JP2011127168A - Plasma cvd device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate inconvenience due to deposition of insulation film, in particular, uneven film thickness and the generation of abnormal discharge, with a simple constitution. <P>SOLUTION: A plasma CVD device 1 includes parallel flat plate electrodes 5 in a vacuum chamber 3 connected with a gas supply mechanism 7 and a gas discharge mechanism 9, wherein the parallel flat plate electrodes 5 is constituted of a high-frequency electrode 5A connected with an alternate power source PS via a matching box MB and a grounded counter electrode 5B via a matching box MB. Such maintenance that insulation material 11 deposited on the surfaces of the parallel flat plate electrodes 5 is covered with a conductive film 15 and is made conductive is performed. The maintenance is performed by depositing the conductive film, for example, amorphous silicon (a-Si) film or SiN film having a refractive index of at least 2.3 while there is no substrate on a substrate holder (the counter electrode) 5B. Thereafter, deposition treatment of the substrate is performed and, thereby, the insulation film having an even thickness can be provided. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a plasma CVD film forming method and a plasma CVD apparatus. In particular, the present invention relates to a method for suppressing abnormal discharge and a method for uniformizing film thickness in a plasma CVD film forming method.

  A general capacitively coupled plasma CVD apparatus is matched with a vacuum chamber, parallel plate electrodes for discharge, a discharge gas supply mechanism, a gas exhaust mechanism, and an AC power source of several tens to several tens of MHz. It is comprised with a box (for example, refer patent document 1).

  The matching box (see FIG. 2, paragraph [0002] of Patent Document 1) inserted between the parallel plate electrode for generating the plasma discharge load and the AC power source is the output impedance of the AC power source side and the matching box. A variable inductor and a variable capacitor are provided so that the input impedance maintains a complex conjugate relationship. The matching box performs impedance matching by adjusting a variable capacitor and a variable inductor in response to a plasma discharge load that dynamically varies due to gas flow rate, pressure, contamination of the chamber 3, and the like. As a result, the reflected power from the plasma discharge electrode side of the parallel plate electrode 5 is eliminated and a constant power is supplied to the plasma discharge load, thereby enabling stable plasma discharge.

  The counter electrode also serves as a substrate holder. The substrate is placed on the substrate holder, the reaction gas is supplied from the gas supply mechanism, and the pressure in the vacuum chamber is maintained at a predetermined pressure by the gas exhaust mechanism. An AC power is supplied from an AC power source to cause plasma discharge, causing plasma generated in the reaction gas to act, and forming an insulating film on the substrate surface with reactive organisms.

JP 2007-227816 A

  However, in a conventionally known capacitively coupled plasma CVD apparatus, as the time and the number of film forming processes elapse, the plasma discharge electrode and the counter electrode (at least the exposed surface, that is, the substrate is not placed). Insulators are successively deposited on the surface portion. As a result, the film thickness of the thin film may become non-uniform or abnormal discharge may occur.

The inventors diligently studied the phenomenon described above and obtained the following findings.
The amount of the insulator deposited on the electrode surface is affected by the gas density and the electrode shape, and varies depending on the location of the electrode. Therefore, current flows easily in the low impedance region, and the plasma density is higher than that in the high impedance region, and the deposition rate is increased. As a result, the film formation rate varies depending on the location of the parallel plate electrodes.

  FIG. 10 is a conceptual diagram for explaining the deterioration of the film formation rate distribution due to the deposition of an insulator. The matching box, AC power supply, gas supply mechanism, and gas exhaust mechanism are omitted, and the substrate exists on the counter electrode in the reaction chamber. The state of the insulator deposited on the surface of the parallel plate electrode in a non-operating state is shown.

  As shown in FIG. 10, the thickness of the deposited insulator 111 gradually increases from both ends of the parallel plate electrode 105 toward the center, and accordingly, the plasma density D is low at the center and both ends. It is getting higher towards. For this reason, the film formation rate is low at the center, while the film formation rate is high at both ends, and a uniform film formation rate cannot be obtained. As a result, the film thickness of the product thin film becomes non-uniform.

  In addition, for example, in the case of a film forming apparatus that forms a passivation film of a semiconductor element using plasma CVD, particularly an apparatus that forms an antireflection film of a crystalline silicon solar cell, a large number of the reaction chamber is used at a time. When the substrate is placed on the substrate holder and the formation of the insulating film is repeated, an insulator is deposited on the portion of the substrate holder that is not covered with the substrate.

  FIG. 11 schematically shows this state. As shown in FIG. 11, the insulator 111 is deposited between the plurality of substrates S arranged on the substrate holder 105B, that is, on the surface of the substrate holder that is not covered with the substrate S, when the film formation is repeated. It becomes the substrate holder surface with.

  In addition, when an excessive current flows, local high-density discharge is caused. FIG. 12 is a conceptual diagram for explaining abnormal discharge AD, where the matching box, AC power supply, gas supply mechanism, and gas exhaust mechanism are omitted, and the surface of the parallel plate electrode in the state where the substrate does not exist on the counter electrode in the reaction chamber. Shows the state of the deposited insulator.

