JP4873455B2 - Optical thin film forming method and apparatus - Google Patents

Description

The present invention uses an optical thin film forming method in which a high refractive index material such as T _i O ₂ and a low refractive index material such as S _i O ₂ are alternately deposited by an ion-assisted deposition method, and is directly used for carrying out this method. The present invention relates to an optical thin film forming apparatus.

In optical lenses and optical filters used in the optical field, optical characteristics are controlled by forming a thin film on the surface of a substrate. For example, an antireflection film is known in which thin films of a high refractive index material such as T _i O ₂ or _{Ta 2} O ₅ and a low refractive index material such as S _i O ₂ are alternately stacked in a predetermined thickness. . Filters that selectively transmit light in a specific wavelength range are also widely used.

  As one of methods for forming a thin film of these high refractive index materials and low refractive index materials, ion beam assisted deposition (IBAD, also called ion beam assisted deposition) is known. In this method, when a neutral thin film material (evaporated particles) evaporated in a vacuum vessel reaches the substrate surface, the ion gun accumulates relatively low energy gas ions (and several hundred eV) on the substrate surface. This is a method of irradiating a substrate with the same amount of electrons for neutralizing positive charges and forming a dense film by its kinetic energy.

JP-A-1-197701 JP-A-2005-42132 JP-A-10-123301

  The conventional ion-assisted deposition method supplies neutral deposition particles and ions at the same time. When the deposition particles adhere to the substrate, the kinetic energy of the ions is used to improve the optical properties such as absorption and scattering of the thin film. It is intended to improve the density of the thin film.

  On the other hand, optical devices are constantly required to improve optical characteristics such as light transmittance. Especially in anti-reflective coatings and optical filters where high refractive index materials and low refractive index materials are alternately stacked in multiple layers, the final product characteristics are significantly reduced due to slight deterioration in optical characteristics such as absorption and scattering of thin films. It will be.

  In general, the vacuum vessel is always evacuated by a vacuum pump. However, since impurities evaporate from various parts such as the evaporation source, the substrate holding means, and the shutter mechanism housed in the vacuum vessel, these impurities are removed from the substrate surface. Adhere to. When such impurities are present, impurities enter the deposited film or the deposited film is easily crystallized, absorption and scattering increase, and the optical characteristics of the multilayer film are degraded. In order to remove impurities, it is conceivable to lengthen the exhaust time or raise the degree of vacuum, but in this case, the processing efficiency is lowered or the vacuum system becomes complicated.

  The present invention has been made in view of such circumstances, and provides an optical thin film forming method capable of easily improving the optical characteristics of a thin film, and particularly capable of improving the optical characteristics when a multilayer structure is used. Is the first purpose. A second object is to provide a similar optical thin film forming apparatus.

According to the present invention, an object of the present invention is to provide an optical thin film forming method in which a high refractive index substance and a low refractive index substance are alternately and multilayerly deposited by ion-assisted deposition on a substrate held in a vacuum vessel.
Before the vapor deposition step of simultaneously supplying the vaporized particles and ions of the high refractive index material to the vapor deposition thin film of the low refractive index material formed on the substrate, a preliminary ion irradiation step for supplying ions for a predetermined time is provided and each vapor deposition is performed. This is achieved by an optical thin film forming method characterized by providing an ion irradiation stop period in which ion irradiation is stopped after the thin film layer deposition step.

The second object is to maintain a predetermined pressure in an optical thin film forming apparatus that deposits a high refractive index material and a low refractive index material alternately and in multiple layers by ion-assisted deposition on a substrate held in a vacuum vessel. A vacuum container, a substrate held in the vacuum container, a high-refractive-index material evaporation means and a low-refractive-index material evaporation means facing the substrate at a predetermined distance, and the evaporation means and the substrate. A first evaporation source shutter and a second evaporation source shutter that move forward and backward in between, an ion gun that irradiates ions to the substrate, an ion gun shutter that controls irradiation of ions to the substrate by the ion gun, It controls the high refractive index material or low refractive index at the same time supplies the deposition process evaporating particles and the ions of the material, prior to pre-supplying ions a predetermined time deposition process of the high refractive index material Characterized in that it comprises a controller for controlling so as to provide an ion irradiation stop period to stop the ion irradiation during the deposition process of the low refractive index material and deposition process of the high refractive index material provided with an ion irradiation step And an optical thin film forming apparatus.

