JP2003229418A - Method of etching - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance selectivity on an SiN film against an SiO<SB>2</SB>film in etching the SiN film on the SiO<SB>2</SB>film to cope with the thinning configuration of an SiO<SB>2</SB>film in the field of device process. <P>SOLUTION: A method of etching is to generate plasma of an etching gas in a process chamber 2 of a parallel-plate etching apparatus 1, and to etch a silicon nitride film that covers a silicon oxide film formed on a wafer W loaded in the inside of the chamber 2. A mixed gas of CH<SB>3</SB>F gas and O<SB>2</SB>gas is used for the etching gas, wherein the mixing ratio (O<SB>2</SB>/CH<SB>3</SB>F) in the mixed gas of O<SB>2</SB>gas to CH<SB>3</SB>F gas is set between 4 and 9. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method, and more particularly, to the selection of a silicon nitride film with respect to a silicon oxide film when etching a silicon nitride film covering a silicon oxide film formed on an object to be processed. The present invention relates to an etching method capable of improving the property.

[0002]

2. Description of the Related Art A silicon nitride film (Si ₃ N ₄ film) covering a silicon oxide film (hereinafter referred to as “SiO ₂ film”) when a device is formed on a wafer (hereinafter referred to simply as “SiN film”).
Membrane ". ) Is dry-etched (hereinafter, simply referred to as “etching”). In this etching process, conventionally, for example, an etching apparatus using plasma is widely used, and the etching gas is SiO ₂
A gas that selectively etches the SiN film with respect to the film is required.

Therefore, for example, CHF ₃ gas or CH ₂ F ₂ gas has been conventionally known as such an etching gas. Further, for example, in JP-A-8-059215, an etching gas containing CH _x F _4-x (x = 2 to 3) and an oxygen-containing gas is used, and a sufficiently low power bias is selected to remove silicon oxide or the like. A nitride etching process has been proposed which selectively etches a SiN film as a formation.

[0004]

[Problems to be Solved by the Invention] However, CHF
_ThreeThe gas is SiO_TwoSelectivity ratio of SiN film to film (SiN
Etching rate / SiO_TwoEtching rate (below,
Simply “SiN film / SiO _TwoMembrane "is displayed. )) Is 5 or more
Below size, CH_TwoF_TwoThe selection ratio of gas is 10 or more
It is the size below. In the field of device processing, SiO
_TwoAs the film is becoming thinner, conventional SiO_TwoAgainst the membrane
The selection ratio of the SiN film is not enough
It If the selection ratio is low, the Si
O_TwoThe film will come off and it will not function as a device.
Become In addition, the nitride etching described in the above publication
Can be etched with low bias power even in process
However, since the selection ratio is about 4,
Is not enough.

[0005] The present invention has been made to solve the above problems, the selection ratio of SiN film to SiO ₂ film when etching the SiN film on the SiO ₂ film (SiN film /
It is an object of the present invention to provide an etching method capable of significantly increasing the SiO ₂ film) as compared with the conventional method.

[0006]

The etching method according to claim 1 of the present invention generates plasma of an etching gas in a processing chamber, and removes a silicon oxide film formed on an object to be processed arranged therein. In the method of etching the covered silicon nitride film, CH _{3 is used} as the etching gas.
A mixed gas of F gas and O ₂ gas is used, and C of the mixed gas is used.
Mixing ratio of O ₂ gas to H ₃ F gas (O ₂ / CH
It is characterized in setting the _{3 F)} to 4-9.

The etching method according to a second aspect of the present invention is the etching method according to the first aspect, wherein the mixture ratio of the O ₂ gas to the CH ₃ F gas (O ₂ / C).
H ₃ F) is set to 4 to 6.

The etching method according to claim 3 of the present invention is the etching method according to claim 1 or 2, wherein the pressure of the mixed gas in the processing chamber is 50 m.
It is characterized by setting to Torr to 200 mTorr.

The etching method according to claim 4 of the present invention is characterized in that, in the invention according to any one of claims 1 to 3, Ar gas is added to the mixed gas. It is a thing.

The etching method according to claim 5 of the present invention is the etching method according to any one of claims 1 to 4, wherein the lower electrode for mounting the object to be processed in the processing chamber. Also, a parallel plate type etching apparatus having an upper electrode facing the lower electrode is used.

