KR20220063927A - Substrate processing method - Google Patents

Abstract

Disclosed is a substrate processing method capable of etching a silicon layer with a high etch selectivity without generating a protective solid by-product on the surface of the silicon compound layer.
The substrate processing method according to the present invention is a substrate processing method for selectively etching a silicon layer on a substrate including a silicon layer and a silicon compound layer, wherein the method is a method for processing the silicon layer by plasmaizing an etching gas containing nitrogen trifluoride and hydrogen. and a plasma etching step of selectively etching

Description

Substrate processing method {SUBSTRATE PROCESSING METHOD}

The present invention relates to a method for processing a substrate. More specifically, the present invention relates to a method of selectively etching silicon and a silicon oxide layer through a plasma etching process using an etching gas composed of nitrogen trifluoride (NF ₃ ) and hydrogen (H ₂ ).

A process of manufacturing a semiconductor device includes, for example, selective etching processes for selectively etching only silicon in a state in which various materials such as silicon, silicon oxide, and silicon nitride are formed.

For example, when a silicon layer and a silicon oxide layer (or silicon nitride layer) coexist on a substrate, the method of selectively etching the silicon layer is a method of etching only the silicon layer with a mask formed on the silicon oxide layer. It is widely known. However, in the case of this method, a separate mask process is required.

To improve this, a method of selectively etching only the silicon layer while suppressing the continuous etching of the silicon oxide layer by generating a protective solid by-product on the surface of the silicon oxide layer has been developed.

The protective solid by-product formed on the surface of the silicon oxide layer is a kind of salt, and is known to be generated at a temperature of room temperature to 80°C. Therefore, it is necessary to perform a silicon etching process at a substrate temperature of room temperature to 80° C. in order to continue to generate a protective solid by-product in the silicon oxide film. After the silicon layer is etched, it is necessary to perform post-heat treatment at a substrate temperature of about 90° C. or higher in order to sublimate the protective solid by-product on the silicon oxide layer.

If the silicon layer is selectively etched in the case where silicon and the silicon oxide film coexist using this method, a protective by-product is generated on the surface of the silicon oxide layer at a low temperature, which is disadvantageous in terms of fume. In addition, if the post-heat treatment is performed at a substrate temperature of 90° C. or higher, the protective by-product is removed, but a loss of the silicon oxide layer may also occur.

An object of the present invention is to provide a method for selectively etching a silicon layer without generating and maintaining a protective by-product on the surface of a silicon compound layer such as a silicon oxide layer or a silicon nitride layer.

In order to solve the above problems, the substrate processing method according to an embodiment of the present invention selectively etches a silicon layer in a substrate including a silicon layer, and a silicon compound layer including at least one of a silicon oxide layer and a silicon nitride layer. As a substrate processing method, the method includes a plasma etching step of selectively etching the silicon layer by converting an etching gas containing nitrogen trifluoride and hydrogen into a plasma, wherein the plasma etching step is a protective property of the silicon compound layer surface It is characterized in that it is carried out at a temperature higher than the solid by-product formation temperature.

As a result of carrying out many studies, the inventors of the present invention performed plasma etching using an etching gas composed of nitrogen trifluoride and hydrogen at a temperature higher than the temperature of generating protective solid by-products on the surface of a silicon compound layer such as a silicon oxide layer or a silicon nitride layer. When carried out, it was found that the silicon layer can be selectively etched with a high etch selectivity without generating a protective by-product on the surface of the silicon compound layer.

The plasma etching step is preferably performed at a substrate temperature of 90 ~ 150 ℃. The etching of the silicon compound layer may be suppressed in the substrate temperature range.

The plasma etching step is more preferably performed at a substrate temperature of 100 ~ 120 ℃. The silicon layer may be etched with a high etch depth with a high selectivity in the substrate temperature range.

The plasma etching step is preferably performed under the condition that hydrogen gas is 74 to 90% of the total volume of the etching gas. In the above range, the silicon layer may be etched with a high selectivity.

