JP2000223404A - Method for detecting mark for alignment in charged particle beam exposure system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakage of marks for alignment of a board in a board using a positive resist, by lessening the dosage of charged particles than the dosage that the pattern at an ordinary exposure face receives, when detecting the marks for register. SOLUTION: Secondary electrons being emitted when an electron beam hits each alignment mark 1 for alignment are detected by a secondary electron detector, and when the number of secondary electrons becomes the largest, it is judged that each electron beam 2 matches with the mark 1 for alignment, and the alignment between a reticle and a wafer is performed, based on this signal. Here, the dosage of the charged particle beam applied to detect the mark for alignment is made half the dosage used for formation of usual pattern. As a result, the resist on the mark for alignment still remains, and the mark for alignment will never be broken.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a positioning mark while protecting a positioning mark provided on a substrate such as a wafer in a charged particle beam exposure apparatus.

[0002]

2. Description of the Related Art In a charged particle beam exposure apparatus, an image of a pattern formed on a reticle or mask (collectively referred to as a reticle) is transferred to a substrate to be exposed (hereinafter simply referred to as a substrate) such as a wafer by a charged particle beam. ing. At this time, in order to accurately align the relative position between the reticle and the substrate, a positioning pattern is provided on the reticle, and a positioning mark is provided on the substrate. Then, the charged particle beam that has passed through the alignment pattern of the reticle is irradiated onto the alignment mark on the substrate to perform scanning, and secondary electrons generated at that time are detected to perform alignment.

[0003]

A resist is applied on the alignment mark formed on the substrate.
When a positive resist is used, the resist is exposed by the irradiation of the charged particle beam for alignment.As a result, the resist is removed when the resist is developed, and the alignment mark is damaged by subsequent etching or the like. Would. In order to cope with this, it is necessary to re-create the alignment mark again, and it is necessary to leave space for making a new mark. Had a reduced effective area.

On the other hand, when a negative resist is used,
Conversely, if the exposure amount at the time of mark detection is insufficient, the resist is removed when the resist is developed, and the alignment mark is damaged by subsequent etching or the like. As a countermeasure against this, in a drawing type charged particle beam exposure apparatus, protection of the alignment mark is performed by preventing the resist from being removed by excessively exposing the area of the alignment mark. . However, the area to be exposed is divided into multiple stripes,
In a charged particle beam exposure apparatus in which transfer is performed from the reticle to the substrate while continuously moving the reticle and the substrate in the longitudinal direction of each stripe (divided projection transfer method), the area of the alignment mark is reduced without reducing the throughput. At present, a method for over-exposure has not been developed.

[0005] The present invention has been made in view of such circumstances, and a substrate using a positive resist is
A method for preventing damage to the alignment mark of the substrate that occurs with the exposure for alignment, in the case of a substrate using a negative resist, even in the divided projection transfer method,
It is an object of the present invention to provide a method for preventing breakage of a positioning mark on a substrate without reducing throughput.

[0006]

According to a first aspect of the present invention, there is provided a charged particle beam exposure apparatus, comprising: a positioning mark on a substrate coated with a positive resist;
A method of scanning and detecting with a charged particle beam, wherein the dose amount of the charged particle beam given to the alignment mark when detecting the alignment mark is calculated from the dose amount received by the pattern on the normal exposure surface. The present invention also provides a method for detecting a positioning mark in a charged particle beam exposure apparatus, wherein the number of alignment marks is reduced.

In this means, since the dose received by the alignment mark is smaller than the dose received by the pattern on the normal exposure surface, when the resist is developed, the thickness of the resist on the alignment mark is reduced. The amount of decrease is reduced. Therefore, if the dose at the time of detecting the alignment mark is managed, the alignment mark will not be damaged.

[0008] A second means for solving the above problems is as follows.
In the first means, the dose of the charged particle beam given to the alignment mark when detecting the alignment mark is set to be smaller than １ ／ of the dose received by the pattern on the normal exposure surface. It is characterized in that it is reduced (claim 2).

In the case of most positive resists, if the dose of the charged particle beam at the time of exposure is set to not more than 1/2 of the dose at which a pattern is formed (that is, the resist is completely removed), the exposure The reduction in resist film thickness is less than 15% of the initially applied resist film thickness.

[0010] A third means for solving the above problems is as follows.
The first means or the second means, wherein the alignment mark and the charged particle beam for detecting the mark each comprise a plurality of patterns arranged at an appropriate pitch. (Claim 3).