The etching method according to claim 6 of the present invention is the method according to claim 5, wherein high frequency power is applied to the lower electrode and the high frequency power is 1.
The temperature is set to 6 W / cm ² or less and the temperature of the lower electrode is set to 50 ° C. or less.

The etching method according to claim 7 of the present invention is the method according to claim 5 or 6, wherein high frequency power is applied to the upper electrode and the high frequency power is 1.6 W / cm. It is characterized in that it is set to ² or less.

The etching method according to claim 8 of the present invention is the etching method according to any one of claims 1 to 7, wherein the plasma has an ion density of 1 × 10 5.
It is characterized in that it is ¹⁰ ions / cm ^{3 to} 5 × 10 ¹⁰ ions / cm ³ .

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below based on the embodiments shown in FIGS. As shown in FIG. 1, for example, the etching apparatus 1 of the present embodiment has a processing chamber 2 which can maintain a desired high vacuum degree and whose surface is anodized and electrically grounded, and this processing chamber 2. A lower electrode 3 which is disposed in the center of the bottom surface of the inside and on which an object to be processed (for example, a wafer) W is mounted; The support 4 is provided, and the upper electrode 5 is formed in a hollow shape and is disposed with a gap from the lower electrode 3. A high frequency power supply 6 of 2 MHz, for example, is connected to the lower electrode 3 through a matching unit 6A, and a high frequency power supply 7 of 60 MHz, which has a higher frequency than the lower electrode 3, is connected to the upper electrode 5 by a matching unit 7A.
Connected through. The lower electrode 3 is grounded via a high pass filter 8 and the upper electrode 5 is grounded via a low pass filter 9. An exhaust device 11 is connected to an exhaust port 2B on the bottom surface of the processing chamber 2 via a pipe 11A. The exhaust device 11 evacuates the inside of the processing chamber 2 to maintain a desired degree of vacuum. In the description below, the lower electrode 3 and the support 4 will be collectively referred to as a mounting table 10 as necessary.

A gas introduction pipe 5A is formed at the center of the upper surface of the upper electrode 5, and the gas introduction pipe 5A penetrates through the upper surface center of the processing chamber 2 via an insulating member 2C. A processing gas supply source 12 is connected to the gas introduction pipe 5A via a pipe 13, and an etching gas is supplied from the processing gas supply source 12. That is, the processing gas supply source 12 is CH
₃ F gas supply source 12A, O ₂ gas supply source 12B and Ar
A gas source 12C, and each of these gas sources 12
A, 12B and 12C are branch pipes 13 of the pipe 13, respectively.
It is connected to A, 13B, and 13C. Each branch pipe 13
CH ₃ F gas supply sources 12A, O for A, 13B, 13C
Flow control devices 12D, 12E, 12F and valve 12 corresponding to the ₂ gas supply source 12B and the Ar gas supply source 12C.
G, 12H, 12I are sequentially provided from the upstream side to the downstream side, and these flow rate control devices 12D, 12E, 12F are provided.
The etching gas supplied into the processing chamber 2 via the valves 12G, 12H, and 12I is controlled to have a predetermined flow rate.

A large number of holes 5B are evenly formed on the lower surface of the upper electrode 5, and the processing gas is evenly supplied into the processing chamber 2 through the holes 5B. Therefore, the exhaust device 11
While the inside of the processing chamber 2 is evacuated, the high frequency power is applied to the lower electrode 3 and the upper electrode 5 while a predetermined etching gas is supplied from the processing gas supply source 12 at a predetermined flow rate. Then, plasma of etching gas is generated, and the wafer W on the lower electrode 3 is subjected to predetermined etching. A temperature sensor (not shown) is attached to the lower electrode 3, and the temperature of the wafer W on the lower electrode 3 is constantly monitored via the temperature sensor.

