JP2005116848A - Projecting aligner and method for manufacturing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projecting aligner capable of preventing the generation of exposure astigmatism and capable of obtaining large focal depth and effective optical performance in a step and scanning type aligner. <P>SOLUTION: In the scanning type projecting aligner, a plurality of illuminating beams of prescribed shapes are included in an effective screen of a projecting optical system and the quantity of exposure obtained by integrating the quantity of exposure in the effective screen of the projecting optical system is uniformed on a wafer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a so-called step-and-scan projection exposure apparatus. Such an exposure apparatus is suitable for use in lithography processes among processes for manufacturing devices such as ICs and LSIs, imaging devices such as CCDs, display devices such as liquid crystal panels, and devices such as magnetic heads. It is.

  Recent progress in the manufacturing technology of semiconductor devices is remarkable, and the progress of microfabrication technology is also remarkable. In particular, optical processing technology is mainly reduced projection exposure equipment with a submicron resolution, commonly called a stepper, and the numerical aperture (NA) of the optical system can be increased and the exposure wavelength can be shortened to further improve the resolution. ing.

  In this stepper, a circuit pattern image of a mask (reticle) is reduced and projected to a predetermined position on a wafer surface via a projection optical system having a predetermined reduction magnification, and after one projection transfer is completed. The entire surface of the wafer is exposed by repeating a step of moving the stage on which the wafer is placed by a predetermined amount and transferring again.

  Recently, a step-and-scan projection exposure apparatus using a scanning mechanism that can obtain a high resolution and can enlarge the screen size has been put into practical use.

  This step-and-scan type exposure apparatus has a slit-shaped exposure area, and shot exposure is performed by scanning a reticle and a wafer. When scanning of one shot is completed, the wafer steps to the next shot, and exposure of the next shot is started. This is repeated to expose the entire wafer.

  FIG. 7 shows a projection exposure apparatus that performs a step-and-scan method that can take a wide exposure region by using a scanning mechanism. In the figure, 101 is a reticle (mask) as a first object, 102 is a projection lens (projection optical system), 104 is a movable stage, and a wafer 103 as a second object is placed thereon. A resist that reacts with ultraviolet light is applied on the surface of the wafer 103. Only the circuit pattern of the portion irradiated with the slit-shaped illumination light beam is projected and transferred onto the wafer 103 by the aperture 106 having a slit opening 106 ′ provided immediately before the reticle 101. 000 indicates a coordinate system indicating the X, Y, and Z axes. The optical axis 108 of the projection lens 102 is aligned with the Z-axis direction, the longitudinal direction of the slit-shaped illumination light beam 106 ′ is aligned with the Y-axis direction, and the short direction is aligned with the X-axis direction.

  The principle of operation will be briefly described with reference to FIG. The pattern on the reticle 101 is projected and transferred only in the portion where the slit-shaped illumination light beam 106 'is hit. Accordingly, by scanning the reticle 101 in the direction of the arrow 114 at a predetermined speed, and simultaneously scanning the stage 104 in the direction of the arrow 115 at a speed obtained by multiplying this speed by the imaging magnification of the projection lens 102, the reticle 101 is scanned. The entire circuit pattern is projected and transferred onto the wafer 103. Further, the scan is controlled by synchronizing the reticle 101 and the wafer 103 by the scan controller 111. After the transfer of the entire circuit pattern is completed, the stage 104 is moved by a predetermined amount, that is, stepped, and the pattern transfer is repeated in the same manner as described above at many different positions on the wafer 103.

  In FIG. 7, the aperture 106 is arranged immediately before the reticle 101 to limit the light beam that illuminates the reticle 101 to a slit shape, but the aperture is arranged on a plane conjugate with the reticle in the illumination system optical path, Therefore, even if the light beam is limited to the slit shape, the same effect can be obtained.

