JP2008095147A - Sputtering film deposition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the secular change of a film thickness distribution caused by target erosion. <P>SOLUTION: In the sputtering system for depositing a thin film on a substrate 10, while allowing a target 5 to be confronted with the substrate 10 and performing scanning, scan film deposition is carried out. During the scan film deposition, using two kinds of gases with different sputtering rates as sputtering gases, the gas flow rates of the two gases are controlled by first and second mass flow controllers 4a, 4b, respectively. The scan film deposition is carried out while the gas flow rate of the first gas with a low sputtering rate is always increased, and the gas flow rate of the second gas with a high sputtering rate is always reduced correspondingly to the secular change of the target shape caused by the erosion of the target 5, thus a film thickness change is prevented. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sputtering film forming method that enables highly accurate film thickness distribution control.

  A parallel plate type magnetron sputtering apparatus has been widely used as an apparatus for forming a thin film on a substrate. In this magnetron sputtering apparatus, a target, which is a thin film material, and a substrate attached to a substrate holder are arranged in a vacuum chamber (vacuum chamber) so as to face each other, and then plasma is generated to sputter the target. . Then, a thin film is formed on the substrate by depositing the sputtered particles knocked out by sputtering on the substrate.

  Such a magnetron sputtering method is simple and has superior characteristics compared to other methods in terms of high-speed film formation, large-area film formation, target life, and the like. In particular, in recent years, there has been a demand for increasing the size of the apparatus, high controllability of the film thickness, compatibility with automatic production machines, and the like, and there has been an increasing demand for forming a thin film by sputtering.

  For example, in the optical film field, particularly in a semiconductor exposure apparatus such as a stepper, a high NA is being promoted in order to improve the printing performance. For this reason, it is desired to increase the lens diameter and to improve the oblique incidence characteristics of light incident on the lens. Further, in the next generation X-ray (EUV) exposure apparatus, a large-diameter and high-precision inclined film (oblique incidence). There is an increasing demand for improvement of characteristics.

  More specifically, for example, an X-ray multilayer mirror made of molybdenum (Mo) and silicon (Si) using an X-ray wavelength of 13.4 nm has a very narrow bandwidth of reflection characteristics. For this reason, when the incident angle of the X-rays incident on the mirror surface changes, the reflection characteristics deteriorate.

  As one of these countermeasures, a method is adopted in which reflection mirror characteristics are adapted to the X-ray incident angle within the reflection mirror surface. However, in this method, it is necessary to control the film thickness distribution of molybdenum (Mo) and silicon (Si) with high accuracy in the reflecting mirror surface.

  Furthermore, the optical elements used in the exposure apparatus are diversified because they have a shorter wavelength and have irregular shapes such as aspheric surfaces, free-form surfaces, and parabolas. Therefore, more accurate film thickness control is required than before.

  For this reason, as described above, it is simpler than other methods, and even in sputtering apparatuses that are superior in high-speed film formation, large-area film formation, etc., optical elements used in the above exposure apparatus, etc. When the film is formed, more accurate film thickness distribution control is required.

Therefore, for example, in Patent Document 1, it is possible to control the film thickness with high accuracy in scan film formation by using a configuration having three or more control axes capable of independently controlling the relative positional relationship between the substrate and the target during film formation. A sputter apparatus has been proposed. In this device, multiple conditions are set so that the target and the substrate face each other and the distance is constant, and the film is deposited while scanning once or multiple times while controlling the staying time of the conditions. Highly accurate film thickness control is possible.
JP 2004-269988 A

  However, even in the sputtering apparatus according to the above-described conventional example, there is a case where satisfaction cannot be obtained in performing highly accurate film thickness control. In the above sputtering apparatus, when the target is sputtered by generating plasma, only the portion where high-density plasma exists on the target is scraped by sputtering, and erosion occurs in this portion. The erosion shape of the target becomes deeper as the film formation progresses.

  Such a change in the target shape changes the emission angle of the sputtered particles, which changes the film thickness distribution in the radial direction of the substrate.

  The present invention has been made in view of the above-mentioned unsolved problems, and provides a sputter film forming method that can control the film thickness distribution by erosion of the target and enables highly accurate film thickness control. It is intended to do.

  The sputter deposition method of the present invention includes a step of scanning and depositing a thin film on a substrate that moves relative to a target, and two types of gases selected from He, Ne, Ar, Xe, Kr, and Rn. Is supplied as a sputtering gas for the target, the scan film formation is performed while increasing the supply amount of one of the two kinds of gases and decreasing the supply amount of the other gas.

  By changing the supply amounts of two kinds of gases having different sputtering rates in accordance with the erosion shape of the target, the change in the sputtering rate due to the target erosion is corrected, and the film thickness distribution of the thin film to be formed is controlled.

  For example, the film thickness distribution in the radial direction of a sample formed under a constant operating condition is immediately after immediately after replacement with a new target until immediately before replacement with the next target with the gas flow ratio of the two gases constant. Measure changes over time. Further, the change in the radial film thickness distribution is measured when the gas flow ratio is changed and the film is formed under the same operating conditions. A change pattern of the gas flow rate ratio for keeping the sputter rate constant is derived by associating a change with time in the film thickness distribution in the radial direction due to the target erosion and a change in the film thickness distribution due to the change in the gas flow rate ratio.

  By changing the gas flow rate ratio according to the change pattern derived in this way, the film thickness distribution of the thin film to be formed can be stabilized.

