JP4013727B2 - Vernier pattern, mask alignment method using the same, and pattern length measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a measurement pattern used for alignment of a measurement object on a wafer and a measurement object on a mask and confirmation of pattern accuracy of the measurement object in mask alignment used in a manufacturing process of a semiconductor device. .
[0002]
[Prior art]
In a conventional semiconductor manufacturing process, after performing drive-in and thin film growth, a resist pattern is formed using photolithography, and then fine processing such as etching is performed, and a desired circuit pattern is formed by repeating these steps. . Here, the superposition in each process is performed by using the measurement object on the photomask in the subsequent process based on the measurement object (usually the pattern of the first photomask) transferred and processed using the photomask. And repeat this superposition. At this time, as a means for evaluating each overlay, positional deviation in each direction is performed by using verniers independently provided in the center line direction of the substrate surface and in the direction perpendicular thereto (hereinafter referred to as X and Y directions, respectively). Quantitative evaluation is performed (for example, refer to Patent Document 1). A vernier pattern capable of simultaneously measuring the X and Y directions with a single measurement pattern has also been proposed (see, for example, Patent Document 2).
[0003]
In addition, the resist pattern formed by photolithography is evaluated and managed by using a length measurement pattern called a rocket mark for the finished pattern with respect to the design dimension. Each pattern dimension to be a circuit pattern is designed in consideration of the shift amount of these mask alignments and the pattern spread and variation in etching with respect to each resist pattern.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 63-83853 [Patent Document 2]
JP-A-5-47621
[Problems to be solved by the invention]
In the above mask alignment, for example, in the method disclosed in Patent Document 1, vernier patterns corresponding to the deviation amounts are formed at regular intervals in the X and Y directions, and the position where the deviation amount and the vernier pattern coincide with each other is read. The amount of deviation was evaluated and managed. However, in this case, since the vernier patterns in the X direction and the Y direction orthogonal to each other are formed independently, there is a problem that the occupied area becomes large.
[0006]
In order to solve the above problem, a method as shown in Patent Document 2 has also been proposed. However, the pattern having the same shape must be overlapped and discriminated from the amount of deviation, and discriminated by a microscope or the like. Hard to do. In addition, since the scale of each pattern is a comb, the area occupied by the vernier itself has not yet been significantly reduced.
[0007]
Furthermore, the rocket mark used in the dimension management of the resist pattern is formed in an independent form in a region different from the vernier for evaluating the alignment displacement. Further, the mask alignment and pattern length measurement have different measuring means from the optical microscope and the electron microscope, respectively, which not only requires management effort and time, but also increases the occupied area.
[0008]
In order to solve the above problems, an object of the present invention is to provide a vernier pattern capable of simultaneously measuring a mask alignment shift amount and a resist pattern accuracy with high accuracy.
[0009]
[Means for Solving the Problems]
The vernier pattern of the present invention is a cross formed on a substrate and having a first arm portion that forms an angle of 45 ° with respect to the center line of the substrate surface, and a second arm portion that is orthogonal to the first arm portion. It is a type | mold pattern, The external shape of said 1st arm part and 2nd arm part is a step shape of a fixed space | interval, respectively, It is characterized by the above-mentioned.
[0010]
According to the configuration of the present invention, compared to the case where vernier patterns in the X direction and the Y direction orthogonal to each other are independently formed, the occupying area of the vernier can be greatly reduced without reducing the measurement accuracy. it can.
[0011]
The steps are preferably formed at right angles, and one side thereof is substantially parallel to the center line of the substrate surface.
[0012]
Further, it is desirable that a pattern indicating a misalignment amount from a design value is formed around the first arm portion and the second arm portion.
[0013]
Furthermore, the pattern accuracy can be improved by forming the cross pattern, particularly the first arm portion and the second arm portion, by using anisotropic etching.
[0014]
In the mask alignment method of the present invention, after the formation of the cross pattern, the amount of misalignment between the cross pattern of the second cross pattern formed to form an angle of 45 ° with the cross pattern is calculated. It measures from the space | interval of the said staircase formed in the external shape of a 1st arm part and a 2nd arm part, It is characterized by the above-mentioned.
[0015]
According to the method of the present invention, it is possible to easily and accurately determine how much the resist pattern to be newly formed is shifted from the already formed vernier pattern.
