JPS59144127A - Optical apparatus with adjustment of image - Google Patents

Abstract

PURPOSE:To adjust magnification error occurring at the image without generating a difficult point by providing, in the optical path, a curved optical means having such an optical thicknes as not giving any substantial influence on performance of focusing an image other than deviation of focusing position. CONSTITUTION:A mask M and a wafer W move integrally in the scanning direction (y). A shielding plate S is provided with a ring-belt shaped aperture and is fixed to the position approximated to the wafer. The center light beam emitted from the mask M is reflected by an optical path converting mirror BS1, and then enters the wafer W after it is sequentially reflected by a concave mirror M1, a convex mirror M2 and a light path converting mirror BS2. A member B fixed to the area near the wafer W is curved half-cylindrically in such a thickness as not giving influence on focusing performance. A curved thin film B is so arranged that its bus matches the scanning direction (y).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging optical device, and more particularly to an optical device capable of adjusting imaging magnification error. The present invention is particularly effective for correcting lateral magnification errors that occur in precision optical systems that project and image semiconductor integrated circuit patterns onto wafers.

In recent years, the demand for miniaturization of semiconductor integrated circuits has been rapidly increasing, and the dimensions of fine patterns in electronic circuits are approaching 1 μm. One of the steps in manufacturing these highly integrated devices is a photo process that transfers a mask pattern onto a wafer.

A so-called semiconductor printing device is a device used for transferring such a mask pattern, and there are several methods thereof. Examples include a contact exposure method in which a mask and a wafer are printed while being in contact with each other, a close exposure method in which a mask wafer is printed at a distance of several micrometers, and an optical projection exposure method in which a mask is printed using a lens or mirror.

In general, semiconductor integrated circuits have a single-layer structure; however, as the degree of integration increases, the number of layers tends to increase.

Therefore, in the photo process, it is necessary to use the several printing methods described above as appropriate to overprint different mask patterns for each layer on a single sheet of wafer with high dimensional accuracy. On the other hand, wafer diameters are being increased in order to increase circuit productivity. Nowadays, 5' diameter ones are becoming mainstream.

No matter how much alignment system production is performed, a phenomenon sometimes occurs in which the two cannot be brought into the desired positional relationship down to a microscopic distance of 1 μm or less. In other words, the existing pattern on the mask image toe bar deviates from the normal relationship.

There are many different ways of this lateral displacement, but most of them are what is called a magnification error, and the magnification error can be expressed as a linear function of position. However, if this magnification error is introduced, the image of the mask on the wafer will be enlarged or reduced from the normal size and transferred, as shown in Figure 1 (A) and (B).
As a result, the combination with the existing pattern is not successful, resulting in a defective product.

Generally speaking, when we consider the causes of magnification errors, the first is the difference in magnification of the mask image depending on the difference in projection method mentioned above, and the second is
Furthermore, even devices of the same type have their own unique magnification differences. In addition, expansion and contraction of the wafer due to temperature changes during the processing process also causes magnification error.

Introducing errors into the mask image is an inconvenience in any method, but it is even more serious in the mirror projection exposure method. Therefore, this method will be explained.

The mirror projection exposure method referred to here is a method in which a mask pattern is printed onto a wafer using an off-axis annular region in which aberrations are corrected in an optical system mainly composed of mirror surfaces.

In this method, the good image area of the optical system is annular. In order to print a mask with a large area onto the sea urchin, the annular zone (T in Figure 2) projected onto the sea urchin must be
) The mask M and the wafer W are scanned synchronously in a direction perpendicular to the direction.

In order to specifically illustrate the above configuration, a configuration diagram is shown in FIG. 3 as an example. In the figure, Is is an illumination system, and AS is an alignment system between the mask and the wafer. PS is rotated by a mirror optical system, whereby the pattern of the striped surface M is transferred onto the wafer W.

The mirror optical system P8 is an axially symmetrical system with respect to its optical axis OO', and aberrations are corrected at the image height R. Then, the above fine pattern is transferred onto the wafer using a ring-shaped area including a part of the circumference of the radius R, which is the good image area. In addition, regarding the image formation relationship, after reflection from the mask M,
Concave binding! The light is reflected by the convex mirror M2, which is J, and then again by the concave mirror M1, and the optical path is bent by the plane M9-E3s2, and it converges on one point on the wafer W.

The magnification error that occurs in this device can be divided into two types: one is optically generated in the projection optical system, and the other is due to mechanical feed error when scanning the mask and wafer.As will be explained later, the latter has its drawbacks. has been resolved.

On the other hand, the following reasons can be considered for the former.

