JP2002305139A - Mark and method for alignment for pattern exposure, and aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mark and a method for alignment for pattern exposure and an aligner where the alignment accuracy is enhanced at low cost, without deterioration in the space efficiency in mark placement. SOLUTION: An aligning method utilizing heterodyne interference method is adopted, and an alignment marks MK1 on a wafer are so designed that a minimum pitch Pm of the alignment marks is smaller than the pitch P of the conventional alignment marks. The aligner is so constituted that alignment light beams (two beams) are projected at an angle, variable controlled in correspondence with the pitch Pm. Variations in the phase of a beat signal, which act as alignment signal, are detected as a value higher, as compared with conventional cases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of semiconductor devices, and more particularly, to pattern exposure alignment for improving the overlay accuracy when sequentially exposing an integrated circuit pattern onto a semiconductor wafer. The present invention relates to a mark, a positioning method, and an exposure apparatus.

[0002]

2. Description of the Related Art A circuit pattern required for manufacturing an LSI is sequentially exposed on a semiconductor wafer by a plurality of reticle patterns. For example, a reduction projection exposure apparatus (not shown) in which a predetermined reticle is set projects and exposes a pattern repeatedly while shifting the projection target area on the wafer one after another. As a result, a predetermined number of integrated circuit chip areas are obtained in the semiconductor wafer.

[0003] Integrated circuit chip areas are separated by a scribe line area. Generally, alignment marks (alignment marks) for aligning a plurality of types of patterns to be exposed are provided in the scribe line area. In addition, a pattern such as a dedicated configuration (TEG (Test Elementary Group)) related to product inspection or evaluation in manufacturing is also provided.

As described above, a plurality of pattern exposures are superimposed on one area of the integrated circuit chip area in accordance with the alignment mark. It is well known that this results in an overlay (alignment) error of the exposure pattern.
Therefore, it is important to reduce the misalignment to an allowable range by appropriately correcting the exposure distance, the stage position, and the like. For that purpose, it is necessary to accurately grasp a positioning error according to the positioning mark.

[0005]

FIG. 7 is a configuration diagram showing an example of a conventional pattern exposure alignment mark and an alignment method. The frequency is slightly different from the alignment mark MK on the wafer (for example, Δf = 25 kHz).
z) Irradiate two light beams (for example, He-Ne laser) a and b obliquely from different angles. At this time, if the angle (θ) formed by the two light beams satisfies the following equation, one + 1st-order diffracted light coincides with and overlaps with the other −1st-order diffracted light. sin (θ / 2) = n · λ / P (1) (P: mark pitch, λ: wavelength of light, n: diffraction order (=
1))

[0006] The overlapped light produces a beat whose frequency is the difference between the frequencies, and this beat becomes a positioning signal. The phase of the light diffracted by the mark MK as a diffraction grating changes according to the mark position (that is, the wafer position), and the amount of change (Δψn) is n the diffraction order, Δx the mark position movement amount, and the mark pitch. To P
Is represented by the following equation. Δψn = n · 2π · Δx / P (2)

Accordingly, the phase change amount Δφ of the beat signal generated by the ± first-order light is represented by the following equation from (Δψ + 1−Δψ−1). Δφ = 4π · Δx / P (3)

In practice, a positioning signal (beat signal)
Changes with time (frequency 25 kHz).
Therefore, a signal serving as a reference (reference signal) is required to detect a phase change of the alignment signal due to the displacement of the wafer. That is, the change in the phase difference between the reference signal and the positioning signal is measured.

By the way, the phase of the positioning signal is ± π
(A shift for a period cannot be detected), it is necessary to drive the wafer position shift to ± P / 4 or less in advance. At present, this driving is performed by using another alignment sensor. This allows
The use of a plurality of alignment sensors causes the system to be complicated, increases the cost, and degrades the space efficiency of the mark arrangement.

Furthermore, since the resolution of the phase difference measuring instrument is fixed, it is not possible to detect a phase change exceeding this resolution, which hinders an increase in the positioning accuracy. In other words, an expensive system is required to increase the resolution itself of the phase difference measuring device, which is not economical.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and does not degrade the space efficiency of the mark arrangement and can achieve an inexpensive improvement in the alignment accuracy. A method and an exposure apparatus are provided.

