JPS627538B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure transfer photomask used during a semiconductor device manufacturing process or a photolithography process, and more particularly to a projection exposure photomask.

During the manufacturing process of semiconductor devices, in the photolithography process,
After coating a photoresist on a semiconductor substrate (wafer) and pre-baking, aligning the wafer and photomask, exposing and developing, a pattern of photoresist corresponding to the pattern on the photomask is formed on the wafer, and the pattern of the photomask is is transferred onto the wafer. After this, post-bake is performed, and the underlying insulating film such as oxide film or nitride film is wet or dry etched, and then unnecessary photoresist is removed to form a pattern of oxide film or nitride film on the wafer. be done.

Conventionally, in the above exposure process, a method in which the wafer and photomask are exposed in close contact, a so-called contact exposure method, has been widely adopted, and a method in which the alignment of the wafer and photomask is automatically processed has been widely adopted. There is. FIG. 1 shows a photomask 2 with target groups 1 and 1' for automatic alignment on the left L and right R, and FIG. 2 shows a wafer with target groups 1 and 1' for automatic alignment with respect to the photomask. 3 is shown. FIG. 3 shows a state in which the mask and wafer are automatically aligned and overlaid. For automatic alignment, one pair of targets from the left and right target groups on the mask and wafer are used. FIG. 4 shows an enlarged view of target groups 1 and 1' arranged on the left and right sides of a conventional mask and wafer, and each number ((1) to
(9)) The target is placed in the area marked ((1') to (9')). For example, targets in areas (1) and (1') are used for the first exposure transfer.
Targets in areas (2) and (2') are used for the second exposure transfer, and from the third time onwards, targets in areas (3) and (3') are used.
......(i), (i′) are used one after another.

In the conventional contact exposure method, the left and right targets are not normally arranged symmetrically, as shown in FIG. 4, but are arranged almost randomly. In contrast to the above-mentioned contact exposure, recently, exposure is performed with the wafer and mask separated.
Projection exposure using reflective mirror optics is widespread. In projection exposure using a reflective mirror optical system, there is no contact between the wafer and the photomask, so it can be combined with a positive photoresist, allowing the high resolution that is an advantage of a positive photoresist to be utilized, and also preventing damage to the photomask. There are advantages such as less On the other hand, in the conventional contact exposure method, the photomask and wafer are in close contact with each other.
Photoresist easily adheres to the photomask,
This can cause defects. In particular, positive type resists tend to adhere more easily than negative type resists, making it virtually impossible to combine contact exposure and positive type resists.

Although the projection exposure method has great advantages as described above, it has the disadvantage that a photomask with a target arrangement as shown in FIG. 4 cannot be used when automatically aligning the wafer and the photomask. That is, FIG. 5 shows a state in which automatic alignment of the wafer 3 and photomask 2 has been completed in a projection exposure method using a reflective mirror optical system. In the projection exposure method using a reflective mirror optical system, the wafer is scanned and exposed by ultraviolet light passing through a slit 4 having a width of 1 to 2 mm. Scanning exposure is performed by moving the wafer 3 in the Y direction. Automatic alignment of wafer and photomask
Since this is done using reflected light from the wafer passing through this slit 4, it is necessary to expose the wafer and the target on the photomask within this slit. In the conventional target arrangement shown in FIG. 4, the slit width is narrow, 1 to 2 mm, so simply moving the wafer 3 or the photomask 2 in the X and Y directions will cause either the left or right target to move out of the narrow slit area. Further, in order to forcibly expose the pair of left and right targets in the slit area 4, rotational movement in the θ direction is required. Conventional projection exposure apparatuses have a drawback in that automatic alignment accuracy is significantly reduced when there is a large amount of rotational movement in the θ direction. Further, as the individual targets or target areas become wider, this tendency becomes stronger, and automatic alignment is virtually impossible. For these reasons, alignment of the wafer and photomask must be done manually, which is inefficient and
Another drawback was that the alignment accuracy was poor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a photomask that allows automatic alignment of a wafer and a photomask in projection exposure using reflective mirror optics.

That is, the present invention provides a photomask for exposure and transfer used in the manufacture of semiconductor devices, which includes a group of targets for automatic alignment of the photomask for exposure and transfer and a semiconductor substrate, and the group of targets is arranged symmetrically, The present invention also relates to a projection exposure photomask characterized in that each pair of targets used for one exposure transfer are arranged symmetrically.

The present invention can be expected to improve productivity and improve alignment accuracy.

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

FIG. 6 shows an enlarged view of target groups 1 and 1' of a photomask for projection exposure according to an embodiment of the present invention. The left and right pairs of targets are arranged symmetrically as (1) and (1'), (2) and (2'), and so on. FIG. 7 shows a state in which automatic alignment has been completed in a projection exposure apparatus using a reflection mirror optical system using a photomask according to an embodiment of the present invention. As can be seen from the figure, the photomask according to this embodiment has pairs of targets (1) and (1'),
(2) and (2'), ......(i) and (i') are arranged symmetrically, so that the wafer 3 and the target of the photomask 2 can be easily exposed within the slit area 4. I understand. In the example in Figure 7
(3) and (3') show examples where targets are exposed within the slit area. To expose another target, it is only necessary to move the wafer and photomask in the X and Y directions, and rotational movement in the θ direction is not necessary.

In this way, the left and right targets can be easily exposed within the slit area by only operating in the X and Y directions, so automatic alignment becomes easy for the reasons mentioned above, and the reproducibility of automatic alignment is significantly improved. It is possible to improve productivity and alignment accuracy.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a photomask with an automatic alignment target, FIG. 2 is a wafer, and FIG. 3 is a plan view showing the photomask and wafer aligned using a conventional contact exposure method. FIG. 4 is a plan view showing an enlarged view of a conventional automatic alignment target group, and FIG. 5 is a projection exposure apparatus that uses a reflection mirror optical system to align a photomask and a wafer. It is a top view which shows the completed state. FIGS. 6 and 7 are plan views showing embodiments of the present invention. The symbols in the figure are 1, 1'... target group, 2... photomask, 3... wafer (semiconductor substrate), 4... slit.

Claims (1)

[Claims] 1. A photomask for exposure and transfer used in the manufacture of semiconductor devices is provided with a group of targets for automatic alignment of the photomask for exposure and transfer with a semiconductor substrate, and the group of targets is arranged symmetrically, and A photomask for projection exposure, characterized in that each pair of targets used for exposure transfer are arranged symmetrically.