Patent Application
20070097342
The present invention relates to an exposure apparatus and method that expose a substrate to exposure light via an original, and a device manufacturing method.
A reduction projection exposure apparatus using ultraviolet (UV) light is currently used in leading-edge lithography for manufacturing a fine semiconductor element of a memory or logic circuit. Along with an increase in the degree of integration of a semiconductor element, the element often has a line width of 50 nm or less but lithography using UV light may not be able to provide sufficient resolving power. To combat this situation, lithography using EUV (Extreme Ultraviolet) light, with a shorter wavelength of 11 to 15 nm, is under development.
Unlike UV lithography, EUV lithography cannot use a transmissive optical element using refraction because EUV light exhibits high absorbance. EUV lithography thus uses a reflective optical element, the surface of which has a multilayer film in which two types of materials having different optical constants are alternately stacked. EUV light having a wavelength of 13.5 nm or in its vicinity is reflected by a reflective optical element having a glass-based substrate surface which is polished into a precise shape and in which molybdenum (Mo) and silicon (Si) are alternately stacked efficiently. An EUV exposure apparatus causes a reduction projection optical system including such a reflective optical element to form a mask pattern image on the wafer.
Since the ambient gas component also absorbs EUV light, the exposure apparatus maintains its interior in an appropriate vacuum state. Gas containing moisture and a caboaceous substance remains in that vacuum atmosphere. The gas containing these substances mainly results from the parts or cables used in the exposure apparatus. The gas also contains a component which vaporizes from the resist (photosensitive material) applied on the wafer. The surface of the optical element adsorbs these residual gas components. Throughout the duration of stay on that surface, EUV light strikes the residual gas components. Since EUV light also has a high substance decomposition ability, it decomposes the caboaceous residual gas component on the surface into carbon, which deposits on that surface. Similarly, the EUV light decomposes the moisture on the surface into active oxygen, which oxidizes the surface material. The presence of carbon and oxygen on the surface allows it to absorb the EUV light in amounts which depend on their thicknesses. The absorption amount is non-negligible, and the reflectance of the optical element to EUV light deteriorates. A reduction projection optical system having excellent resolving power requires a large number of optical elements. Therefore, deterioration in reflectance per element synergistically decreases the amount of light which passes through the optical system. This prolongs the exposure time, resulting in degradation in performance of the exposure apparatus.
There have been proposals for preventing carbon deposition and removing the carbon deposits up to now. To prevent carbon deposition, it is a common practice to decrease the pressure of the target gas in the atmosphere in which the optical element is placed. The target gas is, e.g., a hydrocarbon such as methane, ethane, or propane, a straight-chain organic substance such as isopropyl alcohol or polymethyl methacrylate, or a cyclic organic substance such as phthalate ester (patent reference 1).
There is a proposal for removing deposited carbon in the following method (patent reference 2). This method irradiates the deposited carbon with UV light or EUV light having a wavelength shorter than 250 nm in an environment in which an oxygen-containing species selected from water, nitrogen oxides, and oxygen-containing hydrocarbons exists in the atmosphere in which the optical element is placed. There is also a proposal for removing the carbon in the following method (patent reference 3). This method introduces a processing gas containing at least one of the substances selected from the group consisting of gas of water, oxygen, ozone, and radical element, and irradiates the carbon with an electron beam.
A popular approach effective in preventing oxidation to some extent is to perform exposure after introducing ethanol in the atmosphere in which an optical element having a multilayer film, the uppermost layer of which is Si, is placed (non-patent reference 1). Also, a popular approach which can suppress EUV light absorption to some extent is to form a ruthenium (Ru) protective film on the uppermost layer of the multilayer film because Ru has an anti-oxidative property (non-patent reference 2).
