JP7130548B2 - Film forming method and film forming apparatus - Google Patents

Description

The present disclosure relates to a film forming method and a film forming apparatus.

In recent years, thin film transistors (TFTs) have been increasingly used as a technique for realizing thin displays. An oxide semiconductor composed of indium (In), gallium (Ga), and zinc (Zn), so-called IGZO, is used for the channel of the TFT from the viewpoints of high electron mobility, low power consumption, and the like. IGZO has relatively high electron mobility even in the amorphous state. Therefore, by using an oxide semiconductor such as IGZO for the channel of the TFT, high-speed switching operation can be realized.

In TFTs, the oxide semiconductor is generally covered with a protective film in order to protect the oxide semiconductor from external ions and moisture. For example, there is a technique of forming a silicon oxide (SiO) film as a protective film on an oxide semiconductor by plasma of a processing gas containing an oxygen-containing gas, a silicon fluoride (SiF4) gas, and a silicon chloride (SiCl4) gas. Are known.

JP 2017-11058 A

The present disclosure provides a technique capable of reducing damage given to an oxide semiconductor from plasma when forming a protective film of the oxide semiconductor.

A film formation method according to an aspect of the present disclosure includes generating plasma of a mixed gas containing an oxygen-containing gas, a SiF4 gas, and a SiCl4 gas, and having a first flow rate ratio of the SiCl4 gas to the SiF4 gas, with a first high-frequency power. and a first film forming step of forming a first silicon oxide film on the oxide semiconductor by the generated plasma; A plasma of a mixed gas having a second flow rate ratio of SiCl4 gas to SiCl4 gas is generated using a second high-frequency power, and the generated plasma causes the second silicon oxide film to form on the first silicon oxide film. and a second deposition step of depositing a film, wherein the first high-frequency power is lower than the second high-frequency power, and the first flow rate ratio is higher than the second flow rate ratio. small.

Advantageous Effects of Invention According to the present disclosure, it is possible to reduce damage given to an oxide semiconductor from plasma when forming a protective film of the oxide semiconductor.

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a film forming apparatus according to one embodiment. FIG. 2 is a cross-sectional view showing an example of the structure of a TFT. FIG. 3 is a flow chart showing an example of the film forming process of the passivation layer. FIG. 4 is a diagram for explaining an example of the film forming process of the passivation layer. FIG. 5 is a diagram showing an example of the relationship between the first high frequency power in the first film formation process and the S (subthreshold swing) value of the TFT. FIG. 6 is a diagram showing an example of the relationship between the first flow rate ratio in the first film formation process and the S value of the TFT. FIG. 7 is a diagram showing an example of experimental results for verifying the hydrogen capture function of the SiN film. FIG. 8 is a cross-sectional view showing an example of the configuration of a top-gate TFT. FIG. 9 is a cross-sectional view showing another example (No. 1) of the configuration of a top-gate TFT. FIG. 10 is a cross-sectional view showing another example (No. 2) of the configuration of a top-gate TFT.

Various embodiments are described in detail below with reference to the drawings. In addition, suppose that the same code|symbol is attached|subjected to the part which is the same or equivalent in each drawing.

In recent years, thin film transistors (TFTs) have been increasingly used as a technique for realizing thin displays. An oxide semiconductor composed of indium (In), gallium (Ga), and zinc (Zn), so-called IGZO, is used for the channel of the TFT from the viewpoints of high electron mobility, low power consumption, and the like. IGZO has relatively high electron mobility even in the amorphous state. Therefore, by using an oxide semiconductor such as IGZO for the channel of the TFT, high-speed switching operation can be realized.

In TFTs, the oxide semiconductor is generally covered with a protective film in order to protect the oxide semiconductor from external ions and moisture. For example, there is a technique of forming a silicon oxide (SiO) film as a protective film on an oxide semiconductor by plasma of a processing gas containing an oxygen-containing gas, a silicon fluoride (SiF4) gas, and a silicon chloride (SiCl4) gas. Are known.

By the way, when a protective film is formed by plasma of a processing gas containing oxygen-containing gas, SiF4 gas, and SiCl4 gas, the oxide semiconductor is exposed to the plasma, and the oxide semiconductor is damaged by the plasma. For example, ions or radicals in plasma cause detachment of oxygen (O) atoms from an oxide semiconductor. In addition, chlorine (Cl) atoms contained in the SiCl4 gas react with In, Ga, and Zn in the oxide semiconductor, causing desorption of In, Ga, and Zn from the oxide semiconductor. Detachment of O atoms or detachment of In, Ga, and Zn from the oxide semiconductor degrades the characteristics of the oxide semiconductor, thereby degrading the characteristics of a TFT using the oxide semiconductor. Therefore, it is expected to reduce the damage given to the oxide semiconductor when the protective film of the oxide semiconductor is formed.

