JPH0462452B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alignment method for a step-and-repeat type processing apparatus, and more particularly to an alignment method for a step-and-repeat type projection exposure apparatus (hereinafter referred to as a stepper) used in the manufacturing process of integrated circuit devices.

For example, a stepper repeatedly projects and exposes a pattern for circuit formation on an enlarged original plate (hereinafter referred to as a reticle) onto a semiconductor substrate (hereinafter referred to as a wafer) through a reduction projection optical system (hereinafter referred to as a lens), and then bakes it. It is a device that attaches. In this apparatus, the area that is projected and exposed at one time is usually a small area corresponding to one integrated circuit element portion (hereinafter abbreviated as a chip) to several chips. Therefore, in order to print the pattern on the reticle onto the entire surface of the wafer, exposure is repeated while the wafer is moved relative to the reticle in steps in the XY directions within a plane perpendicular to the optical axis of the lens. Here, the number of exposures ranges from tens to hundreds.

This photo process is usually performed on the wafer several to ten times until the chip is completed, so from the second process onwards, the relative positioning (hereinafter abbreviated as alignment) between the reticle pattern and each chip pattern on the wafer is performed. Is required. Here, alignment methods can be roughly classified into the following two types.

One is to align the reticle between two predetermined points sandwiching two or more chips within the wafer.
This is a method called global alignment, in which exposure is repeated while the wafer is fed step by step using the coordinates obtained through alignment as the origin, relying on a length measurement scale such as a laser interferometer.

The other method is called die-by-die alignment, in which the reticle pattern and the chip pattern on the wafer are directly aligned and exposed through a projection exposure lens at each chip printing position.

By the way, in die-by-die alignment, in order to directly align the wafer chip pattern and reticle pattern on each chip,
Although there is no positional deviation between the reticle pattern image and the wafer chip pattern during exposure, it has the disadvantage that the wafer processing time is long and the throughput is reduced. On the other hand, global alignment is good in terms of throughput, but it poses a problem of positional deviation between the reticle pattern image and the wafer chip pattern.

The present invention was made in view of the above circumstances, and its purpose is to provide an apparatus for processing a plurality of pattern parts on a substrate by step-and-repeat.
An object of the present invention is to provide an alignment method capable of aligning each pattern portion with high precision and without reducing the throughput of the apparatus.

To achieve this object, the present invention provides an alignment method for a step-and-repeat type exposure apparatus in which a pattern on a reticle is sequentially transferred to each shot area on a wafer by moving the wafer stepwise relative to the reticle. Before feeding the wafer into the exposure apparatus, alignment data of at least one shot area on the wafer is detected by an alignment data reading device different from the exposure apparatus, and after feeding the wafer into the exposure apparatus,
At least a portion of the alignment data read by the alignment reader is used for global alignment of the wafer.

Thus, the present invention makes it possible to read the alignment data and transfer the pattern to each shot area on the wafer in parallel operations. According to the present invention, it is possible to obtain alignment data necessary for highly accurate global alignment in advance when the wafer is fed into the exposure apparatus, thereby speeding up the throughput of highly accurate alignment. This can be done without any deterioration.

The alignment method of the present invention will be explained below using a stepper as an example.

Generally, chip patterns arranged on a wafer should originally be arranged at equal intervals along the XY axes, but the arrangement is slightly disordered mainly due to the following two reasons. One reason for this is the nature of the exposure equipment (aligner) used during pattern printing in the first process, or the conditions of the wafer and reticle (mask).The other reason is due to diffusion,
This is caused by distortion of the wafer itself due to heating processes such as oxidation.

When global alignment is performed, for example, between P and Q for a plurality of chips 2 on a wafer 1 as shown in FIG. , Q and the distance that should originally be (distance when the chips are correctly arranged) a difference δx occurs. If this difference occurs, the wafer 1
Assuming that there is a linear pattern array distortion radially from the center of the image, it is conceivable to perform step exposure with the following correction values taken into account.

That is, assuming that L is the actual measurement value, L ₀ is the original dimension, and K=L−L ₀ /L ₀ =δx/L ₀ ...(1), X=(1+K)X ₀ ...(2) Step exposure is performed so that Y=(1+K)Y ₀ ...(3). Here X ₀ , Y ₀
is the original step feed amount. However, the pattern arrangement within the wafer 1 is not always linear. For example, if you have a non-linear array characteristic curve (curve 4) as shown in Figure 2, the reticle pattern will have an alignment error represented by the difference between straight line 3 and curve 4 at each X point. The result is that each chip pattern on the wafer 1 is printed overlappingly. Furthermore, alignment errors also occur when the arrangement of chip patterns on the wafer 1 is not arranged radially. In other words, when step-feeding the wafer 1, if the correction amount K of the step-feed is always constant, the alignment precision will not be sufficient.