[Patent Reference 1] Japanese Patent No. 3467485
[Patent Reference 2] Japanese Patent Laid-Open No. 2003-188096
[Patent Reference 3] Japanese Patent Laid-Open No. 2002-237443
[Non-patent Reference 1] L. Klebanoff, 2nd International EUVL Workshop, [online], Oct. 19-20, 2000, International SEMATECH Manufacturing Initiative, [searched Jun. 10, 2005], Internet <http://www.sematech.org/resources/litho/meetings/euvl/20001019/index.htm>
[Non-patent Reference 2] S. Bajt, H. Chapman, N. Nguyen, J. Alameda, J. Robinson, M. Malinowski, E. Gullikson, A. Aquila, C. Tarrio, S. Granthan, SPIE, 2003, Vol. 5037, p. 236
Problems that the Invention is to Solve
Ru film, which is thought to be the most promising protective film as a multilayer film, at present deteriorates in reflectance of EUV light when an EUV light irradiation experiment in an environment, in which the caboaceous residual gas component exists in small quantities and the exposure apparatus introduces moisture to simulate its environment, promotes oxidation of the Ru film. It is common knowledge that degradation in exposure capability resulting from the deterioration in reflectance is unallowable for an exposure apparatus in practical use.
The present invention has been made in consideration of the above subject, and has as its object to provide a novel technique for reducing at least the former of the oxidation of a ruthenium (Ru) film and the deposition of carbon onto the ruthenium film.
Means of Solving the Problems
According to the first invention, there is provided an exposure apparatus which exposes a substrate to exposure light via an original, characterized by comprising:
According to the third invention, there is provided a device manufacturing method characterized by comprising a step of exposing a substrate to exposure light using an exposure apparatus according to the first invention to expose a substrate.
According to the fourth invention, there is provided an exposure apparatus which exposes a substrate to exposure light via an original, characterized by comprising:
According to the fifth invention, there is provided an exposure method of exposing a substrate to exposure light via an original, characterized by comprising:
According to the sixth invention, there is provided a device manufacturing method characterized by comprising a step of exposing a substrate to exposure light using an exposure apparatus according to the fourth invention to expose a substrate
Other objects, features, and effects of the present invention will become apparent from the following description taken with reference to the accompanying drawings. Note that the same or similar reference numerals denote the same or similar constituent component throughout a plurality of drawings.
The present invention can provide a novel technique for reducing at least the oxidation of a ruthenium film, and possibly the deposition of carbon onto the ruthenium film.
(First Embodiment)
To coat the optical element used for each of the mask 20, illumination optical system 16, and projection optical system 22 with a multilayer film, it is a common practice to obtain the film by depositing about 50 pairs of Si and Mo as described above. A vacuum container 2 accommodates the wafer 26, mask 20, illumination optical system 16, projection optical system 22, mask stage 18, and wafer stage 26. An exhaust means 28 such as a turbo molecular pump temporarily exhausts gas in the vacuum container until it obtains a pressure of around 10−5 to 10−6 Pa. After that, a gas introduction system 30 introduces moisture into the vacuum container until it obtains a predetermined pressure. The exposure apparatus 1 executes exposure while maintaining that state. The characteristic feature of this embodiment is to continuously introduce moisture at a predetermined pressure into the atmosphere in which the optical element is placed, while the exposure apparatus is in operation. When a filter or a path with a very low conductance is to further segment the space in the vacuum container, it suffices to mount the exhaust system 28 and gas introduction system 30 to an appropriate place.
The gas introduction system 30 can supply a plurality of gasses where necessary.
