JP7428528B2 - Etching method - Google Patents

Description

The present application relates to an etching method.

Conventionally, a substrate processing apparatus for etching a silicon oxide film has been proposed (for example, Patent Document 1). Patent Document 1 describes an etching method that can etch a silicon oxide film formed by atomic layer deposition (ALD) with a high selectivity relative to a silicon oxide film formed by other methods such as thermal oxidation. is listed.

JP2016-62947A

However, in Patent Document 1, although the silicon oxide film formed by the ALD method can be selectively etched with respect to the silicon oxide film formed by thermal oxidation, the opposite etching cannot be performed. In other words, a silicon oxide film formed by thermal oxidation cannot be etched with a high selectivity with respect to other films.

Therefore, an object of the present application is to provide an etching method that can selectively etch a silicon oxide film formed by thermal oxidation with respect to other films.

A first aspect of the etching method is an etching method for etching a silicon thermal oxide film formed on a substrate, which includes a substrate mounting step of mounting the substrate on a mounting table in a chamber, and a step of mounting the substrate on the mounting table. a heating step of heating the placed substrate to 160 degrees or more; a pressure control step of maintaining the degree of vacuum in the chamber at a predetermined first degree of vacuum; and supplying anhydrous hydrogen fluoride gas into the chamber. , generating hydrogen fluoride ions by reacting the anhydrous hydrogen fluoride gas with moisture in the silicon thermal oxide film, and selectively forming the silicon thermal oxide film with respect to other oxide films with the hydrogen fluoride ions . and a hydrogen fluoride gas supply step for etching.

A second aspect of the etching method is the etching method according to the first aspect, which further includes a depressurization step performed before the pressure control step to obtain a second degree of vacuum higher than the first degree of vacuum. Be prepared.

A third aspect of the etching method is the etching method according to the first or second aspect, wherein the first degree of vacuum is such that the pressure within the chamber is within a range of 10 Torr to 600 Torr.
A fourth aspect of the etching method is the etching method according to any one of the first to third aspects, in which the other oxide film is an oxide film formed by CVD or ADL.
A fifth aspect of the etching method is the etching method according to the fourth aspect, wherein the other oxide film is any one of a TEOS film, a BSG film, and a BPSG film formed by a CVD method, and an ALD film formed by an ALD method. .
A sixth aspect of the etching method is the etching method according to the fifth aspect, in which the other oxide film is an ALD film.

According to the first and third aspects of the etching method, the thermal oxide film is selectively etched with respect to other films by setting the temperature of the substrate to 140 degrees or higher and supplying anhydrous hydrogen fluoride gas to the substrate. can do.

According to the second aspect of the etching method, moisture in the chamber can be evacuated before supplying anhydrous hydrogen fluoride gas.

FIG. 2 is a side view schematically showing an example of the configuration of an etching apparatus. 2 is a flowchart showing an example of the flow of substrate processing (etching processing) in an etching apparatus. 3 is a graph showing an example of the relationship between substrate temperature and etching rate. FIG. 3 is a side view schematically showing another example of the configuration of the etching apparatus. 7 is a flowchart showing another example of the flow of substrate processing (etching processing) in the etching apparatus.

Embodiments will be described below with reference to the accompanying drawings. Note that the components described in this embodiment are merely examples, and the scope of the present disclosure is not intended to be limited thereto. In the drawings, dimensions or numbers of parts may be exaggerated or simplified as necessary for easy understanding.

Expressions indicating relative or absolute positional relationships (e.g., "in one direction," "along one direction," "parallel," "perpendicular," "centered," "concentric," "coaxial," etc.) are used unless otherwise specified. It does not only strictly represent the positional relationship, but also represents the state of relative displacement in terms of angle or distance within a range where tolerance or the same level of function can be obtained. Unless otherwise specified, expressions indicating equal states (e.g., "same," "equal," "homogeneous," etc.) do not only mean quantitatively strictly equal states, but also mean that tolerances or functions of the same degree can be obtained. It also represents a state in which a difference exists. Unless otherwise specified, expressions that indicate a shape (e.g., "quadrangular shape" or "cylindrical shape") do not only strictly represent the shape geometrically, but also include, to the extent that the same degree of effect can be obtained, e.g. Shapes with irregularities, chamfers, etc. are also represented. The expressions "comprising," "comprising," "comprising," "containing," or "having" one component are not exclusive expressions that exclude the presence of other components. The expression "at least one of A, B, and C" includes only A, only B, only C, any two of A, B, and C, and all of A, B, and C.

