JP2011181599A - Apparatus and method for plasma film-forming - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for plasma film forming whereby film thickness uniformity can be improved. <P>SOLUTION: In a plasma film-forming apparatus 1, a bias is applied to a substrate W when raw material gases are brought into plasma states and the raw material gases in the plasma states are reacted with each other to form a film on the substrate. In the plasma film-forming apparatus, the radius R2 of an electrode 11 applying the bias to the substrate W is made larger than the radius R1 of the substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a plasma film forming apparatus and method for forming a film on a substrate by making a source gas into a plasma state.

  A plasma film forming apparatus, for example, a plasma CVD (Chemical Vapor Deposition) apparatus forms a film on a substrate by bringing a raw material gas into a plasma state and causing the raw material gases in a plasma state to react with each other. In film formation, a bias is often applied to the substrate for the purpose of improving the quality of the formed film.

JP-A-5-82629

  When a film is formed by applying a bias to the substrate, the film thickness at the outer periphery of the substrate becomes high, and a desired film thickness uniformity may not be obtained. In particular, in an insulating film such as a silicon nitride film or a borazine film, the film thickness at the outer peripheral portion of the substrate tends to increase. For example, FIG. 5 shows the results of measuring the radial thickness (X-axis position) of a borazine film formed by a conventional plasma CVD apparatus while changing the bias (LF) applied voltage. As can be seen from FIG. 5, when LF: 0 W, that is, when the bias application is 0, the film thickness of the outer peripheral portion of the substrate (see region A in FIG. 5) is slightly lower than the central portion of the substrate, whereas LF: In the case of 50 W, 100 W, and 180 W, that is, when a bias is applied, the thickness of the substrate outer peripheral portion (see region A in FIG. 5) is higher than the central portion of the substrate, and desired film thickness uniformity can be obtained. I could not.

  The present invention has been made in view of the above problems, and an object thereof is to provide a plasma film forming apparatus and method capable of improving the uniformity of film thickness.

A plasma film forming apparatus according to a first invention for solving the above-mentioned problems is as follows.
In a plasma film forming apparatus for applying a bias to the substrate when forming a film on the substrate by causing the source gas to be in a plasma state and reacting the source gases in a plasma state to each other,
The size of the electrode for applying a bias to the substrate is larger than that of the substrate.

A plasma film forming apparatus according to a second invention for solving the above-mentioned problems is as follows.
In the plasma film forming apparatus described in the first invention,
When the radius of the substrate is R1, and the size of the electrode is R2,
(R2-R1) is at least 1 mm or more.

A plasma film forming method according to a third aspect of the present invention for solving the above problem is as follows:
In the plasma film forming method of applying a bias to the substrate when forming a film on the substrate by causing the source gas to be in a plasma state and reacting the source gases in the plasma state to each other,
A bias is applied to the substrate using an electrode larger than the size of the substrate.

  According to the present invention, since the size of the electrode for applying a bias to the substrate is made larger than the size of the substrate, it is possible to suppress an increase in the thickness of the outer peripheral portion of the substrate and improve the uniformity of the thickness. .

It is a see-through | perspective side view which shows an example of embodiment of the plasma processing apparatus which concerns on this invention. It is a schematic block diagram which shows the electrode for bias application in the plasma processing apparatus shown in FIG. It is the graph which measured the change of the film thickness of a board | substrate outer peripheral part, changing the conditions of (DELTA) R = (R2-R1). Based on the results of FIG. 3, the relationship between the rate of increase in film thickness at the outer periphery of the substrate and ΔR is graphed. It is a graph which shows the result of having measured the film thickness of the borazine film | membrane formed with the conventional plasma CVD apparatus in the radial direction (X-axis position), changing the applied voltage of bias (LF). It is a schematic block diagram which shows the structure of the electrode for the conventional bias application.

  Hereinafter, embodiments of the plasma processing apparatus and method according to the present invention will be described with reference to FIGS.

Example 1
FIG. 1 is a perspective side view showing an example of an embodiment of a plasma processing apparatus according to the present invention, and FIG. 2 is a schematic configuration diagram showing a bias application electrode in the plasma processing apparatus shown in FIG.

  First, the plasma processing apparatus of the present embodiment will be described with reference to FIG. In FIG. 1, an ICP (Inductively Coupled Plasma) type plasma CVD apparatus 1 is shown as an example, but any apparatus having a plasma generation mechanism may be used.