  As shown in FIG. 12, when an insulator is uniformly deposited on the parallel plate electrode 105, it is locally between the end portion 105 </ b> C of the high-frequency electrode 105 </ b> A that is a strong electric field portion of the electrode end portion and the earth shield 113. May cause serious arc discharge. Further, since the insulator 111 becomes a capacitor and charges are stored on the surface of the insulator, when the stored charges are released at once by discharge, a local arc discharge is caused. Such abnormal discharge AD such as local high-density discharge or arc discharge significantly deteriorates the film thickness distribution of the thin film formed on the substrate (not shown). This phenomenon is particularly remarkable in the corner portion 111A of the insulator. In addition, the abnormal discharge AD peels off the insulating film attached to the high-frequency electrode 105A and the earth shield 113, and becomes a particle generation source.

Based on the above findings, the present inventors have created the inventions of the following claims 1 to 9.
(1) The invention of claim 1 is a plasma CVD film forming method for forming a thin film on the surface of a substrate by capacitively coupled plasma CVD using an electrode, and a thin film forming step for forming a thin film on the surface of the substrate; After forming a thin film on the surface of the substrate in the thin film forming step, the method includes a conductive thin film forming step for generating a thin film on the surface of the electrode having a higher conductivity than the thin film without the substrate. Features.
(2) The invention of claim 2 is a plasma CVD apparatus for forming a thin film on the surface of the substrate by capacitively coupled plasma CVD using electrodes, and a thin film forming means for forming a thin film on the surface of the substrate, and the thin film formation And a conductive thin film generating means for generating a thin film having higher conductivity on the surface of the electrode in the absence of the substrate after forming a certain amount of thin film on the surface of the electrode. It is characterized by that.
(3) The invention of claim 3 is a plasma CVD film forming method in which discharge is performed with parallel plate electrodes and a silicon nitride thin film is formed on the surface of the substrate. A thin film forming step for forming a silicon thin film, and after forming a certain amount of silicon nitride thin film on the surface of the substrate, amorphous silicon (hereinafter a-Si) or nitriding with a refractive index of 2.3 or more without a substrate And a silicon nitride thin film forming step for forming a silicon film on the surface of the parallel plate electrode.
(4) The invention of claim 4 is a plasma CVD apparatus in which a silicon nitride thin film is formed on the surface of a substrate by discharging with parallel plate electrodes. After forming a certain amount of silicon nitride thin film on the substrate surface after forming a thin film forming means to be formed, amorphous silicon (a-Si) or a silicon nitride film having a refractive index of 2.3 or more is formed in parallel without the substrate. And a silicon nitride thin film forming means formed on the surface of the plate electrode.
(5) The invention of claim 5 is a method for forming an insulating thin film using a plasma CVD apparatus in which discharge is performed with parallel plate electrodes to form an insulating thin film on a substrate, and the insulating film is provided on the substrate. An insulating film forming step for forming a film, a determining step for determining whether or not maintenance of the surface of the parallel plate electrode is necessary, and when it is determined that the maintenance is required in the determining step, And a conductive film forming step of forming a conductive film on the surface of the parallel plate electrode without a substrate.
(6) The invention of claim 6 is the method for forming an insulating thin film according to claim 5, further comprising an abnormal discharge occurrence detecting step for detecting the occurrence of abnormal discharge, and the maintenance in the determining step is required. The determination of whether or not there is is performed based on the presence or absence of occurrence of the abnormal discharge.
(7) The invention according to claim 7 is the method for forming an insulating thin film according to claim 5, further comprising a limit film formation number setting step for setting the number of film formation processes performed continuously in advance, Whether or not the maintenance is necessary in the determination step is determined by reaching the limit number of film formations set in the limit film formation number setting step.
(8) The invention according to claim 8 is the method for forming an insulating thin film according to claim 5, further comprising a step of inspecting the thickness of the insulating film, and whether or not the maintenance in the determination step is necessary. The determination is made by reaching the film thickness set in the film thickness inspection step.
(9) The invention of claim 9 is the method for forming an insulating thin film according to claim 6, wherein the insulating film forming step, the abnormal discharge occurrence detecting step, and the conductive film forming step are repeated. It is characterized by.
(10) The invention of claim 10 is the method of forming an insulating thin film according to any one of claims 5 to 9, wherein the insulating thin film is a SiN film having a refractive index of less than 2.3, and the conductive The film is an a-Si film or a SiN film having a refractive index of 2.3 or more.

  According to the present invention, it is possible to suppress the adverse effect of the insulating film attached to the electrode without providing an additional component or apparatus in the plasma CVD apparatus.

It is a schematic block diagram of the plasma CVD apparatus of this invention. It is a flowchart explaining the electrically conductive film film-forming process by one embodiment of this invention. It is a flowchart explaining the electrically conductive film film-forming process by other embodiment of this invention. It is process drawing explaining the maintenance process of this invention. 1 is a conceptual diagram of a plasma CVD apparatus according to an embodiment of the present invention. 1 is a conceptual diagram of a plasma CVD apparatus according to an embodiment of the present invention. It is process drawing which shows the film-forming process of an insulating film. It is a graph which shows the film thickness distribution of the insulating film obtained by the insulating film forming method of this invention. It is a graph which shows the change of Vdc of the insulating film obtained by the insulating film forming method of this invention. It is a conceptual diagram explaining the deterioration of the film-forming rate distribution by the deposit of the insulator in a conventional apparatus. It is a conceptual diagram explaining the deposition condition of the insulator on the parallel plate electrode in a conventional apparatus. It is a conceptual diagram explaining the mode of generation | occurrence | production of the abnormal discharge by the insulator deposited on the parallel plate electrode in a conventional apparatus.

