JP2010248594A - Film-forming apparatus and film-forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film-forming apparatus that can form an optical thin film which is uniform, has high precision and has a predetermined thickness distribution, on a large area substrate by using a sputtering method. <P>SOLUTION: The film-forming apparatus for forming the thin film on the substrate by using the sputtering method has a target for discharging sputtered particles and the substrate so that the normal line which penetrates the center of the target and the surface of the substrate cross at right angles; and relatively moves the target and the substrate while keeping the distance between the target and the substrate constant, so as to form the thin film on the substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thin film forming apparatus and a film forming method.

  As a method for producing an optical thin film, a vacuum deposition method, an assist deposition method using plasma or an ion beam, an ion plating method, and the like have been often used. The vacuum evaporation method is a film formation method suitable for performing uniform film formation on a base material (lens) having a large area surrounding the evaporation source from a small evaporation source. The evaporation source and the base material are usually kept at a distance of 500 mm or more, and the base material is revolved or rotated on the planet to make the film uniform. In order to make the film thickness the same every time, a monitor is provided near the substrate holder, the evaporation amount directly entering the monitor is read, and the evaporation rate of the evaporation source is controlled by sensing the film formation speed and the deposition amount. . In order to form an optical thin film having a uniform film thickness distribution corresponding to various deposition conditions, various ideas have been made. For example, in Patent Document 1, a variable mechanism is provided that changes the relative position of a self-revolving base material holder, a vapor deposition source, and a base material holder in at least one of horizontal, vertical, and inclined directions. A vapor deposition apparatus is disclosed.

  On the other hand, the sputtering method is used as a mass production apparatus in thin film manufacturing processes such as semiconductors, flat panel displays, and electronic components. In the sputtering technique, a low-pressure sputtering gas is ionized (plasmaized) by glow discharge, and the plasma ions are accelerated between the electrodes and collide with a target material disposed on the cathode. Next, target material constituent atoms ejected by ion bombardment adhere to and deposit on a substrate provided near the anode to form a thin film of the target material. Thus, since the sputtering method uses a discharge phenomenon, the film must be formed under a higher pressure than the vacuum deposition method. The sputtering technique is characterized in that a dense film can be obtained because the sputtered target material constituent atoms enter the substrate with high energy. However, the sputtered target material constituent atoms lose their initial energy immediately after being sputtered by collision with sputtering gas or the like at a frequency corresponding to the pressure in the film forming chamber before being deposited on the substrate. will have to go. Therefore, in order to obtain a dense film, the distance between the target and the substrate needs to be appropriately shortened to about 150 mm. Also, since the oblique incident film of sputtered particles has a low film density, it is necessary to suppress the oblique incident component of the sputtered particles as much as possible.

For this reason, in the sputtering method, in order to obtain a predetermined film thickness distribution on a large-area base material uniformly and with high precision, it is necessary to make the target size sufficiently larger than the base material size. Alternatively, it is necessary to devise such as relatively moving and scanning the target and the substrate. In the conventional sputtering apparatus, the base material surface and the target surface are arranged in parallel. In such a conventional sputtering apparatus, a target having a diameter larger than that of the substrate is used in order to uniformize the film thickness distribution, composition ratio distribution, impurity distribution, and the like of the film attached to the substrate over a wide range. However, when the base material diameter becomes too large, problems such as the influence of the non-erosion region of the target on the film thickness distribution increase. Therefore, the film thickness distribution, composition ratio distribution, and impurity distribution cannot be made uniform simply by increasing the target diameter.
Therefore, in Patent Document 2, the substrate is rotated at an appropriate speed, and the angle θ of the central axis of the target is maintained at a relationship of 15 ° ≦ θ ≦ 45 ° with respect to the normal of the substrate. A membrane system is disclosed. According to this method, a uniform film thickness and film quality can be generated even if the target diameter is equal to or smaller than that of the base material. Patent Document 3 discloses a method of moving and scanning a target and a base material relatively. According to this method, the uniformity of the deposition amount and the deposition shape within the substrate surface is improved, and the use of a plurality of targets makes it possible to make the target diameter smaller than the substrate diameter.
However, in the field of photolithography in recent years, with the miniaturization of the semiconductor exposure apparatus, the shortening of the wavelength and the increase of the NA have progressed, the base material diameter has increased and the base material shape has diversified, and the accuracy is higher than before. Film thickness control has been required. Therefore, Patent Document 4 discloses a sputtering apparatus characterized by having three or more control axes capable of independently changing the relative positional relationship between the substrate and the cathode during film formation.