  The plasma CVD apparatus 1 of the present embodiment is configured such that the inside of a cylindrical vacuum chamber 2 is configured as a film forming chamber, and a ceramic disk-shaped ceiling plate 3 is formed in the upper opening of the vacuum chamber 2. However, it is arrange | positioned so that an opening part may be plugged up.

  In addition, a high-frequency antenna 4 made of, for example, a plurality of circular rings is arranged on the upper part (directly above) of the ceiling board 3, and a high-frequency power source 6 is connected to the high-frequency antenna 4 via a matching unit 5. The high-frequency power source 6 can feed a high oscillation frequency (for example, 13.56 MHz) to the high-frequency antenna 4 than the low-frequency power source 13 described later, and the electromagnetic waves that generate plasma in the vacuum chamber 2 are transmitted to the ceiling plate 3. Can enter through the light. This is a configuration of a so-called ICP type plasma generation mechanism. With an ICP type plasma generation mechanism, plasma with high electron density can be formed.

  Further, a support base 7 and an electrostatic chuck 8 attached to the support base 7 are provided at the lower part of the vacuum chamber 2, and the upper surface of the electrostatic chuck 8 is made of a semiconductor material such as Si (silicon). A disk-shaped substrate W is electrostatically held by suction. The electrostatic chuck 8 is formed in a disk shape using a ceramic material such as aluminum nitride (AlN). The position of the support table 7 can be moved up and down by an elevating device 9, and the distance between the plasma generated in the vacuum chamber 2 and the substrate W during film formation can be adjusted. ing.

  The electrostatic chuck 8 is provided with a disk-shaped electrode 11, and a low frequency power source 13 is connected to the electrode 11 via a matching unit 12. The low frequency power supply 13 can apply a bias to the substrate W by applying an oscillation frequency (for example, 4 MHz) lower than that of the high frequency power supply 6 to the electrode 11. In addition, although the electrode 11 of a present Example is formed in disk shape, if the orientation flat (Orientation Flat) exists in the board | substrate W, for example, what is necessary is just to form so that the shape may be similar.

  In addition, the support 7 is provided with a temperature control device such as a heater and a refrigerant flow path for controlling the temperature of the substrate W. The temperature control device (not shown) allows the substrate W to have a desired temperature (for example, 150). ˜700 ° C.).

  The substrate W is transported onto the electrostatic chuck 8 by opening the gate door 17 provided on the side wall of the vacuum chamber 2. After placing the substrate W on the electrostatic chuck 8, the gate door 17 is closed. A process to be described later is performed inside the vacuum chamber 2.

  A plurality of gas nozzles 14 are provided on the side wall portion of the vacuum chamber 2 at a position lower than the ceiling plate 3 and higher than the support base 7, and are controlled from the gas nozzle 14 by controlling the gas control device 15. A gas having a desired flow rate can be supplied inside.

  Further, the vacuum chamber 2 is provided with a pressure control device (vacuum pump, pressure control valve, vacuum gauge, etc .; not shown), and the inside of the vacuum chamber 2 is exhausted from the bottom side using the vacuum pump, The inside of the vacuum chamber 2 is adjusted to a desired pressure using a vacuum gauge and a pressure control valve.

  The high-frequency power supply 6, the lifting device 9, the low-frequency power supply 13, the gas control device 15, the temperature control device, the pressure control device, and the like are integrally controlled by the main control device 16, and a desired process set in advance. It is controlled according to the process and process conditions.

  Here, the structure of the electrode 11 in the plasma CVD apparatus 1 of the present embodiment will be described with reference to FIG. For comparison, FIG. 6 shows a configuration of a conventional bias application electrode.

  In the conventional plasma CVD apparatus, the size of the bias applying electrode 22 provided on the electrostatic chuck 21 is slightly smaller than that of the substrate W, as shown in FIG. For example, assuming that the radius of the substrate W is R1 and the radius of the electrode 22 is R2, the relationship of R1> R2 is established by setting R2 = R1−1.0 mm.

  On the other hand, in the plasma CVD apparatus 1 of the present embodiment, the size of the bias application electrode 11 is made larger than that of the substrate W as shown in FIG. For example, assuming that the radius of the substrate W is R1 and the radius of the electrode 11 is R2, the relation of R1 <R2 is established.