  A plasma CVD apparatus according to an embodiment of the present invention will be described below with reference to the drawings. In the following description of the drawings, the drawings are schematic and do not necessarily faithfully represent the actual ones, and the relative positional relationship of each component, element, etc. is for convenience of explanation. Also, the dimensional relationships and ratios are not necessarily the same between the drawings.

  FIG. 1 is a conceptual diagram showing a plasma CVD apparatus according to an embodiment of the present invention. As shown in the figure, the plasma CVD apparatus 1 includes a parallel plate electrode 5 in a vacuum chamber 3. The parallel plate electrode 5 includes a high-frequency electrode 5A connected to an AC power source PS through a matching box MB and a grounded counter electrode (also referred to as a substrate holder) 5B. The distance between the high-frequency electrode 5A and the counter electrode 5B is kept constant regardless of the location. A gas supply mechanism 7 and a gas exhaust mechanism 9 are connected to the vacuum chamber 3. The plasma CVD apparatus 1 also includes a control device 10, a detector 12, and a switch 14. The control device includes a CPU 16 that develops and executes a program or performs various calculations, and a ROM 18 that stores a program for executing a film forming sequence and a maintenance sequence of the present invention described later.

  The gas supply mechanism 7 is provided with a flow rate controller (not shown) to keep the gas supply amount constant during film formation, while the gas exhaust mechanism 9 is provided with a gas pressure regulating valve (not shown). The pressure in the vacuum chamber 3 is kept constant and uniform by the control of 10. Thereby, the gas distribution in the vacuum chamber 3 is kept uniform. The distance between the electrodes and the gas distribution are kept constant regardless of the location, the plasma discharge load becomes uniform, and stable normal glow discharge is possible without excessive local current flowing. .

  The matching box MB inserted between the parallel plate electrode 5 for generating the plasma discharge load and the AC power supply PS is a plasma discharge load that dynamically varies due to gas flow rate, pressure, contamination of the chamber 3, and the like. Corresponding to the above, impedance matching is performed by adjusting the variable capacitor and the variable inductor. As a result, the reflected power from the plasma discharge electrode 5A side of the parallel plate electrode 5 is eliminated, and constant power is supplied to the plasma discharge load, thereby enabling stable plasma discharge.

  According to one embodiment of the present invention, film formation is performed using the plasma CVD apparatus 1 shown in FIG. 1 according to the following sequence. FIG. 2 is a flowchart for explaining an insulating thin film forming method according to an embodiment of the present invention.

  As shown in FIG. 2, in the film formation process, after the apparatus is started (step S1), the supply / exhaust of the gas supply mechanism 7 and the gas exhaust mechanism 9 (flow rate, pressure, etc.), temperature adjustment with a heater (not shown), etc. are performed. A film forming environment is prepared (step S2). Next, the substrate S is placed on the substrate holder, a plasma discharge load is applied to the high-frequency electrode 5A by the AC power source PS, plasma is generated, and the plasma is caused to act on the reaction gas introduced from the gas supply mechanism 7, thereby supplying the material gas. Reaction is performed to deposit a reaction product (insulator) on the surface of the substrate S, and the substrate on which the insulating film is formed is taken out of the vacuum chamber 3 to form an insulating thin film (step S3). Each time a film is formed, the film formation counter is incremented by 1 (C = C + 1) (step S4). Next, it is determined whether the number of film formations C in this insulating film formation process has reached a predetermined limit number of film formations Rc (step S5). That is, in step S5, it is determined whether maintenance is necessary.

  This determination is made as follows. When the film forming process is repeated, the number of times the film thickness distribution of the film after that is formed exceeds the permissible range for the first time and is non-uniform, and the value is set to an appropriate value below that for safety reasons. The limit number of times of film formation is set in advance, and the value (C) of the number of times the film formation process has been performed is compared with the predetermined limit number of film formation value (Rc).

  When C <Rc, it is determined that maintenance of the parallel plate electrode is not required (step S5, NO), and when C = Rc, it is determined that maintenance of the parallel plate electrode is required (step S5, YES). In step S7, the production (film formation) is stopped, and in step S8, the conductive film is formed (maintenance).

  In step S5, when C <Rc, the process proceeds to step S6 to determine whether or not abnormal discharge has occurred. The occurrence of abnormal discharge is performed by detecting the presence or absence of arc discharge and other indicators by the detector (known discharge detector) 14 of FIG. When the occurrence of abnormal discharge is not detected (step S6, NO), the process returns to step S3 and the film formation (production) of the insulating film is continued. On the other hand, when the occurrence of abnormal discharge is detected (YES in step S6), the process proceeds to step S7, the film formation (production) of the insulating film is stopped, and the process further proceeds to step S8, where the electrode surface of the parallel plate electrode 5 is covered. Perform maintenance.

  This maintenance is performed by forming a conductive film on the counter electrode 5B, which is a substrate holder, in a state where no substrate exists. The conductive film is formed using a material having higher conductivity than the thin film of the product.

