JPH08264510A - Method and device for etching silicon nitride film - Google Patents

Abstract

PURPOSE: To set the selective ratio of a silicon nitride film to a silicon substrate or a silicon oxide film at a relatively high value in the case of removing the silicon nitride film on the silicon substrate or the silicon oxide film by selective etching by using CDE. CONSTITUTION: In the case of removing a part of or the whole silicon nitride film formed on a silicon substrate or a silicon oxide film, mixed gas, which is composed of a gas containing fluorine, oxygen gas and a gas containing hydrogen atoms, is introduced into a discharge part 2 to generate plasma, and only the radical of the plasma active species is introduced into a process chamber 5 wherein the silicon substrate is stored. Thus, the silicon nitride film on the silicon substrate is selectively removed by etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for etching a silicon nitride film used for manufacturing a semiconductor device, and more particularly to a method for selectively etching a silicon nitride film with respect to a silicon substrate or a silicon oxide film. Regarding the device.

[0002]

2. Description of the Related Art Dry etching, which is used as a technique for finely processing an insulating film or a conductive film to be etched formed on a semiconductor wafer into a desired pattern, is roughly classified into RIE (reactive ion etching). CD
It becomes E (chemical dry etching).

In RIE, charged particles generated in plasma are accelerated by a self-bias and are incident on a film to be etched, so that the underlying layer of the film to be etched is damaged by ion implantation such as contamination or crystal disorder. This hinders the production of fine elements.

Since the CDE does not use charged particles to cause the above-mentioned disadvantages, the etching rate of the silicon nitride film is slower than that of silicon, so that the selection ratio of the silicon nitride film to silicon is relatively large. Get smaller. As a result, conventionally, there has been a problem that a large amount of underlying silicon is etched during overetching when removing a silicon nitride film formed on silicon.

Further, in the conventional CDE, the selection ratio of the silicon nitride film to the silicon oxide film is about 5, but when the base of the silicon nitride film is very thin like a gate insulating film, the silicon nitride film is formed. There was a problem that the underlying thin silicon oxide film was removed by etching during the over etching.

[0006]

As described above, in the conventional etching method using CDE, since the selection ratio of the silicon nitride film to the silicon substrate or the silicon oxide film is relatively small, the etching method on the silicon substrate or the silicon oxide film is performed. When removing the silicon nitride film, there has been a problem that a large amount of underlying silicon is etched during over-etching, or the underlying thin silicon oxide film is removed by etching.

The present invention has been made to solve the above problems, and when the silicon nitride film on the silicon substrate or the silicon oxide film is selectively removed by using CDE, silicon or the silicon nitride film on the silicon oxide film is removed. An object of the present invention is to provide a silicon nitride film etching method and an etching apparatus capable of setting a relatively high film selection ratio.

[0008]

A method for etching a silicon nitride film according to the present invention includes a step of accommodating a semiconductor wafer having a silicon nitride film formed on a silicon substrate or a silicon oxide film in a processing chamber, and fluorine. Gas, oxygen gas, and a mixed gas containing a gas containing hydrogen atoms as constituent elements are introduced into the discharge part to generate plasma, and only radicals of plasma active species are introduced into the processing chamber, and the silicon nitride is used. And a step of selectively etching away part or all of the film.

The silicon nitride film etching apparatus of the present invention is installed inside a processing chamber for accommodating therein a semiconductor wafer on which a silicon nitride film is formed on a silicon substrate or a silicon oxide film. , A stage for mounting the semiconductor wafer on its upper surface to adjust its temperature, a gas containing fluorine, an oxygen gas, and a mixed gas having a constituent element of a gas containing hydrogen atoms are introduced, and plasma is introduced. And a radical introduction unit that takes out only radicals of plasma active species from the discharge unit and introduces the radicals into the inside of the processing chamber.

[0010]

According to the etching method and the etching apparatus of the present invention, a mixed gas containing a gas containing fluorine, an oxygen gas, and a gas containing hydrogen atoms as constituent elements is introduced into the discharge part to generate plasma, thereby plasma activation. Only the radicals of the seeds are taken out and introduced into a processing chamber having therein a semiconductor wafer having a silicon nitride film formed on a silicon substrate or a silicon oxide film.

As a result, the CDE (Chemical Dry Etching) is performed inside the processing chamber, whereby a part or all of the silicon nitride film is selectively removed by etching with respect to the silicon substrate.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an example of a schematic configuration of a microwave CDE device used in the method for etching a silicon nitride film of the present invention.

