JP2006071402A - Multilayer film thickness control method and film formation apparatus - Google Patents

Abstract

Provided are a multilayer film thickness control method and a film deposition apparatus that can accurately adjust the film thickness of a multilayer film at a low cost without increasing the sampling interval.
[MEANS FOR SOLVING PROBLEMS] (1) Predetermined chromaticity coordinates of each reflected light when a target multilayer film and each multilayer film obtained by changing each layer are irradiated with incident light while changing the incident angle. Plotting the chromaticity points of the target multilayer film and the chromaticity points of each multilayer film on the chromaticity diagram, 2) Reflections when the manufactured multilayer film is irradiated with incident light having an incident angle of 2 or more Plot the chromaticity coordinates of light as chromaticity points of the manufactured multilayer film on the chromaticity diagram. 3) Compare the chromaticity points, and how much the film thickness of the manufactured multilayer film varies. 4) The manufacturing conditions of the multilayer film are corrected and the film thickness of the multilayer film to be manufactured is controlled.
[Selection] Figure 5

Description

  The present invention relates to film thickness control when forming an optical thin film having a multi-layer structure regardless of the film forming method, and in particular, changes from a chromaticity point on a chromaticity diagram of the multi-layer film due to time variation or the like. In particular, the present invention relates to a multilayer film thickness control method and a film formation apparatus that determine a film thickness variation of each layer and correct the film thickness.

  For example, in an apparatus for continuously forming optical thin films based on a multilayer structure in the same apparatus, even if the spectroscopic apparatus is attached in-line, it is obtained for a desired spectroscopic curve. When the spectral curves are different, there is a problem in that it cannot be determined how much the film thickness of which layer has changed from the spectral results obtained from a single angle. In such a case, it is common for a person who operates the apparatus to predict a layer whose film thickness has changed by his / her own judgment and to control the layer. For this reason, in the case of an optical thin film having a multilayer structure, there is a problem that it is not easy to fit the spectral curve.

In addition, if it is not left to the judgment of the person who operates the apparatus, it is necessary to perform spectroscopic measurement at the end of film formation for each layer. When a multilayer film is continuously formed in one apparatus, each layer is formed. It is necessary to install a plurality of spectroscopic devices so that spectroscopic measurement can be performed every time after completion, or it is necessary to increase the number of channels in the spectroscopic device, the device configuration itself becomes complicated, and it is very expensive, There is a problem that the sampling interval becomes long and the control frequency becomes low.
JP-A-9-73667

  In the conventional technology, when the optical thin film having a multilayer structure is continuously formed, the finally laminated multilayer film is spectroscopically measured, and the film thickness is adjusted according to the experience and judgment of the person who operates the apparatus. And therefore uncertain. Further, spectroscopic measurement for each layer for the purpose of stability has a problem that it is very expensive and a sampling interval becomes long.

The present invention has been made to solve the above-described problems, and is capable of accurately adjusting the film thickness of the multilayer film to be formed without increasing the sampling interval and at a low cost. It is an object to provide a thickness control method.
It is another object of the present invention to provide a film forming apparatus using the multilayer film thickness control method.

The present invention relates to a multilayer film thickness control method,
1) Each of the reflected light when the incident light is irradiated to each multilayer film obtained by changing the target multilayer film and each layer constituting the target multilayer film in advance by changing the incident angle. Plot the chromaticity coordinates on the chromaticity diagram as the target chromaticity point of the multilayer film, and the chromaticity point of each multilayer film,
2) Plot the chromaticity coordinates of each reflected light as chromaticity points of the manufactured multilayer film on the chromaticity diagram when the manufactured multilayer film is irradiated with incident light having an incident angle of 2 or more,
3) By comparing the chromaticity point of the manufactured multilayer film with the chromaticity point of the target multilayer film and the chromaticity point of each multilayer film, which of the layers constituting the manufactured multilayer film is selected. Determine how much the layer thickness has changed,
4) Correct the manufacturing conditions of the multilayer film to be subsequently manufactured,
A multilayer film thickness control method characterized by manufacturing a multilayer film.

  Further, the present invention is the multilayer film thickness control method according to the above invention, wherein the incident light irradiation and the reflected light reception are performed by a pair of a light incident part and a detection part, and the pair has two or more, This is a multilayer film thickness control method characterized in that the reflection angle (= incident angle) of the pair is different.

  In the multilayer film thickness control method according to the present invention, the incident light irradiation and the reflected light reception are performed by a pair of a light incident part and a detection part, and the pair of reflection angles (= This is a multilayer film thickness control method characterized in that the incident angle is variable.