[0016]
Further, if the centers of the cross pattern and the second cross pattern overlap, mask alignment can be performed more easily and accurately.
[0017]
In the pattern length measuring method of the present invention, after forming the cross-shaped pattern, the dimension of the length measuring pattern formed so as to overlap the center of the cross-shaped pattern is set to the first arm portion and the second arm in the cross-shaped pattern. It measures from the space | interval of the said staircase formed in the external shape of a part.
[0018]
The length measurement pattern is an arm portion of a second cruciform pattern separately formed on a substrate having an angle of 45 ° with the cruciform pattern, and the center of the cruciform pattern and the second cross It is desirable that the center of the mold pattern overlap.
[0019]
According to the method of the present invention, the step interval for measuring the mask misalignment amount can also be used for measuring the resist pattern, and the misalignment amount and the pattern accuracy can be measured simultaneously and with high accuracy. Can do.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
[0021]
(Embodiment 1)
1 and 2 are structural schematic diagrams of the vernier pattern in the present embodiment and the conventional vernier pattern disclosed in Patent Document 2, respectively.
[0022]
1 and 2, scales are respectively provided for the first arm portion 1 a and the second arm portion 1 b of the vernier pattern 1.
[0023]
In FIG. 1, the cross-shaped center line is formed at an angle of 45 ° with respect to each of the X and Y directions, and the shape of the scale provided on the arm is stepped. This is a very different point.
[0024]
The widths w1 of the first arm portion 1a and the second arm portion 1b were set to 2 μm in the X and Y directions, respectively, and the interval w2 between the staircase patterns 1c was set to 0.2 μm in the X and Y directions. In this case, a maximum deviation amount of 1.0 μm can be measured.
[0025]
In the present embodiment, the X direction coincides with the orientation flat (OF) direction of the substrate.
[0026]
On the other hand, in FIG. 2, five scale patterns 2c each having a width w3 (= 2 μm) are formed at intervals of 2 μm in the X and Y directions, left and right, and up and down, respectively. Yes.
[0027]
3 and 4 are respectively an explanatory diagram of a mask alignment method using a vernier pattern in the present embodiment and an explanatory diagram of a mask alignment method using a conventional vernier pattern disclosed in Patent Document 2.
[0028]
3 and 4, the mask pattern 3 is superimposed on the vernier pattern 1. In FIG. 3, the mask pattern 3 is a cross-shaped pattern, and the extending direction of the cross-shaped arm is the same as the X and Y directions. The line width w4 was 2 μm.
[0029]
On the other hand, in FIG. 4, the mask pattern 3 is formed with scale patterns 3c having a width w5 (= 2 μm) at intervals corresponding to 2 μm + shift amount. That is, s1 (= ± 2.2 μm) is adjacent to the central portion of the five arranged patterns 3c, and s2 (= ± 2.4 μm) is further adjacent to the central portion of the pattern 3c. 3 and 4, in both cases, a deviation amount of a maximum of 1.0 μm can be measured.
[0030]
In FIG. 3, by aligning the centers of the mask pattern 3 and the vernier pattern 1, the misalignment amounts in the X and Y directions can be measured simultaneously.
[0031]
Here, when comparing the size of both patterns in FIGS. 1 and 2, it is 8 μm in each of the X and Y directions in FIG. 1 and 22 μm in FIG. 2, and the occupying area is smaller in the vernier pattern in the present embodiment. I understand that.
[0032]
In the conventional vernier pattern shown in FIG. 2, even if the number of patterns 2c is reduced in order to reduce the occupied area, not only the measurement accuracy is lowered, but also not as small as the pattern shown in the present embodiment. In addition, if the width w3 of the pattern 2c is reduced, the entire size can be reduced. However, if the pattern 2c is made to have the same level as the pattern shown in the present embodiment, the pattern interval must also be reduced and the processing is difficult. Become.
[0033]
FIG. 5 shows a diffusion flowchart for forming a vernier pattern in the present embodiment.