<First embodiment>
FIG. 1 is a side view schematically showing an example of the configuration of an etching apparatus 1. As shown in FIG. The etching apparatus 1 is a single-wafer type etching apparatus that etches substrates W such as semiconductor wafers one by one, and is, for example, a vapor phase etching apparatus that does not use plasma. The etching apparatus 1 can be applied to a part of an apparatus for manufacturing semiconductor devices. Note that the substrate W is not necessarily limited to a substrate for semiconductor devices. The substrate W is, for example, a liquid crystal display substrate, a plasma display substrate, an organic EL substrate, an FED (Field Emission Display) substrate, an optical display substrate, an organic EL substrate, a magneto-optical disk substrate, a photomask substrate, or It may also be a substrate for solar cells.

A thermal oxide film is formed on the surface of the substrate W in a pre-process before the etching apparatus 1 is carried in. Here, as an example, the substrate W is a silicon substrate, and a silicon thermal oxide film is formed on the surface thereof. The thermal oxide film is formed by oxidizing the substrate W from the surface to the inside. Specifically, by exposing the substrate W to oxygen or water vapor in a high-temperature atmosphere, silicon (Si) and oxygen (O ₂ ) are chemically reacted to form a thin film of silicon dioxide (SiO ₂ ). form a thermal oxide film). This thermal oxide film is dense. In other words, the density of the thermal oxide film (film density) is high.

Other films are also formed on the surface of the substrate W. Other films include, for example, TEOS (Tetra Ethoxy Silane) film, BSG (Boron Silicate Glass) film, PSG (Phospho Silicate Glass) film, and BPSG (Boron doped Phospho Silicate Glass) film by chemical vapor deposition (CVD method). Examples include films and oxide films such as ALD oxide films produced by atomic layer deposition (ALD). The densities (film densities) of these oxide films are all lower than that of thermal oxide films.

In the CVD method, for example, the substrate W is exposed to a source gas containing components of a target thin film, and a chemical reaction is caused on the substrate W using heat or plasma. A desired thin film is formed on the substrate W by this chemical reaction. For example, when forming a BSG film by the CVD method, boron (B) is included in the source gas.

Further, in the ALD method, first, the substrate W placed in the chamber is exposed to the precursor A. Subsequently, after the precursor A in the chamber is removed by purging, the substrate is exposed to another precursor B (eg, ozone). Then, the precursor B in the chamber is removed by purging again. By repeating these processes, a single molecule level film is formed one layer at a time. Specifically, when a silicon oxide film is to be formed as an ALD oxide film, aminosilane is used as the source gas (precursor A), and when an aluminum oxide (Al ₂ O ₃ ) film is to be formed. Trimethylaluminum is used as a raw material gas.

In the following, as an example, it is assumed that a thermal oxide film and an ALD oxide film are exposed as a silicon oxide film on the surface of the substrate W. The etching apparatus 1 selectively etches the thermal oxide film of the substrate W with respect to other films (here, the ALD oxide film).

Etching apparatus 1 includes a chamber 2 and a control section 3. The chamber 2 is formed into a hollow shape capable of accommodating the substrate W therein. The internal space of the chamber 2 corresponds to a processing chamber in which a predetermined process is performed on the substrate W. The control unit 3 controls the operations of elements provided in the etching apparatus 1, such as opening and closing of valves (described later).

Inside the chamber 2, a substrate holder 4, a heating mechanism 5 for the substrate W, a gas distribution plate 6, and a pressure sensor 10 are provided.

The substrate holder 4 holds the substrate W in a substantially horizontal position within the chamber 2 . “Horizontal posture” refers to a state in which the substrate W is parallel to a horizontal plane. The substrate W is carried into the chamber 2 from the outside by a transport system (not shown) and placed on the substrate holder 4. The substrate holder 4 may hold the substrate W by suction, or may hold the periphery of the substrate W with a plurality of chuck pins. Note that the substrate holder 4 does not necessarily need to hold the substrate W, and may simply support the substrate W. That is, the substrate holder 4 may be a mounting table on which the substrate W is mounted.