  The present invention is also a film forming apparatus using the multilayer film thickness control method according to claim 1, 2 or 3.

  According to the first, second, and third aspects of the invention, regardless of the film forming means such as various vacuum film formations and various coating film formations, regardless of transmission or non-transmission, regardless of whether continuous or non-continuous, In the formation of an optical thin film having a multilayer structure, each chromaticity point on the chromaticity diagram of the optical characteristics of the formed multilayer thin film was obtained by varying the film thickness of each layer in advance. By comparing with each chromaticity point of the multilayer film, it is possible to correct the film thickness so that the film thickness of each layer that changes with the passage of time or the like becomes a desired spectral curve. In other words, it is a multilayer film thickness control method that can accurately adjust the film thickness of the multilayer film to be formed without increasing the sampling interval and at a low cost.

  Further, the present invention provides a film forming apparatus that realizes film thickness control of the multilayer film that can accurately perform the film thickness adjustment of the multilayer film to be formed without increasing the sampling interval and at a low cost. Become.

An embodiment of a multilayer film thickness control method according to the present invention will be described.
For example, in the case of a multilayer thin film used for optical applications such as an antireflection film, it is well known that the chromaticity of transmission / reflection varies with respect to the incident angle of light. Even with spectral information obtained from measurements from a single angle, it is possible to predict film thickness variations to some extent. However, in the “incident angle-chromaticity” relationship, depending on the position of the chromaticity point on the chromaticity diagram, there may be a case where the variation in film thickness cannot be predicted by measurement from a single angle. In such cases, automatic film thickness control is impossible.
The following is an example that makes it difficult to predict, and by measuring from two or more angles at the same time, it is possible to easily determine film thickness variations that are difficult from this single angle. The invention will be described.

  FIG. 1 is a schematic view of an example of a film forming apparatus used in the multilayer film thickness control method of the present invention. The multilayer film thickness control method of the present invention does not specify the film formation method itself, the multilayer film formation method, or the spectroscopic measurement place. However, in explaining the present invention, the film passes through a black roller whose surface is covered with black rubber or the like after the film formation of the final layer at the production site of the antireflection film by a winding type sputtering film forming machine. In this case, it is assumed that the film on which the antireflection film is formed is subjected to reflection spectroscopic measurement.

In FIG. 1, the number of rollers is not limited in the present invention, but the film 10 is composed of a roller 2, a roller 3, a cooling roller 4, a roller 5, and a black roller 6 between the unwinding roll 1 and the winding roll 9. The roller 7 and the roller 8 are sequentially passed. Further, when the film 10 passes the cooling roller 4, each layer of the antireflection film is formed on the four sputter cathodes SC1, SC2, SC3, and SC4.
Although there is no designation for the target material of the sputter target mounted on the sputter cathodes of SC1, SC2, SC3, and SC4, in explaining the present invention, SC1 is a Ti (titanium) target, SC2 is a Si (silicon) target, and SC3 is The Ti (titanium) target, SC4, is assumed to be composed of a Si (silicon) target.

  Further, when film formation is performed at each sputter cathode, a voltage is applied to the cathode. Examples of the application method include direct current discharge, alternating current discharge, and pulse discharge. The present invention is not limited to the discharge method. Here, all the cathodes of SC1 to SC4 are formed by sputtering with direct current discharge.

(1) Sensor Head FIG. 2 is an enlarged view of a sensor head (a pair of a light incident part and a detection part).
The light source of the light incident portion L shown in FIG. 2 is installed in a box G outside the film forming chamber, and the type and characteristics of the light source are not limited, but here, a halogen lamp is used. The light emitted from the light source G passes through the optical fiber 11, and a black roller on which an antireflection film is formed from the light source side optical fiber head A of the light incident portion L and the light source side optical fiber head B of the light incident portion L. 6 on the film 10.

At this time, A of the light source side optical fiber head and B of the light source side optical fiber head are adjusted and installed so that the light irradiated to the passing film 10 is a point where the black roller 6 and the film 10 are in contact. Further, A of the light source side optical fiber head and B of the light source side optical fiber head are respectively α ₁ degree and β ₁ degree from the perpendicular perpendicular to the tangent of the point where the black roller 6 and the film 10 are in contact, and Let α ₁ ≠ β ₁ . Here, the number of fiber heads is two, A of the light source side optical fiber head and B of the light source side optical fiber head. However, the larger the measurement angle, the better.