[0012]

The alignment mark for pattern exposure according to the present invention irradiates two alignment light beams, each of which has an incident angle variably controlled, when utilizing the alignment system of the heterodyne interference method. Therefore, in addition to the predetermined pitch, at least a smaller pitch is set for the pattern in which the diffraction edges are arranged.

According to the alignment mark for pattern exposure according to the present invention, the alignment light is irradiated from an angle corresponding to a small pitch, and a beat signal serving as an alignment signal is generated. As a result, the phase change of the beat signal is detected as a larger value than in the related art.

In order to further improve the space efficiency of the mark arrangement and to obtain more optimal signal information of the alignment signal, a pattern in which the diffraction edge irradiated with the alignment light is shared in both the x and y directions is provided. It is characterized by doing. Further, the present invention is characterized in that the duty ratio with respect to the adjacent patterns having the diffraction edge irradiated with the alignment light is changed.

In the method of aligning the pattern exposure alignment mark according to the present invention, when using the alignment method of the heterodyne interferometry, each alignment light of two light beams is applied to the alignment mark where the diffraction edge is arranged. Is irradiated by variably controlling the incident angle to obtain an appropriate alignment signal.

According to the method of aligning the alignment mark for pattern exposure according to the present invention, the alignment light is applied to the mark by variably controlling the incident angle. The optimal signal information of the alignment signal can be obtained, and the space efficiency of the mark arrangement is further improved.

An exposure apparatus according to the present invention relates to an exposure apparatus using a positioning method of heterodyne interferometry, and variably controls an incident angle of each of two positioning light beams with respect to a positioning mark having a diffraction edge. And a signal processing unit that calculates a phase difference by comparing a positioning signal obtained from the irradiation of the positioning light with a reference signal.

According to the exposure apparatus of the present invention, the optimal signal information of the alignment signal can be obtained by the control mechanism, and the space efficiency of the mark arrangement is further improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B are configuration diagrams showing a pattern exposure alignment mark and an alignment method according to a first embodiment of the present invention. An alignment method using heterodyne interferometry is adopted.

The alignment marks MK1 on the wafer is smaller than the pitch P of traditional alignment mark MK shown the minimum pitch P _m of the pattern adjacent to each other in FIG 7 with a diffraction edge. And the pitch P _m
Irradiate the alignment light (two light beams) from an angle corresponding to
A beat signal serving as a positioning signal is generated. Thereby, the phase change of the beat signal can be detected as a larger value than in the related art.

[0021] In FIG. 1 (a), for example, the pitch P _m of the alignment mark MK1 is set to 1/2 of the pitch P of the conventional alignment mark MK shown in FIG 7 has (P _m = P / 2). The inside marks MK1 contains an integer N (1, 2, 3 ...) multiple of the pitch of P _m. Two light beams (for example, He−) having slightly different frequencies (for example, Δf = 25 kHz) with respect to such an alignment mark MK1.
Ne lasers) aN and bN are irradiated obliquely from different angles (see FIG. 1B).

In FIG. 1B, the angle of incidence θN is
Ku MK1 pitch P_m, 2P_m, 3P _mThe three types of places
It is variable according to the case. At this time, the two beams
When the angle (θN) satisfies the following equation, one of the + 1st-order diffracted light and
The other -1st-order diffracted lights coincide and overlap. sin (θN / 2) = λ / (N · P_m)… (4) (P_m: Mark pitch (P / 2), λ: wavelength of light, N:
1,2,3)

The overlapped light produces a beat whose frequency is the difference between the frequencies, and this beat becomes a positioning signal. The phase of the light diffracted by the mark MK1 as a diffraction grating changes according to the mark position (that is, the wafer position), and the amount of change (ΔψN) is, for the first-order diffracted light, the amount of movement of the mark position, Δx pitch as P _m is expressed by the following equation. ΔψN = 2π · Δx / (N · P _m ) (5)

Therefore, the phase change amount ΔφN of the beat signal generated by the ± first-order light is expressed by the following equation from (Δψ + N−Δψ-N). ΔφN = 4π · Δx / (N · P _m ) (6)

Actually, a positioning signal (beat signal)
Changes with time (frequency 25 kHz).
Therefore, a signal serving as a reference (reference signal) is required to detect a phase change of the alignment signal due to the displacement of the wafer. That is, the change in the phase difference between the reference signal and the positioning signal is measured.