In this means, a plurality of alignment marks are arranged on the substrate at an appropriate pitch. The charged particle beam for detecting the same is also composed of a plurality of patterns formed at the same pitch as the alignment marks.
In this way, by scanning the charged particle beam, detecting the sum of secondary electrons and the like emitted from the plurality of alignment marks, and performing alignment, the dose received by each alignment mark is obtained. Can be performed in a state in which the number of images is reduced.

A fourth means for solving the above-mentioned problem is as follows.
In a charged particle beam exposure apparatus that divides a region to be exposed into a plurality of stripes and transfers the reticle to the substrate while continuously moving the reticle and the substrate in the longitudinal direction of each stripe, the substrate is coated with a negative resist. This is a method of detecting an alignment mark by scanning with a charged particle beam, using a reticle in which an alignment mark protection pattern area of a substrate is formed in proximity to an alignment mark detection pattern area. Before or after exposure for mark detection, a charged particle beam exposure characterized by including a step of exposing the alignment mark on the substrate by a charged particle beam that has passed through the alignment mark protection pattern on the substrate. A method for detecting a positioning mark in an apparatus (claim 4).

In this means, a reticle is used in which a positioning mark protecting pattern area of the substrate is formed in proximity to the positioning mark detecting pattern area.
Then, before or after the exposure for detecting the mark, the charged mark beam passing through the pattern for protecting the positioning mark on the substrate exposes the positioning mark on the substrate. As a result, the resist on the alignment mark on the substrate receives a sufficient amount of exposure. Exposure of the substrate alignment mark by the charged particle beam that has passed through the substrate alignment mark protection pattern does not require accurate alignment because the exposure position may be slightly shifted.
This can be performed during acceleration or deceleration of the reticle or the substrate. Therefore, the additional exposure for protecting the alignment marks on the substrate does not lower the throughput of the exposure sequence.

A fifth means for solving the above-mentioned problems is as follows.
In the fourth means, the step of exposing the alignment mark is performed during acceleration or deceleration of the sample stage and the reticle stage (claim 5).

In this means, since the step of exposing the alignment mark is performed during acceleration or deceleration of the sample stage and the reticle stage, the mark can be detected without lowering the throughput of the entire exposure process. .

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an exposure dose (μC / cm ² ) of an electron beam when a positive resist is used,
This is a relative value of the remaining resist film thickness. The horizontal axis shows the exposure dose (common logarithmic value), and the vertical axis shows the remaining resist film thickness when the initial film thickness is 1. The letters in the figure correspond to the type of resist. Looking at this, the resist of a and b is 6 (μ
The resist is completely removed by exposure at a dose of not less than C / cm ² ), and a pattern is formed.
/ Cm ² ) or less, 86% or more remains for the resist a and 90% remains for the resist b.

Therefore, if the dose is set to の of the dose used for normal pattern formation, 85% or more of the original film thickness remains. The same applies to the resist c, although the numerical values are different, and are common to most resists. Therefore, by setting the dose of the charged particle beam to be irradiated when detecting the alignment mark to be １ ／ of the dose used for normal pattern formation,
The resist on the alignment mark still remains,
The alignment mark is not damaged. In some cases, the exposure may be performed at a dose reduced according to the γ value of the resist used and the number of exposures of the wafer until completion.

FIG. 2 shows an example of a method for performing exposure with such a reduced dose. In FIG. 2, reference numeral 1 denotes an alignment mark formed on the wafer, and three alignment marks are formed in the figure. The width is A and the pitch is B. Reference numeral 2 denotes an image (electron beam) of a positioning mark provided on the reticle, which is also provided in three pieces, and has a width C and a pitch B which is the same as the pitch of the positioning mark 1. The electron beam 2 is deflected by the deflector and changes the pitch B to the time T
Scan at uniform speed over

Secondary electrons emitted when an electron beam strikes each alignment mark 1 are detected by a secondary electron detector, and when the number of secondary electrons becomes maximum, each electron beam is emitted. 2 is determined to match each alignment mark 1,
Based on this signal, the reticle is aligned with the wafer.

The exposure time of a normal pattern portion is defined as T '.
Assuming that the intensity per unit area of the electron beam irradiating the reticle does not change between the exposure of the normal pattern portion and the exposure for the alignment, the alignment mark 1 is used for the exposure for the alignment. The dose received by the upper resist is C of the dose received by the normal pattern.
The dose amount is T / {(B + C) T ′} times. By appropriately selecting C and T, if this value is set to 1 or less, the dose received by the resist on the alignment mark 1 can be set to an arbitrary value smaller than the dose received by the normal pattern portion. Here, T is the scanning time, which is usually equal to T ′.

