JP2007096051A - Cathode-coupling plasma cvd equipment and thin film manufacturing method by it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the temperature rise of a deposition substrate, and to reduce membrane stress in a formed film by controlling high frequency power and a self bias voltage independently to an arbitrary value in cathode-coupling plasma CVD equipment. <P>SOLUTION: A low pass filter coil and a variable resistor are connected in series between a cathode electrode and a coupling capacitor and grounded. Consequently, the self bias voltage is reduced without decreasing the high frequency voltage. Accordingly, it becomes possible to prevent the temperature rise of the deposition substrate, and to form a low stress film while keeping plasma density as high as that of a conventional cathode-coupling plasma CVD. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cathode-coupled plasma CVD apparatus in which one electrode is grounded and high-frequency power is supplied to the other electrode on which an object to be coated is placed.

  A conventional cathode coupling type plasma CVD apparatus (hereinafter referred to as a cathode CVD apparatus) is shown in FIG. 1 (Patent Document 1). An upper electrode 2 and a lower electrode 3 are placed in the reaction chamber 1 substantially in parallel, the upper electrode 2 is grounded, and the lower electrode 3 is connected to a high frequency power source 6 via a coupling capacitor 4 and a matching unit (MU) 5. Is done. A gas introduction path 7 is connected to the upper electrode 2, and a gas discharge port 8 is provided in the reaction chamber 1.

  Film formation is performed as follows. A substrate 9 to be deposited is placed on the lower electrode 3, and a deposition gas supplied through the gas introduction path 7 is introduced into the reaction chamber 1 from a large number of small holes provided in the upper electrode 2 in a shower shape. When high-frequency power is supplied from the high-frequency power source 6 to the lower electrode 3, the film-forming gas between the electrodes 2 and 3 is turned into plasma and separated into film-forming gas ions and electrons that are positive ions. Among these, film forming gas ions are deposited on the substrate 9 to form a film.

  FIG. 3 shows the plasma potential distribution between the electrodes 2 and 3 in the cathode CVD apparatus. Of the plasma generated between the electrodes 2 and 3, electrons are light and move at a high speed, escape from the plasma in a short time, collide with the device wall, and disappear. On the other hand, positive ions have a much larger mass than electrons and have a slower moving speed, so they continue to exist in plasma for a long time. For this reason, the plasma has a positive charge as a whole. This phenomenon is particularly remarkable in the vicinity of the lower electrode, which is a high-frequency input electrode. This part is called an ion sheath. Attracted by the positive charge of the ion sheath, negative charges are accumulated in the lower electrode, and a negative self-bias voltage is generated. Therefore, the lower electrode is also called a cathode electrode.

  Positive ions (film formation gas ions) in the plasma are accelerated by the negative self-bias voltage and collide with the film formation substrate 9 placed on the lower electrode 3. In the cathode CVD apparatus, a physical force by this ion acceleration is applied to the chemical reaction, so that a dense film is formed at high speed.

JP 07-058103 A Japanese Patent Laid-Open No. 06-002121 Japanese Unexamined Patent Publication No. 08-176854

  In order to improve the characteristics of the film produced on the substrate 9, it is necessary to increase the high frequency power to increase the plasma density and promote the decomposition of the film forming gas. However, in the conventional cathode CVD apparatus, the self-bias voltage is uniquely determined by the high-frequency power supplied to the cathode electrode 3, and when the high-frequency power is increased, the plasma density increases, but at the same time, the self-bias voltage increases negatively. Then, although the decomposition of the film forming gas is promoted, the energy of ions incident on the substrate 9 is increased, and the substrate temperature is increased. Further, when the energy of incident ions increases, the film stress in the film formation on the substrate 9 increases, causing the substrate 9 to warp or peel off.

  On the other hand, when the heat-resistant temperature of the substrate 9 is low, it is necessary to reduce the high-frequency power to prevent the substrate temperature from rising. . The peeled film becomes fine foil pieces (particles) and falls on the substrate 9, and the quality of the film is greatly reduced. In addition, the integrated film thickness that can be continuously formed is reduced, which is a major obstacle to productivity and stability.

  Therefore, the present invention aims to reduce the temperature rise of the film-forming substrate by independently controlling the high-frequency power and the self-bias voltage to an arbitrary value, thereby improving the film characteristics and reducing the film stress. To do.

The cathode coupling type plasma CVD apparatus according to the present invention, which has been made to solve the above problems,
a) A high-frequency input electrode for placing a ground electrode and an object to be coated provided substantially in parallel in the reaction chamber,
b) a high frequency power source connected to the high frequency input electrode via a coupling capacitor;
c) a low-pass filter connected between the high-frequency input electrode and the coupling capacitor and ground,
Is provided.