  A film formation result using the electrode 11 having the above-described structure will be described with reference to FIGS. FIG. 3 shows the change in the film thickness at the outer periphery of the substrate while changing the condition ΔR = (R2−R1). FIG. 4 shows the film at the outer periphery of the substrate based on the result of FIG. The relationship between the rate of increase in thickness and ΔR is graphed. 3 and 4 also show the results of film formation using the conventional electrode 22 for comparison. As process conditions, the diameter of the substrate W is set to 300 mm (radius R1 = 150 mm), and the borazine film is formed as a thin film at LF = 180 W. This condition is a process in which the thickness of the outer peripheral portion of the substrate is increased when the conventional electrode 22 is used.

  In the graph shown in FIG. 3, ΔR = −1 mm indicates a film formation result using the conventional electrode 22. As can be seen, in the case of ΔR = −1 mm, the film thickness of the formed borazine film increases considerably as the outer edge of the substrate W is approached. It is assumed that this is because when the bias is applied to the substrate W, the electric field strength at the outer peripheral portion of the substrate W is increased, and as a result, the film forming rate at the outer peripheral portion of the substrate is increased.

  On the other hand, in the case of ΔR = + 4 mm that satisfies the conditions of this embodiment, the tendency is considerably improved although the film thickness of the formed borazine film increases as it approaches the outer edge of the substrate W. In the case of ΔR = + 9, +14, +19 mm that satisfies the conditions of the present embodiment, the tendency is further improved. This is because the size of the electrode 11 is larger than the size of the substrate W, and therefore, when a bias is applied to the substrate W, the electric field strength increases at the outer peripheral portion of the electrode 11 outside the outer edge of the substrate W. The reason is that the film formation rate at the outer peripheral portion of the substrate is suppressed as compared with the conventional case.

  Based on the results of FIG. 3, the film thickness at a position 140 mm from the substrate center (position 10 mm from the substrate edge) is T1, and the film thickness at a position 147 mm from the substrate center (position 3 mm from the substrate edge) is T2. FIG. 4 is a graph of the rate of increase in peripheral film thickness = (T2−T1) / T1 for each condition. In general, it is desirable that the uniformity of the thin film formed is within 6% of the maximum value to the minimum value in the substrate surface. Therefore, considering this, at least if ΔR ≧ 1 mm, Uniformity can be obtained. Further, when it is desired to be within 3%, at least ΔR ≧ 5 mm may be set. When ΔR ≧ 9 mm, the rate of increase in the outer peripheral film thickness is the lowest. In this case, the uniformity can be improved most.

  Although the case where the diameter of the substrate W is 300 mm is shown here, when the diameter of the substrate W is smaller (for example, 200 mm, 150 mm, etc.), an electrostatic chuck having a size corresponding to the diameter is used. Since they are exchanged, the relation of R1> R2 is established, and the film thickness of the outer peripheral portion of the substrate tends to increase. Therefore, even when the diameter of the substrate W is smaller than 300 mm, the in-plane uniformity can be improved by satisfying the relationship of R1 <R2.

  Thus, by configuring the bias application electrode to be larger than the substrate, the uniformity of the thickness of the thin film formed on the substrate can be improved. Further, suppressing the increase in the film thickness at the outer peripheral portion of the substrate alleviates the film stress at this portion, and as a result, the thin film is prevented from peeling off and the generation of particles is also suppressed.

  Here, the film forming process of the borazine film will be described with reference to the plasma CVD apparatus 1 shown in FIG. The present invention is not limited to a borazine film but can be applied to other insulating films such as a silicon nitride film.

  First, the source gas used when forming the borazine film will be described. When forming a borazine film, an alkyl borazine compound represented by the following chemical formula 1 and a carrier gas are used as the source gas to be supplied.

ここで、上記化学式１中の側鎖基Ｒ１〜Ｒ６は、水素原子あるいは炭素数５以下のアルキル基であり、同一又は異なっていても良い。但し、Ｒ１〜Ｒ６の全てが水素原子である場合を除く。中でも、Ｒ１、Ｒ３、Ｒ５の少なくとも１つが水素原子であるアルキルボラジン化合物が好ましい。

Here, the side chain groups R1 to R6 in the chemical formula 1 are hydrogen atoms or alkyl groups having 5 or less carbon atoms, and may be the same or different. However, the case where all of R1-R6 are hydrogen atoms is excluded. Among these, alkylborazine compounds in which at least one of R1, R3, and R5 is a hydrogen atom are preferable.

