WO2002052345A1

WO2002052345A1 - Method and device for mask cleaning, and device manufacturing system

Info

Publication number: WO2002052345A1
Application number: PCT/JP2001/011170
Authority: WO
Inventors: Naomasa Shiraishi
Original assignee: Nikon Corporation
Priority date: 2000-12-22
Filing date: 2001-12-20
Publication date: 2002-07-04
Also published as: JPWO2002052345A1; JP4096246B2

Abstract

A method and a device for mask cleaning capable of efficiently cleaning reticle without affecting an exposure body part and transferring the cleaned reticle to the exposure body part without being contaminated; the method, comprising the steps of transferring the reticle (R) contained in a normal case (3) into a purge gas substitution chamber (24) to substitute the atmosphere around the reticle with a purge gas with high transmittance to exposure beam, performing an optical cleaning by the ultraviolet ray from an ultraviolet ray source (27), transferring the reticle (R) into a charging chamber (35) to load the reticle (R) air-tight into a clean case (8) in the purge gas atmosphere, and transferring the reticle (R) loaded in the clean case (8) to the exposure body part.

Description

Description Mask cleaning method and apparatus, and device manufacturing system

The present invention relates to a photolithography process for manufacturing various devices such as a semiconductor device, an imaging device (such as a CCD), a liquid crystal display device, or a thin film magnetic head. The present invention relates to a mask cleaning method and apparatus used for cleaning. Further, the present invention relates to a device manufacturing system provided with the mask cleaning device. Background art

In the photolithography process for forming micropatterns for electronic devices such as semiconductor integrated circuits and liquid crystal displays, a reticle (or photo) as a mask that draws a pattern to be formed at a magnification of about 4 to 5 times is used. A method of reducing and transferring a pattern of a mask or the like onto a wafer (or a glass plate or the like) as a substrate to be exposed by using an exposure apparatus of a batch exposure method or a scanning exposure method is used.

In an exposure apparatus used to transfer the fine pattern, if foreign matter such as dust or chemical contaminants adheres to the pattern on the reticle, the transmittance of the pattern in that part decreases, and the pattern on the wafer It may cause erroneous transfer. Therefore, in order to prevent such foreign matter from adhering, the pattern surface of the reticle has been generally covered with a dustproof film having a thickness of about 1 im called a pellicle. The pellicle was stretched about 5 to 7 mm away from the reticle pattern surface via a metal frame called pellicle frame.

Further, in exposure apparatuses, the exposure wavelength has been shifted to shorter wavelengths in order to respond to miniaturization of semiconductor integrated circuits. At present, the exposure wavelength is mainly 248 nm of KrF excimer laser, but the ArF excimer laser, which can be regarded as a shorter wavelength, substantially a vacuum ultraviolet region (VUV), is used. The 193 nm is also entering the practical stage. And the shorter wavelength 1 5 7 nm F ₂ laser or, has also been proposed a projection exposure apparatus that uses exposure light source of vacuum ultraviolet region A r ₂ laser having a wavelength of 1 2 6 nm.

The light in the vacuum ultraviolet region can be supplied to a conventional exposure apparatus having an exposure wavelength of about 200 to 400 nm by using many gases existing on the optical path of the exposure light, such as oxygen, water vapor, and dioxide. Absorption by gases such as carbon and hydrocarbon gas (organic gas) (hereinafter referred to as “absorbent gas”) is extremely large. Therefore, in a projection exposure apparatus using vacuum ultraviolet light, in order to remove the absorbing gas from the light path of the exposure light, the gas in the light path is converted to a gas (such as nitrogen or a rare gas) which has relatively little absorption for the exposure light. Hereinafter, it will be referred to as “low-absorbing gas”.) The gas used to actually replace the gas in the optical path among the low-absorbing gases is called “purge gas”. Regarding the allowable residual concentration of absorbent gas, for example, for organic gases, the average concentration in the optical path must be suppressed to several ppm or less. The same is true for the ArF excimer laser (wavelength: 193 nm), which is the longest in the vacuum ultraviolet region.

As described above, pellicles have been used to protect the reticle surface. In this case, the space surrounded by the reticle, the pellicle frame, and the pellicle (hereinafter referred to as “pellicle space”) is almost the same as the outside air except for small ventilation holes to prevent deformation of the pellicle due to a pressure difference. It is an isolated space with high airtightness. In this pellicle space, air in the atmosphere in the process of extending the pellicle, for example, absorbent gas such as oxygen, water vapor, and organic gas remains.

However, when the exposure light is, for example, an F ₂ laser (wavelength: 157 nm) in the vacuum ultraviolet region, the absorption by oxygen is extremely large, so that the light remains even in an optical path of only a few mm in the pellicle space. Absorption (dimming) by oxygen is extremely large. In addition, organic substances and water adhere to the reticle stored in a normal storage state to a certain extent, and the transmittance of the reticle to exposure light in the vacuum ultraviolet region is significantly reduced due to the absorption of the adhered substances. There is a risk of doing it.

As a countermeasure against this, prior to exposure using a reticle, it is possible to perform the above-mentioned gas replacement in the pellicle space in the lithography equipment ゃ optical cleaning of the reticle. Vibration and heat generated from the light cleaning light source There is a disadvantage that various performances of the exposure apparatus are reduced. In addition, the exposure apparatus performs the reticle cleaning process, so that the exposure processing capability is reduced, and the throughput of the entire process of manufacturing semiconductor devices and the like may be reduced.

In view of the foregoing, the present invention provides a mask cleaning technology capable of efficiently cleaning a mask and maintaining a high transmittance of the mask without adversely affecting an exposure main body that transfers a mask pattern onto a wafer. The primary purpose is to provide

It is a second object of the present invention to provide a mask cleaning technology capable of preventing a decrease in transmittance of exposure light when using a mask provided with a dust-proof member such as a pellicle. Disclosure of the invention

The mask cleaning method according to the present invention is a mask cleaning method for cleaning a mask (R) to which a dustproof member (1) is attached so as to cover a pattern surface and a predetermined exposure beam is irradiated at the time of exposure. A first step of replacing gas in a predetermined range of space surrounding the mask with a gas that transmits the exposure beam, a second step of optically cleaning the mask with ultraviolet light, and a gas filled with the exposure beam. And a third step of loading the mask in a hermetically sealed case (8) in a sealed state.

