JPH09283423A - Aligner and exposing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with a change of a projection optical system by a method wherein a forces detection light is radiated to a body via a projection optical system, a focus state is detected according to a generation state of an astigmatism of a focus detection light and a focus state is controlled. SOLUTION: A focus detection light 14 incident on an exposure lens 8 is condensed on a position which is slid slightly horizontally from a position on a wafer 11 in which a pattern image on a reticle 9 is formed by an irradiation light 13. For example, when a wafer stage 12 moves rightweardly, the focus detection light 14 is condensed more leftwardly than an image formation position by an irradiation light 13. When a face of the wafer 11 is not in an image formation position by the irradiation light 13, namely out of focus, a wafer stage 12 is driven to a Z direction (to a vertical direction) of an optical axis of an exposure lens 8 to be focused, Further, even when an angle of the face of wafer 11 is judge to be slid from a specific angle by the focus detection light 14, the wafer 11 is tilt-driven by the wafer stage 12 in a same manner as correction in a vertical direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus and an exposure method, and in particular, it is suitable for an apparatus for precisely focusing an object such as an exposure apparatus for manufacturing a semiconductor element.

[0002]

2. Description of the Related Art In recent years, semiconductor integrated circuits are becoming more and more miniaturized, but one of the most important steps in the manufacturing process is to transfer a circuit pattern formed on a mask onto a wafer. It is a photo process. An apparatus used in the photo process is called a semiconductor exposure apparatus, and an optical exposure method is currently used as a main force.

The optical exposure method includes a contact method in which a mask and a wafer are brought into contact with each other to print, a proximity exposure method in which a mask and a wafer are separated by a gap of several tens of μm, and a shadow is printed.
There is a step & repeat or a scan & repeat method in which a pattern exposure exposure transfer and a stepwise feeding process are repeated using a high resolution lens. Among them, the step & repeat method or the scan & repeat method is widely used as a powerful method of the present and the next generation.

In the alignment in the focus direction in the optical exposure system, a method is used in which the distance from the reference to the wafer is measured at a place different from the wafer baking position and the position is set at the wafer baking position based on the measured distance. . This system does not require a projection optical system to detect the focus, so it should be called an off-axis system. At that time, the measurement method uses an air sensor method in which an air flow is jetted to the wafer to measure the back pressure of the air to detect the distance to the wafer, a method to measure the electrical capacitance between the wafer and the detection device, and ultrasonic measurement. There are a distance method, a method of obliquely projecting a light beam on the wafer surface, and a method of detecting a positional deviation of reflected light.

[0005]

However, in the case of the off-axis method, the position of the wafer in the optical axis direction with respect to the apparatus can be managed in principle, but the wafer surface is located at the position where the mask image is truly in focus. It is not possible to detect whether or not it is located. This is because the focus position of the projection optical system is not constant with respect to the reference but moves due to heat accumulation of illumination light during wafer baking and fluctuations in the ambient environmental temperature. When the projection optical system itself changes due to these external factors, only a defocused image is actually formed even if the wafer is set at an appropriate position by the off-axis method.

Therefore, in order to cope with such changes in the projection optical system, there is a demand for a method capable of focusing the wafer surface through the projection optical system at the printing position. From this point of view, for example, the air sensor method has angular characteristics of the object to be measured, and if the surface of the object has irregularities, the measured values vary. Therefore, if the surface of the wafer has irregularities of about several microns, accurate focusing may not be possible, and it is excluded from the candidates for the precise focusing method.

[0007] Further, as the size of the circuit further increases in the future, the area for one chip will increase, so that it is said that the scan exposure method for exposing while scanning the reticle and the wafer will become the mainstream, instead of the conventional step & repeat method. ing. In that case, the entire surface of the wafer must be focused at high speed.

[0008]

In order to solve the above problems, the present invention is characterized in that the astigmatism method is used for focus detection and the focus position of the printing position is detected through the projection optical system. In addition, this method not only looks at the resist coated surface of the wafer as when using an air sensor, but it is also possible to focus on the circuit pattern itself underneath, so either surface can be focused during exposure. It also has the advantage that you can choose.