  The alkyl borazine compound is vaporized and then supplied to the vacuum chamber 2 using an inert gas as a carrier gas. As the carrier gas, a rare gas such as helium or argon or nitrogen is generally used. However, a mixed gas thereof or a mixed gas to which hydrogen, oxygen, ammonia, methane, or the like is added as necessary. Also good. The alkyl borazine compound is preferably a liquid at normal temperature and pressure, but may be a solid as long as it can be vaporized (sublimated) by heating or the like.

  And in the plasma CVD apparatus 1, the borazine film | membrane is formed into a film by implementing the following procedures using the source gas mentioned above.

(Step 1)
The substrate W is transferred from the gate door 17 into the vacuum chamber 2 by using a transfer device (not shown), and is placed on the electrostatic chuck 8 and held by suction. The support 7 and the electrostatic chuck 8 are heated to any temperature of 150 ° C. to 700 ° C., which is a temperature range in which the alkyl borazine compound is not liquefied and the borazine skeleton molecules do not begin to condense with each other. The temperature of the substrate W is controlled so that the temperature of the substrate W can be processed at a desired set temperature. Further, the height position of the substrate W is moved by the elevating device 9 to any position within the range of 5 cm to 30 cm from the ceiling plate 3.

  A plasma in which electrons from the plasma generation region are diffused and decreased by separating the distance from the ceiling plate 3 to the substrate W by using the lifting device 9 so as to be spaced from the plasma generation region having a high plasma density. A substrate W is disposed in the diffusion region. Therefore, during film formation, the alkyl group dissociated from the alkylborazine compound by plasma can be neutralized before being transported to the surface of the substrate W. The neutralized alkyl group has a low probability of recombination with the borazine skeleton molecule and is exhausted as it is. As a result, when borazine skeleton molecules undergo gas phase polymerization, the incorporation of alkyl groups into the borazine film is reduced, and the amount of carbon in the thin film can be reduced. Molecules can be made high molecular weight to make a film with good characteristics.

(Step 2)
The gas control device 15 is used to supply a carrier gas (for example, He gas) from the gas nozzle 14 into the vacuum chamber 2, and the degree of vacuum in the vacuum chamber 2 is controlled to about 10 to 50 mTorr by the vacuum control device. An RF power having a frequency of 13.56 MHz is supplied from the high frequency power source 6 to the high frequency antenna 4 through the vessel 5, electromagnetic waves are incident on the vacuum chamber 2, the supplied gas is ionized, and plasma is generated in the vacuum chamber 2. Is generated. The RF power supplied by the high-frequency power source 6 is within a power range in which the plasma is stably ignited until the series of processes is completed, and the side chain group of the borazine skeleton molecule can be dissociated without breaking the borazine skeleton structure. It is controlled by one of power of a ^{800W / m 2 ~53000W / m 2} . The flow rate of the carrier gas supplied from the gas nozzle 14 is controlled to an appropriate flow rate until a series of processes is completed, but is preferably about 200 sccm to 1000 sccm.

(Step 3)
After the stabilization of the plasma, an LF power having a frequency of 4 MHz is supplied from the low frequency power supply 13 to the electrode 11 through the matching unit 12 and the alkylborazine compound shown in the chemical formula 1 vaporized from the gas nozzle 14 in the vacuum chamber 2 is supplied. Supplying while gradually increasing to a predetermined amount, the degree of vacuum in the vacuum chamber 2 is controlled to about 10 to 50 mTorr. At this time, the LF power (bias power) supplied by the low-frequency power source 13 is controlled with a power of 14500 W / m ² or less in the film forming process. When LF power is applied, gas phase polymerization between borazine skeleton-based molecules is promoted, so that not only the mechanical strength is improved but also water resistance, heat resistance, and chemical resistance are improved.

In addition to the alkylborazine compound, at least one selected from the group consisting of ammonia and an amine compound containing an alkyl group having 1 to 3 carbon atoms (for example, C ₂ H ₅ NH ₂ ) may be supplied. About 200 sccm. The alkyl group dissociated from the alkyl borazine compound is desirably not taken into the borazine film to be formed, but at least one selected from the group consisting of ammonia and an amine compound containing an alkyl group having 1 to 3 carbon atoms. By using the seed, it is possible to neutralize the alkyl group more efficiently and prevent it from being taken into the borazine film to be formed. For example, there is ethylamine (C ₂ H ₅ NH ₂ ) as an amine compound having 2 carbon atoms, but when a dissociated alkyl group and a dissociated ethylamine are reacted, an alkylamine which is a neutral molecule is obtained. Is unlikely to recombine with a borazine skeleton molecule, so it will be exhausted as it is.

