KR20110025607A - Plasma etching method - Google Patents

Abstract

PURPOSE: A plasma etching method is provided to implement the etching of a silicon nitride film at high speeds by implementing plasma etching using a mixed gas of oxygen and sulfur hexafluoride or carbonyl difluoride. CONSTITUTION: A silicon nitride film on a processed substrate(S) is etched by plasma. A resist pattern comprises an opening which has a larger top opening area compared to a bottom opening area. A processed substrate is carried into a treatment basin(20). The mixed gas of oxygen and sulfur hexafluoride is supplied into the treatment basin.

Description

Plasma Etching Method {PLASMA ETCHING METHOD}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching method for etching a target object such as an LCD substrate using a plasma gas.

For example, a thin film transistor (TFT) used in a flat panel display (FPD) such as a liquid crystal display (LCD) may be a gate electrode, a gate insulating film, or a semiconductor on a substrate to be processed such as a glass substrate. It is formed by sequentially laminating and winding a film or the like.

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. This contact hole has a tapered surface, the opening area of which gradually decreases from the top to the bottom thereof, whereby the angle of intersection of the surface of the passivation film and the tapered surface becomes an obtuse angle of the wiring embedded in the hole. The disconnection is prevented.

The tapered surface of the contact hole is formed by a so-called resist retreat method or the like which heat-treats the resist pattern formed on the passivation film in advance to form a tapered surface, and transfers the shape of the tapered surface on the resist pattern side to the passivation film side by etching.

In the case where the passivation film described above is a silicon nitride film made of silicon and nitrogen (hereinafter referred to as a SiN film), plasma etching is performed by plasmalizing an etching gas such as sulfur hexafluoride (SF ₆ ).

Usually, plasma etching is performed in a reduced pressure atmosphere, but, for example, as the pressure in the reduced pressure atmosphere is increased, the etching rate of the SiN film can be increased. On the other hand, when the pressure in the reduced pressure atmosphere increases, the etching rate of the SiN film becomes larger than the ashing speed of the resist, and the undercut state described later occurs, and the shape control of the contact hole, that is, the shape of the resist pattern is precisely applied to the passivation film. It becomes difficult to die.

As such, 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, when giving priority to shape control of a taper surface, for example, it is difficult to fully raise an etching rate, and there exists a problem that it is difficult to improve the throughput of an etching process.

Patent Document 1 describes a technique for etching SFN by plasma forming SF ₆ in a pressure atmosphere in the range of 1.33 Pa (10 mTorr) to 133 Pa (1000 mTorr), and Patent Document 2 describes a fluorine gas and an oxygen gas. The technique which etches a SiN film | membrane by making plasma of the mixed gas into the pressure atmosphere of the range of 1 Pa-100 Pa is described. In addition, Patent Document 3 describes a technique of plasma etching a SiN film using a mixed gas of carbonyl difluoride and oxygen.

However, in all the techniques described in Patent Documents 1 to 3, the relationship between the etching rate of the SiN film and the shape control of the tapered surface is not paid attention to, for example, to improve the etching rate while maintaining the shape of the tapered surface satisfactorily. Conditions are not disclosed.

(Prior art technical literature)

(Patent literature)

(Patent Document 1) Japanese Patent Application Laid-open No. 01-146328: Lines 11 to 16 of the upper right column of the third page

(Patent Document 2) Japanese Patent Laid-Open No. 2008-300478: 0014 Paragraph, 0027 Paragraph

(Patent Document 3) Japanese Patent Laid-Open No. 2002-158181: 0043 Paragraph, 0061 Paragraph

This invention is made | formed in view of such a situation, and the objective is to provide the plasma etching method which can perform favorable shape control and can etch a silicon nitride film at high speed.

A plasma etching method according to the present invention is a method of plasma etching a silicon nitride film on a substrate to be formed on a lower layer side of a resist pattern having an opening portion gradually decreasing from an upper portion to a lower portion, wherein the substrate is to be processed in a processing container. Carrying out a step of bringing the mixed gas of sulfur hexafluoride and oxygen into the processing container, and plasma-forming the mixed gas under a pressure atmosphere within a range of 133 Pa or more and 200 Pa or less to etch the silicon nitride film. It is characterized by including.

The mixed gas preferably has a volume ratio of sulfur hexafluoride and oxygen in the range of 1: 6 or more and 1:20 or less.

In addition, a plasma etching method according to another invention is a method of plasma etching a silicon nitride film on a substrate to be formed on a lower layer side of a resist pattern having an opening portion gradually decreasing from an upper portion to a lower portion, wherein the substrate is processed. Supplying a mixed gas of carbonyl difluoride and oxygen into the processing container, and converting the mixed gas into a plasma under a pressure atmosphere within a range of 133 Pa or more and 267 Pa or less to etch the silicon nitride film. It characterized by including a process.

The mixed gas preferably has a volume ratio of carbonyl difluoride and oxygen in the range of 1: 2 or more and 3:20 or less.

Each plasma etching method is preferable 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, plasma is etched using a mixed gas in which sulfur hexafluoride or carbon difluoride is mixed with oxygen, so that a stable plasma is obtained even under a high pressure atmosphere of 1000 mTorr or higher of 133 Pa (silicon nitride) at a high speed. The film can be etched. In addition, since the mixed gas contains oxygen having the ability to ash the resist pattern, the ratio of the etching rate of the silicon nitride film and the ashing speed of the resist pattern can be adjusted, and the opening area gradually decreases from the top to the bottom. The shape of the opening can be accurately transferred from the resist pattern to the silicon nitride film.

