JP2007266056A - Plasma etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma etching method by which the surface of polysilicon can be smoothed by plasma etching and satisfactory etching rate can be also ensured. <P>SOLUTION: A plasma etching apparatus 1 has main etching operation and over-etching operation. The main etching operation is used to etch a polysilicon film by Cl<SB>2</SB>/SF<SB>6</SB>/N<SB>2</SB>plasma that is produced by exciting Cl<SB>2</SB>gas, SF<SB>6</SB>gas and N<SB>2</SB>gas, and the over-etching operation is used to etch a polysilicon film by Cl<SB>2</SB>/HBr/CF<SB>4</SB>plasma that is produced by exciting Cl<SB>2</SB>gas, HBr gas and CF<SB>4</SB>gas. During the main etching operation, the formation of unevenness on the surface of the polysilicon can be suppressed by adding the N<SB>2</SB>gas, and satisfactory etching rate can be ensured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a plasma etching method, and more particularly to a plasma etching method including a step of etching an object to be processed using plasma.

  In recent years, semiconductor devices such as DRAMs (Dynamic Random Access Memory) have been multilayered for high integration, and contact plug formation for interlayer connection has been repeatedly performed in the manufacturing process. As one method of forming the contact plug, a conductive material such as polycrystalline silicon is deposited on the interlayer insulating film so as to fill the contact hole by a CVD (Chemical Vapor Deposition) method or the like, and then the contact hole is formed by an etch back process. A method is known in which the conductive material is left only in the interior.

  By the way, when the polycrystalline silicon which is a collection of crystal grains is etched, irregularities are formed on the etched surface. As described above, when unevenness is formed on the surface of the polycrystalline silicon during the etching process, the unevenness is transferred to the base film (for example, interlayer insulating film) after the etching back, which causes a defect of the semiconductor device. was there.

As a technique for forming a smooth etch-back surface on polycrystalline silicon, an etching gas containing a gas capable of releasing free sulfur in the plasma is used to form a sulfur-based material film on the surface of polycrystalline silicon. A plasma etching method for performing etch back is proposed (for example, Patent Document 1). In this proposal, gases capable of releasing free sulfur into the plasma include halogenated sulfur compounds having a halogen atom / sulfur atom ratio of less than 6 (S ₂ F ₂ , SF ₂ , SF ₄ , S ₂ F ₁₀ , S _{3 C l3, S 2 Cl 2} , SCl 2 , etc.) are mentioned.
JP-A-9-232285 (paragraph 0010)

  In the etch back process, it is important to eliminate irregularities on the polysilicon surface, but it is also important to ensure a practically sufficient etching rate from the viewpoint of improving throughput. However, since the method of Patent Document 1 is a special method in which etching proceeds while forming a sulfur-based material layer on the surface of the polycrystalline silicon that is the film to be etched, it is considered that a sufficient etching rate can be obtained. Hateful. Moreover, since the sulfur-based material layer formed in the etching process must be finally removed by heat treatment or ashing treatment, there is a problem that the number of steps increases.

  Accordingly, an object of the present invention is to provide a plasma etching method in which polycrystalline silicon is plasma-etched to form a smooth surface and a sufficient etching rate is obtained.

In order to solve the above-described problems, a first aspect of the present invention is to use a plasma of an etching gas containing SF ₆ , Cl _2, and N ₂ on a target object on which a polycrystalline silicon film is formed. A first etching step for etching the crystalline silicon film;
And a second etching step of etching the polycrystalline silicon film using a plasma of an etching gas containing Cl ₂ , HBr, and CF ₄ after the first etching step. .

The second aspect of the present invention is to etch the polycrystalline silicon film by using plasma of an etching gas containing SF ₆ , Cl ₂ and N ₂ for the target object on which the polycrystalline silicon film is formed. A first etching step,
After the first etching step, a second etching step of etching the polycrystalline silicon film using plasma of an etching gas containing Cl ₂ , HBr, and CF ₄ ;
After the second etching step, a third etching step of etching the polycrystalline silicon film using plasma of an etching gas containing Cl ₂ , HBr, CF ₄ and N ₂ ;
A plasma etching method is provided.

