JP2005302862A - Exposure apparatus, exposure method, and device manufacturing method - Google Patents

Abstract

An exposure apparatus, an exposure method, and a device manufacturing method using the exposure method capable of forming a reticle image on the wafer surface satisfactorily by performing high-precision focusing, for example, even in the case of an immersion type. Providing a method.
This exposure apparatus illuminates a reticle using exposure light, and projects and exposes a pattern on the reticle onto a substrate via a projection optical system, and corrects the focus position of the substrate with respect to the reticle. In order to achieve this, a reticle drive unit that moves the reticle in at least one of the optical axis direction and the direction inclined with respect to the optical axis is provided.
[Selection] Figure 1

Description

  The present invention relates to an exposure apparatus for exposing a pattern on a substrate (wafer, glass plate, etc.) on a mask or a reticle (in the present application, these terms are used interchangeably) in a manufacturing process of a semiconductor integrated circuit or a liquid crystal display element. The present invention relates to an exposure method and a device manufacturing method using the exposure method. The present invention is suitable, for example, for a scanning projection exposure apparatus.

  Conventionally, when a semiconductor element, a liquid crystal display element, a thin film magnetic head or the like is manufactured by a photolithography process, a photomask or reticle (hereinafter referred to as reticle) pattern is transferred onto a photosensitive substrate wafer or glass plate (hereinafter referred to as wafer). An exposure apparatus has been proposed. As the projection exposure apparatus, in addition to a projection exposure apparatus called a stepper that repeatedly exposes a pattern by a so-called step-and-repeat method, scanning that performs exposure while synchronously scanning a reticle and a wafer by a step-and-scan method. A type of projection exposure apparatus (scanning exposure apparatus) is also being used.

  Since it is necessary to accurately project and expose a fine pattern, this type of projection exposure apparatus is required to have a very high resolution. In order to realize a high resolving power, some have a function of measuring factors affecting the resolving power, such as atmospheric pressure and environmental temperature, and correcting the imaging characteristics according to the measurement results.

In addition, since the numerical aperture of the projection optical system is set large in order to achieve high resolution, the depth of focus of the projection optical system becomes shallow. Therefore, the focus position (position in the optical axis direction of the projection optical system) corresponding to the unevenness of the wafer surface is measured by the oblique incidence type focus position detection system, and the wafer surface position is determined based on the measurement result on the image plane of the projection optical system. Some have an autofocus function for matching the position (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2-102518

  However, in recent years, demands for high accuracy with respect to the focus position and alignment position have further increased, and accordingly, it has become necessary to increase the precision of reticle and wafer stage drive control. As described above, conventionally, focusing is performed by moving the wafer surface position by a driving mechanism, but there is a limit to the driving resolution.

  The immersion projection exposure apparatus increases the numerical aperture of the projection optical system by filling a liquid between the projection lens and the wafer surface. In this immersion projection exposure apparatus, since the distance between the projection lens and the wafer is very narrow, it is difficult to measure the wafer surface position under the projection lens by the oblique incidence type focal position detection system.

  Further, when the wafer is moved in the focus (optical axis) direction or tilt (tilt) direction by the wafer stage, liquid disturbance occurs. Therefore, it is not desirable to move the wafer in the focus direction and the tilt direction in order to make the focus position of the irregularities on the wafer surface coincide with the image plane position.

  The present invention has been made in view of the above circumstances, and by performing high-precision focusing, for example, an exposure apparatus that can satisfactorily form a reticle image on the wafer surface even in the case of an immersion type, It is an exemplary object to provide an exposure method and a device manufacturing method using the exposure method.

  In order to achieve the above object, an exposure apparatus according to an exemplary aspect of the present invention illuminates a reticle using exposure light, and projects and exposes a pattern on the reticle onto a substrate via a projection optical system. In order to correct the focus position of the substrate with respect to the reticle, a reticle driving unit is provided that moves the reticle in at least one of an optical axis direction and a direction inclined with respect to the optical axis.