1 is a longitudinal side view illustrating an example of a substrate to which a plasma etching method according to the present embodiment is applied.
2 is a longitudinal side view illustrating a step of forming a contact hole in a TFT on the substrate to be processed.
It is explanatory drawing which shows typically the method of forming a taper surface in the said contact hole.
4 is a cross-sectional side view showing a plasma etching apparatus for performing the plasma etching method.
5 is a first explanatory diagram showing an experimental result according to the plasma etching.
6 is a second explanatory diagram showing an experimental result according to the plasma etching.
7 is a third explanatory diagram showing an experimental result according to the plasma etching.
It is explanatory drawing which shows the measurement point of the etching rate in the to-be-processed board | substrate used for the said experiment.
9 is a fourth explanatory diagram showing experimental results obtained by plasma etching.
10 is a fifth explanatory diagram showing an experimental result according to the plasma etching.
11 is a sixth explanatory diagram showing an experimental result according to the plasma etching.
12 is a seventh explanatory diagram showing an experimental result obtained by plasma etching.
13 is an eighth explanatory diagram showing an experimental result obtained by plasma etching.
14 is a ninth explanatory diagram showing experimental results obtained by plasma etching.

FIG. 1: shows the longitudinal side view which expanded the area | region of a part of to-be-processed substrate to which the plasma etching method which concerns on this embodiment is applied. The to-be-processed substrate shown in FIG. 1 is an active matrix type LCD, for example, 1a is a terminal side surface of the TFT part provided in each pixel, and 1b is a drive circuit of an LCD provided with the gate electrode provided in the TFT part 1a, for example. It is a longitudinal cross-sectional view of the contact part for connecting to.

The TFT portion 1a forms a gate wiring film 12 on the glass substrate 11, provides a gate insulating film 13 made of a SiN film, or the like thereon, and an amorphous silicon film 14 thereon. The n + amorphous silicon film 15 and the signal line film are sequentially formed, and the signal line film and the n + amorphous silicon film 15 are separated from side to side by etching, so that the source electrode 161, the drain electrode 162, and these electrodes are separated. Channel portions provided between 161 and 162 are formed.

The passivation film 17 which consists of SiN films, for example in order to protect the surface of the TFT part 1a is provided in the upper surface side of the TFT structure formed in this way. In the passivation film 17, a contact hole 103 is provided in contact with the source electrode 161 and the drain electrode 162, and the contact hole 103 is interposed therebetween, for example, indium tin oxide (ITO) or the like. The electrode film 18 made of the transparent electrode is connected, 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 of the gate wiring film 12 connected to the gate wiring film 12 of the TFT portion 1a, for example, the gate insulating film 13 and the passivation film described above all made of SiN films. (17) has a structure laminated in this order from below. A contact hole 103 is formed through these two layers of films 13 and 17 to form an electrode film 18 in the contact hole 103, and the gate wiring film 12 is formed as a gate wiring film 12. Connect to the driving circuit on the side. In the present embodiment, the contact holes 103 provided in the TFT portion 1a and the contact portion 1b face from the top to the bottom in order to prevent the disconnection of the electrode film 18 as described in the background art. The tapered surface in which the opening area becomes small gradually is formed.

In the TFT part 1a and the contact part 1b which have the structure demonstrated above, the contact hole 103 provided in each part 1a, 1b is collectively from a viewpoint of the reduction of the consumption of a resist, the reduction of a manufacturing process, etc. And etching is performed. For example, in the examples shown in FIGS. 2A and 2B, the resist film 101 is coated to cover the entire TFT portion 1a and the contact portion 1b to pattern the etching openings 102. A resist pattern is formed. The passivation film 17 and the gate insulating film 13 are etched with these openings 102 interposed therebetween to form contact holes 103 in the respective portions 1a and 1b.

As described above, in the case where the contact holes 103 are collectively etched by the TFT portion 1a and the contact portion 1b, only the passivation film 17 is etched on the TFT portion 1a side, while the contact portion 1b is etched. The passivation film 17 and the gate insulating film 13 need to be etched at the C) side, and the SiN film having a different thickness is etched. For this reason, even after the contact hole 103 is formed in the TFT part 1a side and the contact to each electrode 161,162 is possible, the contact hole 103 still remains in the contact wiring part 1b side of the gate wiring film 12. ) Is not reached, and continuation of etching may be necessary. For this reason, the etching gas used for the batch etching of the contact hole 103 needs to be a property which does not etch the signal line film (source electrode 161, drain electrode 162) of the TFT part 1a side.

As described above, the contact hole 103 on the side of the contact portion 1b is provided with a tapered surface for preventing disconnection of the electrode film 18, but the tapered surface is formed by a resist retreat method or the like. After the openings 102 are patterned in the coated resist film 101 and then heat-treated, the inner end surface of the openings 102 has a tapered shape, as shown in Fig. 3 (a). do.

When the passivation film 17 is etched in the state in which the tapered surface is formed in the resist film 101 as described above, the passivation film 17 starts to be etched from the thinner region of the resist film 101. As shown, the shape of the tapered surface of the resist film 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 in the reduced pressure atmosphere in which the plasma etching is performed is increased for the purpose of increasing the etching rate, the resist film 101 side. The etching rate of the passivation film 17 is increased compared to the ashing rate of. As a result, as shown in FIG. 3C, the passivation film 17 is etched from the bottom surface of the resist film 101, so that the tapered shape of the resist film 101 can be accurately transferred to the passivation film 17. A number of undercuts occur. This undercut may also occur in the contact hole 103 on the side of the TFT portion 1a.

