JPH05205995A - Alignment mark - Google Patents

Abstract

PURPOSE:To cancel a situation that a positioning value can not be detected in a diffracted light detection alignment method, which is caused by the variation of process conditions such as level difference between marks or the thickness of an applied resist film. CONSTITUTION:It is ensured that a diffracted light of over certain intensity is generated independent of the variation of processing conditions by an alignment mark 12 composed of mark element groups 21a, 21b, and 21c of various kinds where mark elements 20a, 20b, and 20c which are a1, a2, and a3 different from each other in size are arranged in the field of view of an alignment optical system keeping an arrangement pitch (b) constant. By this setup, a situation that a positioning value car not be detected due to the variation of process conditions is canceled, whereby a light exposure device can be automated or operated with no operator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment mark for a target, which is most suitable for a precision alignment apparatus for a substrate such as a wafer in an exposure apparatus used for manufacturing semiconductors and the like.

[0002]

2. Description of the Related Art In semiconductor manufacturing, the required performance of an exposure apparatus for drawing or transferring a fine pattern on a wafer is becoming higher and higher. As for the technique for precisely aligning the wafer (alignment), a highly accurate and highly stable system is desired.

A diffracted light detection alignment method is disclosed in Japanese Patent Laid-Open No.
6-12729 or JP-A-60-186845 is publicly known. The principle will be described with reference to FIG.

In detecting diffracted light, a laser 4 having a high coherency is used as a light source. The laser having the optimum wavelength is selected depending on the application of the exposure apparatus and the object to be measured, such as He-Ne laser and semiconductor laser. The light emitted from the laser 4 is shaped into a desired beam diameter by a beam expander composed of convex lenses a and b of 5 and 6 and a pinhole 7, and then a beam splitter 8 and a relay. Lens 9, tip mirror
An image of the pattern of the reticle 1 is made incident on the center of the entrance pupil 11 of the reduction lens 3 to form an image on the wafer 2 via the alignment mark 12 provided on the wafer 2.
Is irradiated from a direction almost vertical to.

As shown in FIG. 5, the alignment mark 12 has a plurality of element marks 20 of size a, which are arranged at a regular pitch (pitch b) and in a straight line. When illuminated with illumination light, the direction θn of the relationship shown in Equation 1
Diffracted lights D0, D ± 1 and D ± 2 are generated.

[0006]

[Equation 1]

The diffracted light is reduced by the reduction lens 3 and the tip mirror -1.
0, a relay lens 9, a beam splitter 8, and an objective lens 13 to reach a spatial filter 14, where diffracted light of a desired order (usually ± 1st order diffracted light) is selectively passed. After that, it is compressed in the Y direction by the cylindrical lens 15 and an image is formed on the linear image sensor 16 to obtain a detection waveform 17 as shown in FIG. Then, if the wafer 2 moves in the X direction, the image position of the alignment mark 12 on the linear image sensor 16 also changes, and the precise positioning amount can be measured.

[0008]

In the alignment in the actual exposure apparatus, as shown in FIG. 7, the resist is applied on the alignment mark 12 formed by the uneven steps on the wafer 2. Depending on the process conditions, that is, the step t1 of the alignment mark or the coating thickness t2 of the resist, for example, the ± 1st-order diffracted light intensity changes greatly, and depending on the conditions, the diffracted light intensity is too small, Problems have arisen, such as the inability to measure the positioning amount. In order to deal with this, conventionally, (1) the unevenness of the alignment mark is reversed, (2) in FIG. 5, the mark b is kept constant while the pitch b of the mark element 20 is kept constant. Change the size a of 20. For example, a method of preparing a plurality of types of alignment marks and selecting an optimum one according to process conditions has been adopted.

However, as the size of the wafer becomes larger, the variation of the step difference t1 or the variation of the resist coating film thickness t2 in the wafer increases, and the intensity of the diffracted light detected changes greatly even within the same wafer. It started to come. For this reason, it becomes difficult to select the optimum alignment mark as described above, the intensity of the diffracted light is small, and the amount of positioning cannot be detected depending on the conditions, which requires the assistance of the operator. Therefore, the automatic or unmanned operation of the exposure apparatus is hindered, which has become a major problem.

An object of the present invention is to eliminate undetectable conditions caused by process non-uniformity such as alignment mark steps and resist coating film thickness in a diffracted light detection alignment method, and to automatically or unmanner an exposure apparatus. It realizes driving.

[0011]

In order to achieve the above object, the present invention uses a plurality of types of mark element groups in which the ratio of concave or convex steps to the arrangement pitch of the mark elements is different. A method of forming an alignment mark has been devised.