The heating mechanism 5 heats the substrate W held by the substrate holder 4. In the example of FIG. 1, the heating mechanism 5 is located below the substrate W, and is built into the substrate holder 4, for example. The heating mechanism 5 is, for example, a resistance heating electric heater. Note that the heating mechanism 5 may include, for example, a light source such as a lamp instead of the electric heater. The temperature of the substrate W may be controlled to a predetermined temperature by irradiating the substrate W with infrared rays from the light source.

An exhaust pipe 7 is connected to the chamber 2 . In the example of FIG. 1, the exhaust pipe 7 is connected to the bottom of the chamber 2 in communication with the inside of the chamber 2. A vacuum pump 8 is also connected to the exhaust pipe 7. The vacuum pump 8 reduces the pressure inside the chamber 2 by sucking the gas inside the chamber 2 through the exhaust pipe 7 .

The exhaust pipe 7 is provided with an APC (Auto Pressure Controller) valve 9 . The APC valve 9 adjusts the exhaust flow rate of gas in the chamber 2 by adjusting the opening degree in the exhaust pipe 7. Thereby, the pressure within the chamber 2 can be adjusted.

The pressure sensor 10 is connected to the chamber 2 and detects the pressure inside the chamber 2. The pressure sensor 10 outputs an electric signal indicating the detected pressure inside the chamber 2 to the control unit 3. The control unit 3 controls the APC valve 9 to adjust the pressure in the chamber 2 so that the pressure detected by the pressure sensor 10 is within a predetermined pressure range.

After the substrate W is held by the substrate holder 4, the vacuum pump 8 is activated to start evacuation of the chamber 2. In this embodiment, the means for reducing the pressure inside the chamber 2 is described as the vacuum pump 8, but the present invention is not limited to this. For example, it is also possible to reduce the pressure by factory utility exhaust. In short, the specific configuration of the exhaust section that exhausts the gas in the chamber 2 can be changed as appropriate.

A gas supply pipe 11 is connected to the chamber 2 . In the example of FIG. 1, the gas supply pipe 11 is connected to the upper part of the chamber 2 in communication with the inside of the chamber 2. In the example of FIG. 1, the gas supply pipe 11 includes a common pipe 111 and branch pipes 113 and 114. One end of the common pipe 111 is connected to the upper part of the chamber 2 . Branch pipe 113 connects common pipe 111 and an HF (hydrogen fluoride) supply source (not shown). The HF source supplies anhydrous HF gas into the branch pipe 113. The term "anhydrous HF gas" here refers to HF gas that contains almost no moisture, and for example, the moisture content (volume ratio) is several tens (for example, 10) vol. ppm or less. Below, anhydrous HF gas will be simply referred to as HF gas. An HF gas flow controller 14 is installed in the branch pipe 113 . The HF gas flow rate controller 14 is a so-called mass flow controller, and controls the flow rate of the HF gas supplied into the chamber 2 .

An on-off valve 17 is interposed in the branch pipe 113. When the on-off valve 17 opens, HF gas is supplied into the chamber 2 from the gas supply pipe 11 (branch pipe 113 and common pipe 111). The supply flow rate of HF gas is adjusted by an HF gas flow controller 14.

Branch pipe 114 connects common pipe 111 and a nitrogen supply source (not shown). A nitrogen source supplies nitrogen gas into branch pipe 114 . Nitrogen gas also contains almost no moisture, and the moisture content (volume ratio) in nitrogen gas is, for example, several tens (for example, 10) vol. ppm or less. The branch pipe 114 is provided with an on-off valve 18 and a nitrogen gas flow rate controller 15 . By opening the on-off valve 18, nitrogen gas is supplied into the chamber 2 from the gas supply pipe 11 (branch pipe 114 and common pipe 111). The supply flow rate of nitrogen gas is adjusted by a nitrogen gas flow rate controller 15. Nitrogen gas is supplied into the chamber 2 to adjust the pressure inside the chamber 2 or to purge the inside of the chamber 2 after etching processing under reduced pressure. Note that in place of nitrogen gas, an inert gas such as a rare gas (for example, argon gas) may be used. The inert gas referred to here is a gas that has poor reactivity with both the HF gas and the substrate W.