Moreover, the to-be-processed board | substrate to which the plasma etching method which concerns on this embodiment is applied is comprised as a large square substrate whose long side is 2 m or more, for example. Thus, when plasma etching is performed with respect to a large to-be-processed board | substrate, it becomes necessary to make plasma etching gas uniform in the large processing container which can store the to-be-processed board | substrate. In particular, from the viewpoint of increasing the etching rate, when the pressure of the reduced pressure atmosphere in the processing container is increased, deflected plasma is formed, which makes it difficult to perform uniform etching in the surface of the substrate to be processed.

As described above, in the plasma etching in which the contact hole 103 is formed 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 ( In etching of SiN films having different thicknesses in different regions of 1b), the progress of etching in the signal line films (source electrode 161 and drain electrode 162) on the side of the thinner TFT portion 1a can be suppressed. It is necessary to select the etching gas and set the processing conditions in consideration of the fact that (2) undercutting is suppressed, (3) forming a uniform plasma over the entire surface of the substrate. The plasma etching method according to the present embodiment is capable of etching the SiN film at a higher speed than the conventional method while satisfying these requests. Hereinafter, the detail will be described.

4, the structural example of the plasma etching apparatus which implements the plasma etching method which concerns on this embodiment is shown. In the plasma etching apparatus 2 shown in the longitudinal side view of FIG. 4, for example, as shown in FIG. 3A, with respect to the substrate S on which the resist film 101 having the opening 102 patterned is coated on the uppermost surface, It serves to form the contact holes 103 in the TFT portion 1a and the contact portion 1b by plasma etching.

The plasma etching apparatus 2 is provided with the processing container 20 which is a vacuum chamber for plasma-etching the to-be-processed substrate S inside. As described above, the plasma etching apparatus 2 according to the present embodiment can process, for example, a large square substrate having a long side of 2 m or more. For the processing container 20, one side of the horizontal cross section is 3.5, for example. m, the other side is a square of size about 3.0m.

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. A sidewall portion 21 of the processing container 20 is provided with a carrying in and out port 22 for carrying the substrate S into the processing container 20, and the carrying in and out port 22 is a gate valve 23. The opening and closing is freely configured by the.

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

In addition, the circumferential portion and side surfaces of the mounting table 3 are covered by 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 of the region around the substrate S, for example, to concentrate the plasma on the substrate S to improve the etching rate. In this embodiment, the mounting area | region in which the to-be-processed substrate S is mounted is formed over the area | region containing the upper surface of the mounting table 3, and a part of the upper surface of the focus ring 33 around it, for example.

The mounting table 3 is provided with a lifting pin 34 for carrying the substrate S to be processed between a conveying apparatus (not shown) provided outside and the mounting table 3. The lifting pin 34 is connected to the lifting mechanism 35, and is freely driven from the surface of the mounting table 3 so as to freely move in and out of the substrate S to be processed and the mounting described above. The substrate S to be processed can be raised and lowered between the regions. In the figure, 36 is bellows that covers the lift pins 34 to maintain the interior of the processing vessel 20 in a vacuum.

On the other hand, the upper electrode 4 of the flat plate shape is provided above the mounting table 3 so as to face the upper surface of the mounting table 3, and this upper electrode 4 is a plate-shaped upper electrode base ( 41). These upper electrodes 4 and the upper electrode bases 41 are made of aluminum, for example, and are electrically connected to each other. The upper surface of the upper electrode base 41 is attached to the ceiling of the processing container 20 with an insulating member 411 interposed therebetween, and is electrically floating from the processing container 20. The high frequency power supply 48 for plasma generation is connected to the upper electrode base 41, 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 the diffusion space 42 of the etching gas. Hereinafter, these upper electrodes 4 and the upper electrode base 41 are collectively called a gas shower head 40.

The gas supply path 43 is provided in the ceiling part of the processing container 20 so that it may be connected to the said diffusion space 42, The gas supply path 43 branches into two, and one etching gas supply path 431 is etched. The gas supply part 45 is connected, and the oxygen supply part 46 is connected to the other oxygen supply path 432. Sulfur hexafluoride (hereinafter referred to as SF ₆ ) for etching the SiN film of the substrate S to be processed is stored in the etching gas supply part 45, and SF ₆ can be supplied toward the processing container 20 in a gaseous state. On the other hand, oxygen supply unit 46 stores oxygen (hereinafter referred to as 0 ₂ ) for stabilizing the plasma generated in the processing container 20 and controlling the ashing speed of the resist film 101 to suppress the occurrence of undercut. It serves to supply O ₂ in a state mixed with SF ₆ to the processing vessel 20.

In each of the supply paths 431 and 432 between the etching gas supply part 45, the oxygen supply part 46, and the diffusion space 42, a flow rate adjusting part 44 made of, for example, a mass flow controller is provided. have. The flow rate adjusting unit 44 has a function of adjusting the supply amount of SF ₆ and O ₂ to the processing vessel 20 based on an instruction from the controller 6 to be described later, thereby adjusting the mixing ratio of SF ₆ and O ₂ . It plays a role in controlling.

In the plasma etching method according to the present embodiment, the flow rate adjusting unit 44 mixes SF ₆ and O ₂ in a volume ratio in the range of, for example, 1: 6 or more and 1: 20 or less to the processing container 20. Can supply For example, in this example, the flow rate controller 44 adjusts the flow rate of SF ₆ to 100 sccm (sccm: ml / min (0 ° C., 1 atm), hereinafter also), and the flow rate of O ₂ to 600 sccm. It is controlled to supply the mixed gas mixed in the volume ratio of 1: 6 to the processing container 20.

When the mixed gas is supplied to the diffusion space 42 in this way, the mixed gas is supplied to the processing space above the substrate S through the gas supply hole 47 provided in the upper electrode 4, and converted into plasma to be treated. The etching process with respect to the process board | substrate S can be performed.