According to the present invention, by irradiating the mask with ultraviolet rays, organic substances and water adhering to the surface of the mask and the dustproof member (pellicle, etc.) are decomposed and removed. Also, since the atmosphere around the mask is replaced by a gas (purge gas) that transmits the exposure beam, adhesion of organic substances and water to the mask surface is suppressed, and the transmittance of the mask to the exposure beam can be improved. it can. Further, the cleaned mask can be stored in the case and transported while maintaining a high transmittance, so that the cleaning operation can be efficiently performed in a place different from the exposure main body.

In this case, in the first step, the inside of the substantially enclosed space surrounded by the mask, the dustproof member, and the support frame of the dustproof member may be replaced with a gas that transmits the exposure beam. desirable. Thereby, the transmittance for the exposure beam is further improved. In addition, the presence of oxygen around the mask may increase the efficiency of light cleaning, and the first and second steps may be performed substantially simultaneously (in parallel) to reduce the mask cleaning time. It is desirable to execute. Alternatively, the second step may be performed before the first step.

Next, the mask cleaning apparatus according to the present invention is a mask cleaning apparatus for mounting a dustproof member (1) so as to cover a pattern surface, and for cleaning a mask (R) irradiated with a predetermined exposure beam during exposure. A gas replacement mechanism (42, 43, 45A, 46A) that replaces gas in a predetermined area (24) surrounding the mask with a gas that transmits the exposure beam, and the mask An ultraviolet irradiation device (27) for light cleaning, and a loading mechanism (3) for loading the mask in an airtight case (8) filled with a gas that transmits the exposure beam in a hermetically sealed state. 5, 36, 37A, 37B, 38A, 38B).

According to the present invention, the mask cleaning method of the present invention can be implemented.

In this case, the ultraviolet irradiation device and the gas replacement mechanism are at least partially integrated, and the transfer system for transferring the mask between the gas replacement mechanism and the loading mechanism (32, 33). Is desirably provided. This makes it possible to reduce the size of the purification device as a whole and shorten the time required for purification.

The gas replacement mechanism has, for example, an airtight chamber (24) for accommodating the mask and a pressure reducing mechanism (42, 45A) for reducing the pressure in the airtight chamber. Further, as another example, the gas replacement mechanism includes a gas-tight chamber (24) for accommodating the mask, a gas exhaust in the gas-tight chamber, and a flow control of supply of a gas that transmits the exposure beam to the gas-tight chamber. And a supply and exhaust mechanism (42, 43, 45A, 46A). When the pressure reducing mechanism is used as in the former case, the gas can be replaced in a short time. On the other hand, when the flow control is used as in the latter, even if the strength of the dustproof member is low, for example, the air can be replaced without deforming the dustproof member. .

Further, when the dustproof member (1) is fixed to the mask (R) via the support frame (2), the gas displacement mechanism operates with the mask, the dustproof member, and the support frame. Replace the inside of the enclosed space with gas that transmits the exposure beam It is desirable to do. When the mask in this state is put into the exposure apparatus, the exposure beam is not absorbed even in the enclosed space, so that the illuminance on the substrate to be exposed can be increased.

It is desirable that the gas replacement mechanism further replaces the gas in the space between the pattern surface and the dustproof member with a gas that transmits the exposure beam. Thereby, the transmittance for the exposure beam is improved.

In addition, when a frame (2) that holds the dust-proof member and is attached to the pattern surface is provided, the gas displacement mechanism operates through the ventilation holes (2a, 2b) formed in the frame. Alternatively, the space between the pattern surface and the dustproof member may be replaced with a gas that transmits the exposure beam. By utilizing the ventilation holes in this way, there is no need to apply special processing to the frame.

Next, the device manufacturing system according to the present invention is a device manufacturing system for forming a device pattern (Rl, R2) on a work piece (Wl, W2). 4), an exposure apparatus main body (68 A to 68 C) for transferring an image of the device pattern onto the workpiece, and the mask cleaning apparatus between the mask cleaning apparatus and the exposure apparatus main body. And a transfer device (65-67) for transferring the mask cleaned in step (1).

By using the mask cleaning apparatus of the present invention, the exposure apparatus main body can efficiently transfer various device patterns onto a work piece while maintaining a high transmittance to the exposure beam. Mass production with high throughput is possible.

In this case, it is preferable that the exposure apparatus main body has a mask removal mechanism (73) for removing the mask loaded in the case (8A, 8B) by the mask cleaning apparatus. Thereby, the delivery of the mask can be performed smoothly.

Further, it is desirable that the mask cleaning apparatus is shared by a plurality of exposure apparatus bodies. Thus, the operation rate of the mask cleaning device can be increased. Next, the device manufacturing method of the present invention is a device manufacturing method of forming a device pattern on a work piece (W), wherein the dust-proof member ( 1) Remove the mask (R) with A first step of cleaning and loading in an airtight case (8), a second step of storing the cleaned mask in the case, and transporting the mask to the exposure main body (68A); And a third step of exposing the substrate (W) with an exposure beam through the mask taken out of the case in the exposure main body. According to the present invention, for example, the mask purified by the mask purification unit separate from the exposure main unit is housed in a sufficiently clean, gas-exchanged, highly airtight case, and the exposure main unit is Transported to Therefore, it is possible to transfer a circuit pattern of a device such as a semiconductor device using a mask with sufficient transmittance without installing a mask purification section (gas replacement section and ^ 6 cleaning section) in the exposure main body. become.

In this case, it is desirable to share a mask purifying section for purifying the mask with a plurality of the exposure main bodies. As a result, the number of facilities on the entire production line can be reduced. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a partially cutaway configuration view showing a reticle cleaning device according to an example of an embodiment of the present invention. In FIG. 2, (A) is a side view showing a normal case for a reticle, and (B) is a cross-sectional view showing a clean case for a reticle. In Figure 3,

(A) is a bottom view showing an example of a gas replacement mechanism for replacing the pellicle space with a purge gas,

(B) is a partially cutaway front view showing the gas replacement mechanism. FIG. 4 is a perspective view showing a main part of an example of a device manufacturing system including the reticle cleaning device of FIG. FIG. 5 is a diagram illustrating an example of a manufacturing process when a semiconductor device is manufactured using the device manufacturing system according to the embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings. In this example, a reticle purification device is installed, in which a pellicle (dust-proof member) in the form of a thin film is stretched to protect the pattern surface, and the reticle (mask) is irradiated with vacuum ultraviolet light as an exposure beam. The present invention is applied. The reticle cleaning apparatus of the present example is, for example, a photolithography for manufacturing semiconductor devices and the like. : Installed separately from the exposure equipment in the manufacturing line that executes the process.