In this CDE apparatus, a semiconductor wafer 6 and a stage 7 for mounting the semiconductor wafer 6 on the upper surface are housed inside the processing chamber 5. Stage 7 above
It has a temperature adjusting mechanism and can control the temperature of the semiconductor wafer 6.

A radical introduction port is provided on the upper surface of the processing chamber 5, and a gas exhaust port 8 is provided on the lower surface of the processing chamber 5. A transport pipe 3 for introducing a mixed gas of CF ₄ / O ₂ / H ₂ O used as a reaction gas is connected to the radical introducing port. Further, a discharge tube 2 is connected to the other end of the transport tube 3, and a reaction gas is introduced into the discharge tube 2 from a gas introduction port 1. A microwave waveguide 4 is connected to the discharge tube 2.

In the CDE device having the above structure, the reactive gas introduced from the gas inlet 1 is plasmatized to generate active species (ions, radicals), and the short-lived ions are deactivated in the transport pipe 3, Only radicals having a long life pass through the transport tube 3 and are introduced into the processing chamber 5, and react with the semiconductor wafer 6 to perform CDE. Then, the reacted gas is exhausted to the outside of the processing chamber 5 through the exhaust port 8.

As a modification of the radical introduction part in the above CDE apparatus, when a discharge part is provided directly above the processing chamber 5, the ions generated here and the radical ions are punched. Alternatively, the radicals may be blocked and the radicals alone may be introduced into the processing chamber 5.

FIG. 2 shows a silicon nitride film (SiN), silicon (Si), and silicon oxide film (Si) obtained by the first embodiment of the CDE method using the CDE apparatus shown in FIG.
A characteristic example of the etching rate of O ₂ ) will be shown.

In the first embodiment, the high frequency power (Power) = 700 W and the pressure (Pr) are set as the conditions of CDE.
ess. ) = 70 Pa, each flow rate of reaction gas CF ₄ / O ₂ = 270/270 sccm, stage temperature (Tem)
p. ) = 25 ° C. and the amount of H ₂ O added was changed.

The etching rates of Si and SiO ₂ monotonically decrease as the amount of H ₂ O added increases, but the etching rate of SiN shows that the amount of H ₂ O added is 10%.
% (That is, H ₂ O = 60 sccm) takes the maximum value.

Due to such a difference in etching rate, the silicon nitride film is selectively removed by etching with respect to the silicon substrate and the silicon oxide film. That is, as described above, CF ₄ gas and O ₂ gas to less mixed gas than the total flow rate of the amount of H ₂ O as a mixed gas H ₂ O was added the CF ₄ gas and O ₂ gas to the discharge portion By introducing it to generate plasma and introducing only radicals of plasma active species into the etching treatment chamber, a part or all of the silicon nitride film formed on the silicon substrate or the silicon oxide film is selectively selected. Can be removed by etching.

FIG. 3 shows that H ₂ O has the same characteristics as those shown in FIG.
A characteristic example of the emission intensity of the active species in the plasma emission part when the addition amount is changed is shown. The emission intensity of F radicals and O radicals decreases as the amount of H ₂ O added increases, and the emission intensity of H radicals increases as the amount of H ₂ O added increases. The reason why the characteristics shown in FIG. 2 are obtained from these results is considered as follows.

It is considered that etching of Si and SiO ₂ proceeds only by the F radicals. However, by increasing the amount of H ₂ O added, the H radicals generated from H ₂ O are converted to the F radicals generated from CF _4. Scavenging (cleaning), HF is generated. By this reaction, the amount of F radicals supplied to the object to be processed decreases, so that Si and S
The etching rate of iO ₂ decreases as the amount of H ₂ O added increases.

On the other hand, SiN is etched by the reaction represented by the following equation (1). Si ₃ N ₄ + 12F ^* ↑ + 12H ^* ↑ → 3 (SiF ₄ ) ↑ + 4 (NH ₃ ) ↑ (1) That is, SiN etching proceeds by both F radicals and H radicals. As described above, when the amount of H ₂ O added increases, the amount of F radicals decreases and the amount of H radicals increases, but the etching rate of SiN is
Under conditions that balance the amount of H radicals present (in the example shown in FIG. 2, H ₂ O addition amount = 60 sccm),
It is considered to be the maximum.

