JP2011006746A - Method for depositing multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a dispersion in the reflectance for each product when manufacturing a multi-layered film reflecting mirror containing a multi-layered film of Mo and Si.SOLUTION: In a process of depositing a reflecting multi-layered film by alternately sputtering targets 11, 12 of Mo and Si, the internal stress of a Mo layer is changed according to the value of the water partial pressure of atmospheric gas in a vacuum chamber 1 to cause dispersion in the reflectance for each product. In order to reduce the dispersion, in the film deposition process of the Mo layer, the value of water partial pressure of atmospheric gas in the vacuum chamber 1 is controlled to be constant by adjusting the mixing ratio of argon 22 of high purity to be introduced in the vacuum chamber 1 and argon 23 with 0.1% water being added thereto, thereby preventing the reflectance of the multi-layered film from being changed for each lot.

Description

  The present invention relates to a multilayer film forming method for forming a multilayer film such as a multilayer film reflecting mirror.

  In recent years, with the progress of miniaturization of semiconductor integrated circuit elements, lithography technology using soft X-rays (11 to 14 nm) instead of conventional ultraviolet rays has been developed. An optical system using a reflecting mirror is used for light having such a wavelength in the X-ray region, but since the refractive index is close to 1, the reflectivity is very low and most of the X-rays are transmitted. Or it will be absorbed.

  In order to solve this problem, multilayer reflectors have been developed. This is because a material having a large difference between the refractive index in the X-ray wavelength region and the refractive index of vacuum (= 1) and a material having a small difference are alternately laminated to provide a large number of reflecting surfaces at each interface. A multilayer film in which the thickness of each layer is adjusted based on the optical interference theory so that the phases of the reflected waves from the light wave coincide.

  As typical examples of such multilayer mirrors, combinations of W (tungsten) / C (carbon), Mo (molybdenum) / Si (silicon), and the like are known. And these multilayer films are produced by thin film formation techniques, such as sputtering, vacuum evaporation, and CVD.

  However, for example, when a multilayer reflector made of Si and Mo is formed by a sputtering apparatus, the Si layer has a large compressive stress, and the internal stress of the Mo layer varies from a compressive stress to a weak tensile stress depending on the process conditions. . Further, the respective materials are interdiffused at the interface between Si and Mo to form a diffusion layer of Mo and Si, and this diffusion layer also has compressive stress. Therefore, this reflective optical element has the sum of the stress of Si, the stress of Mo, and the stress generated in the diffusion layer of Mo and Si.

  Since the stress generated by the multilayer film formation is replaced as a deformation of the substrate, in a highly designed semiconductor exposure apparatus, the incident angle of light incident on the designed optical element is changed and the wavefront is changed. . This is a serious problem in a semiconductor exposure apparatus.

  In particular, when a multilayer film having a high reflectance is formed, a sputtering method is used. However, when the sputtering method is used, it is known that the formed thin film has an internal stress due to the implantation effect of high energy particles in the plasma.

  When such an internal stress is present, aberration occurs when used in an optical system in which a multilayer mirror is combined. In order to solve this problem, the first multilayer film layer including the Mo layer and the Si layer and the second multilayer film layer including the Mo layer and the Si layer are configured so as to cancel the internal stress. A method for reducing the stress by changing the γ ratio of the multilayer film layer 2 has been proposed (see Patent Document 1). There has also been proposed a method for changing the γ ratio of the second multilayer layer according to the in-plane stress distribution parallel to the substrate.

JP 2007-59743 A

  However, it has been difficult to realize the reduced internal stress value with good reproducibility by the above conventional technique. That is, when a film is formed under the same process conditions using only high-purity argon as a sputtering gas in a conventional sputtering apparatus, there is a problem that the internal stress value of the multilayer film varies with the elapsed film formation time.

