JPH0422118A - Semiconductor aligner - Google Patents

Abstract

PURPOSE:To prevent the precision deterioration an aligner caused by temperature change, by dividing parts into independent spaces, and performing independent air conditioning for each of the spaces. CONSTITUTION:In a space A, the air from a cooler 81a in a machine chamber is adjusted at a specified temperature by a reheater 82a, and supplied to the space A through a cleaning filer 84a. The air in the space A is returned to the machine chamber by a duct 89a. Thus clean air is always supplied to the space A. Temperature is measured by a temperature sensor 85a, and the cooler 81a and the reheater 82a are controlled by a temperature controller 83. To a space B and a space C, the clean air subjected to independent temperature adjustment is always supplied in the same manner as the case of the space A. To a space D, the clean air which is branched from the space A and subjected to temperature adjustment is supplied.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an exposure apparatus used in the manufacture of semiconductor devices such as ICs and LSIs, and particularly to a repetitive exposure apparatus (stepper).
The present invention relates to a temperature control mechanism for improving overlay performance (alignment).

[Background Art] Semiconductor devices (elements) have become increasingly finer and more highly integrated in recent years. D-RAM (dynamic
Random access memory) has already entered the submicron range at the product level, and at the research level, patterning of half a micron (05 μm) or less is being discussed.

256 - An exposure device called a stepper, which was developed in the DRAM era, is the main model in the production of 1M to 4M DRAMs.

Regarding miniaturization, overlay accuracy or resolution is equally important, and the required accuracy is said to be about 1/3 to 115 of the resolution.

Overlay accuracy can be broadly divided into two elements. One is an alignment component, and the other is a magnification and distortion component.

The mainstream of steppers with off-axis alignment systems is TTL alignment systems. Stepper alignment systems can be classified into the following three types. The first is the TTLON AXIS system, which has the advantage of being able to simultaneously observe the reticle and wafer using the same alignment light and exposure light. The second is TTL NO
Since it is a N AXIS system, the alignment light is different from the exposure light or passes through the projection lens. Simultaneous observation of the reticle and veno λ is difficult. The third type is the ophaxis system, in which an alignment microscope is placed completely separate from the projection lens. Among these, off-axis steppers have many indirect error factors in the relative positioning of the reticle and the wafer, and the time and travel distance from alignment to exposure are long. Accuracy cannot be obtained.

The horizontal resolution is based on Rayleigh's formula (Re = k I have been trying to However, this is also Rayleigh's equation (
DOF=±λ/NA2. ), as the NA increases, the depth of focus decreases, and on the other hand, there are limits to the design and manufacture of projection lenses, and the exposure wavelength must be shortened for miniaturization. Currently, an i-line (365 nm) stepper is in practical use, and an excimer stepper using a KrF excimer laser (248 nm) as a light source is being developed.

However, the glass materials that allow the light of the KrF excimer laser (248 nm) to pass through are limited to quartz and fluorite, and it is extremely difficult to correct chromatic aberration for light other than the exposure wavelength in terms of design.

FIGS. 4(a) and 4(b) show the longitudinal chromatic aberration characteristics of a g-line lens and a single quartz lens for excimer. The horizontal axis represents wavelength, and the vertical axis represents longitudinal 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 approaches zero at the target wavelength [2013° in Figure 4 (a)] On the other hand, in excimer lenses, the combination of glass materials Since there are no degrees of freedom, the line becomes almost a straight line that crosses at one point of the target wavelength [20 in Figure 4(b).
2]. If, for example, a HeNe laser (633 nm) is selected as the alignment light for a g-line lens, the axial chromatic aberration is about 10-odd μm.
Even if 0 nm) is selected, the axial chromatic aberration will reach the order of mm. From this reality, it is difficult to realize a non-exposure alignment system for excimer lenses (steppers) unless the axial chromatic aberration characteristic curve can be improved.

This λ3. Improvements to the above-mentioned drawbacks of off-axis type alignment systems based on knowledge have been proposed in Japanese Patent Application No. 115534/1983 by the present applicant.

