JP4153961B2 - Etching method of silicon - Google Patents

Description

  The present invention relates to a method for etching silicon on the surface of a substrate using a fluorine-based gas.

For example, Patent Documents 1 and 2 describe that silicon on the wafer surface is oxidized with ozone to form silicon oxide (Formula 1) and then etched using hydrofluoric acid. The hydrofluoric acid is evaporated by a hydrofluoric acid vapor generator and led to the wafer surface. Further, it is described that the wafer temperature is 50 ° C. or higher, preferably 60 ° C. or higher.
Patent Document 3, HF, and COF _2, etc. generated by causing a pressure near atmospheric pressure discharge fluoric gas such as CF _4, is reacted with water which had been mixed with CF ₄ or the like for further COF ₂ It is described that silicon oxide is etched (formula 3) by HF obtained in this manner (formula 2).
Si + 2O ₃ → SiO ₂ + 2O ₂ (Formula 1)
COF ₂ + H ₂ O → CO ₂ + 2HF (Formula 2)
SiO ₂ + 4HF + H ₂ O → SiF ₄ + 3H ₂ O (Formula 3)
Patent Document 4 describes that HF is obtained from humidified CF ₄ by atmospheric pressure plasma discharge, O ₃ is added thereto, and silicon oxide is etched.
Patent Document 5 describes that CF ₄ and O ₂ are discharged at atmospheric pressure to obtain radicals, which are led from a plasma space to a substrate at a temperature of 20 ° C. or 100 ° C. to etch single crystal silicon.
Patent Document 6 describes that humidified CF ₄ or dry CF ₄ is discharged at atmospheric pressure, and crystalline silicon is etched at a substrate temperature of 90 ° C.
JP 2003-264160 A JP 2004-55753 A JP 2000-58508 A JP 2002-270575 A Japanese Patent Laid-Open No. 04-358076 JP 2000-164559 A

In conventional silicon etching, the etching rate could not be increased so much. The inventor considered the reason as follows.
For example, in Patent Documents 1 and 2 listed above, hydrofluoric acid as an etchant is supplied to a substrate made of a wafer in the form of hydrofluoric acid from the beginning. Therefore, it is considered that only the etching reaction of the above equation 3 occurs on the surface of the substrate except the oxidation reaction of the above equation 1. In the reaction of Formula 3, water (H ₂ O) is newly generated as the silicon oxide becomes volatile SiF ₄ .

Here, when the substrate temperature is low, the newly generated water is condensed and dissolved in the condensed phase of hydrofluoric acid on the substrate surface. For this reason, as the etching reaction proceeds, the condensed phase grows and the thickness increases. On the other hand, ozone necessary for silicon oxidation can contribute to silicon oxidation only after it dissolves in the condensed phase and diffuses in the condensed phase and reaches the substrate surface. The rate of reaching the surface decreases. Therefore, the diffusion rate is limited in the ozone condensed phase, and the silicon oxidation rate is lowered.
In addition, a decrease in the hydrogen fluoride concentration in the condensed phase may also be a factor in reducing the rate.

  Conversely, when the substrate temperature is high, the problem of growth of the hydrofluoric acid condensed phase is eliminated, but on the other hand, as shown in FIG. 4, the partition coefficient between ozone and liquid decreases. That is, the higher the temperature, the more difficult it is for ozone to dissolve in the hydrofluoric acid condensed phase. Therefore, the rate of dissolution of ozone occurs, and the rate of silicon oxidation is also reduced.

Therefore, the substrate temperature has a value that peaks the silicon oxidation rate. Conventionally, a suitable substrate temperature has been around 60 ° C. As shown in FIG. 4, the distribution coefficient in the vicinity of 60 ° C. is about 0.1, which is a level at which only about 10% of the total ozone can be dissolved. However, from the necessity of suppressing the growth of the hydrofluoric acid condensed phase, 60 ° C. is the limit temperature, and it is difficult to lower the temperature further to increase the partition coefficient. In addition, since hydrofluoric acid water with a high concentration tends to evaporate more than water, the hydrofluoric acid concentration itself seems to decrease at higher temperatures.
Under such circumstances, in the conventional silicon etching, the silicon oxidation rate does not become a sufficient value even at the peak point, and the etching rate naturally has to be insufficient.