A coolant passage 1 through which a predetermined coolant (for example, a conventionally known fluorine-based fluid, water, etc.) passes through the mounting table 10 described above.
0A is formed, the lower electrode 3 is cooled while the refrigerant flows through the refrigerant channel 10A, the wafer W is cooled via the lower electrode 3, and the wafer W is controlled to a desired temperature. An electrostatic chuck 14 made of an insulating material is arranged on the lower electrode 3, and an electrode plate 14A in the electrostatic chuck 14 is connected to a high voltage DC power supply 15. The electrostatic chuck 14 electrostatically attracts the wafer W by the static electricity generated on the surface by the high voltage applied from the high voltage DC power supply 15 to the electrode plate 14A. A focus ring 16 that surrounds the electrostatic chuck 14 is arranged on the outer peripheral edge of the lower electrode 3.
Plasma is focused on the wafer W via the.

A gas channel 10B for supplying a heat conductive gas such as He gas as a backside gas to the mounting table 10 described above.
Is formed, and the gas flow path 10B is opened at a plurality of positions on the upper surface of the mounting table 10. These openings coincide with the through holes formed in the electrostatic chuck 14 on the mounting table 10.
Therefore, when the backside gas is supplied to the gas flow path 10B of the mounting table 10, the backside gas flows out from the through hole of the electrostatic chuck 14 via the gas flow path 10B, and the space between the electrostatic chuck 14 and the wafer W is increased. It spreads evenly throughout the gap, increasing the thermal conductivity in the gap. In FIG. 1, 17
Is a gate valve that opens and closes the loading / unloading port of the wafer W formed in the processing chamber 2.

Next, an embodiment of the etching method of the present invention using the above etching apparatus 1 will be described. According to the etching method of the present invention, plasma of an etching gas is generated in the processing chamber 2, and the wafer W placed inside the plasma is generated.
When etching the SiN film covering the SiO ₂ film formed in the above, a mixed gas of O ₂ gas and CH ₃ F gas is used as an etching gas. In addition, Ar gas is added to the mixed gas as needed. Therefore, the following
The etching method of the present embodiment using ₂ gas and CH ₃ F gas as etching gas will be described.

First, the residual gas in the processing chamber 2 was replaced.
After that, the gate valve 17 is opened and SiO _TwoSiN covering film
The wafer W on which the film is formed is loaded and the wafer W is processed into the processing chamber 2
After mounting on the mounting table 10 inside, close the gate valve 17
Jijiru Then, from the gas flow path 10B, backside gas
To improve the thermal conductivity between the wafer W and the electrostatic chuck 14.
The temperature of the wafer W is controlled to a predetermined temperature by cooling the wafer W efficiently.
It

After that, CH ₃ F gas supply sources 12A and O
The valves 12G and 12H of the ₂ gas supply source 12B are opened, and CH ₃ F is supplied via the respective flow rate control devices 12D and 12E.
While controlling the flow rate of the mixed gas of the gas and the O ₂ gas,
The pressure of the mixed gas in the processing chamber is controlled via the exhaust device 11. At this time, in the present embodiment, O for CH ₃ F gas is used.
It is preferable to set the mixing ratio (flow rate ratio) of the _two gases to O ₂ / CH ₃ F = 4 to 9. When the flow rate ratio of O ₂ gas to CH ₃ F gas (O ₂ / CH ₃ F) is less than 4, CH ₃ is further increased.
Since the proportion of F gas increases, CF-based deposits (deposits) tend to adhere to the SiN film, and etching may not be possible due to the influence of the deposits. On the other hand, when the flow rate ratio of O ₂ gas to CH ₃ F gas (O ₂ / CH ₃ F) exceeds 9, the etching rate of the SiN film decreases and the selection ratio of the SiN film to the SiO ₂ film (SiN film / SiO ₂ There is a risk that the film) will deteriorate. Furthermore, it is more preferable to set the flow rate ratio of O ₂ gas to CH ₃ F gas (O ₂ / CH ₃ F) to 4 to 6. By changing the upper limit of the flow rate ratio from 9 to 6, S
It is possible to further improve the selection ratio of the SiN film to the iO ₂ film. In addition, O ₂ gas and CH in the processing chamber 2
The pressure of the mixed gas of ₃ F gas is preferably set to 50 to 200 mTorr, and more preferably 50 to 100 mTorr. Mixed gas pressure is 50mT
If it is less than orr, etching cannot be performed due to the deposit on the SiN film as in the case described above, and 200 mTo
If it exceeds rr, the etching rate of the SiN film decreases and S
Selectivity of SiN film to iO ₂ film (SiN film / SiO
₂ film) may decrease. Further, the etching rate of the SiN film can be adjusted by appropriately adding Ar gas, which promotes dissociation of CH ₃ F, to the above mixed gas as needed.