The gas distribution plate 6 is disposed within the chamber 2 between the substrate holder 4 and the discharge port of the gas supply pipe 11 . The gas distribution plate 6 is formed into a plate shape that extends horizontally within the chamber 2 . A plurality of openings 6H passing through the gas distribution plate 6 in the thickness direction are formed in a distributed manner within a horizontal plane.

The HF gas supplied into the chamber 2 via the gas supply pipe 11 passes through the gas distribution plate 6 and reaches the substrate W. Specifically, the HF gas supplied above the gas distribution plate 6 in the chamber 2 passes through the plurality of openings 6H provided in the gas distribution plate 6 to flow below the gas distribution plate 6. Moving. The HF gas is rectified by passing through the plurality of openings 6H, and is uniformly supplied onto the substrate W. The inner diameter of the opening 6H is, for example, 0.1 mm. Further, the interval between adjacent openings 6H, 6H is, for example, 5 mm. Note that the inner diameter and spacing of the openings 6H are not limited to these. Further, in the example shown in FIG. 1, only one gas distribution plate 6 is installed in the chamber 2, but a plurality of gas distribution plates 6 may be installed so as to overlap vertically in multiple stages. In addition, if there is little need for the HF gas supplied into the chamber 2 to act uniformly on the substrate W, or if the HF gas can be rectified by a configuration other than the gas distribution plate 6, the gas distribution plate 6 is unnecessary.

When the HF gas flows to the surface of the substrate W, it acts on the surface of the substrate W and etches the oxide film. It is known that HF ₂ ⁻ (hydrogen fluoride ions) mainly contributes to the etching of this oxide film (silicon oxide film). This HF ₂ ^- is generated by a reaction between HF gas and moisture (H ₂ O) in the oxide film.

By the way, conventionally, by supplying not only HF gas but also water vapor into the chamber 2, the HF gas and the water vapor were reacted to generate hydrogen fluoride ions. In contrast, in this embodiment, by focusing on the moisture in the oxide film and supplying HF gas into the chamber 2, hydrogen fluoride ions are generated by the reaction between the HF gas and the moisture in the oxide film. do. According to this, there is no need to supply water vapor into the chamber 2, so running costs can be reduced. Further, the configuration for supplying water vapor into the chamber 2 can also be omitted. In this case, the device size and manufacturing cost of the etching device 1 can be reduced.

Now, in one example of this embodiment, a thermal oxide film and an ALD oxide film are formed on the surface of the substrate W as oxide films. By satisfying the temperature conditions described below, the HF gas can selectively etch the thermal oxide film with respect to the ALD oxide film.

The control unit 3 controls the heating mechanism 5, the vacuum pump 8, the APC valve 9, the pressure sensor 10, the HF gas flow controller 14, the nitrogen gas flow controller 15, and the opening/closing valves 17 and 18.

The control unit 3 is an electronic circuit device, and may include, for example, a data processing device and a storage medium. The data processing device may be, for example, an arithmetic processing device such as a CPU (Central Processor Unit). The storage medium may include a non-temporary storage medium (for example, a ROM (Read Only Memory) or a hard disk) and a temporary storage medium (for example, a RAM (Random Access Memory)). The non-temporary storage medium may store, for example, a program that defines the processing that the control unit 3 executes. When the processing device executes this program, the control unit 3 can execute the processing specified in the program. Of course, part or all of the processing executed by the control unit 3 may be executed by a hardware circuit such as a logic circuit.

The control unit 3 controls each flow rate controller 14, 15 so that the supply flow rates of HF gas and nitrogen gas are within their respective ranges. Thereby, the supply flow rates of HF gas and nitrogen gas are appropriately adjusted. The supply flow rates of the HF gas and the nitrogen gas are, for example, several thousand sccm or less (for example, 3000 sccm) and tens of thousands of sccm or less (for example, 10,000 sccm), respectively. These supply flow rates can be changed as appropriate.

The control unit 3 adjusts the opening degree of the APC valve 9 so that the pressure inside the chamber 2 detected by the pressure sensor 10 falls within a predetermined pressure range. Thereby, the pressure within the chamber 2 is adjusted appropriately. During processing of the substrate W, the pressure within the chamber 2 is maintained at a value within the range of 5 Torr to 600 Torr, for example.

<Substrate processing flow>
FIG. 2 is a flowchart showing an example of the flow of substrate processing (etching processing) in the etching apparatus 1. As shown in FIG. The etching process described below can be applied to a part of the manufacturing process of a semiconductor device.