A third aspect of the present invention is to etch back the polycrystalline silicon film of an object to be processed having an insulating film in which a through-opening is formed and a polycrystalline silicon film covering the insulating film so that the polycrystalline silicon film is formed in the through-opening. A plasma etching method for selectively leaving polycrystalline silicon,
There is provided a plasma etching method including a first etching step of etching the polycrystalline silicon film using plasma of an etching gas containing SF ₆ , Cl ₂ and N ₂ .

In the third aspect, after the first etching step, a second etching step of etching the polycrystalline silicon film using plasma of an etching gas containing Cl ₂ , HBr, and CF ₄ is included. Is preferred. In this case, the method further includes a third etching step of etching the polycrystalline silicon film using an etching gas plasma containing Cl ₂ , HBr, CF _4, and N ₂ after the _second etching step. Is more preferable.

In any one of the first to third aspects, the insulating film is preferably a silicon nitride film. In the first etching step, it is preferable that the flow rate ratio of the N ₂ to the total flow rate of the etching gas is 25 to 40%. The polycrystalline silicon film may be composed of polycrystalline silicon doped with phosphorus.

  According to a fourth aspect of the present invention, there is provided a control program that operates on a computer and controls the plasma processing apparatus so that the plasma etching method according to any one of the first to third aspects is performed at the time of execution. I will provide a.

A fifth aspect of the present invention is a computer-readable storage medium storing a control program that operates on a computer,
The control program provides a computer-readable storage medium for controlling the plasma processing apparatus so that the plasma etching method according to any one of the first to third aspects is performed at the time of execution. .

According to a sixth aspect of the present invention, there is provided a processing chamber for performing a plasma etching process on an object to be processed;
A support for placing the object to be processed in the processing chamber;
Exhaust means for depressurizing the processing chamber;
Gas supply means for supplying a processing gas into the processing chamber;
A control unit for controlling the plasma etching method according to any one of the first to third aspects to be performed in the processing chamber;
A plasma processing apparatus is provided.

According to the plasma etching method of the present invention, the polycrystalline silicon film is etched using an etching gas in which N ₂ gas is added to Cl ₂ gas and SF ₆ gas, thereby forming irregularities on the surface of the polycrystalline silicon. And the surface can be smoothed.
Moreover, since a practically sufficient etching rate can be ensured by using the etching gas, there is no possibility of increasing the process time and the number of steps.
Therefore, the plasma etching method of the present invention is a method suitable for forming a contact plug of polycrystalline silicon by, for example, an etch back process, and can be advantageously used for manufacturing a highly reliable semiconductor device.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view showing a plasma etching apparatus that can be suitably used for carrying out the present invention.

  The plasma etching apparatus 1 is configured as a capacitively coupled parallel plate etching apparatus in which electrode plates are opposed in parallel in the vertical direction, and a plasma forming power source is connected to one of them.

  The plasma etching apparatus 1 has a chamber 2 as a processing container formed into a cylindrical shape made of aluminum whose surface is ceramic sprayed, for example, and the chamber 2 is grounded for safety. In the chamber 2, a semiconductor wafer (hereinafter simply referred to as "wafer") W made of, for example, silicon and having a predetermined film formed thereon is horizontally mounted, and also functions as a lower electrode. Is supported by the support member 4. This support member 4 is supported by a support base 6 of a lifting device (not shown) via an insulating plate 5 such as ceramic, and the susceptor 3 can be lifted and lowered by this lifting mechanism. The atmospheric portion at the lower center of the support base 6 is covered with a bellows 7, and the inside of the chamber 2 and the atmospheric portion are separated.