  According to the first aspect of the present invention, the ion irradiation step (preliminary ion irradiation step) is added prior to the vapor deposition step of simultaneously irradiating the evaporated particles and ions of the high refractive index substance. Prior to the deposition of the material, ions impinge on the surface of the deposited film of low refractive index material to clean the surface.

  Prior to the deposition of the high refractive index material, ions are irradiated onto the surface of the low refractive index material vapor deposition thin film, so that the impurities adhering to the surface of the low refractive index material vapor deposition film precede the start of the deposition of the high refractive index material. Immediately thereafter, the high refractive index material is continuously deposited, so that impurities are less likely to be mixed into the thin film. For this reason, optical characteristics such as absorption and scattering of the high refractive index substance can be improved.

The preliminary ion irradiation process preceding the deposition of the high refractive index material only controls the ion gun or the ion gun shutter, so that the processing efficiency is not significantly reduced and the apparatus may be complicated. Absent. In addition, a period for stopping the supply of ions (ion irradiation stop period) is provided after the vapor deposition process of the high refractive index material and the low refractive index material. By providing this period, the rise in the surface temperature of the substrate is suppressed to control the temperature. Is possible.

According to the invention of claim 4 , an optical thin film forming apparatus used directly for carrying out the invention of claim 1 is obtained.

Although the present invention is suitable for vapor deposition of a high refractive index material, a preliminary ion irradiation step may be performed prior to vapor deposition of a low refractive index material .

  The ion irradiation power (power) of ions in the preliminary ion irradiation step may be the same as or larger or smaller than the ion irradiation power during the deposition of the high refractive index material. In particular, when the irradiation power is reduced, there is no possibility of damaging the deposition surface of the low-refractive-index substance serving as a base, which is preferable. Here, the irradiation power density is the product (V · I) of the acceleration voltage (V) of ions and the ion current density (I).

  In this case, the time of the preliminary ion irradiation process is preferably changed depending on the ion irradiation power and the surface state of the base. For example, when the irradiation power is increased, the irradiation time (T) is shortened. On the other hand, when the irradiation power is decreased, the irradiation time (T) is increased to reduce the irradiation energy density (V · I · T). It is good to control.

The high refractive index material to be deposited is T _i O ₂ (titanium dioxide), T _a2 O ₅ (tantalum pentoxide) or the like, and T _i O ₂ is particularly preferable because it is inexpensive. The low refractive index material to be deposited is preferably S _i O ₂ (silicon dioxide). In this case, the ion gun ionizes and ejects O ₂ as a reactive gas and Ar as a rare gas with respect to T _i O ₂ and ionizes only the reactive gas O ₂ with respect to S _i O ₂ . Should be injected.

  In addition, the vacuum vessel is preferably provided with a neutralizer for irradiating electrons, and neutralization of the charging of the substrate surface by ions with electrons is preferable. This is because if the surface of the substrate is charged, the thin film is damaged by discharge and the optical characteristics are deteriorated.

FIG. 1 is a conceptual diagram of an optical thin film forming apparatus according to an embodiment of the present invention. Reference numeral 10 in this figure is a vacuum vessel is evacuated to a predetermined pressure by the exhaust means (not shown) (e.g., degree of _{^{3 × 10 -2 ~10 -4 P a}} ). This vacuum vessel is a vertically-placed cylinder, and a spherical stainless steel substrate holder 12 is held above the inside thereof so as to be rotatable about a vertical axis. A large number of substrates 14 are fixed to the lower surface of the substrate holder 12 with the thin film forming surface facing downward. The substrate 14 is glass or resin processed into a plate shape or a lens.