According to the first embodiment, the minimum pitch P _m of the alignment mark MK1 conventional 1/2 (i.e. P _m
= P / 2). Since in the mark MK1 that contains an integer N (1, 2, 3 ...) multiple of the pitch of P _m, can accommodate more than one pitch at one of the marks MK1, improves space efficiency during mark arrangement.

For example, when the incident angle (θ N) of the alignment light (two light beams) is set to an angle corresponding to the mark pitch 2P _m (= P), alignment can be performed with the same configuration as in the related art.

Further, when the angle of incidence (θN) of the positioning light (two light beams) is set to an angle corresponding to the mark pitch P _m (= P / 2), the phase change of the positioning signal (beat signal) is as follows. It is expressed by an equation.

Δψ (N = 1) = 4π · Δx / 1P _m = 8π · Δx / P (7) Accordingly, the phase change is detected as a value twice as large as the conventional value (the mark pitch is P). As described above, even when the displacement Δx of the wafer is the same, the phase change is measured to be doubled, so that the accuracy of the phase difference measurement can be improved without increasing the resolution of the phase difference measuring device, and the position The alignment accuracy is improved.

When the incident angle (θN) of the positioning light (two light beams) is an angle corresponding to the mark pitch 3P _m (= 3P / 2), the phase change of the positioning signal (beat signal) is as follows. It is expressed by an equation. Δψ (N = 1) = 4π · Δx / 3P _m = 8π · Δx / 3P (8)

Therefore, the phase change is detected as a value of 2/3 of the conventional one (the mark pitch is P). Accordingly, the positional deviation of the wafer before the alignment is within an allowable range up to 3/2 times the conventional value (± P / 4), and the margin is increased 1.5 times.

[0032] Thus, even without forced misalignment of advance wafers with another alignment sensor, implemented alignment for the purpose of thrust in mark pitch 3-Way _m, then the mark pitch P _m or 2P _m And high-accuracy positioning can be performed. As a result, concerns about system complexity and cost increase due to the use of a plurality of alignment sensors are eliminated. Also, it contributes to the improvement of the mark arrangement space.

In the first embodiment, the shape of the alignment mark MK1 is one direction (y) as shown in FIG.
Direction), a vertically elongated slit-like diffraction grating configuration having diffraction edges only in the direction is shown. In the actual mark arrangement space, it is necessary to separately arrange a horizontally long slit-like diffraction grating form having a diffraction edge in the x direction. In order to avoid this form, a form having diffraction edges arranged at the same pitch in the x and y directions in the same alignment mark is also conceivable.

FIG. 2 is a configuration diagram showing a pattern exposure alignment mark according to a second embodiment of the present invention. The alignment mark MK2 on the wafer has a form in which diffraction edges are arranged at the same pitch in both the x and y directions. This makes it possible to share the alignment marks in the x and y directions simultaneously instead of separately arranging them.

[0035] may be smaller than the pitch P of traditional alignment mark MK shown also its minimum pitch P _m in the alignment mark MK2 by FIG 7.
Thus, by irradiating the alignment light (double beam) from an angle corresponding to the pitch P _m, to generate a beat signal as a positioning signal. Thereby, the phase change of the beat signal can be detected as a larger value than in the related art. As described above, since one alignment mark MK2 can also serve as the mark in the x and y directions, the space efficiency at the time of positioning the alignment mark is further improved.

The line width (L) and the space width (S) of the alignment mark MK1 in the first embodiment are each half the mark pitch, that is, the duty ratio (S / L) = 1. Is ideal (the same applies to the second embodiment). However, actually, it does not always coincide with (S / L) = 1 due to the process. When the duty ratio (S / L) changes,
The intensity of the first-order diffracted light also changes. Depending on the value of (S / L), the intensity of the positioning signal becomes weak, which may cause deterioration of the positioning accuracy. You may want to address these concerns as follows:

FIG. 3 is a block diagram showing a method of aligning a pattern exposure alignment mark according to a third embodiment of the present invention. Alignment mark MK3 on wafer
Is the same as the pitch P of the conventional alignment mark MK shown in FIG. Here, a positioning method using heterodyne interferometry is adopted.