  FIG. 4 is a process diagram schematically illustrating a maintenance process. FIG. 4A is a plan view showing a state in which a plurality of substrates S are arranged at a distance from each other on the counter electrode 5B. FIG. 4B is a cross-sectional view showing a state in which the insulator 11 is deposited on the electrode surface on which the substrate of the counter electrode 5B is not placed by repeating the step of forming an insulating film on the substrate of FIG. . The insulator is not deposited on the surface of the electrode where the substrate is placed, and the electrode surface is uneven. FIG. 4C is a cross-sectional view showing a state in which the conductive film 15 is formed on the counter electrode 5B in the state of FIG. 4B and the insulator 11 is completely covered. On the other hand, FIG. 4D is a plan view showing the electrode surface of the high-frequency electrode 5A. FIG. 4E is a cross-sectional view showing a state in which an insulator is deposited also on the electrode surface of the high-frequency electrode 5A because the substrate S is placed on the substrate holder and an insulating film is repeatedly formed on the substrate S. is there. FIG. 4F is a cross-sectional view showing a state in which a dielectric film is entirely formed on the insulator 11 shown in FIG. In this way, maintenance of the high-frequency electrode 5A and the counter electrode 5B is performed.

Examples of the insulating film that can be used in the method for manufacturing an insulating thin film of the present invention include a silicon nitride film (SiN _x ), a silicon oxide film (SiO _x ), and a silicon oxynitride film (SiO _x N _y ). . These insulating films are plasmas of reactive gases selected from silane (SiH ₄ ), oxygen (O ₂ ), nitrogen (N ₂ ), hydrogen (H ₂ ), and ammonia (NH ₃ ) according to the composition of the product thin film. It is produced by reacting in the presence of A silicon nitride film is preferred.

  As the material of the conductive film used for maintenance, any material having higher conductivity than the product thin film can be used. Amorphous silicon (hereinafter referred to as “a-Si”) and silicon nitride are preferable as the material of the conductive film. In the case of a-Si, the deposited a-Si exhibits conductivity under light irradiation, and thus becomes a conductive film by light irradiation of plasma discharge. In addition, the silicon nitride film has a high insulating property when the refractive index is less than 2.3, but the conductivity is increased when the refractive index is 2.3 or more. For this reason, even when a silicon nitride thin film having a refractive index of 2.3 or more is formed, the same conductive effect as that obtained when a-Si is formed can be obtained.

  The maintenance is performed as follows, for example. For example, the following conditions are used in a state where an insulator is deposited on the parallel plate electrode 5 and the substrate S is not placed on the counter electrode 5B. That is, a high frequency voltage (for example, 300 to 600 W) is applied to the parallel plate electrodes 5 while supplying a material gas at a constant flow rate in the vacuum chamber and keeping the pressure in the vacuum chamber constant (for example, 300 to 800 Pa). By applying plasma CVD at a constant substrate temperature (for example, 300 to 670 ° C.), a highly conductive a-Si or silicon nitride thin film having a refractive index of 2.3 or more is formed on the parallel plate electrodes 5. Film. For a-Si, silane, hydrogen, and nitrogen are used for the material gas, and for a silicon nitride thin film having a refractive index of 2.3 or more, silane, ammonia, and hydrogen are used for the material gas.

  Since the deposited a-Si exhibits conductivity under light irradiation, it becomes a conductive film by light irradiation of plasma discharge during the formation of the SiN film. Since the parallel plate electrode 5 is covered with the conductive film, there is no difference in plasma impedance depending on the location, and local excessive current does not flow. Therefore, local arc discharge and abnormal discharge such as high-density discharge can be suppressed. When the refractive index of the silicon nitride film is smaller than 2.3, the insulating property is increased. However, when the refractive index is set to 2.3 or higher, the conductivity is increased. Therefore, when a silicon nitride thin film having a refractive index of 2.3 or higher is formed. In this case, the same effect as that obtained when the a-Si film is formed can be obtained.

  Referring to FIG. 2 again, it is determined in step S5 that the limit number of film formation has been reached (C = Rc), or the occurrence of abnormal discharge is detected in step S6 (that is, it is determined that maintenance is necessary). In step S7, production of the insulating film as a product is temporarily stopped, and a conductive film is formed in step S8. As a result, the insulating deposit 11 is covered with the conductive film 15. When this maintenance is completed, the process proceeds to step S9, where the count of the film formation counter is reset, and C = 0. Then, returning to step S2, preparation for forming an insulating film is performed, and an insulating film is formed in step S3. In this way, the insulating film is formed (produced).

  FIG. 3 is a flowchart for explaining an insulating thin film forming method according to another embodiment of the present invention. The flowchart shown in FIG. 3 is the same as FIG. 2 except that steps S4 and S5 in the flowchart shown in FIG. 2 are replaced with steps S4A and S5A, and step S9 is eliminated. In the film formation method according to the flowchart shown in FIG. 2, whether or not maintenance is necessary is determined by determining whether the number of film formations C in the insulating film formation process has reached a predetermined limit number of film formations Rc. However, in the film formation method according to the flowchart shown in FIG. 3, whether or not maintenance is necessary depends on whether the film thickness of the insulator deposited on the parallel plate electrode in the insulating film formation process reaches a predetermined film thickness (value). It is judged by whether or not. Therefore, in step S4A, the film thickness of the film is preferably inspected in real time using, for example, an optical film thickness measuring device during film formation (production), and the film thickness value obtained by the inspection in step S5A. It is determined whether (D) has reached a predetermined value (Dc) set in advance.

  When D <Dc, it is determined that maintenance of the parallel plate electrode is unnecessary (step S5A, NO), and the process proceeds to step S6 as in the case of the flowchart shown in FIG. When D = Dc, it is determined that the parallel plate electrode needs to be maintained (step S5A, YES), the process proceeds to step S7, the production (film formation) is stopped, and then the conductive film is formed (step S8). Maintenance) is performed. After the dielectric film is formed in step S8, the process returns to step S2, preparation for film formation for forming the insulating film is performed, and the process is repeated.