  An optical monitor 16 and a crystal monitor 18 are disposed in an opening provided in the center of the substrate holder 12. The optical monitor 16 is a transparent plate made of the same material as the substrate 14, and the light supplied from the projector 22 is guided to the optical monitor 16 by the mirror unit 20 provided above the vacuum vessel 10, and this optical monitor 16 The reflected light is guided to the spectroscope 24 through the mirror unit 20, and the optical film thickness is detected by the film thickness detector 26 from the light intensity of a certain wavelength. The crystal monitor 18 detects the physical film thickness by the film thickness detection unit 26 from the change in the resonance frequency due to the thin film adhering to the surface. The film thickness detection result is sent to the controller 28.

  An electric heater 30 is disposed above the substrate holder 12. The temperature of the substrate holder 12 is detected by a temperature sensor 32 such as a thermocouple, and the result is sent to the controller 28. The controller 28 appropriately controls the temperature of the substrate 14 by controlling the electric heater 30 using the output of the temperature sensor 32.

Below the inside of the vacuum vessel 10, an evaporation source 34 that is a high refractive index substance (T _i O ₂ ) evaporation means, an evaporation source 36 that is an evaporation means for a low refractive index substance (S _i O ₂ ), and an ion gun 38. Is arranged. The evaporation sources 34 and 36 heat and evaporate a high refractive index material and a low refractive index material by an electron beam heating method. The ion gun 38 extracts charged ions (O ₂ ⁺ , Ar ⁺ ) from plasma of a reactive gas (such as O ₂ ) or a rare gas (such as Ar), and accelerates them with an acceleration voltage to eject them toward the substrate 14.

  Above the evaporation source 34, a first shutter 34A that can be opened and closed is attached. Above the evaporation source 36, a second shutter 36A that can be opened and closed is attached. Above the ion gun 38, an ion gun shutter 38A is attached so as to be openable and closable.

Reference numeral 40 denotes a neutralizer. The neutralizer 40 emits electrons toward the substrate 14. The neutralizer 40 extracts electrons (e ⁻ ) from a rare gas plasma such as Ar and accelerates them with an acceleration voltage to emit electrons. The electrons emitted from here neutralize the ions attached to the substrate surface.

  Next, the operation of this apparatus will be described with reference to FIG. FIG. 2 is a timing chart for explaining the change over time of the opening / closing timings of the shutters 34A, 36A, 38A. A substrate holder 12 having a substrate 14 fixed thereto is set in the vacuum vessel 10, and the inside of the vacuum vessel 10 is exhausted to a predetermined pressure. Thereafter, the electric heater 30 is heated, and the substrate holder 12 is rotated at a low speed. By this rotation, the temperature and film forming conditions of many substrates 14 are made uniform.

  When the controller 28 determines from the output of the temperature sensor 32 that the temperature of the substrate 14 has reached the set temperature, the controller 28 enters a vapor deposition process. Before that, the ion gun 38 sets the ion source in an idle operation state. The evaporation sources 34 and 36 are also prepared so that the evaporated particles can be immediately diffused (released) by opening the shutters 34A and 36A.

  In FIG. 2, A indicates a vapor deposition process of a high refractive index material, and B indicates a vapor deposition process of a low refractive index material. The controller 28 increases the irradiation power of the ion gun 38 from the idle state to a preset irradiation power prior to the deposition step A of the high refractive index material, and opens the ion gun shutter 38A. This step is a preliminary ion irradiation step (also referred to as pre-irradiation) indicated by C in FIG. This step C is continued for an optimum time determined from the experiment, for example, about 10 to 20 seconds.