FIG. 4 shows SiN, Si, obtained by the second embodiment of the CDE method using the CDE apparatus shown in FIG.
A characteristic example of the etching rate of SiO ₂ will be shown. This second
In the embodiment, the high frequency power = 700 as the CDE condition.
The flow rate ratio of CF ₄ / O ₂ was changed with W, pressure = 70 Pa, H ₂ O addition amount = 60 sccm fixed, and the total flow rate of CF ₄ and O ₂ = 540 sccm.

As can be seen from FIG. 4, the etching rates of SiN, Si and SiO ₂ decrease as the O ₂ flow rate increases. When comparing SiN and Si, Si
In this case, the degree of decrease in etching rate (gradient of characteristics) is remarkable. As a result, when the O ₂ flow rate ratio is increased, the silicon nitride film can be removed by etching with a higher selection ratio with respect to the silicon substrate.

That is, as described above, as a mixed gas obtained by adding H ₂ O to CF ₄ gas and O ₂ gas, a mixed gas in which the flow rate of CF ₄ gas is smaller than that of O ₂ gas is introduced into the discharge section. By generating plasma and introducing only radicals of plasma active species into the etching chamber, part or all of the silicon nitride film formed on the silicon substrate or silicon oxide film is selectively removed by etching. It becomes possible to do.

The reason why the characteristics shown in FIG. 4 are obtained is considered as follows. As the O ₂ flow rate ratio is increased, the surfaces of both SiN and Si are easily oxidized, so that the etching rate is reduced. But S
Comparing iN and Si, Si has a characteristic that it is more likely to be oxidized, so that the etching rate is more significantly reduced. Due to this difference in characteristics, the silicon nitride film can be removed by etching with a high selection ratio with respect to the silicon substrate by increasing the O ₂ flow rate ratio. In this embodiment, C
When F ₄ / (CF ₄ + O ₂ ) is 10%, SiN is added to S
It could be etched at a rate 30 times that of i.

In the above embodiment, it is considered that the same effect can be obtained even if the total flow rate of the mixed gas is changed to about 1000 sccm. FIG. 5 shows C shown in FIG.
A characteristic example of the etching rates of SiN, Si, and SiO ₂ obtained by the third embodiment of the CDE method using the DE device will be shown.

In the third embodiment, the high frequency power = 700 W, pressure = 70 Pa, CF ₄ /
O ₂ flow rate = 270/270 sccm, H ₂ O addition amount =
It was fixed at 60 sccm and the stage temperature (temperature of the object to be processed) was changed.

As can be seen from FIG. 5, Si and SiO ₂ are
While the etching rate monotonously increases as the temperature rises, SiN significantly lowers the etching rate at a temperature of 50 ° C. or higher. Therefore, in order to selectively remove the silicon nitride film by etching with respect to the silicon substrate and the silicon oxide film, the temperature of the object to be processed is set to 5
It is necessary to keep the temperature below 0 ° C. In addition, due to the performance of the device,
The above characteristics were confirmed in the range where the temperature of the object to be treated was -5 ° C or higher.

The reason why the characteristics shown in FIG. 5 are obtained is considered as follows. Si and SiO ₂ are etched only by the F radicals, but by increasing the temperature, the reaction probability between the F radicals and the object to be treated increases, and the etching rate monotonically increases. On the other hand, Si
Both F radicals and H radicals contribute to the etching reaction of N, the reaction rate of each radical varies depending on the temperature, and the etching reaction does not proceed unless it is within an appropriate temperature range.

FIG. 6 shows the relationship between the temperature of the object to be treated and the elemental composition ratio of the SiN surface after the etching treatment in the third embodiment. As can be seen from FIG. 6, the composition ratio of F decreases and the composition ratio of O sharply increases at a temperature of 50 ° C. or higher. As a result, the oxidation reaction of the surface of SiN becomes active at a temperature of 50 ° C. or higher, and it is considered that the etching rate of SiN sharply decreased.

FIG. 7 shows the FT-IR analysis result of the SiN surface etched by the method of the present invention. As can be seen from FIG. 7, an absorption peak believed to be due to NH ₄ ⁺ was observed, and a deposited (altered) layer was formed on the surface. This deposited layer can be removed by washing with water as described below, but from the rinsing water, as shown in Table 1,
NH ₄ ⁺ , F ⁻ , and Si are detected in a composition of approximately 2: 6: 1, and the deposited layer is considered to have a structure like (NH ₄ ) 2 SiF ₆ . This deposited layer is formed only on SiN, not on Si or SiO ₂ . Also, Si
The deposited layer on N does not contribute to the etching reaction of Si or SiO ₂ .