[0012]

That is, (1) In the alignment optical system shown in FIG. 4, the Y direction of the alignment mark 12 shown in FIG. 5 is compressed by the cylindrical lens 15 onto the linear image sensor 16 to form an image. Wide field of view (2) As is generally known, even if the pitch b of the alignment marks 12 is the same, the diffracted light intensity is changed by changing the size a of the mark element 20. Focusing on these two points, by providing a plurality of types of mark element groups having different sizes a in the Y-direction visual field of the linear image sensor 16, there are variations in the mark step and the resist coating film thickness. Even if it is a marker of any size,
It is intended to always guarantee the generation of diffracted light with a certain intensity or more by the group of black elements.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. While the arrangement pitch b of the mark elements relating to the traveling direction of the diffracted light is always kept constant, the sizes are a1 and a.
Mark elements 20a, 20b of three types different from 2, a3,
The mark element groups 21a, 21b, 21c of 20c are arranged in a straight line. When this mark is irradiated with laser light, even if the process conditions such as the step of the mark and the film thickness of the resist coating change within the wafer or between the individual wafers, the size a1, a2, a3 Among the three types of mark element groups 21a, 21b, 21c, diffracted light is generated from at least one type of mark element group, and it is possible to solve the undetectable condition which has been a problem in the past.

FIG. 2 shows a second embodiment of the present invention. In this mark, when the resolution of the alignment optical system in the X direction is small, or in FIG. 4, a photomultiplier tube, a photodiode or the like is directly arranged immediately after the spatial filter 14, while the irradiation laser is used. This is particularly effective for an alignment optical system of the type that scans the light or the like and detects changes in the diffracted light intensity along the time axis. Here, the mark element is made into a polygon, and the mark that is involved in the traveling direction of the diffracted light is used.
The arrangement pitch b of the mark elements is always kept constant, and the mark elements in which the mark element groups having different sizes from a1, a2, and a3 are integrated are arranged in a straight line.
When this mark is irradiated with laser light, similar to the first embodiment, even if the process conditions such as the step of the mark and the resist coating film thickness change within the wafer or between individual wafers. , Out of the three types of mark element groups of sizes a1, a2, and a3, diffracted light is generated from at least one type of mark element group, and the undetectable condition that has been a problem in the past is solved. You can

FIG. 3 shows a third embodiment of the present invention. This is a polygonalization of the alignment mark of the second embodiment of the present invention to the maximum extent, and has the shape of a diamond-shaped mark element. It is considered that the arrangement pitch b of the mark elements involved in the traveling direction of the diffracted light is always kept constant and is composed of an infinitely small mark element group whose size continuously changes from 0 to b. Therefore, as in the first embodiment, even if the process conditions such as the step of the mark and the resist coating film thickness change within the wafer or between the individual wafers, the mark element has at least some size. Since diffracted light is generated from the group, it is possible to solve the undetectable condition, which has been a problem in the past.

The marks shown in the embodiments of the present invention are representative examples showing the basic concept, and the present invention includes marks having similar effects. For example, a mark having different unevenness, a measurement target that generates diffracted light due to a change in reflectance or transmittance, or a plurality of alignment marks, X
Those arranged side by side in the direction may be considered.

Although the present invention has been described with respect to the principle and embodiment of the semiconductor exposure apparatus as an example, the object to be measured may be something other than the wafer as long as it has the same effect.

[0019]

As described above, according to the present invention, the diffracted light for alignment having a stable intensity is always generated even when the process conditions such as the mark step of the alignment mark and the resist coating thickness are changed. Therefore, conventionally, it is possible to stop the exposure apparatus due to the inability to detect the positioning amount or to cancel the assistance by the operator, which is effective in automating or unmanned operation of the exposure apparatus. Further, as a result, it can contribute to the improvement of the productivity of semiconductors and the manufacturing yield.

[Brief description of drawings]

FIG. 1 is an alignment marker according to a first embodiment of the present invention.
It is a top view which shows the shape of a circle.

FIG. 2 is an alignment marker according to a second embodiment of the present invention.
It is a top view which shows the shape of a circle.

FIG. 3 is an alignment marker according to a third embodiment of the present invention.
It is a top view which shows the shape of a circle.

FIG. 4 is a diagram showing an optical path of an alignment optical system.

FIG. 5 is a diagram showing the principle of diffracted light detection.

FIG. 6 is a diagram showing a detection example of a diffracted light detection waveform.

FIG. 7 is a view showing a sectional shape of an actual alignment mark.

[Explanation of symbols]

1 ... Reticle, 2 ... Wafer, 3 ... Reduction lens, 12 ... Alignment mark, 20 ... Mark element, 21 ... Mark element group.

Claims (1)

[Claims] 1. An alignment mark for detecting diffracted light in which a plurality of mark elements having concave or convex steps are arranged in a straight line at equal pitches and the mark is kept constant.
An alignment mark comprising a plurality of types of mark element groups in which concave or convex steps occupy different ratios by changing the size of the mark elements.