[Configuration of film forming apparatus 10]
First, a film forming apparatus 10 according to one embodiment will be described. FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a film forming apparatus 10 according to one embodiment. The film forming apparatus 10 in this embodiment is an inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) apparatus. The film forming apparatus 10 has a substantially rectangular parallelepiped chamber 11 . A mounting table 12 for mounting the substrate S thereon is arranged in the chamber 11 . A temperature control mechanism (not shown) is provided in the mounting table 12, and the temperature of the substrate S mounted on the mounting table 12 is controlled to a predetermined temperature by the temperature control mechanism.

The substrate S is, for example, a glass substrate or a plastic substrate used for FPDs (Flat Panel Displays), sheet displays, and the like. A window member 14 constituting the ceiling of the chamber 11 is provided in the upper part of the chamber 11, and an antenna 13 is arranged on the window member 14 so as to face the mounting table 12 inside the chamber 11. . The window member 14 is made of, for example, a dielectric, and partitions the interior and exterior of the chamber 11 . Note that the window member 14 may be composed of a plurality of split pieces.

A side wall of the chamber 11 is formed with an opening for loading and unloading the substrate S, and the opening is closed by a gate valve 16 . An exhaust port 18 is provided at the bottom of the chamber 11 , and an exhaust device 17 is connected to the exhaust port 18 . The exhaust device 17 evacuates the inside of the chamber 11 through an exhaust port 18 to reduce the pressure inside the chamber 11 to a predetermined pressure.

The window member 14 is supported by the side wall of the chamber 11 via an insulating member (not shown), and the window member 14 and the chamber 11 are not in direct contact and are not electrically connected. Moreover, the window member 14 has a size capable of covering at least the entire surface of the substrate S on the surface substantially parallel to the substrate S placed on the mounting table 12 .

A gas introduction port 15 is provided in the side wall of the chamber 11 , and valves 22 a to 22 d are connected to the gas introduction port 15 via a gas supply pipe 23 . Valve 22a is connected to gas supply source 20a via flow controller 21a. Valve 22b is connected to gas supply source 20b via flow controller 21b. Valve 22c is connected to gas supply source 20c via flow controller 21c. Valve 22d is connected to gas supply source 20d via flow controller 21d.

The gas supply source 20a is a supply source of oxygen (O)-containing gas that does not contain hydrogen (H) atoms. In this embodiment, the gas supply source 20a supplies O2 gas. The gas supply source 20b is a supply source of SiF4 gas. The gas supply source 20c is a supply source of SiCl4 gas. The gas supply source 20d is a supply source of nitrogen (N)-containing gas that does not contain hydrogen (H) atoms. In this embodiment, the gas supply source 20d supplies N2 gas.

The O2 gas supplied from the gas supply source 20a is supplied into the chamber 11 from the gas introduction port 15 via the valve 22a and the gas supply pipe 23 after the flow rate is adjusted by the flow controller 21a. Further, the SiF4 gas supplied from the gas supply source 20b is supplied into the chamber 11 from the gas introduction port 15 via the valve 22b and the gas supply pipe 23 after the flow rate is adjusted by the flow controller 21b. The SiCl4 gas supplied from the gas supply source 20c is supplied into the chamber 11 from the gas introduction port 15 via the valve 22c and the gas supply pipe 23 after the flow rate is adjusted by the flow controller 21c. The N2 gas supplied from the gas supply source 20d has its flow rate adjusted by the flow controller 21d, and is supplied into the chamber 11 from the gas introduction port 15 via the valve 22d and the gas supply pipe 23.

The antenna 13 consists of a ring-shaped or helical conducting wire arranged along the upper surface of the window member 14 and is connected to a high-frequency power source 26 via a matching device 25 . The high-frequency power supply 26 supplies high-frequency power of a predetermined frequency to the antenna 13 and generates a magnetic field inside the chamber 11 through the window member 14 by the high-frequency current flowing through the antenna 13 . An induced electric field is generated in the chamber 11 by the magnetic field generated in the chamber 11, and electrons in the chamber 11 are accelerated by the induced electric field. Electrons accelerated by the induced electric field collide with gas molecules and atoms introduced into the chamber 11 , thereby generating inductively coupled plasma within the chamber 11 .