  FIG. 8 shows the relationship among the luminous flux (slit), the pattern transfer area, and the effective area of the projection optical system on the wafer 107. In most cases, the projection optical system is configured to be axially symmetric and has a circular effective area 201. By design, good imaging characteristics can be obtained at an arbitrary location inside the projection optical system. Among them, the pattern in the region 202 is transferred by illuminating only the slit-shaped portion 202, and the entire pattern in the region 203 is transferred by scanning the stage 104 and the reticle 114 in synchronization. .

In summary, the step-and-scan type exposure apparatus has the following characteristics as compared with the stepper type exposure apparatus.
(1) By scanning the reticle and the stage in synchronization, a pattern in a range larger than the effective area of the projection optical system can be transferred.
(2) Although the projection optical system has a circular area, only a part of the slit-shaped area is used for projection exposure.

  By the way, in the projection exposure apparatus, when the projection optical system absorbs light energy, undesirable performance deterioration, so-called thermal aberration (or exposure aberration) occurs.

  FIG. 9 is a schematic diagram of the projection optical system. The light beam from the reticle 101 passes through the projection optical system 102 and reaches the wafer 103. The projection optical system includes a convex lens 1021, a concave lens 1022, a convex lens 1023, a diaphragm 1024, and a convex lens 1025 in order from the reticle side. Each lens is held by a holding member 1027, and the holding member is supported by a lens barrel 1026.

  During exposure, when each lens is exposed to exposure light, the lens material's optical glass (or synthetic quartz, fluorite, etc.) or antireflection film absorbs light energy slightly, generating heat inside the lens. And cause an increase in temperature. The heat inside the lens is discharged from the holding member 1027 through the lens barrel 1026 to the outside, but since light energy is also supplied one after another, a temperature distribution corresponding to the illuminance distribution is formed inside the lens. Due to this temperature distribution, a refractive index distribution is generated in the lens, or the lens is thermally expanded to cause local surface deformation.

  As a result, when the focus, magnification, etc. of the projection optical system change, or aberrations such as distortion, spherical aberration, and coma occur, undesirable performance changes and performance degradation occur. In order to correct these thermal aberrations (exposure aberrations), the exposure apparatus is usually provided with various detection systems and correction mechanisms.

  One of the above-mentioned exposure aberrations, particularly a problem in a step-and-scan type exposure apparatus, is astigmatism that occurs because only a part of the slit-shaped region is used for projection exposure.

  FIG. 10 schematically shows the illuminance distribution when the light beam illuminated in a slit shape on the reticle is transmitted through each lens constituting the projection optical system. In the drawing, the outer circular line represents the end of the effective area of each lens, and the hatched area represents the area through which light passes. The light beam that was a rectangular slit on the reticle 101 has a shape close to a rectangle when passing through the first lens 1021. As it approaches the second lens 1022, the third lens 1023 and the aperture 1024, it gradually approaches a circle, and when passing through the aperture 1024, it becomes a nearly perfect circle. In the fourth lens 1025, the shape of the light flux approaches the slit again, and in the wafer 103, the light flux is condensed into a rectangular slit shape.

  Here, when the light hits in a long and narrow shape similar to the slit like the first lens 1021, the temperature distribution in the lens becomes different in the X-axis direction and the Y-axis direction. The refractive index distribution in the lens and the shape change due to thermal expansion of the lens also have different distributions and shapes in the X-axis direction and the Y-axis direction. As a result, between a light beam that starts from a certain point on the reticle, spreads in the X-axis direction, and converges again to a single point on the wafer, and a light beam that spreads in the Y-axis direction and converges again to a single point on the wafer. An optical path length difference is generated, which appears as a focus difference between the X-axis direction and the Y-axis direction, that is, astigmatism.

Examples of the exposure apparatus described above include the examples described in documents such as Patent Documents 1 and 2.
JP 09-246177 A JP-A-11-160887

  If there is astigmatism in the projection optical system, it will cause undesirable optical performance degradation such as reduced depth of focus, hole pattern distortion, and transferred pattern dimensional accuracy, which will adversely affect device fabrication and will be eliminated as much as possible. Must.

  An object of the present invention is to eliminate astigmatism during exposure which is a problem in the step-and-scan type exposure apparatus described above.