In order to solve the above problems, the substrate processing method according to an embodiment of the present invention selectively etches a silicon layer in a substrate including a silicon layer, and a silicon compound layer including at least one of a silicon oxide layer and a silicon nitride layer. A substrate processing method comprising: (a) plasma etching an etching gas containing nitrogen trifluoride and hydrogen to selectively etch the silicon layer; (b) performing purging and pumping to discharge the etching product of step (a) to the outside of the reaction chamber, wherein step (a) is performed at a temperature higher than the protective solid byproduct formation temperature on the surface of the silicon compound layer It is characterized in that the unit cycle including the steps (a) and (b) is performed twice or more.

In the case of the cyclic method as in this embodiment, it is easy to discharge the reaction product generated by the reaction of the etching gas and silicon in the plasma etching step, so that silicon can be continuously etched.

The substrate processing method according to the present invention performs plasma etching at a temperature higher than the protective solid by-product formation temperature of the surface of the silicon compound layer, such as a silicon oxide layer or a silicon nitride layer, without generating and maintaining a protective by-product on the surface of the silicon compound layer. The silicon layer may be selectively etched.

In addition, in the substrate processing method according to the present invention, since the protective solid by-product itself is not generated or the protective solid by-product is removed immediately after generation, compared to the method of performing plasma etching while generating the protective solid by-product on the surface of the silicon compound layer, fume It is advantageous in terms of (Fume), and post-heat treatment to remove protective solid by-products can be omitted.

1A schematically shows a method for selectively etching a silicon layer according to an embodiment of the present invention.
FIG. 1B schematically illustrates the selective etching of the silicon layer of FIG. 1A.
2A schematically shows a method for selectively etching a silicon layer according to another embodiment of the present invention.
FIG. 2B schematically shows the selective etching of the silicon layer of FIG. 2A and the discharge of etching products.
3 is a graph showing the etching selectivity of the silicon layer to the silicon oxide layer according to the substrate temperature.
4 is a graph showing the etching selectivity of the silicon layer to the silicon oxide layer according to the hydrogen ratio of the etching gas.
5 is a graph showing the etching selectivity of the silicon layer to the silicon nitride layer according to the hydrogen ratio of the etching gas.

Hereinafter, preferred embodiments of the selective etching method using plasma according to the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily carry out the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be embodied in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout. The sizes and relative sizes of layers and regions in the drawings may be exaggerated for clarity of description.

Reference to an element or layer to be “on” or “on” another element or “over” includes not only directly on the other element or layer, but also intervening other layers or other elements. On the other hand, reference to an element "directly on" or "immediately on" indicates that there are no intervening elements or layers intervening. In addition, when it is described that a component is "connected", "coupled" or "connected" to another component, the components may be directly connected or connected to each other, but other components are "connected" between each component. It should be understood that each component may be “interposed” or “connected”, “coupled” or “connected” through another component.

Spatially relative terms "below", "lower", "above", "upper", etc. facilitate a correlation between one element or components and another element or components as shown in the drawings. can be used to describe Spatially relative terms should be understood as terms including different directions of the device during use or operation in addition to the directions shown in the drawings. For example, when an element shown in the figures is turned over, an element described as "below" another element may be placed "above" the other element. Accordingly, the exemplary term “below” may include both directions below and above.

The terminology used herein is for the purpose of describing the embodiments, and thus is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, "comprises" and/or "comprising" does not exclude the presence or addition of one or more other components, steps, acts and/or elements in a recited element, step, operation and/or element. .

1A schematically shows a method for selectively etching a silicon layer according to an embodiment of the present invention. FIG. 1B schematically shows the selective etching of the silicon layer of FIG. 1A , and in describing the method of selectively etching the silicon layer according to FIG. 1A , reference will be made to FIG. 1B .

Referring to FIG. 1A , the illustrated method of selectively etching a silicon layer includes a substrate preparation step S110 and a plasma etching step S120 .

In the substrate preparation step ( S110 ), a substrate including a silicon layer 110 and a silicon compound layer 120 including at least one of a silicon oxide layer and a silicon nitride layer is prepared.

For example, a substrate in which a silicon oxide (and/or silicon nitride) pattern is formed on a silicon substrate and a part of the silicon substrate is exposed may be provided.