The present invention has been conceived in the process of an acceleration test to be described below. The intensity of EUV light which strikes the projection optical system 22 of the exposure apparatus largely varies within the range of 0.2 to 20 mW/cm2 depending on the optical element in question. The projection optical system of the exposure apparatus desirably has a life of several years or equal to that of the exposure apparatus. An acceleration test which used 10 W/cm2 EUV light around 500 times the high-intensity irradiation with which a mirror is ordinarily irradiated was conducted. This experiment measured the spectrum of the residual gases after evacuating, for several days, the vacuum container used. The measurement result revealed that the major component of the residual gases having a total pressure value of 7×10−5 Pa was water having a mass number of 18. It is a common practice to define 55 as the mass number of a caboaceous gas component which influences the Ru surface upon EUV irradiation. The content of a caboaceous gas component having a mass number of 55 was around 1/10,000 that of water having a mass number of 18. The caboaceous component resulted from the parts or cables used in the laboratory equipment. However, a caboaceous component may exist in the vacuum container 2 of the exposure apparatus as well, even though it might be different in amount from that of the laboratory equipment. To confirm this, EUV light was introduced into the above-described atmosphere so as to irradiate an Mo and Si multilayer film substrate (optical element sample) having an uppermost layer of 2 nm Ru added.
The experimental result revealed that the irradiation center maintained 99% of the initial reflectance even though it received 2.3×105 J/cm2 light. 2.3×105 J/cm2 corresponds to irradiation of 1.2×107 sec (about 3,300 hours) even when an optical element is assumed to be illuminated with 20 mW/cm2. To check the reason why the irradiation center maintained its reflectance in this manner, a method using an Auger electron spectroscope and ion sputtering was used to test the elementary composition of the irradiation position along its depth direction.
It is a fundamental knowledge that an acceleration test requires an increase not only in illuminance but also in the pressure of the moisture. For this purpose, this test introduced moisture next until the total pressure became 1×10−2 Pa to execute an irradiation experiment. This experiment was continued until the irradiation amount became 700 J/cm2. The reflectance of the irradiation center maintained 99% of the initial value as was expected. Detailed evaluation revealed that a caboaceous gas having a mass number of 55 was introduced in proportion to the amount of water introduced. The fact that the irradiation center maintained the reflectance of the EUV light even under that influence indicates that the present invention is widely effective. The material characteristic of Ru supports the probability that a thin carbon protective film forms on the Ru surface depending on the quantity relationship between the caboaceous component and the moisture which exists in the atmosphere in which the optical element is placed. That is, deposition of a thin carbon film on the Ru surface allows the protection of the Ru against oxidation while minimizing decrease in reflectance.
This makes it effective to positively control the moisture content in the atmosphere in which the optical element is placed. An appropriate moisture content depends on the content of the caboaceous residual gas component which exists in the atmosphere. The appropriate moisture content also depends on the intensity of EUV light irradiated. Positively introducing a caboaceous gas component is also effective in producing an optimal state. Simultaneously irradiating EUV light and vacuum ultraviolet light is also effective in forming a protective film.
The experiments up to now showed that a thick carbon layer deposits on a region where the intensity of EUV light is very small, and the reflectance to the EUV light decreases as the deposition progresses. Therefore, it is desirable to select an appropriate method after answering the following questions.
i) Is it possible to produce a desirable effect only by controlling the introduced moisture content in accordance with the atmosphere and irradiation conditions in the exposure apparatus?
ii) Is it necessary to introduce both moisture and an appropriate caboaceous gas?
iii) Is it necessary to further irradiate with vacuum ultraviolet light?
For example, it is desirable to enable the setting of the exposure apparatus so as to produce a desired effect by decreasing, to a practically attainable range, the amount of caboaceous gas which is expressed by the mass number 55 and exists in the atmosphere in which the optical element of the exposure apparatus is placed, and introducing appropriate moisture. It is possible to introduce desired moisture free from any excessive mixture of a caboaceous gas expressed by the mass number 55 by considering the structure of the water supply system. For example, it is effective to use ultra-pure water in the water supply system and sufficiently exhausts gas in the water supply system while water is frozen.
The water pressure in the vacuum container regulated by the regulating means including the water supply system and gas introduction system is preferably 1×10−6 Pa (inclusive) to 1×10−2 Pa (inclusive) . 1×10−6 Pa is the lower limit value at which pressure regulating is practically executable. When the pressure value is less than that lower limit value, no effect of suppressing deposition of a carbon layer is expected. When the pressure value exceeds 1×10−2 Pa as the upper limit, adverse effects such as attenuation of the EUV light and oxidation of the surface of the optical element occur.