  A refrigerant chamber 8 is provided inside the support member 4. In the refrigerant chamber 8, for example, a refrigerant such as Galden is introduced and circulated through the refrigerant introduction pipe 8 a, and the cold heat is supplied to the susceptor 3. Then, heat is transferred to the wafer W through this, whereby the processing surface of the wafer W is controlled to a desired temperature. Further, even if the chamber 2 is held in a vacuum, a heat transfer medium such as He is provided on the back surface of the wafer W as the object to be processed so that the wafer W can be effectively cooled by the refrigerant circulating in the refrigerant chamber 8. A gas passage 9 for supplying gas or the like is provided, and the cold heat of the susceptor 3 is effectively transmitted to the wafer W through this heat transfer medium, and the temperature of the wafer W can be controlled with high accuracy.

  The susceptor 3 is formed in a disc shape having a convex upper central portion, and an electrostatic chuck 11 having an electrode 12 interposed between insulating materials is provided on the susceptor 3. By applying a direct current voltage from the direct current power source 13, the wafer W is electrostatically adsorbed by, for example, Coulomb force. An annular focus ring 15 for improving the uniformity of etching is disposed on the periphery of the upper end of the susceptor 3 so as to surround the wafer W placed on the electrostatic chuck 11.

  Above the susceptor 3, a shower head 21 that functions as an upper electrode is provided in parallel with the susceptor 3. The shower head 21 is supported on the upper portion of the chamber 2 via an insulating material 22, and has a large number of discharge holes 23 on the surface 24 facing the susceptor 3. The surface of the wafer W and the shower head 21 are separated from each other by about 30 to 90 mm, for example, and this distance can be adjusted by the lifting mechanism.

A gas inlet 26 is provided in the center of the shower head 21, and a gas supply pipe 27 is connected to the gas inlet 26. Further, a valve 28 is connected to the gas supply pipe 27 through a valve 28. A processing gas supply system 30 for supplying an etching gas is connected. The processing gas supply system 30 includes a Cl ₂ gas supply source 301, an SF ₆ gas supply source 302, an N ₂ gas supply source 303, an HBr gas supply source 304, and a CF ₄ gas supply source 305, as shown in FIG. A mass flow controller 306 and a valve 307 are provided in the pipes from these gas sources, respectively.

Then, Cl ₂ gas / SF ₆ gas / N ₂ gas or Cl ₂ gas / HBr gas / CF ₄ gas as an etching gas is supplied from each gas supply source of the processing gas supply system 30 to the gas supply pipe 27, gas It reaches the space in the shower head 21 through the inlet 26 and is discharged from the gas discharge hole 23.

  An exhaust pipe 35 is connected near the bottom of the side wall of the chamber 2, and an exhaust device 36 is connected to the exhaust pipe 35. The exhaust device 36 includes a vacuum pump such as a turbo molecular pump, and is configured so that the chamber 2 can be evacuated to a predetermined reduced pressure atmosphere, for example, a predetermined pressure of 1 Pa or less. Further, a loading / unloading port 37 for the wafer W and a gate valve 38 for opening and closing the loading / unloading port 37 are provided on the side wall of the chamber 2, and the wafer is passed through the loading / unloading port 37 with the gate valve 38 opened. W is transported between adjacent load lock chambers (not shown).

  A high frequency power supply 40 is connected to the shower head 21 that functions as an upper electrode, and a matching unit 41 is interposed in the power supply line. The high frequency power supply 40 supplies high frequency power having a frequency of, for example, 60 MHz to the shower head 21 that is the upper electrode, and generates a high frequency electric field for plasma formation between the shower head 21 that is the upper electrode and the susceptor 3 that is the lower electrode. Form. The shower head 21 is connected to a low pass filter (LPF) 42.

  A high frequency power supply 50 is connected to the susceptor 3 functioning as the lower electrode, and a matching unit 51 is interposed in the power supply line. The high-frequency power supply 50 supplies high-frequency power having a frequency of, for example, 13.56 MHz to the susceptor 3 that is the lower electrode, and draws ions in the plasma toward the wafer W, thereby realizing highly anisotropic etching. The susceptor 3 is connected to a high pass filter (HPF) 16.

  Each component of the plasma etching apparatus 1 is connected to and controlled by a process controller 60 having a CPU. The process controller 60 includes a user interface 61 including a keyboard that allows a process manager to input commands to manage the plasma etching apparatus 1, a display that visualizes and displays the operating status of the plasma etching apparatus 100, and the like. It is connected.

