JP4785683B2 - Deposition equipment - Google Patents

Description

  The present invention relates to a film forming apparatus for stably forming a high-quality optical thin film having a low refractive index and porous by a reactive sputtering method.

  In recent years, with the demand for miniaturization of integrated circuits, the wavelength of light used for steppers has been shortened. In the field of optical thin films, the development of new film materials, the improvement of film forming methods, the improvement of film control technology, etc. have been contributed to the improvement of stepper performance in accordance with the shortening of light wavelength.

Recently, however, changes have started to appear in the trend toward shorter wavelengths, which have progressed smoothly with G-line, I-line, KrF laser, and ArF laser. The use of F ₂ laser, which was expected as the next light source of ArF laser, was postponed. One reason is that the wavelength of the light source has been shortened to the limit, and the surrounding technology has become unable to keep up with it.

Therefore, immersion exposure was selected instead of shortening the wavelength of the light source. Rayleigh equation indicating stepper resolution Re = k1 * λ / NA
As can be seen, the resolution can be improved not only by shortening the wavelength of the light source but also by increasing the NA. In immersion exposure, an optical design with a large NA is made possible by filling a space in contact with a wafer with a material having a refractive index greater than 1, such as water. Theoretically, when the NA is increased by making the ArF stepper compatible with immersion exposure, approximately the same resolution as that obtained when normal exposure is performed with the F ₂ stepper can be obtained. Therefore, it is considered that the ArF stepper is more advantageous for immersion exposure than the F ₂ stepper, which has many problems that are difficult to solve, and the ArF immersion stepper is now mainstream.

  However, immersion of the ArF stepper is not easy. For example, in the field of optical thin films, as the NA increases, the maximum incident angle to the lens becomes larger than the conventional one. Therefore, there is a demand for the development of an optical thin film that exhibits sufficient characteristics even for light with a high incident angle.

  As means for meeting the above requirements, there is an increase in the refractive index difference between the high refractive index film and the low refractive index film constituting the optical thin film. To that end, it is conceivable to increase the refractive index of the high refractive index film or lower the refractive index of the low refractive index film. However, based on the detailed calculation results, it is recommended to lower the refractive index of the low refractive index film. However, it has been found that the contribution to the improvement of optical characteristics is large.

One way to lower the refractive index of a low refractive index film is to develop a new film material, but there are limited materials that can be used for light in the vacuum ultraviolet wavelength range, such as ArF lasers. It is very difficult to newly develop a suitable material. Therefore, research for reducing the refractive index of low-refractive index films conventionally used at wavelengths in the vacuum ultraviolet region, such as MgF ₂ , has been conducted eagerly.

For example, in Patent Document 1, after a mixed film made of fluoride and silicon dioxide is formed on a substrate by co-evaporation, only silicon dioxide is selectively removed from the mixed film, thereby making it more porous than a normal fluoride film. Provides a method for obtaining a low refractive index fluoride film. It has been reported that MgF ₂ having a refractive index of 1.42 (wavelength 1193 nm) can be lowered to a refractive index of about 1.35 by using this method. However, in order to remove silicon dioxide, there is a step of contacting with hydrogen fluoride gas or fluorine gas, which complicates the processing. Furthermore, when a non-fluoride substrate such as SiO ₂ is used, care must be taken so that the substrate does not come into contact with the fluorine-based gas.

Further, as disclosed in Patent Document 2, by using MgF ₂ and Si as targets and performing sputtering using Ar and O ₂ , an MgF ₂ film containing Si concentration of 3 to 10 wt% is formed. A method for obtaining a film having a relatively low refractive index is known. This method is a simple method because it uses a sputtering method and does not require post-processing. However, the refractive index can only be lowered to about 1.37, and vacuum ultraviolet rays due to the incorporation of Si-based oxides and the like. There is concern about increased absorption of light.

According to Patent Document 3, porous MgF ₂ can be obtained by preparing an MgF ₂ sol solution containing an organic substance on a substrate and then removing only the organic substance, and its refractive index is 1.16 (wavelength 193 nm). ). However, this method has a problem that carbon impurities remaining in the film cause absorption. Further, this method is a wet method, and there is a concern about the influence on the underlayer when the film is formed on the film formed by the dry method.
JP 2001-11602 A JP-A-10-339801 WO02 / 018982 Publication

  Regarding the refractive index of a porous film, there are the following well-known relational expressions.

N = Nb × P + Na (1-P)
Here, N represents the refractive index of the porous film, Nb represents the refractive index of the film when the filling ratio is 1, Na represents the refractive index of the void portion, and P represents the filling ratio of the porous film. Since the inside of the stepper is normally purged with N ₂ , the value of Na is almost 1. Therefore, according to the above formula, it can be seen that the lower the filling rate of the porous film, the lower the refractive index.