On the other hand, one end of the exhaust passage 24 for exhausting the atmosphere in the processing container 20 is connected to the bottom surface of the processing container 20, and the vacuum pump 51 is connected to the other end via a pressure regulating valve 511. Is connected, and the gas in the processing container 20 is exhausted from this exhaust path 24 toward the decontamination apparatus 52 common to a factory, for example.

In the conventional plasma etching method, the pressure in the processing vessel 20 is, for example, within the high vacuum atmosphere processing vessel 20 in which the pressure is reduced to, for example, less than 133 Pa (1000 mTorr), for example, about 13.3 Pa (100 mTorr), for example, O _2. The SiN film was etched by supplying SF ₆ which did not mix. In such a high vacuum atmosphere, even in the large processing container 20 like this example, plasma may be stable and the occurrence of undercut may also be suppressed. However, in a high vacuum atmosphere, there is a problem that the etching rate of the SiN film is low and a sufficient throughput cannot be obtained.

On the other hand, when the pressure in the processing container 20 was increased while supplying SF ₆ alone, it was difficult to form a stable plasma and there was a high possibility that the occurrence of undercut would become remarkable. Therefore, the conventional plasma etching apparatus is not designed to perform etching under a relatively low vacuum pressure atmosphere of, for example, 133 Pa (1000 mTorr) or more, and a turbo molecule which can form a high vacuum atmosphere even for a vacuum pump and is relatively expensive Vacuum pumps, such as a pump, were employ | adopted.

In contrast, in the plasma etching method according to the present embodiment, O ₂ is mixed with SF ₆ in the range of, for example, volume ratio of 1: 6 to 1: 20 as described above, thereby stably in a relatively high pressure atmosphere. A plasma can be formed, and the ratio of the etching rate of the SiN film and the ashing speed of the resist film 101 can be adjusted to bring the undercut into a difficult state.

In order to create such a pressure atmosphere in the processing container 20, the vacuum pump 51 and the pressure regulating valve 511 according to the present embodiment are provided with a pressure regulating valve 511 based on an instruction of a pressure gauge (not shown). By adjusting the opening degree, the pressure in the processing container 20 can be adjusted to, for example, 133 kPa (1000 mTorr) within a range of 133 kPa (1000 mTorr) or more and 200 kPa (1500 mTorr) or less. Thus, since it is possible to perform plasma etching in the low vacuum state compared with the conventional high vacuum atmosphere, the vacuum pump 51 cannot produce a high vacuum state like a turbomolecular pump, for example, but by a relatively inexpensive dry pump etc. It is composed.

In addition, the plasma etching apparatus 2 is connected to the control part 6. The control part 6 consists of a computer which has a CPU and a program which are not shown in figure, for example, The operation | movement of the said plasma etching apparatus 2, in other words, carries in the to-be-processed board | substrate S in the processing container 20, and processes After adjusting the supply amount of SF ₆ and O _{2 to} the vessel 20, the supply ratio and the pressure in the treatment vessel 20, the etching gas (mixed gas of SF ₆ and O ₂ ) is plasmatized, and the substrate S is treated. Step (command) groups for control and the like according to the operation from carrying out the etching process to carrying out are organized. This program is stored in a storage medium such as a hard disk, a compact disk, a magneto-optical disk, a memory card, etc., and is installed in the computer therefrom.

The operation of the plasma etching apparatus 2 according to the present embodiment will be described below. First, when a user selects a process recipe of a plasma etching process desired by a user through an operation unit (not shown) and inputs it to the control unit 6, the control unit 6 supplies the respective portions of the plasma etching apparatus 2 based on the process recipe. A control signal is supplied and a predetermined plasma etching process is performed on the substrate S in this manner.

First, the gate valve 23 is opened, and the resist film 101 provided with the opening 102 corresponding to the contact hole 103 is opened by an external conveying means (not shown). The to-be-processed board | substrate S formed in the surface is carried in in the processing container 20, and it is conveyed to the delivery location of the upper side of the mounting table 3.

When the to-be-processed board | substrate S reaches a delivery position, the lifting pin 34 is raised and the to-be-processed board S is moved from the conveying means to the lifting pin 34, and the conveying means is taken out of the processing container 20, and the lifting pin ( 34) is lowered and the to-be-processed substrate S is mounted in the mounting area. Then, when the inlet / outlet 22 is closed, the vacuum pump 51 is operated and the pressure control valve 511 controls the inside of the processing container 20 to a pressure of 133 kPa (1000 mTorr), for example, and the flow rate adjusting part ( In step 44, the flow rate is adjusted such that the flow rate of SF ₆ is 100 sccm and the flow rate of O ₂ is 600 sccm (volume ratio 1: 6), so that both gases are transferred from the etching gas supply part 45 and the oxygen supply part 46 to the processing container 20. Supply.

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

Where SF ₆ is O ₂ having an effect of promoting the insulating gas, and a large substrate to be processed, but have difficult to form a uniform plasma characteristics in the processing vessel 20 for storing the S, the SF ₆ haeri (解離) By mixing at a high ratio of the volume ratio 1: 6 to 1:20 of SF ₆ and O ₂ , a uniform plasma can be formed over the entire surface of the processing container 20. This is confirmed also by visually confirming the plasma state in the processing container 20 and the experiment in the Example mentioned later.