  In order to achieve the above object, the projection exposure apparatus of the present invention has a plurality of slits (or openings) in the effective screen of the projection optical system, and scans within the effective screen of the projection optical system on the wafer. It is characterized in that the exposure amount integrated in the above is configured to be uniform.

  As described above, according to the present invention, in a step-and-scan exposure apparatus, exposure astigmatism, which has been a problem in the past, can be prevented, and as a result, a large depth of focus and good optical performance can be obtained. Projection exposure apparatus can be achieved. In addition, depending on the configuration, an apparatus having a higher throughput than the conventional one can be realized.

  FIG. 1 shows a first embodiment of the present invention. The x and y axes are the same as in FIGS. A circular frame 11 indicates an effective system of the projection optical system on the wafer surface, and indicates that good imaging performance can be obtained within this area. A hatched area 12 indicates an area used for projection. In this embodiment, two exposure areas that were conventionally a single slit are used, and exposure is performed using both, thereby eliminating the X and Y asymmetry of the light beam incident on each lens as much as possible. Yes. FIG. 11 schematically shows the illuminance distribution on the first lens 1021 of the projection optical system shown in FIG. 9 when exposure is performed using the projection area of FIG. Compared with the conventional example (1021 in FIG. 10), light is almost irradiated on the entire surface of the lens, which is effective in removing astigmatism.

  Such a plurality of projection areas can be realized by changing the opening shape (106 ′) of the aperture (106 in FIG. 7) arranged immediately before the reticle. Further, the same effect can be obtained even if an aperture is arranged on a plane conjugate with the reticle in the optical path of the illumination optical system and the light beam is limited to a slit shape there. The same applies to the following embodiments.

  FIG. 2 shows a second embodiment of the present invention. In the first embodiment, the length of the slit in the Y-axis direction is shorter than the conventional one, and there is a demerit that a sufficiently wide transfer region cannot be obtained. For example, in Example 1, the length of the projection area in the Y-axis direction (slit length) reaches only about 70% of the effective diameter of the projection optical system on the wafer, and the projection optical system of FIG. The upper and lower parts of the area are wasted without being used for projection. However, in the second embodiment, this is overcome by arranging the projection areas as shown in FIG.

  In Example 2, there are four projection areas. These projection areas are devised in shape and arrangement so that the total length of each projection area in the X direction is the same for any Y coordinate. Has been. In addition, by illuminating each area with a uniform illuminance, when scanning, the light flux of each projection area is integrated, and a uniform illuminance distribution is obtained over the entire transfer area. The same applies to the following embodiments.

  Note that in order to obtain a uniform illuminance distribution on the wafer surface after scanning, it is necessary to make a slight adjustment according to the transmittance distribution of the projection optical system. In general, the projection optical system tends to have slightly lower transmittance than the center due to factors such as the reflectance characteristics of the film. Accordingly, the length (width) of each projection area in the X direction is expected. ) Must be slightly changed for each Y coordinate, or the illumination light beam must have a slight illuminance distribution.

  Further, each projection area is configured to have a portion that overlaps each other when scanned (portion where the upper and lower sides are slanted). This is due to the following reasons. For example, as shown in FIG. 6, when the projection area configuration is such that there are no overlapping portions, when there is an error in the position and size of each projection area shape, An air gap is generated between c, causing a device failure. In order to avoid such a problem, in this embodiment, each projection area is configured to have an overlapping portion. The same applies to Examples 3 and 5 below.

  FIG. 3 shows a third embodiment of the present invention. The effect of making the illuminance distribution of the lenses in the projection optical system more uniform by further increasing the number of projection areas compared to Example 2 and arranging them in the entire effective area of the projection optical system. It is aimed to improve. However, the configuration of the present embodiment has a high effect of making the illuminance distribution of the lens uniform, but on the other hand, when the number of projection areas increases, the control of the illuminance and the position of the projection pattern in the overlapping area of the projection areas Since control (control of distortion of the projection optical system) is complicated, it is necessary to determine in order to appropriately select the number of projection areas.