  The irradiation power (V · I) and time (T) in this preliminary ion irradiation process are such that if the irradiation power (V · I) is too strong or the time (T) is long, the underlying thin film (low refractive index material) Since the deposited thin film) is sputtered little by little, it is preferable to reduce the irradiation power and shorten the time as much as possible within a range where necessary film characteristics with little light absorption / scattering can be obtained. The faster the deposition rate (deposition rate), the stronger the irradiation power and the longer the time.

  Following this step C, the controller 28 opens the first evaporation shutter 34A at the same time so that the irradiation power of the ion gun 38 corresponds to the regular vapor deposition step A while the ion gun shutter 38A is open. For this reason, the high refractive index substance deposition step A is performed, and the high refractive index substance is deposited. In this step A, the controller 28 continues to monitor the film thickness with the optical monitor 16 and the crystal monitor 18, and stops vapor deposition when the film thickness reaches a predetermined value.

  That is, the controller 28 closes the first shutter 34A and the ion gun shutter 38A to end the process A, and returns the ion gun 38 to the idle state. In this state, the evaporation material B is prepared for evaporation (pre-melting), and after the preparation is completed, the controller 28 sets the irradiation power of the ion gun 38 to correspond to the regular deposition process B, and the low refractive index material first. 2 shutter 36A and ion gun shutter 38A are opened simultaneously. For this reason, the evaporated particles of the low refractive index substance adhere to the substrate 14. In this process B, the controller 28 continues to monitor the film thickness and stops when the film thickness reaches a predetermined value.

  That is, the second evaporation shutter 36A and the ion gun shutter 38A are closed, and the ion gun 38 is returned to the idle state. Thus, a multilayer film can be formed by repeating the deposition of the high refractive index substance and the low refractive index substance a plurality of times.

Experimental example 1

  Next, an experimental example according to the present invention performed using this apparatus will be described in comparison with an experimental example according to a conventional method. Here, the conventional method excludes the preliminary ion irradiation step in the present invention.

The film forming conditions in the experimental example are as follows.

Substrate: BK7 (refractive index n = 1.52)
Substrate temperature: 150 ° C
T _i O ₂ during deposition of the ion gun conditions:
Acceleration voltage: 1000V
Ion current density: 110 μA / cm ²
Discharge gas: oxygen 60 sccm + argon 7 sccm
S _i O ₂ evaporation time of the ion gun conditions:
Acceleration voltage: 1000V
Ion current density: 110 μA / cm ²
Discharge gas: oxygen 60sccm
Preliminary ion irradiation conditions:
Acceleration voltage: 300V, 1000V
Ion current density: 35 μA / cm ² , 110 μA / cm ²
Discharge gas: oxygen 60 sccm + argon 7 sccm
Discharge time: 0 to 20 seconds T _i O ₂ deposition rate: 0.3, 0.5, 0.7 nm / s
Evaporation rate of S _i O _2: 1.0nm / s
Nutriza conditions:
Acceleration voltage: 50V
Electron current: 2.0A
Discharge gas: Argon 10 sccm

  In the experimental example according to the present invention, the preliminary ion irradiation process (pre-irradiation) was set to 10 seconds and 20 seconds, whereas the conventional method was set to 0 seconds. In this experimental example, a UV-IR cut filter (filter for making the ultraviolet region and infrared region opaque) formed of a multilayer film of 33 layers was formed, and its optical characteristics were measured. FIG. 3 shows the measurement results, and Table 1 shows the preliminary ion irradiation conditions.

That is, Table 1 shows the relationship between the T _i O ₂ film formation rate (evaporation rate, nm / s) and the preliminary ion irradiation conditions, and × indicates the time when there is no effect, and the result shown in FIG. It becomes. Δ is when the effect is small, and the result shown in FIG. A circle shows a result when the effect is large, as shown in FIG. Note In Table ^{1, 0.01W / cm 2, 0.11W} / cm 2 preliminary ion irradiation power density is the product of accelerating voltage and the ion current density, the former in the case of 300V × 35μA / cm ^2, the latter Is the case of 1000 V × 110 μA / cm ² . In the experiment, an average value of measured values of a plurality (9) of substrates set at different locations on the substrate holder 12 is used as a measured value.

