JPS6216526A - Projection exposure apparatus - Google Patents

Abstract

PURPOSE:To enable the adjustment of focus quickly in a highly precise manner to be performed by a method wherein, when the first object is projected and exposed on the surface of the second object through the intermediary of a projection optical system, a light source is pulse-emitted when the first object reaches the focusing position. CONSTITUTION:When the image of an AF mark 5 is focussed and projected on the surface of a wafer, the image of the AF mark 5 on a slit 13 is clearly image-formed. The maximum quantity of light passing the slit 13 is obtained when the AF mark 5 is completely focused on the surface of the wafer 7 by having the size of the aperture of the slit 13 formed almost same as that of the AF mark 5. The quantity of light passing the slit 13 is detected by a light detector 14, it is converted to an electric signal and inputted to an arithmetic means 15. The stage 8 which retains the wafer 7 is shifted in the direction of optical axis of a projection optical system 6, and the condition of image formation of the AF mark 5 is changed. As a result, the Z-stage where the output signal obtained from the photo detector 14 becomes maximum can be positioned at the focusing position, namely, the position where the circuit pattern on the surface of a reticle 4 is projected and image-formed on the surface of the wafer 7.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a projection exposure apparatus, and in particular to an IC.

2. Projection exposure that allows projection exposure to be carried out automatically and with high precision by projecting and exposing a circuit pattern on the reticle surface 7 on which a fine pattern such as an LSI is formed onto the eight surfaces of the sea urchin through a projection optical system. It is related to the device.

(Conventional technology) Recent semiconductor manufacturing technology is progressing toward higher integration and miniaturization of electronic circuits, and optical exposure methods are also expanding their scope with the development of high-resolution projection optical systems. . In such exposure equipment for semiconductor manufacturing, when transferring and printing the circuit pattern of a mask or reticle onto the eight surfaces of the sea urchin, the resolution line width of the pattern printed on the eight surfaces of the sea urchin is set to l, and the exposure wavelength is In general, when λ is the effective F number of the projection optical system, Fe%CI, is a constant! =C1・λ・Fe. For this reason, various studies have recently been conducted on the use of excimer lasers, which are high-output light sources whose oscillation wavelength is in the far-ultraviolet region, in place of conventional high-pressure mercury lamps in semiconductor manufacturing. It has been pointed out that this excimer laser has high brightness, excellent monochromaticity, and relatively low coherence, and is therefore very effective in projection exposure apparatuses for semiconductor manufacturing.

On the other hand, the resolved line width of the circuit pattern on the wafer surface is greatly influenced by the optical performance of the projection optical system as well as the projection image formation state of the circuit pattern on the wafer surface, that is, the focus state. For example, the depth of focus d of the projection optical system has the following relationship when C2 is a constant: d=C,・λ・Fe''.In other words, the shorter the wavelength, the shallower the depth of focus d becomes.For this reason, the depth of focus d of the projection optical system Precise focus adjustment is always required when performing projection exposure, taking into account focus shifts due to environmental changes such as surrounding air pressure and temperature, and warping of semiconductor substrates such as wafers.

However, in the process of repeatedly projecting and exposing a circuit pattern onto a wafer surface, it is actually very difficult to precisely adjust the focus each time.

(Problems to be Solved by the Invention) An object of the present invention is to provide a projection exposure apparatus that can perform projection exposure of a circuit pattern onto a wafer surface with high precision and automatically.

A further object of the present invention is to provide a projection exposure apparatus that utilizes a pulsed light source, such as an excimer laser, to achieve high throughput.

(Means for solving the problem) When projecting and exposing a first object onto a second object surface via a projection optical system using a pulsed light beam, the second object surface of the first object
A detection means is provided to detect the state of image formation on the object plane,
Pulsed light is emitted using an output signal from the detection means obtained when the second object or the first object is moved in the optical axis direction of the navigation projection optical system.

The features of this shrub invention are described in the Examples.