  FIG. 5 and FIG. 6 are conceptual diagrams of a plasma CVD apparatus according to an embodiment of the present invention, respectively, in which the conductive film 15 covers the insulating deposit 11 deposited on the counter electrode 5B which is a substrate holder. The state where is provided. However, in FIG. 5 and FIG. 6, illustration of the control device 10, the detector 12, and the switch 14 is omitted. By providing the conductive film 15, charges can easily move on the surface of the conductive film 15 and be distributed uniformly. Note that the conductive film 15 is formed on one surface so that there is no portion where the insulating deposit 11 is exposed. As a result, charges are evenly distributed regardless of the position on the electrode holder, and local concentration of charges does not occur.

  Therefore, as shown in FIG. 5 or FIG. 6, when a substrate is newly introduced in step S3 of FIG. 2 and an insulating film is formed using the plasma CVD apparatus after completion of maintenance, the plasma density is biased. Therefore, an insulating film with a uniform thickness can be formed. Further, even if there is a corner portion in the insulator deposited on the counter electrode 5B, it is covered with the conductive film, so that abnormal discharge does not occur. For this reason, stable plasma discharge can be obtained, and an insulating film having a uniform thickness can be formed on the substrate surface.

  As described above, in the CVD apparatus and the CVD film forming method of the present invention, the insulating film is repeatedly formed on the substrate surface, abnormal discharge is detected, or the film is deposited on the predetermined number of film formations or on the parallel electrode surface. Maintenance is performed by forming a conductive film on the deposited insulator on the parallel plate electrodes 5A and 5B, using the index that the predetermined thickness of the insulator is reached. As a result, an adverse effect on the film thickness distribution of the insulator deposited on the opposing surface of the parallel plate electrode can be eliminated without providing any special parts or devices.

[Comparative Example 1]
As described above, the CVD apparatus 1 shown in FIG. 1 can turn on and off the maintenance function shown in FIG. Therefore, the maintenance function of the CVD apparatus 1 shown in FIG. 1 is turned off, and an insulating film is first formed on the electrode surface in accordance with the procedure shown in FIGS. 7A to 7D, and then the insulating film is formed on the substrate surface. did.

  FIG. 7A shows the counter electrode 5B in the vacuum chamber 3 in a state where the substrate S is not placed. First, a highly insulating SiN film having a refractive index of 2.0 (less than 2.3) is repeatedly formed on the surface of the counter electrode 5B using a standard recipe, and a sufficient amount of SiN is sufficiently formed on the counter electrode 5B. A film 11a was formed (FIG. 7B). At this time, a SiN film 11a having a refractive index of 2.0 is also formed on the surface of the high-frequency electrode 5A. The amount of the insulator 11a deposited varies depending on the location of the electrode due to the influence of the gas density and the electrode shape, and the thickness of the insulating film on the surfaces of the parallel plate electrodes 5A and 5B is not uniform. In this way, the surface state of the parallel plate electrode 5 when the insulating film was repeatedly formed on the substrate surface was reproduced.

  The substrate S is placed on the counter electrode 5B covered with the nonuniform SiN film 11a as described above (FIG. 7C), and a refractive index of 2.0 and a film thickness of 80 nm are obtained on the surface of the substrate S. The film was formed under the SiN film formation conditions adjusted as described above (FIG. 7D). The film thickness distribution Dt was 10.58%.

  Using the CVD apparatus 1 shown in FIG. 1, a SiN film 11a having a refractive index of 2.0 was formed on the counter electrode 5B by a standard recipe in the same manner as in Comparative Example 1 (FIG. 7B). At this time, a SiN film 11a having a refractive index of 2.0 is also formed on the surface of the high-frequency electrode 5A. Thus, the state of the parallel plate electrode 5 after repeatedly performing the film-forming process was simulated. In this state, maintenance was performed as follows using the maintenance function of the CVD apparatus 1 of FIG.

  Silane and nitrogen are supplied into the vacuum chamber 3 of the plasma CVD apparatus 1 at a constant flow rate without placing the substrate on the counter electrode 5B. With the pressure in the vacuum chamber 3 kept constant, a high frequency voltage is applied to the high frequency electrode 5A from a constant current controlled AC power supply PS, and the a-Si film 15a is formed on the counter electrode 5B to which the insulating film 11a is adhered. A film was formed. By covering the insulating film 11a of the counter electrode 5B with conductive a-Si 15A, the counter electrode 5B was covered with a conductive thin film having a certain thickness (FIG. 7E). At this time, a-Si 15A is also formed on the surface of the high-frequency electrode 5A. The insulating deposit 11a is covered with an a-Si film 15a, and this a-Si film becomes a conductive film by light irradiation of plasma discharge during the formation of the SiN thin film, so that charges are locally generated during the formation of the SiN thin film. Concentration is eliminated and plasma generation becomes uniform. As a result, when the substrate S is placed and a SiN thin film is formed as an insulating film on the substrate surface, the film thickness becomes uniform.

  Actually, after the formation of the a-Si film 15a of FIG. 7E, the substrate S is placed on the counter electrode 5B (FIG. 7F), and SiN having a refractive index of 2.0 is again applied to the substrate in accordance with the standard film formation recipe. When the film was formed (FIG. 7 (g)), the film thickness distribution Dt of the SiN film on the substrate was 6.70%, and the film thickness of the SiN film formed on the substrate in the parallel plate electrode was made uniform. It was.