On the other hand, since O ₂ does not have the ability to etch a SiN film, if the mixing ratio of O ₂ is made high, the etching rate of a SiN film may become slow. However, in this example, even when the mixing ratio of O ₂ is made high by setting the pressure in the processing container 20 to a relatively high pressure atmosphere of, for example, 133 kPa (1000 mTorr) to 200 kPa (1500 mTorr), SF ₆ in the processing container 20 is increased. The number of molecules of is not less than in the conventional case, or may increase. As the above-described mixed gas with O ₂ , stable plasma is formed as described above, and thus, many active species of SF ₆ are also generated, contributing to the improvement of the etching rate. Thus, the point in which the etching rate of a SiN film improves is also confirmed by the experiment in the Example mentioned later.

In addition, since O ₂ mixed in SF ₆ does not have the ability to etch the SiN film, but has the ability to ash the resist film 101, the improvement in the etching rate of the SiN film is compensated for, so that the ashing speed of the resist film 101 is also high. can do. As a result, the SiN film and the resist film 101 are, for example, shaved evenly to form a SiN film without undercutting, and the shape control of the contact hole 103 can be performed well. This point is also confirmed by experiment in the Example mentioned later.

In addition, when the signal line film constituting the source electrode 161 or the drain electrode 162 contains Mo, such as a Mo / Al / Mo laminated film in which Mo and Al are laminated, SF ₆ etches Mo so that the SiN film and The selectivity of (the ratio of the etching rate of the SiN film to the etching rate of Mo) becomes important. However, the selectivity can also be increased by increasing the mixing ratio of O ₂ .

The plasma-ized gas descends the inside of the processing container 20 to reach the substrate S to be processed, and the etching process is performed on the surface thereof. The gas flows toward the circumferential portion while moving along the surface of the substrate S, and flows into the exhaust passage 24 through the space between the focus ring 33 and the processing vessel 20, thereby Is exhausted out. In this way, if the plasma etching treatment is performed for a predetermined time based on the process recipe, the supply of SF ₆ , O _2, or high frequency power is stopped, the pressure in the processing vessel 20 is returned to its original state, and then reversed from the carry-in. The substrate S to be processed is transferred from the mounting table 3 to an external conveying means in the order of, and taken out from the plasma etching apparatus 2 to complete a series of etching processes.

According to the plasma etching method according to the present embodiment, the following effects are obtained. Plasma etching is performed using a mixed gas mixed with SF ₆ and O ₂ to obtain a stable plasma even in a high pressure atmosphere of 1000 mTorr or higher of 133 Pa (1000 mTorr), thereby allowing etching of the SiN film at high speed. In addition, the mixed gas contains O ₂ having the ability to ash the resist film 101, and it is possible to adjust the ratio of the etching rate of the SiN film and the ashing speed of the resist film 101, and the opening is opened from the top to the bottom. Good shape control can be performed in transferring the shape of the opening 102 whose area gradually decreases from the resist film 101 to the SiN film and forming the contact hole 103.

In addition, since the SiN film can be etched in a lower vacuum atmosphere than in the related art, a relatively inexpensive dry pump or the like is employed as the vacuum pump 51 instead of the turbomolecular pump forming a high vacuum atmosphere, thereby reducing the apparatus cost of the plasma etching apparatus 2. can do.

Next, a plasma processing method according to the second embodiment will be described. Although the plasma processing method according to the second embodiment can be implemented by the plasma etching apparatus 2 having a structure substantially the same as that shown in FIG. 4, the following points are different.

In the plasma etching apparatus 2 according to the second embodiment, carbonyl difluoride (COF ₂ ) having a warming coefficient almost equal to that of carbon dioxide is employed as the etching gas for etching the SiN film, and the etching gas supply part 45 is employed. COF ₂ is stored instead of SF ₆ . Also in this example the flow control unit 44 is the COF ₂ and O _2, for example 1: It is to be supplied to the treatment vessel 20 as a gas mixture mixed in a volume ratio in the range of less than 20: at least 2, 3.

The vacuum pump 51 and the pressure regulating valve 511 which concern on 2nd Embodiment adjust the degree to which the pressure regulating valve 511 opens based on the indication of the pressure gauge which is not shown in figure, For example, it is equipped with the capability which can adjust to the range of 133 mW (1000 mTorr) or more and 267 mW (2000 mTorr) or less.

Under the conditions described above, even in the case where the mixed gas of COF ₂ and O ₂ is converted into plasma to perform plasma etching of the substrate S to be processed, a contact in which the shape of the stable plasma, the improvement of the etching rate of the SiN film, and the occurrence of undercut are suppressed Shape control of hole 103, shaving prevention of signal line film (source electrode 161, drain electrode 162) when etching TFT part 1a and contact part 1b collectively, low vacuum pump Various effects, such as a reduction of equipment cost by employ | adopting this, can be acquired.

Here, in the mixed gas discharged from the processing vessel 20, most of the COF ₂ contained in the gas is collected by the decontamination apparatus 52, and the remaining O ₂ is discharged to the atmosphere. However, since the collection efficiency of COF _{2 in} the removal device 52 is not 100%, a small amount of COF ₂ may be released to the atmosphere. Even in such a case, as described above, since COF ₂ is a material having a warming coefficient equal to that of carbon dioxide, the load on the environment can be kept low.

The plasma etching method according to the first and second embodiments described above is not limited to the case of collectively etching the TFT portion 1a and the contact portion 1b on the substrate S shown in FIG. It is also applicable to the case of etching separately.

In addition, in the above-described plasma processing method of 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 treated. The present invention can also be applied to a plasma ashing method for removing from the substrate S. Conventionally, by ashing in a pressure atmosphere higher than 133 Pa (1000 mTorr) where plasma ashing is performed, damage to a device formed on the substrate S to be processed is low and fast ashing can be performed.