First, a substrate W to be etched is prepared (step S1: preparation step). A thermal oxide film and an ALD oxide film are formed and exposed on the upper surface of the substrate W.

In step S1, when the substrate W is prepared, a transport system (not shown) transports the substrate W into the chamber 2 and places it on the substrate holder 4 (step S2: substrate mounting step). The substrate W is placed with the surface on which the thermal oxide film and the ALD oxide film are formed facing upward.

After the substrate W is placed on the substrate holder 4, the control unit 3 reduces the pressure inside the chamber 2 to a high vacuum state by controlling the vacuum pump 8 (step S3: process chamber pressure reduction step). The degree of pressure reduction is appropriately determined depending on the capacity of the vacuum pump 8 used and the allowable pressure reduction time. By reducing the pressure in the chamber 2 as much as possible, the atmosphere within the chamber 2 can be exhausted as much as possible, thereby increasing the cleanliness inside the chamber 2. Moreover, since the moisture in the chamber 2 can also be exhausted, the amount of moisture in the chamber 2 can be reduced. In step S3, the vacuum pump 8 sets the pressure in the chamber 2 to, for example, 1 Torr or less, more preferably 0.1 Torr or less.

Once the pressure inside the chamber 2 is reduced to a high vacuum state, the control section 3 supplies nitrogen gas into the chamber 2 by opening the on-off valve 18 . As a result, the pressure within the chamber 2 increases. Further, the control unit 3 controls the nitrogen gas flow rate controller 15 to adjust the supply flow rate of nitrogen gas based on the pressure detected by the pressure sensor 10, and also adjusts the opening degree of the APC valve 9. Through these adjustments, the control unit 3 adjusts the pressure within the chamber 2 within a predetermined pressure range (step S4: pressure control step). The pressure within the chamber 2 is, for example, in the range of 10 Torr to 600 Torr. That is, in step S4, the degree of vacuum in the chamber 2 is made lower than the degree of vacuum in step S3.

Furthermore, the control unit 3 controls the temperature of the substrate W within a predetermined temperature range by controlling the heating mechanism 5 (step S5: heating step). The control unit 3 preferably starts temperature control (heating) of the substrate holder 4 at approximately the same time as starting the pressure reduction in the chamber 2 in step S3, for example.

As will be described in detail later, the temperature of the substrate W affects the etching selectivity of the thermal oxide film to the ALD oxide film. This selectivity is the ratio of the etching rate of the thermal oxide film to the etching rate of the ALD oxide film. In the heating step of step S5, the temperature of the substrate W is adjusted to within a predetermined temperature range so that this selection ratio is within a predetermined range. The specific temperature value of the substrate W will be explained in detail later.

After starting the temperature control in step S5, the control unit 3 supplies HF gas into the chamber 2 by opening the on-off valve 17 (step S6: HF gas supply step). As a result, HF gas is supplied into the chamber 2. In this embodiment, water vapor is not actively supplied into the chamber 2, and the content of water in the chamber 2 in step S6 is very small. The HF gas supplied into the chamber 2 passes through the plurality of openings 6H formed in the gas distribution plate 6 and comes into contact with the entire surface of the substrate W substantially uniformly. At this time, the thermal oxide film is selectively etched with respect to the ALD oxide film by the HF gas (etching process).

After the start of the etching process, when a first predetermined time suitable for removing the thermal oxide film has elapsed, the control unit 3 closes the on-off valve 17 to stop the supply of HF gas. This essentially ends the etching process.

When a second predetermined time period has elapsed since the supply of HF gas was stopped, the control unit 3 purges the inside of the chamber 2 with nitrogen gas (step S7: purge step). At this time, the control unit 3 controls the nitrogen gas flow rate controller 15 to adjust the supply flow rate of nitrogen gas. In this way, the control unit 3 returns the inside of the chamber 2 to atmospheric pressure by purging the inside of the chamber 2, which has been in a reduced pressure state, with nitrogen gas, so that the substrate W can be unloaded. The substrate W, which can now be carried out, is suitably carried out from the substrate holder 4 by a transport system (not shown).

<Explanation of selective etching>
Next, etching conditions for selectively etching the thermal oxide film with respect to the ALD oxide film will be described. The etching conditions include the temperature of the substrate W.

