JP2000012531A - Plasma processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable plasma to be quickly stabilized in a process of etching an Si film layer with use of Cl2. SOLUTION: A wafer W is mounted on a lower electrode 106 disposed within a processing chamber 104 of an etching apparatus 100, and a predetermined rate of Cl2 is introduced into the chamber 104. A pressure in the chamber 104 is set at an initial level by adjusting the amount of Cl2 to be discharged. The initial pressure is found by processing the wafer W having a coverage ratio (of an area of an SiO2 divided by an area of an Si film layer) varying depending on the flow rate of Cl2, finding a difference between internal pressures of the chamber 104 before and after plasma generation, and adding a value obtained from the coverage ratio and pressure difference to a processing pressure value. When a high frequency power is supplied to a lower electrode 104 for plasma generation after the internal pressure of the chamber 104 reaches the initial pressure, the pressure dropped after the plasma generation becomes substantially equal to the processing pressure, and thus stable plasma can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a plasma processing method.

[0002]

2. Description of the Related Art Conventionally, a Si film layer constituting an object to be processed,
When etching the Si film layer covered with the SiO ₂ film layer, Cl ₂ or a mixed gas obtained by adding O ₂ or N ₂ to Cl ₂ is used as a processing gas. For example, when etching a Si film layer with Cl ₂ , first, a predetermined flow rate of Cl ₂ is introduced into a processing chamber in which an object to be processed is placed, and the amount of exhaust of the atmosphere in the processing chamber is appropriately adjusted. The pressure is increased to a predetermined process (set) pressure. afterwards,
For example, a plasma is generated by generating a discharge in the processing chamber,
The plasma is used to etch the Si film layer.

Further, as described above, in the process of etching the Si film layer with Cl ₂ , the pressure in the processing chamber is temporarily increased relatively at the same time as the plasma is generated.
Immediately after that, the pressure in the processing chamber rapidly decreases. As described above, when the pressure in the processing chamber is relatively lower than the processing pressure, the plasma is not stable, and it is difficult to perform uniform processing on the object. Therefore, in the above-described etching process, the amount of exhaust in the atmosphere in the processing chamber is appropriately adjusted, and the pressure in the processing chamber, which has been reduced after plasma generation, is increased to the processing pressure to stabilize the plasma.

[0004]

However, in the above-described etching process, since the pressure difference between the processing pressure set before and after plasma generation, that is, before plasma generation, and the processing chamber pressure reduced after plasma generation is large,
In order to increase the reduced pressure to the processing pressure only by adjusting the displacement of the atmosphere in the processing chamber, it may take about 10 seconds or more. As a result, until the pressure in the processing chamber recovers to the processing pressure, the state of the plasma becomes unstable, and not only cannot uniform processing be performed, but also the plasma disappears and the processing cannot be performed. There is also.

[0005] In addition, the etching apparatus is usually provided with a security device that issues a warning when the generated plasma is unstable, stops the process, and protects the object being processed. The operation time of the apparatus is set to about 5 seconds in an etching process other than the above in order to reliably protect the object to be processed. However, in the above process, as described above, since the plasma is not stable for about 10 seconds after the generation of the plasma, the operation time of the security device cannot be set in the same manner as in the other etching processes. Even if is set to about several tens of seconds, the object already etched by the unstable plasma cannot be reused because the processing is already in progress.

The present invention has been made in view of the above-mentioned problems of the prior art, and maintains the pressure in the processing chamber at the processing pressure immediately after plasma generation to quickly stabilize the plasma. It is an object of the present invention to provide a new and improved plasma processing method that can be achieved.

[0007]

According to the present invention, in order to solve the above-mentioned problems, as in the first aspect of the present invention,
In a plasma processing method, a plasma is generated in a processing chamber after introducing a processing gas containing at least Cl ₂ into a processing chamber, and an etching process is performed on a Si film layer formed on an object to be processed placed in the processing chamber by the plasma. The plasma processing method is characterized in that plasma is generated after increasing the pressure in the processing chamber to an initial pressure value relatively higher than the processing pressure after plasma generation.

According to this configuration, the pressure in the processing chamber before the plasma generation is set to an initial pressure value relatively higher than a predetermined processing pressure, that is, the pressure in the processing chamber reduced after the plasma generation becomes substantially equal to the processing pressure. Since the plasma is generated after the pressure is increased to a certain value, the processing chamber is maintained at the processing pressure immediately after the generation of the plasma, and stable plasma can be generated. That is, if the present invention is adopted,
Since the pressure reduced after plasma generation can be used as the processing pressure as it is, the step of increasing the pressure reduced after plasma generation to the processing pressure can be omitted. As a result, even if there is a large difference in the pressure in the processing chamber before and after plasma generation, such as in a process of etching a Si film layer with a gas containing at least Cl ₂ , plasma can be quickly and reliably stabilized. Uniform processing can be performed. Further, if the present invention is adopted, the plasma can be stabilized in a short time, so that if the above-mentioned security device is provided in the processing device, the operation time thereof can be reduced, and the processing time when a processing failure occurs can be reduced. The object to be processed can be reliably protected.