(Example)

(Experiment 1)

4 using an etching apparatus of a plasma etching apparatus, equivalent structures, and (2) as described in, by performing the etching of the SF ₆ and O ₂ mixed gas plasma, the resist film 101 is patterned SiN substrate to the surface of, The etching rate (E / R) of the SiN, 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. The high frequency power supply unit 48 was supplied with high frequency power of 13.56 MHz and 3000 W for 30 seconds. In addition, the temperature of the mounting table 3 was adjusted to 25 degreeC.

A. Experimental Conditions

(Example 1-1) 100 sccm of SF ₆ and 600 sccm of O ₂ were supplied (volume ratio 1: 6), and the pressure in the processing vessel 20 was set to 133 kPa (1000 mTorr).

(Example 1-2) It set as the conditions similar to (Example 1-1) except having set the pressure in the process container 20 to 160 mPa (1200 mTorr).

(Comparative Example 1-1A) The conditions were the same as in (Example 1-1) except that the pressure in the processing vessel 20 was set to 26.7 kPa (200 mTorr).

(Comparative Example 1-2A) The conditions were the same as that of (Example 1-1) except that the pressure in the processing vessel 20 was set to 53.3 kPa (400 mTorr).

(Comparative Example 1-3A) The conditions were the same as those of (Example 1-1) except that the pressure in the processing vessel 20 was set to 107 Pa (800 mTorr).

B. Experimental Results

The results of (Examples 1-1 to 1-2) and (Comparative Examples 1-1A to 1-3A) are shown in FIG. 5. The horizontal axis of FIG. 5 has shown the pressure in the processing container 20, The numerical value of the upper stage has shown the unit of [mTorr], and the numerical value of the lower side shows the unit of [kPa]. The vertical axis on the right shows the etching rate of SiN or the ashing speed [nm / min] of the resist film 101, and the vertical axis on the left shows the selectivity ratio [-], which is the ratio of the ashing speed of the resist film 101 to the etching rate of SiN. ].

The plot of the white rhombus shown in FIG. 5 has shown the etching rate of SiN in each Example and a comparative example, and the solid line has shown the trend line. Further, the plot of black rhombus is the ashing speed of the resist film 101 (PR), and the broken line is this tendency line. On the other hand, the black triangular plot shows the above-mentioned selection ratio, and the dashed-dotted 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 an error bar shows the value of the actual experiment result by the 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 made high from (Comparative Example 1-1A) to (Comparative Example 1-3A), the etching rate of SiN will rise accordingly. Doing. And the change of the etching rate does not fluctuate largely from (Comparative Example 1-3A) to (Example 1-2), and even if the pressure in the processing container 20 is made high, a large rise of an etching rate is not seen. This tendency can be said to be the same for the ashing speed of the resist film 101.

On the other hand, with respect to the selection ratio, as the pressure in the processing vessel 20 is increased, the etching amount of SiN increases relatively, and the selection ratio gradually decreases from (Comparative Example 1-1A) to (Comparative Example 1-3A). Doing. In addition, in the range of (Comparative Example 1-3A) to (Example 1-2), the selection ratio does not vary greatly.

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

Experimental results of (Comparative Examples 1-1B to 1-3B) of Figs. 6 (a) to 6 (c) and (Comparative Examples 1-1C to 1-3C) of Figs. 7 (a) to 7 (c). In comparison, the occurrence of undercut was observed relatively remarkably in the volume ratio of SF ₆ and O ₂ of 1: 4 (Comparative Examples 1-1C to 1-3C). On the other hand, undercut was hardly generated in (Comparative Examples 1-1B), and a slight undercut was observed in (Comparative Examples 1-2B, 1-3B). Small compared to 3C).

From this, it can be compared to a case in which the mixing ratio of O ₂ as a sense of increasing the mixing ratio of O ₂ to SF ₆ small found that to suppress the degree of the occurrence of undercut. And it is thought that this also has the same tendency with respect to (Example 1-1, 1-2) in which the pressure in the process 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 volume ratio 1: 6, when the pressure in the processing vessel 20 is increased to 133 kPa (1000 mTorr) or higher, plasma becomes unstable, Experiments corresponding to Comparative Examples 1-1C to 1-3C are not performed.

(Experiment 2)

The SiN film was formed in the mass production substrate for LCD, the resist film 101 was apply | coated and patterned on the upper surface, the to-be-processed substrate S was created, and the plasma etching of the SiN film was performed. In the plasma etching, the mixed gas of SF ₆ and O ₂ is plasmified using an etching processing apparatus having a configuration equivalent to that of the plasma etching apparatus 2 to etch rate (E / R) of SiN and ashing rate of the resist film 101. (A / R) and selectivity (ratio of ashing rate of resist film 101 to etching rate of SiN) were measured. The high frequency power supply unit 48 was supplied with high frequency power of 13.56 MHz and 3000 W for 30 seconds. In addition, the temperature of the mounting table 3 was adjusted to 25 degreeC.

A. Experimental Conditions

(Example 2-1) 100 sccm of SF ₆ and 600 sccm of O ₂ were supplied (volume ratio 1: 6), and the pressure in the processing vessel 20 was set to 133 kPa (1000 mTorr). The etching amount of the SiN film and the ashing amount of the resist film 101 at each point to which the numerical value of "1-13" of the to-be-processed substrate S shown in FIG. 8 were attached were measured.

(Example 2-2) The conditions were the same as that of (Example 2-1) except that the pressure in the processing container 20 was set to 160 mPa (1200 mTorr).

(Example 2-3) The same conditions as in (Example 2-1) were used except that the pressure in the processing vessel 20 was set to 200 mPa (1500 mTorr).

