, wherein the test pattern is formed by arranging pattern elements extending in a direction orthogonal to the inclined direction of the inclined surface, in a uniform line in the inclined direction. Reticle. 5. A method for detecting a focal position of an exposure apparatus for projecting and exposing a transfer pattern on a sensitive substrate, comprising: disposing a reticle having a test pattern formed in a different region in an optical axis direction of a projection optical system on the sensitive substrate. A method of detecting a focal position, comprising: an exposure step of performing a batch exposure; a development step of developing the test pattern exposed on the sensitive substrate; and a measurement step of measuring the developed test pattern. 6. The focus position detecting method according to claim 5, wherein a pattern forming area where the test pattern is formed is an optimum focus position based on a result measured in the measuring step. A focus position detection method, further comprising: 7. The method according to claim 5, wherein the pattern forming surface of the reticle is formed in a step shape. 8. The focus position detecting method according to claim 5, wherein the pattern forming surface of the reticle is formed in an inclined shape.