  FIG. 5 shows a graph in which the number of deposition lots when a multilayer film is formed by a sputtering apparatus, the measured moisture pressure during deposition, and the internal stress value of the deposited multilayer film are shown. The horizontal axis of this graph shows the film formation after opening the film formation chamber of the sputtering device to the atmosphere, exhausting the film formation chamber sufficiently with a vacuum pump, attaching a dummy substrate, and performing the aging process in the same process as the actual It is the number of lots. The vertical axis on the left side of the graph is a plot of the water pressure during multilayer film formation, and the water pressure gradually decreases as the number of deposition lots increases. This is because when a multilayer film is formed by sputtering, the sputtered particles reach the chamber walls other than the substrate, and a metal film of Mo or Si is formed. It is caused by adsorbing water.

  The vertical axis on the right side of the graph is a plot of the stress value obtained from the substrate deformation amount of the multilayer film formed in each lot, which may gradually change from the tensile stress to the compressive stress side as the number of deposition lots increases. Recognize.

  An object of the present invention is to provide a multilayer film forming method capable of avoiding the performance of the multilayer optical element from being varied for each product due to fluctuations in the internal stress value of the multilayer film.

  The multilayer film deposition method of the present invention is a multilayer film deposition method in which a plurality of target materials are sputtered in a deposition chamber, and Mo layers and Si layers are alternately deposited on a substrate. It is characterized by having a step of controlling the moisture pressure value in the film formation chamber to be constant when the Mo layer is formed by introducing the film into the film formation chamber.

  In the step of forming the Mo layer of the multilayer film, the moisture pressure value of the atmospheric gas in the film forming chamber is kept constant, thereby reducing variations in optical element performance due to fluctuations in the internal stress value.

It is the schematic which shows the sputtering device which concerns on one Embodiment. It is a graph which shows the relationship between the state which attached the film | membrane stress evaluation apparatus to the sputtering device of FIG. 1, and the water pressure and Mo layer stress which were experimented by film | membrane stress evaluation. It is a graph which shows the relationship between the water pressure and stress by film | membrane stress evaluation, and the graph which shows the relationship between the water pressure and the reflectance of a Mo / Si multilayer film. It is a graph which shows the number of film-forming lots which carried out the continuous film-forming, and the stress value of a multilayer film. It is a graph which shows the film-forming lot frequency by one prior art example, and the stress value of a multilayer film.

  The sputtering apparatus shown in FIG. 1 includes an exhaust system 2 that exhausts a vacuum chamber 1 that is a film forming chamber, a gas supply system 3 that supplies a sputtering gas into the film forming chamber, and a power source 4 that supplies sputtering power to a plurality of cathodes. And having. The power source 4 may be connected to each cathode, or may be of a type that supplies power only to the cathode to be used by using a switch with one power source.

  Inside the vacuum chamber 1, a cathode unit 5 having a cathode to which a plurality of target materials are attached, and a substrate holder unit 7 for forming a film while rotating the substrate 6 are arranged. The cathode unit 5 is supported from the bottom and top surfaces of the vacuum chamber 1 via magnetic seals 8 and 9, and a cathode drive system 10 is disposed below the magnetic seal 9.

  A plurality of electrically insulated cathodes are disposed on the side surface of the polygonal column cathode unit 5, and Mo and Si targets 11 and 12 are attached thereto. Each cathode is provided with a shutter and can be opened and closed independently. The cathode rotating shaft 13 is hollow, and cathode cooling water, sputtering power supply cable, sputtering gas, shutter driving air, and the like are supplied therein. With such a configuration, it is possible to switch to a desired target and perform sputtering to form a multilayer film.

  In the substrate holder unit 7, a substrate holder 14 that holds the substrate 6 is fixed to the tip of the rotating shaft 15. The rotating shaft 15 is rotationally driven by a motor 17 via a magnetic seal 16.

  A load lock chamber 19 is installed outside the vacuum chamber 1 through a gate valve 18. The load lock chamber 19 is provided with a load lock exhaust system 20 for exhausting the load lock chamber and a transport system 21 for transporting the substrate from the load lock chamber 19 to the vacuum chamber 1.

