JP2011054909A - Plasma etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma etching method for carrying out satisfactory shape control and high speed etching of a silicon nitride film. <P>SOLUTION: The plasma etching method includes: a step of carrying a substrate S to be processed to a treatment container 20 in carrying out plasma etching of a silicon nitride film on the substrate S formed at the lower layer side of a resist pattern equipped with an opening whose opening area is gradually made smaller as it goes from the upper part to the lower part; and a step of supplying the mixed gas of sulfur hexafluoride and oxygen to the inside of the treatment container 20 and integrating it into plasma under a pressure atmosphere within the range of 133 Pa or more and 200 Pa or less to etch the silicon nitride film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a plasma etching method in which an object to be processed such as an LCD substrate is etched using a plasma gas.

  For example, a thin film transistor (TFT) used in an FPD (Flat Panel Display) such as a liquid crystal display (LCD) is formed on a substrate to be processed such as a glass substrate, a gate electrode, a gate insulating film, It is formed by sequentially laminating semiconductor films and the like while patterning.

  After the TFT is formed on the substrate to be processed, the surface protective film (passivation film) formed on the uppermost layer is, for example, plasma etched to form a contact hole for wiring connection. Some of these contact holes have a tapered surface whose opening area gradually decreases from the top to the bottom, so that the crossing angle between the surface of the passivation film and the tapered surface becomes an obtuse angle. This prevents disconnection of the wiring embedded in the hole.

  The tapered surface of the contact hole is a so-called resist recession in which a resist pattern formed on the passivation film is preheated to form a tapered surface, and the shape of the tapered surface on the resist pattern side is transferred to the passivation film side by etching. It is formed by law.

Here, when the above-described passivation film is, for example, a silicon nitride film made of silicon and nitrogen (hereinafter referred to as an SiN film), an etching gas such as sulfur hexafluoride (SF ₆ ) is converted into plasma to perform plasma etching. Done.

  Normally, plasma etching is performed in a reduced pressure atmosphere. For example, the etching rate of the SiN film can be increased as the pressure in the reduced pressure atmosphere is increased. On the other hand, when the pressure in the reduced-pressure atmosphere is increased, the etching rate of the SiN film is increased as compared with the ashing rate of the resist, and an undercut state described later occurs. It becomes difficult to accurately transfer the shape to the passivation film.

  Thus, there is a trade-off relationship between the etching rate when etching the SiN film and the shape control of the contact hole. For this reason, for example, when priority is given to the shape control of the tapered surface, it is difficult to sufficiently increase the etching rate, and it is difficult to improve the throughput of the etching process.

Here, Patent Document 1 describes a technique for plasmaizing SF ₆ and etching a SiN film under a pressure atmosphere in a range of 1.33 Pa (10 mTorr) to 133 Pa (1000 mTorr). A technique is described in which a mixed gas of fluorine gas and oxygen gas is turned into plasma under a pressure atmosphere in the range of 1 Pa to 100 Pa to etch the SiN film. Patent Document 3 describes a technique for plasma etching a SiN film using a mixed gas of carbonyl difluoride and oxygen.

  However, in any of the techniques described in Patent Documents 1 to 3, attention is not paid to the relationship between the etching rate of the SiN film and the shape control of the tapered surface, and for example, the shape of the tapered surface is kept good. Conditions for improving the etching rate are not disclosed.

Japanese Patent Laid-Open No. 01-146328: Third page, upper right column, lines 11 to 16 JP 2008-300478 A: 0014 paragraph, 0027 paragraph JP 2002-158181 A: 0043 paragraph, 0061 paragraph

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a plasma etching method capable of good shape control and capable of etching a silicon nitride film at high speed. There is to do.

The plasma etching method according to the present invention is a method of plasma etching a silicon nitride film on a substrate to be processed formed on a lower layer side of a resist pattern having an opening that gradually decreases in opening area from the top to the bottom. There,
Carrying the substrate to be processed into a processing container;
Supplying a mixed gas of sulfur hexafluoride and oxygen into the processing vessel, converting the mixed gas into a plasma under a pressure atmosphere in a range of 133 Pa or more and 200 Pa or less, and etching the silicon nitride film; It is characterized by including.
The mixed gas preferably has a volume ratio of sulfur hexafluoride to oxygen in the range of 1: 6 or more and 1:20 or less.

According to another aspect of the present invention, there is provided a plasma etching method for plasma-etching a silicon nitride film on a substrate to be processed formed on a lower layer side of a resist pattern having an opening that gradually decreases in opening area from the top to the bottom. A method,
Carrying the substrate to be processed into a processing container;
Supplying a mixed gas of carbonyl difluoride and oxygen into the processing vessel, converting the mixed gas into a plasma under a pressure atmosphere within a range of 133 Pa or more and 267 Pa or less, and etching the silicon nitride film; It is characterized by including.
The mixed gas preferably has a volume ratio of carbonyl difluoride to oxygen in the range of 1: 2 or more and 3:20 or less.

  Each of the plasma etching methods described above is suitable when the opening of the silicon nitride film formed by etching has a shape in which the opening area gradually decreases from the top to the bottom.

  According to the present invention, by performing plasma etching using a mixed gas in which oxygen is mixed with sulfur hexafluoride or carbonyl difluoride, a stable plasma can be obtained even in a high pressure atmosphere of 133 Pa (1000 mTorr) or more. Thus, the silicon nitride film can be etched at a high speed. Further, since the mixed gas contains oxygen having the ability to ash the resist pattern, it is possible to adjust the ratio between the etching rate of the silicon nitride film and the ashing rate of the resist pattern, and the opening from the top to the bottom is possible. The shape of the opening having a gradually reduced area can be accurately transferred from the resist pattern to the silicon nitride film.

It is a vertical side view which shows an example of the to-be-processed substrate to which the plasma etching method which concerns on this Embodiment is applied. It is a vertical side view which shows the process of forming a contact hole in TFT on the said to-be-processed substrate. It is explanatory drawing which shows typically the method of forming a taper surface in the said contact hole. It is a cross-sectional side view which shows the plasma etching apparatus for enforcing the said plasma etching method. It is the 1st explanatory view showing the experimental result concerning plasma etching. It is the 2nd explanatory view showing the experimental result concerning plasma etching. It is the 3rd explanatory view showing the experimental result concerning plasma etching. It is explanatory drawing which shows the measurement point of the etching rate in the to-be-processed substrate used for the said experiment. It is the 4th explanatory view showing the experimental result concerning plasma etching. It is a 5th explanatory view showing the experimental result concerning plasma etching. It is the 6th explanatory view showing the experimental result concerning plasma etching. It is a 7th explanatory view showing the experimental result concerning plasma etching. It is the 8th explanatory view showing the experimental result concerning plasma etching. It is a 9th explanatory view showing the experimental result concerning plasma etching.

  FIG. 1 shows a longitudinal side view in which a region of a substrate to be processed to which the plasma etching method according to the present embodiment is applied is enlarged. The substrate to be processed shown in FIG. 1 is, for example, an active matrix type LCD. In the figure, 1a is a vertical side surface of the TFT portion provided in each pixel, and 1b is, for example, a gate electrode provided in the TFT portion 1a. It is a longitudinal cross-sectional view of the contact part for connecting to the drive circuit of LCD.

  In the TFT section 1a, a gate wiring film 12 is formed on a glass substrate 11, a gate insulating film 13 made of a SiN film or the like is provided thereon, and an amorphous silicon film 14 or an n + amorphous silicon film 15 and a signal are formed thereon. A line film is sequentially formed, and the signal line film and the n + amorphous silicon film 15 are separated into left and right by etching to form a source electrode 161, a drain electrode 162, and a channel portion provided between these electrodes 161 and 162. ing.

  On the upper surface side of the TFT structure formed in this way, a passivation film 17 made of, for example, a SiN film is provided to protect the surface of the TFT portion 1a. In the passivation film 17, a contact hole 103 is provided in contact with the source electrode 161 and the drain electrode 162, and an electrode film 18 made of a transparent electrode such as ITO (Indium Tin Oxide) is connected through the contact hole 103. For example, the source electrode 161 is connected to the drive circuit on the source electrode 161 side, and the drain electrode 162 is connected to the drive electrode of each liquid crystal pixel.

  On the other hand, the contact portion 1b is formed on the upper surface side of the gate wiring film 12 connected to the gate wiring film 12 of the TFT portion 1a, for example, and the gate insulating film 13 and the passivation film 17 each made of a SiN film are formed from below. The structure is laminated in this order. Then, a contact hole 103 penetrating these two layers of films 13 and 17 is provided, an electrode film 18 is formed in the contact hole 103, and the gate wiring film 12 is connected to the driving circuit on the gate wiring film 12 side. In the present embodiment, the contact hole 103 provided in the TFT portion 1a and the contact portion 1b is opened from the top to the bottom for the purpose of preventing the disconnection of the electrode film 18 as described in the background art. A tapered surface with a gradually decreasing area is formed.

  In the TFT portion 1a and the contact portion 1b having the above-described configuration, the contact holes 103 provided in the portions 1a and 1b are collectively etched from the viewpoint of reducing resist consumption and manufacturing processes. For example, in the example shown in FIGS. 2A and 2B, a resist film 101 is applied so as to cover the entire TFT portion 1a and the contact portion 1b, and the opening 102 for etching is patterned to form a resist pattern. Form. Then, the passivation film 17 and the gate insulating film 13 are etched through these openings 102 to form contact holes 103 in the respective parts 1a and 1b.

  When the contact hole 103 is etched at the TFT portion 1a and the contact portion 1b in this way, only the passivation film 17 is etched on the TFT portion 1a side, while the passivation film 17 is on the contact portion 1b side. In addition, the gate insulating film 13 needs to be etched, and SiN films having different thicknesses are etched. For this reason, even after the contact hole 103 is formed on the TFT portion 1a side and the electrodes 161 and 162 can be contacted, the contact hole 103 still reaches the gate wiring film 12 on the contact portion 1b side. In some cases, continuation of etching may be necessary. For this reason, the etching gas used for batch etching of the contact hole 103 needs to have a property that does not etch the signal line film (source electrode 161, drain electrode 162) on the TFT portion 1a side.

  As described above, the contact hole 103 on the contact portion 1b side is provided with a tapered surface for preventing disconnection of the electrode film 18. This tapered surface is formed by a resist receding method or the like. By patterning the opening 102 in the applied resist film 101 and then performing heat treatment, the inner end surface of the opening 102 becomes tapered as schematically shown in FIG.

  When the passivation film 17 is etched in a state where the tapered surface is formed on the resist film 101 in this way, the passivation film 17 starts to be etched from the thin region side of the resist film 101, so that the resist film as shown in FIG. The shape of the tapered surface 101 can be transferred to the passivation film 17. As described in the background art, in the case where the passivation film 17 is etched by plasma etching, if the pressure of the reduced pressure atmosphere in which plasma etching is performed for the purpose of increasing the etching rate is increased, the resist film 101 side is increased. The etching rate of the passivation film 17 is increased as compared with the ashing rate. As a result, as shown in FIG. 3C, the etching of the passivation film 17 proceeds on the lower surface of the resist film 101, and there is an undercut state in which the taper shape of the resist film 101 cannot be accurately transferred to the passivation film 17. Will occur. This undercut may also occur in the contact hole 103 on the TFT portion 1a side.

  The substrate to be processed to which the plasma etching method according to the present embodiment is applied is configured as a large square substrate having a long side of 2 m or more, for example. When plasma etching is performed on a large substrate to be processed as described above, it is necessary to uniformly convert the etching gas into a plasma in a large processing container capable of storing the substrate to be processed. In particular, from the viewpoint of increasing the etching rate, if the pressure of the reduced-pressure atmosphere in the processing container is increased, a problem occurs that uneven plasma is formed and it is difficult to perform uniform etching on the surface of the substrate to be processed. There is also.

  As described above, in the plasma etching for forming the contact hole 103 in the substrate to be processed shown in FIG. 1, in order to improve the throughput by increasing the etching rate, (1) the TFT portion 1a and the contact portion 1b are different. When etching SiN films having different thicknesses in regions, the progress of etching in the signal line films (source electrode 161, drain electrode 162) on the TFT portion 1a side where the SiN film is thin is suppressed, and (2) occurrence of undercut It is necessary to select the etching gas and set the processing conditions in consideration of suppressing the above, and (3) forming a uniform plasma over the entire surface of the substrate to be processed. The plasma etching method according to the present embodiment can perform etching of the SiN film at a higher speed than the conventional method while satisfying these requirements. The detailed contents will be described below.

  FIG. 4 shows a configuration example of a plasma etching apparatus that performs the plasma etching method according to the present embodiment. The plasma etching apparatus 2 shown in the longitudinal side view of FIG. 4 is applied to the substrate S to be processed on which the resist film 101 patterned in the opening 102 is applied on the uppermost surface as shown in FIG. It plays a role of forming the contact hole 103 in the TFT portion 1a and the contact portion 1b by plasma etching.

  The plasma etching apparatus 2 includes a processing container 20 that is a vacuum chamber for plasma etching the substrate S to be processed. As described above, the plasma etching apparatus 2 according to the present embodiment can process a large square substrate having a long side of 2 m or more, for example, and the processing vessel 20 also has, for example, one side of a horizontal section. Is a square shape with a size of about 3.5 m and the other side of about 3.0 m.

  The processing container 20 is made of a material having good thermal conductivity and conductivity, such as aluminum, and the processing container 20 is grounded. In addition, a loading / unloading port 22 for loading the substrate to be processed S into the processing container 20 is formed in one side wall portion 21 of the processing container 20, and the loading / unloading port 22 is configured to be opened and closed by a gate valve 23. ing.

  Inside the processing container 20, a mounting table 3 for mounting the substrate S to be processed is arranged on the upper surface thereof. The mounting table 3 is disposed on the bottom surface of the processing container 20 so as to be electrically connected, serves as a lower electrode, and functions as an anode electrode.

  Further, the peripheral edge and the side surface of the mounting table 3 are covered with a focus ring 33 made of, for example, a ceramic material for uniformly forming plasma above the mounting table 3. The focus ring 33 serves to adjust the plasma state in the peripheral region of the substrate to be processed S, for example, to concentrate the plasma on the substrate to be processed S and to improve the etching rate. In the present embodiment, the placement region on which the substrate to be processed S is placed is formed across, for example, a region including the top surface of the placement table 3 and a part of the top surface of the surrounding focus ring 33. .

  The mounting table 3 is provided with elevating pins 34 for transferring the substrate S to be processed between a transfer device (not shown) provided outside and the mounting table 3. The raising / lowering pin 34 is connected to the raising / lowering mechanism 35, freely protrudes and sinks from the surface of the mounting table 3, and the processing target is between the position where the processing target substrate S is transferred and the mounting region described above. The substrate S can be raised and lowered. In the figure, 36 is a bellows that covers the elevating pins 34 in order to keep the inside of the processing container 20 in a vacuum.

  On the other hand, a flat plate-like upper electrode 4 is provided above the mounting table 3 so as to face the upper surface of the mounting table 3, and the upper electrode 4 is supported by a square plate-like upper electrode base 41. Yes. The upper electrode 4 and the upper electrode base 41 are made of, for example, aluminum and are electrically connected to each other. The upper surface of the upper electrode base 41 is attached to the ceiling portion of the processing container 20 via the insulating member 411 and is in an electrically floating state from the processing container 20. The upper electrode base 41 is connected to a high frequency power supply 48 for generating plasma, and as a result, the upper electrode 4 functions as a cathode electrode. The space surrounded by the upper electrode base 41 and the upper electrode 4 constitutes an etching gas diffusion space 42. Hereinafter, the upper electrode 4 and the upper electrode base 41 are collectively referred to as a gas shower head 40.

A gas supply path 43 is provided at the ceiling of the processing container 20 so as to be connected to the diffusion space 42, and the gas supply path 43 is branched into two and is connected to the etching gas supply path 431 on one side. The etching gas supply unit 45 is connected to the other side, and the oxygen supply unit 46 is connected to the oxygen supply path 432 on the other side. The etching gas supply unit 45 stores sulfur hexafluoride (hereinafter referred to as SF ₆ ) for etching the SiN film of the substrate S to be processed, and the SF ₆ is directed to the processing container 20 in a gas state. Can be supplied. On the other hand, oxygen (hereinafter referred to as O ₂ ) for stabilizing the plasma generated in the processing vessel 20 and adjusting the ashing speed of the resist film 101 to suppress the occurrence of undercut is stored in the oxygen supply unit 46. It is stored and serves to supply O ₂ mixed with SF ₆ to the processing vessel 20.

In each of the supply paths 431 and 432 between the etching gas supply unit 45, the oxygen supply unit 46, and the diffusion space 42, a flow rate control unit 44 including a mass flow controller or the like is interposed. The flow rate adjusting unit 44 has a function of adjusting the supply amount of SF ₆ and O ₂ to the processing container 20 based on an instruction from the control unit 6 described later, thereby adjusting the mixing ratio of SF ₆ and O _2. Playing a role.

In the plasma etching method according to the present embodiment, the flow rate adjusting unit 44 supplies SF ₆ and O ₂ to the processing vessel 20 in a state where the volume ratio is in the range of, for example, 1: 6 or more and 1:20 or less. Can do. Specifically, in this example, the flow rate adjusting unit 44 adjusts the flow rate of SF ₆ to 100 sccm (sccm: ml / min (0 ° C., 1 atm), the same applies hereinafter) and the O ₂ flow rate to 600 sccm. : Control is performed so that the mixed gas mixed at the volume ratio of 6 is supplied to the processing container 20.

  When the gas thus mixed is supplied to the diffusion space 42, the mixed gas is supplied to the processing space above the substrate to be processed S through the gas supply hole 47 provided in the upper electrode 4 and is converted into plasma. Thus, the etching process can be performed on the substrate S to be processed.

  On the other hand, one end side of an exhaust passage 24 for exhausting the atmosphere in the processing container 20 is connected to the bottom surface of the processing container 20, and a vacuum pump 51 is connected to the other end side via a pressure control valve 511. The gas in the processing container 20 is exhausted from the exhaust path 24 toward, for example, a detoxifying device 52 common to factories.

Here, in the conventional plasma etching method, the pressure in the processing vessel 20 is reduced to, for example, about 13.3 Pa (100 mTorr) less than 133 Pa (1000 mTorr), for example, O ₂ in the processing vessel 20 in a high vacuum atmosphere. The SiN film was etched by supplying unmixed SF ₆ . In such a high vacuum atmosphere, the plasma is stable even in the large processing container 20 as in this example, and the occurrence of undercut may be suppressed in some cases. However, there is a problem that the etching rate of the SiN film is slow in a high vacuum atmosphere, and sufficient throughput cannot be obtained.

On the other hand, when the pressure in the processing container 20 is increased while supplying SF ₆ alone, it is difficult to form a stable plasma and the occurrence of undercuts becomes significant. Therefore, the conventional plasma etching apparatus is not designed to perform etching under a relatively low-pressure atmosphere such as 133 Pa (1000 mTorr) or more, and a high-vacuum atmosphere can be formed even with a vacuum pump. An expensive vacuum pump such as a turbo molecular pump was used.

On the other hand, in the plasma etching method according to the present embodiment, as described above, O ₂ is mixed with SF ₆ in a volume ratio of, for example, 1: ₆ to 1:20. Plasma can be stably formed even in a high atmosphere, and the ratio between the etching rate of the SiN film and the ashing rate of the resist film 101 can be adjusted to make it difficult for undercut to occur.

  In order to form such a pressure atmosphere in the processing container 20, the vacuum pump 51 and the pressure control valve 511 according to the present embodiment adjust the opening of the pressure control valve 511 based on an instruction of a pressure gauge (not shown). By doing so, the pressure in the processing container 20 can be adjusted to, for example, 133 Pa (1000 mTorr) in the range of 133 Pa (1000 mTorr) or more and 200 Pa (1500 mTorr) or less. As described above, since the plasma etching can be performed in a low vacuum state as compared with the conventional high vacuum atmosphere, the vacuum pump 51 cannot create a high vacuum state like a turbo molecular pump, for example. A relatively inexpensive dry pump is used.

The plasma etching apparatus 2 is connected to the control unit 6. For example, the control unit 6 includes a computer having a CPU and a program (not shown). The program carries the operation of the plasma etching apparatus 2, that is, carries the substrate S to be processed into the processing container 20, and the SF into the processing container 20. _After adjusting the supply amount of ₆ and O ₂ , the supply ratio, and the pressure in the processing container 20, the etching gas (mixed gas of SF ₆ and O ₂ ) is turned into plasma, and the substrate to be processed S is etched. A group of steps (commands) for control related to the operation from unloading to unloading. This program is stored in a storage medium such as a hard disk, a compact disk, a magnetic optical disk, or a memory card, and installed in the computer therefrom.

  Hereinafter, the operation of the plasma etching apparatus 2 according to the present embodiment will be described. First, when a user selects a target process recipe for plasma etching processing and inputs it to the control unit 6 via an operation unit (not shown), the control unit 6 controls each part of the plasma etching apparatus 2 based on this process recipe. Thus, a predetermined plasma etching process is performed on the substrate S to be processed.

  First, the gate valve 23 is opened, and a substrate to be processed on which a resist film 101 having an opening 102 corresponding to the contact hole 103 is formed on the surface as shown in FIG. S is carried into the processing container 20 and conveyed to the delivery position above the mounting table 3.

When the substrate to be processed S reaches the transfer position, the lift pins 34 are raised to transfer the substrate S to the lift pins 34 from the transfer means, and the transfer means are moved out of the processing container 20 and the lift pins 34 are lowered. The substrate S to be processed is placed on the placement area. Thereafter, when the loading / unloading port 22 is closed, the vacuum pump 51 is operated to adjust the inside of the processing container 20 to a pressure of, for example, 133 Pa (1000 mTorr) by the pressure adjustment valve 511, and the flow rate of the SF ₆ is 100 sccm at the flow rate adjustment unit 44. The flow rate is adjusted so that the flow rate of O ₂ is 600 sccm (volume ratio 1: 6), and both gases are supplied from the etching gas supply unit 45 and the oxygen supply unit 46 to the processing vessel 20.

SF ₆ and O ₂ are sufficiently mixed in the gas supply path 43 and the diffusion space 42 and discharged into the processing container 20 through the gas supply hole 47. Then, high frequency power is supplied from the high frequency power supply 48 to the upper electrode 4 to form plasma in the space above the substrate S to be processed, and plasma etching is performed on the SiN film.

Here, SF ₆ is an insulating gas and has a characteristic that it is difficult to form a uniform plasma in the processing container 20 for storing the large substrate S, but has an effect of promoting the dissociation of SF _6. the O _2, at a volume ratio of SF ₆ and _{O 2} 1: _6~1: by mixing at a high rate of 20, it is possible to form a uniform plasma over the entire surface of the processing vessel 20. This has also been confirmed by visually confirming the plasma state in the processing container 20 and by experiments in examples described later.

On the other hand, since O ₂ does not have the ability to etch the SiN film, if the mixing ratio of O ₂ is increased, the etching rate of the SiN film may be decreased. However, by the present example a relatively high pressure atmosphere pressure in the processing container 20 for example 133Pa (1000mTorr) ~200Pa (1500mTorr) , the SF ₆ in any processing chamber 20 when increasing the mixing ratio of _{O 2} The number of molecules may not be less than the conventional case, or may increase. Since a mixed plasma with O ₂ forms a stable plasma as described above, a large amount of SF ₆ active species is generated, which contributes to an improvement in the etching rate. The point that the etching rate of the SiN film is improved in this way has also been confirmed by experiments in examples described later.

Further, O ₂ mixed with SF ₆ does not have the ability to etch the SiN film, but has the ability to ash the resist film 101. The ashing speed can also be increased. As a result, the SiN film and the resist film 101 are removed evenly, for example, and the SiN film can be formed without causing an undercut, and the shape control of the contact hole 103 can be performed satisfactorily. This point has also been confirmed by experiments in examples described later.

Further, when the signal line film constituting the source electrode 161 and the drain electrode 162 contains Mo like a Mo / Al / Mo laminated film in which Mo and Al are laminated, the SF ₆ etches Mo to form SiN. The selectivity with the film (ratio of the etching rate of the SiN film to the etching rate of Mo) is important. However, this selectivity can be increased by increasing the mixing ratio of O ₂ .

The plasmaized gas descends in the processing container 20 and reaches the substrate to be processed S, and the etching process proceeds on the surface thereof. The gas flows along the surface of the substrate S to be processed toward the peripheral edge, flows into the exhaust path 24 through the space between the focus ring 33 and the processing container 20, and is exhausted outside the processing container 20. The After performing plasma etching processing for a predetermined time based on the process recipe in this way, the supply of SF ₆ , O ₂ and high frequency power is stopped, the pressure in the processing container 20 is returned to the original state, In the reverse order, the substrate S to be processed is transferred from the mounting table 3 to an external transfer means and unloaded from the plasma etching apparatus 2 to complete a series of etching processes.

The plasma etching method according to the present embodiment has the following effects. By performing plasma etching using a mixed gas of SF ₆ and O ₂ , a stable plasma can be obtained even under a high pressure atmosphere of 133 Pa (1000 mTorr) or higher, and the SiN film can be etched at a high speed. Can do. Further, since the mixed gas contains O ₂ having the ability to ash the resist film 101, the ratio between the etching rate of the SiN film and the ashing rate of the resist film 101 can be adjusted. When the contact hole 103 is formed by transferring the shape of the opening 102 gradually decreasing in area toward the SiN film from the resist film 101, good shape control can be performed.

  Further, since the SiN film can be etched in a lower vacuum atmosphere than in the prior art, a relatively inexpensive dry pump or the like is employed as the vacuum pump 51 in place of the turbo molecular pump that forms a high vacuum atmosphere. The apparatus cost of the etching apparatus 2 can be reduced.

  Next, a plasma processing method according to the second embodiment will be described. The plasma processing method according to the second embodiment can be performed by the plasma etching apparatus 2 having substantially the same configuration as that shown in FIG. 4 except for the following points.

In the plasma etching apparatus 2 according to the second embodiment, carbonyl difluoride (COF ₂ ) having a warming coefficient substantially equal to that of carbon dioxide is employed as an etching gas for etching the SiN film, and an etching gas supply unit 45 stores COF ₂ instead of SF ₆ . Further, the flow rate adjusting unit 44 of this example is configured to supply the processing container 20 as a mixed gas in which COF ₂ and O ₂ are mixed at a volume ratio in the range of, for example, 1: 2 or more and 3:20 or less.

  The vacuum pump 51 and the pressure control valve 511 according to the second embodiment adjust the opening of the pressure control valve 511 based on an instruction from a pressure gauge (not shown), thereby changing the pressure atmosphere in the processing container 20 to, for example, It has an ability to be adjusted within a range of 133 Pa (1000 mTorr) or more and 267 Pa (2000 mTorr) or less.

Under the conditions described above, even when plasma etching is performed on the substrate S to be processed by converting the mixed gas of COF ₂ and O ₂ into plasma, stable plasma formation, improvement in the etching rate of the SiN film, Control of the shape of the contact hole 103 that suppresses the occurrence of cut, prevention of the signal line film (source electrode 161, drain electrode 162) from being scraped when the TFT portion 1a and the contact portion 1b are etched together, and a low vacuum pump Various effects such as reduction in equipment cost can be obtained by adopting the system.

Here, most of the COF ₂ contained in the gas discharged from the processing container 20 is collected by the detoxifying device 52, and the remaining O ₂ is released to the atmosphere. However, since the collection efficiency of COF ₂ in the abatement apparatus 52 is not 100%, a small amount of COF ₂ may be released to the atmosphere. Even in such a case, as described above, COF ₂ is a substance having a warming coefficient equivalent to that of carbon dioxide, so that the load on the environment can be kept low.

  The plasma etching methods according to the first and second embodiments described above are not limited to the case where the TFT portion 1a and the contact portion 1b on the substrate S to be processed shown in FIG. It can also be applied to the case where two regions are etched separately.

Further, in the above plasma processing method for generating plasma by adjusting the pressure of the processing container 20 to 133 Pa (1000 mTorr) or more, only the O ₂ is supplied into the processing container 20 to ash the resist film 101 to be processed substrate. It can also be applied to a plasma ashing method for removing from S. Conventionally, by performing ashing under a pressure atmosphere higher than, for example, 133 Pa (1000 mTorr) where plasma ashing is performed, damage to a device formed on the substrate S to be processed can be reduced, and high-speed ashing can be performed. it can.

(Experiment 1)
Using an etching processing apparatus having the same configuration as the plasma etching apparatus 2 shown in FIG. 4, the mixed gas of SF ₆ and O ₂ is turned into plasma, and the SiN substrate with the resist film 101 patterned on the surface is etched. The etching rate (E / R) of SiN, the ashing rate (A / R) of the resist film 101, and the selection ratio (ratio of the ashing rate of the resist film 101 to the etching rate of SiN) were measured. High frequency power of 13.56 MHz and 3000 W was supplied from the high frequency power supply unit 48 for 30 seconds. The temperature of the mounting table 3 was adjusted to 25 ° C.

A. Experimental conditions
(Example 1-1) SF ₆ was supplied at 100 sccm and O ₂ at 600 sccm (volume ratio 1: 6), and the pressure in the processing container 20 was set at 133 Pa (1000 mTorr).
(Example 1-2) The conditions were the same as in Example 1-1 except that the pressure in the processing container 20 was set to 160 Pa (1200 mTorr).
(Comparative Example 1-1A) The conditions were the same as in Example 1-1 except that the pressure in the processing container 20 was 26.7 Pa (200 mTorr).
(Comparative Example 1-2A) The conditions were the same as in Example 1-1 except that the pressure in the processing container 20 was set to 53.3 Pa (400 mTorr).
(Comparative Example 1-3A) The conditions were the same as in Example 1-1 except that the pressure in the processing container 20 was set to 107 Pa (800 mTorr).

B. Experimental result
The results of (Examples 1-1 to 1-2) and (Comparative Examples 1-1A to 1-3A) are shown in FIG. The horizontal axis of FIG. 5 indicates the pressure in the processing container 20, and the upper numerical value is displayed in [mTorr] and the lower numerical value is displayed in [Pa]. The vertical axis on the right side shows the etching rate of SiN or the ashing rate [nm / min] of the resist film 101, and the vertical axis on the left side shows a selection ratio [− that is the ratio of the ashing rate of the resist film 101 to the etching rate of SiN. ] Is shown.

  The white rhombus plots shown in FIG. 5 indicate the etching rate of SiN in each of the examples and comparative examples, and the solid line indicates the trend line. The black diamond plot represents the ashing speed of the resist film 101 (PR), and the broken line is the trend line. On the other hand, the black triangle plot shows the above-mentioned selection ratio, and the alternate long and short dash line shows this trend line. Here, (Comparative Example 1-3A) performs the same experiment twice, each plot shows the average value of these experiment results, and the error bar shows the value of the actual experiment result in a range display.

  When the tendency of the etching rate of SiN shown in FIG. 5 is seen, when the pressure in the processing container 20 is increased from (Comparative Example 1-1A) to (Comparative Example 1-3A), along with this, The etching rate of SiN is increasing. And from (Comparative Example 1-3A) to (Example 1-2), the change in the etching rate is almost flat, and even if the pressure in the processing container 20 is increased, the etching rate is significantly increased. can not see. The same can be said for the ashing speed of the resist film 101.

  On the other hand, with respect to the selection ratio, the etching amount of SiN becomes relatively larger as the pressure in the processing container 20 is increased, and the selection ratio is increased from (Comparative Example 1-1A) to (Comparative Example 1-3A). Is gradually decreasing. In the range from (Comparative Example 1-3A) to (Example 1-2), the selection ratio is almost flat.

6 (a) to 6 (c) (Comparative Example 1-1B) in which the temperature of the mounting table 3 was adjusted to 90 ° C. under the same conditions as in (Comparative Examples 1-1A to 1-3A). The photograph of the enlarged longitudinal section of the resist film 101 in each example of Example 1-3B) and a SiN substrate is shown. 7A to 7C are the same conditions as those of (Comparative Examples 1-1B to 1-3B) at a SF ₆ flow rate of 100 sccm and an O ₂ flow rate of 400 sccm (volume ratio 1: 4). It is a photograph of the enlarged longitudinal section showing the result of etching of a SiN substrate (Comparative Examples 1-1C to 1-3C).

Experiments of (Comparative Examples 1-1B to 1-3B) in FIGS. 6 (a) to 6 (c) and (Comparative Examples 1-1C to 1-3C) in FIGS. 7 (a) to 7 (c). Comparing the results, undercutting is observed relatively remarkably in the case where the volume ratio of SF ₆ to O ₂ is 1: 4 (Comparative Examples 1-1C to 1-3C). On the other hand, almost no undercut occurs in (Comparative Example 1-1B), and a slight undercut occurs in (Comparative Examples 1-2B and 1-3B). Smaller than Examples 1-2C and 1-3C).

From these facts, it can be seen that by increasing the mixing ratio of O ₂ with respect to SF ₆ , the degree of occurrence of undercut can be suppressed as compared with the case where the mixing ratio of O ₂ is small. This is considered to be the same for (Examples 1-1 and 1-2) in which the pressure in the processing container 20 is 133 Pa (1000 mTorr) or more.

In the region where the mixing ratio of O _{2 to} SF ₆ is smaller than 1: 6 by volume, the plasma becomes unstable when the pressure in the processing container 20 is increased to 133 Pa (1000 mTorr) or more. Experiments corresponding to (Comparative Examples 1-1C to 1-3C) in the pressure region were not performed.

(Experiment 2)
A SiN film was formed on a mass production substrate for LCD, a resist film 101 was applied on the upper surface, and patterning was performed to create a substrate S to be processed, and plasma etching of the SiN film was performed. In plasma etching, an etching processing apparatus having the same configuration as that of the plasma etching apparatus 2 is used, and a mixed gas of SF ₆ and O ₂ is turned into plasma to etch SiN (E / R) and ashing speed of the resist film 101 ( A / R) and selectivity (ratio of the ashing rate of the resist film 101 to the etching rate of SiN) were measured. High frequency power of 13.56 MHz and 3000 W was supplied from the high frequency power supply unit 48 for 30 seconds. The temperature of the mounting table 3 was adjusted to 25 ° C.

A. Experimental conditions (Example 2-1) SF ₆ was supplied at 100 sccm and O ₂ was supplied at 600 sccm (volume ratio 1: 6), and the pressure in the processing vessel 20 was set at 133 Pa (1000 mTorr). The etching amount of the SiN film and the ashing amount of the resist film 101 at each point given the numerical values “1 to 13” of the substrate S to be processed shown in FIG.
(Example 2-2) The conditions were the same as in Example 2-1 except that the pressure in the processing container 20 was set to 160 Pa (1200 mTorr).
(Example 2-3) The conditions were the same as (Example 2-1) except that the pressure in the processing container 20 was set to 200 Pa (1500 mTorr).
(Comparative Example 2-1) The conditions were the same as in Example 2-1 except that the pressure in the processing container 20 was set to 107 Pa (800 mTorr).

B. Experimental result
The results of (Examples 2-1 to 2-3) and (Comparative Example 2-1) are shown in FIGS. FIG. 9 shows the result of plotting the etching rate of the SiN film and the in-plane uniformity of the etching rate for each measurement point on the substrate S to be processed. The horizontal axis in FIG. 9 indicates the pressure in the processing container 20 in [mTorr] units on the top and [Pa] units on the bottom. The vertical axis on the right side shows the etching rate [nm / min] of the SiN film, and the vertical axis on the left side shows the uniformity [±%] in the surface of the substrate S to be processed. The in-plane uniformity of the etching rate was calculated based on the following equation (1). The in-plane uniformity indicates that the smaller the value is, the smaller the variation in etching rate is in the plane of the substrate S to be processed.
In-plane uniformity [±%] = ± [{(E / R) _MAX− (E / R) _MIN }
/ {(E / R) _MAX + (E / R) _MIN }] × 100 (1)
However, (E / R) _MAX ; etching rate maximum value [nm / min],
(E / R) _MIN : The minimum value of the etching rate [nm / min].

  In FIG. 9, the white circle plot indicates the etching rate at the center position “7” of the substrate S to be processed shown in FIG. 8, and the black circle plot indicates the middle position “4, The average values of the etching rates at four points of “5, 9, 10” are shown. Further, the maximum and minimum values of the etching rates at the eight points at the edge positions “1, 2, 3, 6, 8, 11, 12, 13” shown in FIG. The asterisk plot indicates the average value of the etching rate at each point from “1 to 13” of the entire substrate S to be processed. The white triangular plot represents the in-plane uniformity of the etching rate over the entire substrate S to be processed.

  FIG. 10 shows the etching rate of the SiN film, the ashing rate of the resist film 101, and the selection ratio on the average of the substrate to be processed S. The horizontal axis, the left and right vertical axes, each plot, and the meaning of each trend line are shown. This is the same as FIG.

  Regarding the results of (Examples 2-1 to 2-3) and (Comparative Example 2-1), first, the tendency of the etching rate of the SiN film shown in FIG. In either case, the etching rate of the SiN film increases as the pressure in the processing vessel 20 is increased from (Comparative Example 2-1) to (Example 2-2). This shows the same tendency as the results of the examples and comparative examples of (Experiment 1) using the SiN substrate. Further, when the pressure in the processing container 20 was increased to 200 Pa (1500 mTorr) (Example 2-3), the measurement result at any position was lower than that in Example 2-2.

  Thus, in the case where the mass production substrate for LCD was used (Experiment 2), the etching rate was observed to have a convex curve upward as the pressure in the processing container 20 was increased. On the other hand, regarding the in-plane uniformity of the etching rate, a tendency to draw a downward convex curve was observed as the pressure in the processing container 20 was increased, contrary to the etching rate.

This is because, under the condition where the volume ratio of SF ₆ and O ₂ is constant, a relatively stable plasma is formed in the pressure region below (Example 2-2), and the pressure in the processing vessel 20 is reduced. It is shown that the etching rate of the SiN film can be improved as the value is increased. Further, when the pressure in the processing container 20 exceeds the value of (Example 2-2), the effect of stabilizing the plasma by O ₂ becomes relatively small, and a biased plasma is formed, the etching rate of the SiN film, It can be interpreted that both in-plane uniformity is reduced.

  Next, looking at the results of (Examples 2-1 to 2-3) and (Comparative Example 2-1) shown in FIG. 10, the average value of the etching rate is the pressure in the processing vessel 20 as described above. On the other hand, while a convex curve is drawn, the ashing speed of the resist film 101 decreases as the pressure in the processing container 20 increases. As a result, the selection ratio of the resist film 101 to the SiN film gradually decreases as the pressure in the processing container 20 is increased, and in the range of (Example 2-2) to (Example 2-3). The selectivity is almost flat.

  Also in the result shown in FIG. 10, in the pressure region below (Example 2-2), a relatively stable plasma is formed, and the etching rate of the SiN film improves as the pressure in the processing vessel 20 increases. As a result, the selectivity decreases, and when the pressure in the processing container 20 exceeds the value of (Example 2-2), stable plasma is less likely to be formed. As a result, the selectivity may be flat. Conceivable.

  FIG. 11A to FIG. 11C show enlarged vertical cross-sectional photographs of the resist film 101 and the SiN film in each example of (Examples 2-1 to 2-3). In (Examples 2-1 and 2-2) shown in FIGS. 11 (a) and 11 (b), the occurrence of undercutting is not observed, but as shown in FIG. 11 (c) (Example 2-3). ), A slight undercut was observed. However, also in (Example 2-3), the degree of occurrence of undercut is, for example, compared with the case of (Comparative Examples 1-1C to 1-3C) shown in FIGS. 7 (a) to 7 (c). small.

Summarizing the results of (Experiment 1) and (Experiment 2) shown above, when the volume ratio of SF ₆ and O ₂ is 1: 6, the SiN content increases as the pressure in the processing vessel 20 increases. The etching rate is improved. When the pressure in the processing vessel 20 is further increased, the etching rate of SiN becomes flat (in the case of using the SiN substrate (in the case of Experiment 1)), or it started to decrease with a convex curve (LCD) A mass production substrate was used (in the case of Experiment 2)).

For these reasons, the pressure atmosphere in which the plasma etching of the SiN film is performed has a relatively high etching rate even when the etching rate of SiN remains high or decreases in a convex curve. It can be said that it is preferable to set the pressure in the range of 1000 mTorr) to 200 Pa (1500 mTorr). Further, when the volume ratio of SF ₆ and O ₂ exceeds 1:20, it is considered that SF ₆ becomes too small and etching hardly proceeds even if the pressure is increased. Incidentally, preferable range of the volume ratio of SF ₆ and _{O 2} is, for example, 1: 6 to 1: believed 20 the range of about.

(Experiment 3)
Using an etching apparatus having the same configuration as that of the plasma etching apparatus 2 shown in FIG. 4, the mixed gas of COF ₂ and O ₂ is turned into plasma, and the SiN etching rate (E / R), the ashing rate (A / R) of the resist film 101, and the selectivity (ratio of the ashing rate of the resist film 101 to the etching rate of SiN) were measured.

A. Experimental conditions
(Example 3-1) 300 sccm of COF ₂ and 600 sccm of O ₂ were supplied (volume ratio 1: 2), and the pressure in the processing container 20 was set to 160 Pa (1200 mTorr).
(Example 3-2) The conditions were the same as (Example 3-1) except that the pressure in the processing container 20 was 240 Pa (1800 mTorr).
(Example 3-3) The conditions were the same as in Example 3-1 except that the pressure in the processing container 20 was set to 253 Pa (1900 mTorr).
(Comparative Example 3-1) The conditions were the same as in (Example 3-1) except that the pressure in the processing container 20 was set to 107 Pa (800 mTorr).

  The results of (Examples 3-1 to 3-3) and (Comparative Example 3-1) are shown in FIGS. FIG. 12 shows the etching rate of SiN, the ashing rate of the resist film 101, and the selection ratio. The horizontal axis, left and right vertical axes, each plot, and the meaning of each trend line are the same as those in FIG.

  FIG. 13 is a diagram showing variations in the etching rate at the center position of the SiN substrate and the etching rate at the corner. The horizontal axis in FIG. 13 indicates the pressure in the processing container 20 in [mTorr] on the upper stage and [Pa] in the lower stage, and the vertical axis indicates the etching rate [nm / min] at each position. . In FIG. 13, the white diamond plot indicates the etching rate at the center position of the SiN substrate, and the range indicated by the error bar indicates the variation range of the etching rate at the corner position of the SiN substrate.

Referring to FIG. 12, when COF ₂ and O ₂ and a mixed gas are used, both the etching rate of SiN and the ashing rate of the resist film 101 are compared with those of (Comparative Example 3-1) to (Example 3- As the pressure in the processing vessel 20 is increased toward 3), the etching rate and the ashing rate increase in proportion to the increase in pressure, and these rates become flat within the experimental range. Was not observed. As for the selection ratio, as the pressure in the processing container 20 is increased, the value of the selection ratio gradually decreases, but it is a change that can be said to be almost flat.

These are considered to be a result of COF ₂ forming a relatively stable plasma in the experimental pressure range and reflecting the increase in pressure on the improvement of the etching rate. In FIG. 13, since the etching progresses uniformly at substantially the same etching rate at both the central position and the corner position, it is possible to perform plasma etching uniformly within the SiN substrate surface. It can be confirmed that a proper plasma is formed.

  FIG. 14 shows a photograph of an enlarged vertical section of the resist film 101 and the SiN substrate in (Example 3-2). Even if the pressure in the processing container 20 is increased, undercut does not occur and the SiN substrate side is not generated. It can be seen that a tapered surface can be formed.

As shown in FIGS. 12 and 13, from the result of (Experiment 3), when the volume ratio of COF ₂ and O ₂ is 1: 2, the pressure atmosphere is in the range of 133 Pa (1000 mTorr) or more. The SiN film can be etched at a high speed of about 6000 / min or more. And, in the range of 267 Pa (2000 mTorr) or less, which is close to the experimental range, it is considered that a sufficiently high etching rate can be realized without a sharp decrease in the etching rate. Further, when the volume ratio of COF ₂ and O ₂ exceeds 3:20, it is considered that COF ₂ becomes too small and etching is hardly performed even if the pressure is increased. Note that a preferable range of the volume ratio of COF ₂ and O ₂ is, for example, a range of about 1: 2 to 3:20.

S Substrate 1a TFT part 1b Contact part 101 Resist film 102 Opening part 103 Contact hole 17 Passivation film 2 Plasma etching apparatus 3 Mounting table 4 Upper electrode 45 Etching gas supply part 46 Oxygen supply part 51 Vacuum pump 511 Pressure control valve 6 Control Part

Claims (5)

A method of plasma etching a silicon nitride film on a substrate to be processed formed on a lower layer side of a resist pattern having an opening that gradually decreases in area from the top to the bottom,
Carrying the substrate to be processed into a processing container;
Supplying a mixed gas of sulfur hexafluoride and oxygen into the processing vessel, converting the mixed gas into a plasma under a pressure atmosphere in a range of 133 Pa or more and 200 Pa or less, and etching the silicon nitride film; A plasma etching method comprising:   2. The plasma etching method according to claim 1, wherein the mixed gas has a volume ratio of sulfur hexafluoride to oxygen within a range of 1: 6 or more and 1:20 or less. A method of plasma etching a silicon nitride film on a substrate to be processed formed on a lower layer side of a resist pattern having an opening that gradually decreases in area from the top to the bottom,
Carrying the substrate to be processed into a processing container;
Supplying a mixed gas of carbonyl difluoride and oxygen into the processing vessel, converting the mixed gas into a plasma under a pressure atmosphere within a range of 133 Pa or more and 267 Pa or less, and etching the silicon nitride film; A plasma etching method comprising:   The plasma etching method according to claim 3, wherein the mixed gas has a volume ratio of carbonyl difluoride to oxygen within a range of 1: 2 or more and 3:20 or less.   4. The plasma etching method according to claim 1, wherein the opening of the silicon nitride film formed by etching has a shape in which the opening area gradually decreases from the upper part toward the lower part.

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