  An exposure apparatus according to another exemplary aspect of the present invention is an exposure apparatus that illuminates a reticle using exposure light, and projects and exposes a pattern on the reticle onto a substrate via a projection optical system. And a projection optical system drive unit that moves at least a part of the projection optical system in an optical axis direction or a direction inclined with respect to the optical axis. At least a part of the projection optical system may be a projection lens in the projection optical system.

  An exposure apparatus according to still another exemplary aspect of the present invention illuminates a reticle using exposure light, and projects a pattern on the reticle via a projection optical system, a liquid filled between the projection optical system and the substrate. An exposure apparatus that performs projection exposure on a substrate, comprising a control device that adjusts at least one of the temperature and density of the liquid. It is desirable to further have a circulation device for circulating the liquid. It is further desirable that the exposure apparatus further includes a storage unit that stores the correction amount of the focus position.

  According to still another exemplary aspect of the present invention, there is provided a device manufacturing method including a step of projecting a pattern onto a substrate by the exposure apparatus described above, and a step of performing a predetermined process on the projection-exposed substrate. And

  An exposure method as still another exemplary aspect of the present invention is an exposure method for illuminating a reticle using exposure light and projecting and exposing a pattern on the reticle onto a substrate via a projection optical system. In order to correct the focus position of the substrate, at least one of the reticle and the projection optical system is moved in the optical axis direction.

  According to still another exemplary aspect of the present invention, an exposure method illuminates a reticle using exposure light, and a pattern on the reticle is projected via a projection optical system, a liquid filled between the projection optical system and the substrate. An exposure method in which projection exposure is performed on a substrate, comprising the step of adjusting at least one of the temperature and density of the liquid. These exposure methods measure the surface shape and back surface shape of the substrate and calculate the difference value, and measure the back surface shape of the substrate during exposure and reflect the difference value on the back surface shape to expose the substrate. And calculating a surface shape at the time. The method may further include a step of detecting an image of the substrate-side reference mark formed on the substrate or a surface equivalent to the substrate on a reticle disposed at a position substantially conjugate with the substrate using exposure light. .

  Other objects and further features of the present invention will be made clear by embodiments described below with reference to the accompanying drawings.

  According to the present invention, the accuracy of focus correction of the projection exposure apparatus can be improved according to the projection exposure magnification. Also in the immersion projection exposure apparatus, focus instability due to liquid disturbance accompanying focus correction can be reduced, and stable focus correction can be performed.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a step-and-scan type immersion projection exposure apparatus will be described as an example. FIG. 1 is a block diagram showing a schematic configuration of a projection exposure apparatus S according to this embodiment. In FIG. 1, the reticle R is held by vacuum suction with a reticle holder (not shown) with the surface on which the pattern is formed facing downward (the −Z direction in FIG. 1). The reticle R and the reticle holder are placed on a reticle stage RST that can be moved in the XYZ directions and rotated around each axis in order to enable scanning exposure and focus correction of the entire wafer surface as a substrate.

  A light source 1 that outputs exposure light is provided above the reticle (+ Z direction in FIG. 1), and an illumination optical system 2 is provided between the light source 1 and the reticle R. Below the reticle R, a wafer W to be exposed is disposed via the projection optical system PL. Wafer W is held by wafer chuck 32 for holding the wafer, and the wafer chuck is placed on wafer stage WST. Wafer stage WST is movable in the XYZ directions, and aligns wafer W at exposure station 13 for projection exposure.

  The projection exposure apparatus S has a measurement station 14 for measuring the wafer W separately from the exposure station 13 for exposing the wafer W. For example, after measuring the shape of the wafer W at the measurement station 14, the wafer W may be moved to the exposure station 13 together with the wafer stage WST. Also, wafer stage WST is prepared in each of exposure station 13 and measurement station 14, and after wafer W measurement at measurement station 14 is completed, wafer chuck 32 is detached from wafer stage WST in measurement station 14, and wafer chuck is provided. The entire wafer W may be attached to the wafer stage WST of the exposure station 13. A liquid for improving the numerical aperture is filled between the projection optical system PL and the wafer W.