As another example, a silicon layer is formed on a substrate of a material different from silicon, a silicon oxide (and/or silicon nitride) pattern is formed on the silicon layer, and a substrate in which a part of the silicon layer is exposed. can

The silicon layer 120 or the silicon compound layer 120 of the substrate may be formed in a chamber separate from the chamber in which the silicon layer is selectively etched. As another example, the silicon compound layer 120 may be formed in a chamber in which the silicon layer is selectively etched.

In FIG. 1B , a silicon oxide layer 120 having a specific pattern is formed on the silicon layer 110 , and the silicon layer 110 is exposed between the silicon oxide patterns.

Next, in the plasma etching step ( S120 ), an etching gas (NF ₃ +H ₂ ) containing nitrogen trifluoride and hydrogen is supplied into the reaction chamber to selectively etch the silicon layer. At this time, the etching gas is plasmaized remotely or in the reaction chamber to react with the silicon of the silicon layer to cause etching.

The reaction between the plasmaized or ionized etching gas and silicon is as follows.

5NF ₃ + 9H ₂ + 3Si → 3SiF ₄ + 3HF +5NH ₃

In the present invention, the plasma etching step (S120) is performed at a temperature higher than the protective solid by-product generation temperature on the surface of the silicon compound layer. As mentioned in the prior art, a protective solid by-product formed on the surface of a silicon compound layer such as a silicon oxide layer is a kind of salt, and is known to be generated at a temperature of room temperature to 80°C. Therefore, a temperature higher than the protective solid by-product formation temperature of the surface of the silicon compound layer is, for example, a substrate temperature of 80° C. or higher.

As can be seen in FIG. 3 below, when plasma etching is performed at a temperature higher than the protective solid by-product formation temperature on the surface of the silicon compound layer, any protective solid by-product is not generated on the surface of the silicon compound layer or is removed immediately after formation. It is possible to selectively etch the silicon layer at a selectivity. In the present invention, "a protective solid by-product is not produced" is a concept that includes a case in which the protective solid by-product itself is not produced and a case in which the protective solid by-product is removed immediately after formation.

In addition, the substrate processing method according to the present invention is advantageous in terms of fume. Fume refers to fluorine (F) and fluorine compounds remaining on the substrate without etching byproducts being completely volatilized by heat. Examples of fumes include NH ₄ F or NH ₂ F ₂ in particulate form, and may originate from a protective solid by-product. In the case of such fumes, it may cause contamination of the surface of the membrane or the surface of equipment, and also affect the reliability of the fine pattern. In the present invention, also, in the substrate processing method according to the present invention, since the protective solid by-product itself is not generated or is removed immediately after generation, it is possible to lower the probability of fumes.

On the other hand, plasma etching using nitrogen trifluoride and hydrogen plasma is preferably performed at a substrate temperature of 90 ~ 150 ℃. At a substrate temperature of 90° C. or higher, a protective solid by-product may not be generated on the surface of a silicon compound layer such as a silicon oxide layer more stably. However, when the substrate temperature exceeds 150° C., the etching amount of the silicon layer becomes too small, and the etching selectivity may become meaningless.

More preferably, plasma etching using nitrogen trifluoride and hydrogen plasma is more preferably performed at a substrate temperature of 100 to 120°C. In the above temperature range, the silicon layer can be etched with a high etching selectivity of 500 or more of the silicon layer to the silicon compound layer through the extremely low etching depth of the silicon compound layer, and an appropriate silicon layer etching depth can be obtained.

In addition, the plasma etching using nitrogen trifluoride and hydrogen plasma is preferably performed under the condition that hydrogen gas is 74 to 90% of the total volume of the etching gas. If the ratio of hydrogen gas is less than 74% by volume, etching of the silicon compound layer may occur and the etching selectivity may not be high. If the ratio of hydrogen gas exceeds 90% by volume, the etching amount of the silicon layer may be too insufficient. there is.

On the other hand, in plasma etching using nitrogen trifluoride and hydrogen plasma, it is preferable that an inert gas such as argon gas (Ar) is supplied into the reaction chamber before and if necessary, together with the supply of the etching gas. The inert gas may serve as a plasma ignition gas, and the etching rate of the silicon layer may be adjusted according to the amount of gas.