When the regulating means regulates the pressure of the caboaceous gas in the vacuum container, a gas to be supplied into the vacuum container is desirably at least one of either hydrocarbon or alcohol. At this time, the regulating means desirably regulates the gas in the vacuum container to 1×10−10 Pa (inclusive) to 1×10−6 Pa (inclusive) . 1×10−10 Pa is the lower limit value at which pressure regulating is practically executable. When the pressure value is less than that lower limit value, no effect of generating a carbon layer which suppresses oxidation of the surface of the optical element is expected. When the pressure value exceeds 1×10−6 Pa as the upper limit, adverse effects such as a decrease in reflectance of the optical element due to excessive deposition of the carbon layer occur.
Another embodiment according to the present invention will be explained next.
A vacuum container 2 of the EUV exposure apparatus incorporates not only a projection optical system but also a mask stage and wafer stage. For this reason, the residual gas component in the atmosphere of the vacuum container 2 will not become clear until the design and manufacture of the exposure apparatus is complete. Also, the residual gas component changes over time depending on the use status or the like. Therefore, the exposure apparatus includes a detector 31′ to detect the content of the residual gas component in the vacuum container 2. The detector 31′ may be, e.g., a quadrupole mass spectrometer. In this embodiment, the exposure apparatus further includes a caboaceous gas supply source 34 to supply a caboaceous gas into the vacuum container 2, in addition to a water supply source 33 to supply water (gas) into the vacuum container 2. The caboaceous gas can be selected from, e.g., a group of compounds specified as hydrocarbons or alcohols.
A controller 35 can regulate the water supply amount by controlling the degree of opening of a valve 32 on the basis of the content of the gas component detected by the detector 31′. The controller 35 can also regulate the supply amount of the caboaceous gas by controlling the degree of opening of a valve 32′ on the basis of the content of the gas component detected by the detector 31′. A storage device (memory) 36 stores information for determining the supply amount of at least one of water and caboaceous gas, e.g., information about the relationship between the water amount and the caboaceous gas amount. The memory 36 preferably stores the relationship information under each of a plurality of exposure conditions. The exposure conditions include, e.g., the exposure light (EUV light) irradiation condition or exposure light energy.
The relationship information can take, e.g., a table format which shows the correspondence between the water amount and the caboaceous gas amount, that is prepared for each exposure condition.
The operation of the EUV exposure apparatus according to this embodiment will be explained below with reference to
For example, it is possible to determine the relative quantity of the caboaceous residual gas component to the water on the basis of the contents of a gas component having a mass number of 18 (water) and a gas component having a mass number of 45 or more. In practice, the amount of a gas having a mass number of 55 often enables determination. As one example, it is possible to determine that the caboaceous residual gas component exists in large quantities when its content exceeds 1/10,000 that of the water (mass number: 18), and to determine that the caboaceous residual gas component exists in small quantities when its content is equal to or smaller than 1/10,000 that of the water. However, this determination criterion depends on the type of existing gas, and may also be a numerical value different from 1/10,000 of the water content.
As described above, it is preferable to calculate in advance an appropriate quantity relationship between the water and the caboaceous gas for each exposure condition by actually measuring the element distribution of the Ru film surface exposed with the EUV light in the vacuum container 2. The appropriate quantity relationship indicates one which allows to suppress the oxidation of the Ru film and to suppress the deposition of carbon onto the Ru film. The above-described storage device stores the calculated quantitative relationship. The controller 35 uses the stored quantity relationship to determine the supply amount of at least one of water and a caboaceous gas.