Particularly, in the exposure apparatus of the present invention, in the exposure apparatus which transfers the image of the first object onto the second object by using the projection optical system, the focus detection light is transmitted through the projection optical system to the second focus detection light.
It is characterized in that the focused state is detected by irradiating the object and the astigmatism of the focused detection light is generated to control the focused state.

Further, in the exposure method of the present invention, in the exposure method in which the image of the first object is exposed and transferred onto the second object by using the projection optical system, the focus detection light is transmitted through the projection optical system. Two
It is characterized in that the focused state is detected by irradiating the object and the astigmatism of the focused detection light is generated to control the focused state.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of the present invention. In the figure, a configuration diagram of a semiconductor exposure apparatus of a scan and repeat method equipped with a focus detection device is shown.
It forms the basic form of the present invention. In the figure, 1 is a laser diode, 2 is a lens, and 3 and 4 are dichroic hardware.
Fumira-5 is a condenser lens, 6 is a cylindrical lens, 7 is a two-dimensional CCD, 8 is an exposure lens (projection optical system), 9 is a reticle (first object), 10 is a reticle stage, 11 is a wafer (first). 2 objects), 12 is a wafer station
In the figure, 13 indicated by a chain line indicates illumination light (exposure light), and 14 indicates focus detection light.

In the scan and repeat exposure,
There is a base pattern transferred by exposure on the reticle 9, and the base pattern is illuminated with illumination light 13. With respect to this fixed illumination light, the reticle stage 10 moves in the X direction shown by the arrow and all the patterns on the reticle 9 are illuminated. The illuminated light passes through the exposure lens 8 to reduce the pattern on the wafer 11 and print it. At this time, the wafer stage 12 on which the wafer 11 is placed also moves in the X direction indicated by the arrow and in the Y direction perpendicular to the plane of the drawing, so that the wafer 1
1 The pattern is baked on the entire surface.

On the other hand, the focus detection light 14 passes from the laser diode 1 through the lens 2 to the dichroic hammilla-3.
Is reflected by and is merged with the exposure light flux 13. After merging, the focus detection light 14 passes through another dichroic hammilla-4 and enters the exposure lens 8. The dichroic hammillas-3 and 4 have wavelength selectivity, work only as a hammilla for the wavelength of the focus detection light, and do not affect the light of the wavelength of the illumination light 13 for exposure. It only lets through.

After the focus detection light 14 that has entered the exposure lens 8 exits the exposure lens 8, the illumination light 13 causes the focus detection light 14 to move slightly laterally beyond the position on the wafer 11 where the pattern on the reticle 9 is imaged. It is focused on the place where it is deviated. The position where the light is focused is the same as the position where the pattern is imaged and the optical axis direction of the exposure lens 8, but the position where the light is focused is set slightly before the position where the exposure is performed by scanning. To be done.
For example, when the wafer stage 12 is moving to the right as shown in FIG. 1A, the focus detection light 14 is focused on the left side of the imaging position of the illumination light 13. When the surface of the wafer 11 is not in the image forming position by the illumination light 13, that is, when it is out of focus, the wafer stage 12 must be driven in the Z direction (vertical direction) which is the optical axis of the exposure lens 8 to focus. . If the focus position of the focus detection light 14 is intentionally shifted in the lateral direction, the wafer 1 can be exposed before the exposure light 13 is exposed.
Since the position of 1 in the vertical direction can be detected, the feedback time required from detection to signal processing and driving can be taken, and focused imaging control can be performed.

When it is determined by the focus detection light 14 that the angle of the surface of the wafer 11 is deviated from a predetermined angle,
Wafer stage 12 performs wafer 1 as well as vertical correction.
1 needs to be tilt-driven. Even in this case, if the focus position of the focus detection light 14 is placed on the side of the exposure position in advance and pre-detected, the feedback time required for tilt correction / driving can be taken and good tilt control can be performed. It can be performed.

When the focus detection light 14 is made incident on the wafer 11, it is possible to select which part of the wafer 11 the light collection point is to be collected. FIG. 1A shows the case where the focus position is aligned with the resist coating surface of the wafer 11, and FIG. 1B is the case where it is aligned with the substrate under the resist layer. But you can choose. This is because the fact that the resist and the substrate surface have different reflectivities of light is used, and it is possible to discriminate the difference in light amount with a two-dimensional CCD described later.