  In addition, as in Patent Document 5, etc., when etching is performed using radicals generated by plasma, if the distance between the plasma space and the substrate is too far, the radicals are deactivated before reaching the substrate. As a result, the etching rate is reduced. On the other hand, if the distance between the plasma space and the substrate is too close, the substrate may be damaged by the plasma. Therefore, the degree of freedom of the setting range of the separation distance between the plasma space and the substrate is small.

By the way, the reason why new water is generated by the etching reaction of Formula 3 is that a fluorine-based etching gas such as HF has hydrogen atoms. From the above consideration, the inventor has found that the presence of hydrogen atoms in the etching gas has a negative effect on silicon etching.
The present invention has been made based on the above findings,
In a method of etching a workpiece made of silicon,
By generating ozone as an oxidizing gas that can oxidize silicon, and by passing a gas containing fluorine-based raw material that is not reactive with silicon and water through a plasma space near atmospheric pressure separately from this ozone generation A fluorine-based reactive gas is generated, and the ozone and the fluorine-based reactive gas are sprayed on an object to be processed at a temperature of 10 ° C. to 50 ° C. ,
The fluorine-based reactive gas includes a non-radical fluorine-based intermediate gas selected from COF ₂ , CF ₃ OH, and F ₂ , and the ratio of the number of fluorine atoms (F) to the number of hydrogen atoms (H) is (F) /(H)>1.5 der is,
The fluorine-based intermediate gas reacts with water to generate HF as a fluorine-based etching gas having silicon oxide etching ability, and water is generated by etching reaction of silicon oxide with the fluorine-based etching gas. .
As a result, a generation reaction of a fluorine-based etching gas by the fluorine-based intermediate gas and water can be caused on the surface of the object to be processed. Even if water is generated during the etching reaction between the fluorine-based etching gas thus formed and silicon oxide formed by oxidizing the object to be processed, the water is consumed for the etching gasification reaction of a new fluorine-based intermediate gas. Can do. Therefore, it is not necessary to prevent the condensation of water generated during the etching reaction of silicon oxide, and the condensed phase grows on the surface of the object to be processed even if the object temperature is a low temperature of 10 ° C. to 50 ° C. Can be suppressed. The solubility of the oxidizing gas in the condensed phase can be improved by lowering the temperature of the workpiece, and the diffusion degree of the oxidizing gas in the condensed phase can be ensured by suppressing the growth of the condensed phase. In addition, the ratio of the number of hydrogen atoms (H) to the number of fluorine atoms (F) in the fluorine-based reactive gas mainly composed of a fluorine-based intermediate gas should be (F) / (H)> 1.5. Thus, water generated by the etching reaction can be reliably consumed by the etching gasification reaction of the fluorine-based intermediate gas, and the growth of the condensed phase can be reliably suppressed. As a result, the diffusivity of the oxidizing gas in the condensed phase can be more sufficiently ensured. As a result, the silicon oxidation rate can be improved, and consequently the etching rate can be improved.
In addition, by using a non-radical fluorine-based intermediate gas, the etching rate may be lowered or the object to be processed may be damaged depending on the separation distance between the reactive gas blowing portion and the object to be processed. This can be avoided, and the degree of freedom of design such as distance setting can be improved.
In order to obtain the first fluorine-based etching gas, water vapor may be added to the fluorine-based intermediate gas only at the beginning of the reaction. If the object to be processed is amorphous silicon, it is included in the object to be processed. Water may be obtained from hydrogen and the oxidizing gas, and the first fluorine-based etching gas may be obtained from the water and the fluorine-based intermediate gas. Alternatively, a fluorine-based etching gas may be supplied to the surface of the object to be processed separately from the fluorine-based intermediate gas only at the beginning, and the fluorine-based intermediate gas may be converted into an etching gas by water generated by the etching reaction.
Depending on the temperature of the object to be treated, water may evaporate and the hydrofluoric acid condensed phase may disappear, so in that case, the evaporated water should be supplemented by etching reaction or addition of water vapor to the supply gas. Is preferred.