In the film forming apparatus 10 according to the present embodiment, when forming a passivation layer, which will be described later, first, O2 gas, SiF4 gas, and SiCl4 gas are supplied into the chamber 11, and an inductively coupled plasma is generated from a mixed gas of the supplied gases. is generated. Then, a first silicon oxide (SiO) film is formed on the substrate S mounted on the mounting table 12 by the generated inductively coupled plasma. Subsequently, O2 gas is supplied into the chamber 11, and inductively coupled plasma is generated from the supplied O2 gas. Then, the first SiO film is exposed to the generated inductively coupled plasma (that is, O2 gas plasma). Subsequently, O2 gas, SiF4 gas, and SiCl4 gas are supplied into the chamber 11, and inductively coupled plasma is generated from a mixed gas of the supplied gases. A second SiO film is formed on the first SiO film by the generated inductively coupled plasma. Subsequently, N2 gas, SiF4 gas, and SiCl4 gas are supplied into the chamber 11, and inductively coupled plasma is generated from a mixed gas of the supplied gases. A silicon nitride (SiN) film is formed on the second SiO film by the generated inductively coupled plasma. As a result, a passivation layer, which is a multilayer film including the first SiO film, the second SiO film and the SiN film, is formed. The passivation layer has a function of protecting the oxide semiconductor formed on the substrate S from moisture and the like. A passivation layer is an example of a protective film that protects an oxide semiconductor.

The film forming apparatus 10 includes a controller 27 including a processor, memory, and the like. The control unit 27 controls each unit of the film forming apparatus 10 according to data such as recipes and programs stored in the memory. For example, the control unit 27 controls the exhaust device 17, the flow controllers 21a-21d, the valves 22a-22d, and the high-frequency power supply 26, respectively. The control unit 27 is realized by a computer having various integrated circuits such as an ASIC (Application Specific Integrated Circuit) and a CPU (Central Processing Unit), electronic circuits, and the like.

[Configuration of TFT 30]
FIG. 2 is a cross-sectional view showing an example of the configuration of the TFT 30. As shown in FIG. The TFT 30 in this embodiment is of the back channel etch type.

The TFT 30 includes, for example, an undercoat layer 31 formed on a substrate S, a gate electrode 32 partially formed on the undercoat layer 31, an undercoat layer 31 and a gate electrode 32, as shown in FIG. and a gate insulating layer 33 formed to cover the . In this embodiment, as the undercoat layer 31 and the gate insulating layer 33, for example, a SiO film or a SiN film is used.

The TFT 30 has a channel 34 formed on the gate insulating layer 33 so as to be directly above the gate electrode 32 , and source electrodes 35 formed on both sides of the channel 34 on the gate insulating layer 33 . and a drain electrode 36 . In this embodiment, the channel 34 is an oxide semiconductor. In the present embodiment, the channel 34 uses, for example, so-called IGZO, which is an oxide semiconductor made of indium (In), gallium (Ga), and zinc (Zn). Note that the material of the channel 34 is not limited to IGZO as long as it is an oxide semiconductor.

The TFT 30 also includes a passivation layer 37 formed on the gate insulating layer 33 to cover the channel 34 , the source electrode 35 and the drain electrode 36 .

In this embodiment, the passivation layer 37 is a multilayer film including a first SiO film 371 , a second SiO film 372 and a SiN film 373 . The first SiO film 371 is formed on the channel 34 by plasma of a mixed gas containing oxygen-containing gas such as O2 gas, SiF4 gas, and SiCl4 gas. The second SiO film 372 is formed on the first SiO film 371 by plasma of a mixed gas containing oxygen-containing gas such as O2 gas, SiF4 gas, and SiCl4 gas. The SiN film 373 is formed on the second SiO film 372 by plasma of a mixed gas containing nitrogen-containing gas such as N2 gas, SiF4 gas, and SiCl4 gas.

By the way, when the first SiO film 371 is formed by plasma of a mixed gas containing oxygen-containing gas such as O2 gas, SiF4 gas, and SiCl4 gas, the channel 34 is exposed to the plasma. Damage is applied to channel 34 . For example, ions and radicals in the plasma cause detachment of O atoms from the channel 34 . In addition, Cl atoms contained in the SiCl4 gas react with In, Ga, and Zn in the channel 34, causing detachment of O atoms from the channel 34. FIG. Detachment of O atoms and detachment of In, Ga, and Zn from the channel 34 degrades the characteristics of the channel 34 and the characteristics of the TFT 30 using the channel 34 .

Therefore, in the present embodiment, the high-frequency power used to generate the plasma of the mixed gas in the deposition process of the first SiO film 371 is lowered, and the flow ratio of the SiCl4 gas to the SiF4 gas is decreased. This suppresses an increase in the plasma density during the period in which the first SiO film 371 is formed on the channel 34, and can reduce the damage given to the channel 34 by the plasma. As a result, deterioration of the characteristics of the channel 34 can be suppressed, and deterioration of the characteristics of the TFT 30 using the channel 34 can be suppressed.