  In the gas supply system 3, high-purity argon 22 as a first sputtering gas and argon 23, which is a second sputtering gas obtained by adding 0.1% of water to high-purity argon, are introduced into the vacuum chamber 1, respectively. A tank is installed. Connected to the stainless steel pipe of the gas supply system 3 are mass flow controllers 24 and 25 for controlling the gas flow rate and a valve for supplying or stopping the sputtering gas.

  During film formation using this apparatus, the atmospheric gas released from the vacuum chamber 1 has a great influence on the internal stress of the multilayer film, and in particular, there is a strong correlation with water among the released gas species components. I understood.

  A film stress evaluation apparatus using an optical insulator shown in FIG. 2 (a) in order to investigate the influence of the moisture pressure value of the atmospheric gas during the film formation when the Mo layer and the Si layer are alternately formed on the substrate. Was attached to the apparatus of FIG. 1 and the film stress was measured. The substrate 6 of FIG. 1 is replaced with a stress measurement holder 27, and a thin stress evaluation glass substrate 28 fixed to the holder in a cantilever manner is attached to the stress measurement holder 27. A laser 30 is installed on the atmosphere side.

  The laser beam 31 emitted from the laser 30 is reflected by the glass substrate 28. The reflected laser reflected light 32 passes through the introduction window 33 and is projected as a spot on the screen 34. The spot is copied by the image processing camera 35, and the center of gravity of the spot is stored as position data by the image processing system 36.

  When a film is formed on the glass substrate 28 fixed in a cantilever manner, the film is deformed by the internal stress of the film. The reflection angle of the laser reflected light 32 changes due to the deformation of the substrate due to the internal stress of the film, and the reflected spot on the screen moves. The compression or tensile stress value of the deposited material can be measured while forming a film according to the moving change amount and moving direction of the laser spot with respect to the film thickness formed on the glass substrate 28.

FIG.2 (b) is a graph when the water pressure value during Mo film-forming is changed with the stress evaluation apparatus of (a). As can be seen in this graph, the tensile stress in the water pressure value is 6 × 10 -6 ^Pa indicates a peak value, tensile stress values and further increase the water pressure value gradually decreases, water pressure value 1 × 10 ^{- When} it exceeds ⁶ Pa, it becomes a compressive stress.

In FIG. 3A, the water pressure value is changed during the Si film formation by the same method as described above, and the water pressure value (H ₂ O partial pressure value) is constant (1 × 10 ⁻⁶ Pa during the Mo film formation). It is a graph when it forms into a film, keeping it. As a result of measuring the reflectance of the multilayer film sample manufactured in this experiment, as shown in FIG. 3B, the reflectance tends to decrease when the moisture pressure value is high.

From the above experimental results, the stress of the Mo layer varies depending on the moisture pressure value, and the stress of the Si layer is a substantially constant compressive stress regardless of the moisture pressure value, and considering the reflectance of the multilayer film, the moisture pressure of the Si layer We found that the lower the value, the better. In addition, the Mo layer exhibits a peak value of tensile stress at a moisture pressure value of 6 × 10 ⁻⁶ Pa, and when the moisture pressure value exceeds 1 × 10 ⁻⁶ Pa, the Mo layer shifts to compressive stress.

  From the above, the internal stress value of the multilayer film fluctuated with the elapsed time of multilayer film formation because the moisture pressure change in the vacuum chamber affected the stress value of the Mo layer. I found out that Therefore, in the multilayer film forming method of the present invention, the internal stress of the multilayer film is controlled by the following method.

  First, after performing an air release operation in the chamber for target replacement, maintenance of chamber internal parts, etc., the exhaust system 2 is sufficiently evacuated. When the degree of vacuum reaches a set value, an aging process is performed in which film formation is performed by introducing only high-purity argon 22 as a sputtering gas from the gas supply system 3 under the same conditions as those for forming an actual multilayer film. The purpose of the aging process is to suppress degassing by depositing Mo or Si having a gettering effect on the inner wall of the chamber because the exhaust of the exhaust system 2 mainly involves degassing of water mainly from the inner wall of the chamber.