  Further, the process controller 60 has a storage unit 62 in which a recipe in which a control program for realizing various processes executed by the plasma etching apparatus 1 is realized under the control of the process controller 60 and processing condition data is stored. It is connected.

  Then, if desired, an arbitrary recipe is called from the storage unit 62 by an instruction from the user interface 61 and is executed by the process controller 60, so that a desired one in the plasma etching apparatus 1 is controlled under the control of the process controller 60. Is performed. The recipe may be stored in a computer-readable storage medium such as a CD-ROM, a hard disk, a flexible disk, or a flash memory, or may be a dedicated line from another device. It is also possible to transmit and use it as needed.

  Next, a procedure for forming a contact plug by etching back polycrystalline silicon using the plasma etching apparatus 1 configured as described above will be described.

3-6 is drawing explaining the process sequence of the plasma etching method which concerns on this embodiment.
On the Si substrate 101, a silicon oxide (SiO ₂ ) film 102 as a first interlayer insulating film and a silicon nitride (Si ₃ N ₄ ) film 103 as a second interlayer insulating film are stacked in order from the bottom. In addition, a contact hole 104 that penetrates these and reaches the Si substrate 101 is formed. A polycrystalline silicon film 105 is formed so as to fill the contact hole 104 and cover the silicon nitride film 103. Here, an etch-back process is performed in which the polycrystalline silicon film 105 is removed by etching and the polycrystalline silicon is selectively left only in the contact holes 104.

  Such an etch-back process of the polycrystalline silicon 105 has a problem that irregularities are easily formed on the surface of the polycrystalline silicon film 105 during the etching process. The unevenness formed on the surface of the polycrystalline silicon film 105 is transferred to the silicon nitride film 103 as it is even after the polycrystalline silicon film 105 is removed by etch back, and the surface shape of the silicon nitride film 103 becomes uneven. Therefore, it becomes a cause of defects in semiconductor devices. The mechanism for forming irregularities on the surface of the polycrystalline silicon film 105 is presumed as follows.

The polycrystalline silicon film 105 finally remaining in the contact hole 104 as a contact plug is formed by, for example, a CVD method using SiH ₄ and PH ₃ as raw materials, and a high concentration of phosphorus is contained in the film. Is doped to increase the conductivity. Since polycrystalline silicon has relatively large crystal grains, it is assumed that dopants such as phosphorus are unevenly distributed at the grain boundaries. It is considered that such a dopant concentration distribution causes a difference in etching rate between the crystal grains and the grain boundaries, which is manifested as irregularities on the etching surface.

  As described above, when the polycrystalline silicon film 105 is etched, it is necessary to form the etching surface smoothly in order to avoid adverse effects on the device. In consideration of practicality, it is important to ensure a sufficient etching rate in addition to smoothing the etching surface. That is, even if the surface can be smoothed, a process that causes a decrease in throughput and an increase in man-hours is not realistic. Therefore, in the present embodiment, the etching is divided into a main etching process and an over-etching process, and by selecting a combination of gases used for etching in each process, the polycrystalline silicon film 105 is maintained while maintaining a sufficient etching rate. It has become possible to etch the etched surface smoothly.

First, as shown in FIG. 3, main etching of the polycrystalline silicon film 105 is performed by Cl ₂ / SF ₆ / N ₂ plasma in which Cl ₂ gas, SF ₆ gas and N ₂ gas are excited. When the polycrystalline silicon film 105 is etched using the plasma etching apparatus 1 of FIG. 1, first, the gate valve 38 is opened and a wafer W having such a structure is loaded into the chamber 2, and the susceptor 3. Then, the gate valve 38 is closed. Next, the susceptor 3 is raised and the distance between the surface of the wafer W on the susceptor 3 and the shower head 21 is adjusted to about 30 to 90 mm, for example. Then, the inside of the chamber 2 is exhausted through the exhaust pipe 35 by the vacuum pump of the exhaust device 36, and the inside of the chamber 2 is depressurized, and then a DC voltage is applied from the DC power source 13 to the conductor 12 in the electrostatic chuck 11, The wafer W is electrostatically adsorbed on the electrostatic chuck 11.