The ratio of the number of fluorine atoms (F) to the number of hydrogen atoms (H) in the fluorine-based reactive gas is more preferably (F) / (H)> 3. Thereby, water (H ₂ O) can be consumed more reliably, and the growth of the condensed phase can be more reliably suppressed.
In addition, said ratio (F) / (H) can be measured as follows.
(1) The concentration of the fluorine-based intermediate gas in the fluorine-based reactive gas is measured with a Fourier transform infrared spectrometer (FTIR) to determine the number of hydrogen atoms (H) in the fluorine-based intermediate gas.
(2) A predetermined amount of the fluorine-based reactive gas is passed through water (alkaline water) and Ph is measured, and a change in hydrogen concentration ΔH before and after passing is obtained. This change in concentration is due to the HF generation reaction of the fluorine-based reactive gas with water, and from this, the number of fluorine atoms (F) in the fluorine-based reactive gas can be determined.
(3) The ratio (F) / (H) is calculated from the above (1) and (2).

The fluorine-based intermediate gas is preferably a fluorine-based molecule that does not contain hydrogen. For example, COF ₂ is preferable, but if it reacts with water to generate a fluorine-based etching gas such as HF, It may contain hydrogen such as CF ₃ OH or F ₂ .

The fluorine-based reactive gas is obtained by adding water in an amount such that a dew point is 10 ° C. to 40 ° C. (water vapor partial pressure 1.2282 kPa to 7.3844 kPa) to a fluorine-based raw material that is not reactive with silicon. It is preferable that the dew point fluorine-based source gas is obtained by passing it through a plasma space near atmospheric pressure. Thereby, a fluorine-based reactive gas containing abundant fluorine-based intermediate gas such as COF ₂ can be obtained. In addition, handling can be facilitated. In addition, when the input power of plasma discharge is relatively large, it is preferable to add oxygen in addition to adding water to the fluorine-based raw material.
Here, the vicinity of atmospheric pressure means a range of 0.5 bar to 2 bar, preferably a range of 0.9 to 1.1 bar.

A fluorine-containing raw material containing fluorine and not having reactivity with silicon is added with an amount of water such that the dew point is 10 ° C. to 40 ° C. (water vapor partial pressure 1.2282 kPa to 7.3844 kPa). A water addition step to obtain;
A plasma process for passing the low dew point fluorine-based source gas through a plasma space near atmospheric pressure;
A spraying step of spraying a reactive gas containing an oxidizing gas capable of oxidizing silicon and a gas that has undergone the above-described plasma forming step onto an object to be processed at a temperature of 10 ° C. to 50 ° C .;
Is preferably performed.
By the plasma treatment step, a fluorine-based reactive gas component containing a large amount of fluorine-based intermediate gas can be obtained from the fluorine-based raw material.

The oxidizing gas is preferably ozone. Thereby, the silicon which comprises a to-be-processed object can be oxidized reliably.
The oxidizing gas is preferably obtained by passing oxygen gas through an ozonizer. Thereby, high concentration ozone can be obtained as oxidizing gas.
It is preferable to increase the amount of ozone added as much as possible. When the fluorine-based intermediate gas is COF ₂ and the fluorine-based etching gas is HF, the addition flow rate of ozone must be at least the sum of the volume flow rate of COF _{2 and one half} of the volume flow rate of HF. Preferably, it is about twice that.

The oxidizing gas may be obtained by passing oxygen gas through a plasma space near atmospheric pressure.
This plasma space may be the same as or different from the plasma space for converting the low dew point fluorine-based source gas into plasma. In the case of the former, one plasma generation apparatus can be shared, and the apparatus configuration can be simplified. In the latter case, an oxidizing gas such as high-concentration ozone can be obtained, and the low dew point fluorine-based source gas can be efficiently converted to plasma.

A fluorine-based raw material that contains fluorine and has no reactivity with silicon, water in an amount such that the dew point is 10 ° C. to 40 ° C. (water vapor partial pressure of 1.2282 kPa to 7.3844 kPa), oxygen, Mixing step to obtain a mixed gas by mixing
A plasma process for obtaining a reactive gas by passing the mixed gas through a plasma space near atmospheric pressure;
A spraying step of spraying the reactive gas on an object to be processed at a temperature of 10 ° C. to 50 ° C .;
May be executed.
Thereby, in one plasma space, a fluorine-based intermediate gas can be obtained from the fluorine-based source gas, and an oxidizing gas can be obtained from the oxygen gas.