If the caboaceous residual gas component exists in large quantities, the controller 35 opens the valve 32 of the water supply means comprising the water supply source 33 to supply water into the vacuum container 2. At this time, the controller 35 automatically controls the degree of opening of the valve 32 so as to obtain a proper partial pressure of the water to retard the progress of oxidation of the Ru film. On the other hand, if the hydrocarbon-based residual gas component exists in small quantities, the controller 35 opens the valve 32′ of the caboaceous gas supply means comprising the caboaceous gas supply source 34 to supply a caboaceous gas (for example, at least one of a hydrocarbon and alcohol) into the vacuum container 2. At this time, the controller 35 automatically controls the degree of opening of the valve 32′ so as to obtain a proper partial pressure of the caboaceous gas to prevent carbon from excessively depositing on the Ru film.
When the supply amount or exhaust amount of the caboaceous gas decreases or increases so that the partial pressure of the caboaceous gas decreases to the requested value, the partial pressure of the water sometimes decreases at the same time. Additionally, appropriate amounts of water and caboaceous gas may optimally exert an effect of reducing oxidation and/or carbon deposition. In such cases, it is effective to introduce both water and a caboaceous gas into the vacuum container 2 so as to appropriately control their partial pressures.
In this manner, in step S63, the controller 35 determines the supply amount of at least one of water (gas) and a caboaceous gas on the basis of the content (partial pressure) of the residual gas component in the vacuum container 2 detected using the detector 31′. The determination refers to the above-described information about an appropriate quantity relationship between the water and the caboaceous gas for each exposure condition, which is calculated in advance and stored in the storage device 36.
Subsequently, in step S64, the controller controls the degree of opening of at least one of the valves 32 and 32′ on the basis of the determined supply amount of at least one of water and a caboaceous gas. This allows to supply at least one of water (gas) and a caboaceous gas into the vacuum container 2. The controller regulates its supply amount by the degree of opening of at least one of the valves 32 and 32′.
The above-described method reduces the deposition of carbon onto the Ru film in the vacuum container 2 or reduces both the deposition of carbon onto the Ru film and the oxidation of the Ru film. The exposure apparatus exposes a wafer (substrate) 26 in the vacuum container 2 via reflecting means (mirror) 16 and 22 and reflecting mask 20 in step S65.
This embodiment has exemplified the case in which the exposure apparatus has both the water supply source 33 and caboaceous gas supply source 34. However, it is conceivable that the content (partial pressure) of one of water (gas) and caboaceous gas is always larger than that of the other one in the vacuum container 2 depending on the apparatus arrangement and/or apparatus use condition. In this case, the exposure apparatus may have a necessary one of the water supply source 33 and caboaceous gas supply source 34.
A device manufacturing process using the above-described exposure apparatus will be explained next by taking a semiconductor device as an example.
In step 3 (wafer manufacture), a wafer (also called a substrate) is manufactured using a material such as silicon. In step 4 (wafer process) called a preprocess, the above-described exposure apparatus forms an actual circuit on the wafer by lithography using the mask and wafer. In step 5 (assembly) called a post-process, a semiconductor chip is formed from the wafer manufactured in step 4. This step includes processes such as assembly (dicing and bonding) and packaging (chip encapsulation). In step 6 (inspection), inspections including operation check test and durability test of the semiconductor device manufactured in step 5 are performed. A semiconductor device is completed with these processes and shipped in step 7.
The wafer process in step 4 includes the following steps: an oxidation step of oxidizing the wafer surface; a CVD step of forming an insulating film on the wafer surface; an electrode formation step of forming an electrode on the wafer by vapor deposition; an ion implantation step of implanting ions in the wafer; a resist processing step of applying a photosensitive agent to the wafer; an exposure step of causing the above-described exposure apparatus to expose the wafer having undergone the resist processing step; a development step of developing the wafer exposed in the exposure step; an etching step of etching portions other than the resist image developed in the development step; and a resist removal step of removing any unnecessary resist remaining after etching. By repeating these steps, a multilayered structure of circuit patterns is formed on the wafer.
This application claims the benefit of Japanese Patent Application No. 2005-255090 filed Sep. 2, 2005 which are hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-255090 | Sep 2005 | JP | national |