JP 2001-152336 A JP 2000-265263 A JP-A-5-234893 JP 2004-269988 A

  However, it is difficult to predict the film formation distribution. In complex sputtering processes involving particle scattering and particularly reactions, high-density and high-quality films can be simply and independently varied to accurately form target film thickness irregularities on various uneven base materials. It is not enough to have many control axes. It is difficult to investigate exactly how the emission distribution of atoms constituting the target material during sputtering is. Even if it is found, it is difficult to accurately predict and simulate what kind of scattering or reaction occurs in the subsequent transport process until reaching the substrate. Therefore, how to predict the film thickness distribution and control and determine the relative positional relationship between the substrate and the target during film formation becomes a problem. In addition, in order to form a high-quality film having a high density, it is necessary to consider to suppress the oblique incident component of the sputtered particles as much as possible.

  In view of the above, an object of the present invention is to provide a film forming apparatus capable of obtaining an optical thin film having a predetermined film thickness distribution that is homogeneous and highly accurate with respect to a large-area substrate using a sputtering method.

  In order to solve the above problems, a film forming apparatus of the present invention is a film forming apparatus that forms a thin film on a substrate using a sputtering method, and a normal passing through the center of a target that emits sputtered particles and the surface of the substrate. The target and the base material are arranged so as to be orthogonal to each other, and the target and the base material are relatively moved while keeping the distance between the target and the surface of the base material constant. A thin film is formed on a substrate.

  According to the present invention, it is possible to obtain an optical thin film having a predetermined film thickness distribution that is homogeneous and highly accurate with respect to a large-area substrate by using a sputtering method.

It is the schematic of the film-forming apparatus of Embodiment 1 of this invention. It is a schematic diagram of the mask of Embodiment 1 of this invention. 3 is a graph showing the film thickness distribution of Embodiment 1 of the present invention. It is a graph showing the film thickness distribution function of Embodiment 1 of the present invention. It is a model drawing of the base-material surface for the film thickness calculation of Embodiment 1 of this invention. It is a model drawing of the base-material surface for the film thickness calculation of Embodiment 1 of this invention. It is a graph of the rotationally symmetric film thickness distribution of Embodiment 1 of the present invention. It is a table | surface of the speed | rate and time of the film thickness distribution of FIG. It is a graph of the film thickness distribution formed into a film on the conditions of FIG. It is the graph showing the film thickness distribution which is the non-rotation object of Embodiment 2 of this invention. It is a table | surface of the speed | rate and time of the film thickness distribution of FIG. It is a graph of the film thickness distribution formed into a film on the conditions of FIG. It is a graph of the mask effect of Embodiment 3 of the present invention.

FIG. 1 shows a schematic cross-sectional view of a film forming apparatus according to Embodiment 1 of the present invention. The film forming apparatus 100 is a film forming apparatus that forms a thin film on a base material having a spherical shape using a sputtering method. Hereinafter, the function and structure of the film forming apparatus 100 will be described step by step with reference to the drawings.
(STEP 1) The normal line 50 passing through the center of the target 11 and the base material surface 20 having a curvature are always arranged so as to be orthogonal to each other. The target 11 and the substrate 21 are arranged at a certain distance suitable for obtaining a dense film, and the target 11 is relatively scanned (moved) between the center 22 and the outer periphery 23 of the substrate 21. A film is formed and the film formation distribution in the substrate surface 20 is experimentally confirmed. At this time, the target 11 has a target structure that is rotationally symmetric with respect to the normal 50 that passes through the center of the target 11, and the normal 50 that passes through the center of the target 11 and the base material surface 20 that has a curvature are always orthogonal to each other. The film is formed in a proper arrangement. The sputtered particles emitted from the target 11 are emitted from the center of the target 11 in a rotationally symmetrical manner, and the film thickness formed on the base material surface 20 is also equal to the normal line 50 passing through the center of the target 11 and the base material surface 20. It has a rotationally symmetric distribution around the intersection Q. This is shown in FIG. Here, when a rotationally symmetric distribution cannot be obtained due to the introduction conditions of the sputtering gas and the reactive gas, the gas introduction conditions have a rotationally symmetric shape with respect to the normal 50 that penetrates the center of the target 11. Gas inlets 18 and 19 must be provided. Therefore, the film thickness at an arbitrary point in the base material surface 20 can be expressed by “a function (film thickness function) of the distance X from the intersection point Q between the normal 50 penetrating the center of the target and the base material surface 20”. This is shown in FIG. A polynomial function can be used as the film thickness function.