On the other hand, the above-mentioned magnification and distortion components are mainly problems related to the performance of the projection lens, and this change over time is the main error factor due to the change over time in the environment in which the projection lens is placed.

This is because the refractive index of the air changes due to changes in the atmospheric pressure and humidity of the air, the refractive index of the lens glass material changes due to temperature changes, and the air gap between lenses changes due to thermal expansion of the lens barrel. ing. Also, this is
It is also well known for causing changes in the focal position of the projection lens.

FIG. 3 shows the configuration of a conventional stepper. 1 is the photo original (
2 is a semiconductor substrate (hereinafter referred to as a wafer). When the light beam 39 emitted from the exposure light source 3o passes through the optical system 3 to illuminate the reticle 1, the pattern on the reticle can be transferred to the photosensitive layer on the wafer by the projection lens 4. In the illumination optical system, mirror 3]
The light beam directed upward by the fly eye lens 33
, condenser lenses 34a, 34b, and mirror 35 to reach the masking image plane. 36 is a masking plate, 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 to light while being vacuum-adsorbed by the wafer chuck 21.

The wafer chuck is movable in each axis direction by the wafer stage 5. The wafer stage 5 is supported by a stage base 50. The wafer stage 5 is Y according to the conventional technology.
On the stage 51 and the X stage 52, for example, there are leveling by three piezoelectric elements (Vinizo elements) 53 and two fine movement stages 54, and above them, a rotation (θ) fine movement stage 55, and a vertical (Z) tra movement stage 56. will be accomplished.

The wafer chuck 21 is placed on the Z fine movement stage 56. On top of the leveling and second fine movement stage 54, mirrors 57 are placed in each of the X and Y directions, which serve as a reference for the position coordinates of the wafer stage system, and reflect the beam from the laser interferometer 58. It is possible to know the position and travel distance of the wafer stage. 59 is a receiver that converts an optical signal into an electrical signal.

A reticle optical system 6 is arranged above the reticle 1.

The reticle optical system is a binocular optical system with two objective lens systems 60, and the CCD marks on the reticle.
61, it is possible to detect the amount of positional deviation of the reticle.

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).
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 enlarge and project the wafer pattern onto an imaging plane 74 . erector lens 77
and 78 are low magnification erectors when both are inserted on the optical axis.
As a lens, when the lens 78 is withdrawn, it functions as a back magnification erector and projects an aerial image of the imaging surface 74 onto the light receiving surface of the CCD 79. Reference numeral 25 denotes an optical fiber that guides light from a light source (not shown), which illuminates the wafer via an illumination lens 26 and a beam splitter 73. Similarly, 27 is an optical fiber that guides light from a light source (not shown), and illuminates the reference mark 70 via an illumination lens 28. The beam splitter 75 is arranged so that the pattern surface of the reference mark 70 and the imaging surface 74 have the same optical path length, so that the reference mark is also projected and imaged onto the light receiving surface of the CCD 79 by the erectors 77 and 78.

Inside the chamber 8, air whose temperature has been adjusted by a cooler 81a and a reheat heater 82a in the machine room 80 is used, or one or more cleaning filters 84a are supplied by a blower 86a.
The air is supplied into the chamber 8 through the air, making it possible to keep the temperature of the environment where the device is placed constant and to keep the air clean. A control circuit 9 is used to control each of the above-mentioned components. The CPU 91 issues commands to each element according to predetermined sequence software, and also judges data from each element to determine the next procedure. The calculation circuit 92 is mainly used for calculation processing that requires high speed and high accuracy, such as calculating the relative position of the reticle and wafer from stage coordinates and detection results of an off-axis microscope, and the storage circuit 93 stores these measurement data. I remember 7 Tora calculation deku,
9. Further, in the chamber 8, a reticle library 100 and a wafer carrier 10, which are peripheral devices, are arranged adjacent to the main body of the stepper.
20 and the wafer transport device 130, the wafer is transported to the stepper main body. This is a schematic configuration of a conventional stepper.