Specifically, the high-frequency power used to generate the plasma of the mixed gas in the deposition process of the first SiO film 371 is the same as the high-frequency power used to generate the plasma of the mixed gas in the deposition process of the second SiO film 372 . lower than electricity. This suppresses an increase in the plasma density during the period in which the first SiO film 371 is formed on the channel 34, and can reduce the damage given to the channel 34 by the plasma. For example, the number of O atoms leaving the channel 34 is suppressed.

Also, the flow rate ratio of SiCl4 gas to SiF4 gas in the deposition process of the first SiO film 371 is smaller than the flow rate ratio of SiCl4 gas to SiF4 gas in the deposition process of the second SiO film 372 . As a result, the reaction between Cl atoms contained in the SiCl4 gas and In, Ga, and Zn in the channel 34 is suppressed during the period in which the first SiO film 371 is formed on the channel 34. The numbers of desorbed In, Ga and Zn are suppressed.

[Deposition procedure]
FIG. 3 is a flow chart showing an example of the film forming process of the passivation layer 37. As shown in FIG. FIG. 4 is a diagram for explaining an example of the film forming process of the passivation layer 37. As shown in FIG. The flow chart shown in FIG. 3 is executed by the controller 27 controlling the operation of each part of the film forming apparatus 10 according to a predetermined program.

First, the gate valve 16 is opened, and, for example, as shown in FIG. S101). The channel 34, the source electrode 35, and the drain electrode 36 are exposed in the substrate S carried into the chamber 11. As shown in FIG. After the substrate S is loaded into the chamber 11, the gate valve 16 is closed. Depending on the process, the substrate may be a substrate on which part of the gate electrode 32, the channel 34, the source electrode 35, and the drain electrode 36 are formed.

Next, the control unit 27 executes a first film forming step of forming a first SiO film 371 on the channel 34 (S102). In the first film forming process, the controller 27 controls the exhaust device 17 to exhaust the inside of the chamber 11 to a predetermined degree of vacuum. Then, the control unit 27 controls the valves 22a to 22c to open. The valve 22d is controlled to be closed.

Then, the controller 27 controls the flow rate controller 21a so that the flow rate of the O2 gas supplied from the gas supply source 20a becomes a predetermined flow rate. Then, the controller 27 controls the flow rate controller 21b so that the flow rate of the SiF4 gas supplied from the gas supply source 20b becomes a predetermined flow rate. Then, the controller 27 controls the flow rate controller 21c so that the flow rate of the SiCl4 gas supplied from the gas supply source 20c becomes a predetermined flow rate. In the first film forming process, the controller 27 controls the flow rate controllers 21b and 21c so that the flow rate ratio of the SiCl4 gas to the SiF4 gas becomes the "first flow rate ratio". Thereby, a mixed gas containing O2 gas, SiF4 gas, and SiCl4 gas is supplied into the chamber 11 .

Also, in the first film forming process, the control unit 27 controls the high frequency power supply 26 to apply the “first high frequency power” to the antenna 13 . As a result, an induced electric field is generated in the chamber 11, and plasma of a mixed gas containing O2 gas, SiF4 gas and SiCl4 gas is generated. A first SiO film 371 is laminated on the channel 34, the source electrode 35 and the drain electrode 36 by the generated plasma. As a result, a first SiO film 371 having a predetermined thickness is formed on the channel 34, the source electrode 35 and the drain electrode 36, for example, as shown in FIG. 4B. The thickness of the first SiO film 371 is thinner than the thickness of the second SiO film 372 which is formed on the first SiO film 371 in the second film forming process which will be described later. The first high frequency power and the first flow rate ratio in the first film forming process will be described later.

Next, the control unit 27 executes an exposure step of exposing the first SiO film 371 to O2 gas plasma (S103). In the exposure step, the controller 27 controls the valves 22b and 22c to close while maintaining the valve 22a open. Then, the controller 27 controls the flow rate controller 21a so that the flow rate of the O2 gas supplied from the gas supply source 20a becomes a predetermined flow rate. O 2 gas is thereby supplied into the chamber 11 .

Also, in the exposure step, the control unit 27 controls the high-frequency power source 26 to apply high-frequency power of a predetermined magnitude to the antenna 13 . As a result, an induced electric field is generated in the chamber 11, and plasma of O2 gas is generated. By exposing the first SiO film 371 to the O 2 gas plasma, O atoms are supplied to the channel 34 from the O 2 gas plasma through the first SiO film 371 . As a result, oxygen defects in the channel 34 are repaired without exposing the channel 34 directly to O2 gas plasma. If the channel 34 is exposed to plasma of O2 gas, damage will be caused to the channel 34 . Here, since the thickness of the first SiO film 371 is thinner than the thickness of the second SiO film 372 formed on the first SiO film 371, the O atoms passing through the first SiO film 371 are reduced. Supply is smooth.