[0034]

[Table 1]

When the above-mentioned deposited layer on SiN becomes thick, the etching reaction of SiN is hindered. However, by removing this deposited layer by the method described below, the etching can be advanced again. Will be possible.

FIG. 8 shows the XPS analysis results before and after etching SiN by the method of the present invention, after washing with water, and after heating. As can be seen from FIG. 8, on the surface after etching, S
There is a chemical shift in the electron peaks of i _2p and N _1s , and a deposited layer is formed. No such chemical shift is observed after washing with water or after heating at 300 ° C., and the deposited layer can be easily removed by such treatment.

Next, an example in which the silicon nitride film having the structure as shown in FIG. 9A is actually etched by using the above-described silicon nitride film etching method will be described. FIG. 9 (a)
In the above, in the silicon substrate 11, a silicon nitride film 14 is formed on the upper surface of the silicon substrate 11 via the buffer oxide film 13, and the trench is RIE-processed using this silicon nitride film 14 as a mask.
2 is embedded.

In the step of etching the silicon nitride film 14 in this state, in the conventional etching method, the etching selection ratio of the silicon nitride film to silicon is
Since only about 0.3 can be obtained, after the silicon nitride film 14 is removed by etching, as shown by the dotted line in FIG. 9B, the embedded polycrystalline silicon 12 has a thickness of, for example, 870 nm.
A large amount will be etched to the depth of.

Next, the results of etching SiN by the method of the present invention will be shown. High frequency power = 7 for CDE
00 W, pressure = 70 Pa, each flow rate of CF ₄ / O ₂ = 224
/ 316sccm (total flow rate = 540sccm), H ₂
O addition amount = 60 sccm, stage temperature = 25 ° C. In this case, the etching selection ratio of the silicon nitride film to silicon is 9.

Under this condition, the silicon nitride film 14 having the structure shown in FIG. 9A was etched. The silicon nitride film had a thickness of 200 nm and was overetched by 30%. In this case, as shown by the solid line in FIG. 9B, the etching amount of the embedded polycrystalline silicon 12 after the silicon nitride film 14 is removed is 30 nm (870 nm in the conventional method), and the embedded polycrystalline silicon 12 is removed.
It was possible to greatly reduce the etching amount.

Even under this condition, the etching amount of the buried polycrystalline silicon 12 could be greatly reduced as compared with the conventional method, but a method of further reducing the etching amount will be described below.

The conditions for CDE are: high frequency power = 700 W,
Pressure = 70 Pa, CF ₄ / O ₂ flow rate = 140/400
sccm (total flow rate = 540 sccm), H ₂ O addition amount = 60 sccm, and stage temperature = 25 ° C. In this case, the etching selection ratio of the silicon nitride film to silicon is 30.

Under this condition, as described above, there is a phenomenon that the etching reaction does not proceed due to the influence of the deposited layer when the etching depth of the silicon nitride film 14 is 100 nm. Therefore, as shown in FIG. A 200 nm thick silicon nitride film cannot be removed by a single etching process. Therefore, a step of removing the deposited layer formed on the surface during the etching by washing with water or heat treatment as described above is required.

By this method, 3 is added to the silicon nitride film 14.
When 0% over-etching was performed, the silicon nitride film 14 could be completely removed by etching with almost no confirmed etching amount of the embedded polycrystalline silicon 12.

As described in detail above, the silicon nitride film is selectively etched with respect to silicon by CDE using a mixed gas composed of a gas containing fluorine, an oxygen gas, and a gas containing hydrogen atoms. Could be removed.

In each of the above embodiments, CF ₄ was used as the source gas for producing F ^* , but NF ₃ , S
Any gas containing F such as F ₆ , XeF and F ₂ may be used. In addition, in each of the above-mentioned embodiments, H is used as the gas containing H.
_{Although 2} O is used, any gas containing H such as H ₂ and NH ₃ may be used.

In each of the above embodiments, the pressure in the processing chamber is not limited to 70 Pa, and it has been confirmed that the same effect can be obtained even when the pressure is changed to 90 Pa, and it is about 1 Torr (approximately 133 Pa). It is thought that the same effect can be obtained even if it is changed to.