  FIG. 8 is a diagram showing the distribution of the thickness of the SiN film on the substrate formed before and after forming the a-Si film. FIG. 8A shows a case where a SiN thin film is formed on the substrate surface without forming an a-Si film on the surface of the parallel plate electrode 5. The film formation rate was 28.4 mm / min, and the film thickness distribution was 10.58%. FIG. 8B shows a case where a SiN thin film is formed on the substrate surface after the a-Si film is formed on the surface of the parallel plate electrode 5. The film formation rate was 30.3 mm / min, and the film thickness distribution was 6.70%.

  FIG. 9 is a graph showing the effect of the a-Si coating. As is clear from FIG. 9, the fluctuation of the DC voltage Vdc during the formation of the thin film on the substrate occurs when the SiN film is continuously formed without performing the a-Si film formation (maintenance) (FIG. 9, ◆) Since the electrode is covered with a highly insulating film (SiN having a refractive index of 2.0), the time constant until Vdc becomes stable is as long as about 150 seconds. After the a-Si film is formed on the surface of the parallel plate electrode 5, Vdc is rapidly stabilized in both the first insulating film formation (FIG. 9, ▲) and the second (FIG. 9, ■). I understand that

[Modification 1]
In Example 1, the a-Si film and the silicon nitride (SiN) film having a refractive index of 2.3 or more were formed using a gas composition containing nitrogen, hydrogen, and ammonia in addition to silane. . A result almost similar to that of Example 1 was obtained.

  Using the CVD apparatus 1 shown in FIG. 1, a SiN film 11a having a refractive index of 2.0 was formed on the counter electrode 5B by a standard recipe in the same manner as in Comparative Example 1 (FIG. 7B). At this time, a SiN film 11a having a refractive index of 2.0 is also formed on the surface of the high-frequency electrode 5A. Thus, the state of the parallel plate electrode 5 after repeatedly performing the film-forming process was simulated. In this state, maintenance was performed as follows using the maintenance function of the CVD apparatus 1 of FIG. The difference from Example 1 is that SiN is used instead of a-si as the conductive thin film.

  In a state where the substrate is not placed on the counter electrode 5B, silane and nitrogen are supplied at a constant flow rate into the vacuum chamber 3 of the plasma CVD apparatus 1 and the pressure in the vacuum chamber 3 is kept constant. A high frequency voltage was applied from the AC power source PS controlled at a constant current to 5 to form a SiN film (n = 2.3 SiN) 15b having a refractive index of 2.3 on the parallel plate electrode to which the insulating film 11a was adhered. The SiN film with a refractive index of 2.3 has higher conductivity than the SiN film with a refractive index of 2.0 (n = 2.0 SiN) 11a, and the insulating films of the parallel plate electrodes 5A and 5B are made of SiN with a refractive index of 2.3. By covering, the parallel plate electrode was made to be uniformly conductive like the a-Si film 15 in FIG. The insulating deposit 11 was covered with the SiN film 15b having a refractive index of 2.3 and became conductive. In this state, when the substrate is placed on the counter electrode 5B and an insulating film (SiN film having a refractive index of 2.0) is formed on the substrate surface, charges are not concentrated locally, and plasma generation is uniform. As a result, the thickness of the obtained SiN film becomes uniform.

  Actually, after the formation of the SiN film having a refractive index of 2.3 in FIG. 7E, the substrate S is placed on the counter electrode 5B (FIG. 7F), and again according to the standard film formation recipe (refractive index of 2). 0.0) (FIG. 7 (g)), the film thickness distribution of the substrate is almost the same as in the case of using a-Si in Example 1, and the SiN film formed on the substrate in the parallel plate electrode The film thickness was made uniform regardless of the location.

[Comparative Example 2]
Using the CVD apparatus 1 shown in FIG. 1, a SiN film 11a having a refractive index of 2.0 was formed on the counter electrode 5B by a standard recipe in the same manner as in the comparative example (FIG. 7B). At this time, a SiN film 11a having a refractive index of 2.0 is also formed on the surface of the high-frequency electrode 5A. Thus, the state of the parallel plate electrode 5 after repeatedly performing the film-forming process was simulated. Since the surface of the electrode is almost completely covered with the insulating film 11, when the deposition of the SiN film is continued, a high-density plasma discharge is visually observed near the end of the high-frequency electrode 5A ( (See FIG. 12). Further, during the discharge, the negative DC potential Vdc of the high frequency electrode 5A fluctuated and was not constant, and the amount of charge accumulated in the high frequency electrode 5A was unstable (see FIG. 9).

  Using the CVD apparatus 1 shown in FIG. 1, a SiN film 11a having a refractive index of 2.0 was formed on the counter electrode 5B by a standard recipe in the same manner as in Comparative Example 2 (FIG. 7B). At this time, a SiN film 11a having a refractive index of 2.0 is also formed on the surface of the high-frequency electrode 5A. Thus, the state of the parallel plate electrode 5 after repeatedly performing the process of forming the insulating film was simulated. In this state, when the film formation is continued using the maintenance function of the CVD apparatus 1 in FIG. 1, discharge is detected (see FIG. 2, step S6), and the film formation (production) of the SiN film is stopped. Maintenance was performed.