FIG. 1 shows the reticle cleaning apparatus of the present embodiment. In FIG. 1, the reticle cleaning apparatus is stored in a normal case 3 (reticle case) stored in a reticle storage device (not shown) under an atmospheric environment. The reticle R as a mask is loaded into an airtight clean case 8 (clean reticle case) after being replaced with a gas transmitting the exposure light and washed with light, and the clean case 8 seals the reticle R. Then, it is transported to an exposure device (not shown) in a state where it is incorporated. The reticle R is equipped with a pellicle 1 as a dustproof member to protect the surface of the reticle.

Fig. 2 (A) shows the normal case 3, and in Fig. 2 (A),

3 is constructed by connecting the upper lid 5 to the bottom plate 4 so that it can be opened and closed about two fulcrum portions 7 as axes, and four pedestals 6 on the bottom plate 4 (Fig. 2 (A) The reticle R is placed via the reticle R. A thin pellicle 1 having a thickness of about 1 m is provided on a reticle R surface (lower surface) via a rectangular frame-shaped metal pellicle frame 2. As the pellicle 1, for example, a flat plate having a thickness of about 300 to 800 / xm of fluoride crystal can be used. In Case 3, the gas density is quite low even when the top lid 5 is closed, and the gas in Case 3 is almost the same as the surrounding gas. Therefore, Case 3 is used to store the reticles individually when the reticles are stored in a reticle storage device in the same atmosphere as normal air.

FIG. 2 (B) is a cross-sectional view showing the clean case 8, and in FIG. 2 (B), the clean case 8 is mounted on the upper surface of a flat mount portion 9 having an opening formed in the center. Then, fix the box-shaped receiving section 10 with an open bottom, and then press the flat bottom plate 11 on the bottom of the mounting section 9 with two spring-type clamps 14 A, 14 B that hang the flat bottom plate 11. The reticle R is mounted on the bottom plate 11 via four pedestals 12. In this case, the mounting portion 9 and the housing portion 10 are fixed by welding, integral molding, or the like in order to maintain the airtightness inside, and the mounting portion 9 and the bottom plate portion detachable from the mounting portion 9 are provided. In order to improve the airtightness when the bottom plate 1 1 is attached to the mount 9, the ring 1 3 (seal member) Is arranged. Also, the mounting portion 9, the housing portion 10, and the bottom plate portion 11 are made of a material such as stainless steel or metal such as aluminum, which has a small outgassing and can maintain a high internal airtightness. With the bottom plate 11 fixed to the mount 9 with the clamps 14A and 14B, the inside of the clean case 8 becomes an airtight chamber, and the reticle R inside is locally isolated almost completely from the outside air. This means that it is installed in a comfortable environment.

The mechanism of the clamps 14A and 14B is not limited to the spring type.For example, the mount 9 and the member attached to and detached from the mount 9 may be connected at a plurality of locations using a port, and a permanent magnet may be used. The mount 9 and the vacuum pump may be connected to each other via a flexible pipe, and the mount 9 and its members may be connected by vacuum suction. Alternatively, the mount 9 and its members may be connected to each other by electrostatic attraction, adsorption by an electromagnet, or the like.

In recent photolithography projects, technologies for keeping the environment of a large space clean, such as a clean room or a chamber that covers the entire exposure apparatus, and a local area such as the inside of a wafer case for transporting a predetermined number of wafers have been developed. The importance of the local clean environment (mini-environment: mini-environineiil;) technology that keeps the natural environment clean has been recognized. Since the clean case 8 of this example is highly airtight, the space surrounding the reticle R inside it can be said to be a local clean environment in which foreign matter is prevented from adhering.

Recently, for example, in order to standardize the transfer of reticles and wafers between various devices during the photolithographic process, SMIF (Standard mechanical i.m.) is a mechanical interface technology that standardizes the case for storing reticles and wafers. nterface) technology has been proposed. Therefore, as the clean case 8 in this example, a case standardized based on the SMIF technology, for example, SMIpod (product name) may be used.

Further, the reticle R of this embodiment, the wavelength 2 0 0 nm approximately following the vacuum ultraviolet light is used as the exposure light, oxygen from the optical path of such exposure light, water vapor, carbon dioxide (C 〇 ₂ It is necessary to eliminate “absorbent gas” which is a gas that has a strong absorption rate for exposure light such as, and hydrocarbon (organic) gases. On the other hand, it transmits the exposure beam In this example, the "low-absorbing gas" that has low absorption for exposure light in the vacuum ultraviolet region includes nitrogen and noble gases (helium, neon, argon, krypton, xenon, radon), and a mixture thereof. is there. In the exposure apparatus using the reticle R of the present example, the `` purge gas '' selected from the low-absorbing gas based on, for example, the required stability of the imaging characteristics and the operating cost is used. The gas in the light path of the exposure light is replaced. As the purge gas, for example, nitrogen is used in applications where the operation cost is to be kept low, and helium is used in applications where importance is placed on the stability of the imaging characteristics.

In this regard, assuming that the gas in the clean case 8 is ordinary air containing a low-absorbing gas, the clean case 8 is transported to the exposure apparatus, and when the reticle R is taken out of the clean case 8, the clean case 8 is removed. The air inside may mix into the purge gas on the optical path of the exposure light, reducing the intensity of the exposure light. Therefore, in this example, the gas inside the clean case 8 is also replaced with the purge gas supplied from the exposure apparatus using the reticle R.

Further, in FIG. 2B, reticle R, pellicle 1, and pellicle frame

The space surrounded by 2 (pellicle space) has a short optical path for the exposure light, but it is desirable that the inside of the space is also replaced with a purge gas. In this regard, the pellicle frame 2 is provided with extremely small ventilation holes 2a and 2b in order to prevent deformation and breakage of the pellicle 1 due to a difference in pressure between the inside and outside of the pellicle space. Then, the gas in the pellicle space is replaced with a purge gas through the ventilation holes 2a and 2b (details will be described later).