[0034]
After the wafer cleaning, a silicon thermal oxide film (SiO ₂ ) is formed with a thickness of 800 nm by mask oxidation. Thereafter, a resist pattern is formed by photolithography. At this time, a vernier pattern was simultaneously inserted near the alignment mark. Subsequently, the SiO ₂ film was etched using a dry etching apparatus to form a vernier pattern 1. The gas used for silicon etching is CF ₄ + O ₂ . When the dimensions of the vernier pattern formed using an electron microscope were measured, it was confirmed that the vernier pattern was formed as designed. Next, an Al film was formed on the entire surface of the wafer by sputtering, and a resist pattern was formed again by photolithography. At this time, the mask pattern was transferred so as to overlap the vernier pattern. The mask alignment was performed with reference to alignment marks formed by patterning with the first mask. After positioning with the alignment mark, exposure was performed by intentionally shifting in the X direction by ± 0.2 μm on the setting of the exposure apparatus to form a pattern. As a result of visual inspection of the amount of deviation from the vernier using an optical microscope, it was confirmed that the amount of deviation in mask alignment could be determined by the vernier.
[0035]
By using the vernier pattern in the present embodiment, the vernier occupying area is greatly reduced without degrading the measurement accuracy as compared with the case where the vernier patterns in the X direction and the Y direction orthogonal to each other are formed independently. Can be small.
[0036]
Even when the amount of deviation of the pattern formed after etching Al and removing the resist was confirmed, the result of reproducing the deviation of the resist pattern confirmed by vernier was obtained.
[0037]
Further, the width w1 of the first arm portion 1a and the second arm portion 1b and the interval w2 of the staircase pattern 1c can be set to arbitrary dimensions corresponding to the ability in each process, and are shown in the present embodiment. It is not limited to the dimensions.
[0038]
(Embodiment 2)
In this embodiment, a method for measuring a dimension of a mask pattern using the vernier pattern used in Embodiment 1 is described.
[0039]
In the conventional method, the amount of mask displacement and the resist dimensions are managed separately, and the resist dimensions are measured with an electron microscope by providing a pattern for measuring dimensions called a rocket mark separately from the vernier. . On the other hand, if the vernier pattern of the present embodiment is used, the mask misalignment and the pattern dimension misalignment can be simultaneously measured with a single vernier.
[0040]
In the diffusion flowchart shown in FIG. 5, a rocket mark was formed at the same time when the resist pattern was formed after the Al film was formed, and the workmanship comparison between the vernier of the present invention and the rocket mark was performed. The result is shown in FIG. As the exposure conditions, pattern formation was performed under basic exposure conditions and exposure times of 10% and 20%, and the rocket marks were measured with an electron microscope. As a result, resists of 2.0 μm, 2.2 μm, and 2.4 μm were respectively obtained. It was confirmed that dimensions were formed.
[0041]
Here, when the overlap of the mask pattern 3 and the vernier pattern 1 shown in FIG. 6 was observed with an optical microscope for each condition wafer, the center part and the staircase pattern shifted by one step from the center part, two steps, respectively. It was confirmed that the edge of the mask pattern 3 coincided with the shifted staircase pattern. That is, by measuring a region where the vernier pattern 1 and the mask pattern 3 overlap, it is possible to easily verify how much the resist dimension is deviated from the mask design value.
[0042]
Accordingly, by using the vernier pattern of the present invention, it is possible to easily and accurately determine how much the resist pattern to be newly formed is shifted from the vernier pattern. It is possible to provide a vernier pattern capable of simultaneously measuring the misalignment amount and the resist pattern accuracy with high accuracy.
[0043]
As a method for forming a vernier pattern, when SiO ₂ was etched using a mixed solution of HF + NH ₄ F, the pattern edge was blurred, and an accurate dimension could not be specified. This is because wet etching is isotropic etching, and as a result of uniform etching from the resist pattern edge as a starting point, the cross-sectional structure is formed obliquely and the pattern edge is blurred.
[0044]
On the other hand, when SiO ₂ is etched by anisotropic dry etching, the cross-sectional structure is formed vertically. As a result, the pattern edge is etched at the same position with respect to the resist dimension, and an accurate pattern is formed. Therefore, it is desirable to use anisotropic dry etching for forming the vernier pattern in this embodiment.
[0045]
Whether or not the pattern dimension after etching is formed as designed can be verified by measuring a region where the vernier pattern 1 and the mask pattern 3 overlap.
[0046]
Further, by designing the width w4 of the mask pattern 3 to be larger than the width w1 of the arm portion of the vernier pattern 1, it is possible to evaluate not only the spread of the resist pattern but also the narrowing of the pattern due to insufficient exposure. it can.
[0047]
In FIG. 6, the mask pattern 3 and the vernier pattern 1 are centered so that the centers of the mask pattern 3 can be measured from the staircase pattern of the vernier pattern 1 in both the X and Y directions. .