The applicant conducted an experiment to measure the etching rate of a thermal oxide film and the etching rate of an ALD oxide film while changing etching conditions. Specifically, etching is performed for the same processing time on a first substrate on which a thermal oxide film is formed on the entire surface and a second substrate on which an ALD oxide film is formed on the entire surface. The etching amount was measured, and the etching rate was calculated from the etching amount. As etching conditions, the supply flow rates of HF gas and nitrogen gas were set to 3000 sccm and 10000 sccm, respectively, the pressure inside the chamber 2 was set to 80 Torr, and the temperature of the substrate W was changed. The temperature of the substrate W is adjusted by a heating mechanism 5.

FIG. 3 is a graph showing the experimental results, showing the temperature dependence of the etching rate for a thermal oxide film and an ALD oxide film. In the example of FIG. 3, the etching rate for the thermal oxide film is shown by a black circle, and the etching rate for the ALD oxide film is shown by a black square. As illustrated in Figure 3, when the temperature is approximately below 140 degrees, the etch rate for thermal oxide is slightly lower than that for ALD oxide, whereas when the temperature is above 140 degrees, the etch rate is slightly lower than that for ALD oxide. , the etching rate of the thermal oxide film is higher than the etching rate of the ALD oxide film. Furthermore, in a high temperature region of 140 degrees or higher, the etching rate for a thermal oxide film increases sharply with an increase in temperature, whereas the etching rate for an ALD oxide film gradually increases with an increase in temperature. only increases. Therefore, it can be seen that the higher the temperature, the more selectively the thermal oxide film can be etched with respect to the ALD oxide film.

The reason why the etching rate for a thermal oxide film increases sharply as the temperature increases, and the etching rate for an ALD oxide film does not increase much with an increase in temperature can be considered as follows.

First, let us consider the oxide film removal reaction using HF gas. When the HF gas adheres to the surface of the oxide film, the HF gas reacts with moisture in the oxide film to generate hydrogen fluoride ions, and the hydrogen fluoride ions mainly contribute to the removal of the oxide film.

In order for the HF gas to adhere to the surface of the oxide film and react with the moisture in the oxide film, the HF gas needs to penetrate to the moisture in the oxide film. It is thought that the ease with which HF gas enters the oxide film is different between the thermal oxide film and the ALD oxide film, as will be described later.

Now, HF gas includes multimers (including, for example, dimers, tetramers, and octamers) in which HF molecules are associated with each other, and monomers in which HF molecules are not associated with each other. It is considered that multimeric HF gas has a large size and therefore has difficulty penetrating into the oxide film, whereas monomeric HF gas has a small size and therefore has difficulty penetrating into the oxide film. The higher the temperature, the higher the proportion of HF gas present as a monomer, so the higher the temperature, the easier it is to enter the oxide film in terms of size.

Incidentally, the thermal oxide film is denser than the ALD oxide film, and the film density of the thermal oxide film is higher than that of the ALD oxide film. Conversely, the ALD oxide film is a more porous film than the thermal oxide film, and the number of dangling bonds in the ALD oxide film is greater than the number of dangling bonds in the thermal oxide film. It is considered that this dangling bond can react with the HF gas that has entered the oxide film and trap the HF gas.

As mentioned above, the higher the temperature of HF gas, the higher the proportion of monomers, and from the viewpoint of size, it becomes easier to enter the inside of the thermal oxide film. Since the thermal oxide film is dense and has a small number of dangling bonds, HF gas is difficult to be trapped by the dangling bonds and easily enters the inside of the thermal oxide film from the surface. Therefore, when the temperature of the substrate W increases, the HF gas also enters the inside of the thermal oxide film, and the HF gas also reacts with the moisture inside the thermal oxide film, making it possible to quickly etch the thermal oxide film. It is considered that.

On the other hand, the number of dangling bonds in the ALD oxide film is greater than that in the thermal oxide film. Therefore, even if the temperature rises and the proportion of HF gas existing as a monomer increases, the HF gas is trapped by the dangling bonds in the ALD oxide film and is difficult to enter into the film. Therefore, it is considered that even if the temperature increases, the etching rate of the ALD oxide film does not increase much.