(STEP 2) As shown in FIG. 5, the normal 50 penetrating the center of the target 11 and the base material surface 20 having a curvature are always arranged so as to be orthogonal to each other, and the normal 50 penetrating the center of the target 11 and the base material Let Q be the intersection with the surface 20. On the base material curved surface 20 including Q, attention is paid to “intersection point Q” and “point P having a distance of radius r from the center in the base material surface 20”. Here, the curved surface of the base material is simplified to a plane, and a point Q (s, 0) and a point P (r cos θ, r sin θ) are defined as shown in FIG. Here, when the trajectory passing through the point P is considered when the substrate rotates, the film forming rate at each position of the trajectory passing through the point P is obtained from the distance between the point Q and the point P by the film thickness function. That is, the film thickness function that is a polynomial function

に点ＰＱ間の距離

Distance between points PQ

を代入して得られた値が成膜レートとなることを特徴とする。さらに膜厚関数をθ：０→２πで積分すると、基材が自転して１回転した際に点Ｐに成膜される膜厚の合計を計算することができる。

The value obtained by substituting is the film forming rate. Further, by integrating the film thickness function from θ: 0 → 2π, the total film thickness formed at the point P when the substrate rotates and rotates once can be calculated.

なお、簡素化のため基材曲面２０を平面に置き換えて考えたが、曲面であっても同様に点Ｑと点Ｐを結ぶ弧または弦の長さを考えればよく、本質的には何ら変わらない。

For simplicity, the base material curved surface 20 is replaced with a flat surface. However, even if it is a curved surface, the length of the arc or chord connecting the point Q and the point P may be considered in the same manner, and there is essentially no change. Absent.

  (STEP 3) The target 11 and the base material 21 have a structure in which the normal line 50 penetrating the center of the target 11 and the base material surface 20 having a curvature are always perpendicular to each other. A film is formed by scanning the target 11 between the center 22 and the outer periphery 23 of the base material 21 while keeping the distance between the target 11 and the base material 21 constant. In this case, the film formation rate at an arbitrary point on the substrate surface 20 can be expressed by the distance (film thickness function) between the intersection point Q and the intersection point P at each position when the scanning operation is cut into frames. To do.

  (STEP 4) When the inside of the surface 20 of the substrate having the outer diameter F is equally divided into m in the radial direction and n in the circumferential direction, the point R in the substrate surface is obtained using polar coordinates.

（ただしｊ＝0〜ｍ、ｋ＝0〜ｎの整数）
と表すことができる。この座標系を使って所定の膜厚分布を表現しておく。
（ＳＴＥＰ５）ＳＴＥＰ２とＳＴＥＰ３において、レンズの自転速度をω（ｔ）としターゲット１１の走査速度（ターゲット１１の基材２１に対する相対速度）をｖ（ｔ）として速度制御すると、

(However, j = 0 to m, k = integer from 0 to n)
It can be expressed as. A predetermined film thickness distribution is expressed using this coordinate system.
(STEP 5) In STEP 2 and STEP 3, when the speed of the lens is rotated by ω (t) and the scanning speed of the target 11 (relative speed of the target 11 with respect to the base material 21) is v (t),

と表すことができる。すると、成膜開始時間ｔ０から成膜終了時間ｔ１までの間にＲ(ｒ_ｊ、θ_ｋ)の点に成膜される膜厚は、前記積分を改良して以下のように表記することができる。（式１）

It can be expressed as. Then, the film thickness formed at the point of R (r _j , θ _k ) between the film formation start time t0 and the film formation end time t1 can be expressed as follows by improving the integration. it can. (Formula 1)