Next, Cl ₂ gas, SF ₆ gas, and N ₂ gas are introduced into the chamber 2 as an etching gas from the processing gas supply system 30. Then, a high frequency power of, for example, 60 MHz is applied from the high frequency power source 40 to the shower head 21, thereby generating a high frequency electric field between the shower head 21 as the upper electrode and the susceptor 3 as the lower electrode, and the Cl ₂ gas Then, SF ₆ gas and N ₂ gas are converted into plasma.

  The main etching of the polycrystalline silicon film 105 is performed by the plasma of the etching gas thus generated. At this time, a high frequency power of a predetermined frequency, for example, 13.56 MHz, is applied from the high frequency power supply 50 to the susceptor 3 which is the lower electrode so that ions in the plasma are drawn to the susceptor 3 side.

  Etching is performed in this manner, and as shown in FIG. 4, the main etching is completed with the polycrystalline silicon film 105 remaining slightly on the silicon nitride film 103 with a film thickness of, for example, 20 to 30 nm.

In main etching, the surface of the polycrystalline silicon film 105 can be planarized by adding N ₂ gas to Cl ₂ gas and SF ₆ gas as an etchant supply source. Here, the Cl ₂ gas is a gas that contributes to a high etching rate by ion etching with Cl ions in plasma. In addition, SF ₆ gas has a density of F atoms generated in plasma several times higher than other fluorine-based gases, and S ₆ contained in SF ₆ prevents etching on the Si surface to promote etching. Therefore, it is a gas species that provides a high etching rate, shortens the process time of the main etching process, and contributes to the improvement of the throughput of the entire etch back.

Next, Cl ₂ gas, HBr gas, and CF ₄ gas are introduced into the chamber 1 as an etching gas from the processing gas supply system 30. Then, a high frequency power of, for example, 60 MHz is applied from the high frequency power source 40 to the shower head 21, thereby generating a high frequency electric field between the shower head 21 as the upper electrode and the susceptor 3 as the lower electrode, and the Cl ₂ gas Then, HBr gas and CF ₄ gas are turned into plasma. At this time, a high frequency power of a predetermined frequency, for example, 13.56 MHz, is applied from the high frequency power supply 50 to the susceptor 3 which is the lower electrode so that ions in the plasma are drawn to the susceptor 3 side.

With the Cl ₂ / HBr / CF ₄ plasma generated in this way, over-etching is performed as shown in FIG. In this overetching, the remaining film (film thickness 20 to 30 nm) of the polycrystalline silicon film 105 remaining on the silicon nitride film 103 is completely removed, and the silicon nitride film 103 is slightly etched (for example, less than 10 nm). It is done until.

In the over-etching process, by using HBr gas that easily forms a reaction product (SiBr _x ) with silicon and CF ₄ that easily forms a polymer, the polycrystalline silicon film has a lower etching rate than the main etching process. The remaining film 105 is removed. Thus, it is possible to prevent the polycrystalline silicon filling the contact hole 104 from being excessively etched.

As described above, by combining the main etching process using Cl ₂ gas, SF ₆ gas and N ₂ gas with the over etching process using Cl ₂ gas, HBr gas and CF ₄ gas, The contact plug 106 can be formed as shown in FIG. 6 by performing etch back while suppressing the formation of unevenness. As a result of the smooth etching of the surface shape of the polycrystalline silicon film 105, the unevenness of the polycrystalline silicon film 105 is not transferred to the surface of the silicon nitride film 103 after the etch back, and the surface of the silicon nitride film 103 is removed. It can be formed smoothly.