Further, the initial pressure value is defined as, for example, the coverage of the SiO ₂ film layer covering the Si film layer (the area of the SiO ₂ film layer / the area of the Si film layer). You may set according to it. According to the findings of the inventors, the decrease in the pressure in the processing chamber after the plasma is generated decreases the number of molecules in the atmosphere in the processing chamber due to the reaction between Cl ions or Cl radicals in the plasma and Si forming the object to be processed. It is thought to occur due to: Therefore, if the initial pressure value is set based on the ratio of the Si film layer exposed to the plasma atmosphere, that is, based on the above-mentioned coverage, the initial pressure value can be reliably obtained.

Further, if the pressure in the processing chamber is controlled by the amount of exhaust of the atmosphere in the processing chamber, for example, as in the third aspect of the invention, the pressure can be set to a predetermined initial pressure value or processing pressure without fail. , Can be maintained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment in which a plasma processing method according to the present invention is applied to an etching method will be described in detail with reference to the accompanying drawings.

(1) Configuration of Etching Apparatus First, an etching apparatus 100 to which the etching method of the present embodiment can be applied will be described with reference to FIG. Processing vessel 102 of etching apparatus 100 shown in FIG.
Inside, a processing chamber 104 is formed.
A lower electrode 106 that constitutes a susceptor that can move up and down is arranged in 04. Above the lower electrode 106,
An electrostatic chuck 110 connected to a high-voltage DC power supply 108 is provided, and an object to be processed, for example, a semiconductor wafer (hereinafter, referred to as a Si wafer) made of a Si substrate is provided on an upper surface of the electrostatic chuck 110.
Called "wafer". ) W is placed. Further, an insulating focus ring 112 is arranged around the wafer W mounted on the lower electrode 106. Further, a high frequency power supply 116 for outputting high frequency power for plasma generation is connected to the lower electrode 106 via a matching unit 114.

A large number of gas discharge holes 118a are formed in the ceiling of the processing chamber 104 facing the mounting surface of the lower electrode 106.
Is disposed, and in the illustrated example, the upper electrode 118 forms a part of the processing container 102. Further, the gas supply pipe 12 is provided in the gas discharge hole 118a.
0, an opening / closing valve 122, and a flow rate adjusting valve (mass flow controller) 124,
A gas supply source 126 for supplying l ₂ is connected. In addition, the above-mentioned processing gas includes
For example, various gases such as O ₂ and N ₂ may be added.

An exhaust pipe 128 communicating with a not-shown evacuation mechanism is connected below the processing vessel 102. Further, the exhaust pipe 128 is provided with a displacement adjusting mechanism 130 such as a butterfly valve. Further, a controller 132 is connected to the exhaust amount adjusting mechanism 130, and further, the controller 132 is connected to the above-described flow rate adjusting valve 124 and a pressure sensor 134 for measuring the pressure in the processing chamber 104. ing. Further, the magnet 1 is provided outside the processing chamber 104 so as to surround the outer side wall of the processing chamber 102.
The magnet 136 forms a rotating magnetic field in the plasma region between the upper electrode 122 and the lower electrode 106.

(2) Etching Step Next, an etching step when an etching process is performed on the wafer W by the above-described etching apparatus 100 will be described. First, after placing the wafer W on the lower electrode 106,
Cl ₂ as a processing gas is introduced into the processing chamber 104 from a gas supply source 126. At this time, the flow rate of Cl ₂ is appropriately adjusted by the flow rate adjustment valve 124, and in this embodiment, it is 15 (s).
ccm) to 40 (sccm). At the same time, the atmosphere in the processing chamber 104 is exhausted through the exhaust pipe 128, and the exhaust amount is adjusted by the exhaust amount adjusting mechanism 130, and the pressure in the processing chamber 104 is increased to the initial pressure value according to the present embodiment. Let it. This initial pressure value is a pressure value relatively higher than the processing pressure in the processing chamber 104 after plasma generation, as described later. The pressure in the processing chamber 104 is
The controller 132 adjusts the opening degree of the displacement adjusting mechanism 130 based on the pressure information detected by the pressure sensor 134 as needed. The opening of the flow control valve 124 is also appropriately controlled by the controller 132. After the pressure in the processing chamber 104 reaches the initial pressure value, a high-frequency power of 300 W is applied to the lower electrode 106 at 13.56 MHz to generate plasma in the processing chamber 104, and the Si of the wafer W is generated by the plasma. The film layer is subjected to an etching process. Further, the pressure in the processing chamber 104 decreases after the plasma is generated as described later. In the present embodiment, the pressure in the processing chamber 104 before the plasma generation is set to the processing pressure. Pressure becomes a predetermined processing pressure, and processing can be performed with uniform and stable plasma.