(Embodiment) FIG. 1 is a schematic diagram of an embodiment of the present invention. In the figure, reference numeral 1 denotes a light source that emits pulsed light and is composed of, for example, an excimer laser. 2 is a mirror that reflects the light beam from the light source 1; 3 is an illumination optical system that converts the light beam into a light beam with a predetermined numerical aperture NA to uniformly illuminate the 4 surfaces of the reticle, which will be described later; 4 is the first object, which is an electron It is a reticle on which a fine pattern such as a circuit is formed, and on a part of its surface there is an autofocus mark (hereinafter referred to as AF mark) 5 for automatic focus detection consisting of a fine blank pattern similar to the circuit pattern. It is provided. Reference numeral 6 denotes a projection optical system that projects the circuit pattern on the 4th surface of the reticle onto the 7th surface of the wafer, which is the second object. This projection is generally a reduced projection of 18, l/1°, etc. The wafer 7 is held on an XY stage 9 for relative positioning of the reticle 4 and two stages 8 that move in the optical axis direction of the projection optical system 6 for focus adjustment. The projection optical system is an exit telecentric system, so that the projection magnification does not change due to movement of the projection surface, that is, the wafer 7 in the optical axis direction. The Unihuff, 2nd stage 8, and XY stage 9 are placed on a surface plate 10, and anti-vibration measures are taken. Reference numeral 11 denotes a half mirror. 12 is an optical system for detecting a focus, and is comprised of, for example, a microscope. 13 is a slit, 14 is a photodetector, and optical system 12. Slit 13. The photodetector 14 constitutes a part of the detection means. 15 is a processing means that generates a trigger pulse from an internal trigger pulse generation circuit in response to a signal from the photodetector 14 to generate the light I1.
1 to emit pulsed light.

In this shrub embodiment, an alignment optical system for relative positioning of the reticle 4 and the wafer 7 is provided, but it is omitted in the figure for the sake of simplicity.

In this embodiment, the AF mark 5 provided on a part of the reticle 4 surface together with the circuit pattern on the reticle 4 surface is projected onto the UniHaf surface by the projection optical system 6. wafer 7
The image of the AF mark 5 on the surface is reflected and formed on the primary imaging surface 16 via the projection optical system 6 and half mirror 11, and then re-imaged near the slit 13 by the focus detection optical system 12. are doing. The slit 13 and the reticle 4 are arranged at optically conjugate positions. Therefore, when the image of the AF mark 5 is focused and projected onto the surface of the wafer 7, the slit 13
The image of the upper AF mark 5 is clearly formed.

By setting the opening size of the slit 13 to be approximately the same as the size of the AF mark 5, the amount of light passing through the slit 13 is maximized when the AF mark 5 is completely focused on the Unihaf surface. . In other cases, the image of the AF mark 5 on the slit 13 surface will be blurred, so the slit 1
The amount of light passing through 3 decreases. The amount of light passing through the slit 13 is detected by a photodetector 14, converted into an electrical signal, and inputted to the calculation means 15. At this time, in this embodiment, the two stages 8 holding the wafer 7 are moved in the direction of the optical axis of the projection optical system 6 to adversely change the imaging condition of the AF mark 5 projected onto the Uniform surface. As a result, the output signal obtained from the photodetector 14 becomes as shown in FIG. 2, when the horizontal axis represents the amount of movement of the two stages 8. The position aF of the second stage where the output signal obtained from the photodetector Wk14 is maximum is the focus position, that is, the position where the circuit pattern on the 4th surface of the reticle is projected and imaged best on the wafer 7th surface. In the embodiment, focus adjustment is performed by detecting the position F at this time. Then, the calculation means 15 stores the output signal from the photodetector 14 at position F or position rtF, moves the Z stage 8 again, and when the wafer 7 reaches position F, a trigger pulse is generated from the trigger pulse generation circuit. is generated to cause the light source 1 to emit pulsed light. As a result, the circuit pattern on the 4th surface of the reticle is projected and exposed onto the 7th surface of the wafer.