As shown in FIG. 2, the light irradiated to the film on which the antireflection film is formed is reflected from A of the light source side optical fiber head and B of the light source side fiber head, and C of the light receiving side optical fiber head of the detection unit M, as incorporated into the D of the light receiving side optical fiber head, C of the light receiving side optical fiber head, the D of the light receiving side optical fiber head, from normal is perpendicular to the tangent line at a point where the black roller 6 and the film 10 are in contact, respectively alpha ₁ = It is installed at an angle of α ₂ degrees and β ₂ degrees such that α ₂ and β ₁ = β ₂ .

The sensor head is composed of a pair of a light incident part and a detection part, and the light source side optical fiber head A and the light reception side optical fiber head C form a pair, and the light source side optical fiber head B and the light reception side optical fiber head. D forms another pair.
The sensor head is a pair of one light source side optical fiber head as the light incident part L and one light receiving side optical fiber head as the detection part, and this pair forms an arc with respect to the black roller, and the reflection angle (= incidence) A mechanism that can change the angle may be used. The sensor head may have one light source side optical fiber head as the light incident part L, and the one light source side optical fiber head may draw an arc with respect to the black roller to change the incident angle.

(2) Color measurement The reflected light received by the light source side optical fiber head B and the light receiving side optical fiber head D propagates through the optical fiber 11 and is installed in the spectrometer H outside the film forming chamber shown in FIG. Is incident on a light receiving sensor such as a CCD or a photomultiplier (PMT), and information on reflected light is obtained. At this time, the spectroscopic method of the spectroscope is not limited. However, here, it is assumed that the spectrophotometer is a double beam spectrophotometer, the light from the light source G is branched, and the light source information is obtained by the spectroscopic sensor in the spectroscope H. Using the incident light “a” from the light source and the reflected light “b” incident on the light receiving sensor, the calculation was performed on the film 10 by using the mathematical formula (1) shown below in the computer J. The spectral reflectance R of the antireflection film is calculated.

R = b / a (1)
Further, when measuring the spectral reflectance R, there is no limitation on the method of performing the spectrum for each wavelength, and the reflected light b is captured by dispersing light with a color filter, a prism, a diffraction grating, or the like. At this time, the smaller the wavelength interval of the light to be captured, the better, and the same wavelength range from 380 nm to 780 nm can be measured.

  The spectral reflectance R of each wavelength is sent to the control box K by Equation (1), and chromaticity (chromaticity coordinates) is calculated from the obtained spectral reflectance R. The chromaticity coordinates may be any kind of chromaticity coordinates such as XYZ color system, L * a * b * color system, L * u * v * color system, etc., but here, L * a * b * table. A color system (CIE 1976) is calculated. In addition, there may be a display that displays a spectral curve or a calculated L * a * b * value from the obtained spectral reflectance R at each wavelength.

  After starting the film formation, if the anti-reflection film after reaching the target spectral curve is regarded as non-defective, and the person operating the device determines that the target spectral curve has been reached, this target spectral curve and calculation It is assumed that the a * b * value of the chromaticity coordinates obtained can be recorded in the control box K for each incident angle.

In the apparatus shown in FIG. 1, when TiO ₂ and SiO ₂ of SC1 to SC4 are subjected to DC sputtering discharge, control of applied voltage, DC current value, gas flow rate of gas used, atmospheric pressure, plasma density, electron temperature, etc. If the relationship between each control parameter to be formed and the deposition rate of TiO ₂ and SiO ₂ to be deposited, the refractive index of the film, the extinction coefficient of the film, etc. is known, this information is also controlled by the control box K. It is possible to record in At the same time, it is possible to record data and spectral curves of each chromaticity obtained when the formed film is measured at multiple angles between incident angles of 0 degrees and 90 degrees.

(3) Configuration of Antireflection Film As shown in FIG. 1, each layer is formed by sputtering using four sputter cathodes SC1 to SC4, but the type and thickness of the film are not limited. Here, as shown in 1 of FIG. 3, TiO ₂ and SiO ₂ are alternately formed on a 100 μm-thick PET film, one layer for each cathode, and a four-layer antireflection film is formed. To do.
Although a four-layer structure is used here, the present invention is not limited to this. Here, the film is formed in one pass from the unwinding roll 1 to the winding roll 9.