Suitable conditions for performing main etching using the plasma etching apparatus 1 are as follows.
First, as the flow rate of the processing gas, for example, the flow rate of Cl ₂ is 100 to 200 mL / min (sccm), the flow rate of SF ₆ is 100 to 200 mL / min (sccm), and the flow rate of N ₂ is 50 to 200 mL / min (sccm). It is preferable that In this case, in order to sufficiently obtain a flattening effect on the etching surface, the N ₂ gas flow rate is preferably set to, for example, 25 to 40% with respect to the total gas flow rate. If the ratio of the N ₂ gas flow rate to the total gas flow rate is less than 25%, a sufficient flattening effect cannot be obtained. On the other hand, even if the ratio exceeds 40%, further improvement in the effect cannot be expected, and the etching rate may be lowered.

  The pressure in the chamber 2 during the main etching is preferably 4.0 to 12.0 Pa (30 to 90 mTorr), for example.

  Moreover, it is preferable that the susceptor temperature in the case of an etching shall be 40-70 degreeC, for example.

Suitable conditions for performing overetching using the plasma etching apparatus 1 are as follows.
First, as the flow rate of the processing gas, for example, the flow rate of Cl ₂ is 30 to 100 mL / min (sccm), the flow rate of HBr is 100 to 200 mL / min (sccm), and the flow rate of CF ₄ is 30 to 100 mL / min (sccm). It is preferable to do.

  The pressure in the chamber 2 and the susceptor temperature during overetching can be performed under the same conditions as in the main etching.

In a preferred embodiment, it is also possible to add N ₂ gas in overetching. By adding N ₂ to Cl ₂ gas, HBr gas, and CF ₄ that are gas systems for over-etching, the effect of smoothing the surface of the silicon nitride film 103 is further ensured. In this case, N ₂ gas may be introduced over the entire over-etching process, or the over-etching process may be divided into a plurality of steps, and N ₂ gas may be introduced into only a part thereof. For example, the flow rate of Cl ₂ is 30 to 100 mL / min (sccm), the flow rate of HBr is 100 to 200 mL / min (sccm), and the flow rate of CF ₄ when N ₂ gas is introduced into overetching. Is preferably 30 to 100 mL / min (sccm), and the flow rate of N ₂ is preferably 50 to 200 mL / min (sccm).

Next, test results for confirming the effects of the present invention will be described.
Using the plasma etching apparatus 1 of FIG. 1, a plasma etching process was performed on the laminated body having the same structure as that of FIG. 3 under the following conditions to etch back the polycrystalline silicon film. The plasma etching process was performed separately for main etching and over etching.
The initial film thickness of the silicon nitride film 103 in the stacked body was 167 nm, and the initial film thickness of the polycrystalline silicon film 105 was 245 nm. Further, the polysilicon film 105 is formed under the temperature condition of about 530 to 580 ° C. by the CVD method using SiH ₄ and PH ₃ as raw materials, and 3 × 10 ^{19 to} 5 × 10 6 is included in the film. A material doped with ²⁰ atoms / cm ² of phosphorus was used.

Etching conditions are as follows.
<Main etching>
Cl ₂ / SF ₆ / N ₂ = 150/150/100 mL / min (sccm)
Pressure = 6.7 Pa (50 mTorr)
Upper electrode RF power (60 MHz) = 600 W
Lower electrode RF power (13.56 MHz) = 400 W
Back pressure (center portion / edge portion) = 1333 Pa / 1333 Pa (10/10 Torr; He gas)
Distance between upper and lower electrodes = 170 mm
Temperature (upper electrode / chamber sidewall / lower electrode) = 80 ° C./60° C./60° C.

<Over-etching>
Cl ₂ / HBr / CF ₄ = 70/150/60 mL / min (sccm)
Pressure = 6.7 Pa (50 mTorr)
Upper electrode RF power (60 MHz) = 300 W
Lower electrode RF power (13.56 MHz) = 300 W
Back pressure (center portion / edge portion) = 1333 Pa / 1333 Pa (10/10 Torr; He gas)
Distance between upper and lower electrodes = 170 mm
Temperature (upper electrode / chamber sidewall / lower electrode) = 80 ° C./60° C./60° C.

For comparison, the stacked body having the same structure was etched under the same conditions as above except that N ₂ gas was not added in the main etching.