As mentioned earlier, with the increase in wafer diameter, 5-inch diameter wafers are currently being used. In the mirror projection exposure method, in order to print a wafer of this size, the concave mirror M1 has a diameter of nearly 400'mm.

While responding to the increase in the diameter of mirrors, on the other hand, it is possible to faithfully transfer minute turns of nearly 1 μm onto the Ueno surface (in order to reduce the surface distortion after polishing the mirror surface to a wavelength of ゛-〇 It must be kept to the following high precision.This is because, as shown by the dotted line in Figure 6, if there is surface distortion at the position on the mirror surface where the light beam hits, the light beam will be reflected from the direction it should originally be reflected. As a result, the image is formed on the wafer at a position displaced from the specified position in the direction perpendicular to the optical axis, resulting in a magnification error in the image.

In a scanning mirror optical system, this type of error occurs mainly in a direction perpendicular to the scanning direction y on the wafer, and this is schematically shown by a small arrow in FIG. 4(5). On the other hand, dimensional errors caused by the second mechanical cause occur as the mask and wafer move, and are mainly caused in the scanning direction as shown in Figure 4 (b). Occurs along yl.

Therefore, by removing these two magnification errors independently, the accuracy of overprinting of integrated circuits over the entire wafer can be improved.
This allows for mixed use with other printing devices.

In particular, this mirror optical system has telescopic links on both the object side and the image side, and has an optical special feature in that the imaging magnification does not change at all even if the position of the object mask or wafer in the optical axis direction changes. have sex. Therefore, the magnification error in the scanning direction and vertical direction is determined by the optical system.
No means were known to correct this.

On the other hand, the main mechanical causes of magnification errors are thought to be poor machine assembly and machining accuracy. For example, as shown in Figure 5 (
If the sliding body K on which the mask and wafer are placed on the guide surface G is moved while being supported by the hydrostatic gas bearings bl and b2, if the guide surface has an upwardly convex shape, In this case, the sliding body will be inclined at the front and rear of the scanning range. Therefore, the wafer surface is also tilted, which causes an error of the type shown in FIG. 4(B). Therefore, one way to prevent this is to increase the pressure supplied to the bearing bl at the front end of the scanning range, and to increase the pressure supplied to the bearing b! at the rear end. It is preferable to increase the pressure supplied to and control the pressure so that the sliding body K always moves horizontally.

In addition to this, there is also a method of eliminating the magnification error by controlling the temperature of the wafer, and a method of correcting it by moving an optical member that contributes to the imaging characteristics within the optical system. However, in the temperature control method, since the wafer expands and contracts radially with respect to its center, magnification errors cannot be corrected independently in the scanning direction and in the direction perpendicular thereto. Moreover, it also has the disadvantage that it takes time to utilize heat conduction. Additionally, a method has been announced in which compensation is performed by moving an optical member that contributes to the imaging characteristics within the optical system, but in this case, there is a risk that the imaging performance of the projection system itself will be deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to adjust magnification errors occurring in imaging without introducing any disadvantages. In order to achieve this purpose, in the embodiments described below, an image is formed in the optical path connecting the object and the image, and more preferably in the vicinity of the object, image, or intermediate image formation plane, except for the deviation of the image formation position of the projection optical system. A transparent thin film member that has little effect on performance is inserted, and this part is curved to correct the imaging position.

The present invention will be explained in detail below. Most of the parts constituting the optical system in FIG. 6 have already been explained. That is, M is a mask, W
are wafers that move together in the scanning direction y.

Reference numeral S denotes a light-shielding plate, which is provided with an annular opening in the shape shown by T in FIG. BS'l and BS2 are optical path changing mirrors, and concave mirror M1 and convex mirror M
! is placed on the optical axis OO' with its spherical center shifted. The light then enters the illuminated area.

Next, the member B fixedly installed near the wafer W is a member characteristic of the present invention, and is formed by bending a thin body into a semi-cylindrical shape with a thickness that does not affect the imaging performance. The curved thin film B is arranged so that its generating line coincides with the scanning direction y, and its appearance in the direction perpendicular to the drawing is as shown in FIGS. 6 and 7.

In general, an optical thin film such as a pellicle can be optically thought of as a very thin parallel surface. . Since this optical member is very thin and has no power, it is known that the imaging performance hardly deteriorates. Therefore, the extent to which the i-characteristics are degraded by having an inclination with respect to the ray (principal ray) which is the center of the luminous flux in the vicinity of the object or the image plane is small. Nevertheless, the chief ray proceeds while undergoing refraction at the thin body B, as shown in FIG. 6, according to Snell's law.

For the above reasons, in semiconductor printing equipment, a transparent optical thin body with an appropriate curve is inserted near the mask, which is the object plane, or the wafer, which is the image plane, in the printing optical path. /N - The printed image on the image can be moved without deteriorating its imaging characteristics.