In FIG. 2, a positioning mark 1 and
The plurality of alignment mark images (electron beams) 2 provided on the reticle are provided because the amount of secondary electrons required for alignment is generated by the electron beam received by the alignment mark 1. This is to reduce the dose. In FIG. 2, three are provided, respectively. However, if this number is increased, the dose of the electron beam received by the alignment mark area can be further reduced.

Next, with reference to FIGS. 3 and 4, a description will be given of a division projection transfer type exposure apparatus based on the present invention with respect to protection of a substrate alignment mark using a negative resist.

FIG. 3 is a diagram showing a unit of division exposure. First, a plurality of chips are formed on a substrate (usually a wafer), and the chips are divided into stripes, and the stripes are divided into subfields. The reticle is similarly divided.

In a divided projection exposure apparatus, exposure is usually performed by a method as shown in FIG. First, the reticle stage and the wafer stage move at a constant speed along the center of the corresponding stripe at a speed according to the reduction ratio. The electron beam illuminates a subfield on the reticle, and a pattern formed on the reticle is projected and exposed on a sample by a projection optical system.

Then, the electron beam is deflected in a direction substantially perpendicular to the traveling direction of the reticle stage, and the subfields arranged in a row are sequentially subjected to projection exposure. When the projection exposure of one row of subfields is completed, the projection exposure of the next row of subfields is started. At this time, the direction of electron beam deflection is reversed as shown in FIG. Is performed to increase the throughput.

Since the exposure is performed by such a method, compared with the conventional charged particle beam exposure apparatus, the subfield area is exposed at a time and the reticle has all the patterns to be exposed. The throughput can be improved.

The reticle used in this exposure method is divided into a subfield portion (pattern portion) and a beam portion around it, unlike an exposure device using light. The beam portion is provided for the purpose of maintaining the strength of the reticle itself and for selecting only a subfield to be reliably exposed to the illumination beam.

FIG. 5 is a view showing a part of a reticle used in correspondence with a wafer coated with a negative resist in a division projection type electron beam exposure apparatus, which is used in the embodiment of the present invention. It is something that can be done. In FIG. 5, 1
0 indicates one stripe, and 11 indicates a beam. Reference numeral 12 denotes a general subfield in which a transfer pattern is formed. 13 is a subfield for creating a beam for detecting a mark for x-direction alignment, 14 is a subfield for creating a beam for detecting a mark for y-direction alignment, 15 is a subfield for creating a beam for protecting marks, and 16 is x.
An axial alignment mark pattern 17 is a y-axis alignment mark pattern.

The reticle moves in the longitudinal direction of the stripe 10, that is, in the y direction. At both ends of the stripe 10 in the y direction, subfields 15 for forming beams for protecting marks are provided as shown in the figure.
Subfields 13 for forming a beam for detecting a mark for x-direction alignment and subfields 14 for forming a beam for detecting a mark for y-direction alignment are provided alternately as shown in the figure. The composition of the wafer subfield is
The configuration is the same as that of the subfield of the reticle, except that the subfield 15 for forming a mark protection beam is not provided. Although the subfields 13, 14, and 15 are provided on both sides of the stripe in the drawing, they may be provided only on the side on which the stripe is first exposed.

The electron beam emitted from the illumination optical system scans the subfield 15 first, and transfers the beam of the hole pattern formed therein to the subfield provided with the alignment mark on the wafer. . At this time, since the position in the y direction of the subfield where the alignment mark of the wafer is provided corresponds to the position of the subfields 13 and 14, an extra deflection by one subfield is applied in the y direction. Thus, the image of the subfield 15 is transferred to the subfield provided with the alignment mark on the wafer side. As a result, the subfield provided with the wafer alignment mark includes:
Sufficient exposure is performed in advance.

Subsequently, the electron beam emitted from the illumination optical system is divided into a sub-field 13 for forming a beam for detecting an x-direction alignment mark, and a sub-field 14 for forming a beam for detecting a y-directional alignment mark. And scanning is performed while irradiating the electron beam of the pattern on the subfield provided with the alignment mark on the wafer side. This scanning is performed in the x direction when detecting the x-direction alignment mark, and in the y-axis direction when detecting the y-direction alignment mark.
The subfields 13 and 14 arranged in the horizontal direction are sequentially scanned.

When the pattern of the electron beam that has passed through the subfields 13 and 14 irradiates the alignment mark on the wafer, secondary electrons are emitted from the alignment mark. The relative positional relationship between the wafers is detected. Then, the reticle and the wafer are aligned based on the detected relative positional relationship, and thereafter, the normal exposure and transfer of the subfield 12 are performed.