  The best mode for carrying out the present invention will be described with reference to the drawings.

A sputtering apparatus shown in FIG. 1 includes an exhaust system 2 that exhausts a vacuum chamber 1, a gas supply system 3 that supplies first and second gases having different sputtering rates, and first and second mass flows. And controllers 4a and 4b. Furthermore, a target 5, a power supply 6, a substrate holder 11 that holds the substrate 10, a process controller 20, and the like are provided. When the power supply 6 is turned on due to the start of sputtering, the control signal S ₁ is output and the process controller 20 is turned on. The process controller 20 controls the first and second mass flow controllers 4a and 4b to control the gas flow rates (supply amounts) of the first and second gases in response to changes in the sputtering rate. Signals S ₂ and S ₃ are output. In this way, the gas is supplied.

  The substrate 10 rotates and simultaneously moves in the radial direction. Thus, in the sputtering apparatus that scans while the target 5 and the substrate 10 face each other, a sputtering gas composed of any two kinds of gases of He, Ne, Ar, Xe, Kr, and Rn having different sputtering rates is used. . Then, by performing the scan film formation while constantly increasing the gas flow rate of one gas and constantly decreasing the gas flow rate of the other gas, the film thickness distribution that changes as the film formation progresses is stabilized. That is, the sputtering rate is kept constant by using a gas supply means that changes the gas flow rate ratio of the two types of sputtering gases, and the change with time in the film thickness distribution is suppressed.

  FIG. 2 shows the change over time of the film thickness distribution of the silicon single-layer films of the samples A to D formed by scanning in the sputtering apparatus according to the conventional example, and the film thickness at each central portion is expressed as 100%. Sample A is a sample prepared immediately after replacement of the silicon target. Sample B is a sample prepared after film formation was continued for 20 hours after preparation of Sample A. Samples C and D were samples prepared after film formation was continued for 40 hours and 60 hours after preparation of sample A, respectively. As the film formation progresses, the film thickness in the peripheral part increases from the central part. This is presumably because the target erosion increased as the film formation progressed and the emission angle distribution of the sputtered particles changed.

  FIG. 3 shows the film thickness distribution of the silicon monolayer films of the samples E to H which are formed by scanning in the sputtering apparatus of FIG. Each sample E, F, G, and H is a silicon single layer film formed using argon gas and xenon gas as sputtering gas. Under the same operating conditions, the argon gas flow rate is E> F> G> H and the xenon gas flow rate is E <F <G <H. In all samples, the sum of the flow rates of the two gases is the same.

  In the graph of FIG. 3, the film thickness of the peripheral portion when the center portion of the substrate is 100% is E> F> G> H. From this, it can be seen that when the argon gas flow rate with a high sputter rate is decreased and the xenon gas flow rate with a low sputter rate is increased under the same operating conditions, the film thickness of the peripheral portion is further reduced.

  According to the graphs of FIG. 2 and FIG. 3, if the xenon gas is increased while decreasing the argon gas in the sputtering gas in correspondence with the increase in the film thickness of the peripheral part than the central part due to the target erosion, It is possible to stabilize the film thickness distribution.

  In the sputtering apparatus provided with the gas supply means shown in FIG. 1, scan film formation was performed on a planar substrate having a diameter of 320 mm. Silicon was used as the target, and the film formation time was 1 hour. A spectroscopic ellipsometer was used to measure the thickness distribution of the silicon monolayer. The change in the film thickness distribution due to the change in the film thickness distribution in the radial direction of the silicon single layer film and the change in the gas flow ratio of the two kinds of gases, argon gas and xenon gas, was measured in advance. From these measurement results, as shown in FIG. 4, a temporal change pattern of the gas flow rate with which the film thickness distribution becomes constant was derived.

  FIG. 5 shows the results of examining the film thickness distribution after 10 hours and 40 hours when film formation was performed under such gas flow conditions. As can be seen from FIG. 5, there is almost no change over time compared to the film thickness distribution immediately after the target replacement.

  According to the present embodiment, in the sputtering apparatus for performing the scan film formation with the target and the substrate facing each other, the film thickness distribution can be suppressed from being changed by the target erosion, and the film thickness can be controlled with high accuracy.

It is a figure which shows the sputtering device used for one Example. It is a graph which shows a time-dependent change of the film thickness distribution of the silicon single layer film when a scan film is formed by a sputtering apparatus according to a conventional example. 2 is a graph showing a film thickness distribution of a silicon single layer film when a scan film is formed by changing the gas flow rate ratio of two gases in the sputtering apparatus of FIG. 1. It is a graph which shows the change pattern of the gas flow rate ratio in a present Example. It is a graph which shows stability of the film thickness distribution in a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Exhaust system 3 Gas supply system 4a 1st mass flow controller 4b 2nd mass flow controller 5 Target 6 Power supply 20 Process controller

Claims (3)

Scanning the thin film on the substrate moving relative to the target,
Two types of gases selected from He, Ne, Ar, Xe, Kr, and Rn are supplied as the sputtering gas for the target, the supply amount of one of the two types of gas is increased, and the other A sputter deposition method, wherein the scan deposition is performed while reducing the amount of gas supplied.   2. The sputter deposition method according to claim 1, wherein supply amounts of the two kinds of gases are changed so as to compensate for a change in a sputtering rate during the scan deposition.   The sputter deposition method according to claim 1 or 2, wherein a sum of supply amounts of the two kinds of gases during the scan deposition is kept constant.

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