The present invention also relates to a method for etching a workpiece made of silicon,
A mixing step of mixing a fluorine raw material having no reactivity with silicon, an amount of water having a dew point of 10 ° C. to 40 ° C. with respect to the fluorine raw material, and obtaining a mixed gas;
A plasma process for generating a reactive gas by passing the mixed gas through a plasma space near atmospheric pressure;
A spraying step of spraying the reactive gas on an object to be processed at a temperature of 10 ° C. to 50 ° C .;
Is executed, the percentage of oxygen in the mixed gas, Ri 5～20Vol% der respect to the fluorine-based material,
The reactive gas is
(A) ozone as an oxidizing gas capable of oxidizing silicon;
(B) a non-radical fluorine-based intermediate gas selected from COF ₂ , CF ₃ OH, and F ₂ , and the ratio of the number of fluorine atoms (F) to the number of hydrogen atoms (H) is (F) / (H)> A fluorine-based reactive gas which is 1.5;
The fluorine-based intermediate gas reacts with water to generate HF as a fluorine-based etching gas having silicon oxide etching ability, and water is generated by the etching reaction of silicon oxide with the fluorine-based etching gas. Other features.
By setting the lower limit of the proportion of oxygen in the mixed gas to 5 vol%, it is possible to sufficiently generate a fluorine-based intermediate gas even when the input power of plasma discharge is high. The reason why the upper limit is set to 20 vol% is that when the upper limit is exceeded, the production of the fluorine-based intermediate gas is saturated. The oxygen ratio is more preferably 7 to 13 vol% with respect to the fluorine-based raw material, although it depends on the input power of plasma discharge.

The fluorine-based material is preferably CF ₄ .
This makes it possible to obtain COF ₂ and _CF 3 OH and _{F 2} as the fluorine-based intermediate gas in said plasma space.

In the plasmification step, it is preferable that the concentration of water after passing through the plasma space is 1/10 or less before passing.
Thereby, most of the water can be consumed in the etching gasification reaction of the fluorine-based intermediate gas, the growth of the condensed phase on the surface of the object to be processed can be reliably suppressed, and the etching rate can be reliably improved.
can do.

The dew point is preferably 10 ° C. to 30 ° C. (water vapor partial pressure 1.228 kPa to 4.2467 kPa), more preferably 10 ° C. to 20 ° C. (water vapor partial pressure 1.228 kPa to 2.3392 kPa). More preferably, it is 10 to 17 ° C. (water vapor partial pressure 1.2282 kPa to 1.9383 kPa).
As a result, the etching rate can be reliably improved.

The upper limit of the temperature of the object to be processed may be lower than 50 ° C or 40 ° C or lower.
More preferably, the temperature of the object to be processed is 10 ° C to 30 ° C.
Thus, an oxidizing gas such as ozone can be easily dissolved in the condensed phase on the surface of the object to be processed, and the silicon oxidation rate can be improved. Or hydrogen fluoride etc. become easy to melt | dissolve and a hydrofluoric acid density | concentration can be raised. Therefore, the etching rate can be further improved.

The reason why the lower limit of the temperature range of the object to be processed is 10 ° C. is to prevent condensation on the surface of the object to be processed. (When the room temperature is 25 ° C., the relative humidity may be within 38%.)
The lower limit of the temperature range of the object to be processed may be an indoor dew point instead of 10 ° C.
Thereby, it is possible to prevent moisture in the room from condensing on the surface of the object to be processed, and it is possible to more reliably prevent the growth of the condensed phase on the surface of the object to be processed.

It is more preferable that the temperature of the object to be processed is room temperature.
Accordingly, it is not necessary to heat or cool the object to be processed, and the temperature adjustment process of the object to be processed can be omitted.

  According to the present invention, even if water is generated during the etching reaction, the water can be used for the generation reaction of the fluorine-based etching gas. Therefore, it is possible to suppress the growth of the condensed phase on the surface of the workpiece even when the workpiece temperature is low. As a result, the silicon oxidation rate can be improved, and consequently the etching rate can be improved.

Hereinafter, a first embodiment of the present invention will be described.
As shown in FIG. 1, a silicon film 91 (object to be processed) is formed on the upper surface of a substrate 90 such as glass. The silicon constituting the silicon film 91 may be amorphous silicon or crystalline silicon such as microcrystalline Si or polycrystalline Si. A film containing silicon as a main component and containing about 0 to 20% hydrogen may be used. The substrate 90 may be made of silicon such as a wafer, and the silicon substrate 90 itself may be an object to be etched as an object to be processed. N-type or P-type silicon doped with P or B may be used. As an example, in a substrate used for a TFT for liquid crystal, SiN is formed on a glass, and thereafter, amorphous Si, which is an object to be processed in this embodiment, is formed by plasma CVD.
In the drawing, the thickness of the substrate 90 and the silicon film 91 is exaggerated.