  In addition, supply of ammonia, amine compounds containing an alkyl group having 1 to 3 carbon atoms, in addition to reducing incorporation of alkyl groups into the borazine film, in addition to cross-linking between borazine skeleton structures, There is also an effect that a structure (B—N—B bond) in which nitrogen dissociated from an amine compound containing an alkyl group having 1 to 3 carbon atoms enters as a spacer (B—N—B bond) is formed and the borazine skeleton structures are difficult to condense. .

  The film forming reaction in the film forming process is performed under the above process conditions. Specifically, the borazine skeleton molecule (borazine ring) and the side chain group in the alkyl borazine compound are dissociated by plasma, and the borazine skeleton molecules in the plasma state are vapor-phase polymerized to form a substrate W. A desired borazine film is formed by adsorbing to the surface.

(Step 4)
When the film forming process is performed for a predetermined time and a borazine film having a desired film thickness is formed on the substrate W, the film forming process ends, and subsequently, a reaction promoting process is performed. Specifically, the LF power from the low-frequency power source 13 that supplies power to the electrode 11 is made larger than the LF power in the film forming process, and the alkylborazine compound, ammonia, and carbon number 1 supplied from the gas nozzle 14 into the vacuum chamber 2. The amine compound containing the alkyl group of ˜3 is gradually reduced to a rare gas (He, Ar, etc.) that does not react with the borazine film itself, or an inert gas such as N ₂ , and the vacuum in the vacuum chamber 2 The degree is controlled to about 10 to 50 mTorr. In this reaction promotion step, [LF power × application time] by the low-frequency power source 13 is controlled by electric power at which the LF power is not less than 254500 W / m ² · sec and the LF power is not more than 127400 W / m ² . This is a condition for accelerating the crosslinking reaction between borazine skeleton molecules but not causing damage to the thin film. The above process conditions promote the reaction in the reaction promoting step, that is, the crosslinking reaction between borazine skeleton-based molecules.

  In this reaction promoting step, the reactive group remaining in the borazine film formed in the film forming step is condensed to promote the crosslinking reaction and remove the B—H bond. Therefore, by promoting the crosslinking reaction, the lowering of the dielectric constant is further promoted, and the change with time is suppressed by the removal of the B—H bond serving as the active site of the reaction with moisture, thereby improving the stability. Further, by promoting the crosslinking reaction, higher mechanical strength can be achieved (mechanical strength Young's modulus of 10 GPa or more). As a result, chemical resistance, workability, and CMP (Chemical Mechanical Polish) resistance are improved. It will be. In addition, heat resistance can also be achieved because an inorganic polymer material superior in heat resistance compared to an organic polymer material is used.

By implementing the above procedure, in addition to realizing a borazine film having low dielectric constant, low leakage current, and high mechanical strength, a borazine film having a small change with time in these characteristics is also realized. be able to. For example, as its specific characteristics, low dielectric constant (relative dielectric constant 3.5 or less), low leakage current (leakage current 5E-8A / cm ² or less), and high mechanical strength (Young's modulus 10 GPa or more) are realized. In addition, as the stability of the characteristics, it is possible to realize the stability of the relative permittivity (change in the relative permittivity with time of 0.1 or less).

  The present invention is suitable for a thin film formed by applying a bias, such as a borazine film or a silicon nitride film.

DESCRIPTION OF SYMBOLS 1 Plasma CVD apparatus 2 Vacuum chamber 3 Ceiling board 4 High frequency antenna 5 Matching device 6 High frequency power supply 7 Support stand 8 Substrate 9 Lifting device 11 Electrode 12 Matching device 13 Low frequency power supply 14 Gas nozzle 15 Gas control device 16 Main control device 17 Gate door

Claims (3)

In a plasma film forming apparatus for applying a bias to the substrate when forming a film on the substrate by causing the source gas to be in a plasma state and reacting the source gases in a plasma state to each other,
A plasma film forming apparatus, wherein a size of an electrode for applying a bias to the substrate is larger than that of the substrate. The plasma film forming apparatus according to claim 1,
When the radius of the substrate is R1, and the size of the electrode is R2,
(R2-R1) is at least 1 mm or more. In the plasma film forming method of applying a bias to the substrate when forming a film on the substrate by causing the source gas to be in a plasma state and reacting the source gases in the plasma state to each other,
A plasma film forming method, wherein a bias is applied to the substrate using an electrode larger than the size of the substrate.

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