JPS6333702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a method for printing photo masks used in manufacturing semiconductor devices and the like.

(b) Background of the Technology Masks used in the manufacture of integrated circuits consist of more than ten layers for each type of integrated circuit, and overlapping between each layer is an important issue.

One circuit is formed by overlapping many layers of circuit patterns, and ideally they must be printed by overlapping each other accurately at positions determined in the circuit design. However, when exposing each layer, the exposure system is not necessarily exposed under ideal conditions.
It is affected by various distortions in the optical system and the exposure environment. Therefore, in circuit design, an overlay tolerance is set. This is the limit on the worst overlay error that a printed circuit pattern can tolerate within a chip, and the value must be 1/3 or less of the minimum line width of the circuit pattern.

When performing so-called step-and-repeat exposure, in which a chip pattern is sequentially sent and exposed step by step (chip array pitch) directly onto a semiconductor substrate, an alignment target pattern is placed on each chip on the semiconductor substrate. Since we have
Local alignment is possible for each chip. Alternatively, since simultaneous alignment can be performed between two alignment target patterns provided on the semiconductor substrate, highly accurate alignment can be achieved for each layer.

The alignment target pattern may have any shape, but it is formed in a previous lithography process, is recognized by the alignment mechanism of the exposure device, and the pattern is aligned based on this.

On the other hand, in the case of a mask, the dry plate does not have the above-mentioned alignment target pattern, and a laser interferometer reads the XY coordinates of the stage on which the dry plate is placed, and the stage is moved for each step size for step-and-repeat exposure. is going on.
In such a method, the overlay error between each layer becomes large, and in severe cases reaches 1 μm or more.
Since there are limits to the accuracy of the laser interferometer and the positioning accuracy of the stage, some kind of improvement measure is desired by considering the entire system of the exposure apparatus.

(c) Prior art and problems When printing a dry plate by step-and-repeat exposure, as mentioned above, there is no target pattern for alignment, so alignment of each chip is not performed, and the precision of the laser interferometer is , the position of the dry plate is determined and exposure is performed depending on the positioning accuracy of the stage. This is an exposure known as blind exposure. In this case, the apparatus is stable when each layer is exposed for a relatively short time, but when exposed for a long time, the apparatus is affected by temperature and atmospheric pressure, causing problems such as malfunction of the laser interferometer, meandering of the stage, etc. Furthermore, due to equipment errors in the stage of the dry plate, the overlapping of each layer may be misaligned. This deviation may be sudden or continuous.

FIG. 1 shows an example of the latter deviation. In the figure, solid lines represent the first layer pattern for each step, and dotted lines represent the second layer pattern.

The length measurement system always measures the coordinates from the origin using a laser, but the above-mentioned deviation occurs for unknown reasons. Also, this deviation is, for example, on the orthogonal XY coordinates of the stage,
Although the No. 1 machine is good in the X direction, it has some peculiarities in each device, such as misalignment in the Y direction, so we cannot expect highly accurate pattern matching with good reproducibility.

(d) Object of the Invention The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a mask using step-and-repeat exposure that can be overlaid with high precision even on a dry plate that does not have a target pattern for alignment.・Providing a printing method.

(e) Structure of the Invention According to the present invention, when manufacturing a plurality of photo masks for forming a multilayer pattern, an integrated circuit chip is placed on a first layer photo mask substrate. When repeatedly exposing a pattern using the reduction projection exposure method, the coordinates of the exposed area of the pattern on each chip are read and stored as reference coordinates. Compare the coordinates of the exposure area determined by step feeding with the array pitch of and the reference coordinates,
This is achieved by providing a mask printing method characterized in that each step is aligned based on the reference coordinates.