Returning to FIG. 1, the reticle purifying apparatus of the present example is divided into a plurality of hermetic chambers surrounded by a loading side loader 21 for transferring a reticle R in a case 3 and an airtight housing 23. A vacuum pump 42 such as a dry type as a pressure reducing mechanism for exhausting gas from a plurality of hermetic chambers in the main body, and a purge gas supply including a gas cylinder for supplying the purge gas to the hermetic chambers. And a control system 41 composed of a computer for controlling the operation of the entire apparatus. Further, the inside of the housing 23 is divided into a purge gas replacement chamber 24 as a plurality of airtight chambers, a lamp chamber 26, a loader chamber 30 and a chamber 35 for loading a clean case. Loading chamber 35 It can also be called a lean case interface. In this case, the openable and closable shirt 28 is partitioned between the purge gas exchange chamber 24 and the outside air, and the fluorescent gas through which ultraviolet light for light cleaning passes is provided between the purge gas exchange chamber 24 and the lamp chamber 26. A window member 25 made of a fluoride crystal such as stone (CaF ₂ ) is provided. The window member 25 is provided between the purge gas replacement chamber 24 and the loader chamber 30, and the mouth chamber 30 and the loading chamber 35. Are separated from each other by shutters 31 and 34 which can be freely opened and closed. These shirts 28, 31 and 34 are opened only when reticle R passes, and closed at other times to maintain airtightness.

First, the loading-side loader 21 sucks and holds the bottom surface of the reticle R (having the pellicle 1 stretched out) taken out of the case 3 by a mouth pot arm (not shown) and transports the reticle R into the purge gas replacement chamber 24. A drive unit 22 for sliding, rotating, and moving up and down the carry-in port 21 is also provided. In the purge gas replacement chamber 24, four holding mechanisms 29 for holding the loaded reticle by suction etc. are arranged, and in the lamp chamber 26, an ultraviolet light source 27 such as an excimer lamp is installed. I have. Although the exhaust pipe and the supply pipe for the purge gas are not connected to the lamp chamber 26 in this example, a purge gas replacement mechanism must also be installed in the lamp chamber 26 to maintain the intensity of ultraviolet rays high. Is desirable. However, when using a light source with a wavelength that does not absorb much oxygen, such as an ArF excimer lamp (wavelength: 193 nm), as the ultraviolet light source 27, the purge gas replacement mechanism must not be provided. Good.

In order to transport the reticle R in the purge gas replacement chamber 24 to the load chamber 35 for loading into the clean case, the loader chamber 30 has two arms that hold the bottom surface of the reticle R by suction. A side loader 32 is arranged, and a drive unit 33 for sliding, rotating, and vertically moving the unloading side loader 32 is also provided. A vertical movement device 36 that holds the bottom plate 11 of the clean case 8 and moves up and down is installed in the clean case loading chamber 35. The housing 23 at the top of the loading chamber 35 is provided with an opening 35a through which the bottom plate 11 passes, so that the opening 35a is covered to maintain airtightness. The mounting part 9 and the housing part 10 of the clean case 8 are mounted on the housing 23 by two clamping mechanisms 38 A and 38 B. It is fixed to the surface. In this example, the space surrounded by the loading chamber 35 and the accommodating section 10 of the clean case 8 is one airtight chamber. Further, in the vicinity of the opening 35a on the inner surface of the loading chamber 35, the clamp release mechanisms 37A and 37B for removing the two clamps 14A and 14B of the mount 9 of the clean case 8 are provided. Is installed. A loading mechanism for loading the reticle into the clean case 8 is constituted by the vertical movement device 36, the clamp release mechanisms 37A and 37B, and the clamp mechanisms 38A and 38B.

In this case, the mounting part 9 of the closed clean case 8 shown in FIG. 2B is placed on the housing 23 so as to cover the opening 35 a of the loading chamber 35, and the clamping mechanism 38 A and

3 Fix the mount 9 with 8 B. At this time, in order to increase the airtightness between the mounting portion 9 and the housing 23, a concave portion is formed in a contact portion of the upper surface of the housing 23 with the mounting portion 9, and a ring (seal member) is formed in the concave portion. May be arranged. After that, the tip of the vertical movement device 36 is raised so as to be almost in contact with the bottom plate portion 11, and then the clamps 14A and 14B are removed by the clamp release mechanisms 37A and 37B. Thus, the bottom plate 11 provided with the pedestal 12 can be transferred to the vertical movement device 36 while being separated from the mount 9. FIG. 1 shows the state in which the vertical movement device 36 is lowered from this state. The operation of the loading side loader 21, the ultraviolet light source 27, the loading side loader 32, the mechanism for loading into the clean case, and the shirts 28, 31, 34 are controlled by the control system 41. ing.

Further, the purge gas replacement chamber 24, the loader chamber 30 and the loading chamber 35 and the vacuum pump 42 are respectively provided with exhaust pipes 45A, 45B,

The purge gas replacement chamber 24, the loader chamber 30, the loading chamber 35, and the purge gas supply source 43, which are connected via 45 C, are each provided with an electromagnetically openable and closable air supply pipe 46. A, 46 B, and 46 C are connected. The vacuum pump 42 is also connected to a pipe 46 for sending gas exhausted from each hermetic chamber to an exhaust gas treatment facility (not shown) of the factory. A gas replacement mechanism is composed of a vacuum pump 42, a purge gas supply source 43, an exhaust pipe 45A to 45C, and an air supply pipe 46A to 46C. In addition, gas sensors 44 A, 44 B and 44 C for measuring the residual concentration of impurities such as absorptive gas are arranged in the purge gas replacement chamber 24, the loader chamber 30 and the loading chamber 35, respectively. The concentration of impurities measured by these gas sensors 44A to 44C Information is supplied to the control system 41. When measuring the oxygen concentration as the impurity, for example, a galvanic cell-type oxygen concentration meter can be used as the gas sensor 44A to 44C.

