JP2821795B2 - Semiconductor exposure equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an exposure apparatus used for manufacturing semiconductor elements such as ICs and LSIs, and more particularly, to a repetition exposure apparatus (stepper) and its overlaying performance (stepper). The present invention relates to a temperature control mechanism for improving alignment.

[Prior Art] In recent years, semiconductor devices (elements) have been increasingly miniaturized and highly integrated. D-RAM (Dynamic
(Random access memory) has already entered the submicron area at the product level, and at the research level, patterning of less than half micron (0.5 μm) is being discussed.

An exposure apparatus called a stepper developed in the era of 256K DRAM is the main model in the production of 1M to 4MDRAM.

For miniaturization, the overlay accuracy is as important as the resolution, and the required accuracy is about 1/3 to 1/5 of the resolution.

The overlay accuracy can be largely separated into two factors. 1
One is an alignment component, and the other is a magnification and distortion component.

TTL alignment systems are the mainstream in steppers with off-axis alignment systems. Stepper alignment systems are classified into the following three types. The first is the TTL ON AXIS system, which has the feature that the alignment light is the same as the exposure light and the reticle and wafer can be observed simultaneously. The second is a TTL NON AXIS system, in which the alignment light is different from the exposure light but the projection lens light passes. Simultaneous observation of the reticle and wafer is difficult. The third is an off-axis system in which an alignment microscope is arranged completely separate from the projection lens. Of these, the off-axis stepper has many indirect error factors in the relative positioning of the reticle and wafer, and the time and moving distance from alignment to exposure are long, so the error component changes over time and high overlay accuracy is high. I can't get it.

On the other hand, the resolution is improved by increasing the numerical aperture (NA) of the projection lens while fixing the exposure wavelength to the g-line (436 nm), based on the Rayleigh formula {Re = k × (λ ÷ NA)}. Has been planned. But this is also Rayleigh's formula ｛DOF = ±
As is clear from λ / NA ²深度, the depth of focus decreases with an increase in NA. On the other hand, the design and manufacture of the projection lens are limited, and the exposure wavelength must be shortened for miniaturization. At present, an i-line (365 nm) stepper has been put to practical use, and an excimer stepper using a KrF excimer laser (248 nm) as a light source has been developed.

However, the glass material that transmits the light of the KrF excimer laser (248 nm) is slightly limited to quartz and fluorite, and it is very difficult in design to correct chromatic aberration for light other than the exposure wavelength.

4 (a) and 4 (b) show the axial chromatic aberration characteristics of the g-line lens and the single glass lens for excimer quartz. The horizontal axis represents wavelength, and the vertical axis represents axial chromatic aberration. In the case of a g-line lens, it is usually possible to design a combination of glass materials so that the characteristic curve contacts at a zero point at a target wavelength [201 in FIG. 4 (a)]. On the other hand, in the excimer lens, since there is no degree of freedom of the glass material, it becomes a substantially straight line crossing at one point of the target wavelength [20 in FIG. 4 (b)].
2]. For example, H as alignment light for the g-line lens
When the eNe laser (633 nm) is selected, the axial chromatic aberration is about tens of μm, but even if an Ar laser (500 nm) is selected as the non-exposure alignment light for the excimer lens, the axial chromatic aberration is It will reach the order. From this reality, it is difficult to realize a non-exposure alignment system in an excimer lens (stepper) unless the axial chromatic aberration characteristic curve can be improved.

Based on this recognition, an improvement plan for the above-mentioned disadvantage of the off-axis type alignment system has been proposed in Japanese Patent Application No. 63-115534 filed by the present applicant.

On the other hand, the aforementioned magnification and distortion components are mainly related to the performance of the projection lens, and the temporal change is mainly caused by the temporal change of the environment in which the projection lens is placed.

This is because the refractive index of air changes due to changes in atmospheric pressure and humidity of air, the refractive index of lens glass material changes due to temperature changes, and the air gap of the lens changes due to thermal expansion of the lens barrel. ing. It is also well known that this causes a change in the focal position of the projection lens.

FIG. 3 shows the configuration of a conventional stepper. Reference numeral 1 denotes a photo original (hereinafter referred to as a reticle or mask), and reference numeral 2 denotes a semiconductor substrate (hereinafter referred to as a wafer). When the light beam 39 emitted from the exposure light source 30 illuminates the reticle 1 through the illumination optical system 3, the projection lens 4
Thus, the pattern on the reticle can be transferred to the photosensitive layer on the wafer. In the illumination optical system, the light beam directed upward by the mirror 31 reaches the masking image plane via the fly-eye lens 33, the condenser lenses 34a and 34b, and the mirror 35. 36 is a masking blade, and 37a and 37b are masking imaging lenses.