The focus detection light 14 which is incident on the wafer 11 and reflected by the wafer 11 is directly reversed from the incident light path from the laser diode 1 when the wafer 11 is coincident with the predetermined angle and is in focus. Then, the light enters the detection optical system after being reflected by the dichroic mirror-4. In the detection optical system, after passing through the condenser lens 5 and the cylindrical lens 6, it is incident on the two-dimensional CCD 7 and a spot image is formed. In this case, in the reference state, setting is made in advance so that a circular spot is connected to the center position of the two-dimensional CCD 7. FIG. 1 shows the shape of a spot on a two-dimensional CCD, where the vertical size of the spot shape is d1 and the horizontal size is d2. Reference state is d
When 1 = d2 and this condition is satisfied, it is determined to be in focus. The position of the focused spot corresponds to the angular deviation of the wafer. The fact that the position of the spot is at the center of the two-dimensional CCD 7 indicates that the surface of the wafer 11 coincides with a predetermined angle.

2 and 3 show the case where defocusing is performed. In FIG. 2, the focusing position of the focus detection light 14 is on the wafer 11
Above, that is, in the rear pin state, and the wafer 1
This is the case where the angle 1 corresponds to the predetermined angle. In this case, the return light 1 of the focus detection light 14 reflected by the wafer 11
Since 4'returns the optical path like a dotted line, a laterally long spot C is formed on the two-dimensional CCD 7 by the effect of the cylindrical lens 6.
Connect to the center of CD7. In this case, d2> d1.

FIG. 3 shows the case where the focus position of the focus detection light 14 is below the wafer 11, that is, in the front focus state, and the angle of the wafer 11 matches a predetermined angle.
In this case, the return light 14 ′ of the focus detection light 14 reflected by the wafer 11 returns along the optical path shown by the dotted line, and the cylindrical lens 6 produces a vertically long spot on the two-dimensional CCD 7.
Connect to the center of 7. In this case, d2 <d1.

As described above, in the astigmatism method using the cylindrical lens, by comparing and detecting the size of the major axis and the minor axis of the spot connected on the CCD, if d1 = d2, the focus is achieved.
If d2> d1 as shown in FIG.
If 2 <d1, the front focus state and the focus state can be easily discriminated.

Although the wafer 11 is in focus in FIG. 4,
This is the case where they are displaced from a predetermined angle. An enlarged view of the vicinity of the focal point of the focus detection light 14 on the wafer 11 is shown in FIG.
(A). In this case, the return light 14 ′ is re-incident on the exposure lens 8 with a slight shift to the right according to the inclination of the wafer 11. Therefore, the spot light deviates slightly downward on the two-dimensional CCD 7 as compared with the case where the surface of the wafer 11 is at a predetermined angle, and the center of gravity of the spot light is formed at a position away from the central position of the two-dimensional CCD 7. Since the angular shift is two-dimensional, it appears as a vertical shift dz and a horizontal shift dy in the arrow view of the two-dimensional CCD 7 shown in FIG. However, even if the wafer 11 is deviated in angle, the shape of the spot light is circular and d1 = d2. Therefore, it is possible to determine that it is in focus.

The angle of the surface of the wafer 11 and the positional relationship from the center of the two-dimensional CCD to the center of gravity of the spot light have a one-to-one correspondence. Therefore, if the device side is calibrated by checking the correspondence between a flat plate whose angle is already known and the spot light on the CCD in advance, it is possible to discriminate the focus state and the angle even for a wafer whose surface angle is unknown. It is possible to simultaneously measure

