JP5312138B2 - Sputtering method - Google Patents

Description

  The present invention relates to a sputtering method for forming a thin film on a substrate.

  In the manufacturing process of a semiconductor integrated circuit (hereinafter referred to as IC), various dielectric films are formed. The purpose is, for example, interlayer insulation, etching, mask, passivation, capacitor dielectric film formation, etc., and the material and plasma processing method are selected according to the purpose. As the plasma processing method, for example, various methods such as CVD, dry etching, and sputtering are used.

  In recent years, plasma processing for forming a dielectric film of a capacitor with a high dielectric material such as barium strontium titanate (BST) or strontium titanate (STO) has been studied for miniaturization of ICs. Plasma processing for forming a film for sensors, actuators, and nonvolatile memory devices with a ferroelectric material such as lead zirconate titanate (PZT) or strontium bismastantalate (SBT) is also being studied.

Further, plasma processing for forming an optical thin film such as an antireflection film or an edge filter has been studied. These optical thin films usually have a low refractive index material (SiO ₂ , MgF, etc.), a high refractive index material (Ta ₂ O ₅ , TiO ₂ , Nb ₂ O _5, etc.) and a material having an intermediate refractive index (Al _2). a laminated structure of O _3, etc.), because each layer of the optical film thickness (refractive index × physical thickness) determines the device characteristics, it requires high thickness uniformity and high film thickness controllability. These optical thin films are mainly formed by vapor deposition, but film formation by sputtering is also performed from the viewpoint of film quality.

  On the other hand, the diversification of needs in recent years has led to a reduction in the number of products of various types, and there is a demand for conversion from large lot production to small lot production using conventional large-scale equipment such as vapor deposition. In addition, the shortening of the product management cycle for the purpose of reducing the inventory of products is progressing, and it is also required to shorten the production lead time. In order to meet these demands, efficient production by a small film forming apparatus using sputtering or the like is being studied.

  For the formation of an insulator (dielectric) by sputtering, RF sputtering in which an insulator is used as a target and RF power is applied to the target is the mainstream. In this method, since alternating positive and negative voltages are applied to the target, the insulator can be formed relatively stably, but the film formation rate is slow and the mass productivity is poor.

  Therefore, DC reactive sputtering has been studied in which an insulator is formed by applying a DC voltage to a target in a reactive gas atmosphere using a conductor or a semiconductor as a target. This method is suitable for mass production because the conductor and the semiconductor are sputtered and the film formation rate is high. Further, by turning on / off the reactive gas with one target, it is possible to form a plurality of types of films such as a conductor, a semiconductor, and an insulator. However, on the other hand, it is necessary to modify the surface of the target and the inside of the apparatus when switching the type of film by turning ON / OFF of the reactive gas, and the disadvantage is that the processing time becomes longer due to the modification work. is there.

  A magnetron sputtering apparatus, which is an example of a sputtering apparatus, includes a cathode on which a target is placed, a magnet that generates lines of magnetic force, and a gas adjusting unit that exhausts gas while introducing gas into the vacuum container. . In an apparatus for forming an optical thin film for an optical device, since the optical thin film is generally formed by alternately laminating a low refractive index film and a high refractive index film, two or more cathodes are arranged, and a plurality of targets are arranged. Has been.

When performing a film forming process with this magnetron sputtering apparatus, the substrate is held on the substrate holder so as to face the target, and a predetermined gas (for example, Ar, Ar + O ₂ gas) is flown through the vacuum container by the gas adjusting means. While being introduced and evacuated, the inside of the vacuum vessel is adjusted to a predetermined pressure, a negative DC voltage is applied to the target to cause glow discharge, and plasma is generated.

The generated electrons in the plasma are trapped by the magnetic field lines generated by the magnet to further promote ionization and improve the plasma density. Further, + ions (for example, Ar ⁺ , O ₂ ^+, etc.) in the plasma are attracted to the target by the negative DC voltage described above, sputter the constituent atoms of the target, and the sputtered particles ejected thereby reach the substrate. It becomes a thin film.

  In this way, when the target material is not deposited as it is but the reaction product of the target material is deposited, the reactive gas is mixed into the predetermined gas and introduced. Thereby, the sputtered particles that have jumped out of the target react with the reactive gas in the space to become a compound and deposit on the substrate.