(Comparative Example 2-1) The same conditions as in (Example 2-1) were used except that the pressure in the processing vessel 20 was set to 107 Pa (800 mTorr).

B. Experimental Results

The results of (Examples 2-1 to 2-3) and (Comparative Example 2-1) are shown in Figs. 9 and 10. 9 shows the results of plotting the in-plane uniformity of the etching rate and etching rate of the SiN film for each measurement point on the substrate S to be processed. In the horizontal axis of FIG. 9, the pressure in the processing container 20 is expressed in [mTorr] units at the upper end and in [kPa] at the lower end. 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 uniformity [±%] in the substrate S surface of the etching rate. In-plane uniformity of the etching rate was calculated based on the following formula (1). In-plane uniformity shows that the smaller the value is, the smaller the variation in the 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 }] x 100. (One)

However, (E / R) _MAX ; maximum value of etching rate [nm / min],

(E / R) _MIN ; It is the minimum value of etching speed [nm / min].

In FIG. 9, the plot of a white circle shows the etching rate of the part of the center position "7" of the to-be-processed substrate S shown in FIG. 8, and the plot of a black circle shows the intermediate position "4, 5, 9, 10 of FIG. The average value of the etching rate of four parts of "is shown. In addition, the etching speed of 8 parts of the edge positions "1, 2, 3, 6, 8, 11, 12, 13" shown in FIG. The plot of an asterisk (*) has shown the average value of the etching rate of each part to "1-13" of the whole to-be-processed substrate S. FIG. The white triangle plots show in-plane uniformity of the etching rate in the entire substrate S.

In addition, FIG. 10 shows the etching rate of the SiN film on the substrate S average and the ashing speed and selectivity of the resist film 101. The meanings of the horizontal axis, the left and right vertical axes, the respective plots, and the trend lines are the same as in FIG. 5. .

Results of (Examples 2-1 to 2-3) and (Comparative Example 2-1) First of all, the tendency of the etching rate of the SiN film shown in FIG. Also, the etching rate of the SiN film is increased by increasing the pressure in the processing container 20 from (Comparative Example 2-1) to (Example 2-2). This shows the same tendency as the result of each Example and the comparative example of (Experiment 1) using a SiN substrate. And in the case where the pressure in the processing container 20 was raised to 200 kPa (1500 mTorr) (Example 2-3), the etching rate also became small compared with (Example 2-2).

In this manner (Experiment 2) using the mass production substrate for LCD, the etching rate tended to draw a convex curve upward as the pressure in the processing vessel 20 was increased. On the other hand, the in-plane uniformity of the etching rate was observed to have a tendency to draw a convex curve downward as the pressure in the processing vessel 20 was increased, contrary to the etching rate.

This is because under a condition where the volume ratio between SF ₆ and O ₂ is constant (Example 2-2), a relatively stable plasma is formed in the pressure region below (Example 2-2), and the etching rate of the SiN film is increased as the pressure in the processing vessel 20 is increased. It shows that it can improve. In addition, when the pressure in the processing container 20 exceeds the value of (Example 2-2), the effect of stabilizing the plasma by O ₂ is relatively small, and a deflected plasma is formed, so that the etching rate and in-plane uniformity of the SiN film are formed. It can be interpreted as if the sex is deteriorated together.

Next, in the results of (Examples 2-1 to 2-3) and (Comparative Example 2-1) shown in FIG. 10, as described above, the average value of the etching rates is convex upward with respect to the pressure in the processing vessel 20. While the curve is drawn, the ashing speed of the resist film 101 decreases with the increase in the pressure in the processing container 20. As a result, the selectivity of the resist film 101 to the SiN film is gradually decreased as the pressure in the processing container 20 is increased, and the range of (Example 2-2) to (Example 2-3) The selectivity does not change significantly.

Also in the results shown in FIG. 10 (Example 2-2), a relatively stable plasma was formed in the pressure region below (Example 2-2), and as the pressure in the processing vessel 20 was increased, the selectivity was lowered as the etching rate of the SiN film was improved. When the pressure in the processing container 20 exceeds the value of (Example 2-2), it becomes difficult to form stable plasma, and as a result, it is considered that the selectivity may not be greatly changed.

11A to 11C show enlarged longitudinal cross-sectional photographs of the resist film 101 and the SiN film in each example of (Examples 2-1 to 2-3). Although the occurrence of undercut is not seen in (Examples 2-1 and 2-2) shown in Figs. 11 (a) and 11 (b), some undercuts are shown in (Example 2-3) shown in Fig. 11 (c). The occurrence of was observed. However, also in (Example 2-3), the degree of occurrence of undercut is small as compared with the case of (Comparative Examples 1-1C to 1-3C) shown in Figs. 7 (a) to 7 (c), for example.

When the results of the above (Experiment 1) and (Experiment 2) are summed up, when the volume ratio of SF ₆ and O ₂ is 1: 6, the etching rate of SiN is increased by increasing the pressure in the processing vessel 20. Is improved. If the pressure in the processing vessel 20 is higher, the etching rate of the SiN does not change significantly (in the case of (Experiment 1) using the SiN substrate), or it changes to decrease by drawing a convex curve upward (using the mass production substrate of the LCD ( For experiment 2)).

From this, the pressure atmosphere in which the plasma etching of the SiN film is carried out is performed at a rate of 133 Pa (1000 mTorr) or more and 200 Pa (resulting in a relatively high etching rate even when the SiN etching rate remains in a high state or draws a convex curve. 1500 mTorr) or less can be said to be preferable. In addition, when the volume ratio of SF ₆ and O ₂ exceeds 1:20, it is considered that SF ₆ is too small and etching hardly proceeds even if the pressure is increased. The preferred range of the volume rate of the SF ₆ and O ₂ is, for example, 1: 6 to 1: is believed to range from 20 degree.