The optical system of a semiconductor printing apparatus is usually called a telecentric system, and is designed so that the principal rays of all points within the printing screen are projected perpendicularly to the wafer surface. By doing so, there is an advantage that even when the urchin/.-- is out of focus, the center of the light beam does not shift laterally on the urchin/.--, so no magnification error occurs.

In Figure 6, the thickness of the optical thin film just inserted is dmm.
, the refractive index is L, the direction in which the printed image is to be laterally shifted on the wafer is the X axis, and the direction of the chief ray perpendicular to this is the 2nd axis, then the amount of curvature of the inserted optical thin film in the two directions is zmm.
is expressed as a function of X.

The amount of lateral shift ΔX of the printed image in the X direction obtained at this time is dz Δ−Z−d(1−−)・−・■ru d
It is x.

In particular, when an optical thin body is stretched into a spherical shape with radius H, 2 2! Since there is a relationship of ″−π, the formula 0 is 1 Δ-1(1-)f...■ n.

becomes. %-'1.5 and changing d/R, the 8th
The figure can be changed. Using this diagram, good results were obtained using a pellicle with the correct thickness, but a thicker or thinner one can be used depending on the performance of the optical system. However, in a precision optical system, one standard is to suppress the wavefront aberration before and after inserting the thin body to be between λ (wavelength) and 7λ.

Returning to Figure 6, when there is no thin body, a on Ueno-W,
Assume chief rays incident on b, c, d, and e, respectively. now,
When the thin body B is inserted with its concave surface facing the sea urchin/...-W, each ray is refracted to a'.

Images are formed on b/, d/, and e/. As a result, the imaging magnification can be reduced in the direction of the X axis in the figure.

Conversely, if the thin body B is inserted with its convex surface facing the wafer W as shown in FIG. do. Therefore, the image can be enlarged in the direction of the X axis in the figure.

That is, any magnification error can be dealt with by determining the direction of curvature of the thin body B and the numerical value according to the above equation 0.

Note that since the curved thin body B is formed in a semi-cylindrical shape, it acts as a mere parallel plane plate in the direction perpendicular to the drawing, that is, in the direction parallel to the generatrix, and the magnification in this direction is No impact. In addition, in the above explanation, it is assumed that the magnification plate member is inserted into the wafer side B in Fig. 6, but even if this rule is inserted into the mask, . However, in this case, the relationship between enlargement and reduction is different from when it is inserted into the wafer side B.In other words, when it is inserted into the wafer side B, the 1 wafer printed image is enlarged. , A, if the wafer is inserted so that it is convex on the mask, the wafer printed image will be reduced.Furthermore, a thin body may be moved between the optical path switching mirror BS1 or BSz and the concave mirror M1. If there is an imaging plane, a thin body can be placed near it.

As described above, as the first embodiment of the present invention, an optical thin film member is attached to an optical system PS in a semi-cylindrical curved metal frame suitable for each correction document.
One method is to insert it inside.

By inserting this member, it becomes possible to correct the delicate magnification light between many machines. Also, if there is expansion or contraction due to the wafer process, the correction member of the present invention can be replaced depending on the amount of expansion or contraction, and if the curvature can be changed freely,
It is possible to freely control changes in magnification with one member.

Next, the correction member including the frame for holding the optical thin body will be explained in detail. First, as shown in FIG. 10(8)(B), an example is given in which an optical thin film several microns thick is applied to a metal frame curved into a semi-cylindrical shape, and the curvature of the circumference of the curved frame is changed. Specifically, a rectangular metal frame is provided with a ring-shaped aperture AP that allows enough light to pass through, and force is applied from both sides to make it into a semi-cylindrical shape. An optical thin film is placed on this metal frame, and by adjusting the force applied to the metal frame, the curvature of the semicircular circumference can be freely applied. Therefore, the magnification of the image printed on the wafer can be corrected. As a sixth embodiment, there is a case where the thin film is stretched in a general shape other than a single-sided semi-cylindrical shape. When the tab p1 thin film is formed into a semi-cylindrical shape, the amount of correction of the position on the wafer surface is a linear function of the position on the wafer, as shown in FIG. However, some of the printing image deviations that actually occur are expressed as a quadratic or higher function of position. In order to eliminate these image shifts, it is necessary to curve the optical member into an appropriate shape that satisfies Equation 0. For example, image shift can be expressed as a quadratic or sixth-order relationship of position ( If this is to be corrected in the case of Figure 11), the amount of curvature of the thin film must follow a 6th or 4th order function of position, respectively, from equation 0.