  In this case, if the above-described method, that is, a method of forming a plurality of types of films by turning on and off the reactive gas with one target, the surface of the target and the wall surface in the container are formed by the adhesion of the generated compound. Since the member or member changes to a conductor, a semiconductor, or an insulator, the discharge state becomes unstable. Further, the film forming rate and the film quality are changed by the remaining reactive gas. For this reason, when switching the type of film by the target or the reactive gas, pre-sputtering is required in which the substrate is shielded from the target by the substrate shutter provided in the vacuum vessel and discharged for a predetermined time.

  FIG. 9 shows a step of continuously laminating a dielectric film and a conductor film. In order to form a dielectric on the first target, first, the substrate shutter is closed (step S1), a sputtering gas and a reactive gas are introduced (step S2), and pre-sputtering is performed on the target 1 for a predetermined time. (Step S3). Thereafter, the substrate shutter is opened (step S4), and a dielectric is formed on the substrate by sputtering the first target (step S5).

  Subsequently, in order to form a conductor on the second target, first, the substrate shutter is closed (step S6), the supply of reactive gas is stopped (step S7), and only the sputtering gas is supplied. Pre-sputtering is performed for a predetermined time with the target 2 (step S8). Thereafter, the substrate shutter is opened (step S9), and a conductor is formed on the substrate by sputtering the second target (step S10). In the case of further laminating, pre-sputtering is performed by the same procedure as this when switching the type of film.

  In such a conventional method, since it is necessary to modify the surface of the target and the surface in the apparatus, the processing time becomes long. On the other hand, methods for modifying the target surface and the surface in the apparatus have been conventionally proposed. One of the methods is disclosed in Patent Document 1.

In Patent Document 1, one target material is used, Ti is added to the target material, and pre-sputtering is performed for a predetermined time, thereby reducing residual oxygen, shortening the pre-sputtering time, and improving the film quality in the apparatus. .
JP 58-93346 A

  However, even in the method of Patent Document 1, after an insulator is formed by introducing a reactive gas using a certain target, the conductor (or semiconductor) is formed before another conductor (or semiconductor) is formed using another target. Since the pre-sputtering is performed for a predetermined time with a semiconductor target, it is inevitable that the production efficiency is lowered.

  In order to efficiently produce multiple devices, including optical devices that require high-quality films with high in-plane uniformity, in a small device, it is necessary to ensure high in-plane uniformity at a high deposition rate. is there. In addition, it is necessary to stabilize discharge, reduce lot-to-lot variation, and shorten film formation time during the production of a plurality of devices.

  In other words, in order to efficiently produce multiple devices in a small apparatus (especially to produce optical devices that require high in-plane uniformity and high-quality films), high in-plane at high film formation speed. It is necessary to ensure uniformity and stabilize discharge.

  In view of the above-described conventional problems, the present invention provides a method for switching the type of film when forming a conductor / semiconductor / insulator by turning on / off reactive gases with a plurality of targets in one vacuum vessel. An object of the present invention is to provide a sputtering method capable of suppressing the pre-sputtering time to be performed and stabilizing the discharge.

The sputtering method of the present invention is a sputtering method in which a substrate to be formed and a plurality of target materials as film materials are opposed to each other, and plasma is generated while introducing a sputtering gas alone or together with a reactive gas to form a film. there are a first sputtering step of forming by sputtering a first target material of the plurality of target material while using the reactive gas, the plurality of the target material with not using the reactive gas A plurality of targets between the second sputtering step of forming a film by sputtering a second target material different from the first target material, and between the first sputtering step and the second sputtering step. while shielded from the material, changing the power applied to each of the first and second target material sputtered Possess a pre-sputtering step of packaging, the in the pre-sputtering process, the sputtering the first target material while gradually lowering the power supplied to the first target material, supplied to the second target material The second target material is sputtered while gradually increasing the power applied, and both the first and second target materials are sputtered simultaneously, and then the sputtering of the first target material is performed by sputtering the second target material. It is characterized by stopping before .

  When sputtering a reactive gas is turned on / off with a plurality of targets in a single vacuum vessel to form a plurality of types of films, the sputtering method of the present invention shortens the surface of the target and the walls and members in the vacuum vessel. The discharge can be stabilized by modifying the pre-sputtering time. In addition, the variation between lots can be reduced, the film formation time can be shortened, and high-quality film formation and high-efficiency production can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals and description thereof is omitted.
(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a sputtering apparatus according to Embodiment 1 of the present invention, and more specifically shows a schematic configuration of a DC reactive magnetron sputtering apparatus.