According to this method, the subfield provided with the alignment mark of the wafer has been sufficiently exposed to the electron beam passing through the hole formed in the subfield 15, so that the negative resist Will remain when developed and the underlying alignment marks will not be damaged.

As described above, in order to irradiate the subfield provided with the alignment mark of the wafer with the electron beam passing through the hole formed in the subfield 15, in addition to the normal y-axis deflection, as described above. The y-axis deflection of the subfield (for example, about 250 μm) must be added,
In the exposure for protecting the alignment mark, there is no particular problem even if the position is displaced by about several μm, so that the problem of aberration does not need to be particularly considered. Further, since the position may be slightly shifted, this exposure can be performed during acceleration / deceleration of the stage where normal exposure transfer is not performed, so that the throughput is not reduced.

As shown in FIG. 5, if the x-axis direction alignment mark pattern 16 and the y-axis direction alignment mark pattern 17 are too long, they become thermally unstable. Many things are arranged.

[0036]

As described above, according to the first aspect of the present invention, the resist is reduced even if the alignment mark is detected by reducing the dose according to the γ value of the positive resist. If it remains, the alignment mark will not be damaged.

According to the second aspect of the present invention, the resist still remains after the mark detection,
It can withstand mark detection sufficiently.

According to the third aspect of the present invention, the positioning can be performed in a state where the dose received by each positioning mark is reduced.

In the invention according to claim 4, even if such additional exposure for protecting the alignment mark of the substrate is performed, the throughput of the exposure sequence does not decrease.

According to the fifth aspect of the present invention, it is possible to detect a mark without lowering the throughput of the entire exposure process.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between an exposure dose and a residual resist film thickness when a positive resist is used.

FIG. 2 is a diagram illustrating an example of a method for performing exposure with a reduced dose.

FIG. 3 is a view showing a unit of division exposure of an exposure apparatus of a division projection transfer system.

FIG. 4 is a diagram illustrating an exposure method of a divided projection exposure apparatus.

FIG. 5 is a diagram showing an example of a reticle used in a divided projection exposure apparatus in the embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 alignment mark formed on wafer 2 alignment mark image (electron beam) provided on reticle 10 stripe 11 beam 12 general subfield on which transfer pattern is formed 13 x Subfield for forming a beam for detecting a mark for directional alignment 14... Subfield for forming a beam for detecting a mark for y-directional alignment 15... Subfield for forming a beam for protecting a mark 16... Pattern 17: Pattern for y-axis direction alignment mark

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tomoharu Fujiwara 3-2-3 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (72) Inventor Teruaki Okino 3-2-2 Marunouchi, Chiyoda-ku, Tokyo F-term in Nikon (reference) 2H097 AA03 BB01 CA16 KA20 LA10 5F056 BD08 CB03 FA06

Claims (5)

[Claims] In a charged particle beam exposure apparatus, a method for scanning and detecting an alignment mark on a substrate coated with a positive type resist with a charged particle beam is used. Characterized in that the dose of the charged particle beam given to the alignment mark area is made smaller than the dose received by the pattern on the normal exposure surface. . 2. A method for detecting an alignment mark in the charged particle beam exposure apparatus according to claim 1, wherein the charged particle beam given to the alignment mark area when the alignment mark is detected. A method for detecting an alignment mark in a charged particle beam exposure apparatus, wherein the dose is set to be less than half the dose received by a pattern on a normal exposure surface. 3. The method for detecting a positioning mark in the charged particle beam exposure apparatus according to claim 1, wherein the positioning mark and a charged particle beam for detecting the mark are: A method for detecting alignment marks in a charged particle beam exposure apparatus, each method comprising a plurality of patterns. 4. A charged particle beam exposure apparatus which divides a region to be exposed into a plurality of stripes and transfers a reticle and a substrate while continuously moving the reticle and the substrate in the longitudinal direction of each stripe, wherein a negative resist is applied. A method for scanning and detecting a positioning mark on a substrate by a charged particle beam, wherein a pattern area for protecting the positioning mark on the substrate is formed in proximity to the pattern area for detecting the positioning mark. Using a reticle, before or after exposure for mark detection, by a charged particle beam that has passed through the alignment mark protection pattern of the substrate, including a step of exposing the alignment mark of the substrate Method of detecting alignment mark in charged particle beam exposure apparatus. 5. The method for detecting a positioning mark in the charged particle beam exposure apparatus according to claim 4, wherein the step of exposing the positioning mark is performed during acceleration or deceleration of the sample stage and the reticle stage. Detecting method of alignment mark in charged particle beam exposure apparatus