After controlling the flow rate and pressure of the mixed gas within the above range, high frequency power is applied to the lower electrode 3 and the upper electrode 5, respectively. At this time, the plasma of the mixed gas is generated by the high frequency power of 60 MHz applied to the upper electrode 5, and the bias potential is generated on the wafer W by the high frequency power of 2 MHz applied to the lower electrode 3. Depending on the potential difference between the plasma potential and the bias potential, S
Promotes etching of the iN film.

At this time, when etching a wafer having a diameter of 200 mm, the high frequency power of the lower electrode 3 is set to 5
It is preferably set to 00 W or less, and more preferably set to 0 to 300 W. The surface temperature of the wafer W is preferably set to 20 to 80 ° C. In order to realize the surface temperature of the wafer W, the temperature of the lower electrode 3 may be set to approximately 50 ° C. or lower, and more preferably 20 to 40 ° C. This temperature is comparable. When etching a wafer having a diameter of 200 mm, the high frequency power of the upper electrode 5 is preferably set to 500 W or less, more preferably 0 to 300 W. By setting the electric power of the upper electrode 5 to 500 W or less, the ion density of plasma can be controlled to 1 × 10 ¹⁰ ions / cm ^{3 to} 5 × 10 ¹⁰ ions / cm ³ , and a good selection ratio and in-plane Can be uniformly etched. If the ion density deviates from the above range, the above selection ratio may decrease or etching may stop. Here, the optimum setting value of the high frequency power is described for the wafer having a diameter of 200 mm, but when the diameter is 300 mm, it is preferable to set the upper and lower electrodes to 1200 W or less.
It is more preferable to set it to 0W. That is, both upper and lower electrodes are 1. depending on the size of the wafer to be etched.
It is preferably set to 6 W / cm ² or less, and 0 to 1.
It is more preferable to set it to 0 W / cm ² .

By etching the SiN film under the above-mentioned etching conditions, it is possible to obtain a selectivity ratio of the SiN film to the SiO ₂ film of at least 10 or more, and in many cases 20 or more. It is possible to obtain a much higher selection ratio as compared with the conventional one while avoiding the stop of the above. Therefore, the SiO that constitutes the device
It also ₂ film thinning of proceeding would missing SiO2 film during the etching of the SiN film (SiO ₂ film break)
Can be prevented, only the SiN film can be reliably etched, and a device having excellent electrical performance can be manufactured.

[0025]

EXAMPLE In this example, a wafer having a SiN film formed on its surface and a wafer having a SiO ₂ film formed on its surface were used.
Each wafer was separately etched by the etching method of the present invention. Then, the SiN film and the SiO
₂ film was measured in-plane uniformity of each etching rate and etching selection ratio from the ratio of the etching rate of the SiN film to the SiO ₂ film on the basis of these measurement results (Si
(N film / SiO ₂ film) was determined. Hereinafter, specific examples will be described.

Examples 1 to 4 In these Examples, the pressure of the mixed gas of CH ₃ F gas and O ₂ gas in the processing chamber 2, the power of the upper electrode 5 and the CH ₃ F gas were used on the basis of the following etching conditions. The respective flow rates were changed as shown in Table 1 below, and the other conditions were set to the following etching conditions to etch the SiN film and the SiO ₂ film. The measurement results of the etching rate and the in-plane uniformity of etching are shown in Table 2 below. According to the results shown in Table 2, in these examples, a minimum of 1
A selectivity of 1.85 and a maximum of 20.75 was obtained. [Basic etching conditions] 1. Pressure of mixed gas: 50 mTorr 2. Electric power of high frequency power source (T / B): 500 W / 100 W where T is an upper electrode and B is a lower electrode. The same applies to the following. 3. 3. Distance between upper electrode and lower electrode: 45 mm 4. Flow rate ratio of mixed gas (CH ₃ F / O ₂ ): 35/200 sccm 5. Backside gas pressure (C / E): 10/35 Torr where C is the center of the mounting table and E is the peripheral portion of the mounting table. The same applies to the following. 6. Temperature of each part (B / T / W): 20/60/50 ° C. However, B is the lower electrode, T is the upper electrode, and W is the inner peripheral surface of the processing chamber. The same applies to the following. 7. Wafer diameter used: 200 mm