  In the sputtering apparatus according to the first embodiment, a sputtering chamber is constituted by a container 1 that can be evacuated (hereinafter referred to as a vacuum container 1). Lower electrodes 3 and 5 are disposed in the lower part of the vacuum vessel 1, and conductive Nb target 2 and Si target 4 are fixedly held thereon. The outer circumferences of the Nb target 2 and the Si target 4 are covered with earth shields 20 and 21 that are at ground potential.

  The lower electrodes 3 and 5 are electrically insulated from the vacuum vessel 1, and predetermined DC power is applied between the lower electrodes 3 and 5 and the vacuum vessel 1 (ground) by DC pulse power sources 17 and 18. The lower electrodes 3 and 5 incorporate a water cooling mechanism (not shown) for preventing the Nb target 2 and the Si target 4 from rising in temperature.

  On the back side of the Nb target 2 and Si target 4, magnets 6 and 7 and magnets 8 and 9 surrounding the ring are arranged. Magnets 8 and 9 have opposite magnetization components to magnets 6 and 7. Further, yokes 10 and 11 for magnetically coupling the inner magnets 6 and 7 and the outer magnets 8 and 9 are arranged on the back side of the Nb target 2 and the Si target 4, and these magnets 6 to 9 are arranged. As a result, arc-shaped magnetic force lines 12 and 13 are formed on the surface of the Nb target 2 and the Si target 4.

  A substrate holder 14 that holds a substrate 15 such as a semiconductor wafer at the center thereof is disposed in parallel with the lower electrodes 3 and 5 in the upper part of the vacuum chamber 1. The substrate holder 14 is a floating potential substrate that is electrically insulated from the vacuum vessel 1 and incorporates a heating mechanism (not shown) for maintaining the substrate 15 at a predetermined temperature. 16 is a substrate holder rotating mechanism, and 19 is a substrate shutter.

FIG. 2 shows a flowchart of the film forming process by this sputtering apparatus.
In this embodiment, a Si substrate as the substrate 15, Nb is a conductor, semiconductor such as Si, in order to form a thin film of _{Nb 2 O} 5, SiO 2 is a dielectric, Nb as the target 2 Nb ( A rectangle having an outer diameter of 300 mm × 100 mm is used, and Si (a rectangle having an outer diameter of 300 mm × 100 mm) is used as the Si target 4. And each is arrange | positioned so that the distance between the centers of Nb target 2 and Si target 4 may be 100 mm, and the distance between Nb target 2 and Si target 4 and the board | substrate 15 may be 100 mm.

First, in order to form a film with the Nb target 2, the substrate shutter 19 is closed (step S11), and the vacuum vessel 1 is set to 5 × 10 ⁻⁴ Pa by a turbo molecular pump (not shown) and a rotary pump (not shown). After evacuating to 90 ° C., Ar and O ₂ gases were introduced at 90 sccm and 70 sccm, respectively, and by adjusting the exhaust with a variable conductance valve (not shown), the pressure inside the vacuum vessel 1 was kept constant at 0.5 Pa (step) S12).

  Then, 3 kW of electric power is applied to the lower electrode 3 on the back surface of the Nb target 2 by the DC pulse power source 17, thereby generating glow discharge on the Nb target 2 and performing sputtering (pre-sputtering) for a predetermined time (step S13). . At this time, a positive reverse pulse voltage is applied to the Nb target 2 in order to suppress arc discharge.

Next, the substrate shutter is opened (step S14), and Nb ₂ O ₅ is formed on the substrate by sputtering the Nb target 2 for a predetermined time (step S15).
Subsequently, in order to form a film on the Si target 4, the substrate shutter 19 is closed to shield the substrate 15 from the Nb target 2 and the Si target 4 (step S16), the reactive gas O ₂ gas is stopped, and sputtering is performed. It is assumed that only Ar gas, which is a gas, is supplied (step S17).

  Then, 3 kW of power is applied to the lower electrode 5 on the back surface of the Si target 4 by the DC pulse power supply 18 to perform pre-sputtering for modifying the surface of the Si target 4 and the wall surfaces and members of the vacuum vessel 1 ( Step S18a). At the same time as the pre-sputtering of the Si target 4, the Nb target 2 is pre-sputtered by applying a power of 3 kW from the DC pulse power source 17 (step S 18 b). Monitor voltage fluctuations to determine pre-sputtering time. The correlation between the voltage and the film formation rate is confirmed in advance (this correlation will be described later with reference to FIG. 3).