  By the way, in the conventional step-and-scan type exposure apparatus, in the parts processing and assembly adjustment of the projection optical system, the imaging performance is improved only in the elongated slit-like portion to be used, and the performance of other portions is ignored. By adopting this method, it was possible to perform high-precision processing and assembly adjustment compared to a stepper type exposure apparatus that uses the entire screen. On the other hand, in Examples 1 to 3 described so far, the advantage is lost because a wide part of the effective area is used. The solution to this is the fourth embodiment shown in FIG.

  As shown in FIG. 4, in the present embodiment, of the effective area of the projection optical system, an area having a substantially constant distance from the center (optical axis) is used as the projection area. By adopting such a configuration, the projection optical system needs to be designed, assembled and adjusted so that a good imaging performance is obtained only in a region with a constant angle of view (object height). Contribute to the realization of In addition, since the projection area has a substantially axisymmetric shape, the illuminance distribution of the lens in the projection optical system also has a substantially axisymmetric shape, and astigmatism hardly occurs.

  FIG. 5 shows a fifth embodiment of the present invention. Examples 2 to 4 so far have a feature that it is difficult to obtain high illuminance. For example, as a means for illuminating the projection area as in Example 3, it is possible to illuminate the entire effective area of the projection system with the illumination optical system, and to cut out and use only the projection area in the aperture, In this case, only about 32% of the illuminating light is used, resulting in poor utilization efficiency. The situation is the same in the other Examples 2 and 4. This embodiment solves this problem.

  If the configuration has a projection area as shown in FIG. 5, it is sufficient to illuminate the two rectangular areas 51 and 52 shown by dotted lines in the figure. A highly efficient illumination system can be realized by a method such as mounting two optical systems. In particular, when two illumination optical systems are mounted, it is possible to obtain higher illuminance than before, and as a result, high throughput can be realized.

  Further, the present invention is not limited to the above-described embodiment, and can be applied to a device manufacturing method using the exposure apparatus described in this embodiment. Specifically, using the above-described exposure apparatus, a step of exposing an object to be exposed such as a wafer or a glass substrate, a step of developing the exposed object to be exposed, and a step of further developing the exposed object to be exposed A method for manufacturing a device.

The figure explaining 1st Example of this invention The figure explaining 2nd Example of this invention The figure explaining 3rd Example of this invention The figure explaining the 4th example of the present invention. The figure explaining the 5th Example of this invention The figure explaining supplementary Example 2 Schematic diagram of step-and-scan exposure equipment Explanatory drawing of slit and transfer area of step and scan exposure system Schematic diagram of projection optical system Diagram showing the illumination distribution of the lens in the projection optical system FIG. 6 is a diagram showing the illuminance distribution of the first lens in the projection optical system in Embodiment 1.

Claims (5)

  A pattern on the reticle (mask) is illuminated with an illumination beam having a predetermined shape, and the reticle and the movable stage are placed on the wafer (substrate) surface on which the pattern on the reticle is placed on the movable stage by a projection optical system. In a scanning projection exposure apparatus that performs projection exposure while scanning in synchronization with a speed ratio corresponding to the projection magnification of a projection optical system, the projection optical system has a plurality of illumination beams of the predetermined shape in an effective screen of the projection optical system, A projection exposure apparatus characterized in that an exposure amount obtained by integrating an effective screen of the projection optical system in a scan direction on a wafer is uniform.   2. The projection exposure apparatus according to claim 1, wherein the slit length on the wafer (the length of the entire projection area in the direction perpendicular to the scan) is 0.7 times or more the effective diameter of the projection optical system on the wafer.   2. The projection exposure apparatus according to claim 1, wherein a substantially annular zone of the effective area of the projection optical system is used as a projection area.   3. The projection exposure apparatus according to claim 2, wherein the number of projection areas is two and each has a trapezoidal shape or a rectangular shape. 5. A device manufacturing method, comprising: a step of exposing an object to be exposed using the projection exposure apparatus according to claim 1; and a step of developing the exposed object to be exposed.

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