When the aging process is completed, the moisture pressure becomes about 1 × 10 ⁻⁶ Pa, and the film can be formed. After loading the substrate into the load lock chamber 19, the exhaust system 2 performs an exhaust operation. When the evacuation operation is completed, the gate valve 18 is opened, the substrate 6 is transferred to the vacuum chamber 1 by the transfer system 21, and the multilayer film forming process is started.

As the first layer of the multilayer film, a Si layer is formed using only high-purity argon 22. After the first Si layer is formed, the cathode drive system 10 is operated to switch the target to Mo. After the target switching operation is completed, the water pressure is measured, and the flow rate ratio between the high purity argon 22 and the argon 23 added with 0.1% water is adjusted so that the water pressure value becomes 6 × 10 ⁻⁶ Pa. The deposition of the second Mo layer is started so that the argon flow rate becomes constant.

In order to control the moisture pressure, it is necessary to introduce a very small amount of water, and a mass flow controller currently used cannot control a flow rate of 0.1 sccm or less. For this reason, as described above, the moisture pressure is controlled by adjusting the flow rate ratio (mixing ratio) of high purity argon and argon added with 0.1% of water. In the above experiment, since the moisture pressure value is 1 × 10 ⁻⁶ Pa when the aging process is completed, in order to control the water pressure to 6 × 10 ⁻⁶ Pa, the flow rate of the high purity argon 22 is set in the first lot film formation. The flow rate of argon 23 to which 96 sccm and 0.1% of water were added was 4 sccm. Such film formation was repeated about 100 layers to form a multilayer film.

Control range of the water pressure value of Mo layer, the vacuum chamber 1 because the water pressure value in a state after the completion of the air release and aging process is approximately ^{1 × 10 -6 Pa, 1 ×} 10 -6 Pa or more, Mo layer Is 1 × 10 ⁻⁴ Pa or less, which changes from tensile stress to compressive stress. It is preferable that the tensile stress value is controlled to be constant at 6 × 10 ⁻⁶ Pa at which the tensile stress value is maximized. Since the moisture pressure value of the Si layer does not affect the film stress, it is preferably 1 × 10 ⁻⁶ Pa or less so that a high reflectance can be obtained.

  FIG. 4 is a graph in which the stress value inside the multilayer film is measured when several lots of the multilayer film are continuously formed by the film forming method described above. As can be seen from this graph, by controlling the moisture pressure when forming the Mo layer, the stress value of the multilayer film can be made constant regardless of the number of deposition lots.

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Exhaust system 3 Gas supply system 11, 12 Target 22 High purity argon 23 Argon which added water 0.1%

Claims (3)

In a multilayer film forming method in which a plurality of target materials are sputtered in a film forming chamber, and Mo layers and Si layers are alternately formed on a substrate.
Introducing a sputtering gas to which water has been added into the film forming chamber, the method includes a step of controlling the moisture pressure value in the film forming chamber to be constant when forming the Mo layer. Membrane method. Controlling the moisture pressure value in the film formation chamber when forming the Mo layer to 1 × 10 ⁻⁶ Pa or more and 1 × 10 ⁻⁴ Pa or less;
2. The multilayer film forming method according to claim 1, further comprising: controlling a moisture pressure value in the film forming chamber to 1 × 10 ⁻⁶ Pa or less when forming the Si layer.   The moisture pressure value in the film formation chamber when the Mo layer is formed is determined by introducing a first sputtering gas to which water is not added and a second sputtering gas to which water is added into the film formation chamber. 3. The multilayer film forming method according to claim 1, wherein the multilayer film forming method is controlled by adjusting a mixing ratio between the first sputtering gas and the second sputtering gas.

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