上記積分計算をω（ｔ）とｖ（ｔ）を未知数としてｍ×ｎ個の点について実施する。ｍ×ｎ個の各点について積分計算した結果が、ＳＴＥＰ４で準備した所定の膜厚分布になるように、「積分計算の結果（算出された膜厚）−所定の膜厚」の２乗が最小になるように、レンズの自転速度ω（ｔ）とターゲット１１の走査速度ｖ（ｔ）を決定する。レンズの自転速度ω（ｔ）とターゲット１１の走査速度ｖ（ｔ）の速度分布の具体的な関数モデルは、所定の膜厚分布の形状に応じて様々な型を考えることができる。（相関がある）

The integration calculation is performed for m × n points with ω (t) and v (t) as unknowns. The square of “integration calculation result (calculated film thickness) −predetermined film thickness” is set so that the result of the integral calculation for each of the m × n points becomes the predetermined film thickness distribution prepared in STEP 4. The rotation speed ω (t) of the lens and the scanning speed v (t) of the target 11 are determined so as to be minimized. Various types of function models of the speed distribution of the rotation speed ω (t) of the lens and the scanning speed v (t) of the target 11 can be considered according to the shape of a predetermined film thickness distribution. (There is a correlation)

  A film forming apparatus 100 according to Embodiment 1 will be described with reference to FIG. The film forming apparatus 100 is provided with a film forming chamber 1 for maintaining the inside in a vacuum state, and an exhaust system 2 including a vacuum pump for exhausting the film forming chamber 1. A base material holder 3 for holding the base material 21 is provided on the side surface in the film forming chamber 1. The base material holder 3 operates back and forth, and a normal line 60 penetrating the center of the base material surface 20 is set as a rotation axis. As a mechanism that rotates during film formation. In addition, a target and mask unit drive system 4 is provided on another side surface of the film forming chamber 1 where the substrate holder 3 is provided. The target and mask unit drive system 4 can operate back and forth. Further, a target unit 5 and a mask unit 12 which can be rotationally driven and have the same rotational axis are provided on the upper surface of the target and mask unit drive system 4. The target unit 5 is provided with a cooling box 6 in which a magnet 25 is housed and cooling water supplied from the outside can be circulated to cool the target 11. The magnet 25 has a magnetic field in a direction parallel to the surface of the target 11 and is arranged so as to be rotationally symmetric with respect to a normal 50 that penetrates the center of the target 11. A backing plate 7 is disposed on the side surface of the cooling box 6 as a cathode electrode.

  Further, on the side surface of the backing plate 7, a mesh plate 9, which is a partition plate having a plurality of apertures as anode electrodes via an insulating material 8, has a rotationally symmetric shape with respect to a normal 50 passing through the center of the target 11. It is built as a unit. A DC voltage can be applied to the backing plate 7 and the mesh plate 9 by a DC power source 10. The mesh plate 9 also has a role of improving the separation between the sputtering gas and the reactive gas. A target 11 having a rotationally symmetric structure with respect to a normal 50 passing through the center of the target 11 is attached to the side surface of the backing plate 7. As a material for the target 11, it is desired to use a metal having low electrical resistance, a fluorine-added metal, or the like. In particular, the arrangement of the magnets 25 and the shape of the target 11 are rotationally symmetric with respect to the normal 50 passing through the center of the target 11. In addition, among the material constituent atoms of the target 11 to be deposited on the sputtered substrate surface 20, a component and a sputter whose distance to be deposited on the substrate is an appropriate distance or more for obtaining a dense film. Cut the grazing incidence component of particles. For this purpose, a mask unit 12 (mask mechanism) that can be disposed between the target 11 and the base material 21 and has a rotationally symmetric structure with respect to the normal 50 that penetrates the center of the target 11 is provided. As an example of the mask unit 12 having a rotationally symmetric structure, a schematic diagram of a mask having a circular opening is shown in FIG.