The reticle 1 is supported by a reticle stage 11 for holding and moving the reticle. The wafer 2 is exposed while being vacuum-sucked by the wafer chuck 21. The wafer chuck can be moved in each axis direction by the wafer stage 5. The wafer stage 5 is supported on a stage base 50. The wafer stage 5 is formed by leveling by, for example, three piezoelectric elements (piezo elements) 53 on a Y stage 51 and an X stage 52 according to the prior art, and a fine movement stage 54 of Z.
However, a rotary (θ) fine movement stage 55 and a vertical (Z) fine movement stage 56 are further formed thereon. Wafer chuck 21
Is mounted on the Z fine movement stage 56. Leveling and Z
On the fine movement stage 54, mirrors 57 serving as references for the position coordinates of the wafer stage system are mounted in the X and Y directions, respectively. The mirror 57 reflects the beam from the laser interferometer 58 to You can know the location and the mileage. Reference numeral 59 denotes a receiver that converts an optical signal into an electric signal.

Above the reticle 1, a reticle optical system 6 is arranged. The reticle optical system is a binocular optical system having two objective lens systems 60.
By observing at 1, the amount of displacement of the reticle can be detected.

An off-axis microscope 7 is arranged above the wafer stage 5 and adjacent to the projection lens 4. The off-axis microscope 7 is a monocular microscope that handles non-exposure light (white light), and its main role is to detect the relative position between the internal reference mark 70 and the alignment mark on the wafer. The objective lens 71 and the relay lens 72 magnify and project the wafer pattern and project it on an image forming plane 74. The erector lenses 77 and 78 function as a low-magnification erector lens when both are inserted on the optical axis, and as a high-magnification erector when the 78 is retracted, and project the aerial image of the imaging surface 74 onto the light receiving surface of the CCD 79. Reference numeral 25 denotes an optical fiber for guiding light from a light source (not shown).
The light becomes illumination light for the wafer via the beam splitter 73. Similarly, 27 is an optical fiber for guiding light from a light source (not shown),
The reference mark 70 is illuminated via the illumination lens 28. The beam splitter 75 includes a pattern surface of the reference mark 70 and an image forming surface 74.
Are arranged so as to have the same optical path length, so that the reference marks are also projected and imaged on the light receiving surface of the CCD 79 by the eleectors 77 and 78.

In the chamber 8, air whose temperature has been adjusted by the cooler 81 a and the reheater 82 a in the machine room 80 is supplied to the blower 8.
6a is supplied into the chamber 8 through one or a plurality of cleaning filters 84a, thereby making it possible to keep the environment temperature where the apparatus is placed at a constant level and keep the air clean. The control circuit 9 is used to control each of the above-described components. The CPU 91 issues a command to each element according to the determined sequence software, and determines the next procedure by judging data from each element. The arithmetic circuit 92 is mainly used for arithmetic processing that requires high speed and high precision, such as calculating the relative position between the reticle and the wafer from the stage coordinates and the detection result of the off-axis microscope. Used to store operation data.
In the chamber 8, a reticle library 100 and a wafer carrier elevator 110, which are peripheral devices, are disposed adjacent to the stepper main body. Necessary reticles and wafers are transferred to the stepper main body by the reticle transfer device 120 and the wafer transfer device 130. Conveyed. The above is the schematic configuration of the conventional stepper.

[Problems to be Solved by the Invention] In the stepper body, a heat source such as an actuator for driving a wafer stage or a reticle stage or an exposure light source is incorporated in each part. Even if the stepper body is inserted, spatial temperature unevenness cannot be avoided. The air at a constant temperature supplied from the clean filter 84a is affected by heat sources scattered as it goes downstream, and fluctuations due to convection occur as the temperature rises, and its temperature stability also deteriorates.

23 ° C at the outlet of the clean filter
Air temperature controlled to ± 0.03 ° C deteriorated to 24 ° C ± 0.5 ° C downstream. In addition, dust generated upstream of the air accumulates downstream and deteriorates the cleanliness of the space.