  The projection exposure operation by the projection exposure apparatus S is the same as the operation of a general projection exposure apparatus. That is, the exposure light emitted from the light source 1 is irradiated onto the reticle R by the illumination optical system 2. Then, an image of the pattern drawn on the reticle R is projected onto the wafer W by the exposure light via the projection optical system PL. Reticle R and wafer W are synchronously scanned in a direction orthogonal to the paper surface (ie, the Y direction), and one-shot exposure is performed.

  As shown in FIG. 1, the projection exposure apparatus S is provided with a wafer position detection system 31a below the exposure station 13 and wafer surface position detection systems 31b and 31c above and below the measurement station 13, respectively. These wafer surface position detection systems 31a to 31c are for aligning the exposure surface of the wafer W with the imaging surface of the projection optical system PL, and have the same configuration as a conventional oblique incidence type focus sensor. Yes. Since the configuration of these wafer surface position detection systems 31a to 31c is the same as that of a reticle surface position detection system 35 described later, description thereof will be omitted.

  In the measurement station 14, it is possible to directly measure the positions of the front and back surfaces of the wafer W from the top and bottom. However, in the exposure station 13 disposed below the projection optical system PL, the distance between the projection lens disposed below the projection optical system PL and the wafer W is short. Moreover, since the liquid is filled in the meantime, it is difficult to configure a detection system that directly measures the surface (upper surface) position of the wafer W.

  Therefore, only the detection system (focus sensor) 31a for measuring the position of the back surface (lower surface) of the wafer W is disposed in the exposure station 13. Then, based on the measurement results by the wafer surface position detection systems 31a to 31c, the surface position of the wafer W at the exposure station 13 is calculated. FIG. 2 is a graph for explaining the calculation method. FIG. 2A is a graph showing the measurement result of the wafer W surface position by the wafer surface position detection system 31b and the measurement result of the wafer W back surface position by the wafer surface position detection system 31c in the measurement station 14. There is a difference between the two measurement results. FIG. 2B shows a measurement result of the back surface position of the wafer W by the wafer surface position detection system 31 a in the exposure station 13. By reflecting the difference shown in FIG. 2A in the measurement result shown in FIG. 2B, the surface position of the wafer W in the exposure station 13 can be obtained as shown in FIG.

  A reticle surface position detection system 35 for detecting the position of the pattern surface is also provided on the reticle R side. The reticle surface position detection system 35 has a light irradiation part and a light detection part and is generally configured. The reticle surface position detection system 35 detects the position of the test surface by irradiating the test surface with the detection light from the light irradiation unit and detecting the reflected light with the light detection unit.

  The light irradiating unit is generally configured to include a light source 5 such as a light emitting diode, a projection mark slit 6, and a projection lens 7. The light detection unit is generally configured to include a light receiving lens 8 and a detector 9 such as a CCD sensor. For example, a plurality of light irradiation units and light detection units are arranged in a direction orthogonal to the scanning direction of the reticle R, and the shape of the test surface can be measured by scanning the reticle R. Such a configuration is the same in the wafer surface position detection systems 31a to 31c.

  In the conventional projection exposure apparatus, since the focus position correction is performed by driving the stage in the Z direction on the wafer side, the resolution is limited. In particular, in an immersion projection exposure apparatus, if an attempt is made to correct a focus shift caused by a wafer surface shape or a projection lens by driving in the Z direction on the wafer side, the liquid may be disturbed and focus stability may be deteriorated.

  For this reason, in the present embodiment, the focus shift component caused by the surface shape of the wafer W, the exposure heat of the projection lens, the weight of the projection lens, and the like is shown in FIG. Correct by tilt drive. The wafer W side is configured to drive only in the scan direction and not drive in the focus / tilt direction. According to this correction method, as a result, the correction accuracy is improved by the exposure projection magnification.