The etching apparatus 1 includes a substrate temperature adjusting unit 2, a transport unit 3, and a reactive gas supply system 4.
The substrate temperature adjusting means 2 includes a heater and a cooler (not shown), and adjusts the temperature of the substrate 90 to be processed to a predetermined temperature. The temperature of the substrate 90 is preferably 10 ° C. to 50 ° C., more preferably 10 ° C. to 30 ° C., and even more preferably room temperature. The lower limit of the temperature range may be an indoor dew point instead of 10 ° C. When the substrate temperature is set to room temperature, the substrate temperature adjusting means 2 may be omitted.
The transport means 3 moves the substrate 90 relative to the reactive gas supply system 4 in the left-right direction of FIG.

The reactive gas supply system 4 includes an ozone supply system 10 and a fluorine-based gas supply system 20.
The ozone supply system 10 includes an oxygen supply unit 11 and an ozonizer 12 connected to the oxygen supply unit 11. Although not shown in detail, the oxygen supply unit 11 includes an oxygen gas cylinder and a mass flow controller, and supplies a predetermined flow rate of oxygen gas (O ₂ ) to the ozonizer 12. The ozonizer 12 generates ozone (O ₃ ), which is an oxidizing gas, from oxygen gas. The ozone concentration at the outlet of the ozonizer 12 is preferably 1 to 15 vol% in terms of oxygen ratio.

The fluorine-based gas supply system 20 includes a fluorine-based material supply unit 21, a humidifier 22 connected to the fluorine-based material supply unit 21, and a remote plasma head 23 connected to the humidifier 22. . Although detailed illustration is omitted, the fluorine-based raw material supply unit 21 includes a tank or a mass flow controller that stores CF ₄ as a fluorine-based raw material, and supplies a predetermined flow rate of CF 4 to the humidifier 22. The humidifier 22 is configured to add a predetermined amount of water to the CF ₄ gas from the fluorine-based raw material supply unit 21. The amount of water added is preferably such that the dew point of CF ₄ gas after addition is 10 ° C. to 40 ° C., more preferably 10 ° C. to 30 ° C., and more preferably 10 ° C. to 20 ° C. It is more preferable that the amount becomes. As a result, CF ₄ gas having a lower dew point than conventional is generated.

The remote plasma head 23 is arranged above the substrate 90 that is relatively moved by the transfer means 3. The plasma head 23 includes a pair of electrodes 24 and 24. A power source 25 is connected to one electrode 24, and the other electrode 24 is electrically grounded. A slit-like space 26 is formed between the pair of electrodes 24. A gas path from the humidifier 22 is connected to the upper end portion of the interelectrode space 26. A solid dielectric layer is provided on the opposing surface of the electrode.
By supplying a voltage from the power supply 25 to the one electrode 24, an atmospheric pressure glow discharge is formed in the interelectrode space 26. Thereby, the interelectrode space 26 becomes an atmospheric pressure plasma space.
The supply voltage is preferably Vpp = 10 to 15 kV. The voltage waveform may be an intermittent wave such as a pulse or a continuous wave such as a sine wave.

  A short blowing path 27 extends from the lower end of the interelectrode space 26 of the remote plasma head 23, and the lower end of the blowing path 27 is opened on the lower surface of the plasma head 23. An ozone supply path 13 from the ozonizer 12 is joined to an intermediate portion of the blowout path 27. An end opening (suction port) of the suction path 41 is disposed in the vicinity of the lower end opening (blowing port) of the blowing path 27 on the lower surface of the plasma head 23 so as to be separated from the substrate 90 in the direction of relative movement. The suction path 41 is connected to an exhaust means 42 such as a vacuum pump.

A method for etching the silicon film 91 of the substrate 90 using the etching apparatus 1 will be described.
Substrate temperature adjusting step The substrate 90 to be processed is adjusted to a predetermined temperature of 10 ° C. to 50 ° C., preferably 10 ° C. to 30 ° C., by the substrate temperature adjusting means 2. When the predetermined temperature of the substrate 90 is room temperature, it is not necessary to adjust the temperature.
The substrate 90 is disposed below the plasma head 23.

Ozonation process will be ozonized in an ozonizer 12 oxygen from the oxygen supply unit 11. Thereby, ozone-containing oxygen gas is obtained. This ozone-containing oxygen gas is led out to the ozone supply path 13.