  A shielding plate 13 is provided between the substrate holder 3 and the mesh plate 9 so that the substrate 21 is not formed until the discharge is stabilized. The shielding plate 13 can be opened and closed at high speed. The film formation chamber 1 is connected to the load lock chamber 15 through the gate valve 14. The load lock chamber 15 has an exhaust system (LL chamber) 16 in addition to the film formation chamber 1, and the substrate holder 3 is connected to a moving mechanism 17 to freely move the load lock chamber 15 and the film formation chamber 1. Is possible. A gas can be supplied from a sputtering gas introduction port 18 and a reactive gas introduction port 19 by a gas supply system (not shown) including a mass flow controller. The sputtering gas introduction port 18 and the reactive gas introduction port 19 have shapes that are rotationally symmetric with respect to the normal 50 that penetrates the center of the target 11. A gas such as an inert gas Ar, He, Ne, Kr, or Xe and hydrogen are introduced from the sputtering gas introduction port 18 as a sputtering gas. Further, from the reactive gas introduction port 19, it is possible to switch and introduce, as necessary, a gas such as CF4 or NF3 containing fluorine or a gas obtained by diluting F2 with a rare gas as a reactive gas. ing. The gas introduced here can be highly accurately limited in flow rate, purity, and pressure by a mass flow controller (not shown) or a gas purifier.

  Next, a method for forming a low-absorption multilayer film in which a high refractive material LaF3 and a low refractive material MgF2 are laminated on a CaF2 substrate using the film forming apparatus 100 of Embodiment 1 of the present invention shown in FIG. 1 will be described in detail. . The substrate holder 3 is moved to the load lock chamber 15 and the load lock chamber 15 is leaked. When the leak is completed, the CaF 2 base material is introduced and exhausted by the exhaust system (LL chamber) 16. At this time, the film forming chamber 1 is evacuated to about 5 × 10 −5 Pa by an exhaust system (film forming chamber) 2. Exhaust system (film formation chamber) 2 uses a highly corrosive pump such as F2 to flow highly corrosive gas, and shaft purge, dilution of exhaust gas with inert gas, and installation of exhaust gas treatment equipment (not shown) It is necessary to. When the pressure in the load lock chamber 15 reaches about 1 × 10 −4 Pa, the gate valve 14 is opened, and the substrate holder 3 on which the CaF 2 substrate is placed is moved to the film forming chamber 1 by the moving mechanism 17. When the movement is completed, Ar gas is introduced with the shielding plate 13 closed, and when a DC power source is applied to the backing plate 7 from the DC power source 10, it discharges and the Ar gas is ionized. This plasma is stable even when the pressure in the film forming chamber 1 is about a few Pa. The reason why plasma is generated even at such a low pressure is that the magnetron effect of the magnet housed in the cooling box 6 causes the electrons to perform cyclotron motion in a plane perpendicular to the magnetic field, thereby increasing the electron density near the target 11. Because you can.

  The discharge forms a sheath in the vicinity of the surface of the target 11, and Ar + ions in the plasma are accelerated by the sheath and collide with the target 11, and the target material is sputtered. The target 11 uses high purity La (99.999%) and Mg (99.999%). The temperature and flow rate of the target cooling water is controlled by a chiller (not shown), and the surface temperature of the target 11 is kept constant in order to stabilize the film formation rate. Next, F2 gas is introduced from the reactive gas introduction port 19. When depositing LaF3, the Ar gas is set to 150 SCCM, the F2 gas is set to 20 SCCM, and the DC power supply is set to 400 W. When depositing MGF2, it is preferable to set the Ar gas to 150 SCCM, the H2 gas to 25 SCCM, the F2 gas to 16 SCCM, and the DC power supply to 400 W. If the flow rate of fluorine is further reduced, the formed film cannot satisfy the stoichiometric ratio of MgF 2 and LaF 3, respectively, and becomes a fluorine defect film. Conversely, if fluorine is further increased, the flow rate of the reactive gas F2 increases with respect to the Ar flow rate of the sputtering gas, and the gas separation performance deteriorates. As a result, (1) near the target 11 The amount of F ions will increase. Since negative ions having a large mass cannot be bent orbited by the magnetron of the magnet provided in the cooling box 6, F- ions accelerated by a sheath of several hundred volts enter the CaF2 substrate, It causes damage to the film.