[Problems to be Solved by the Invention] The stepper body has heat sources such as actuators for driving the wafer stage and reticle stage and an exposure light source built-in in various parts, and as described in the conventional example above, the stepper body has built-in heat sources such as actuators for driving the wafer stage and reticle stage, and the air conditioning chamber 8 as described in the conventional example above. Even if the stepper body is placed in the room, spatial temperature unevenness cannot be avoided.

The air at a certain temperature supplied from the clean filter 84a is
As it goes downstream, it is affected by scattered heat sources, and as the temperature rises, fluctuations due to convection occur, and the temperature stability also deteriorates.

According to actual measurements, it was 23℃ at the outlet of the clean filter.
Air temperature controlled to ±0.03℃ or 24℃±0 downstream
．． The temperature deteriorated to 5°C. Further, the dust generated upstream of the air accumulates as it goes downstream, deteriorating the cleanliness of the space.

However, as mentioned in the conventional example, off-axis alignment systems require a long time from alignment to exposure, and a long travel distance from alignment to exposure.
The error component changed over time, and as a result, high overlay accuracy could not be obtained. This change in error component over time is largely due to environmental temperature fluctuations. For example, in FIG. 3, the value of the distance 11tL between the optical axis center of the objective lens 71 of the off-axis microscope 7 and the projection 1/lens 4 depends on the elongation due to thermal expansion of the members fixing them and the wafer stage 5. This includes error components such as changes in the position of the reference mirror 57 due to thermal expansion of the fine movement stage 54 that fixes the reference mirror 57, which serves as a distance measurement reference. The amount of error due to thermal expansion is 2 when the material of the target member is a low expansion alloy mesh.
ppm/℃, 7ppm/℃ for alumina ceramics
l, and the length of these members is 200 mm, then
The expansion amount is 0.4 μm/t and 14 μm, respectively.
/'C, which is a value that cannot be ignored for the required alignment accuracy.

Regarding the performance of the projection lens 4, for example, the refractive index change of quartz glass material with respect to temperature is 153 x 10-6/°C, and although this value varies depending on the individual properties of the projection lens, the focal position change This corresponds to 4 to 8 μm/'C, and the magnification and distortion also vary greatly.

From the above, the conventional air-conditioning system using a chamber has the disadvantage that stable overlay accuracy cannot be obtained, but rather deteriorates it.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and it is an object of the present invention to provide an air conditioning system that prevents deterioration of the precision of an exposure apparatus due to temperature fluctuations.

[Means and effects for solving the problem] In order to achieve the above object, the present invention solves the problem of spatial temperature unevenness in the environment, temporal temperature stability, and individual parts that greatly affect overlay accuracy. The temperature control accuracy of these individual spaces is improved by partitioning them into separate spaces and air-conditioning each of these independent spaces independently.

[Example] FIG. 1 shows an example of the present invention. In FIG. 1, 8 is a chamber, 80 is a machine room where air temperature is adjusted, 8fa, 81b, and 8IC are coolers arranged in the machine room 80, and 82a, 82b, and 82c are reheat heaters;
6a, 86b, 86C are blowers, 84a, 84b, 84
c, 84d are air cleaning filters, 85a, 85b, 85
c is a temperature sensor, 87a, 87b, 87c are chambers 8
Separation walls 88a, 88b, 88c that separate spaces within the machine room 80 are supply tactors 89a, 89b that supply temperature-controlled air into the chamber 8.

89c and 89cl are return ducts that return the air in the chamber 8 to the machine room 80.

In this configuration, the internal space of the chamber 8 has a dividing wall 87a.
, 87b, and 87c, a space A where the reticle (or mask) stage 11, reticle optical system 6, illumination optical system 3, and exposure light source 30 are arranged, and a space where the wafer stage 5 and off-axis microscope 7 are arranged. B, and the space C where the projection lens 4 is arranged, the reticle library 100, the reticle 1112 transport system 120, the wafer carrier electric heater +10, and the wafer transport system] 3
They are each separated by the space in which they are placed.