Therefore, in the present embodiment, the heating mechanism 5 heats the substrate W so that the temperature of the substrate W becomes 140 degrees or higher in the heating process of step S5. The heating mechanism 5 preferably raises the temperature of the substrate W to 160 degrees or more, more preferably 180 degrees or more. For example, 200 degrees can be adopted as the upper limit value of the temperature of the substrate W. The temperature control of the substrate W is also performed in the HF gas supply process of step S6.

Thereby, the etching apparatus 1 can etch the thermal oxide film with high selectivity with respect to the ALD oxide film in the HF gas supply process of step S6.

As described above, in this embodiment, when etching an oxide film using moisture in the oxide film without supplying water vapor, the proportion of monomers in the HF gas increases as the temperature increases. It has been explained that by paying attention to the difference in the number of dangling bonds between the thermal oxide film and the ALD oxide film, the thermal oxide film can be etched more than the ALD oxide film by increasing the temperature of the substrate W.

Conventionally, HF gas and water vapor were supplied into the chamber 2 to etch the oxide film with a sufficient amount of water. However, when HF gas and water vapor are supplied, the etching rate for an ALD oxide film with a low film density is higher than that for a thermal oxide film with a high film density, and it is difficult to selectively etch the thermal oxide film with respect to the ALD oxide film. could not.

On the other hand, in this embodiment, the oxide film is etched using moisture contained in the oxide film without supplying water vapor. This cannot be derived from conventional technical ideas that simply consider the amount of water. This is because the content of water contained in the thermal oxide film is much smaller than the content of water contained in the ALD oxide film. Specifically, the thermal oxide film contains water on the order of 10 ¹⁸ /cm ³ , and the ALD oxide film contains water on the order of 10 ²⁰ /cm ³ . Therefore, assuming that the supply of water vapor is stopped and etching is performed using moisture in the oxide film, it is expected that the ALD oxide film, which has a higher moisture content, will be etched more than the thermal oxide film. Therefore, with conventional technical thinking, it is impossible to even imagine stopping the supply of water vapor.

On the other hand, in this embodiment, as mentioned above, by focusing on the temperature dependence of the monomer abundance ratio of HF gas and the difference in dangling bonds in the oxide film, a thermal oxide film can be formed for the first time. This led us to the possibility of selectively etching the ALD oxide film.

In the above example, although water vapor is not supplied into the chamber 2, a very small amount of water may enter the chamber 2 through a small gap in the chamber 2. Alternatively, water vapor may be supplied into the chamber 2 at a small flow rate as long as the selectivity in the above-mentioned temperature range is not impaired. More specifically, the moisture content in the chamber 2 is, for example, 1 vol% or less, more preferably 1000 vol. ppm, more preferably 10 vol. Water vapor may be supplied in small amounts to meet the ppm.

Further, in the above example, the vacuum pump 8 increases the degree of vacuum in the chamber 2 in step S3. Thereby, the moisture in the chamber 2 can be exhausted, and the moisture content in the chamber 2 in the HF supply process of step S5 can also be reduced. On the other hand, in step S4, the degree of vacuum in the chamber 2 is adjusted to be lower than that in step S3, and in the HF supply step of step S5, the degree of vacuum is also adjusted to be lower than that in step S3. According to this, it is possible to secure the amount of HF gas for etching. In other words, if the degree of vacuum in the chamber 2 remains high, the HF gas will be exhausted in step S5 and the amount of HF gas will decrease, but by lowering the degree of vacuum in step S4, step S5 This ensures the amount of HF gas in the chamber 2. Thereby, the etching rate for the thermal oxide film can be improved.

Further, in the above example, the selection ratio of the thermal oxide film to the ALD oxide film is taken into consideration. However, since thermal oxide films are denser than the other types of oxide films mentioned above, it is thought that oxide films other than ALD oxide films exhibit a similar tendency. For example, a thermal oxide film is denser than an oxide film formed by a CVD method other than the ALD method, and is also denser than an oxide film formed by a coating method such as SoC (Spin on Dielectrics). . Therefore, by raising the temperature of the substrate W to 140 degrees or more and supplying anhydrous HF gas to the substrate W, the thermal oxide film can be etched selectively with respect to these other oxide films.