(Experiment 3)

Also using an etching apparatus of the same structure as the plasma etching apparatus (2) according to 4, COF by plasmanizing a gas mixture of ₂ and O ₂ etching rate of SiN under the same conditions as described in (experiment 1) (E / R) The ashing speed (A / R) of the resist film 101 and the selectivity (ratio of the ashing speed 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 vessel 20 was set to 160 kPa (1200 mTorr).

(Example 3-2) Except having made the pressure in the process container 20 into 240 kPa (1800 mTorr), it was set as the conditions similar to (Example 3-1).

(Example 3-3) The conditions were the same as that of (Example 3-1) except that the pressure in the processing container 20 was set to 253 kPa (1900 mTorr).

(Comparative Example 3-1) The same conditions as in (Example 3-1) were used except that the pressure in the processing vessel 20 was set at 107 Pa (800 mTorr).

The results of (Examples 3-1 to 3-3) and (Comparative Example 3-1) are shown in Figs. 12 and 13. Fig. 12 shows the etching rate of SiN, the ashing speed and selectivity of the resist film 101, and the meanings of the horizontal axis, the left and right vertical axes, the respective plots and the trend lines are the same as in Fig. 10 described above.

It is a figure which shows the deviation of the etching rate of the center position of a SiN substrate, and the etching rate of a corner part. The horizontal axis of FIG. 13 shows the pressure in the processing container 20 in [mTorr] units at the upper end and [kPa] at the lower end, and the vertical axis shows the etching rate [nm / min] at each position. In FIG. 13, the white rhombus plot shows the etching rate of the center position of a SiN substrate, and the range shown by the error bar has shown the deviation range of the etching rate of the corner position of a SiN substrate.

Referring to FIG. 12, in the case where a mixed gas of COF ₂ and O ₂ is used, also in both the etching rate of SiN and the ashing rate of the resist film 101 from (Comparative Example 3-1) (Example 3-3) When the pressure in the processing container 20 is increased over, the etching rate and the ashing rate increase in proportion to the increase in the pressure, and the phenomenon that these speeds do not fluctuate significantly within the range of the experiment was not observed. In addition, about the selection ratio, if the pressure in the processing container 20 is made high, the value of the selection ratio will gradually decrease, but it is a change as much as if it does not change substantially.

This is considered to be the result of COF ₂ forming a relatively stable plasma in the pressure range in which the experiment was performed, and the increase in pressure can be reflected in the improvement of the etching rate. This shows that in Fig. 13, even when the etching is performed uniformly at almost the same etching rate at any of the center position and the corner position, a stable plasma capable of performing plasma etching uniformly in the surface of the SiN substrate is formed. You can check it.

Fig. 14 shows a photograph of an enlarged longitudinal section of the resist film 101 and the SiN substrate in (Example 3-2), and the tapered surface on the SiN substrate side where undercut does not occur even if the pressure in the processing container 20 is increased. It can be seen that it can form.

12, Figure 13, from the results of (Test 3), the volume ratio of COF ₂ and O ₂ 1: In the case of a second, in the range not less than the atmosphere pressure 133㎩ (1000mTorr) of about 6000Å / min The SiN film can be etched at the above high speed. In the range of 267 Pa (2000 mTorr) or less close to the range where the experiment was conducted, it is considered that the etching rate can be sufficiently high without the rapid decrease in the etching rate. Further, the volume ratio of COF ₂ and O ₂ 3: The COF ₂ is thought beorindago becomes too low when it exceeds 20 increases also does not substantially etch the pressure. The preferable range of the volume ratio of COF ₂ and O ₂ is, for example, 1: it is considered in a range of 20: 2-3.

S: substrate to be processed
1a: TFT section
1b: contact part
101: resist film
102: opening
103: contact hole
17: passivation film
2: plasma etching apparatus
3: mounting table
4: upper electrode
45: etching gas supply unit
46: oxygen supply unit
51: vacuum pump
511: pressure regulating valve
6: control unit

Claims (6)

A method of plasma etching a silicon nitride film on a substrate to be formed on a lower layer side of a resist pattern having an opening portion gradually decreasing from an upper portion to a lower portion,
Carrying in the substrate to be processed into a processing container;
Supplying a mixed gas of sulfur hexafluoride and oxygen into the processing container, plasmating the mixed gas under a pressure atmosphere within a range of 133 Pa or more and 200 Pa or less to etch the silicon nitride film;
Plasma etching method comprising a.
The method of claim 1,
The mixed gas has a volume ratio of sulfur hexafluoride and oxygen in the 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 formed on a lower layer side of a resist pattern having an opening portion gradually decreasing from an upper portion to a lower portion,
Carrying in the substrate to be processed into a processing container;
Supplying a mixed gas of carbonyl difluoride and oxygen into the processing container, forming a plasma, and etching the silicon nitride film
Plasma etching method comprising a.
The method of claim 3, wherein
The mixed gas has a volume ratio of carbonyl difluoride and oxygen in the range of 1: 2 or more and 3:20 or less.
The method according to claim 1 or 3,
And the opening area of the silicon nitride film formed by etching gradually decreases from the upper side to the lower side.
After carrying in a to-be-processed board | substrate into a process container, supplying the mixed gas of sulfur hexafluoride and oxygen into the process container, adjusting the pressure in the said process container, the said mixed gas is made into plasma, and the silicon nitride is carried out by the plasma. A storage medium storing a program for controlling an etching apparatus to etch a film.

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