Next, the control unit 27 executes a second film forming step of forming a second SiO film 372 on the first SiO film 371 (S104). In the second film forming step, the control unit 27 controls the valves 22b and 22c to be opened while maintaining the valve 22a open.

Then, the controller 27 controls the flow rate controller 21a so that the flow rate of the O2 gas supplied from the gas supply source 20a becomes a predetermined flow rate. Then, the controller 27 controls the flow rate controller 21b so that the flow rate of the SiF4 gas supplied from the gas supply source 20b becomes a predetermined flow rate. Then, the controller 27 controls the flow rate controller 21c so that the flow rate of the SiCl4 gas supplied from the gas supply source 20c becomes a predetermined flow rate. In the second film forming process, the controller 27 controls the flow rate controllers 21b and 21c so that the flow rate ratio of the SiCl4 gas to the SiF4 gas becomes the "second flow rate ratio". Thereby, a mixed gas containing O2 gas, SiF4 gas, and SiCl4 gas is supplied into the chamber 11 .

Also, in the second film forming process, the control unit 27 controls the high frequency power supply 26 to apply the “second high frequency power” to the antenna 13 . As a result, an induced electric field is generated in the chamber 11, and plasma of a mixed gas containing O2 gas, SiF4 gas and SiCl4 gas is generated. Then, the second SiO film 372 is laminated on the first SiO film 371 by the generated plasma. As a result, a second SiO film 372 having a predetermined thickness is formed on the first SiO film 371, as shown in FIG. 4C, for example. The second high-frequency power and the second flow rate ratio in the second film forming process will be described later.

Next, the control unit 27 executes a third film forming step of forming a SiN film 373 on the second SiO film 372 (S105). In the third film forming process, the control unit 27 controls the valves 22a to 22c to be closed. The controller 27 then controls the exhaust device 17 to exhaust the gas in the chamber 11 . Then, the control unit 27 controls the valves 22b to 22d to open.

Then, the controller 27 controls the flow rate controller 21b so that the flow rate of the SiF4 gas supplied from the gas supply source 20b becomes a predetermined flow rate. Then, the controller 27 controls the flow rate controller 21c so that the flow rate of the SiCl4 gas supplied from the gas supply source 20c becomes a predetermined flow rate. Then, the controller 27 controls the flow rate controller 21d so that the flow rate of the N2 gas supplied from the gas supply source 20d becomes a predetermined flow rate. Thereby, a mixed gas containing N2 gas, SiF4 gas and SiCl4 gas is supplied into the chamber 11 .

Also, in the third film forming process, the control unit 27 controls the high frequency power supply 26 to apply high frequency power of a predetermined magnitude to the antenna 13 . As a result, an induced electric field is generated in the chamber 11, and plasma of a mixed gas containing N2 gas, SiF4 gas and SiCl4 gas is generated. Then, the SiN film 373 is laminated on the second SiO film 372 by the generated plasma. As a result, a SiN film 373 having a predetermined thickness is formed on the second SiO film 372, for example, as shown in FIG. 4(D). Thereby, the passivation layer 37 including the first SiO film 371, the second SiO film 372 and the SiN film 373 is formed. Thus, the TFT 30 of this embodiment is manufactured. The significance of forming the SiN film 373 will be described later.

After that, the control unit 27 stops the high-frequency power supply 26, controls the valves 22b to 22d to be closed, and controls the exhaust device 17 to exhaust the gas in the chamber 11. FIG. Then, the gate valve 16 is opened and the substrate S is unloaded from the chamber 11 (S106).

[First high-frequency power and first flow rate ratio in first film formation step]
Here, the first high-frequency power and the first flow rate ratio in the first film formation step will be further described. FIG. 5 is a diagram showing an example of the relationship between the first high-frequency power in the first film formation process and the S (sub-threshold swing) value of the TFT 30. As shown in FIG. The S value is the gate voltage applied to increase the current value of the TFT 30 by one order of magnitude. A smaller S value indicates better characteristics of the TFT 30, and a larger S value indicates that the channel 34 of the TFT 30 becomes conductive.

As shown in FIG. 5, the lower the first high frequency power, the smaller the S value. That is, it was confirmed that the lower the first high-frequency power, the better the characteristics of the TFT 30 . This is because the lower the first RF power, i.e., the lower the density of the plasma generated using the first RF power, the more the flow from the plasma to the channel 34 of the TFT 30 during the first deposition step. It is thought that this is because the damage applied is reduced.

FIG. 6 is a diagram showing an example of the relationship between the first flow rate ratio and the S value of the TFT 30 in the first film formation process.