  The focus / tilt drive surface of the reticle stage RST at this time is obtained by determining the surface position (shape) of the wafer W obtained above and the defocus amount of the best imaging surface position due to the exposure heat in the projection lens and the change in the weight of the lens. The corrected surface is reflected. In the latter case, the change with time is predicted using the best imaging position measurement system 16 in FIG. That is, when the pattern on the reference plate (reference mark) 15a on the wafer stage WST is illuminated with exposure light, the diffracted light is near the reference plate 15b on the reticle stage RST via the projection optical system PL. To form an image. Then, the position at which the exposure amount passing through the pattern of the reference plate (reference mark) 15b on the reticle stage RST is maximized on the photoelectric sensor 18 is detected while moving the reticle stage RST in the optical axis direction of the projection optical system PL. Then, the position of the reference plate 15b at that time, that is, the position where the reticle pattern surface is imagewise conjugate with the wafer surface is measured by the focus detection system and used as the origin of the detection system. By periodically repeating this measurement, it is possible to predict the defocus amount over time caused by the projection lens, and by reflecting this defocus amount on the reticle scan correction surface, it is possible to perform good exposure (see FIG. 4).

  Further, as shown in FIG. 1, the surface shape of the wafer W is measured at the exposure station 13 and the measurement station 14, the component of the focus deviation due to the exposure heat of the projection lens and its own weight is detected by the best imaging position measurement system 16, and Based on the result, as shown in FIG. 5, correction is performed by aligning the best imaging plane with the surface of the wafer W by driving a part of the lenses of the projection optical system PL by a projection optical system drive unit (not shown). Good. Alternatively, a correction method may be used in which the focus position is corrected by changing the refractive index and density of the liquid between the wafer W and the projection lens after measuring the positional relationship between the image plane and the surface of the wafer W using the detection system. .

  Next, a procedure for correcting the defocus component of the projection lens in the projection exposure apparatus S will be described. FIG. 6 is a procedure diagram for explaining the correction procedure of the defocus component of the projection lens in the projection exposure apparatus S divided into steps 0 to 3.

[Step 0]
The image formation change due to exposure heat in the projection lens and its own weight is periodically measured by the best imaging position detection system 16 in FIG. 1, and the image plane shift amount with time is obtained and reflected in the correction amount at the time of reticle scanning. (Understanding of the projection lens exposure image plane position).

[Step 1]
The wafer surface position detection systems 31b and 31c of the measurement station 14 are used to measure the surface shape of all shots of the wafer W, and the measured values and the front and back surface difference values are stored in the shape storage unit 10 as a storage unit (S.1). ). If there is a possibility that a scan direction difference has occurred during this measurement, a measurement value for each scan direction is stored. After the measurement is completed, the wafer W is moved to the exposure station 13 (S.2). Then, a reference reticle R is set (S.3), and the back surface position of the reference shot area on the wafer W is measured. Here, the result of reflecting the difference value (the value at the reference shot equivalent position) already stored in the shape storage unit 10 in the back surface measurement value is stored as the reference shot surface position on the wafer W (S.4). Thereafter, the reference shot area is scan-exposed. Based on the resolution evaluation on the wafer W, the scan drive surface of the reticle R is measured by the reticle surface position detection system 35 and stored in the shape storage unit 10 (S.5) (the exposure result of the reticle scan correction drive surface is displayed). Based on).

[Step 2]
After the wafer W is moved horizontally in order to expose another shot on the wafer W (S.6), the back surface of the wafer W is measured at the same time as the exposure at the exposure station 13, and the result is a table of the shot at the measurement station 14. The difference value when the back surface position is measured is reflected. A value obtained by subtracting the value of the reference shot surface position from the result of reflecting the difference value is converted to the reticle side, and the value is measured by the position of the scan drive surface obtained using the reference shot (measured by the reticle surface position detection system 35). (S.7), the defocus component can be corrected even in regions with different flatness on the wafer W (correction operation during normal exposure).

[Step 3]
When exposure is performed using another exposure reticle R, the reticle R surface is first measured by the reticle surface position detection system 35 (S.8). Then, the difference between the surface position measured value with the reference reticle and the value measured with the reticle R is obtained, and the amount is reflected on the reticle scan drive surface to be corrected (S.9). Similarly, the wafer surface position measurement value difference between the reference shot and the exposure shot is reflected on the reticle scan driving surface to perform correction (S.10) (management of reticle / wafer scan posture & shape difference).