As shown in FIG. 3, two light fluxes for generating a beat signal serving as a positioning signal are not fixed to ± 1st-order diffracted lights, and higher-order diffracted lights can be selected and used. . Two light beams (for example, He-Ne lasers) an and bn having slightly different frequencies (for example, Δf = 25 kHz) are irradiated obliquely from different angles to the alignment mark MK3.

At this time, if the angle (θn) formed by the two light beams satisfies the following equation, one + n-order diffracted light coincides with the other −n-order diffracted light and overlaps. sin (θn / 2) = n · λ / P (9) (P: mark pitch, λ: wavelength of light, n: diffraction order)

The overlapped light produces a beat having a frequency difference between the frequencies, and this beat becomes a positioning signal. The phase of the light diffracted by the mark MK3 as a diffraction grating changes in accordance with the mark position (that is, the wafer position). Is represented by the following equation, where P is P. Δψn = n · 2π · Δx / P (10)

Therefore, the phase change amount Δφn of the beat signal generated by the ± n-order light is represented by the following equation from (Δψ + n−Δψ-n). Δφn = 4nπ · Δx / P (11)

Actually, a positioning signal (beat signal)
Changes with time (frequency 25 kHz).
Therefore, a signal serving as a reference (reference signal) is required to detect a phase change of the alignment signal due to the displacement of the wafer. That is, the change in the phase difference between the reference signal and the positioning signal is measured.

According to the method of the third embodiment, even if the duty ratio of the alignment mark MK3 changes and the intensity of the ± 1st-order diffracted light decreases, the position is switched to the higher-order diffracted light and the positioning signal (beat) is changed. Signal).
Of course, the minimum pitch of the alignment mark MK3 may be smaller than the pitch P of the conventional alignment mark MK shown in FIG. 7, as in the first embodiment. Similar effects can be obtained by applying the method of the third embodiment to those sharing the alignment marks in the x and y directions as in the second embodiment.

Further, as a method for solving the concern that a change in the duty ratio (S / L) of the alignment mark may cause deterioration of the alignment accuracy, the following other forms are also conceivable.

FIG. 4 is a configuration diagram showing a pattern exposure alignment mark according to a fourth embodiment of the present invention. The alignment mark MK4 on the wafer has a configuration in which the duty ratio (S / L) of the mark is continuously changed while the pitch P of the conventional alignment mark MK shown in FIG. 7 is fixed. For such a mark MK2, a positioning method using heterodyne interferometry is adopted.

According to the configuration of the fourth embodiment, the shape of the alignment mark MK4 positively changes the deughness ratio (S / L) within the same mark. For this reason, even if the deughness ratio changes due to the manufacturing process, a duty ratio at which the alignment signal can be obtained with a stable intensity always exists in the mark. That is, a positioning signal (beat signal) based on ± 1st-order diffracted light
Even if only the signal is used, a positioning signal (beat signal) can be obtained in a duty ratio region where a stable intensity can be obtained.

The alignment mark MK4 on the wafer
Has a configuration in which the duty ratio (S / L) is continuously changed. However, the configuration is not limited to this, and a configuration in which the duty ratio is intermittently changed may be used.

FIG. 5 is an enlarged view of a diffraction edge portion showing a configuration of a pattern exposure alignment mark as a modification of FIG. The alignment mark MK5 has a configuration in which the duty ratio (S / L) of the mark is intermittently changed. An alignment method using heterodyne interferometry is adopted for the mark MK5. Even with such a configuration, the duty ratio at which the positioning signal (beat signal) can be obtained with a stable intensity always exists in the mark.

According to the configuration of the fourth embodiment and its modification, even if the duty ratio (S / L) of the alignment mark changes due to the manufacturing process, it is possible to prevent the alignment from being impossible and the deterioration of the alignment accuracy. be able to.
Conventionally, the duty ratio (S
/ L) has been set for each manufacturing process in order to make it close to 1, but there is also an advantage that it is not necessary.

FIG. 6 is a schematic view showing the structure of a main part of an exposure apparatus according to a sixth embodiment of the present invention. As described above, in the alignment method using the heterodyne interference method, the exposure apparatus 60 changes the incident angle of the alignment light (two light beams) to be irradiated on the alignment mark MK on the wafer WF. That is, a control mechanism 61 for controlling the optical path shift units OPS1 and OPS2 provided at the preceding stage of the lens AL required for alignment and switching the incident angle to the mark is provided.