In this embodiment, the optical system 12 is not used and the slit 13 is
may be arranged directly at the position of the primary imaging plane 16.

Further, in this embodiment, instead of the wafer 7, which is the second object, the reticle 4, which is the first object, may be moved in the optical axis direction of the projection optical system 6.

Also, number 1. The imaging state may be changed by fixing the second object and moving some of the optical members constituting the projection optical system 6 in the optical axis direction.

In this embodiment, the depth of focus and the amount of variation in focus position of the projection optical system 6 are each about several micrometers, so a driving stroke of the two stages 8 of about 20 micrometers is sufficient. Therefore, even if the two stages are repeatedly moved several times in order to improve the focus detection accuracy, the process can be completed in a short time, so that focus detection can be performed with high precision and quickly. The two stages may be moved continuously or may be moved in stages.
If an excimer laser is used as the light source in this embodiment, the pulse width of the excimer laser is generally lO~20n.
Since it is very short, on the order of seconds, even if exposure is performed without stopping the stage within the light emission time, the amount of movement of the two stages is small and the out-of-focus can be ignored. Therefore, if an excimer laser is used, high throughput is possible.

In this embodiment, if there is a time delay between sending a focusing signal from the processing means to the light source and causing the light source to emit pulses due to electrical circuit reasons, a correction circuit that takes into account that time is installed in advance to cause the light source to emit pulses. Preferably, it is configured to advance the time. In this embodiment, any method may be used to detect the in-focus position. For example, the center of gravity position of the light intensity distribution may be used as the evaluation quantity, or the differential value of the change in light intensity with respect to the displacement of the two stages may be used as the evaluation quantity. You can choose the focus position F where the differential value becomes 0. If you use the differential value, you only need to move the two stages one way from the reference position to position glF. Focus detection becomes possible faster.

In this embodiment, a plurality of detecting means having AP marks may be provided within the screen of the projection optical system, which allows for more accurate focus detection taking into account the brightness and inclination of the wafer.

Furthermore, instead of arranging the detection means between the reticle and the projection optical system, it may be arranged between the projection optical system and the wafer.

In this embodiment, the object of the present invention can also be achieved by using a combination of a conventional continuous wave light source such as a mercury lamp and a high-speed scissor instead of a light source that emits pulsed light.

Furthermore, when the projection optical system 6 is an incident telecentric system, focusing may be performed by fixing the wafer 7 and moving the reticle 4 up and down. In this case, the depth of focus near the reticle 4 increases by the square of the reduction rate of the projection optical system 6 (for example, 25 times for a 115 projection system) compared to near the wafer 7, so more accurate focusing can be achieved. .

(Effects of the Invention) According to the present invention, when projecting and exposing a first object onto a second object surface via a projection optical system, the light source emits pulse light when the in-focus position is reached, thereby achieving high precision and A projection exposure apparatus with rapid focus adjustment can be achieved.

[Brief explanation of the drawing]

7jS1 is a schematic diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of an output signal from a photodetector when focus detection is performed in the present invention. In the figure, 1 is a light source, 3 is an illumination optical system, 4 is a reticle as a first object, 5 is an AF mark, 6 is a projection optical system, and 7 is a second object.
A wafer as an object, 8 a Z stage, 11 a half mirror, 112 an optical system for focus detection, 13 a slit, 1
4 is a photodetector, and 15 is a processing means.

Claims (3)

[Claims] (1) To detect the imaging state of the first object on the second object surface when projecting and exposing the first object onto the second object surface via the projection optical system using a pulsed light flux. A detection means is provided, and a pulse is emitted using an output signal from the detection means obtained when the second object or the first object is moved in the optical axis direction of the projection optical system. Projection exposure equipment. (2) The projection according to claim 1, wherein the detection means detects the image formation state of the first object on the second object plane via the projection optical system. Exposure equipment. (3) The projection exposure apparatus according to claim 2, wherein the second object or the first object is continuously moved back and forth in the optical axis direction of the projection optical system.