As shown in FIG. 6, the smaller the first flow rate ratio, the smaller the S value. That is, it was confirmed that the smaller the first flow rate ratio, the better the characteristics of the TFT 30 . This is because the smaller the first flow rate ratio, that is, the smaller the flow rate ratio of SiCl4 gas to SiF4 gas, the less damage given to the channel 34 of the TFT 30 from the plasma during the execution of the first film formation process. This is thought to be for the purpose of

From the results of FIGS. 5 and 6, in order to obtain favorable characteristics of the TFT 30, it is preferable that the first high-frequency power in the first film formation step is low and the first flow ratio is small.

Therefore, in the present embodiment, the first high frequency power in the first film forming process is set to be lower than the second high frequency power in the second film forming process. Furthermore, the first flow rate ratio in the first film forming process is set to be smaller than the second flow rate ratio in the second film forming process. As a result, it is possible to reduce the damage given to the channel 34 from the plasma when the protective film of the channel 34 is formed, and as a result, it is possible to suppress deterioration of the characteristics of the TFT 30 using the channel 34 .

[Significance of forming the SiN film 373]
Here, the significance of forming the SiN film 373 on the second SiO film 372 will be described. The SiN film has a function of trapping hydrogen (H) atoms (hereinafter referred to as "hydrogen trapping function"). FIG. 7 is a diagram showing an example of experimental results for verifying the hydrogen capture function of the SiN film. In the experiment of FIG. 7, a first sample having only a SiN film containing hydrogen (H) atoms (hereinafter referred to as "SiN:H film") was prepared. Also, in the experiment of FIG. 7, a second sample having a SiN:H film and an SiO film formed on the SiN:H film was prepared. Also, in the experiment of FIG. 7, a third sample having a SiN:H film and a SiN film formed on the SiN:H film was prepared. FIG. 7 shows that each sample (each of the first sample, the second sample, and the third sample) is heated, and the number of hydrogen (H) atoms desorbed from each sample is measured as the number of ions by a measuring instrument. This is the result of In FIG. 7, graph 511 corresponds to the first sample, graph 512 corresponds to the second sample, and graph 513 corresponds to the third sample.

As shown in FIG. 7, the third sample with the SiN film has a higher count of H ions, i.e., desorbed H atoms, than the first and second samples without the SiN film. small number of Further, even when the third sample having the SiN film was heated to around 400° C., desorption of H atoms from the third sample was suppressed.

From the results of FIG. 7, it was confirmed that the SiN film traps H atoms more efficiently than the SiO film. Since H atoms affect the deterioration of the characteristics of the channel 34, the protective film (for example, the passivation layer 37) that protects the channel 34 should contain a SiN film capable of efficiently trapping H atoms. is preferred.

Therefore, in this embodiment, a SiN film 373 is formed on the second SiO film 372 . As a result, the SiN film 373 can efficiently capture the H atoms passing through the SiN film 373 and heading toward the channel 34, and as a result, the deterioration of the characteristics of the TFT 30 using the channel 34 can be suppressed. .

As described above, the film forming method according to one embodiment includes the first film forming process and the second film forming process. In the first film forming step, plasma of a mixed gas containing an oxygen-containing gas, a SiF4 gas, and a SiCl4 gas and having a first flow rate ratio of the SiCl4 gas to the SiF4 gas is generated using a first high-frequency power. Generate. In the first film forming process, the generated plasma forms a first SiO film 371 on the channel 34 . In the second film forming step, plasma of a mixed gas containing an oxygen-containing gas, a SiF4 gas, and a SiCl4 gas and having a second flow rate ratio of the SiCl4 gas to the SiF4 gas is generated using a second high-frequency power. Generate. In the second film formation process, a second SiO film 372 is formed on the first SiO film 371 by the generated plasma. Here, the first high frequency power is lower than the second high frequency power and the first flow ratio is lower than the second flow ratio. As a result, it is possible to reduce the damage given to the channel 34 from the plasma when the protective film of the channel 34 is formed, and as a result, it is possible to suppress deterioration of the characteristics of the TFT 30 using the channel 34 .

In addition, the film forming method according to one embodiment further includes an exposing step of exposing the first SiO film 371 to O2 gas plasma between the first film forming step and the second film forming step. . As a result, O atoms are supplied to the channel 34 from the O 2 gas plasma through the first SiO film 371 . As a result, oxygen defects in the channel 34 are repaired without exposing the channel 34 directly to O2 gas plasma. As a result, deterioration of the characteristics of the TFT 30 using the channel 34 can be further suppressed.

In addition, in the film forming method according to one embodiment, a third film forming method for forming a SiN film 373 on the second SiO film 372 by plasma of a mixed gas containing nitrogen-containing gas, SiF4 gas, and SiCl4 gas is performed. Further comprising steps. As a result, the SiN film 373 can efficiently capture the H atoms passing through the SiN film 373 and heading toward the channel 34, and as a result, the deterioration of the characteristics of the TFT 30 using the channel 34 can be suppressed. .