When replacing the gas in the three airtight chambers (purge gas replacement chamber 24, loader chamber 30 and loading chamber 35) with the purge gas, the control system 41 responds via a vacuum pump 42. The gas in the sealed chamber is exhausted, and a purge gas is supplied from the purge gas supply source 43 into the sealed chamber. This operation is performed until the impurity concentration measured by the gas sensors 44A to 44C becomes equal to or lower than a predetermined allowable level. In addition, the purging gas replacement operation is performed by a vacuum pump 42 (a depressurizing mechanism) in which a corresponding airtight chamber is depressurized to a pressure greater than the atmospheric pressure and exhausted, and then a purge gas is supplied. The purge gas supply source 4 3 (supply / exhaust mechanism) supplies exhaust gas and purge gas almost continuously at atmospheric pressure (approximately equal exhaust volume and supply volume). May go. The depressurization method can be used, for example, immediately after the start of operation of the reticle purifying apparatus of the present example to replace the air in each airtight chamber with purge gas in a short time. In the decompression method, the pellicle 1 stretched on the reticle R may be deformed, but pass through the ventilation holes 2 a and 2 b (see FIG. 2B) provided in the pellicle frame 2. The pumping speed at which the pellicle 1 hardly deforms is determined in advance in accordance with the gas flow rate, and the pressure may be reduced below this pumping speed.

Next, an example of the overall operation of the reticle cleaning device of the present example will be described. In FIG. 1, the reticle R with the pellicle 1 in the case 3 is carried into the purge gas replacement chamber 24 via the loading side loader 21, and the position P 1 on the holding mechanism 29. Is held in In this state, the shirts 28 and 31 are closed, and the gas in the purge gas replacement chamber 24 is replaced by the purge gas by the vacuum pump 42 and the purge gas supply source 43. Further, light emission of the ultraviolet light source 27 is started, and light cleaning of the reticle R is performed by ultraviolet light L from the ultraviolet light source 27.

Reticle R stored in a normal atmospheric environment contains foreign substances such as organic substances and water. Therefore, ultraviolet light from an ultraviolet light source 27 such as an excimer lamp is irradiated to vaporize and remove those foreign substances. In addition, new reticle R to be purified At the time of loading (replacement), the purge gas replacement chamber 24 is open to the atmosphere and is contaminated. To minimize the area open to the atmosphere, the ultraviolet light source 27 is installed in the purge gas replacement chamber. It is arranged in a lamp room 26 different from 24.

Further, it is more efficient to perform the above-described light cleaning by ultraviolet irradiation in an environment where oxygen is present to some extent. This is because UV irradiation generates ozone from oxygen, which accelerates the decomposition of organic matter. Therefore, the optical cleaning should be performed not only after the replacement with the purge gas in the purge gas replacement chamber 24 is completed but also during (substantially simultaneously with) the purge gas replacement operation. Is desirable. Further, the ultraviolet irradiation may be started at the same time when the reticle R is carried into the purge gas replacement chamber 24, and then the replacement with the purge gas may be performed.

After being purified by the above steps, the shirt 31 is opened, and the reticle R is transferred from the purge gas replacement chamber 24 to the loader chamber 30 by the unloader 32. Then, after closing the shirt 31 and opening the shirt 34, the reticle R is loaded into the loading room 35 (clean case interface) with the bottom plate 1 1 (clean case 8). Is placed at the position P 2 on the pedestal 1 2. The bottom plate 11 is held on a vertical movement device 36 which is a part of the loading mechanism. Subsequently, the shirt 34 is closed, and the space surrounded by the loading room 35 and the housing 10 of the clean case 8, that is, the space in which the reticle R is housed, becomes a sealed space. Until the impurity concentration falls below the allowable level, the purge gas is replaced by the vacuum pump 42 and the purge gas supply source 43.

Then, the vertical motion device 36 is raised, and the clamp release mechanisms 37 A and 37 B are moved from the clamps 14 A and 14 B while the bottom plate 11 is in contact with the bottom surface of the mount 9. 2B, the reticle R is held in the atmosphere of the purge gas in the hermetically sealed clean case 8 as shown in FIG. 2 (B). This completes the reticle R purification process using the reticle purification device of the present example.

As described above, according to the purifying operation using the reticle purifying apparatus of the present embodiment, the atmosphere around the reticle R on which the pellicle 1 is mounted is replaced with the purge gas, the reticle R is optically cleaned, and the reticle R is cleaned into the clean case 8. Effective loading in purge gas atmosphere It can be performed efficiently. Further, it is clear that the reticle cleaning apparatus of the present example can be applied not only to the reticle R equipped with the pellicle 1 but also to the reticle not equipped with the pellicle. One

Although the replacement with the purge gas is also performed in the loader chamber 30 in FIG. 1, the loader chamber 30 is not opened to the atmosphere under the normal use condition. Is good. On the other hand, when the clean case 8 is attached to and detached from the loading chamber 35 (accurately, when the clean case 8 is not mounted), the loading chamber 35 is opened to the atmosphere, so that the clean case 8 is mounted. Needless to say, it is necessary to replace the inside of the loading chamber 35 with a purge gas before the clamps 14 A and 14 B of the bottom plate 11 are detached after the mounting of the contact portion 9. After replacement of the purge gas, the bottom plate 11 is lowered to open the shirt 34, and the reticle R is carried into the loading chamber 35.

In the above embodiment, the configuration in which the reticle R stored in the normal case 3 is transported to the reticle cleaning device has been described, but the present invention is not limited to this configuration. For example, reticle R not stored in case 3 may be transported to a reticle cleaning device to purify reticle R. Alternatively, the reticle R stored in the clean case may be transported to the reticle cleaning device, where the reticle R is purified, and then the purified reticle R may be returned to the clean case. Next, an example of a local replacement mechanism for replacing the inside of the pellicle space surrounded by the reticle R, the pellicle 1, and the pellicle frame 2 with a purge gas will be described with reference to FIG. The local replacement mechanism is provided around the holding mechanism 29 in the purge gas replacement chamber 24 in FIG. 1.In this example, in parallel with the operation of replacing the atmosphere around the reticle R with the purge gas, The gas in the pellicle space is replaced with a purge gas. In this regard, since the pellicle is originally provided for the purpose of preventing foreign matter from adhering to the reticle pattern, it is preferable that air permeability between the pellicle space and the outside is low. However, in order to prevent the pellicle space from expanding and damaging the pellicle when the atmospheric pressure drops due to, for example, a typhoon or the like, as described with reference to FIG. 2B, the pellicle frame 2 as a side wall of the pellicle space is used. Has small air holes 2a and 2b at two locations to ensure a slight air permeability between the pellicle space and the outside air. Have been. Therefore, in purging the pellicle space with the purge gas, the vent holes 2a and 2b are positively used in this example.