[0048]
(Embodiment 3)
FIG. 7 shows a structural schematic diagram of a vernier pattern provided with a pattern indicating the amount of misalignment in the present embodiment.
[0049]
In the first resist pattern forming step of the diffusion flowchart shown in FIG. 5, a resist pattern for forming a pattern indicating a deviation amount is provided in the vicinity of the vernier. Etching SiO ₂ , removing the resist and observing with an optical microscope, it can be determined that a pattern showing a deviation amount is formed in the vicinity of the vernier, and the deviation amount of the mask alignment and the vernier indicated in the pattern It was confirmed that the amount of deviation was consistent.
[0050]
That is, by forming the pattern 4 indicating the amount of deviation from the design value around the vernier pattern in the present embodiment, the amount of deviation can be visually determined. A vernier pattern capable of measuring the pattern accuracy simultaneously and with high accuracy can be provided.
[0051]
In the pattern indicating the amount of deviation, the display of the amount of deviation is not limited to a real number as long as the amount of deviation can be determined by a sign or a symbol.
[0052]
【The invention's effect】
By using the vernier pattern of the present invention, it is possible to reduce the occupied area of the vernier without degrading the measurement accuracy as compared with the case where the vernier patterns in the X direction and the Y direction orthogonal to each other are independently formed. it can.
[0053]
Further, it is possible to provide a vernier pattern capable of measuring the mask alignment deviation amount and the resist pattern accuracy simultaneously and with high accuracy, thereby simplifying the semiconductor manufacturing process and leading to cost reduction.
[Brief description of the drawings]
FIG. 1 is a structural schematic diagram of a vernier pattern in the first embodiment of the present invention. FIG. 2 is a structural schematic diagram of a vernier pattern in the prior art. FIG. 3 is an explanatory diagram of a mask alignment method in the first embodiment of the present invention. FIG. 4 is an explanatory view of a conventional mask alignment method. FIG. 5 is a diffusion flowchart for forming a vernier pattern in the first embodiment of the invention. FIG. 6 is a mask using a vernier pattern in the second embodiment of the invention. FIG. 7 is a structural schematic diagram of a vernier pattern provided with a pattern indicating a misalignment amount in Embodiment 3 of the present invention.
1 Vernier Pattern 1a First Arm 1b Second Arm 1c Stair Pattern 2 Conventional Vernier Pattern 2c Scale Pattern (Vernier Side)
3 Mask pattern 3c Scale pattern (mask pattern side)
4 Pattern indicating the amount of mask deviation from the design value

Claims (8)

A first cruciform pattern having a first arm portion formed on the substrate and a second arm portion orthogonal to the first arm portion; and an angle of 45 ° with the first cruciform pattern. A vernier formed of a second cruciform pattern superimposed on the first cruciform pattern, wherein the first arm portion and the second arm portion each have a stepped shape with a constant interval. pattern.   The vernier pattern according to claim 1, wherein the first arm portion forms an angle of 45 ° with respect to a center line of the substrate surface.   3. The vernier pattern according to claim 2, wherein the steps are formed at right angles, and one side thereof is substantially parallel to a center line of the substrate surface.   4. The vernier pattern according to claim 1, wherein the vernier pattern is formed by using anisotropic etching. After forming the first cross-shaped pattern, which is formed misalignment amount between the first cross-shaped pattern before Symbol second cross pattern on said first arm portion and the outer shape of the second arm portion The mask alignment method using a vernier pattern according to any one of claims 1 to 4, wherein measurement is performed from an interval between the steps.   6. The mask alignment method according to claim 5, wherein mask alignment is performed so that the center of the cross pattern overlaps the center of the second cross pattern.   After forming the cross-shaped pattern, the steps formed on the outer shape of the first arm portion and the second arm portion of the cross-shaped pattern with the dimension of the length measurement pattern formed so as to overlap the center of the cross-shaped pattern The pattern length measuring method using a vernier pattern according to any one of claims 1 to 4, wherein the pattern length is measured from the interval of the vernier pattern.   The length measurement pattern is an arm portion of a second cruciform pattern that forms an angle of 45 ° with the cruciform pattern, and is formed so that the center of the cruciform pattern and the center of the second cruciform pattern overlap. The pattern length measuring method according to claim 7, wherein:

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