Water addition step In addition, CF ₄ from the fluorine-based raw material supply unit 21 is introduced into the humidifier 22, and in this humidifier 22, an amount of water with a dew point of 10 ° C. to 40 ° C., preferably 10 ° C. to 30 ° C. Added. This amount of added water is preferably such that the concentration of water after passing through the plasma space 26 is 1/10 or less of that before passing in the plasma forming step.

CF ₄ after the addition of water into the plasma process is introduced into the interelectrode space 26 of the plasma head 23. In parallel, by supplying a voltage from the power source 25 to the electrode 24, an atmospheric pressure glow discharge is generated in the interelectrode space 26, and the interelectrode space 26 is made a plasma space. As a result, CF ₄ is turned into plasma and reacts with the added water to generate fluorine-based intermediate gas such as COF ₂ , CF ₃ OH, F ₂ , HF as a fluorine-based etching gas, or the like. Moreover, by setting the water addition amount, more intermediate gas such as COF ₂ is generated than HF. Thereby, for example, COF ₂ rich fluorine-based reactive gas can be led out to the blow-out path 27.
In addition, when the input power of plasma discharge is relatively large, in addition to adding water to CF ₄ , it is preferable to add, for example, about 10 vol% oxygen (O ₂ ) to CF ₄ . Thereby, COF ₂ can be more reliably generated as the fluorine-based intermediate gas.

Mixing Step Ozone-containing oxygen gas from the ozone supply path 13 is mixed with this COF ₂ rich gas. This mixed gas constitutes a “reactive gas containing an oxidizing gas and a fluorine-based intermediate gas”.

Blowing Step This mixed gas is blown out from the blowout path 27 and blown onto the surface of the silicon film 91 of the substrate 90. As a result, a reaction occurs on the surface of the silicon film 91, and the silicon film 91 is etched. Since COF ₂ , HF, O _3, etc. involved in the reaction are non-radicals, it is possible to avoid the etching rate from being lowered or the substrate 90 being damaged according to the working distance between the plasma head 23 and the substrate 90. In addition, the setting of the head height can be facilitated, and the degree of freedom in design can be improved.
The treated gas is sucked in by the suction passage 41 and discharged by the exhaust means 42. Further, the substrate 90 is relatively moved by the transfer means 3 and the entire substrate 90 is etched.

Although the detailed mechanism of this silicon etching is not definitive, it is considered that the following reaction occurs. HF in the supply gas from the plasma space 26 is ignored.
[Case 1]
(Oxidation process)
Si + 2O ₃ → SiO ₂ + 2O ₂ (Formula 11)
(HF generation process)
2COF ₂ + 2H ₂ O → 2CO ₂ + 4HF (Formula 12)
(Hydrofluoric acid dissolution process)
4HF + 4HF + 4H ₂ O → 4HF ₂ ⁻ + 4H ₃ O ⁺ (Formula 13)
(Etching process)
SiO ₂ + 4HF ₂ ⁻ + 4H ₃ O ⁺ → SiF ₄ + 2H ₂ O + 4H ₂ O + 4HF (Formula 14)

As shown in Expression 13, a condensed phase of hydrofluoric acid is formed on the surface of the silicon film 91. Each component in the blown gas comes into contact with the surface of the condensed phase.
When ozone in the blown-out gas comes into contact with the condensed phase surface, it dissolves into the condensed phase at a rate according to the distribution coefficient (FIG. 4) with respect to the substrate temperature. Since the substrate temperature is set to a low temperature such as 10 ° C. to 50 ° C., the distribution coefficient is large, and the solubility of ozone in the condensed phase can be sufficiently increased. Moreover, since it is under low temperature, it can prevent that ozone decomposes | disassembles and can make ozone life long enough. The ozone dissolved in the condensed phase diffuses in the condensed phase and reaches the surface of the silicon film 91. This ozone oxidizes the silicon constituting the silicon film 91 to form silicon oxide (Formula 11). Since the ozone solubility is high, the silicon oxidation rate can be sufficiently increased.

The hydrofluoric acid constituting the condensed phase comes into contact with the silicon oxide thus formed, and the silicon oxide becomes volatile SiF ₄ and is sucked and removed from the suction port (Formula 14). As a result, silicon etching is performed. Since the silicon oxidation rate is high, the etching rate can be sufficiently increased.