[0048]

As described above, according to the silicon nitride film etching method and etching apparatus of the present invention, the CD
When the silicon nitride film on the silicon substrate or the silicon oxide film is selectively removed by using E, the selection ratio of the silicon nitride film to the silicon or the silicon oxide film can be set relatively high.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of a CDE device used in a method for etching a silicon nitride film of the present invention.

FIG. 2 is an etching rate of H ₂ O of each object to be processed in the first embodiment of the method for etching a silicon nitride film according to the present invention.
The figure which shows the dependence of a flow volume.

FIG. 3 is a graph showing emission intensity H of each radical in Example 1.
_The figure which shows the dependency of ₂ O flow rate.

FIG. 4 is a graph showing the etching rate CF ₄ of each object in the second embodiment of the silicon nitride film etching method of the present invention.
/ (CF ₄ + O ₂₎ shows the dependence of the flow ratio.

FIG. 5 is a diagram showing the temperature dependence of the etching rate of each object to be processed in the third embodiment of the silicon nitride film etching method of the present invention.

FIG. 6 is a graph showing the processing temperature dependence of the surface element composition ratio after etching in the third embodiment.

FIG. 7 is a diagram showing the FT-IR analysis result of the SiN surface after etching in the method of the present invention.

FIG. 8 is a diagram showing an XPS analysis result of the SiN surface after etching in the method of the present invention.

FIG. 9 is a cross-sectional view schematically showing an example of the structure of a target object to which the method of the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactant gas inlet, 2 ... Discharge tube, 3 ... Transport tube, 4 ... Microwave waveguide, 5 ... Processing chamber, 6 ... Semiconductor wafer, 7
... stage, 8 ... exhaust port, 11 ... silicon substrate, 12 ...
Buried polycrystalline silicon, 13 ... Buffer oxide film, 14 ...
Silicon nitride film.

Claims (8)

[Claims] 1. A process of accommodating a semiconductor wafer having a silicon nitride film formed on a silicon substrate or a silicon oxide film in a processing chamber, a gas containing fluorine, an oxygen gas, and a gas containing hydrogen atoms. A mixed gas as a constituent element is introduced into the discharge part to generate plasma, only radicals of plasma active species are introduced into the processing chamber, and part or all of the silicon nitride film is selectively removed by etching. An etching method for a silicon nitride film, comprising: an etching step. 2. The method of etching a silicon nitride film according to claim 1, wherein the gas containing hydrogen is H 2.
_A method for etching a silicon nitride film, characterized in that any one of ₂ O, H ₂ and NH ₃ is used. 3. The method for etching a silicon nitride film according to claim 1, further comprising the step of removing a deteriorated deposition layer formed on the surface of the silicon nitride film during the etching. 4. The method for etching a silicon nitride film according to claim 3, wherein the step of removing the altered deposition layer formed on the surface of the silicon nitride film is performed by washing with water or heat treatment. 5. When selectively removing part or all of a silicon nitride film formed on a silicon substrate or a silicon oxide film in a processing chamber by etching and removing, H ₂ O is added to CF ₄ gas and O ₂ gas. H ₂ as a mixed gas containing
A mixed gas, in which the amount of O added is less than the total flow rate of CF ₄ gas and O ₂ gas, is introduced into the discharge part to generate plasma, and only radicals of plasma active species are introduced into the processing chamber. A method for etching a silicon nitride film. 6. When a part or all of the silicon nitride film formed on the silicon substrate or the silicon oxide film is selectively removed by etching in the processing chamber, H ₂ O is added to CF ₄ gas and O ₂ gas. CF as a mixed gas containing
A silicon nitride film characterized in that a mixed gas having a flow rate of ₄ gas lower than that of O ₂ gas is introduced into a discharge part to generate plasma, and only radicals of plasma active species are introduced into the processing chamber. Etching method. 7. A processing chamber for accommodating therein a semiconductor wafer having a silicon nitride film formed on a silicon substrate or a silicon oxide film, and inside the processing chamber, the semiconductor wafer is mounted on the upper surface thereof. And a stage for adjusting the temperature thereof, a gas containing fluorine, an oxygen gas, and a mixed gas having a constituent element of a gas containing a hydrogen atom are introduced, and a discharge section for generating plasma, and the discharge section An etching apparatus for a silicon nitride film, comprising: a radical introducing unit for extracting only radicals of plasma active species and introducing the radicals into the processing chamber. 8. The etching apparatus for a silicon nitride film according to claim 7, wherein the radical introducing unit has a transport pipe arranged between the discharge unit and the radical introducing unit of the processing chamber. .