[Other embodiments]
Although the film forming method and film forming apparatus according to one embodiment have been described above, the disclosed technology is not limited to this. Other embodiments are described below.

For example, in the above-described embodiments, a back channel etch type TFT was described as an example, but the disclosed technique can also be applied to a top gate type TFT. FIG. 8 is a cross-sectional view showing an example of the configuration of a top-gate type TFT 40. As shown in FIG.

For example, as shown in FIG. 8, the TFT 40 includes an undercoat layer 45 formed on a substrate S, a base layer 46 covering the undercoat layer 45, and a channel 47 partially formed on the base layer 46. Prepare. The underlying layer 46 is, for example, a SiO film. The channel 47 is an oxide semiconductor such as IGZO.

The TFT 40 also includes a gate insulating layer 48 formed to cover the underlying layer 46 and the channel 47 .

In addition, the TFT 40 includes a gate electrode 49 partially formed on the gate insulating layer 48 so as to be directly above the channel 47 , and an interlayer insulating layer formed on the gate insulating layer 48 to cover the gate electrode 49 . and a membrane 50 . The TFT 40 also includes a source electrode 51 and a drain electrode 52 formed on the interlayer insulating film 50 and connected to the channel 47 through the interlayer insulating film 50 and the gate insulating layer 48 . The TFT 40 also includes a passivation layer 53 formed to cover the interlayer insulating film 50 , the source electrode 51 and the drain electrode 52 .

In the TFT 40 , the gate insulating layer 48 is a multilayer film including a first SiO film 481 , a second SiO film 482 and a SiN film 483 . The gate insulating layer 48 prevents direct conduction between the gate electrode 49 and the channel 47 when an electric field is applied from the gate electrode 49 to the channel 47 to switch between conduction and interruption between the source electrode 51 and the drain electrode 52 . It also has a function of protecting the channel 47 from moisture and the like while having a role of an insulating layer. The gate insulating layer 48 is also an example of a protective film that protects the oxide semiconductor. The film forming process of the passivation layer 37 according to the embodiment described above is applied to the film forming of the gate insulating layer 48 . As a result, it is possible to reduce the damage given to the channel 47 from the plasma when the protective film (gate insulating layer 48) of the channel 47 is formed, and as a result, the deterioration of the characteristics of the TFT 30 using the channel 47 is suppressed. can do.

Also, the TFT 40 is not limited to the structure of FIG. 8, and may have another structure. FIG. 9 is a cross-sectional view showing another example (No. 1) of the configuration of the top-gate type TFT 40. As shown in FIG. The TFT 40 shown in FIG. 9 has a structure obtained by removing the gate insulating layer 48 from the structure shown in FIG. 8 except the portion overlapping the gate electrode 49 . In this structure, the interlayer insulating film 50 is a multilayer film including a first SiO film 501 , a second SiO film 502 and a SiN film 503 . The interlayer insulating film 50 has a function as a protective film for the channel 47 like the gate insulating layer 48, and is formed as a multilayer film like the gate insulating layer 48, thereby reducing damage to the channel 47 from the plasma. do. The film forming process of the passivation layer 37 according to the embodiment described above is also applied to the film forming of the interlayer insulating film 50 shown in FIG. As a result, it is possible to reduce the damage given to the channel 47 from the plasma when the protective film (interlayer insulating film 50) of the channel 47 is formed, and as a result, the deterioration of the characteristics of the TFT 40 using the channel 47 is suppressed. can do.

FIG. 10 is a cross-sectional view showing another example (part 2) of the configuration of the top-gate type TFT 40. As shown in FIG. The TFT 40 shown in FIG. 10 has a structure in which the gate insulating layer 48 other than the portion overlapping the gate electrode 49 is thinner than the structure shown in FIG. In this structure, the first SiO film 481 of the gate insulating layer 48 covers the channel 47 . However, since the first SiO film 481 is thin, the channel 47 may be affected by plasma through the first SiO film 481 . Therefore, in the structure of FIG. 10, the interlayer insulating film 50 is a multilayer film. That is, the interlayer insulating film 50 is a multilayer film including a first SiO film 501 , a second SiO film 502 and a SiN film 503 . The interlayer insulating film 50 has a function as a protective film for the channel 47 like the gate insulating layer 48, and is formed as a multilayer film like the gate insulating layer 48, thereby reducing damage to the channel 47 from the plasma. do. The film forming process of the passivation layer 37 according to the embodiment described above is also applied to the film forming of the interlayer insulating film 50 shown in FIG. As a result, it is possible to reduce the damage given to the channel 47 from the plasma when the protective film (interlayer insulating film 50) of the channel 47 is formed, and as a result, the deterioration of the characteristics of the TFT 40 using the channel 47 is suppressed. can do.