FIG. 3 (A) is a bottom view showing an example of a mechanism for replacing the pellicle space with a purge gas, and FIG. 3 (B) is a partially cutaway front view showing the mechanism. The four holding mechanisms 29 a to 29 supporting the reticle R at the bottom correspond to the holding mechanisms 29 in the purge gas replacement chamber 24 in FIG. In FIGS. 3A and 3B, a reticle R is stretched over a pellicle 1 via a pellicle frame 2 provided with ventilation holes 2a and 2b. In this example, one vent hole 2 a of the pellicle frame 2 is connected to a vacuum pump 42 via an exhaust pipe 45 D, and the other vent hole 2 b is connected to a purge gas supply source 4 via an air supply pipe 46 D. The purge gas is flowed into the pellicle space via the air supply pipe 46D in parallel with the flow out of the gas in the pellicle space via the exhaust pipe 45D by the flow control method. This makes it possible to efficiently replace the pellicle space with the purge gas even if the air holes 2a and 2b have a slight air permeability. Further, in order to improve the adhesion between the exhaust pipe 45 D and the air supply pipe 46 D and the pellicle frame 2, a fluorine-based resin such as Teflon or the like is provided at the tip of the exhaust pipe 45 D and the air supply pipe 46 D. Hollow elastic members 47 A and 47 B made of another soft material are provided. In addition, as the elastic members 47A and 47B, a fluorine-based resin such as Viton (trade name), Kalrez (trade name), or Armacrystal (trade name) can be used.

In order to check whether the residual concentration of impurities in the pellicle space has fallen below an allowable level, as an example, a gas sensor for measuring the impurity concentration is provided in the exhaust pipe 45D. It may be provided.

Further, since the pellicle 1 is a very thin film, if the pressure difference between inside and outside increases, the pellicle 1 may expand and be damaged. Therefore, as shown in FIG. 3 (B), a pellicle surface displacement meter 48 is installed to monitor the displacement amount with respect to the reticle R at the center of the pellicle 1. In the pellicle surface displacement meter 48, the detection light DL emitted from the light source 49 forms a slit image obliquely on the central surface of the pellicle 1 via the slit plate 50 and the condenser lens 51. Then, the detection light DL reflected on the surface of the pellicle 1 re-forms the slit image on the slit plate 53 via the condenser lens 52, and the slit image is formed. The detection light DL that has passed through the plate 53 is received by the photoelectric detector 54 such as a photodiode, and the detection signal of the photoelectric detector 54 is supplied to the signal processing device 55.

In this case, the slit plate 53 on the light receiving side vibrates in a direction corresponding to the vertical movement of the pellicle 1, and the signal processing device 55 uses the drive signal of the slit plate 53 as an example for photoelectric detection. The detection signal of the detector 54 is synchronously rectified to obtain a surface position signal. Since the surface position signal changes almost linearly within a predetermined range according to the vertical movement of the pellicle 1, the signal processor 55 calculates the amount of vertical displacement of the pellicle 1 from the surface position signal. The information on the displacement is supplied to the control system 41. Note that even if a line sensor (one-dimensional image sensor) is installed instead of the slit plate 53 and the photoelectric detector 54, the surface position signal can be obtained. The control system 41 adjusts the exhaust speed by the vacuum pump 42 and the air supply speed by the purge gas supply source 43 so that the measured value of the displacement amount of the pellicle 1 falls within an allowable range. As a result, the pellicle space can be efficiently replaced with the purge gas within a range where the pellicle 1 is not damaged.

Next, an example of a configuration of a semiconductor device manufacturing system including the reticle purifying apparatus of FIG. 1 will be described with reference to FIG.

Fig. 4 shows the main parts of the device manufacturing system of this example. In Fig. 4, the normal case in the reticle storage force 62 under the atmospheric environment (the same as case 3 in Fig. 2 (A)) is shown. Cases) 3 A, 3 B, 3 C,. Then, a loading port 21 is installed near the reticle stocker 62 together with the drive unit 22, and thereafter a reticle purifying device 64 identical to the reticle conversion device shown in FIG. 1 is installed. A highly airtight clean case 8A (the same case as the clean case 8 in Fig. 2 (B)) is installed on the upper surface of the end of the purifier 64, and a reticle is placed in the clean case 8A in the atmosphere of purge gas. Will be loaded. Further, a transport line 66 for transporting a clean case loaded with a reticle is installed near the end of the reticle cleaning device 64, and a slider 67 moving along the transport line 66 is provided. The clean case 8B loaded with the reticle is held. Along the transfer line 6, a plurality of (three in FIG. 4) projection exposure apparatuses 6 of a batch exposure method or a scanning exposure method such as a step-and-scan method are used. 8 A, 68 B, 68 C and a foreign matter inspection device 69 are installed. Projection exposure equipment

6 8 A is, A r F excimer laser (wavelength 1 9 3 nm), F ₂ laser (wavelength 1 5 7 nm), or A r ₂ laser (wavelength 1 2 6 nm) in the vacuum ultraviolet region such as an exposure light ( An exposure optical system (not shown), a reticle stage 70 for driving a reticle, a projection optical system PLA, a wafer stage 71 for driving a wafer as a substrate to be exposed, and a wafer base. The pattern of the reticle R1 is transferred to each shot area on the wafer W1 via the projection optical system PLA. Similarly, the other projection exposure apparatuses 68 B and 68 C transfer the patterns of the reticles R 2 and R 3 to the respective shot areas on the wafers W 2 and W 3 via the projection optical systems PLB and PLC.

The gas in the optical path of the exposure light of these projection exposure apparatuses 68A to 68C is replaced by a purge gas that transmits the exposure light. Further, each of the projection exposure apparatuses 68 A to 68 C is provided with a reticle loader system 73, and a reticle opening system 73 is provided with a slider 6 moving along a transfer line 66. When a clean case 8B loaded with a reticle is received from 7, a reticle with a pellicle stretched out is taken out of the clean case 8B in an atmosphere of purge gas, and the reticle is placed on a reticle stage.

Place it on 70. Further, the reticle loader system 73 stores the used reticle in a normal case (the same case as case 3), and transfers the normal case through a reticle storage line via a return transport line (not shown). 6 Return to 2.