  In the state where the raw material gas adjusted so that SiN having a refractive index of 2.3 is obtained in the vacuum chamber 3 of the plasma CVD apparatus 1 is introduced from the gas supply mechanism 7 and the pressure in the vacuum chamber 3 is kept constant. A high frequency voltage was applied to the parallel plate electrode 5, and a SiN film having a refractive index of 2.3 was formed on the parallel plate electrode 5. By covering the deposited insulator 11 of the parallel plate electrode 5 with SiN (refractive index 2.3), the parallel plate electrode 5 is made conductive, and the amount of charge accumulated in the parallel plate electrode 5 is uniformly distributed when plasma is generated. It became a state.

  After the surface of the parallel plate electrode 5 was uniformly covered with an SiN (refractive index 2.3) film, an SiN (refractive index 2.0) film was formed again by a standard film formation recipe. Thereby, generation | occurrence | production of local high-density plasma discharge (abnormal discharge) AD was not detected. Vdc during film formation was a constant value, the amount of charge accumulated in the high-frequency electrode was stable, and no excessive current flowed locally. The fluctuation of the DC voltage Vdc during the film formation after the SiN (refractive index 2.3) film was formed was almost the same as that in FIG.

[Modification 2]
In Example 3, an a-Si film and a silicon nitride (SiN) film having a refractive index of 2.3 or more were formed using a gas composition containing nitrogen, hydrogen, and ammonia in addition to silane. Almost the same result as in Example 3 was obtained.

  In Examples 1 to 3, an insulating film is intentionally deposited on the surface of the parallel plate electrode without placing a substrate, and the state of the parallel plate electrode of the plasma CVD apparatus in which the deposited insulator 11 exists is simulated. However, in this example, the insulating film was actually formed (produced) with the maintenance function turned on using the CVD apparatus 1 of FIG.

  The apparatus is activated by the switch 14 and film formation is performed by a film formation processing program stored in the ROM 18 of the control apparatus 10. A film forming condition for forming a SiN film (refractive index 2.0) by a standard recipe is set in a storage device (not shown) by an input means (not shown). The CPU 16 of the control device 10 refers to the data of the set conditions to control the gas supply mechanism 7 and the gas exhaust mechanism 9 and the like, thereby preparing for film formation based on the control of the control device 10 (FIG. 2). Step S2). When an abnormal discharge is detected by the detector 12 during repeated film formation, a detection signal is transmitted from the detector 12 to the control device 10. When the CPU of the control device 10 receives a signal from the detector 12, it sends a film formation stop command to the gas supply mechanism 7, the gas exhaust mechanism 9, etc., and the film formation (production) of the insulating film is stopped. When the production is stopped, the control device 10 issues a command to start forming a conductive film to the gas supply mechanism 7 and the gas exhaust mechanism 9 and the maintenance is started. An a-Si film is formed on the electrode surface of the parallel plate electrode 5 without placing the substrate S on the substrate holder. When this maintenance is completed, according to the program, the control device 10 prepares to form a film on the surface of the substrate in accordance with the previously set insulating film forming conditions, and forms an insulating film on the substrate surface (production ) Is resumed.

  In the above case, when the abnormal discharge is detected by the detector 12 at the stage where the number of film formation processes (C) of the insulating film is smaller than the predetermined limit film formation number (Rc) (C <Rc) after starting the apparatus. It is. When abnormal discharge is not detected at the stage of C <Rc, the production stop command is transmitted by the control device 10 at the stage when the number of film forming processes becomes C = Rc, and the production is stopped. When production is stopped, the above-described maintenance is performed. When the maintenance is completed, film formation is prepared according to the set film formation conditions, and the film formation of the insulating film is resumed. In this manner, the insulating film is repeatedly formed on the substrate surface while performing appropriate maintenance. As a result, a product having an insulating film having a uniform thickness was obtained.

  When a SiN film having a refractive index of 2.3 was formed as a conductive film in Example 4 instead of the a-Si film in the same manner as in Example 2, an insulating film having a uniform film thickness was obtained in the same manner.

  As a preparatory stage, the number of film formations in which it was observed that the film thickness was not uniform for the first time was recorded after the insulating film was formed repeatedly. Based on the recorded number of times, the number of inner rings, for which safety is anticipated, for example, 8 is set as the limit film formation number, and the product is formed when the number of insulating film formation processes reaches the limit film formation value. As in Example 1, the conductive film is formed on the substrate holder 5 without the substrate S. After performing this maintenance, an insulating film is repeatedly formed on the substrate in the same manner as in the first embodiment. When the target number of film formation is reached, the film formation process is terminated. If the limit number of film formation is reached before reaching the target number of film formation, the production of the product is temporarily stopped, maintenance is performed, and then the product is produced. This cycle is repeated until the target number of film formation is reached.

  In the sixth embodiment, whether or not to perform maintenance is determined by setting the above-mentioned limit film formation frequency and determining whether or not the film formation frequency has reached the limit film formation frequency. The manufacturing of the product is repeated, and when the abnormal discharge is first observed or detected, the manufacturing of the product is once stopped, and the maintenance similar to the other embodiments is performed.

[Modification 3]
In Example 7, the limit number of film formations may be set in consideration of the number of film formations at which abnormal discharge is observed or detected for the first time.

  The method of setting the limit number of film formation has an advantage that the yield of the product is further improved as compared with the case where the occurrence of abnormal discharge is used as an index.

[Modification 4]
In Examples 1 to 4 and Modifications 1 to 3, the detection of abnormal discharge was detected by the detector 12, but the occurrence of abnormal discharge may be detected visually. In addition, the film forming process is automatically advanced according to the program, but the transition to each process may be performed manually.