Moreover, in the above-described embodiment, a fourth film forming step of forming an organic film on the SiN film 373 may be further performed. In this case, the organic film formed on the SiN film 373 constitutes the flattening layer of the TFT 30 .

Further, in the above-described embodiment, the film forming apparatus 10 that forms a film by a CVD method using inductively coupled plasma as a plasma source has been described as an example, but the disclosed technique is not limited to this. In the film forming apparatus 10 that forms a film by a CVD method using plasma, the plasma source is not limited to inductively coupled plasma, and any plasma source such as capacitively coupled plasma, microwave plasma, and magnetron plasma may be used. can be done.

Further, the film forming method in the above-described embodiments is realized by the controller 27 executing a program for realizing the film forming method, for example. A program for realizing the film forming method is provided via a storage medium such as an optical recording medium, a magneto-optical recording medium, a tape medium, a magnetic recording medium, or a semiconductor memory. As an optical recording medium, for example, DVD (Digital Versatile Disc), PD (Phase change rewritable Disc), etc. are used. MO (Magneto-Optical disk) or the like is used as the magneto-optical recording medium. The control unit 27 reads a program from the storage medium and executes the read program to control each unit of the film forming apparatus 10 and realize the film forming method in the above-described embodiment. Note that the control unit 27 may acquire a program for realizing the film forming method from another device such as a server that stores the program via a communication medium and execute the program.

S Substrate 10 Film forming apparatus 11 Chamber 12 Mounting table 13 Antenna 14 Window member 15 Gas introduction port 16 Gate valve 17 Exhaust device 18 Exhaust ports 20a to 20d Gas supply sources 21a to 21d Flow controllers 22a to 22d Valve 23 Gas supply pipe 25 Matching box 26 High frequency power supply 27 Control section 30 TFT
34 channel 37 passivation layer 371 first SiO film 372 second SiO film 373 SiN film 40 TFT
47 channel 48 gate insulating layer 50 interlayer insulating film 481 first SiO film 482 second SiO film 483 SiN film 501 first SiO film 502 second SiO film 503 SiN film

Claims (7)

A plasma of a mixed gas containing an oxygen-containing gas, a SiF4 gas, and a SiCl4 gas and having a first flow rate ratio of the SiCl4 gas to the SiF4 gas is generated using a first high-frequency power, and the generated plasma , a first film forming step of forming a first silicon oxide film on the oxide semiconductor;
A plasma of a mixed gas containing an oxygen-containing gas, a SiF4 gas, and a SiCl4 gas and having a second flow rate ratio of the SiCl4 gas to the SiF4 gas is generated using a second high-frequency power, and the generated plasma a second film forming step of forming a second silicon oxide film on the first silicon oxide film;
including
the first high frequency power is lower than the second high frequency power,
The film forming method, wherein the first flow rate ratio is smaller than the second flow rate ratio. 2. The film forming method according to claim 1, further comprising an exposing step of exposing said first silicon oxide film to oxygen gas plasma between said first film forming step and said second film forming step. . 3. The film forming method according to claim 1, wherein the thickness of said first silicon oxide film is thinner than the thickness of said second silicon oxide film. The method according to any one of claims 1 to 3, further comprising a third film forming step of forming a silicon nitride film on said second silicon oxide film by plasma of a mixed gas containing nitrogen-containing gas, SiF4 gas and SiCl4 gas. The film forming method according to any one of the above. Said first silicon oxide film, said second silicon oxide film and said silicon nitride film constitute at least one of a passivation layer, a gate insulating layer and an interlayer insulating film of a TFT (Thin Film Transistor). Item 5. The film forming method according to item 4. 6. The film forming method according to claim 4, further comprising a fourth film forming step of forming an organic film on said silicon nitride film. a chamber for forming a protective film that protects the oxide semiconductor;
a gas supply unit that supplies a processing gas into the chamber;
a plasma generator that generates plasma of the processing gas in the chamber;
a control unit;
with
The control unit
A plasma of a mixed gas containing an oxygen-containing gas, a SiF4 gas, and a SiCl4 gas and having a first flow rate ratio of the SiCl4 gas to the SiF4 gas is generated using a first high-frequency power, and the generated plasma , a first film forming step of forming a first silicon oxide film on the oxide semiconductor;
A plasma of a mixed gas containing an oxygen-containing gas, a SiF4 gas, and a SiCl4 gas and having a second flow rate ratio of the SiCl4 gas to the SiF4 gas is generated using a second high-frequency power, and the generated plasma a second film forming step of forming a second silicon oxide film on the first silicon oxide film;
and run
the first high frequency power is lower than the second high frequency power,
The film forming apparatus, wherein the first flow rate ratio is smaller than the second flow rate ratio.

Images