(3) Phenomenon of pressure drop in processing chamber after plasma generation Next, referring to FIGS. 2 (a) and 3, the plasma after the plasma generation generated in the process of etching the Si film layer with Cl ₂ will be described. The pressure drop phenomenon in the processing chamber 104 will be described. In the above process, the processing chamber 1
It has been empirically found that the pressure in the chamber 04 is relatively lower than the pressure before plasma generation. Therefore, according to the conventional etching method, as shown in FIG. 2A, after the plasma is generated, the displacement adjusting mechanism (in FIG. 2, "APC"
And ) The opening of 130 is reduced, and the processing chamber
Although the internal pressure of the chamber 04 is raised to a set pressure value as a processing pressure value before plasma generation, it takes about ten and several seconds to recover to the set pressure value as described above. In addition,
When the opening degree of the displacement adjusting mechanism 130 is not adjusted, as shown in the figure, the pressure in the processing chamber 104 after the plasma is generated remains reduced.

Therefore, the present inventors consider that the decrease in the pressure in the processing chamber 104 after the plasma generation is caused by a change in the number of molecules in the atmosphere in the processing chamber 104 before and after the plasma generation. When the number of molecules was measured, the results shown in FIG. 3 were obtained. Note that the measurement of the number of molecules is performed by an etching apparatus 100 having a processing chamber 104 of 38.2 liters.
The pressure of the processing chamber 104 before plasma generation was set to 20 mTorr by introducing sccm Cl ₂ . Further, the temperatures of the lower electrode 106, the upper electrode 118, and the inner wall surface of the processing chamber 104 were set to 60 ° C., respectively. Further, 300 W high-frequency power at 13.56 MHz was applied to the lower electrode 106, and an etching process was performed on each of the Si wafer W and the SiO ₂ wafer W mounted on the lower electrode 106.

Then, as shown in FIG. 3, a molecular intensity ratio indicating the number of molecules in the atmosphere in the processing chamber 104 before and after the supply of high-frequency power, that is, before and after plasma generation, was determined for each wafer W. It should be noted that the dotted line in FIG. 5 indicates that the high-frequency power is not supplied to the lower electrode 106 (in FIG.
Time. " 4) shows the molecular intensity ratio of the atmosphere in the processing chamber 104, and the atmosphere in the processing chamber 104 at this time is only Cl ₂ .

As a result, as shown in the figure, when a wafer W made of Si is used, Cl ₂ and C
l radical (Cl ^* ), Cl ⁺ , Cl ^- etc.
Called "Cl". ) Was reduced before the plasma generation,
The respective molecular intensity ratios of Cl ₂ , SiCl _3, and SiCl ₄ increased. On the other hand, when a wafer W made of SiO ₂ is used as the object to be processed, the above-described SiC
l, SiCl ₂ , SiCl ₃ and SiCl ₄ are not generated,
Only the molecular intensity ratio increased.

From the above results, the following is considered. That is, when the etching target is a Si film layer, Cl ions or Cl radicals react with Si after plasma generation to generate SiCl, SiCl ₂ , SiCl _3, or SiCl _4. For example, SiCl ₄ is generated. Then, a reaction of Si + 2Cl ₂ → SiCl ₄ occurs, and the number of molecules relatively decreases. Therefore,
When a reaction product such as SiCl _{4 is} generated after the plasma is generated, the number of molecules in the atmosphere in the processing chamber 104 is relatively reduced as compared to before the generation of the plasma. As a result, since the pressure in the processing chamber 104 depends on the number of molecules in the atmosphere in the processing chamber 104, it is considered that the pressure after plasma generation is also relatively reduced as compared to before the plasma generation.

On the other hand, when the wafer W made of SiO ₂ was used, it was found that SiO ₂ did not react with Cl ions or Cl radicals because only the molecular intensity ratio of Cl increased as described above. Therefore, it is considered that the decrease in the pressure in the processing chamber 104 after the plasma generation is a peculiar phenomenon that occurs only when the etching target is the Si film layer. When the wafer W made of SiO ₂ was used, the molecular intensity ratio of Cl increased, but this was caused by the dissociation of Cl ₂ → 2Cl ^* , and the number of molecules in the atmosphere in the processing chamber 104 was relatively increased. It is thought that it increased.