In space A, a cooler 8 located in the machine room
1a is adjusted to a predetermined temperature by a reheat heater 82a, and then sent to a supply duct 88a by a blower 86a.
, air is supplied to the space A via the cleaning filter 84a. The return duct 89a returns the air in the space A to the machine room, thereby constantly supplying clean, temperature-controlled air to the space A. Further, the temperature of the air co-supplied to the space A is measured by a temperature sensor 85a,
In order to maintain the air temperature at a predetermined temperature, the temperature controller 83 controls the cooling power of the cooler 81a and the reheater 82a.
reheater or controlled. In space B and space C, similarly to space A, independently temperature-controlled clean air is constantly supplied. In addition, the temperature sensor 85
b measures the temperature of clean air supplied to space B, and temperature sensor 85c measures the temperature of clean air supplied to space C, and a temperature controller is used to maintain the respective air temperatures at predetermined temperatures. The temperature of the clean air supplied by 83 is controlled. In the space, the air supplied to the space A is branched before the clean filter 84a, and temperature-adjusted clean air is supplied to the space via the clean filter 84d. and return duct 89d
The air in the space is returned to the machine room 80.

By configuring the air conditioning chamber in this way, the space inside the chamber is kept clean, the influence of the heat sources scattered in each part of the stepper is minimized, and the space inside each of Space A, Space B, and Space C is kept clean. The target temperature unevenness is reduced, temporal temperature stability is also improved, and the temperature of a predetermined space can be controlled with high precision. Also, if a heat insulating material is used for the separation walls 87a, 87b, and 87c that separate each space,
Transfer of heat between the spaces is suppressed, making it possible to control the temperature of a given space with even higher precision.

Another configuration of the machine room is shown in FIG. In this embodiment, the coolers 81b and 81c shown in FIG.
e, space B is replaced by reheat heaters 82b and 82c.
and space C are each independently temperature controlled. In this way, the volume of the machine room can be reduced. The configuration of the machine room can be changed in various ways depending on the configuration of the exposure apparatus, temperature conditions, etc.

[Effects of the Invention] As explained above, the spaces within the chamber that require highly accurate temperature control are individually separated, and the temperature of the air supplied to these individually separated spaces is controlled by controlling the temperature of the air that is supplied to each of the separated spaces. By independently controlling the space inside the chamber, the space inside the chamber can be kept cleaner, and the influence of heat sources scattered in each part of the stepper can be kept to a minimum. This reduces spatial temperature unevenness within the space and improves temporal temperature stability, making it possible to control the temperature of a given space with high precision.

Furthermore, according to the present invention, it is possible to control each separated space within the chamber to a separate set temperature, and the temperature of the space other than the separated space surrounding the projection lens can be controlled by controlling the temperature of the space where the chamber and the machine room are placed. It is possible to make the temperature the same as the temperature, and it is also possible to reduce the energy consumed for temperature control.

This is because the performance of the projection lens can only be guaranteed at the environmental temperature in which the projection lens is manufactured.

[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, and Fig. 3 is a block diagram of a conventional exposure apparatus. The configuration diagram and FIGS. 4(a) and 4(b) are explanatory diagrams of the characteristic curves of the g-line lens and the excimer lens. Reticle, 2 Wafer, 3 Fuming optical system projection lens, 5
Wafer stage, reticle microscope, off-axis microscope, 8 chambers, machine room.

Claims (4)

[Claims] (1) In the chamber, an illumination optical system, a reticle holding mechanism on which a pattern to be exposed is formed, and a projection lens system;
A wafer holding mechanism for exposing and transferring the pattern, a reticle and wafer alignment mechanism, and a reticle storage and transport mechanism are provided, the chamber is divided into a plurality of spaces, and each space is provided outside the chamber. A semiconductor exposure apparatus characterized in that it is connected to a system air conditioning means. (2) The air conditioning means has a cooler and a reheater, and a temperature detection means is provided for each system, and at least one of the cooler and the reheater can be controlled based on the detected temperature. A semiconductor exposure apparatus according to claim 1. (3) A semiconductor exposure apparatus according to claim 1, wherein the cooler is used in common for a plurality of systems of air conditioning means. (4) The semiconductor exposure apparatus according to claim 1, wherein the projection lens system is communicated with a separate system of air conditioning means.