FIG. 5 is a schematic view of the essential portions of Embodiment 2 of the present invention. The figure shows a semiconductor exposure apparatus. In the figure, the same members as those in the first embodiment are given the same numbers. In the figure, 15 is a half mirror and 16 is a case. In FIG. 1, the focus detection light is introduced into the illumination light flux 13 and the return light 1
The separation of 4'was carried out by the dichroic mirrors-3 and 4, but in the present embodiment, the separation of the returning light 14 'is carried out by a half mirror arranged at a position different from that of the first embodiment. . That is, the present embodiment is characterized in that the incident light and the return light are separated immediately after the light is emitted from the laser diode 1. Since the illumination light 13 and the light flux do not overlap in the vicinity of the separation position, the object can be achieved by arranging the half mirror 15 smaller than that in the first embodiment.
Furthermore, in this arrangement, the laser diode 1, the lens 2, and the
Since the positions of the fumilla-15 and the focus detection section (the condenser lens 5, the cylindrical lens 6, and the two-dimensional CCD 7) are close to each other, by enclosing these parts with the case 16, all the necessary focus detection is performed. It is possible to compactly combine units including parts.

[0024]

As described above, according to the present invention, the astigmatism method and the two-dimensional image element such as the two-dimensional CCD are combined for the function of detecting the in-focus state of the semiconductor exposure apparatus through the projection optical system. Thus, it becomes possible to detect the in-focus state of the wafer with respect to the projection optical system, and by performing drive correction of the wafer based on the detected value, it becomes possible to perform exposure in a focused state. Since the detected value can detect the in-focus state of the wafer as well as the angular deviation at the same time, the drive correction of the wafer can be performed not only in the optical axis direction of the projection optical system but also in the tilt correction which is the tilt.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an exposure apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part showing a detection state of a rear pin in a defocus state according to the first embodiment of the present invention.

FIG. 3 is a schematic view of a main part showing a detection state of a front pin in a defocus state according to the first embodiment of the present invention.

FIG. 4 is a schematic view of a main part showing a detection state when the wafer surface is tilted according to the first embodiment of the present invention.

FIG. 5 is a schematic view of a main part of an exposure apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 1 laser diode 2 lens 3 dichroic hammilla 4 dichroic hammilla 5 condenser lens 6 cylindrical lens 7 two-dimensional CCD 8 exposure lens 9 reticle 10 reticle stage 11 wafer 12 wafer stage 13 illumination light 14 Focus detection light 15 Harm mirror 16 cases

Claims (13)

[Claims] 1. An exposure apparatus for exposing and transferring an image of a first object onto a second object using a projection optical system, wherein focus detection light is radiated onto the second object via the projection optical system, The in-focus state is detected by the astigmatism generation state of the in-focus detection light,
An exposure apparatus which controls a focused state. 2. The exposure apparatus according to claim 1, wherein the focus detection light has a common optical path with the exposure light when the image of the first object is transferred onto the second object by exposure. 3. The exposure apparatus according to claim 2, wherein the in-focus state is detected by a two-dimensional image detection element. 4. The exposure apparatus according to claim 4, wherein an angular deviation of the second object is detected based on a position of the focus detection light formed on the two-dimensional image element. 5. The exposure apparatus according to claim 4, wherein the exposure apparatus employs a scan-and-repeat exposure method. 6. The focus detection light is condensed at a position deviated from the image formation position of the illumination light for exposure, and the position of the second object is controlled based on the detection value by the focus detection light. The exposure apparatus according to claim 5, wherein: 7. An exposure method for exposing and transferring an image of a first object onto a second object using a projection optical system, wherein focus detection light is radiated onto the second object via the projection optical system, The in-focus state is detected by the astigmatism generation state of the in-focus detection light,
An exposure method characterized by controlling a focused state. 8. The exposure method according to claim 7, wherein the focus detection light has a common optical path with the exposure light when the image of the first object is transferred onto the second object by exposure. 9. The exposure method according to claim 8, wherein a position where the focus detection light is detected on the second object can be selected by a converging position of the focus detection light. 10. The exposure method according to claim 9, wherein the in-focus state is detected by a two-dimensional image detection element. 11. The exposure method according to claim 10, wherein an angular deviation of the second object is detected by a position of the focus detection light formed on the two-dimensional image element. 12. The scan and repeater is the exposure apparatus.
The exposure method according to claim 11, wherein 13. The focus detection light is condensed at a position deviated from an image formation position of illumination light for exposure, and the position of the second object is controlled based on a detection value by the focus detection light. 13. The exposure method according to claim 12, wherein: