JP2016058544A - Etching method, storage medium and etching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for etching a SiN film 73 with high selection ratio for a SiOfilm 74, without generating plasma, in the etching method of a wafer W having the SiN film 73 and SiOfilm 74 on the surface.SOLUTION: A wafer W having a SiN film 73 and a SiOfilm 74 on the surface is mounted on a stage 4 provided in a processing container 3, and heated by means of a heater 46. After a vacuum atmosphere is brought in the processing container 3, a not yet excited process gas containing ClFgas is supplied from a gas shower head 31 to the wafer W. Although the SiN film 73 reacts quickly on the process gas containing ClFgas, reaction rate of the SiOfilm 74 to the process gas containing ClFgas is much slower. As it can be seen from the experimental results, the SiN film 73 can be etched with high selection ratio for the SiOfilm 74, without generating plasma.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technique for performing an etching process by supplying a processing gas to the surface of a substrate to be processed.

In a semiconductor manufacturing process, for example, a part of an insulating film or a SiN (silicon nitride) film as a hard mask is formed on a semiconductor wafer (hereinafter referred to as “wafer”) as a substrate, and a part of the SiN film or There is a process in which everything is removed by etching. As a method for etching a SiN film, for example, as described in Patent Document 1, plasma etching is known in which etching is performed by converting a compound gas containing fluorine, for example, ClF ₃ (chlorine trifluoride) gas into plasma. However, plasma etching is liable to damage the wafer. Therefore, in recent years, a method called chemical oxide removal (COR) has attracted attention. As a method of etching a SiN film by this method, for example, as described in Patent Document 2, HF ( A method using a processing gas containing hydrogen fluoride gas and F ₂ (fluorine) gas is known.

However, in addition to the SiN (silicon nitride) film, an SiO ₂ (silicon oxide) film is formed on the substrate surface on the wafer. For example, the SiO ₂ film is the base of the SiN film, or both films are exposed. There may be. When etching the SiN film to such a wafer in HF gas and _{F 2} gas, the NH ₃ gas and HF gas produced as a reaction product SiO ₂ film is etched, the SiN film to the SiO ₂ film There is a problem that it is difficult to increase the etching selectivity. There is also a problem that the etching rate of the SiN film is slow and the etching rate is lowered.

JP 2003-264183 A JP 2010-182730 A

The present invention has been made under such circumstances, and an object thereof is to provide a technique capable of etching a SiN film with a high selectivity with respect to a SiO ₂ film without generating plasma.

An etching method of the present invention is a method of selectively etching a silicon nitride (SiN) film with respect to a substrate to be processed having a silicon nitride (SiN) film and a silicon oxide (SiO ₂ ) film on a surface portion.
A step of supplying an unexcited processing gas containing chlorine trifluoride (ClF ₃ ) gas to the heated substrate to be processed is performed in a vacuum atmosphere.

The storage medium of the present invention is a storage medium storing a computer program used in an etching apparatus provided with a processing container in which a mounting portion on which a substrate to be processed is mounted is provided.
The computer program includes a group of steps so as to perform the above-described etching method.

An etching apparatus of the present invention is an apparatus for selectively etching a silicon nitride (SiN) film with respect to a substrate to be processed having a silicon nitride (SiN) film and a silicon oxide (SiO ₂ ) film on the surface portion.
A processing container having a mounting portion for mounting the substrate to be processed;
A heating unit for heating the substrate to be processed placed on the placement unit;
A gas supply unit for supplying a processing gas that contains chlorine trifluoride (ClF ₃ ) gas and is not excited to the substrate to be processed heated by the heating unit;
And an evacuation unit for evacuating the inside of the processing vessel.

In the present invention, a heated substrate to be processed having a SiN film and a SiO ₂ film on the surface is exposed to an unexcited processing gas containing ClF ₃ gas. Therefore, damage to the substrate can be suppressed, and the SiN film can be etched with a high selectivity with respect to the SiO ₂ film as can be seen from the experimental results described later.

1 is a plan view of a substrate processing apparatus to which the present invention is applied. It is a longitudinal section showing an etching device concerning an embodiment of the invention. It is a longitudinal cross-sectional view which shows the surface vicinity of a to-be-processed substrate. It is a longitudinal cross-sectional view which shows the surface vicinity of a to-be-processed substrate. It is a characteristic view which shows the characteristic of the process pressure and the etching amount in the etching method concerning an Example. It is a characteristic view which shows the characteristic of the process pressure and the etching amount in the etching method concerning an Example. It is a characteristic view which shows the characteristic of the process pressure and the etching amount in the etching method concerning an Example. It is a characteristic view which shows the characteristic of the preset temperature and etching amount of a board | substrate in the etching method concerning an Example. Is a SEM photograph showing the surface when the substrate was deposited an SiN film (a) and the substrate was deposited an SiO ₂ film (b) is etched by the etching method according to the embodiment. It is a characteristic diagram showing the characteristics of the supply time and the amount of etching of the ClF ₃ gas in the etching method according to an embodiment. It is a characteristic diagram showing the characteristics of the supply time and the amount of etching of the ClF ₃ gas in the etching method according to an embodiment. It is a characteristic diagram showing the characteristics of the supply time and the amount of etching of the ClF ₃ gas in the etching method according to an embodiment. It is a characteristic diagram showing the characteristics of the supply flow rate and the etching amount of ClF ₃ gas in the etching method according to an embodiment.

  An etching apparatus 10 used in the etching method according to the embodiment of the present invention will be described. First, a substrate processing apparatus provided with the etching apparatus 10 will be described. As shown in FIG. 1, the substrate processing apparatus includes a horizontally long normal pressure transfer chamber 12 whose internal atmosphere is changed to a normal pressure atmosphere by, for example, nitrogen gas. In front of the normal pressure transfer chamber 12, for example, a load port 11 for transferring a substrate to a transfer container C for loading a wafer W as a substrate to be processed is installed.

  An opening / closing door 17 that is opened and closed together with a lid (not shown) provided in the transfer container C is attached to the front wall of the normal pressure transfer chamber 12. In the normal pressure transfer chamber 12, a first transfer arm 20, which is a substrate transfer mechanism composed of an articulated arm for transferring the wafer W, is provided. An alignment chamber 16 for adjusting the orientation and eccentricity of the wafer W is provided on the left side wall of the normal pressure transfer chamber 12 as viewed from the load port 11 side. Further, an exhaust port for exhausting the inside of the normal pressure transfer chamber 12 is provided on the bottom surface of the normal pressure transfer chamber 12 and is configured to be exhausted by an exhaust means such as an exhaust fan.

  On the opposite side of the load port 11 in the normal pressure transfer chamber 12, the internal atmosphere is switched between the normal pressure atmosphere and the vacuum atmosphere while the wafer W is waiting, for example, two load lock chambers 13 on the left and right. It arrange | positions so that it may be located in a line and each is divided by the door valve 18. FIG. The first transfer arm 20 plays a role of delivering the wafer W to the transfer container C, the alignment chamber 16 and the load lock chamber 13.

  Etching devices 10 are arranged through gate valves 23 on the back side of each load lock chamber 13 as viewed from the normal pressure transfer chamber 12 side. Each load lock chamber 13 includes, for example, a second transfer arm 24 configured by an articulated arm having a support portion that supports the wafer W substantially horizontally at the tip.

  The overall processing of the wafer W in the substrate processing apparatus will be described. For example, the unprocessed wafer W in the transfer container C transferred into the load port 11 by OHT or the like is transferred into the alignment chamber 16 through the atmospheric pressure transfer chamber 12 and alignment is performed. Then, it is transferred into the etching apparatus 10 via the second transfer arm 24 and an etching process is performed. The processed wafer W that has been etched is transferred through the reverse path (but not through the alignment chamber 16) in the substrate processing apparatus and returned to the predetermined transfer container C.

  An etching apparatus 10 according to an embodiment of the present invention will be described. As shown in FIG. 2, the etching apparatus 10 includes a processing container 3 that is a vacuum chamber having a square cross section. A loading / unloading port 32 for transferring the wafer W is provided on the side surface of the processing container 3, and a gate valve 23 for opening and closing the loading / unloading port 32 is provided at the loading / unloading port 32.

  A cylindrical stage 4, which is a mounting portion for the wafer W, is provided inside the processing container 3. Further, through holes 40 penetrating the bottom surface of the stage 4 and the processing container 3 are provided at three locations at equal intervals in the circumferential direction. The through hole 40 is provided with a push-up pin 41 for transferring the wafer W so as to protrude from the upper surface of the stage 4 by the lifting mechanism 43. The lower side of the push-up pin 41 is covered with a bellows 44 for making the processing container 3 airtight.

  A heater 46 serving as a heating unit is provided inside the stage 4, and the wafer W placed on the stage 4 is heated to a set temperature. An exhaust port 34 is provided on the bottom surface of the processing container 3. An exhaust pipe 35 is connected to the exhaust port 34, and a pressure adjusting unit 36 and an opening / closing valve 37 are interposed from the exhaust port 34 side, and are connected to a vacuum exhaust pump 38 that is a vacuum exhaust mechanism. These parts such as the exhaust pipe 35 constitute a vacuum exhaust section.

  A gas shower head 31 serving as a gas supply unit is provided on the upper surface of the processing container 3, and a diffusion plate 50 is provided on the gas shower head 31 so as to face the mounting surface of the stage 4. The diffusion plate 50 is formed in a disc shape using a material having high thermal conductivity such as stainless steel, and is configured as a punching plate in which gas supply holes 51 penetrating in the thickness direction are arranged vertically and horizontally, for example. A buffer chamber 39 is formed above the diffusion plate 50.

The shower head 31 is connected to a downstream end of a gas supply pipe 60 formed of a pipe for supplying ClF ₃ (chlorine trifluoride) gas so as to communicate with the buffer chamber 39. The gas supply pipe 60 is provided with a ClF ₃ gas supply source 61, a flow rate adjusting unit 62, and a valve V1 in this order from the upstream side. A downstream end of an N ₂ (nitrogen) gas supply pipe 63 that is a purge gas (dilution gas) is connected to the downstream side of the valve V1 in the gas supply pipe 60, and N ₂ gas supply pipe 63 is connected to N ₂ from the upstream side. _Two gas supply sources 64, a flow rate adjusting unit 65, and a valve V2 are provided in this order.

  The etching apparatus 10 includes a control unit 9. The control unit 9 is formed of a computer, for example, and includes a program, a memory, and a CPU. The program incorporates a group of steps so as to perform a series of operations in the description of the action described later. According to the program, the valves V1 and V2 are opened and closed, the flow rate of each gas is adjusted, and the pressure in the processing container 3 is adjusted. And so on. This program is stored in a computer storage medium such as a flexible disk, a compact disk, a hard disk, a magneto-optical disk, etc., and is installed in the control unit 9.

  Subsequently, the operation of the embodiment of the present invention will be described. First, an example of the surface structure of the wafer W, which is the substrate to be processed, carried into the etching apparatus 10 will be described. FIG. 3 shows the structure of the wafer W in the middle stage of a CMOS (Complementary MOSFET) manufacturing process. In this surface structure, an insulating film 72 is buried between a convex pattern 76 of silicon 71 via a barrier layer 75, and a SiO2 film 74 and a SiN film 73 film are laminated in this order from the bottom on the top of the pattern 76. ing. The film thickness of the SiN film 73 is, for example, 100 nm. The chemical formula of silicon nitride is abbreviated as “SiN” without considering the stoichiometric ratio.

After the wafer W is loaded into the load lock chamber 13 as described above, the wafer W is loaded into the processing container 3 of the etching apparatus 10 by the second transfer arm 24, and the second transfer arm 24 and the push-up pin 41 are brought into contact with each other. It is placed on the stage 4 by the cooperative action and heated to, for example, 120 ° C. by the heater 46. On the other hand, after the gate valve 23 is closed and the processing container 3 is sealed, the valve V1 is opened and the ClF ₃ gas is supplied from the gas shower head 31 to the wafer W in a shower shape.

In this etching process, the temperature of the wafer W is preferably 70 ° C. to 200 ° C. When it is 70 ° C. or lower, the etching rate becomes slow. The pressure of the processing atmosphere is preferably 133 Pa (1 Torr) to 6.67 × 10 ³ Pa (50 Torr). When the pressure is 133 Pa (1 Torr) or less, the etching rate is slow. Further, when the pressure is higher than 667 Pa (5 Torr), the etching rate of the SiN film 74 tends to decrease as the pressure increases, and it is preferable to set the pressure to 6.67 × 10 ³ Pa (50 Torr) or less. Furthermore, the flow rate of the ClF ₃ gas is set to, for example, 10 sccm to 200 sccm.

After supplying the ClF ₃ gas to the wafer W for a set time, the valve V1 is closed to stop the supply of the ClF ₃ gas, and the valve V2 is opened to supply N ₂ gas as a purge gas into the processing container 3, The ClF ₃ gas in ₃ is replaced, and then the wafer W is unloaded from the processing container 3.

In the above-described embodiment, the SiN film 73 on the heated wafer W is etched using a ClF ₃ gas that is not plasmatized (excited) as an etching gas. Since this process has a high etching selectivity of the SiN film 73 with respect to the SiO ₂ film 74, as will be confirmed from an experimental example described later, the SiN film is removed while suppressing over-etching of the underlying SiO ₂ film 74 of the SiN film 73. can do.

In the present invention, after the etching process is performed, the residue after the etching process may be skipped by heating. For example, a vacuum chamber provided with a heating stage for heating the wafer W is provided between the load lock chamber 13 and the etching apparatus 10. The second transfer arm 24 provided in the load lock chamber 13 is configured to be accessible to the heating stage of the vacuum chamber and the mounting table of the etching apparatus. Then, the wafer W that has been subjected to the etching of the SiN film 73 by being exposed to the ClF ₃ gas in the etching apparatus 10 is placed on the heating stage in the vacuum chamber and heated. Thereby, the reaction product residue on the wafer W may be volatilized and removed.

In the present invention, the ClF ₃ gas may not be supplied alone into the processing vessel 3 but may be diluted with an inert gas such as N ₂ gas or Ar gas. When supplied into the processing chamber 3 as a mixed gas of an inert gas and ClF ₃ gas is set so that the supply flow rate of ClF ₃ gas is for example 10～200Sccm. The “film” of the SiO ₂ film 74 and the SiN film 73 used in the specification does not mean only a thin layer but also includes a block-like one.

Examples carried out to verify the effects of the present invention will be described.
[Example 1]
The dependence of the process pressure (pressure in the processing vessel 3) on the etching amount of the SiN film and the etching selectivity of the SiN film to the SiO ₂ film was examined.

(Example 1-1)
Using two evaluation substrates made of silicon, a SiO ₂ film is formed on one substrate, and a SiN film is formed on the other substrate by CVD (Chemical Vapor Deposition) using dichlorosilane gas and ammonia gas. did. Etching was performed on these substrates using an evaluation etching apparatus at a flow rate of 200 sccm and a supply time of 1 minute for ClF ₃ gas.
The temperature of the substrate was set to 200 ° C. The process pressure is 66.7 Pa (0.5 Torr), 133 Pa (1 Torr), 400 Pa (3 Torr), 667 Pa (5 Torr), 4.0 × 10 ³ Pa (30 Torr), 6.67 × 10 ³ Pa (50 Torr). The etching amount was checked with a film thickness meter.
(Example 1-2)
The test was performed in the same manner as in Example 1-1 except that the temperature of the substrate was set to 120 ° C. and the supply time of the ClF ₃ gas was set to 2 minutes.
(Example 1-3)
The substrate temperature was set to 70 ° C., the supply time of ClF ₃ gas was set to 2 minutes, and the process pressure was set to nine ways including three ways of 533 Pa (4 Torr), 800 Pa (6 Torr), and 933 Pa (7 Torr), The others were tested in the same manner as in Example 1-1.

(Results and discussion)
5 to 7 show the relationship between the etching amount and pressure of the SiN film and the SiO ₂ film in Example 1-1 to Example 1-3, respectively. The unit of pressure on the horizontal axis of each graph is “Torr”. According to this result, in Example 1-1, the etching amount of the SiN film is large at pressures of 4.0 × 10 ³ Pa (30 Torr) and 6.67 × 10 ³ Pa (50 Torr), and the SiN film with respect to the SiO ₂ film The etching selectivity is also large. At 400 Pa (3 Torr) and 667 Pa (5 Torr), the etching amount of the SiN film is large, but the etching selectivity is small. At 133 Pa (1 Torr), the etching amount of the SiN film is smaller than that at 400 Pa (3 Torr) or more, but the etching selectivity is as large as 38.2.

In Example 1-2, considering that the processing time is twice that in Example 1-1, the etching rate of the SiN film is lower than that in Example 1-1. The etching selectivity is small at 667 Pa (5 Torr), but 15 or more at 133 Pa (1 Torr) and 400 Pa (3 Torr), and 4.0 × 10 ³ Pa (30 Torr) and 6.67 × 10 ³ Pa ( 50 Torr) is 20 or more.

In Example 1-3, the etching selectivity is generally large, but the etching rate is small because the process temperature is low.
General consideration regarding the above Examples 1-1 to 1-3 will be described in conjunction with the examples described later.

[Example 2]
In order to investigate the relationship between the set temperature of the substrate and the etching amount of the SiN film, the following test was performed. In the same manner as in Example 1, the substrate temperature was set to four types of 30 ° C., 70 ° C., 100 ° C., and 200 ° C. using the evaluation etching apparatus for the evaluation substrate, and ClF ₃ gas was used for each temperature. Was supplied at a flow rate of 200 sccm for 2 minutes to perform etching. The process pressure was set to 6.67 × 10 ³ Pa (50 Torr). The etching amount was measured by analyzing an SEM (scanning electron microscope) image.

(Results and discussion)
FIG. 8 is a graph showing the results of Example 2, with the vertical axis representing the etching amount and the horizontal axis representing the temperature. According to this result, when the substrate temperature exceeded 100 ° C., the etching amount of SiN increased rapidly, and when the substrate temperature was set to 200 ° C., the etching amount was 294 nm.

FIG. 9 shows (a) a substrate on which an SiN film is formed and (b) a substrate on which an SiO ₂ film is formed after etching with the substrate temperature set to 200 ° C. in Example 2. It is a SEM image which shows the surface and side surface image | photographed from diagonally upward about each of these. As can be seen from the image, the entire SiN film is etched, and further the silicon layer of the substrate body is etched, but the SiO ₂ film is hardly etched.

[Example 3]
In order to investigate the relationship between the supply time of the ClF ₃ gas and the etching amount, the following test was performed.
(Example 3-1)
As in Example 1, an evaluation etching apparatus is used for the evaluation substrate.
Etching was performed with a ClF ₃ gas flow rate of 200 sccm and a supply time of 60, 80, 100, and 120 seconds. The substrate temperature was set to 200 ° C., and the process pressure was set to 6.67 × 10 ³ Pa (50 Torr). The etching amount was measured with a film thickness meter.
(Example 3-2)
The test was performed in the same manner as in Example 3-1, except that the process pressure was set to 133 Pa (1 Torr) and the ClF ₃ gas supply time was set to 60 and 120 seconds.
(Example 3-3)
The test was performed in the same manner as in Example 3-1, except that the substrate temperature was set to 70 ° C., the process pressure was set to 667 Pa (5 Torr), and the ClF ₃ gas supply time was set to 120 and 240 seconds. .