  As shown in FIG. 5, when reactive sputtering is performed under a higher pressure than usual, the number of collisions between the sputtered particles P between the target 111 and the substrate 112 increases as compared with the normal case, and the sputtered particles P have clusters. Form. Since a cluster-like film has a larger particle diameter than a normal film, the obtained film is a porous film with many voids.

  At this time, it is impractical to increase the flow rate of the supply gas or to reduce the exhaust capacity as a method for realizing a higher pressure than usual. This is because, in order to sufficiently promote the clustering of sputtered particles, the film forming chamber must be set to a considerably high pressure condition (20 Pa or higher), but conversely, the film forming speed is too low under such a high pressure condition.

  Therefore, in order to promote clustering while maintaining an appropriate film formation rate, as shown in FIG. 6, the discharge space near the target in the film formation chamber 120 is surrounded by a partition member 113, and the sputtering gas is supplied by the sputtering gas supply means 121. There is known a configuration for supplying the discharge space directly to the discharge space. The partition member 113 is provided with a hole for allowing the sputtered particles to pass through. However, by reducing the conductance, the pressure in the discharge space inside the partition can be increased to 3 to 5 times the pressure in the film formation chamber 120. it can. Therefore, even if the pressure in the discharge space is increased to a level at which clustering occurs sufficiently, the film formation chamber 120 is maintained at 3 to 5 Pa, so that an appropriate film formation rate can be obtained.

  However, the reactive gas supply method becomes a problem at this time. When the reactive gas is directly supplied to the discharge space from the reactive gas supply means 122 as in the case of the sputter gas in the above configuration, the partial pressure of the reactive gas in the discharge space increases, Reacts, causing discharge instability and a decrease in film formation rate. On the other hand, when the reactive gas is supplied not to the discharge space but to the film forming chamber 120 as shown in FIG. 8, the film obtained is rich in metal that has not undergone sufficient oxidation reaction. This means that the metal target is sputtered only with the sputtering gas in the discharge space, and naturally the cluster formed in the discharge space is a metal cluster. This is because even if the metal cluster undergoes an oxidation reaction by the reactive gas in the film forming chamber 120, it remains only on the surface and the inside remains in a metal-rich state.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and forms an optical thin film with low absorption and reduced refractive index to about 1.33 by reactive sputtering. An object of the present invention is to provide a film forming apparatus capable of performing the above.

In order to achieve the above object, a film forming apparatus of the present invention is a film forming apparatus for forming a thin film on a substrate by a reactive sputtering method, and a target for generating sputtered particles and a first discharge space of the target. A first partition member surrounding the space, a sputtering gas supply means for supplying a sputtering gas to the first space, a first opening disposed in the first partition member, and the first A second partition member surrounding the second space portion adjacent to the first space portion through the opening, a reactive gas supply means for supplying a reactive gas to the second space portion, and the second A second opening having a smaller opening diameter than the first opening disposed in the partition member, and a substrate holder for fixing the substrate so as to face the second opening. To do.

  By adjusting the amount of reactive gas that flows to the second space portion that is the reaction space and the amount of sputtering gas that flows to the first space portion that is the discharge space, a differential pressure is generated between both space portions, It is possible to prevent the reactive gas from flowing excessively into the discharge space. Therefore, problems such as unstable discharge and a decrease in film formation rate do not occur. In addition, since the partial pressure of the reactive gas can be maintained high in the second space for supplying the reactive gas, the reactivity is very strong. Therefore, the clustered sputtered particles can undergo a sufficient oxidation reaction when passing through the second space for supplying the reactive gas, and have a high quality and low refractive index porous film satisfying the stoichiometric ratio. Can be obtained.

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

  As shown in FIG. 1, in a film forming apparatus for forming a film by depositing sputtered particles generated from a target 11 on a substrate 12, a first partition surrounding a discharge space (first space) in the vicinity of the target 11. A member 13 and a second partition member 14 surrounding the reaction space (second space portion) are provided. The reaction space surrounded by the partition member 14 in the film forming chamber 20 is disposed on the substrate side of the discharge space so as to be adjacent to the discharge space, and each partition member 13, 14 has a hole through which sputtered particles pass. (Openings) 13a and 14a are formed. A sputtering gas supply means 21 is connected to the discharge space, and a reactive gas supply means 22 is connected to the reaction space.

In this film forming apparatus, a porous MgF ₂ film or the like having a low refractive index is formed by performing film formation while controlling the pressure of at least one of the discharge space and the reaction space to 3.0 Pa or higher. Can do.