  In Example 6, the limit number of film formation is set, and whether or not the number of film formation reaches the limit number of film formation, and in Modification 3, the occurrence of abnormal discharge is observed or detected for the first time. It is determined whether or not to perform. In this example, the film thickness of the insulator deposited on the electrode surface of the parallel plate electrode during film formation (production) is measured in real time by an optical film thickness measuring device (not shown), and the film thickness is adjusted to a predetermined film thickness. When it reaches, the production of the product is temporarily stopped, and maintenance similar to the other embodiments is performed. After maintenance is completed, film formation preparation is performed, and film formation (production) is resumed.

  The above description is merely an example, and the present invention is not limited to the above-described embodiments and modifications unless the features of the present invention are impaired. Further, it is possible to combine the embodiment and one of the modified examples, or to combine the embodiment and a plurality of modified examples. Furthermore, it is possible to combine the modified examples in any way. Alternatively, part of the steps in the embodiment, the example, or the modification can be used in or replaced with another embodiment, the example, or the modification. Furthermore, other forms conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

  The present invention can form a thin film having a uniform film thickness distribution without adding an apparatus or parts to a conventional plasma CVD apparatus, and can be suitably used particularly for the production of an insulating thin film for solar cells.

DESCRIPTION OF SYMBOLS 1 Plasma CVD apparatus 3 Vacuum chamber 5 Parallel plate electrode 5A High frequency electrode 5B Counter electrode (substrate holder)
7 Gas supply mechanism 9 Gas exhaust mechanism 11 Insulator 11a SiN film (refractive index 2.0)
12 detector 13 earth shield 14 switch 15 conductive film 15a a-Si film 15b SiN film (refractive index 2.3)
16 CPU
18 ROM
105C End 111A Insulator corner MB Matching box AD Abnormal discharge D Plasma discharge (Glow discharge)
PS AC power supply S Substrate

Claims (10)

In a plasma CVD film forming method of forming a thin film on the surface of a substrate by capacitively coupled plasma CVD using an electrode,
Forming a thin film on the surface of the substrate; and
After forming a thin film on the surface of the substrate in the thin film forming step, a conductive thin film forming step of generating a thin film on the surface of the electrode having a higher conductivity than the thin film without the substrate. The plasma CVD film-forming method characterized by these. In a plasma CVD apparatus for forming a thin film on the surface of a substrate by capacitively coupled plasma CVD using an electrode,
A thin film forming means for forming a thin film on the surface of the substrate;
A conductive thin film generating means for forming a thin film having a higher conductivity on the surface of the electrode in the absence of the substrate after forming a certain amount of thin film on the surface of the substrate by the thin film forming means; A plasma CVD apparatus comprising: In a plasma CVD film forming method in which discharge is performed with parallel plate electrodes and a silicon nitride thin film is formed on the surface of the substrate,
A thin film forming step of forming a silicon nitride thin film having a refractive index of less than 2.3 on the surface of the substrate;
After a certain amount of silicon nitride thin film is formed on the surface of the substrate, amorphous silicon (hereinafter a-Si) or a silicon nitride film having a refractive index of 2.3 or more is formed on the surface of the parallel plate electrode without the substrate. A plasma CVD film forming method comprising: forming a silicon nitride thin film forming step. In a plasma CVD apparatus that discharges with parallel plate electrodes and forms a silicon nitride thin film on the surface of the substrate,
Thin film forming means for forming a silicon nitride thin film having a refractive index of less than 2.3 on the substrate surface;
After a certain amount of silicon nitride thin film is formed on the surface of the substrate, amorphous silicon (a-Si) or a silicon nitride film having a refractive index of 2.3 or more is formed on the surface of the parallel plate electrode without the substrate. A plasma CVD apparatus comprising: a silicon nitride thin film forming unit. A method of forming an insulating thin film using a plasma CVD apparatus that discharges with parallel plate electrodes and forms an insulating thin film on a substrate,
An insulating film forming step of forming an insulating film on the substrate;
A determination step of determining whether maintenance of the surface of the parallel plate electrode is necessary;
An insulating thin film forming method comprising: a conductive film forming step of forming a conductive film on a surface of the parallel plate electrode without the substrate when it is determined that the maintenance is necessary in the determining step . In the insulating thin film formation method according to claim 5,
Furthermore, an abnormal discharge occurrence detection process for detecting the occurrence of abnormal discharge is provided,
A method for forming an insulating thin film, comprising: determining whether or not the maintenance is necessary in the determining step based on whether or not the abnormal discharge has occurred. In the insulating thin film formation method according to claim 5,
Furthermore, a limit film formation number setting step for setting the number of film formation processes performed continuously in advance is provided,
An insulating thin film forming method, wherein the determination in the determining step whether or not the maintenance is necessary is performed by reaching a limit film forming number set in the limit film forming number setting step. In the insulating thin film formation method according to claim 5,
In addition, the film thickness inspection process of the insulating film,
A method for forming an insulating thin film, comprising: determining whether the maintenance in the determining step is necessary or not by reaching a film thickness set in the film thickness inspection step. The insulating thin film formation method according to claim 6,
An insulating thin film forming method comprising repeating the insulating film forming step, the abnormal discharge occurrence detecting step, and the conductive film forming step. In the insulating thin film formation method according to any one of claims 5 to 9,
The insulating thin film forming method, wherein the insulating thin film is a SiN film having a refractive index of less than 2.3, and the conductive film is an a-Si film or a SiN film having a refractive index of 2.3 or more.

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