Observation results with an electron microscope of the surface of the polycrystalline silicon film 105 after the main etching and the surface of the silicon nitride film 103 after the over-etching in each of the cases where N ₂ gas is added to the main etching gas and in the case where N ₂ gas is not added ( The photograph is shown in FIG. 7, and the measurement results of the surface roughness (Ra) are shown in Table 1.

7 and Table 1, when N ₂ gas is not added, a large number of irregularities are formed on the surface of the polycrystalline silicon film 105 after the main etching, which is the surface of the silicon nitride film 103 after the over etching. You can see that it was also transferred. On the other hand, when N ₂ gas is added to the main etching gas, the surface of the polycrystalline silicon film 105 after the main etching is clearly flattened, and the surface of the silicon nitride film 103 after the over etching is also It was smooth.

The etching rate in the main etching step when N ₂ gas was added to the main etching gas was 530 nm / min, and a practically sufficient etching rate was ensured. Note that the etching rate in the main etching step when N ₂ gas was not added to the main etching gas was 565 nm / min, and no significant change was observed in the etching rate due to the addition of N ₂ gas.

Next, FIG. 8 is an electron micrograph showing the surface state of the polycrystalline silicon film 105 after performing the main etching step under the same conditions as described above except that the amount of N ₂ gas added is changed. Here, if not adding _{N 2} gas, (25 percent versus the total gas flow rate ratio) of _{N 2} gas 100 mL / min (sccm) when added and _{N 2} when the gas was added 200 mL / min (sccm) Comparison was made at 40% as a total gas flow rate ratio. Table 2 shows the measurement results of the surface roughness (Ra) of the polycrystalline silicon film 105 after the main etching step under each condition.

From FIG. 8 and Table 2, when the flow rate ratio is increased to 40% compared to the case where the flow rate ratio of N ₂ in the main etching gas is 25%, the surface of the polycrystalline silicon 105 after the main etching becomes more flat. It was shown that it can be done.

The etching rate when N ₂ gas is added to the main etching gas at 100 mL / min is 581 nm / min, and the etching rate when N ₂ gas is added at 200 mL / min is 554 nm / min. The etching rate was sufficient for practical use.

From the above results, it was confirmed that if the flow rate ratio of N ₂ in the main etching gas is set in the range of 25% to 40%, an excellent planarization effect can be obtained for the polycrystalline silicon film 105.

Next, after performing the main etching process under the same conditions as above (N ₂ gas flow rate: 100 mL / min), the over-etching process is performed in two steps, and in the latter half (second step), N ₂ gas Was introduced. That is, the first seven seconds of over-etch process uses a _{Cl 2 / HBr / CF 4 =} 70/150 / 60mL / min (sccm) as an etching gas, the following 13 seconds, _Cl 2 / HBr as an etching gas / CF ₄ / N ₂ = 70/150/60/40 mL / min (sccm) was used. Other conditions in over-etching are the same as above.

FIG. 9 is an electron micrograph showing the surface state of the silicon nitride film 103 after over-etching performed in two steps. Further, the surface roughness (Ra) at this time was measured and found to be 5.7 nm. These results after performing the main etch by adding _{N 2} to Cl ₂ and SF _6, by adding _{N 2} to _Cl 2, HBr and CF ₄ in further over-etch process, the silicon nitride film 103 It was confirmed that the surface can be reliably flattened.

As described above, according to the plasma etching method of the present invention, it is possible to perform etching while suppressing the formation of irregularities on the surface of the polycrystalline silicon that is the film to be etched, so that, for example, a contact plug using polycrystalline silicon is formed. By applying the etching back process, it is possible to prevent device defects caused by the transfer of the concavo-convex shape from the surface of the polycrystalline silicon to the surface of the interlayer insulating film.
Therefore, the processing method of the present invention can be suitably used in the manufacture of a semiconductor device such as a DRAM in which contact formation by an etch back process is repeatedly performed, for example.

  As mentioned above, although embodiment of this invention was described, this invention is not restrict | limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, a parallel plate type plasma etching apparatus that performs etching by applying high-frequency power to the upper and lower electrodes is used, but the present invention is not limited to this, and high-frequency power is applied only to the upper electrode or only the lower electrode. Or a magnetron RIE plasma etching apparatus using permanent magnets. Further, not only the capacitively coupled plasma etching apparatus but also other types of plasma etching apparatuses such as an inductively coupled type can be used.