(Results and discussion)
10 to 12 show the relationship between the etching amounts of the SiN film and the SiO ₂ film and the supply time of ClF ₃ in Example 3-1 to Example 3-3. According to this result, in Example 3-1, the etching amount of the SiN film when supplying ClF ₃ for 60 seconds was 21.9 nm, and the etching amount when supplying ClF ₃ for 120 seconds was 310.4 nm. In Example 3-2, the etching amount of the SiN film when ClF ₃ was supplied for 60 seconds was 11.1 nm, and the etching amount when it was supplied for 120 seconds was 15.3 nm. In Example 3-3, the etching amount of the SiN film when supplying ClF ₃ for 120 seconds was 15.2 nm, and the etching amount when supplying ClF ₃ for 240 seconds was 35.2 nm.

From the results of Examples 1 to 3, the substrate temperature is advantageously 70 ° C. to 200 ° C. When the supply time of ClF ₃ gas exceeds a certain time (100 seconds in the example of FIG. 10), the etching amount of the SiO ₂ film does not increase, but the etching amount of the SiN film increases. In consideration, by adjusting the temperature of the substrate and the gas supply time, the etching pressure of the SiN film is large and the etching selection is performed in the process pressure range of 133 Pa (1 Torr) to 6.67 × 10 ³ Pa (50 Torr). A process with a large ratio can be expected. Moreover, it can be said that the process pressure is preferably 400 Pa ( ³ Torr) or higher, and more preferably 4.0 × 10 ³ Pa (30 Torr) or higher.

[Example 4]
The following test was conducted to examine the relationship between the supply amount of ClF ₃ and the etching amount. In the same manner as in Example 1, the evaluation etching apparatus is used for the evaluation substrate, and the supply flow rate of ClF ₃ is set to 10, 50, 100, and 200 sccm. The substrate temperature was set to 120 ° C., and the process pressure was set to 667 Pa (5 Torr). The etching amount was measured with a film thickness meter.
(Results and discussion)

FIG. 13 is a graph showing the results of Example 4. The vertical axis represents the etching amount, and the horizontal axis represents the supply flow rate of ClF 3. According to this result, when the supply flow rate of ClF ₃ was set in the range of 10 sccm to 200 sccm, the etching amount of the SiN film was 35 nm or more. On the other hand, the etching amount of SiO ₂ was 5.3 nm or less. In the range from 10 sccm to 200 Sccm, the etching selectivity tends to decrease as the supply flow rate of ClF ₃ increases.

3 Processing Vessel 4 Stage 10 Etching Device 23 Carry In / Out Port 31 Gas Shower Head 34 Exhaust Port 39 Buffer Room 46 Heater 50 Diffusion Plate 51 Gas Supply Hole 60 Gas Supply Pipe 71 Silicon Substrate 72 Insulating Film 73 SiN Film 74 SiO ₂ Film

Claims (5)

In a method of selectively etching a silicon nitride film on a substrate to be processed having a silicon nitride film and a silicon oxide film on the surface portion,
An etching method comprising a step of supplying an unexcited processing gas containing chlorine trifluoride gas to a heated substrate to be processed in a vacuum atmosphere.   The etching method according to claim 1, wherein the temperature of the substrate to be processed when performing the step is 70 ° C. or higher and 200 ° C. or lower. ^3. The etching method according to claim 1, wherein the process atmosphere is performed at a pressure of 133 Pa (1 Torr) or more and 6.67 × 10 ³ Pa (50 Torr) or less. . A storage medium storing a computer program used in an etching apparatus provided with a processing container in which a mounting portion on which a substrate to be processed is mounted is provided;
A storage medium in which the computer program has a set of steps so as to implement the etching method according to any one of claims 1 to 3. In an apparatus for selectively etching a silicon nitride film on a substrate to be processed having a silicon nitride film and a silicon oxide film on the surface portion,
A processing container having a mounting portion for mounting the substrate to be processed;
A heating unit for heating the substrate to be processed placed on the placement unit;
A gas supply unit for supplying a processing gas that contains chlorine trifluoride gas and is not excited to the substrate to be processed heated by the heating unit;
An etching apparatus comprising: an evacuation unit for evacuating the inside of the processing container.