  Furthermore, (2) the surface of the target 11 is fluorinated to form an insulating fluoride. Then, this insulator is charged up, and it is broken down by ions and electrons, causing abnormal discharge. When abnormal discharge occurs, foreign matter enters the film, resulting in a film with a rough surface. As a countermeasure, when an alternating current of about several kHz is superimposed on a voltage on a direct current, charge cancellation is performed and abnormal discharge can be prevented. However, it was found that if the frequency to be superimposed is increased too much, a base material self-bias voltage is generated, and this time, cations in the plasma enter the CaF2 base material and cause damage. In order to eliminate the damage, it is necessary to superimpose a voltage having a frequency of 20 kHz or less. Further, it is better to flow in H2 when depositing MgF2. As Mg is used as a getter, the sputtered Mg easily reacts with and binds to gas molecules such as H 2 O and O 2 caused by residual moisture in the film forming chamber 1 and forms a film on the substrate in the form of MgO. . Since MgO has a large absorption in the vacuum ultraviolet region, MgF2 into which MgO has been incorporated has a large film absorption. Therefore, when H2 is added, an effect of suppressing the generation of MgO is produced by a reduction reaction with active hydrogen such as hydrogen radicals, and a low-absorption MgF2 film can be formed.

  Next, it waits until the target voltage confirmed by the DC power supply 10 is stabilized in this state. In the meantime, the target 11 and the base material 21 are arranged in a face-to-face relationship so that the normal 50 penetrating the center of the target 11 and the base material surface 20 having a curvature are orthogonal to each other. At this time, the base material holder 3 is not rotated. When the target voltage is stabilized, the shielding plate 13 is opened and film formation is started. The target voltage at this time was about 330 V when the LaF 3 film was formed, and about 320 V when the MgF 2 film was formed. Thereafter, the spectral characteristics of the LaF3 single layer film or the MgF2 single layer film formed on the CaF2 base material are measured by a spectrophotometer (not shown), and the film thickness distribution in the base material surface 20 is calculated. From this result, a function (film thickness function) of the distance x from the intersection of the normal 50 penetrating the center of the target 11 and the base material surface 20 is determined.

  The case where a rotationally symmetric MGF2 single layer film is formed will be described below. The film thickness function could be expressed by a polynomial function shown in FIG. A predetermined film thickness distribution of the rotationally symmetric film formed on the base material 21 having an outer diameter of 300 mm is divided into 40 parts in the radial direction and 40 parts in the circumferential direction, as shown in FIG. Keep it. In this case, the target is that the film thickness is constant within the substrate surface 20. Next, a model function of the rotation speed ω (t) of the substrate 21 and the scanning speed v (t) of the target 11 is given. The target 11 and the base material 21 are arranged in a face-to-face relationship so that the normal 50 penetrating the center of the target 11 and the base material surface 20 having a curvature are orthogonal to each other. Assuming the case where the film is formed by scanning from the center of the base material 21 to the outer periphery while keeping the direct positional relationship and the distance between the target 11 and the base material 21 constant, the following setting is made. The model function of the rotation speed ω (t) of the base material 21 has a speed distribution within one rotation, and is a periodic function that repeats the distribution. The time from film formation start time T0 to film formation end time T1 is T (= T1-T0), and the number of rotations of the lens is U, and the time T / U per rotation is divided into eight, Δt1, Δt2,. .., Δt8. The rotation speed of the base material 21 at time Δt1, Δt2,..., Δt8 was set to ω1, ω2,. Next, the target scanning speed v (t) is divided into eight parts from time T (= T1−T0) from film formation start time T0 to film formation end time T1, and set to Δu1, Δu2,. . The target scanning speed at the time Δu1, Δu2,..., Δu8 is set to v1, v2,. Substituting these Δt1 to Δt8, ω1 to ω8, Δu1 to Δu8, v1 to v8 into [Equation 1] as unknowns, about 40 × 40 points in the lens surface of interest as a predetermined film thickness distribution diagram 7 Set up simultaneous equations. The unknowns were determined so that the square of “integral calculation (calculated film thickness) −predetermined film thickness” was minimized for 40 × 40 points. The concrete calculation result of the unknown is as shown in FIG. Further, the experimental result of actually forming a film of MgF 2 based on this condition is as shown in FIG. The deviation from the predetermined film thickness distribution was about several percent.

