JPS60192945A - Mask printing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) 9 Technical Field of the Invention The present invention relates to a method of printing a photomask 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 the layers 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 by circuit design. However, the exposure of each layer is not necessarily carried out under ideal conditions by the exposure system, and is affected by various distortions of the optical system and the exposure environment. Therefore, in circuit design, an overlay tolerance is set. This is the limit of 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 depth pattern is sequentially sent step by step (chip arrangement pitch) directly onto the semiconductor substrate, an alignment target pattern is attached to each chip on the semiconductor substrate. Therefore, local alignment is possible for each chip. Alternatively, since simultaneous alignment can be performed between two alignment target patterns provided on the semiconductor substrate, high precision alignment can be achieved for each layer.

The alignment target pattern may have any shape, but it is formed in a previous process and is recognized by the alignment mechanism of the exposure apparatus, 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 target pattern for alignment, and the XY coordinates of the stage on which the dry plate is placed are read using a laser interferometer.
Stages are moved for each size and step-and-repeat exposure is performed.

In such a method, the overlay error between each layer becomes large, and in severe cases, it becomes 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 only the laser interferometer is used. Depending on the precision and positioning accuracy of the stage, the position of the dry plate is determined and exposure is performed. 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 errors in mounting the dry plate on the stage, the overlapping between 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 due to the peculiarity of each device, for example, on the orthogonal XY coordinates of the stage, the first machine is good in the X direction, but it is misaligned in the Y direction, so we cannot expect high precision pattern alignment with good reproducibility. I can't.

(d)9 Object of the invention The object of the invention is to eliminate the above-mentioned drawbacks of the prior art,
It is an object of the present invention to provide a mask printing method using step-and-reveat exposure, which allows highly accurate overlaying even on a dry plate without an alignment target pattern.

(e) 3 Structure of the Invention According to the present invention, in manufacturing a plurality of photomasks for forming a multilayer pattern,
When the integrated circuit chip pattern is repeatedly exposed on the first layer photomask substrate using the reduction projection exposure method, the coordinates of the exposed area of each chip pattern are read and stored as reference coordinates, and When exposing a photomask substrate, the coordinates of the exposure area determined by step feeding at the arrangement pitch of each chip are compared with the reference coordinates, and alignment for each step is performed based on the reference coordinates. This is achieved by providing a mask printing method that achieves this.

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 without depending on the absolute value by the length measurement system, and when printing the first layer mask. By reading and storing the coordinates of the reference point of the chip, and using this as a reference to determine the position of each depth on the dry plate to be exposed, the overlay error between each layer is reduced. The overlay accuracy between each layer is
Rather than using an absolute value standard, it is better to perform alignment for each chip by relative correction based on a reference mask as in the present invention. 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) 9 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 apparatuses are used to print fine patterns of about 2 μm.

By applying the present invention to this device, an overlay error of about 0.2 pm 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. On top of XY stage 1,
Attach dry plate 2. The dry plate 2 is placed under the reduction projection optical system 5, and the chip printed on the reticle 4 is magnified.
The pattern is sent step by step, projected in a reduced size onto a dry plate, and exposed by the exposure illumination system 6.

The first layer mask is made by printing a chip pattern for each step size on a dry plate by blind printing. At this time, the coordinates for 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 layers, local alignment is performed step by step using this mask as a reference.

Alignment for each step for the second and subsequent layers of masks is performed as follows.

The dry plate 2 on the XY stage l is linked to the laser length measurement system, so the XY coordinates (X2, Y
2) and this value is sent to the computer 7.

The computer 7 compares this with the XY coordinates (X+, Y+) of the corresponding step of the reference mask already stored, and calculates how much the stage position has shifted relative to each other. When this value is reached, 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 correcting by moving the stage, the gist of the invention does not change even if a method of correcting by moving the reticle is used. In this case, the position of the reticle is corrected by the reticle control system 9 according to instructions from the computer 7, as shown by the broken line in the figure. The positioning error of the XY stage is usually about 0.5/J m,
When an amount corresponding to this error is corrected by moving the reticle, the positioning error becomes a 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) 1 Effect of the Invention As explained in detail above, according to the present invention, mask printing by step-and-rebeat exposure enables highly accurate overlay even on a dry plate without an alignment target pattern. method can be provided.

[Brief explanation of drawings]

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] When manufacturing multiple photomasks to form a multilayer pattern, when the pattern of an integrated circuit chip is repeatedly exposed on the first layer photomask substrate using the reduction projection exposure method, the pattern of each chip is exposed. The coordinates of the area are read and stored as reference coordinates, and when exposing the second layer and subsequent photomask substrates, the coordinates of the exposure area determined by step-feeding with the array pinch of each chip and the reference coordinates are read. A mask printing method characterized by comparing and performing alignment of each step based on the reference coordinates.