Here, the first layer of TiO _{2 formed} from the PET film is referred to as the first layer, and the final layer of SiO ₂ is referred to as the fourth layer. When the antireflection film is formed, the target film thickness is, as shown in 1 of FIG. 3, the first layer TiO ₂ = 29 nm, the second layer SiO ₂ = 25 nm, the third layer TiO ₂ = 46 nm, 4 Assuming that the layer SiO ₂ = 99 nm, FIG. 4 shows a spectral curve from a wavelength of 380 nm to 780 nm. In addition, the displacement of each a * b * value when the angle of incidence is changed by 5 degrees from 0 degrees to 90 degrees with respect to the antireflection film formed with this target film thickness is the chromaticity point, that is, Plotted as chromaticity points of the target multilayer film are shown in FIG.
The spectral curve shown in FIG. 4 is measured with an incident angle of 5 degrees.

(4) Film thickness fluctuation during film formation After reaching this target film thickness, the discharge is maintained with each control parameter that has reached this target film thickness, and film formation is performed on the PET film. Over time, the discharge state, the sputtering rate, and the like change slightly. At this time, it is difficult for a human to read the change in film thickness of each layer with the change from the spectral curve, and considerable skill is required.

For example, as the time elapses, the thickness of each layer becomes the first layer TiO ₂ = 29 nm, the second layer SiO ₂ = 23.5 nm, the third layer TiO ₂ = 47.8 nm, and the fourth layer SiO 2 as shown in FIG. _{It is} assumed that ₂ changes to 100 nm. The obtained spectral curve from the wavelength of 380 nm to 780 nm is shown as the film thickness fluctuation 1 in FIG. 4 with respect to this film thickness fluctuation. It is difficult.
Displacement of each a * b * value when the angle of incidence is changed by 5 degrees from 0 degree to 90 degrees with respect to the antireflection film formed with this target film thickness is a chromaticity point, that is, manufacturing. The chromaticity point of the first multilayer film thus prepared is plotted and shown in FIG.

  With respect to the film thickness fluctuation 1, it is assumed that the light source side optical fiber head and the light receiving side optical fiber head in the apparatus shown in FIG. 1 perform single angle measurement only for incident angle = reflection angle = 35 degrees. As shown in FIG. 5, the a * b * value at the target film thickness (target chromaticity point of the multilayer film) and the a * b * value of the film thickness variation 1 (of the manufactured first multilayer film) It can be seen that the value differs greatly from the (chromaticity point).

On the other hand, as the time elapses, the thickness of each layer becomes the first layer TiO ₂ = 28.4 nm, the second layer SiO ₂ = 23.5 nm, the third layer TiO ₂ = 48.2 nm, and the fourth layer as shown in FIG. It is assumed that the eye SiO ₂ = 100 nm. The resulting spectral curve from the wavelength of 380 nm to 780 nm is shown as film thickness fluctuation 2 in FIG.
In addition, the displacement of each a * b * value when the angle of incidence is changed by 5 degrees from 0 degrees to 90 degrees with respect to the antireflection film formed with this target film thickness is the chromaticity point, that is, 5 is plotted as the chromaticity point of the produced second multilayer film and is shown as film thickness variation 2 in FIG.

With respect to the film thickness variation 2, it is assumed that the light source side optical fiber head and the light receiving side optical fiber head in the apparatus shown in FIG. 1 perform single angle measurement only for incident angle = reflection angle = 35 degrees. As shown in FIG. 5, the a * b * value at the target film thickness (target chromaticity point of the multilayer film) and the a * b * value of film thickness variation 2 (color of the manufactured second multilayer film) It can be seen that the value is greatly different from that in (degrees).
However, when film thickness variation 1 and film thickness variation 2 are compared only for incident angle = reflection angle = 35 degrees, both a * b * values (that is, the chromaticity point of the manufactured first multilayer film and the second The chromaticity point of the multilayer film) shows almost the same value, and from this a * b * value, it is determined whether the target film thickness has changed to film thickness fluctuation 1 or film thickness fluctuation 2. It is difficult.

  On the other hand, in the apparatus shown in FIG. 1, both the light source side optical fiber head and the light receiving side optical fiber head have an incident angle = reflection angle = 35 degrees, and both the light source side optical fiber head and the light receiving side optical fiber head have incident angle = reflection angle = 5 degrees. As shown in FIG. 5, in the comparison of incident angle = reflection angle = 5 degrees, the a * b * value of film thickness variation 1 (the second color of the manufactured first multilayer film) It can be seen that the value is sufficiently different from the a * b * value (second chromaticity point of the manufactured second multilayer film) of the film thickness variation 2.

