JPS60233823A - Fresnel zone target - Google Patents

Abstract

PURPOSE:To enable alignment of stability and high accuracy by preventing the phenomenon of light disturbance in a target made of resist by a method wherein a plurality of concentric rings constituting the Fresnel zone target are composed of assemblages of micro plane parts each isolated at micro intervals. CONSTITUTION:The surface of an Si substrate 17 is coated with a thin film of SiO2, polycrystalline Si, Al, or the like, which is then patterned into the Fresnel zone target 10. In this construction, the target 10 is composed of four concentric rings 11-14 as a whole, and the widths and the gaps of the respective concentric rings 11-14 in the radius direction are successively reduced from the center toward the periphery. In such a manner, micro plane parts 11b-14b are generated in the concentric rings 11-14, thus making the coating state uniform when the whole surface is coated with the resist 16, and making the film thickness of each part uniform. Such a manner can prevent the light disturbance due to light interference at the time of alignment; then, stable diffraction is caused, and the alignment becomes increased in accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to pattern transfer alignment technology during the manufacture of semiconductor devices, and particularly to improvements in Fresnel zone targets used as targets for chip alignment.

[Background technology]

With the increasing integration of semiconductor devices such as LSI and VLSI, element patterns are also becoming increasingly finer, and pattern transfer technology for forming these element patterns, especially pattern alignment, is also required to be highly accurate. There is. For this reason, an aligner using a Fresnel zone target can be considered, especially as a target for chip alignment.

As shown in Figure 1, a Fresnel zone target is an arrangement of multiple concentric rings 1, 2, 3.4, and the inner diameter and width of each concentric ring are adjusted to the wavelength of the light (alignment light) used. By setting the values based on the respective values, the light intensity at the focal position can be extremely increased due to the light diffraction phenomenon.

Therefore, if this target is used as an alignment target, a light spot with high light intensity can be obtained even if the target size is small or the intensity (illuminance) of the alignment light is low, and the position of this light spot can be detected. This makes it possible to perform position detection with extremely high precision, that is, alignment.

However, when the present inventor actually applied this target to various processes, the optimal conditions were different for each process, and each process had different corrections (each dimension of the concentric ring) for the target on the design value. It has been experienced that corrections are required.

For this reason, the inventor investigated the cause of this problem and found that the resist applied on the Fresnel zone target (
Photoresists, electron beam resists, etc.) were found to be one of the influencing factors. That is, the Fresnel zone target is usually formed by patterning a thin film of AM or the like as shown in FIG. The film thickness of the resist 6 applied thereon varies irregularly as shown by film rows dlyd2+d3 in the figure. Therefore, this irregular film thickness change and light interference disturbs the original reflection and diffraction phenomenon of light by the target, causing areas that should appear bright to become dark, or vice versa. The inventors have found that accurate alignment will be hindered by this. In the figure, 7 is a wafer.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a Fresnel zone target that can prevent light disturbances in the Fresnel zone target by using a resist, thereby allowing stable and highly accurate alignment throughout each process.

The above-mentioned objects and novel features of the present invention are as follows:
It will become clear from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief overview of typical inventions disclosed in this application is as follows.

In other words, by configuring a plurality of concentric rings constituting the Fresnel zone target to have a configuration in which minute surface portions separated by minute intervals are assembled, irregular changes in the film thickness of the resist can be prevented due to the presence of each minute interval.

This prevents disturbance due to optical interference, produces a stable diffraction phenomenon, and enables highly accurate alignment.

〔Example〕

FIGS. 3(A) and 3(B) show a Fresnel zone target 1o of the present invention. For example, a silicon oxide film, a polysilicon film, a polysilicon film, It is formed by patterning a thin film such as an AM film. This Fresnel zone target 1o has four concentric rings 11, 12, 13, 14 as a whole, and the radial width and interval of each concentric ring 11, 12, 13, 14 gradually decreases from the center to the periphery. are doing.

It goes without saying that each dimension of these two-width intervals is set by a design formula based on the wavelength of light used for alignment. In this example, each of the concentric rings 11, 12,
13. Small intervals 11a, 12a in the circumferential direction in each of 14
, 13a, 14a are arranged equally, thereby each concentric ring 11,
12, 13° 14 are a plurality of minute surface portions 11b, 12b,
13b.