2A schematically shows a method for selectively etching a silicon layer according to another embodiment of the present invention. FIG. 2B schematically shows the selective etching of the silicon layer of FIG. 2A and discharge of the etching product, and FIG. 2B will be referred to in describing the selective etching method of the silicon layer of FIG. 2A .

Referring to FIG. 2A , the illustrated substrate processing method includes a substrate preparation step S210 , a plasma etching step S220 , a purge step S230 , and a pumping step S240 . Also, referring to FIG. 2A , when the plasma etching step ( S220 ), the purge step ( S230 ), and the pumping step ( S240 ) are unit cycles, this unit cycle is repeated.

In the substrate preparation step ( S210 ), a substrate including a silicon layer 110 and a silicon compound layer 120 including at least one of a silicon oxide layer and a silicon nitride layer is prepared.

In the plasma etching step ( S120 ), the silicon layer is selectively etched by turning an etching gas containing nitrogen trifluoride and hydrogen into plasma remotely or in a reaction chamber. In this case, the plasma etching is performed at a temperature higher than the temperature at which the protective solid by-product is generated on the surface of the silicon compound layer.

(c) In the purge step (S230), in a state in which the plasma is turned off, only an inert gas such as argon gas (Ar), nitrogen gas (N ₂ ), etc. is supplied into the reaction chamber to accumulate SiF ₄ and The same etch product flows out of the trench.

Thereafter, in the pumping step, pumping is performed without gas supply to pump all by-products and gases in the reaction chamber.

A trench having a large aspect ratio may be formed by selective etching of the silicon layer by plasma. In this case, according to the cyclic method in which the unit cycle is repeated, the etching product ( 130 in FIG. 1B ) accumulated in the trench can be more smoothly discharged, so that the silicon layer can be continuously etched.

As described above, the substrate processing method according to the present invention performs plasma etching using nitrogen trifluoride and hydrogen plasma at a temperature higher than the protective solid by-product generation temperature, thereby forming a protective solid by-product on the surface of the silicon oxide layer or silicon nitride layer. It is possible to selectively etch the silicon layer without creating and maintaining it. Accordingly, the present invention is advantageous in terms of fume compared to a method of performing plasma etching while generating a protective solid by-product on the surface of the silicon compound layer, and post-heat treatment for removing the protective solid by-product can be omitted.

Hereinafter, preferred examples are presented to help the understanding of the present invention. However, the following examples are only provided for easier understanding of the present invention, and the contents of the present invention are not limited by the following examples.

3 is a graph showing the etching selectivity of the silicon layer to the silicon oxide layer according to the substrate temperature.

In FIG. 3 , the silicon layer was formed of a polysilicon layer and denoted as POLY. And, in FIG. 3, the silicon oxide layer was formed by thermal oxidation and was denoted by TOX.

In FIG. 3 , the ratio of hydrogen gas (H ₂ ) in the etching gas (NF ₃ +H ₂ ) supplied to the inside of the reaction chamber (H ₂ /(NF ₃ +H ₂ )) is fixed to 74% by volume % of the substrate The etching depth (Å) of the silicon layer and the etching depth (Å) of the silicon oxide layer were measured while the temperature was changed from 80° C. to 150° C., and based on this, the etching selectivity of the silicon layer to the silicon oxide layer (POLY/TOX SEL) was measured. ) was calculated and shown. For example, at a substrate temperature of 100° C., the etch depth of the polysilicon layer was measured to be about 370 Å, and the etch depth of the silicon oxide layer was measured to be 0.4 Å. Accordingly, the etch selectivity of the silicon layer to the silicon oxide layer can be calculated as 370 Å/0.4 Å = 925.

Meanwhile, at a substrate temperature of 80° C., a solid by-product was present on the surface of the silicon oxide layer, and the etch depth of the silicon oxide layer was measured after the solid by-product was removed. The presence of solid by-products on the surface of the silicon compound layer is undesirable in terms of selective etching because it can be considered that etching is also performed on the silicon compound considering that such solid by-products must be removed.