  As a sputtering gas to be used, it is desirable to use Ar, Xe, Ne, Kr, or a mixed gas thereof.

It is desirable to use F ₂ , C _m F _n (m and n are integers), NF ₃ , SF ₆ , O ₂ , H ₂ or H ₂ O as the reactive gas.

  It is desirable to use Mg, Al, Si, La, Gd, Nd, Na or a compound thereof as a target.

  FIG. 2 shows one embodiment. This film forming apparatus has a preliminary chamber 30 in addition to the film forming chamber 20, and the substrate 12 is fixed to the substrate holder 31 in the preliminary chamber 30 and then evacuated to 1.0 E to 4 Pa or less by a vacuum pump 32. Then, the film is transferred to the film forming chamber 20 by the substrate transfer means 33. For this reason, air contamination into the film forming chamber 20 can be minimized. Further, when the film is not formed, the substrate 12 is returned to the preliminary chamber 30 and the gate valve 34 is closed, whereby the substrate 12 can be isolated from the film forming chamber 20 and unnecessary film adhesion can be prevented. A vacuum pump 23 and a pressure gauge 24 are installed in the film forming chamber 20 and can constantly monitor the pressure. Further, the opening degree of the exhaust valve 25 can be freely set, and the pressure in the film formation chamber during film formation can be adjusted.

  Gas required for film formation is supplied to each space while controlling the flow rate with flow rate regulators 21a and 22a, and a negative potential is applied to the target 11 from the outside with a DC power supply 26 to cause plasma discharge. A rectangular high frequency superimposing device 27 can superimpose a high frequency on the DC power source as necessary.

The width of the partition member 13 in the discharge space is 50 mm, the size of the hole 13a is 50φ, the width of the partition member 14 in the reaction space is 30mm, and the size of the hole 14a facing the substrate side is 40φ. The target 11 was Mg, the sputtering gas was Ar at a flow rate of 400 sccm, the reactive gas was F ₂ at a flow rate of 20 sccm, H ₂ at a flow rate of 25 sccm, and a film was formed on the SiO ₂ substrate 11 with an applied power of 450 W. . At that time, the opening degree of the exhaust valve 25 in the film forming chamber was adjusted so that the pressure in the film forming chamber 20 was 4.2 Pa.

The reflectance characteristics of the resulting MgF ₂ film are shown in FIG. Analysis of the results in FIG. 3 shows that the refractive index has dropped to about 1.33. In addition, since the film formation speed in this example was about 3.0 nm / s, it has a speed enough for practical use.

FIG. 4 shows the absorptivity characteristics of the MgF ₂ film obtained in this example. The absorptance was obtained by [100−transmittance (%) − reflectance (%)]. The thickness of the obtained film was about 50 nm, and the absorption rate at 193 nm from FIG. 4 was about 0.15% (substrate absorption). This shows that a very good MgF ₂ film is obtained.

It is a figure explaining one embodiment. It is a schematic diagram which shows an Example. Is a graph showing reflectance characteristics of the MgF ₂ film produced examples. Is a graph showing the absorption rate properties of MgF ₂ film produced examples. It is a figure which shows a mode that sputtered particles cluster by high pressure. It is a schematic diagram which shows one prior art example. It is a schematic diagram which shows another prior art example. It is a schematic diagram which shows another prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Target 12 Substrate 13, 14 Partition member 20 Deposition chamber 21 Sputter gas supply means 22 Reactive gas supply means

Claims (6)

In a film forming apparatus for forming a thin film on a substrate by a reactive sputtering method, a target that generates sputtered particles, a first partition member that surrounds a first space that is a discharge space of the target, and the first Sputtering gas supply means for supplying sputtering gas to the space, a first opening disposed in the first partition member, and a second adjacent to the first space via the first opening. Than a second partition member surrounding the space portion, a reactive gas supply means for supplying a reactive gas to the second space portion, and the first opening disposed in the second partition member. A film forming apparatus comprising: a second opening having a small opening diameter ; and a substrate holder for fixing the substrate so as to face the second opening.   2. The film forming apparatus according to claim 1, wherein a pressure in at least one of the first and second space portions is controlled to 3.0 Pa or more.   3. The film forming apparatus according to claim 1, wherein Ar, Xe, Ne, Kr, or a mixed gas thereof is used as the sputtering gas. The F ₁ , C _m F _n (m and n are integers), NF ₃ , SF ₆ , O ₂ , H ₂ or H ₂ O are used as the reactive gas. 2. The film forming apparatus according to 1.   5. The film forming apparatus according to claim 1, wherein Mg, Al, Si, La, Gd, Nd, Na, or a compound thereof is used as the target. A film forming method comprising forming a film of MgF ₂ by the film forming apparatus according to claim 1.

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