Further, in the above example, the thermal oxide film is selectively etched with respect to other oxide films, but the nitride film (silicon nitride film) can also be selectively etched. For example, when the temperature of the substrate W is 140 degrees or more and, for example, 200 degrees or less, the etching rate of the thermal oxide film is sufficiently higher than the etching rate of the nitride film. As a specific example, the etching rate for a silicon nitride film was 0.8 nm/min when the temperature of the substrate W was 140 degrees.

<Second embodiment>
FIG. 4 is a diagram schematically showing an example of the configuration of the etching apparatus 1A. The etching apparatus 1A has the same configuration as the etching apparatus 1 except for the presence or absence of the heating mechanism 30 for the chamber 2. Heating mechanism 30 heats chamber 2 . In the example of FIG. 4, the heating mechanism 30 is attached to the side wall of the chamber 2. As a more specific example, the heating mechanism 30 is attached to the outer wall surface of the side wall of the chamber 2 over the entire circumference.

The heating mechanism 30 is, for example, a resistance heating electric heater. Note that the heating mechanism 30 may include, for example, a lamp instead of the electric heater. The temperature of the substrate W may be controlled to a predetermined temperature by irradiating the substrate W with infrared rays from the lamp. Alternatively, the heating mechanism 30 may be a heat pump unit that exchanges heat between the heat medium and the chamber 2. The heating mechanism 30 is controlled by the control section 3. The heating mechanism 30 raises the temperature of the chamber 2 above the boiling point of water. For example, the heating mechanism 30 heats the chamber 2 so that the temperature of the chamber 2 is 100 degrees Celsius or more and 200 degrees Celsius or less.

FIG. 5 is a flowchart showing an example of the operation of the etching apparatus 1A. According to this operation, step S5A is further executed compared to the operation of the etching apparatus 1. Step S5A is executed, for example, between steps S5 and S6. In step S5A, the control unit 3 controls the heating mechanism 30 to increase the temperature of the chamber 2 to 100° C. or higher (chamber temperature control step). More specifically, the temperature of the chamber 2 is, for example, the temperature of the inner wall surface of the chamber 2. Note that the chamber temperature control step (step S5A) may start approximately at the same time as the pressure control step (step S3).

According to this, even if some water vapor is contained in the chamber 2, the possibility that the water vapor will liquefy and adhere to the inner wall surface of the chamber 2 can be reduced. Thereby, the possibility that the chamber 2 will corrode can be reduced.

As mentioned above, the etching apparatuses 1 and 1A have been described in detail, but the above description is in all aspects just an example, and the etching apparatuses 1 and 1A are not limited thereto. It is understood that countless variations not illustrated can be envisioned without departing from the scope of this disclosure. The configurations described in each of the above embodiments and modifications can be appropriately combined or omitted as long as they do not contradict each other.

1,1A Etching apparatus 2 Chamber 5 Heating mechanism W Substrate S2 Substrate mounting process (step)
S3 Decompression process (step)
S4 Pressure control process (step)
S5 Heating process (step)
S6 Hydrogen fluoride gas supply process (step)

Claims (6)

An etching method for etching a silicon thermal oxide film formed on a substrate, the method comprising:
a substrate mounting step of mounting the substrate on a mounting table in a chamber;
a heating step of heating the substrate placed on the mounting table to 160 degrees or more;
a pressure control step of maintaining the degree of vacuum in the chamber at a predetermined first degree of vacuum;
Anhydrous hydrogen fluoride gas is supplied into the chamber to cause the anhydrous hydrogen fluoride gas to react with moisture in the silicon thermal oxide film to generate hydrogen fluoride ions, and the hydrogen fluoride ions cause the silicon to react with water in the silicon thermal oxide film. An etching method comprising a step of supplying hydrogen fluoride gas to selectively etch a thermal oxide film with respect to other oxide films . The etching method according to claim 1,
The etching method further comprises a depressurization step performed before the pressure control step to achieve a second degree of vacuum higher than the first degree of vacuum. The etching method according to claim 1 or 2,
In the etching method, the first degree of vacuum is such that the pressure within the chamber is within a range of 10 Torr to 600 Torr. The etching method according to any one of claims 1 to 3,
In the etching method, the other oxide film is an oxide film formed by CVD or ADL. The etching method according to claim 4,
In the etching method, the other oxide film is any one of a TEOS film, a BSG film, and a BPSG film formed by a CVD method, and an ALD film formed by an ALD method. The etching method according to claim 5,
An etching method, wherein the other oxide film is an ALD film.

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