For example, He-Ne from a light source (not shown)
The laser light Lf passes through the respective acousto-optic devices AOM1 and AOM2 and the respective diffraction optical filters FLT1 and FLT2 via the beam splitter BS. The two light beams having slightly different frequencies obtained in this way pass through, for example, the optical path shift units OPS1 and OPS2 and the lens AL that involve the rotation control of the harvesting mirror. As a result, the two light beams for positioning are shifted by the optical path shift units OPS <b> 1
By the control of 2, the target alignment mark is irradiated at a predetermined angle corresponding to each of the first and third embodiments.

Also, by using the mark shapes as in the second and fourth embodiments, it is possible to obtain more positioning signals in a limited space and select an optimum positioning signal from the signals. Yes (or more). The positioning signal and the reference signal are digitized by the signal processing unit 62, and the arithmetic processor calculates the phase difference between them. It may be determined from a plurality of types of phase difference calculation results different in the incident angle of the alignment signal and the signal acquisition region. In this way, the measurement range can be widened and the misalignment can be driven in, thereby realizing highly accurate alignment.

According to each of the above-described embodiments, a highly accurate alignment can be achieved by effectively utilizing the alignment mark arrangement in a small space without using another alignment sensor to drive in advance the wafer positional deviation. can do.
As a result, concerns about system complexity and cost increase due to the use of a plurality of alignment sensors are eliminated. .

[0054]

As described above, according to the present invention,
In using the alignment method of heterodyne interferometry, an alignment mark arrangement devised in a small space is effectively used. For this purpose, the incident angle of the positioning light (two light beams having slightly different frequencies) is variably controlled. Thus, high-accuracy alignment can be achieved without using another alignment sensor to drive the wafer in advance. As a result, it is possible to provide an alignment mark for pattern exposure, an alignment method, and an exposure apparatus capable of realizing an improved alignment accuracy at low cost without deteriorating the space efficiency of the mark arrangement.

[Brief description of the drawings]

FIGS. 1A and 1B are configuration diagrams showing a pattern exposure alignment mark and an alignment method according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a pattern exposure alignment mark according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a method of aligning a pattern exposure alignment mark according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a pattern exposure alignment mark according to a fourth embodiment of the present invention.

FIG. 5 is an enlarged view of a diffraction edge portion showing a configuration of a pattern exposure alignment mark as a modified example of FIG. 4;

FIG. 6 is a schematic diagram illustrating a main configuration of an exposure apparatus according to a fifth embodiment of the present invention.

FIG. 7 is a configuration diagram showing an example of a conventional pattern exposure alignment mark and an alignment method.

[Explanation of symbols]

 MK, MK1-5 alignment mark 60 exposure apparatus 61 control mechanism 62 signal processing section AOM1,2 acousto-optic element AL lens BS beam splitter FLT1, FLT1, optical filter OPS1, optical path shift section WF … Wafer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/30 525W F-term (Reference) 2F065 AA02 AA03 BB28 CC19 FF52 GG05 HH12 LL04 LL12 LL21 5F046 EA07 EB01 FA05 FA06 FB10 FC04

Claims (5)

[Claims] When using the alignment method of the heterodyne interferometry, at least a predetermined pitch is added to a pattern in which diffraction edges are arranged in order to irradiate each of two alignment light beams whose incident angles are variably controlled. An alignment mark for pattern exposure characterized by setting a small pitch. 2. The alignment mark for pattern exposure according to claim 1, wherein the diffraction edge irradiated with the alignment light has a pattern shared in both x and y directions. 3. The pattern exposure position according to claim 1, wherein a duty ratio between adjacent patterns having a diffraction edge irradiated with the positioning light is changed. Alignment mark. 4. When using the alignment system of the heterodyne interferometry, the alignment mark on which the diffraction edge is arranged is irradiated with each of two alignment light beams by variably controlling the incident angle, and is adjusted to an appropriate position. A method of positioning a pattern exposure alignment mark, characterized by obtaining an alignment signal. 5. An exposure apparatus using an alignment method of heterodyne interferometry, wherein two alignment beams of two light beams can be irradiated to an alignment mark on which a diffraction edge is arranged by variably controlling an incident angle. An exposure apparatus, comprising: a control mechanism for performing a positioning process; and a signal processing unit that calculates a phase difference by comparing a positioning signal obtained from the irradiation of the positioning light with a reference signal.