14b are arranged in the circumferential direction.

In this case, the minute intervals and minute surfaces are each concentric ring 11°12
．． It is preferred to dimension them equally at 13.14.

Therefore, the Fresnel zone target 10 with this configuration
According to FIG. 4, when a resist 16 is applied to the upper surface, a minute interval 11a is formed.

Since the resists 12a, 13a, and 14a exist and their dimensions are approximately equal, the coating state of the resist 16 in the vicinity of each concentric ring 11, 12, 13°14 is also approximately equal,
This makes the film thickness of each part of the resist 16 uniform.

Therefore, if alignment is performed in this state, the film thickness of the resist 16 will be uniform, preventing light disturbance due to light interference, and stable diffraction development will occur, making highly accurate alignment possible. It is.

Alignment using the Fresnel zone target 1o is conceptually shown in FIG. 5, for example.

Parallel light 2o from a light source (not shown) is incident on the reduction lens 21, the beams are crossed at a position 5000 μm above the wafer 17, and the Fresnel zone target 10 on the wafer is irradiated. The beam irradiated onto the Fresnel zone target 10 with a required spread angle is reflected and diffracted by the Fresnel zone target, and is 200 μm above the wafer 17.
The focal point 22 is set at the position. Then, by forming this focal image (focal image) 25 on the quarter-divided detector 24 using the hall system 21.23 and detecting its position, the position of the Fresnel zone target lO1, that is, the wafer 17 can be detected, and the alignment can be performed. Can be completed. The focal image 25 has a beam diameter of approximately 1.25 mm, and the deviation from the center position of the 1/4-split detector 24 can be determined by the balance of light quantity of the detector. In this optical system,
The 6 μm movement of the wafer 17 is detected on the detector 24 by 1.
It can be detected as a movement of the focal image 25 of 2+m+, and a movement of 0.1 μm of the wafer can be detected as a movement of the focal image 25 of 0.02 ngn with a light amount balance difference of 2%. After all, alignment with an accuracy of 0.1 μm is possible.

Here, the Fresnel zone target may have a structure in which a large number of circular minute surface portions (dots) 26 are arranged at minute intervals as shown in FIG. The dots 26 may be square or other shapes.

〔effect〕

(1) Since each concentric ring constituting the Fresnel zone target is made up of a large number of microscopic surface portions separated by microscopic distances, the film thickness of the resist applied to the upper surface is This makes the beam uniform, thereby preventing light disturbance and producing stable diffraction, which enables highly accurate alignment.

(2) Since minute intervals may be equally distributed in the circumferential direction of each concentric ring, the two radius widths and the radial interval of each concentric ring may remain as they are, and the formation of the target pattern will not become difficult.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor. For example, each concentric ring of the target may be formed in a concave shape, or a resist with low viscosity may be applied to reduce the difference in film thickness.

[Application field]

In the above explanation, the invention made by the present inventor was mainly applied to a target for chip alignment, which is the background of the invention, but it is not limited to this, and can be applied to targets for various alignments. Applicable.

[Brief explanation of drawings]

Fig. 1 is a plan view illustrating a Fresnel zone target, Fig. 2 is a central cross-sectional view illustrating conventional defects, and Figs. 3 (A) and (B) are (A) of the target of the present invention. A plan view, a cross-sectional view taken along the line BB in FIGS. Conceptual configuration diagram, FIG. 6 is a partial plan view of a modified example. 10... Prenel zone target, 11-14...
・Concentric ring, 11a" 14a... minute interval, llb~1
4b...Minute surface portion, 16...Resist, 17...
Wafer, 21... Reducing lens, 24... 174-divided detector, 25... Focused image, 26... Dot. Figure 1 Figure 2 Figure 3 (β2 Figure 4

Claims (1)

[Claims] 1. A planel zone-shaped target consisting of a plurality of concentric rings and performing alignment using light diffraction, each of the concentric rings having a large number of microscopic surfaces arranged at microscopic intervals. A Fresnel zone target characterized by its composition. 2. The Fresnel zone target according to claim 1, wherein minute intervals in the circumferential direction are equally distributed in each concentric ring. 3. The Fresnel zone target according to claim 1, wherein each concentric ring is constructed by aggregating a large number of minute dots in a state of minute separation.