Further, as shown in FIG. 2A, high-frequency power is supplied to the lower electrode 106 ("power ON" in FIG. 2).
And Immediately after), the pressure in the processing chamber 104 temporarily increases, but this is due to the dissociation of Cl ₂ and Cl ions and C
This is considered to be due to the formation of 1 radical, which increases the number of molecules in the atmosphere in the processing chamber 104. Note that the present embodiment is not limited to the process conditions described in the measurement of the number of molecules in the atmosphere in the processing chamber 104.

(4) Setting of Initial Pressure Value Next, the setting of the initial pressure value according to the present embodiment will be described with reference to FIG. As described above, the decrease in the pressure in the processing chamber 104 after the generation of the plasma is caused by the difference between the Si constituting the Si film layer of the wafer W and the dissociated Cl ions or Cl ions.
It occurs by reaction with radicals. Therefore, in the present embodiment, the pressure difference between the internal pressure of the processing chamber 104 before and after plasma generation is determined in advance according to the ratio of the Si film layer exposed to the plasma atmosphere, and the initial pressure value is required. It is calculated from the processing pressure. At this time, the ratio of the Si film layer exposed in the processing chamber 104 is determined by the SiO ₂ layer formed on the Si film layer.
Film layer coverage (SiO ₂ film area / Si film layer area)
And

That is, as shown in FIG. 4, the etching process is first performed on the wafer W having the different covering ratio for each flow rate of Cl ₂ supplied into the processing chamber 104, and the pressure in the processing chamber 104 before and after the plasma is generated. Is measured. In the example shown in the figure, the etching process is performed under the process conditions in which the number of molecules in the atmosphere of the processing chamber 104 is obtained, and the flow rates of Cl ₂ are 20 sccm, 50 sccm, and 80 sccm.
m. Next, the processing chamber 10 before and after plasma generation is performed.
4) From the internal pressure, a pressure difference (pressure in the processing chamber 104 before plasma generation—pressure in the processing chamber 104 after plasma generation) is obtained,
The following linear function is obtained for each Cl ₂ flow rate from each pressure difference and coverage.

For example, when the flow rate of Cl ₂ is 80 sccm, Y = −0.3X + 29.7 (1). Similarly, when the flow rate of Cl ₂ is 50 sccm, Y = −. when 0.2X + 15.1 ... (2), and the addition flow rate of Cl ₂ is 20sccm becomes Y = -0.1X + 5.8 ... (3 ). It should be noted that the above equation is not limited to the above-mentioned respective gas flow rates, but can be obtained as appropriate based on the flow rate actually applied to the processing process.

The initial pressure value is obtained by substituting the pressure difference calculated by substituting the coverage of the Si film layer of the wafer W to be processed into the linear function obtained as described above with a predetermined processing pressure value. Is calculated by adding For example, processing room 1
In the process of introducing Cl ₂ at a flow rate of 50 sccm into the wafer W and setting the processing pressure to 30 mTorr, and performing processing on a wafer W having a coverage of 40%, X in the above formula (2) is coated. When the rate is substituted, the pressure difference Y is 7.1 m
Torr, and if this pressure difference Y is added to the processing pressure, the initial pressure value becomes 37.1 mTorr.

As shown in FIG. 2B, for example, in the above example, the pressure in the processing chamber 104 is raised to 37.1 mT
If the plasma is generated after the pressure is increased to orr, the pressure in the processing chamber 104 that has decreased after the plasma is generated becomes the processing pressure of 30 mTorr, and a predetermined uniform and stable plasma can be generated. Further, in the present embodiment, even after the plasma is generated, the opening degree of the exhaust amount adjustment mechanism 130 is appropriately adjusted, and the pressure in the processing chamber 104 is maintained at the processing pressure, so that more stable plasma can be generated.

The present embodiment is configured as described above, and the plasma is generated after the pressure in the processing chamber 104 before the plasma generation is increased to a predetermined initial pressure value.
The internal pressure of the processing chamber 104, which has been reduced after the generation of plasma, can be made substantially equal to the processing pressure value. As a result, the plasma can be stabilized in a short time,
A uniform process can be performed on the wafer W immediately after the plasma generation. Further, once a relational expression between the flow rate of Cl ₂ , the coverage of the wafer W, and the pressure difference in the processing chamber 104 before and after plasma generation is obtained once, the processing pressure and the flow rate of Cl ₂ can be changed. Even when processing is performed on wafers W having different coverages, the initial pressure value can be easily obtained from the coverage of the wafers W.