[0027]

[Table 1]

[0028]

[Table 2] However, in Table 2, E / R indicates the etching rate, and the unit is angstrom / min. The in-plane uniformity is the result of calculating [(maximum value-minimum value) / (average value × 2)] × 100 at a plurality of points on the wafer in%.

Examples 5-8 In these examples, CH ₃ F was added under the following etching conditions.
While maintaining the flow rate ratio of O ₂ gas to gas (O ₂ / CH ₃ F) to be substantially constant at 5.7, each flow rate was set to 160
sccm / 28sccm, 200sccm / 35scc
m, 280 sccm / 49 sccm and 400 sccm
/ 70 sccm, and using a wafer having a SiN film formed on the surface and a wafer having a SiO ₂ film formed on the surface, each wafer was separately etched by the etching method of the present invention. Then, the respective etching rates and the in-plane uniformity of the etching were measured, and the respective results are shown in FIG. According to the results shown in FIG. 2, a minimum selection ratio of 46.5 was obtained in these examples.
In FIG. 2, there is a portion which is not shown the etch rate and in-plane uniformity of the SiO ₂ film, which is because the SiO ₂ film can not be measured without being hardly etched.
Further, in FIG. 2, the selection ratio of the SiO ₂ film which is hardly etched is shown as infinity (∞) for convenience. The same applies to FIG. [Etching conditions] 1. Mixed gas pressure: 100 mTorr 2. Power of high frequency power source (T / B): 100W / 100W 3. 3. Distance between upper electrode and lower electrode: 45 mm 4. Backside gas pressure (C / E): 10/35 Torr 5. Temperature of each part (B / T / W): 40/60/50 ° C. 6. Diameter of wafer W used: 200 mm

Examples 9 to 14 In these examples, the temperature of the lower electrode and the high-frequency power were changed as shown in FIG. 3 under the following etching conditions, and the wafer on which the SiN film was formed and the SiO on the surface were changed.
Using the wafer on which _two films were formed, each wafer was separately etched by the etching method of the present invention. The results of the respective etching rates and the in-plane uniformity are shown in FIG. According to the results shown in FIG. 3, a minimum selection ratio of 26.6 was obtained in these examples. [Etching conditions] 1. Mixed gas pressure: 100 mTorr 2. Electric power of the high frequency power source of the upper electrode: 100 W 3. 3. Distance between upper electrode and lower electrode: 45 mm 4. Flow rate ratio of mixed gas (CH ₃ F / O ₂ ): 35/200 sccm 5. Backside gas pressure (C / E): 10/35 Torr 6. Temperature of each part (T / W): 60/50 ° C 7. Diameter of wafer W used: 200 mm

As described above, according to this embodiment,
Etching in the processing chamber 2 of the parallel plate type etching apparatus 1
A plasma of green gas is generated on the lower electrode 3 inside the plasma.
The silicon oxide film formed on the wafer W placed in
When etching the silicon nitride film,
O as su_TwoGas and CH_ThreeUsing a mixed gas of F gas,
O of mixed gas_TwoGas and CH_ThreeF gas flow rate ratio (O_Two/
CH_ThreeBy setting F) to 4-9, SiO_Twofilm
Selective ratio of SiN film to at least 10 or more, many
In the case of, it is possible to obtain a selection ratio of 20 or more,
In comparison, selection is performed while avoiding etching stop due to deposits.
The selection ratio can be significantly increased. Therefore, the device
Constituting SiO_TwoEven if the film becomes thinner, SiO_TwoMembrane blur
To prevent erosion and selectively etch only the SiN film
It is possible to manufacture good devices with excellent electrical performance.
Wear. Furthermore, CH_ThreeO for F gas_TwoGas flow ratio
(O _Two/ CH_ThreeBy setting F) to 4-6, S
iO_TwoTo further improve the selection ratio of the SiN film to the film
You can