  The present invention can be suitably used in the process of manufacturing various semiconductor devices such as DRAMs.

Sectional drawing which shows schematic structure of the plasma etching apparatus which can be utilized suitably for implementation of the plasma etching method of this invention. The block diagram of a process gas supply system. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state where main etching is performed. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state after main etching. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state where over etching is carried out. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state after over etching. With or without the addition of N ₂ gas is a diagram showing a difference in etching the surface. Is a drawing showing the state of etching the surface of the case of changing the flow rate of N ₂ gas. Is a drawing showing the state of etching the surface of the case of adding N ₂ gas during overetching.

Explanation of symbols

1: Plasma etching device 2: Chamber (processing vessel)
3: Susceptor (lower electrode)
21: Shower head 30: Process gas supply system 36: Exhaust device 40: High frequency power supply 101: Si substrate 102: Silicon oxide film (SiO ₂ )
103: Silicon nitride film (Si ₃ N ₄ )
104: Contact hole 105: Polycrystalline silicon film 106: Contact plug W: Semiconductor wafer

Claims (11)

A first etching step of etching the polycrystalline silicon film using a plasma of an etching gas containing SF ₆ , Cl _2, and N _{2 on the} object to be processed on which the polycrystalline silicon film is formed;
And a second etching step of etching the polycrystalline silicon film using plasma of an etching gas containing Cl ₂ , HBr, and CF ₄ after the first etching step. A first etching step of etching the polycrystalline silicon film using a plasma of an etching gas containing SF ₆ , Cl _2, and N _{2 on the} object to be processed on which the polycrystalline silicon film is formed;
After the first etching step, a second etching step of etching the polycrystalline silicon film using plasma of an etching gas containing Cl ₂ , HBr, and CF ₄ ;
After the second etching step, a third etching step of etching the polycrystalline silicon film using plasma of an etching gas containing Cl ₂ , HBr, CF ₄ and N ₂ ;
A plasma etching method comprising: The polycrystalline silicon film of the object to be processed having an insulating film in which a through opening is formed and a polycrystalline silicon film covering the insulating film is etched back to selectively leave polycrystalline silicon in the through opening. A plasma etching method comprising:
A plasma etching method comprising a first etching step of etching the polycrystalline silicon film using plasma of an etching gas containing SF ₆ , Cl ₂ and N ₂ . 4. The plasma according to claim 3, further comprising a second etching step of etching the polycrystalline silicon film using a plasma of an etching gas containing Cl ₂ , HBr, and CF ₄ after the first etching step. Etching method. 5. The method according to claim 4, further comprising a third etching step of etching the polycrystalline silicon film using a plasma of an etching gas containing Cl ₂ , HBr, CF _4, and N ₂ after the _second etching step. Plasma etching method.   The plasma etching method according to claim 3, wherein the insulating film is a silicon nitride film. 7. The plasma etching method according to claim 1, wherein, in the first etching step, a flow rate ratio of the N ₂ with respect to a total flow rate of the etching gas is 25 to 40%.   8. The plasma etching method according to claim 1, wherein the polycrystalline silicon film is made of polycrystalline silicon doped with phosphorus. 9.   A control program that operates on a computer and controls a plasma processing apparatus so that the plasma etching method according to any one of claims 1 to 8 is performed at the time of execution. A computer-readable storage medium storing a control program that runs on a computer,
A computer-readable storage medium for controlling the plasma processing apparatus so that the plasma etching method according to any one of claims 1 to 8 is performed when the control program is executed. A processing chamber for performing a plasma etching process on an object to be processed;
A support for placing the object to be processed in the processing chamber;
Exhaust means for depressurizing the processing chamber;
Gas supply means for supplying a processing gas into the processing chamber;
A control unit that controls the plasma etching method according to any one of claims 1 to 8 to be performed in the processing chamber;
A plasma processing apparatus comprising:

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