While the preferred embodiment of the present invention has been described with reference to the accompanying drawings, the present invention is not limited to such a configuration. In the scope of the technical idea described in the claims, those skilled in the art
Various changes and modifications can be conceived, and it is understood that these changes and modifications also belong to the technical scope of the present invention.

For example, in the above embodiment, Cl ₂
Flow rate and wafer coverage (SiO ₂ film layer area / Si
Although the configuration in which the initial pressure value is obtained from the pressure difference (the pressure in the processing chamber before plasma generation—the pressure in the processing chamber after plasma generation) and the pressure difference (the area of the film layer) have been described as an example, the present invention is limited to such a configuration. Not something. For example, if the coverage of the wafer W is not known, the wafer W is first subjected to the processing at each flow rate of Cl ₂ , and the processing chamber 104 before and after plasma generation is performed.
Obtain the pressure value inside. Next, FIG.
Is determined. Then, an initial pressure value may be obtained from the curve according to the flow rate of Cl ₂ and the required processing pressure. That is, in the illustrated example, the flow rate of Cl ₂ is set to 30.
When the pressure is set to sccm and the processing pressure is set to 33 mTorr, the initial pressure value becomes 60 mTorr.

Further, in the above-described embodiment, the etching apparatus for applying high-frequency power to only the lower electrode has been described as an example. However, the present invention is not limited to such a configuration, and the present invention is not limited to this configuration. The present invention can also be applied to an etching apparatus that applies high-frequency power only to both electrodes and only to the upper electrode. Furthermore, in the above-described embodiment, an explanation has been given by taking an example of an etching apparatus having a magnet, but the present invention is not limited to such a configuration, and various plasma processing apparatuses such as various etching apparatuses without a magnet are provided. The present invention can be applied to

[0032]

According to the present invention, the pressure in the processing chamber which has been reduced after the plasma generation becomes substantially the processing pressure, so that there is no need to increase the processing chamber pressure to the processing pressure as in the conventional plasma processing method. Becomes As a result, the plasma can be stabilized immediately after the generation of the plasma, so that the object to be processed can be uniformly processed. Also,
Once the equation for calculating the initial pressure value is obtained, the initial pressure value can be easily obtained even in a process in which the pressure in the processing chamber, the flow rate of the processing gas, and the film quality of the wafer are different.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an etching apparatus to which the present invention can be applied.

FIG. 2 is a schematic explanatory diagram for explaining a relationship between a pressure in a processing chamber and generation of plasma.

FIG. 3 is a schematic explanatory diagram for explaining a relationship between the number of molecules in an atmosphere in a processing chamber before and after plasma generation and a constituent material of a wafer.

FIG. 4 is a schematic explanatory diagram for explaining a calculation process of an initial pressure value.

FIG. 5 is a schematic explanatory diagram for explaining another calculation process of an initial pressure value.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Etching apparatus 104 Processing chamber 106 Lower electrode 116 High frequency power supply 118 Upper electrode 118 a Gas discharge hole 124 Flow control valve 126 Gas supply source 128 Exhaust pipe 130 Exhaust amount adjusting mechanism 132 Controller 134 Pressure sensor W Wafer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Fumihiko Higuchi 7-30, Sumiyoshi-cho, Fuchu-shi, Tokyo Tokyo Electron Yamanashi Co., Ltd. F-term (reference) 4K057 DA16 DB06 DB15 DB20 DE01 DG07 DG08 DM18 DN01 5F004 BA04 BA08 BB08 BB13 CA02 CA07 CA09 DA04 DA25 DA26 DB01 EA06

Claims (3)

[Claims] After introducing a processing gas containing at least Cl ₂ into a processing chamber, a plasma is generated in the processing chamber.
In a plasma processing method in which an etching process is performed on a Si film layer formed on an object to be processed placed in the processing chamber by the plasma, an initial pressure in the processing chamber is relatively higher than a processing pressure after plasma generation. A plasma processing method comprising generating plasma after increasing the pressure value. 2. The method according to claim 1, wherein the initial pressure value is set according to a coverage ratio of the SiO ₂ film layer covering the Si film layer (the area of the SiO ₂ film layer / the area of the Si film layer). The plasma processing method according to claim 1. 3. The processing chamber according to claim 1, wherein the pressure in the processing chamber is controlled by an exhaust amount of an atmosphere in the processing chamber.
Or the plasma processing method according to any one of 2.