[Step 4]
Further, as determined in step 0, the refractive index of the liquid L used in the immersion projection exposure apparatus S is changed by external control with respect to the change with time of the best imaging plane caused by repeated exposure. Correction is performed (S.11). A specific control method will be described next.

  In the immersion projection exposure apparatus S, the refractive index of the liquid L (for example, pure water) filled between the projection lens and the wafer W can be controlled by an external control device (not shown). Since it is known that the correlation between the refractive index and the temperature of the liquid L shows a tendency as shown in FIG. 7, the temperature history and the history of the best imaging plane are always measured, and the exposure is repeatedly performed while correcting. The generated exposure defocus can be corrected at any time.

  However, since the liquid L used in the immersion projection exposure apparatus S is disposed on the surface of the wafer W scanned in the Y direction, density unevenness due to disturbance of the liquid L may occur. Therefore, it is considered difficult to accurately adjust the image plane by changing the refractive index in the short term, for example, for each shot. Therefore, in order to perform high-precision and short-term focus correction, first, reticle stage RST is driven in the Z direction so that the exposure image surface comes to an average position on the surface of wafer W. Then, the remaining partial wafer surface shape is corrected by the focus and tilt driving scan of the reticle stage RST and lens driving. Long-term correction, for example, for each wafer W, can be achieved by performing correction based on a change in refractive index.

  The liquid between the projection lens and the wafer W may be disturbed by the wafer W drive. As a result, density distribution unevenness occurs in the liquid and the best imaging plane becomes unstable. Therefore, as shown in FIG. 8, a circulation device 37 for generating a flow of liquid L from the outside is installed. Thereby, since the liquid L under the projection lens flows at a constant speed, uneven density distribution can be reduced. The circulation device 37 has a function capable of changing the flow velocity and the flow direction of the liquid L depending on the speed and direction of the wafer W drive. Thereby, it becomes possible to always stabilize the best imaging plane.

  Next, referring to FIGS. 9 and 10, an embodiment of a device manufacturing method using the above-described exposure apparatus S will be described. FIG. 9 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 101 (circuit design), a device circuit is designed. In step 102 (reticle fabrication), a reticle on which the designed circuit pattern is formed is fabricated. In step 103 (wafer manufacture), a wafer (substrate) is manufactured using a material such as silicon. Step 104 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the reticle and wafer. Step 105 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer created in step 104, and includes processes such as an assembly process (dicing and bonding), a packaging process (chip encapsulation), and the like. . In step 106 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 105 are performed. Through these steps, the semiconductor device is completed and shipped (step 107).

  FIG. 10 is a detailed flowchart of the wafer process in Step 104. In step 111 (oxidation), the wafer surface is oxidized. In step 112 (CVD), an insulating film is formed on the surface of the wafer. In step 113 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. In step 114 (ion implantation), ions are implanted into the wafer. In step 115 (resist process), a photosensitive agent is applied to the wafer. Step 116 (exposure) uses the exposure apparatus S to expose a reticle circuit pattern onto the wafer. In step 117 (development), the exposed wafer is developed. In step 118 (etching), portions other than the developed resist image are removed. In step 119 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer. According to the manufacturing method of the present embodiment, it is possible to manufacture a higher-quality device than before.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these, A various deformation | transformation and change are possible within the range of the summary.