Further, according to this embodiment, the inside of the processing chamber 2 is
O in_TwoGas and CH_ThreeThe pressure of the mixed gas of F gas is 50
Set to mTorr ~ 200mTorr,
Wafer service with high frequency power of pole 3 etched
1.6 W / cm corresponding to the is^TwoSet below
Set the temperature of the lower electrode 3 below 50 ° C, and
Wafer support to which high frequency power of pole 5 is etched
1.6 W / cm corresponding to the is^TwoSet below, Ion
Density is 1 × 10¹⁰Ion / cm^Three~ 5 x 10 ¹⁰Io
/ Cm^ThreeDeposits by generating plasma
Ensures high selectivity while avoiding etching stop due to
Can be obtained. Also, O_TwoGas and CH_ThreeOf F gas
The above selection ratio can be obtained by adding Ar gas to the mixed gas.
To improve the etching rate of the SiN film.
You can

The present invention is not limited to the above embodiment. For example, in the above embodiment, the etching apparatus that applies high-frequency power to the upper and lower electrodes 3 and 5 has been described as an example. However, in the parallel-plate type etching apparatus that applies high-frequency power to the lower electrode and grounds the upper electrode. The present invention can also be applied. Further, the object to be processed is not limited to the wafer.

[0034]

The effects of the invention described in claims 1 to 8 are as follows.
According to Ming, SiO_TwoEtching the SiN film on the film
When SiO_TwoSelectivity ratio of SiN film to film (SiN film /
SiO _TwoMembrane) can be significantly improved compared to the past.
A touch-up method can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of an etching apparatus preferably used in an etching method of the present invention.

FIG. 2 shows CH ₃ F gas and O of the etching apparatus shown in FIG.
₃ is a graph showing the relationship between the etching rate, in-plane uniformity, and selectivity of the SiN film and the SiO ₂ film when the flow rates of the _two gases are set to be substantially constant and the respective flow rates are changed.

3 is a graph showing the relationship between the etching rate, in-plane uniformity and selectivity of the SiN film and the SiO ₂ film when the temperature of the lower electrode of the etching apparatus shown in FIG. 1 and the high frequency power are changed.

[Explanation of symbols]

1 Etching Device 2 Processing Chamber 3 Lower Electrode 5 Upper Electrode 6 Lower Electrode High Frequency Power Supply 7 Upper Electrode High Frequency Power Supply 12A CH ₃ F Gas Supply Source 12B O ₂ Gas Supply Source 12C Ar Gas Supply Source 16 Ar Supply Source (Gas Supply Source ) W wafer (processing target)

Claims (8)

[Claims] 1. A method of etching plasma of an etching gas in a processing chamber to etch a silicon nitride film covering a silicon oxide film formed on an object to be processed, the etching gas being CH ₃ as the etching gas. Using a mixed gas of F gas and O ₂ gas, CH ₃ F of the above mixed gas
The mixing ratio of O ₂ gas to gas (O ₂ / CH ₃ F) is 4
Etching method and setting the 1-9. 2. CH of the mixed gas_ThreeO for F gas
_TwoMixing ratio of gas (O _Two/ CH_ThreeSet F) to 4-6
The etching method according to claim 1, further comprising:
Addition). 3. The etching method according to claim 1, wherein the pressure of the mixed gas in the processing chamber is set to 50 mTorr to 200 mTorr. 4. The etching method according to claim 1, wherein Ar gas is added to the mixed gas. 5. A parallel plate type etching apparatus having a lower electrode for mounting the object to be processed and an upper electrode facing the lower electrode in the processing chamber is used. The etching method according to claim 1. 6. A high frequency power is applied to the lower electrode and the high frequency power is set to 1.6 W / cm ² or less,
The etching method according to claim 5, wherein the temperature of the lower electrode is set to 50 ° C. or lower. 7. The etching method according to claim 5, wherein high frequency power is applied to the upper electrode and the high frequency power is set to 1.6 W / cm ² or less. 8. The ion density of the plasma is 1 × 10.
¹⁰ ion / ^cm 3 to 5 × ^{10 10} etching method according to any one of claims 1 to 7, characterized in that the ion / cm ^3.