On the other hand, if information regarding the pattern arrangement of the wafer is obtained, it becomes possible to apply accurate correction to global alignment using the information. The means for this purpose are (A) means for reading the arrangement of chip patterns on the wafer 1, (B) means for calculating and/or storing the read information, and (C) means for associating the information with the wafer 1 for global alignment. It is broadly classified into means that make it possible to use information, and several effective processes (procedures) can be considered in combination.

First, we will discuss individual methods.

As for the means (A) for reading the arrangement of chip patterns on the wafer 1, there is a method (1) of using the stepper measuring means itself. After one die-by-die alignment, if the alignment position of each individual chip is read by a built-in laser interferometer or other length measurement function, the data can be used as a correction value for subsequent global alignment of the wafer 1. Or (2)
It may be an independent device having only an alignment function. It is a device similar to a stepper with the projection exposure function removed, and can be thought of as an improved version of the current coordinate measuring machine.

Next, regarding the means for calculating and/or storing the information in (B), first, (1) for the coordinates based on a specific chip pattern in the wafer 1,
A possible method is to store all measurement data in a storage device. However, this method has the disadvantage of requiring a huge storage capacity when applied to all wafers 1 in the middle of the process. In that case, (2) means for storing the obtained data as a constant of a mathematical formula for pattern arrangement distortion predicted in advance becomes effective. The majority of current aligners other than Steppers are contact or proximity type aligners and mirror projection type aligners. It is known with which type of aligner the first photo process was performed on the target wafer 1, and the characteristics of these aligners during patterning can be expressed in the form of a mathematical formula. For example, for some mirror projection types, X=x+Δx=x+G(x,y)sθx+G(x,y)sθ
y−√ 2｜y｜α+G(x,y)lφx+kx……(4) Y=y+Δy=y−k(y)(θx+θy)+y(θx+θ
y) + 2G (x, y) sθx + (√ 2K (y) ± √ 2S) α + 2G (x, y)
lφy＋ky……(5). Here, s, l are machine-specific constants, G
(x, y), K(y) are values determined by the coordinates of wafer 1, θx, θy, φx, φy, α are the angular errors of the optical system, and kx, ky are the radiation due to the temperature of the mask and wafer. It shows linear growth in the direction. By substituting the obtained data into the equation, a simultaneous equation is established, and the unknowns θz, θx, φx, φy, and α can be obtained, and these can be stored in a storage device. The number of distortion factors is much smaller than the number of data in (1), making it possible to store a larger amount of general data. In this method, ()
Data acquisition can be limited to the minimum amount of data necessary to solve the equation, or () data from all measurement points can be used to improve the accuracy of variables, () or unpredictable distortion can be avoided. It is also possible to add the habit of each aligner as a variable term.

Next is (C), a means for associating information with wafers, and wafer 1 is generally managed on a lot-by-lot basis.
For example, one carrier is handled in units of 25 wafers, and since the wafers in a lot go through the process under almost the same conditions, a method can be considered in which one of the wafers is regarded as a representative and associated. Alternatively, a code mark, number, symbol, etc. may be marked on a part of the wafer to manage each wafer.

Next, consider combinations of the above means.

1 If the process of wafers is controlled on a lot-by-lot basis, it is effective to use a stepper to perform die-by-die alignment for the first wafer in the lot, and at the same time import that information to globally align the second and subsequent wafers. become. In this case, even if all data is stored, once all wafers in the lot have been processed, the stored data will become unnecessary and can be deleted.

2. Similarly, in the case of lot-by-lot management, it is also possible to place a dedicated alignment device in front of the stepper and memorize the positions of all chips before sending them to the stepper. This procedure is nothing but saving the time lost due to the serial operation of alignment and exposure in die-by-die alignment using the stepper by removing only the alignment operation and performing parallel operations. In this case as well, it is advantageous to use all the data as is. According to this method, all error components can be read because they are measured immediately before exposure.

3. When management is performed on a wafer basis, it is effective to store the information in the form of variables in the above-mentioned formula. In this case, the information can be captured by die-by-die alignment using the first stepper in the repeated photo process, or a special alignment machine is placed in front of the first stepper to capture the data, and then the data can be captured in the subsequent global alignment. These data will be used. Various other combinations can be considered based on the above three combinations, but these will ultimately be considered by the process manager based on the balance between alignment accuracy and throughput required in the actual process.

As described above, according to the present invention, a highly accurate alignment method using global alignment can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a wafer having a plurality of chip patterns, and FIG. 2 is a diagram showing an arrangement error curve of the chip patterns of the wafer shown in FIG. 1...wafer, 2...chip.

Claims (1)

[Claims] 1. In an alignment method for a step-and-repeat type exposure apparatus in which a pattern on the reticle is sequentially transferred to each shot area on the wafer by moving the wafer in steps with respect to the reticle, before the wafer is sent into the exposure apparatus. The alignment data of at least one shot area on the wafer is detected by an alignment data reading device different from the exposure device, and the alignment data read by the alignment reading device after the wafer is sent to the exposure device. An alignment method characterized in that at least a portion of the wafer is used for global alignment of the wafer.