Further, the foreign matter inspection device 69 receives, for example, a laser light source 74, a scanner 75 scanning a laser beam from now on, and reflected light from a reticle R 4 to be inspected via a lens system 76. It is equipped with a photoelectric detector 77 and a stage device 78 that moves the reticle R 4 in a direction intersecting the scanning direction of the laser beam, and checks whether there is any foreign matter exceeding an allowable level on the pattern surface of the reticle R 4. inspect. The foreign matter inspection device 69 also includes a reticle loader system 79 that takes out a reticle from the clean case 8B received from the slider 67 of the transfer line 66 and installs the reticle on the stage device 78.

In the present embodiment, the reticle R, which has been inspected for foreign matter by the foreign matter inspection device 69, may be returned to the clean case. In this case, the reticle R may be transported again to the projection exposure apparatus via the transport line 66. Or, inspected The returned reticle R may not be returned to the clean case, but may be installed directly on the reticle stage 70 of the projection exposure apparatus from the foreign matter inspection device 69. When the reticle R is installed on the reticle stage 70 directly from the foreign matter inspection device 69, the transport path of the reticle R may be shielded from the outside air and set to a purge gas atmosphere.

Further, between the reticle storage device 62 and the reticle purifying device 64, and between the reticle purifying device 64 and the transfer line 66, a multi-joint robot for transferring the reticle and the clean case respectively. Hands 63 and 65 are installed. A host computer that controls the operations of the mouth pot hands 63, 65, the reticle cleaning device 64, the slider 67, the projection exposure devices 68A to 68C, and the foreign material inspection device 69. 6 1 are provided. Although not shown, a transfer line and a wafer loader system of FIG. 8 are also provided.

In the photolithography process for manufacturing semiconductor devices using the device manufacturing system of this example, the reticle with a pellicle in a normal case (for example, case 3A) in a reticle stocker 62 in an atmospheric environment is The reticle carried into the reticle cleaning device 64 via the loader 21 and the loader 21 is replaced with a purge gas and subjected to light cleaning.The reticle is highly airtight and has a clean case 8A with little organic contamination. After being loaded, it is conveyed to any of the projection exposure apparatuses 68 A to 68 C via the robot hand 65 and the slider 67. Then, the reticle in the clean case 8A is loaded on the reticle stage 70 by the reticle loader system 73 without being exposed to the atmosphere, and exposure is performed.

Then, the reticle used in the projection exposure apparatuses 68 A to 68 C is stored in a normal case as an example and returned to the reticle stocker 62. In addition, the reticle cleaning device 64 has a mechanism to store the reticle in the clean case in the normal case, and the reticle used in the projection exposure device 68 A to 68 C is cleaned again. It may be stored in a case and returned to the reticle cleaning device 64, where it may be taken out of the clean case and stored in a normal case, and this case may be returned to the reticle stocker 62.

In addition, especially for mass-produced products having fine patterns such as memories, the number of semiconductor wafers that can be exposed with one type of reticle is large, so the reticle replacement frequency is low. You don't have to. Therefore, in the projection exposure apparatus 68 A to 68 C for a fine pattern using vacuum ultraviolet light as exposure light, the frequency of reticle replacement and the frequency of reticle cleaning using the reticle cleaning apparatus 64 are low. Therefore, by associating a plurality of projection exposure apparatuses 68 A to 68 C with one reticle purifying apparatus 64, the number of reticle purifying apparatuses 64 installed can be reduced, and production line costs can be reduced. It is possible to reduce it.

In the present embodiment, a transfer line 66 is disposed near the reticle cleaning device 64, and the clean case loaded with the reticle is transferred to a plurality of exposure apparatuses via the transfer line 66. However, the reticle cleaning device 64 may be configured to be able to run on its own. That is, the reticle cleaning device 64 may have a function of an unmanned transporter (AGV: Automated Guided Vehicle) for transporting the reticle case. In this case, the clean case can be directly transferred from the reticle cleaning device 64 to a plurality of exposure devices.

Note that a plurality of reticle cleaning devices 64 may be provided corresponding to each of the plurality of exposure devices.

In addition, when replacing the purge gas in the reticle atmosphere, particularly when replacing the purge gas in the pellicle space, a high-speed gas flow is generated in the pellicle space, and consequently foreign substances such as dust adhering to other parts are removed from the reticle space. There is a risk of flowing on the pattern surface. Therefore, after purging of the reticle atmosphere with the reticle purifying device 64 shown in FIG. 4, the purified reticle is transported to the foreign material inspection device 69, where the particle surface is inspected for foreign matter. It is desirable to carry out. Alternatively, the foreign matter inspection function may be incorporated in the reticle cleaning device 64. For this purpose, for example, a foreign substance inspection apparatus similar to the foreign substance inspection apparatus 69 in FIG. 4 may be installed in the loader chamber 30 of the reticle cleaning apparatus in FIG.

The present invention is applicable to a case where a proximity exposure apparatus that exposes a mask pattern by bringing a mask into close contact with a substrate without using a projection optical system is also used as an exposure apparatus in the device manufacturing system of this example. can do.

The reticle purifying apparatus of the embodiment shown in FIG. 1 includes a purge gas replacement chamber 24, a lamp chamber 26, a loader chamber 30, and a plurality of airtight chambers inside the housing 23. Separately into the clean room loading chamber 35, mechanical components are incorporated into each hermetic chamber, and these multiple hermetic chambers are connected to the vacuum pump 42 and the purge gas supply source 43 by piping. It can be manufactured by connecting the unit and the control system 41 with wiring, and then performing overall adjustment (electrical adjustment, operation confirmation, etc.). It is desirable to manufacture the reticle purifier in a clean room where the temperature and cleanliness are controlled.

Next, an example of a manufacturing process for manufacturing a semiconductor device on a wafer using the device manufacturing system of the above embodiment will be described with reference to FIG.