Therefore, for a single angle = 35 degrees, it is difficult to judge the difference between film thickness fluctuation 1 and film thickness fluctuation 2, and the film thickness fluctuation from the target value is clear from the measurement result of the other angle of 5 degrees. become. Further, by measuring from two angles, the a * b * values obtained from the incident angles α ₁ and α ₂ / reflection angles β ₁ and β ₂ are connected, so that the control box K knows in advance It is possible to compare the chromaticity of the film with the dependency on the incident angle, and it is possible to predict the film thickness variation with higher accuracy when determining the film thickness variation.
In addition, as the measurement angle of the light source side optical fiber head and the light receiving side optical fiber head increases, it becomes possible to predict the film thickness variation with higher accuracy.

If it is determined from multi-angle measurements that the target film thickness has changed to film thickness fluctuation 1, control box K changes the control parameters of DC sputtering discharge for TiO ₂ and SiO ₂ of SC1 to SC4 in control box K. The film thicknesses of TiO ₂ and SiO ₂ from the first layer to the fourth layer are set to the target values, that is, the a * b * value measured at multiple angles is set to the a * b * value at the target film thickness. To control. Also, it is possible to perform film thickness control automatically instead of human judgment.

  Further, it is possible to determine the control parameters based on the information stored in the control box K and to automatically adjust the film thickness without performing the completion of the condition by human judgment.

As described above, it is difficult to determine how much the film thickness of each layer is fluctuated by measurement from a single angle, and in the present invention, measurement from two or more angles is performed. Thus, it is explained that it is difficult to easily determine how much the film thickness of which layer has changed.
For convenience of explanation, the film thickness fluctuation 1 and the film thickness fluctuation 2 in which the film thickness fluctuation of each layer is obvious are used. However, in actual production, incident light having an incident angle of 2 or more is applied to the manufactured multilayer film. The a * b * value (chromaticity point) of each reflected light when irradiated is plotted on the chromaticity diagram, and the chromaticity diagram obtained from each multilayer film in which the film thickness variation of each layer is known in advance. The variation of the manufactured multilayer film is judged by comparison with the above chromaticity points.

It is the schematic of an example of the film-forming apparatus used with the film thickness control method of the multilayer film of this invention. It is an enlarged view of a sensor head (a pair of a light incident part and a detection part). It is explanatory drawing which shows an example of the film thickness fluctuation | variation of a multilayer film. FIG. 4 is an example spectral curve shown in FIG. 3. FIG. It is a chromaticity point on the chromaticity diagram of an example shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Unwinding roll 2, 3, 5, 7, 8 ... Roller 4 ... Cooling roller 6 ... Black roller 9 ... Winding roll 10 ... Film A, B ... Light source side optical fiber head C, D ... Light receiving side optical fiber head G ... Light source storage box H ... Spectroscope J ... Calculator K ... Control boxes SC1, SC1, SC1, SC1 ... Spatter Cathode a ... Incident light b ... Reflected light

Claims (4)

In the multilayer film thickness control method,
1) Each of the reflected light when the incident light is irradiated to each multilayer film obtained by changing the target multilayer film and each layer constituting the target multilayer film in advance by changing the incident angle. Plot the chromaticity coordinates on the chromaticity diagram as the target chromaticity point of the multilayer film, and the chromaticity point of each multilayer film,
2) Plot the chromaticity coordinates of each reflected light as chromaticity points of the manufactured multilayer film on the chromaticity diagram when the manufactured multilayer film is irradiated with incident light having an incident angle of 2 or more,
3) By comparing the chromaticity point of the manufactured multilayer film with the chromaticity point of the target multilayer film and the chromaticity point of each multilayer film, which of the layers constituting the manufactured multilayer film is selected. Determine how much the layer thickness has changed,
4) Correct the manufacturing conditions of the multilayer film to be subsequently manufactured,
A method for controlling a film thickness of a multilayer film, comprising producing a multilayer film.   The incident light irradiation and the reflected light reception are performed by a pair of a light incident part and a detection part, the pair has two or more, and the reflection angle (= incidence angle) of each pair is different. 2. A method for controlling the thickness of a multilayer film according to 1.   2. The multilayer according to claim 1, wherein the irradiation of the incident light and the reception of the reflected light are performed by a pair of a light incident portion and a detection portion, and the pair of reflection angles (= incident angles) are variable. A film thickness control method.   A film forming apparatus using the multilayer film thickness control method according to claim 1, 2 or 3.

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