In the present invention, when a chip pattern is arranged and printed step by step on a dry plate, the position of each chip is determined by the first
When printing a layer mask, the coordinates of the reference point of each chip are read and memorized, and the position of each chip on the dry plate to be exposed is determined based on this, thereby reducing overlay errors between each layer. It is intended to reduce Regarding the overlay accuracy between each layer, it is better to perform alignment for each chip by relative correction based on a reference mask as in the present invention, rather than by using an absolute value standard. This is because the latter allows local alignment for each chip, and eliminates environmental and temporal random errors in the length measurement system, errors in mounting the dry plate on the stage, etc.

(f) Embodiments of the Invention The present invention can also be used for conventional same-magnification batch exposure, but in this case, the accuracy of the blind exposure described above is sufficient. As integrated circuits become more highly integrated and densely packed, circuit patterns become finer, and reduction projection exposure equipment is used to print fine patterns of about 2 μm. By applying the present invention to this device, an overlay error of about 0.2 μm can be obtained.

FIG. 2 is an explanatory diagram showing an embodiment of the present invention. In the figure, 1 is an XY stage, 2 is a dry plate to be exposed, 3 is a reticle, and 4 is a reduction projection optical system.

The length of the XY stage 1 is measured by a laser length measuring system 5 in X and Y directions orthogonal to each other. Mount the dry plate 2 on top of the XY stage 1. The dry plate 2 is placed under the reduction projection optical system 5, and the enlarged and printed chip pattern is sent to the reticle 4 for each step size, and is sequentially reduced and projected onto the dry plate and exposed by the exposure illumination system 6. go.

The first layer of mask is made by blind stamping.
Each size is made by printing a chip pattern on a dry plate. At this time, the coordinates of each step are stored in the computer 7 by the monitoring laser length measurement system 5A. This first layer mask is used as a reference mask, and in the exposure of the second layer and subsequent masks, local alignment is performed for each step using this mask as a reference.

For the second and subsequent layers of masks, alignment for each step is performed as follows.

Since the dry plate 2 on the XY stage 1 is linked to the laser length measurement system, the XY coordinates (X ₂ , Y ₂ ) of the detected pattern are determined and these values are sent to the computer 7 . The computer 7 compares it with the XY coordinates (X ₁ , Y ₁ ) of the corresponding step of the reference mask already stored, and calculates how much the stage position is relatively shifted. Based on this value, the stage is automatically moved to a predetermined position by the stage control system 8 and aligned according to the coordinates of the reference mask.

Although the embodiment of the present invention uses a method of making correction by moving the stage, the gist of the invention does not change even if a method of making correction by moving the reticle is used. In this case, the reticle control system 9 corrects the reticle position according to instructions from the computer 7, as shown by the broken line in the figure. The positioning error of the XY stage is normally about 0.5 μm, but if the amount equivalent to this error is corrected by moving the reticle, the positioning error becomes the value obtained by dividing the above error by the magnification of the reduction projection optical system. Since the magnification is usually 10 times, the positioning error is reduced by about one order of magnitude. This method of correcting by moving the reticle requires less precision than the method of correcting by moving the stage, which simplifies the design of the device and enables high-speed movement.

(g) Effects of the Invention As explained in detail above, according to the present invention, there is provided a mask printing method using step-and-repeat exposure that allows highly accurate overlay even on a dry plate that does not have a target pattern for alignment. can be provided.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing pattern deviation according to a conventional example, and FIG. 2 is an explanatory diagram showing an embodiment of the present invention. In the figure, 1 is an XY stage, 2 is a dry plate to be exposed, 3 is a reticle, and 4 is a reduction projection optical system.

Claims (1)

[Claims] 1. When manufacturing multiple photo masks for forming a multilayer pattern, each chip is The coordinates of the exposure area of the pattern are read and stored as reference coordinates, and when exposing the second layer and subsequent photo mask substrates, the coordinates of the exposure area determined by step feeding at the arrangement pitch of each chip and the corresponding A mask printing method characterized by comparing the coordinates with reference coordinates and aligning each step based on the reference coordinates.