  Note that the modification in this embodiment means that the potential state in the device is stabilized by oxidizing, covering the surface with an oxide, removing the oxide, or covering the surface with a conductor. To do.

  Thereafter, the substrate shutter 19 is opened (step S19), and Si is deposited on the substrate 15 by sputtering for a predetermined time using the Si target 4 (step S20). In the case of further laminating, pre-sputtering is performed by the same procedure at the time of switching the type of film to form a film.

  FIG. 3 is a diagram showing the correlation between the voltage at the Si target and the film formation rate under the conditions of the present embodiment. In FIG. 3, the horizontal axis represents the voltage applied to the Si target, and the vertical axis represents the deposition rate at that time. As shown in FIG. 3, when a Si target is used, the deposition rate is proportional to the voltage.

  FIG. 4 is a diagram showing voltage fluctuations in the conventional flow described above with reference to FIG. As shown in FIG. 4, even if the pre-sputtering process is continued for 10 minutes (600 seconds) or longer in the conventional flow, the voltage is not stable. Therefore, from the correlation between the voltage and the film formation rate as shown in FIG. 3, the film formation rate is not stable, and when the conventional flow is used, the film quality of the laminated film may deteriorate as a result. This is because the film formation rate is not stable, so that the film thickness fluctuates or an oxygen-deficient film (a film whose refractive index fluctuates in the film) is generated.

  On the other hand, in the pre-sputtering of the flow of the present invention shown in FIG. 2 (steps S18a and S18b), since the power of the Nb target 2 is gradually lowered, the amount of sputtered particles from the Nb target 2 to the Si target 4 is reduced. Reduced gradually. On the other hand, since the power of the Si target 4 is gradually increased, in order to remove sputtered particles from the Nb target 2, the time for discharging the Si target 4 can be shortened, and the surface modification efficiency in the vacuum vessel is improved. Get better. Furthermore, since the sputtered particles from the Nb target 2 are removed after the discharge of the Nb target 2 is completed, the pre-sputtering time using only the Si target 4 can be shortened, and the surface modification efficiency in the vacuum vessel is further improved.

  Preferably, for the pre-sputtering of the Nb target 2 and the Si target 4, when starting, the power application to the Nb target 2 is started earlier than the power application to the Si target 4. Thereby, the reactive gas in the vacuum vessel can be removed by the sputtered particles of the Nb target 2. When stopping, the power application to the Nb target 2 is stopped earlier than the power application to the Si target 4. As a result, the surface of the Si target 4 can be more reliably modified, the pre-sputtering time can be shortened, and the surface modification efficiency in the vacuum vessel is improved.

  In addition, due to various studies, even if the pre-sputtering time with only the Nb target 2 at the start is too short or too long, the surface modification in the vacuum vessel is not sufficient, and the pre-sputtering with only the Nb target 2 at the start The optimum sputtering time was found to be 5 to 30 seconds. Moreover, the same examination showed that the pre-sputtering time with only the Si target 4 at the time of stop is optimal for 5 to 30 seconds. This is because if 5 seconds or less, the effect of stabilizing the potential is not sufficient, so 5 seconds or more are necessary, and if it is 30 seconds or less, the effect of reforming is sufficiently obtained.

  The optimum pre-sputtering profile obtained from the above results is shown in FIG. Moreover, the voltage fluctuation of the Si target 4 at that time is shown in FIG. From FIG. 5, it was found that in the Si target 4, the time lags at the start and stop were about 5 seconds and about 30 seconds, respectively.

(Embodiment 2)
In the second embodiment, the film is formed on SiO ₂ which is a reaction product of the Si target 4, contrary to the order of forming the film on the Si target 4 after forming the film on the Nb target 2 of the first embodiment. After that, the film is formed with Nb as a conductor.

  FIG. 7 shows a pre-sputtering profile optimized for the second embodiment as in the first embodiment. Moreover, the voltage fluctuation of the Nb target 2 at that time is shown in FIG. As shown in FIG. 7, it is found that the time lag at the start and stop is about 30 seconds and about 5 seconds are optimal in the Nb target 2 by monitoring the voltage fluctuation and obtaining the stabilized time. It was.