  Controllability is further enhanced by connecting a variable resistor in series with this low-pass filter.

  In the present invention, the operation of “putting” the object to be coated on the high-frequency input electrode not only indicates that the high-frequency input electrode is below and the object to be coated is placed thereon, In addition, when a high frequency input electrode is arranged on the top and the object to be coated is fixed on the surface of the upper side of the high frequency input electrode on the ground electrode side, or both electrodes are erected in parallel and the object to be coated is a high frequency input electrode. Also refers to fixing to the side.

  By connecting a low-pass filter between the high-frequency input electrode (cathode electrode) and the coupling capacitor and the ground, the self-bias voltage, which is a DC voltage, can be reduced without reducing the high-frequency voltage. . As a result, it is possible to prevent the temperature rise of the film formation substrate while keeping the plasma density high and to reduce the film stress while improving the film characteristics.

  In addition, by connecting a variable resistor in series with the low-pass filter and adjusting the resistance value as appropriate, the magnitude of the self-bias voltage can be arbitrarily controlled. Thereby, the function or characteristic of the film | membrane produced | generated by the board | substrate on a high frequency input electrode is controllable. For example, a film having characteristics equivalent to those of an anode coupling type plasma CVD apparatus and a film formed by a normal cathode coupling type CVD apparatus can be continuously laminated in one reaction chamber.

Patent Document 2 discloses an apparatus in which a coil 9 and a variable resistor 10 are provided between a high-frequency power source 8 and a high-frequency coil 6, and this is the same as the cathode-coupled plasma CVD apparatus according to the present invention. Is an ion plating device that operates on a completely different principle. That is, in the ion plating apparatus, the self-bias is generated around the high-frequency coil, whereas in the cathode coupling type plasma CVD apparatus, the self-bias is generated in the vicinity of the electrode on which the substrate is placed. Therefore, the cathode coupling type plasma CVD apparatus has an effect that a dense film can be formed on the substrate at high speed by using a self-bias generated in the vicinity of the electrode on which the substrate is placed.
Patent Document 3 discloses a plasma CVD apparatus in which a high frequency power source 9 is connected to the lower electrode 3 and a DC power source is connected between the lower electrode 3 and the high frequency power source 9 and a ground via a low pass filter. Has been. Although this device can control the self-bias voltage generated in the vicinity of the lower electrode to some extent, it requires a direct current power source, which complicates the configuration of the device.

[Example 1]
One structural example of the cathode coupling type plasma CVD apparatus according to the present invention is shown in FIG. As is clear from comparison with FIG. 1, the basic configuration of the apparatus is the same as that of the conventional cathode coupling type plasma CVD apparatus, but in the apparatus according to the present invention, a lower electrode (cathode electrode) 3 to which high-frequency power is input. And a coupling capacitor 4, a low-pass filter coil 10 is connected, and a variable resistor 11 for adjusting the self-bias voltage is connected in series and grounded. The low-pass filter coil 10 and the variable resistor 11 can be separated from the lower electrode 3 by the switch 12. When separated, it becomes the same as the conventional cathode coupling type plasma CVD apparatus (FIG. 1).

  When the plasma generated between the electrodes 2 and 3 is considered as a power generation field, the coupling capacitor 4 has a time constant (the product of the coupling capacitor capacitance C and the resistance value R of the variable resistor for self-bias voltage control: CR Depending on the value of (product), it becomes overloaded. Since the low-pass filter coil 10 allows DC voltage to pass freely, negative charges accumulated in the coupling capacitor 4 are grounded from the low-pass filter coil 10 via the resistor 11. For this reason, the absolute value of the self-bias voltage decreases. In addition, the amount of negative charge flowing into the ground can be controlled by changing the CR product. Therefore, the magnitude of the self-bias voltage can be arbitrarily set by adjusting the value of the variable resistor 11.

Depending on the value of the self-bias voltage, the energy of ions that collide with the surface of the film-forming substrate 9 changes and affects the properties of the film to be generated. Therefore, by adjusting the variable resistance value, the temperature rise of the film formation substrate 9 can be controlled, and the function or characteristic of the film to be generated can be controlled.
Specifically, by changing the variable resistance value and controlling the self-bias voltage, it is possible to create a film with characteristics equivalent to those of an anode-coupled plasma CVD device, and to use a normal cathode-coupled CVD. It is also possible to create a membrane that is created with an apparatus. Further, by alternately producing them, both can be alternately and continuously stacked in one reaction chamber.

The high frequency power dependence of the high frequency voltage and the self-bias voltage was measured in the following three device configurations.
(1) A conventional apparatus configuration in which the low-pass filter coil 10 and the resistor 11 are not connected (separated).
(2) Device configuration in which a low-pass filter coil 10 (L = 102 μH) is connected and the size of the variable resistor 11 is 19 kΩ.
(3) Device configuration in which the low-pass filter coil 10 (L = 102 μH) is connected and the size of the variable resistor 11 is 1.9 kΩ.