However, as described in the conventional example, in the off-axis alignment system, the time from alignment to exposure is long, and the movement distance from alignment to exposure is long. Was not obtained. This change with time of the error component is largely caused by the temperature fluctuation of the environment. For example, in FIG. 3, the objective lens 71 of the off-axis microscope 7
The value of the distance L between the optical axis of the projection lens 4 and the center of the optical axis of the projection lens 4 may be extended by thermal expansion of a member that fixes them, or a fine movement stage that fixes a reference mirror 57 serving as a distance measurement reference of the wafer stage 5 An error component such as a change in the position of the reference mirror 57 due to the thermal expansion of 54 is included. The error amount due to thermal expansion is 2 ppm / ° C when the material of the target member is a low expansion alloy net,
In the case of alumina ceramics, it is 7 ppm / ° C. When the length of these members is 200 mm, the expansion amount is
0.4 μm / ° C. and 1.4 μm / ° C., which cannot be ignored for the required alignment accuracy.

Regarding the performance of the projection lens 4, for example, the change in the refractive index with respect to the temperature of the quartz glass material is 15.3 × 10 ⁻⁶ / ° C., and this value varies depending on the individual properties of the projection lens.
The change in the focal position corresponds to 4 to 8 μm / ° C., and the magnification and the distortion also change greatly.

As described above, the conventional air-conditioning system using a chamber cannot provide stable overlay accuracy, but rather has a disadvantage of causing deterioration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described drawbacks of the related art, and has as its object to provide an air-conditioning system in which the accuracy of an exposure apparatus is prevented from deteriorating due to temperature fluctuation.

[Means and Actions for Solving the Problems] In order to achieve the above object, a semiconductor exposure apparatus according to the present invention includes a reticle stage, a projection lens system, a wafer stage, a reticle and a wafer positioned in a chamber. A microscope for detection, a reticle library for storing a plurality of reticles, and a wafer transfer system for transferring the introduced wafer to the wafer stage, and the inside of the chamber is separated by first, second, and second separation walls. And the microscope and at least one of the wafer stage and the reticle stage are arranged in the first space, and the projection lens system is arranged in the second space. At least one of the reticle library and the wafer transfer system is disposed in the space, and each of the spaces is communicated with an air conditioner provided outside the chamber. A first clean filter is provided at a place where air is supplied, and a second clean filter is provided at a place where air is supplied above the third space, and a place where the air is discharged from the first space is provided more than the microscope. A position where the air in the third space is discharged is located below the reticle library or the wafer transfer system;
The air conditioning means supplies air to the first space and the third space independently from the upper space and discharges the air from the lower space.

Embodiment FIG. 1 shows an embodiment of the present invention. In FIG. 1, 8 is a chamber, 80 is a machine room for controlling the temperature of air, 81a, 81b, 81c are coolers disposed in the machine room 80, 82a, 82b, 82c are reheat heaters, 86a , 86b, 86c are blowers,
84a, 84b, 84c, 84d are air purification filters, 85a, 85b, 85c are temperature sensors, 87a, 87b, 87c are separation walls for separating the space in the chamber 8, and 88a, 88b, 88c are temperature controlled in the machine room 80. Supply ducts 89a, 89b, 89c, for supplying the supplied air into the chamber 8.
A return duct 89d returns the air in the chamber 8 to the machine room 80.

In this configuration, the internal space of the chamber 8 is divided into the separation walls 87a,
The spaces A and B, which are the first spaces, that is, the space A in which the reticle (or mask) stage 11, the reticle optical system 6, the illumination optical system 3, and the exposure light source 30 are arranged, and the wafer stage 5 B in which the optical system 7 and the off-axis microscope 7 are arranged, the second space C in which the projection lens 4 is arranged, the reticle library 100, the reticle transport system 120, the wafer carrier elevator 110 and the wafer transport system 130 are arranged. Are separated into third spaces D, respectively.

In space A, a cooler arranged in the machine room
The air cooled by 81a is adjusted to a predetermined temperature by the reheater 82a, and the air is supplied to the space A by the blower 86a through the supply duct 88a and the clean filter 84a. Then, the air in the space A is returned to the machine room by the return duct 89a, so that the temperature-controlled clean air is constantly supplied into the space A. The air supplied to the space A is
The temperature controller 85 controls the cooling power of the cooler 81a and the reheater of the reheater 82a so that the temperature is measured by the temperature sensor 85a and the air temperature is maintained at a predetermined temperature. In the space B and the space C, as in the case of the space A, clean air whose temperature is independently controlled is always supplied. Further, the temperature sensor 85b measures the temperature of the clean air supplied to the space B, and the temperature sensor 85c measures the temperature of the clean air supplied to the space C, and these air temperatures are respectively maintained at predetermined temperatures. So temperature controller
The temperature of the clean air supplied by 83 is controlled.
In the space D, the air supplied to the space A is branched before the clean filter 84a, and the clean air whose temperature is adjusted is supplied to the space D via the clean filter 84a. Then, the air in the space D is returned to the machine room 80 by the return duct 89d.