  Next, Embodiment 2 of the present invention will be described. Unlike the rotationally symmetric example of the first embodiment, an example in which a non-rotationally symmetric MgF 2 single layer film is formed will be described. The film thickness function can also be expressed by a polynomial function shown in FIG. The predetermined film thickness distribution of the non-rotationally symmetric film formed on the base material 21 having an outer diameter of 300 mm is divided into 40 parts in the radial direction and 40 parts in the circumferential direction as shown in FIG. Express it. Next, a model function of the rotation speed ω (t) of the substrate 21 and the scanning speed v (t) of the target 11 is given. The target 11 and the base material 21 are arranged in a face-to-face relationship so that the normal 50 penetrating the center of the target 11 and the base material surface 20 having a curvature are orthogonal to each other. Assuming the case where film formation is performed by scanning from the center to the outer periphery of the base material 21 while keeping the direct positional relationship and the distance between the target 11 and the base material constant, the following setting is made. The model function of the rotation speed ω (t) of the base material 21 has a speed distribution within one rotation, and is a periodic function that repeats the distribution. The time from the film formation start time T0 to the film formation end time T1 is T (= T1-T0), and the number of lens rotations during that time is U. The time T / U per one rotation is divided into eight to be Δt1, Δt2,..., Δt8, and the rotation speeds of the base material 21 at times Δt1, Δt2,. ..., ω8. Next, the scanning speed v (t) of the target 11 is divided into 8 times from the film formation start time T0 to the film formation end time T1 (= T1-T0), and Δu1, Δu2,. It was. The target scanning speed at the time Δu1, Δu2,..., Δu8 is set to v1, v2,. Substituting these Δt1 to Δt8, ω1 to ω8, Δu1 to Δu8, and v1 to v8 into [Equation 1] as unknowns, a predetermined film thickness distribution As for FIG. 10, about 40 × 40 points in the lens surface of interest Set up simultaneous equations. The unknowns were determined so that the square of “integral calculation (calculated film thickness) −predetermined film thickness” was minimized for 40 × 40 points. The specific calculation result of the unknown is as shown in FIG. Further, the experimental result of actually forming the MgF 2 film based on this condition is as shown in FIG. The deviation from the predetermined film thickness distribution was about several percent.

  Next, an example of the mask effect according to the third embodiment of the present invention will be described. FIG. 13 shows the difference between when the mask is used and when it is not used for the film thickness distribution and the refractive index distribution in the substrate surface 20 when the LaF3 single layer film is formed. The opening shape of the mask is a circle of φ72 mm. By using a φ mask, the non-uniformity of the refractive index (= ((maximum value) − (minimum value)) / ((maximum value) + (minimum value))) is 1.84% to 1.09%. Improved.

11 target 50 normal line passing through center of target 20 base material surface 21 base material 22 center of base material 23 outer periphery of base material
100 Deposition system

Claims (8)

In a film forming apparatus that forms a thin film on a substrate using a sputtering method,
The target and the base material are arranged so that the normal passing through the center of the target that emits sputtered particles and the surface of the base material are orthogonal to each other, and the distance between the target and the surface of the base material is made constant. The film forming apparatus is characterized in that the target and the base material are relatively moved to form a thin film on the base material.   The film forming apparatus according to claim 1, wherein the thin film is formed on the base material by moving the target relative to the base material between a center and an outer periphery of the base material.   The film forming apparatus according to claim 1, wherein a surface of the base material is a spherical surface.   The film forming apparatus according to claim 1, wherein the target has a rotationally symmetric structure with respect to a normal passing through the center of the target. A substrate holder for holding the substrate;
The film forming apparatus according to claim 1, wherein the base material holder rotates the base material around a normal line penetrating a center of the surface of the base material as a rotation axis.   6. The film forming apparatus according to claim 5, wherein the relative speed of the target with respect to the base material and the rotation speed of the base material have a distribution correlated with a film thickness distribution.   7. The mask unit according to claim 1, further comprising a mask unit disposed between the target and the base material and provided with an opening rotationally symmetric with respect to a normal passing through the center of the target. 2. The film forming apparatus according to 1. In a film forming method for forming a thin film on a substrate using a sputtering method,
The target and the base material are arranged so that the normal passing through the center of the target that emits sputtered particles and the surface of the base material are orthogonal to each other, and the distance between the target and the surface of the base material is made constant. A thin film is formed on the base material by relatively moving the target and the base material.

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