The measurement conditions were an O ₂ flow rate of 680 sccm, a pressure of 100 Pa, a temperature of the anode electrode 2 and a temperature of the cathode electrode 3 of 100 ° C., and the high-frequency power was changed between 50 and 400 W.

  FIG. 4 shows the relationship between the high frequency power (RF) and the high frequency voltage (Vpp), and FIG. 5 shows the relationship between the high frequency power (RF) and the self-bias voltage (Vdc). Although the high frequency voltage increases as the high frequency power (RF) increases, there is almost no difference between the three device configurations. On the other hand, the self-bias voltage (Vdc) increases negatively with the increase of high-frequency power (RF) in any device configuration, but (1) is most negatively biased in the range of all high-frequency power, The absolute value of the self-bias voltage decreases as the series resistance value decreases with (2) and (3). That is, according to the device configuration (3), the absolute value of the self-bias voltage Vdc can be minimized.

  From the above results, it is found that the absolute value of the self-bias voltage can be greatly reduced by grounding the lower electrode 3 through the low-pass filter coil 10 and the resistor 11 without changing the relationship between the high-frequency power and the high-frequency voltage. did. The absolute value of the self-bias voltage greatly decreased as the resistance value was further reduced. This indicates that the connection of the low-pass filter and the resistor can suppress the ion drawing force while maintaining a high plasma density, and can reduce inconveniences such as a temperature rise of the film formation substrate 9. Furthermore, by arbitrarily setting the resistance value, it is possible to independently set the high frequency voltage and the self-bias voltage to desired values within the range of 0 V to −300 V, as shown in FIG. it is obvious.

[Example 2]
A film formation example using the cathode coupling type plasma CVD apparatus of the present invention will be shown in comparison with a film formation example using a conventional apparatus.
With the three apparatus configurations shown in Example 1, an SiO ₂ film was prepared using tetraethoxysilane and oxygen O _2, and the stress of the obtained film was measured. The high frequency power was fixed at 300 W. At this time, the self-bias voltage is -272 V in (1), -198 V in (2), and -95 V in (3). The film formation conditions were as follows: tetraethoxysilane flow rate 20 sccm, O ₂ flow rate 680 sccm, pressure 100 Pa, and the temperatures of the anode electrode 2 and the cathode electrode 3 were both 150 ° C. The film formation time was 5 minutes.

  FIG. 6 shows the relationship between the self-bias voltage (Vdc) and the film stress (Stress) of the generated film. The film prepared by the device configuration of (1) has a large compressive stress of −220 MPa because of a high self-bias voltage. On the other hand, in the films prepared by the device configurations of (2) and (3), the film stress decreased due to the reduction of the self-bias voltage.

FIG. 7 shows the relationship between the self-bias voltage (Vdc) and the deposition substrate temperature. In (1), the temperature rose from the set temperature of 150 ° C. to 190 ° C. after film formation for 5 minutes. On the other hand, the temperature is 170 ° C. in (2) and 160 ° C. in (3), and the temperature rise of the film formation substrate can be reduced by lowering the self-bias voltage.
From the above results, it was found that by reducing the self-bias voltage, a low-stress film can be formed and a film can be formed without increasing the film formation substrate temperature.

[Example 3]
A film prepared using the cathode coupling type plasma CVD apparatus of the present invention is compared with a film prepared using an anode coupling type plasma CVD apparatus (hereinafter referred to as an anode CVD apparatus).
A low stress SiCN film was prepared with the apparatus configuration of Example 1 (3) and compared with the SiCN film obtained with the anode CVD apparatus. As a film forming gas, 1,1,1,3,3,3-hexamethyldisilazane (hereinafter referred to as HMDS) and hydrogen H ₂ were used. The film formation conditions were as follows: HMDS flow rate 10 sccm, H ₂ flow rate 200 sccm, pressure 67 Pa, anode electrode 2 temperature, and cathode electrode 3 temperature were both 70 ° C.

  FIG. 8 shows FT-IR spectra of the SiCN film prepared by the anode CVD apparatus and the SiCN film prepared by the cathode CVD apparatus. Although there is a slight difference between the two, the wave numbers of the peaks that appear are almost the same, and qualitatively equivalent SiCN films are obtained. The film stress produced by the anode CVD apparatus is -5.5 MPa, and that produced by the cathode CVD apparatus is -6.6 MPa, which is almost the same value.

  From the above, it can be concluded that a low stress SiCN film equivalent to the anode CVD apparatus can be obtained by connecting a low-pass filter coil and a resistor and reducing the self-bias voltage.