  In the case of forming a film using Si, which is a semiconductor, it takes time to modify the surface of the vacuum vessel because Si has a lower electrical conductivity than a conductor such as Nb. Furthermore, since Si has a very high reactivity, it easily reacts with a reactive gas, and it takes time to modify the target surface. Therefore, when the film is formed with Si, the time required for pre-sputtering tends to be long. Therefore, for Si, the effect of the present invention is greater than for a conductive material such as Nb. The pre-sputter profile can be similarly optimized depending on the target material and target size, power, pressure, and other conditions.

  As described above, when forming a plurality of film types by turning on / off reactive gases with a plurality of targets in one vacuum vessel, the first target is at least one of the plurality of targets. After forming the reaction product of the insulator with one target, before forming the conductor / semiconductor with the second target that is at least one other than the first target, the first and second By pre-sputtering these targets simultaneously while changing the film formation rate, it is possible to modify the target surface, the vacuum vessel wall surface, and the members in the vacuum vessel in a short pre-sputter time, thereby achieving stable discharge. Thereby, improvement of film quality and productivity can be realized.

  In the first and second embodiments, the example in which the film formation rate is adjusted by the input power has been described. However, it is considered that the same effect can be realized even if the film forming rate is adjusted by other methods such as pressure / power pulse conditions. . Moreover, although the example in which the pre-sputtering time is determined by monitoring the voltage has been described, the emission intensity from the plasma may be monitored alone or simultaneously with the voltage, and thereby an effect equivalent to or higher than that of voltage monitoring can be expected.

  Sputtering according to the present invention can greatly reduce the switching time of film types when forming a plurality of film types with a small number of targets, and can secure a high-quality film stably and stably. It is very useful for forming a thin film in a small apparatus.

Schematic configuration diagram of sputtering apparatus in Embodiment 1 Flowchart of film forming process in Embodiment 1 The figure which shows the correlation of the voltage fluctuation and film formation rate with Si target The figure which shows the voltage fluctuation at the time of pre-sputtering with respect to the Si target by the conventional sputtering method The figure which shows the profile of the pre-sputter | spatter with respect to Si target in Embodiment 1. The figure which shows the voltage fluctuation at the time of the pre-sputtering in Si target in Embodiment 1. The figure which shows the profile of the pre-sputtering with respect to the Nb target in Embodiment 2. The figure which shows the voltage fluctuation at the time of the pre-sputtering by the Nb target in Embodiment 2. Flow chart of conventional film formation process

DESCRIPTION OF SYMBOLS 1 Vacuum container 2 Nb target 4 Si target 3,5 Lower electrode 15 Substrate 19 Substrate shutter

Claims (8)

A sputtering method in which a substrate to be deposited and a plurality of target materials as film materials are opposed to each other, and plasma is generated while introducing a sputtering gas alone or together with a reactive gas,
A first sputtering step of forming a film by sputtering the first target material of the plurality of target materials while using the reactive gas ;
A second sputtering step of forming a film by sputtering a second target material that does not use the reactive gas and is different from the first target material among the plurality of target materials;
Wherein between the first sputtering step and the second sputtering step, while shielding the substrate from the plurality of target materials, the first and second pre-sputtering respectively varying the power applied to the target material is sputtered by It possesses a step,
In the pre-sputtering process,
Sputtering the first target material while gradually decreasing the power supplied to the first target material, and sputtering the second target material while gradually increasing the power supplied to the second target material. ,
A sputtering method, wherein both the first and second target materials are simultaneously sputtered, and then the sputtering of the first target material is stopped before the sputtering of the second target material . The sputtering method according to claim 1, wherein in the pre-sputtering step, sputtering of the first target material is started before sputtering of the second target material . 2. The sputtering method according to claim 1, wherein in the pre-sputtering step, the voltage of the second target material is monitored, and the end of pre-sputtering is determined based on the voltage . 2. The sputtering method according to claim 1, wherein in the pre-sputtering process, the emission intensity of the second target material is monitored, and the end of pre-sputtering is determined based on the emission intensity . The sputtering method according to claim 1, wherein the plurality of target materials include at least one of Si, Ti, Nb, Ta, Al, and Mg . The sputtering method according to claim 1, wherein the reactive gas contains at least one of oxygen, nitrogen, and fluorine . The sputtering method according to claim 1, wherein the second target material is a semiconductor . The sputtering method according to claim 1, wherein the second target material is Si .

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