Furthermore, since the optical thin body is three-dimensionally curved and the image is printed on the thin body in the area of the projection exposure device using the projection lens PL, the correction means has a three-dimensional hemispherical shape. Become. A hemispherical member can be made of a solid material such as glass or plastic, or a nitrocellulose film can be stretched inside an airtight box and expanded into a hemispherical shape using the difference in air pressure. can also be realized.

Furthermore, the technical idea of the present invention can also be used to correct minute distortions in lens optical systems.

For example, in a lens system, there may be a slight difference in magnification between a specific direction and a direction perpendicular to the specific direction due to the accumulation of glass processing errors and assembly errors. Even in such a case, it is possible to adjust the magnification difference using optical members such as those described in the present invention in the optical path. At this time, the generatrix of the cylinder is set in a direction that substantially coincides with one of the two directions in which the magnification difference is greatest. This situation is shown in FIG. 16, where an optical member called CL corrects the anisotropic magnification. Of course, this correction may be performed on the mask (or reticle) side indicated by M.

In the example explained above, a curved optical thin film with a uniform refractive index and thickness was used. The changing flat plate may be placed near the object plane, image plane, or intermediate imaging plane. In this case, the ability to change the refractive index or thickness of the flat plate (a small prism-like refraction effect can be applied to the light rays and the desired magnification can be adjusted. For example, to form a refractive index distribution on a parallel flat plate made of glass, ion diffusion is used. In addition, one method to form a thickness variation is to deposit a material having the same refractive index on the thin film.

According to the present invention described above, it is possible to modify the lateral magnification without modifying the conventional optical system. In order to prevent this, the pellicle is stretched flat with a slight distance from the wafer, but this type of pellicle can be positively utilized to realize the present invention.

By shaping the optical thin film into a predetermined shape according to the present invention, it has become possible to correct subtle mechanical differences or expansion and contraction of the wafer due to the process. This fact has a very important meaning in VLSI manufacturing where alignment errors are on the order of 0.1 μm.

Furthermore, when applied to a mirror optical system, the magnification in the direction orthogonal to the scanning direction can be freely changed, which is an advantage not seen in the past.

By implementing the present invention, 9. alignment errors in LSI manufacturing have been dramatically reduced, and production with a high p1 yield υ has become possible. Furthermore, the technical idea of the present invention is not limited to these fields, but can be applied to any field that requires minute alignment.

[Brief explanation of the drawing]

FIGS. 1A and 1B are plan views schematically showing magnification errors. FIG. 2 is a plan view showing an image on a wafer. FIG. 6 is an optical sectional view showing an embodiment of the present invention. Figure 4 (A), (B)
is a plan view schematically showing magnification errors. FIG. 5 is an auxiliary explanatory diagram of the scanning mechanism. FIG. 6 is an enlarged view of the main parts of the embodiment. FIG. 7 is a lateral optical cross-sectional view of the embodiment. Figure 8 is a diagram with radius and thickness as variables. Figure 9 is a modified view of the main part. Section 10 is a plan view of the constituent members, and section 10) is a perspective view. 1st
Figure 1 is a diagram showing the position and amount of deviation. 12 and 13 are perspective views of the optical system. In the figure, M is a mask, W is a wafer, Ml is a concave value, and M2
is a convex mirror, B and B' are thin bodies, C is a coffin with an aperture, and y is the scanning direction. Applicant Canon Co., Ltd. Tsutsu82 Wq Punu Right 10th Garden (A) No. 10 Kasumi (8) 8 animals No. 11M (

Claims (1)

[Scope of Claims] (1) Optical means that is equipped with an imaging optical system and has an optical thickness and a curved shape that does not substantially affect imaging performance other than the deviation of the imaging position. An image-adjusted optical device characterized in that an image-adjusted optical device is arranged in an optical path. (2) A patent claim in which the optical means is modified by image-adjusted light according to claim 1, wherein the optical means is arranged near the object plane, image plane, or intermediate image plane of the imaging optical system. The image-adjusted optical device according to item 1. (4) The optical device is a device that exposes a band-shaped image of the object by the imaging optical system and the photosensitive surface by relatively scanning it, and the optical means has a cylindrical shape whose generating line substantially coincides with the scanning direction. An image-adjusted optical device according to claim 1, which is curved. (5) The image-adjusted optical device according to claim 1, wherein the optical means is a pellicle held in a frame. (6) Equipped with an imaging optical system, which has an optical thickness that does not substantially affect the imaging performance other than the deviation of the imaging position, and has a continuously changing refractive index distribution or thickness distribution. 1. An image-adjusted optical device, characterized in that an optical device having an optical function is provided in an optical path.