  If the low-pass filter coil 10 and the variable resistor 11 connected in this embodiment are electrically disconnected from the lower electrode 3 by the switch 12, it is possible to easily return to the conventional device configuration (FIG. 1). Therefore, it is obvious that a film having characteristics equivalent to those of a film formed by anode CVD and a film equivalent to a film formed by normal cathode CVD can be continuously stacked in one reaction chamber.

  That is, the results of Examples 2 and 3 indicate that the function or characteristics of the film to be formed can be changed by changing the value of the variable resistor 11.

  An apparatus embodying this is shown in FIG. In this cathode coupling type plasma CVD apparatus, the self-bias for adjusting the value of the variable resistor 11 so that the value becomes a predetermined value while monitoring the self-bias voltage of the lower electrode (cathode electrode) 3 by the voltmeter 13. A voltage control device 14 is provided. By putting a predetermined program in the self-bias voltage control device 14 in advance, it is possible to generate a homogeneous film having desired characteristics. In addition, films having different characteristics or layers having different characteristics can be formed. A laminated film or the like can also be generated.

  The present invention can also be applied to a parallel plate type reactive etching apparatus. In this case as well, the self-bias voltage (Vdc) can be controlled independently of the high-frequency voltage. As shown in FIG. 10, the present invention can also be applied to a CVD apparatus or RIE apparatus having an inductively coupled coil. In this case, the self-bias voltage (Vdc) is controlled independently of the high-frequency voltage. can do. In this case, the coil voltage can be further reduced, and for example, the degree to which the dielectric plate installed under the coil is damaged by plasma ions can be reduced.

The schematic block diagram of an example of the conventional cathode coupling type plasma CVD apparatus. 1 is a schematic configuration diagram of an example of a cathode coupling type plasma CVD apparatus according to the present invention. The graph showing the electric potential distribution of the plasma between both electrodes in a cathode coupling type plasma CVD apparatus. The graph which shows the relationship between high frequency electric power (RF) and high frequency voltage (Vpp) in a cathode coupling type plasma CVD apparatus. The graph which shows the relationship between high frequency electric power (RF) and self-bias voltage (Vdc) in a cathode coupling type plasma CVD apparatus. The graph which shows the relationship between the self-bias voltage (Vdc) and film | membrane stress in a cathode coupling type plasma CVD apparatus. The graph which shows the relationship between the self-bias voltage (Vdc) and the film-forming substrate temperature in a cathode coupling type plasma CVD apparatus. The graph of the FTIR spectrum of the SiCN film produced with the anode CVD apparatus and the SiCN film produced with the cathode CVD apparatus. The schematic block diagram of the 2nd example of the cathode coupling type plasma CVD apparatus which concerns on this invention. The schematic block diagram of the CVD apparatus which has the inductive coupling coil to which this invention is applied.

Explanation of symbols

1 ... Plasma CVD reaction chamber 2 ... Upper electrode (anode electrode)
3. Lower electrode (cathode electrode)
DESCRIPTION OF SYMBOLS 4 ... Coupling capacitor 5 ... Matching unit 6 ... High frequency power supply 7 ... Gas introduction path 8 ... Exhaust port 9 ... Film-forming board | substrate 10 ... Low pass filter coil 11 ... Variable resistance

Claims (5)

a) A high-frequency input electrode for placing a ground electrode and an object to be coated provided substantially in parallel in the reaction chamber,
b) a high frequency power source connected to the high frequency input electrode via a coupling capacitor;
c) a low-pass filter connected between the high-frequency input electrode and the coupling capacitor and ground,
Cathode coupling type plasma CVD device with   The cathode coupling type plasma CVD apparatus according to claim 1, wherein a variable resistor is connected in series with the low-pass filter.   3. The cathode coupling type plasma CVD apparatus according to claim 2, further comprising: a voltmeter that measures a potential of the high-frequency input electrode; and a self-bias voltage control unit that controls the variable resistance based on a value detected by the voltmeter. A ground electrode and a high-frequency input electrode are provided in the reaction chamber substantially in parallel, and a high-frequency power source is connected to the high-frequency input electrode via a coupling capacitor to form a thin film on the surface of the coating object placed on the high-frequency input electrode. In a thin film manufacturing method using a cathode coupling type plasma CVD apparatus,
A low pass filter and a variable resistor are connected in series between the high frequency input electrode and the coupling capacitor and the ground.
A method for producing a thin film by a cathode coupling type plasma CVD apparatus, characterized in that a self-bias voltage of a high frequency input electrode is adjusted by changing a value of the variable resistance. 5. The method of manufacturing a thin film by a cathode coupling type plasma CVD apparatus according to claim 4, wherein films having different characteristics are laminated by changing the value of the variable resistance for each layer and changing the self-bias voltage of the high-frequency input electrode.

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