It is a block diagram which shows schematic structure of the projection exposure apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the procedure which calculates the surface position of the wafer in the exposure station of the projection exposure apparatus shown in FIG. 1, Comprising: (a) is the measurement result of the wafer surface position in the measurement station, and the measurement result of the wafer back surface position. (B) is a graph showing the measurement result of the wafer back surface position at the exposure station, and (c) is the wafer surface at the exposure station calculated from the results of (a) and (b). It is a graph which shows a position. FIG. 2 is a schematic perspective view showing a state of focus / tilt driving of a reticle stage in the projection exposure apparatus shown in FIG. 1. It is a graph which shows the time-dependent change of the exposure image surface on a wafer, and the mode of the correction | amendment. It is a schematic block diagram which shows a mode that the focus correction | amendment of a wafer surface position is performed by driving the one part lens of a projection optical system. It is a procedure figure explaining the correction procedure of the defocus component of the projection lens in the projection exposure apparatus shown in FIG. It is a graph which shows the relationship between the refractive index of the liquid used for the projection exposure apparatus shown in FIG. 1, and temperature. It is sectional drawing which shows schematic structure of the control apparatus which generates a flow in a liquid. It is a flowchart for demonstrating the device manufacturing method by the projection exposure apparatus shown in FIG. 10 is a detailed flowchart of step 104 shown in FIG. 9.

Explanation of symbols

L ... Liquid PL ... Projection optical system S ... Projection exposure apparatus R ... Reticle RST ... Reticle stage (reticle drive unit)
W ... Substrate WST ... Substrate stage 1 ... Light source 2 ... Illumination optical system 5 ... Light source 6 ... Projection mark slit 7 ... Projection lens 10 ... Shape storage unit (storage unit)
13 ... Exposure station 14 ... Measurement stations 15a, 15b ... Reference plate (reference mark)
16 ... Best imaging position measurement system 18 ... Photoelectric sensors 31a to 31c ... Wafer surface position detection system 32 ... Wafer chuck 35 ... Reticle surface position detection system 37 ... Circulation device

Claims (11)

An exposure apparatus that illuminates a reticle using exposure light and projects and exposes a pattern on the reticle onto a substrate via a projection optical system,
An exposure apparatus comprising: a reticle driving unit that moves the reticle in at least one of an optical axis direction and a direction inclined with respect to the optical axis in order to correct a focus position of the substrate with respect to the reticle. apparatus. An exposure apparatus that illuminates a reticle using exposure light and projects and exposes a pattern on the reticle onto a substrate via a projection optical system,
A projection optical system driving unit configured to move at least a part of the projection optical system in an optical axis direction or a direction inclined with respect to the optical axis in order to correct a focus position of the substrate with respect to the reticle; Exposure device.   The exposure apparatus according to claim 2, wherein at least a part of the projection optical system is a projection lens in the projection optical system. An exposure apparatus that illuminates a reticle using exposure light, and projects and exposes a pattern on the reticle onto the substrate via a projection optical system and a liquid filled between the projection optical system and the substrate. ,
An exposure apparatus comprising: a control device that adjusts at least one of temperature and density of the liquid.   The exposure apparatus according to claim 4, further comprising a circulation device that circulates the liquid.   The exposure apparatus according to claim 1, further comprising a storage unit that stores a correction amount of the focus position.   A device manufacturing method comprising: a step of projecting and exposing a pattern onto a substrate by the exposure apparatus according to claim 1; and a step of performing a predetermined process on the substrate subjected to the projection exposure. An exposure method of illuminating a reticle using exposure light and projecting and exposing a pattern on the reticle onto a substrate via a projection optical system,
An exposure method comprising a step of moving at least one of the reticle or the projection optical system in an optical axis direction in order to correct a focus position of the substrate with respect to the reticle. An exposure method for illuminating a reticle using exposure light, and projecting and exposing a pattern on the reticle onto the substrate via a projection optical system and a liquid filled between the projection optical system and the substrate. ,
An exposure method comprising adjusting at least one of temperature and density of the liquid. Measuring the surface shape and the back surface shape of the substrate, and calculating the difference value;
10. The method according to claim 8, further comprising: calculating a surface shape at the time of exposure of the substrate by measuring the back surface shape of the substrate at the time of exposure and reflecting the difference value on the back surface shape. The exposure method as described.   Detecting an image of a substrate-side reference mark formed on the substrate or an equivalent surface thereof on the reticle disposed at a position substantially conjugate with the substrate using the exposure light. The exposure method according to claim 8 or 9.