By configuring the air-conditioning chamber in this manner, the space in the chamber is kept clean, the influence of the heat sources scattered in each part of the stepper is minimized, and the space in each of the space A, the space B, and the space C is reduced. Target temperature unevenness is reduced,
In addition, the temporal temperature stability is improved, and the temperature of a predetermined space can be controlled with high accuracy. Further, if a heat insulating material is used for the separation walls 87a, 87b, 87c that separate the spaces, the transfer of heat between the spaces can be suppressed, and the temperature of the predetermined space can be controlled with higher accuracy. .

Another construction of the machine room is shown in FIG. In this example,
The coolers 81b and 81c shown in FIG. 1 are replaced with one cooler 81e, and the temperatures of the space B and the space C are controlled independently by the reheaters 82b and 82c. In this way, the volume of the machine room can be reduced. The configuration of the machine room can be variously changed according to the configuration of the exposure apparatus, temperature conditions, and the like.

[Effects of the Invention] As described above, the spaces in the chamber where high-precision temperature control is required are individually separated, and the air supplied to the individually separated first to third spaces is separated. By controlling the temperature independently from the other spaces in the chamber, the space inside the chamber is kept cleaner and the effect of heat sources scattered in each part of the stepper is minimized, resulting in high-precision temperature control Can be reduced in spatial temperature unevenness in a required space, and temporal temperature stability can be increased, so that the temperature of a predetermined space can be controlled with high accuracy.

Further, according to the present invention, it is possible to control each separated space in the chamber to a different set temperature,
The temperature of the space other than the separation space surrounding the projection lens can be made the same as the temperature of the space in which the chamber and the machine room are placed, and the energy consumed for temperature control can be reduced. This is because the performance of the projection lens can only be guaranteed at the ambient temperature at which the projection lens is manufactured.

Further, according to the present invention, the third space, which is a main dust source, is separated from the first and second spaces, and is supplied with air from the upper part of the space to discharge air from the lower part of the space, thereby cleaning the space. Properties can be further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a block diagram of another embodiment of the chamber machine room according to the present invention, FIG. 3 is a block diagram of a conventional exposure apparatus, FIG. 7A and 7B are explanatory diagrams of characteristic curves of a g-line lens and an excimer lens. 1: reticle, 2: wafer, 3: illumination optics, 4: projection lens, 5: wafer stage, 6: reticle microscope, 7: off-axis microscope, 8: chamber, 80: machine room.

Claims (5)

(57) [Claims] 1. A reticle stage, a projection lens system, a wafer stage, a microscope for detecting alignment between a reticle and a wafer, and a reticle library for accommodating a plurality of reticles are introduced into a chamber. A wafer transfer system for transferring a wafer to the wafer stage, wherein the chamber is separated into first, second, and third spaces by a separation wall, and the first space includes the microscope and the wafer stage. Arranging at least one of the reticle stages,
An air-conditioning unit in which the projection lens system is arranged in the second space, at least one of the reticle library and the wafer transfer system is arranged in the third space, and each space is provided outside the chamber; And a first clean filter is provided at a location where air is supplied above the first space, and a second clean filter is provided at a place where air is supplied above the third space. The position for discharging the air is positioned below the microscope, and the position for discharging the air in the third space is positioned below the reticle library or the wafer transfer system. A semiconductor exposure apparatus, wherein air is supplied to the first space and the third space independently from the upper space and the air is discharged from the lower space. 2. The semiconductor exposure apparatus according to claim 1, wherein said air conditioning means has a plurality of systems corresponding to the space, and the temperature is independently adjusted for each system. 3. The semiconductor exposure apparatus according to claim 1, wherein said reticle stage and said wafer stage are arranged in different spaces. 4. The semiconductor exposure apparatus according to claim 1, wherein said separation wall uses a heat insulating material. 5. The semiconductor exposure apparatus according to claim 1, further comprising air conditioning means for supplying air to said second space independently of said first and third spaces.