  According to FIG. 3A, when the preliminary ion irradiation (pre-irradiation) time is set to 0 second (that is, according to a conventional method in which preliminary ion irradiation is not performed), the measured value of the light transmittance T is visible. It can be seen that it is about 87% in the wavelength range of light. For comparison, the design value at this time is added by a broken line. This design value is about 95%. Thus, it can be seen that the design value (about 95%) and the measured value (about 87%) are greatly different. According to FIG. 3B, the measured value of the light transmittance T is about 92%, which is still quite different from the designed value of 95%.

According to FIG. 3C, the measured value of the light transmittance T is about 95% in the visible light wavelength range, and it was found that a value almost as designed (shown by a broken line) can be obtained. This is presumably because the film quality of T _i O ₂ is improved by preliminary ion irradiation (pre-irradiation), the refractive index fluctuation of the film is uniformed, and the light absorption coefficient is stabilized at a certain level or less.

Conceptual diagram of an apparatus according to the present invention The figure which shows the time change of the shutter opening and closing timing and the ion irradiation power of the ion gun Figure showing the measured value of the light transmittance of the multilayer film compared to the design value

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vacuum container 12 Substrate holder 14 Substrate 28 Controller 34 Evaporation source (evaporation means) of high refractive index substance
34A First shutter 36 Low-refractive-index substance evaporation source (evaporation means)
36A Second shutter 38 Ion gun 38A Ion gun shutter 40 Neutralizer A High refractive index material deposition process B Low refractive index material deposition process C Preliminary ion irradiation process

Claims (5)

In an optical thin film forming method in which a high-refractive index material and a low-refractive index material are alternately and multilayerly deposited by ion-assisted deposition on a substrate held in a vacuum vessel,
Before the vapor deposition step of simultaneously supplying the vaporized particles and ions of the high refractive index material to the vapor deposition thin film of the low refractive index material formed on the substrate, a preliminary ion irradiation step for supplying ions for a predetermined time is provided and each vapor deposition is performed. An optical thin film forming method characterized by providing an ion irradiation stop period in which ion irradiation is stopped after a thin film layer deposition step.   2. The method of forming an optical thin film according to claim 1, wherein a preliminary ion irradiation step is provided before the vapor deposition step of the high refractive index material and before the vapor deposition step of the low refractive index material. _{3. The} method of forming an optical thin film according to claim 1, wherein the high refractive index material deposited on the substrate is T _i O ₂ and the low refractive index material is S _i O ₂ . In an optical thin film forming apparatus that deposits a high refractive index substance and a low refractive index substance alternately and in multiple layers on a substrate held in a vacuum vessel by an ion-assisted deposition method.
A vacuum vessel maintained at a predetermined pressure, a substrate held in the vacuum vessel,
A high refractive index substance evaporation means and a low refractive index substance evaporation means facing the substrate at a predetermined distance;
A first evaporation source shutter and a second evaporation source shutter that move forward and backward between the evaporation means and the substrate, respectively.
An ion gun for irradiating the substrate with ions;
An ion gun shutter for controlling ion irradiation to the substrate by the ion gun;
A preliminary ion irradiation step of controlling a vapor deposition step of simultaneously supplying vaporized particles and ions of the high refractive index material or the low refractive index material and supplying ions for a predetermined time prior to the vapor deposition step of the high refractive index material; A controller for controlling to provide an ion irradiation stop period for stopping ion irradiation between the high refractive index material vapor deposition step and the low refractive index material vapor deposition step, and
An optical thin film forming apparatus comprising:   5. The optical thin film forming apparatus according to claim 4, further comprising a neutralizer that irradiates electrons toward the substrate.

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