FIG. 5 shows an example of a manufacturing process of a semiconductor device. In FIG. 5, first, a wafer W is manufactured from a silicon semiconductor or the like. Thereafter, a photoresist is applied on the wafer W (step S10), and the wafer W is loaded on, for example, a wafer stage of a projection exposure apparatus 68A (scanning exposure method) in FIG. In the next step S12, the reticle R1 taken out from the reticle storage force 62 of FIG. 4 is loaded onto the reticle stage of the projection exposure apparatus 68A via the reticle cleaning apparatus 64. Then, the reticle R1 is moved below the illumination area, and the pattern of the reticle R1 is scanned and exposed on all the shot areas SE on the wafer W. The wafer W is, for example, a wafer having a diameter of 300 mm (12-inch wafer). The size of the shot area SE is, for example, 25 mm in the non-scanning direction and 33 mm in the scanning direction. This is a rectangular area. Next, in step S14, a predetermined pattern is formed in each shot region SE of the wafer W by performing development, implantation of an etching zone, and the like. Next, in step S16, a photoresist is applied on the wafer W, and the wafer W is loaded again on the wafer stage of the projection exposure apparatus 68A in FIG. Thereafter, in step S18, another reticle R2 taken out of the reticle stocker 62 is loaded onto the reticle stage of the projection exposure apparatus 68A via the reticle cleaning apparatus 64. Then, the reticle R2 is moved below the illumination area, and the pattern of the reticle R2 is scanned and exposed on each shot area SE on the wafer W. Then, in step S20, a predetermined pattern is formed in each shot region of the wafer W by performing development of the wafer W, implantation of an etching zone, and the like. The above exposure process to pattern formation process (Step S16 to Step S20) Is repeated as many times as necessary to produce the desired semiconductor device. Then, through a dicing process (step S22) for separating each chip CP on the wafer W one by one, a bonding process and a packaging process (step S24), a semiconductor device as a product is obtained. SP is manufactured.

The application of the device manufacturing system of the present invention is not limited to semiconductor device manufacturing. For example, a liquid crystal display element formed on a square glass plate, or an exposure apparatus for a display device such as a plasma display, It can be widely applied to the process of manufacturing various devices such as imaging devices (such as CCDs), micro machines, thin film magnetic heads, and DNA chips. Further, the present invention can be applied to an exposure step (exposure apparatus) when manufacturing a mask (photomask, reticle, or the like) on which mask patterns of various devices are formed using a photolithography process.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention. In addition, all disclosures in Japanese Patent Application No. 2000-1991-1988 filed on February 22, 2000, including the specification, claims, drawings, and abstract Is incorporated herein by reference as it is. Industrial applicability

According to the present invention, since the mask after the light cleaning is loaded in an airtight case filled with a gas that transmits the exposure beam, the mask is placed in a different place from the exposure main body (exposure apparatus). Can be efficiently cleaned, and the cleaned mask can be transported to the exposure main body in a state where no foreign matter adheres.

When the gas in the space surrounded by the mask and the dustproof member (pellicle) is also replaced by a gas that transmits the exposure beam, even if the mask provided with the dustproof member is used, the gas transmitted through the exposure beam is not removed. The rate can be prevented from lowering.

Claims

The scope of the claims

1. A mask cleaning method for cleaning a mask to which a dustproof member is attached so as to cover a pattern surface and is irradiated with a predetermined exposure beam at the time of exposure, wherein the gas in a predetermined range of space surrounding the mask is exposed to light. A first step of replacing the beam with a gas that is permeable,

A second step of optically cleaning the mask with ultraviolet light;

A third step of loading the mask in a hermetically sealed state into a gas-tight case filled with a gas that transmits the exposure beam.

2. The mask cleaning method according to claim 1, wherein the first and second steps are performed simultaneously.

3. The mask cleaning method according to claim 1, wherein the first step further comprises replacing a gas in a space between the pattern surface and the dustproof member with a gas that transmits the exposure beam. .

4. A mask cleaning device for cleaning a mask to which a predetermined exposure beam is irradiated at the time of exposure while a dustproof member is attached so as to cover a pattern surface, wherein the gas in a predetermined range surrounding the mask is exposed to the gas. A gas replacement mechanism for replacing the beam with a gas that passes therethrough,

An ultraviolet irradiation device for optically cleaning the mask,

A masking mechanism for mounting the mask in a hermetically sealed state in a case filled with a gas that transmits the exposure beam and having airtightness.

5. The ultraviolet irradiation device and the gas replacement mechanism are at least partially integrated,

5. The gas mask cleaning apparatus according to claim 4, wherein a transfer system for transferring the mask is provided between the gas replacement mechanism and the loading mechanism.

6. The mask purifying apparatus according to claim 4, wherein the gas replacement mechanism has an airtight chamber for accommodating the mask, and a pressure reducing mechanism for reducing the pressure in the airtight chamber.

7. The gas replacement mechanism has an airtight chamber for accommodating the mask, a gas supply / exhaust mechanism for exhausting gas in the airtight chamber, and supplying a gas transmitting the exposure beam to the airtight chamber by flow control. The mask purification device according to claim 4 or 5, wherein

8. The dustproof member is fixed to the mask via a support frame, and the gas replacement mechanism also exposes the inside of a closed space surrounded by the mask, the dustproof member, and the support frame. 6. The mask cleaning apparatus according to claim 4, wherein the gas is replaced by a gas that transmits the beam.

9. The mask cleaning apparatus according to claim 4, wherein the gas replacement mechanism further replaces a gas in a space between the pattern surface and the dustproof member with a gas that transmits the exposure beam. .

10. A frame that holds the dustproof member and is attached to the pattern surface.

The gas replacement mechanism replaces a space between the dust pad and the dustproof member with a gas that transmits the exposure beam, through a ventilation hole formed in the frame. 10. The mask purification device according to claim 9.

1 1. In a device manufacturing system that forms a device pattern on a single piece,

Mask cleaning device according to any one of claims 4 to 10,

An exposure apparatus main body that transfers the image of the device pattern onto the mask piece; and a transport device that transports the mask that has been cleaned by the mask cleaning apparatus between the mask cleaning apparatus and the exposure apparatus main body. Device manufacturing characterized by having

12. The device manufacturing system according to claim 11, wherein the exposure apparatus main body has a mask removal mechanism for removing the mask loaded in a case by the mask cleaning device. .

13. The device manufacturing device according to claim 11, wherein the mask cleaning device is shared by a plurality of the exposure apparatus main bodies. twenty four

1. In a device manufacturing method for forming a device pattern on a work piece, a mask provided with a dust-proof member so as to cover a pattern surface is air-tightly sealed by using the mask cleaning method according to claim 1 or 2. A first step of loading into a flexible case,

A third exposing main body that accommodates the cleaned mask in the case and conveys the substrate to the exposing main body, exposing a substrate with an exposing beam through the mask taken out of the case; And a device manufacturing method.

15. The device manufacturing method according to claim 14, wherein a mask purifying unit that purifies the mask is shared by a plurality of the exposure main units.