Referring to FIG. 3 , when the substrate temperature was 80° C., etching was also performed on the silicon oxide layer, and thus the etching selectivity of the silicon layer to the silicon oxide layer was not high.

On the other hand, when the substrate temperature is 90° C. or higher, the etching depth of the silicon oxide layer is very small, and when the substrate temperature is 100° C. or higher, it can be seen that the etching depth of the silicon oxide layer is almost absent. The small etching depth of the silicon oxide layer advantageously increases the etching selectivity of the silicon layer to the silicon oxide layer.

In particular, referring to FIG. 3 , when the substrate temperature was 100 to 120° C., the etching selectivity of the silicon layer to the silicon oxide layer was particularly high. This is related to the etch depth of the silicon layer. Referring to FIG. 3 , it can be seen that there is no significant difference in the etching depth of the silicon layer until the substrate temperature is 100° C., but when the substrate temperature is higher than 100° C., the etching depth of the silicon layer gradually decreases. Accordingly, in order to obtain a sufficient etching depth of the silicon layer while having a high etching selectivity of the silicon layer to the silicon oxide layer, it is preferable to perform the etching at a substrate temperature of 100 to 120°C.

In FIG. 3 , in a state where the ratio of hydrogen gas (H ₂ /(NF ₃ +H ₂ )) of the etching gas supplied into the reaction chamber is fixed to 74% by volume%, the silicon layer to the silicon oxide layer according to the change in the substrate temperature of etch selectivity. Although not shown, in the state where the ratio of hydrogen gas (H ₂ /(NF ₃ +H ₂ )) in the etching gas supplied into the reaction chamber is fixed to 90% by volume %, the silicon to the silicon oxide layer according to the change in the substrate temperature Similar results were also found when the layer etch selectivity was evaluated. In addition, in a state where the ratio of hydrogen gas in the etching gas (H ₂ /(NF ₃ +H ₂ )) was fixed to 74% and 90% by volume%, the etching selectivity of the silicon layer to the silicon nitride layer according to the change in the substrate temperature Changes were also similar.

4 is a graph showing the etching selectivity of the silicon layer to the silicon oxide layer according to the hydrogen ratio of the etching gas.

In FIG. 4 , the silicon layer was formed of a polysilicon layer and denoted as POLY. And, in FIG. 4 , the silicon oxide layer was formed by thermal oxidation and was denoted by TOX.

In FIG. 4, the ratio (H ₂ /(NF3+H2)) of the hydrogen gas (H ₂ ) among the etching gas (NF ₃ +H ₂ ) supplied into the reaction chamber in a state where the substrate temperature is fixed at 100° C. is expressed as a volume % The etch depth (Å) of the silicon layer and the etch depth (Å) of the silicon oxide layer were measured while changing from 23% to 100%, and based on this, the etch selectivity of the silicon layer to the silicon oxide layer (POLY/TOX SEL) was calculated indicated.

Meanwhile, at a substrate temperature of 80° C., a solid by-product was present on the surface of the silicon oxide layer, and the etch depth of the silicon oxide layer was measured after the solid by-product was removed.

Referring to FIG. 4 , the ratio of hydrogen gas (H ₂ ) in the etching gas (NF ₃ +H ₂ ) made of nitrogen trifluoride and hydrogen gas is up to 50% by etching the silicon oxide layer to the silicon layer by etching the silicon oxide layer. etch selectivity was not very high.

However, when the ratio of hydrogen gas (H ₂ ) in the etching gas (NF ₃ +H ₂ ) is 74% to 90%, the silicon oxide layer is hardly etched, and thus the silicon layer is etched with respect to the silicon oxide layer. The selection ratio was very high.

As the ratio of hydrogen gas in the etching gas increases, the etching depth of the silicon layer also tends to decrease, but when the ratio of hydrogen gas in the etching gas is in the range of 74 to 90%, the etching depth of the silicon layer is similar.

However, when the ratio of hydrogen gas (H ₂ ) exceeds 90% or when the ratio of hydrogen gas (H ₂ ) is 100%, the amount of fluorine in the etching gas is too small or does not contain fluorine in the etching gas. Therefore, the silicon layer was also almost not etched.

Based on the above, a high etching selectivity can be obtained when the ratio of hydrogen gas (H ₂ ) in the etching gas (NF ₃ +H ₂ ) consisting of nitrogen trifluoride and hydrogen gas is 74% to 90% by volume%. there is.

5 is a graph showing the etching selectivity of the silicon layer to the silicon nitride layer according to the hydrogen ratio of the etching gas.

In FIG. 5 , the silicon layer was formed of a polysilicon layer and was denoted as POLY. And, in FIG. 5, the silicon nitride layer was formed by vapor deposition and was denoted by SiN.

Referring to FIG. 5 , as in the case of FIG. 4 , when the ratio of hydrogen gas (H ₂ ) in the etching gas (NF ₃ +H ₂ ) made of nitrogen trifluoride and hydrogen gas is 50%, etching of the silicon nitride layer exists. did The etching selectivity of the silicon layer to the silicon nitride layer was not very high by the etching of the silicon nitride layer.

On the other hand, when the ratio of hydrogen gas (H ₂ ) in the etching gas (NF ₃ +H ₂ ) is 74% to 90% by volume, the silicon nitride layer is hardly etched while the silicon layer is etched smoothly. As a result, the etch selectivity of the silicon layer to silicon nitride was very high. However, in the case of FIG. 5 as in the case of FIG. 4 , when the ratio of hydrogen gas (H ₂ ) is 100%, the silicon layer is also not etched.

4 and 5, in order to maximize the etching selectivity of the silicon layer to the silicon compound layer, hydrogen gas (H ₂ ) of the etching gas (NF ₃ +H ₂ ) made of nitrogen trifluoride and hydrogen gas It can be seen that it is preferable to make the ratio of 74% to 90% by volume%.

In the above, an embodiment in which only a silicon layer and a silicon oxide layer exist and an embodiment in which only a silicon layer and a silicon nitride layer exist have been described. It is obvious that it can be applied to existing examples as well.

In the above, although the embodiment of the present invention has been mainly described, various changes or modifications may be made at the level of those skilled in the art. Accordingly, it will be understood that such changes and modifications are included within the scope of the present invention without departing from the scope of the present invention.

110: silicon layer
120: silicon compound layer
130: etching product

Claims (8)

A substrate processing method for selectively etching a silicon layer on a substrate including a silicon layer, a silicon compound layer including at least one of a silicon oxide layer and a silicon nitride layer,
The method includes a plasma etching step of selectively etching the silicon layer by plasmaizing an etching gas containing nitrogen trifluoride and hydrogen,
The plasma etching step is a substrate processing method, characterized in that it is performed at a temperature higher than the protective solid by-product generation temperature of the surface of the silicon compound layer.
According to claim 1,
The plasma etching step is a substrate processing method, characterized in that performed at a substrate temperature of 90 ℃ or more.
According to claim 1,
The plasma etching step is a substrate processing method, characterized in that performed at a substrate temperature of 100 ~ 120 ℃.
According to claim 1,
The plasma etching step is a substrate processing method, characterized in that the hydrogen gas is performed under the condition of 74 to 90% of the total volume of the etching gas.
A substrate processing method for selectively etching a silicon layer on a substrate including a silicon layer, a silicon compound layer including at least one of a silicon oxide layer and a silicon nitride layer,
(a) plasma etching an etching gas containing nitrogen trifluoride and hydrogen to selectively etch the silicon layer;
(b) performing purging and pumping to discharge the etching product of step (a) to the outside of the reaction chamber,
The step (a) is carried out at a temperature higher than the protective solid by-product formation temperature on the surface of the silicone compound layer,
A method for processing a substrate, characterized in that the unit cycle including the steps (a) and (b) is performed twice or more.
6. The method of claim 5,
The step (a) is a substrate processing method, characterized in that carried out at a substrate temperature of 90 ~ 150 ℃.
6. The method of claim 5,
The step (a) is a substrate processing method, characterized in that carried out at a substrate temperature of 100 ~ 120 ℃.
6. The method of claim 5,
The step (a) is a substrate processing method, characterized in that the hydrogen gas is performed under the condition of 74 to 90% of the total volume of the etching gas.

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