Water (steam) is generated by the etching reaction (Formula 14). A part of this water (2H ₂ O in the second term on the right side of Formula 14) reacts with COF ₂ in the blown gas to generate HF (Formula 12). Therefore, this water (2H ₂ O) behaves like a catalyst in the two reactions of Formula 12 and Formula 14. The remainder of the water produced by the etching reaction (4H ₂ O in the third term on the right side of Equation 14) is used to form a hydrofluoric acid condensed phase (the third term on the left side in Equation 13), and silicon oxide. (Equation 14).

Thereby, it is possible to prevent or suppress the growth of the condensed phase on the surface of the substrate. Therefore, it is possible to prevent the rate of diffusion of ozone in the condensed phase from occurring, and ozone can be reliably diffused to the surface of the silicon film 91. Therefore, coupled with the above-described improvement in the solubility of ozone in the condensed phase, the oxidation rate of the silicon film 91 can be further increased.
In addition, it is possible to prevent diffusion rate-limiting from occurring with hydrofluoric acid, and to ensure that the etching reaction takes place.
Furthermore, by suppressing the growth of the condensed phase, SiF ₂ generated by the etching reaction can be promptly released from the surface of the substrate 90, and reprecipitation of SiO ₂ can be prevented. As a result, the etching rate can be further improved.

In Formula 12, HF made from COF ₂ dissolves in the hydrofluoric acid condensed phase (the first term on the left side of Formula 13) and can contribute to the etching of silicon oxide (Formula 14). Similarly, HF generated by the etching reaction (the fourth term on the right side of Equation 14) is also dissolved in the hydrofluoric acid condensed phase (the second term on the left side of Equation 13), and can contribute to the etching of silicon oxide (Formula). 14).

Formulas 11 to 14 are summarized in the following reaction formulas.
Si + 2O ₃ + 2COF ₂ → SiF ₄ + 2O ₂ + 2CO ₂ (Formula 15)
Theoretically, if H ₂ O is supplied only at the beginning of the treatment, the HF conversion reaction (formula 12) of the intermediate gas COF ₂ occurs, and this causes the reactions of formulas 11 to 14 to be chained. The reaction represented by 15 will proceed. Therefore, once the reaction is started, after that, even if the HF is not included at all in the COF ₂ rich supply gas from the plasma space 26, the silicon etching is performed as long as the intermediate gas COF ₂ is included. Processing can continue.
Here, among the components contained in the supply gas from the plasma space 26, the ratio of the total number of hydrogen atoms (H) and the number of fluorine atoms (F) of the fluorine-based etching gas, the fluorine-based intermediate gas, and water ( Considering F) / (H), in Formula 15, since the number of fluorine atoms (F) is 4 in 2COF ₂ and the hydrogen atoms (H) are zero, (F) / (H) = infinite Become big.

On the other hand, in order to cause the etching reaction of Formula 14, it is considered necessary that a condensed phase with a certain thickness exists on the surface of the silicon film 91. However, if the condensed phase is too thin, it is easily evaporated by evaporation of water. End up. Also, the water produced by the etching reaction (the second term on the right side of Formula 14) may be sucked from the suction port together with SiF ₄ or the like before encountering COF ₂ and causing the HF reaction (Formula 12). possible. Therefore, in practice, it is preferable to continuously perform the water addition step.
In the case of amorphous silicon produced by plasma CVD, which is generally used for TFTs (thin film transistors) for driving liquid crystals, about 10% of hydrogen is contained in the film. In this case, as shown in the following formula 11a, water is generated by an oxidation reaction with ozone. This water can be used to cause the first HF reaction (Formula 12) or to supply water thereafter.
SiH _2x + (2 + x) O ₃ → SiO ₂ + (2 + x) O ₂ + xH ₂ O (Formula 11a)
Here, SiH _2x indicates that 2x hydrogen atoms are contained in each silicon atom of the object to be processed. In amorphous silicon, 2x≈0.1, and in normal silicon, 2x = 0.
The overall reaction formula when considering the hydrogen content of the workpiece is as follows.
SiH _2x + (2 + x) O ₃ + 2COF ₂ → SiF ₄ + (2 + x) O ₂ + 2CO ₂ (Formula 15a)

In the case 1 described above, the reaction has been considered focusing on COF ₂ among the components of the gas supplied from the plasma space 26, but the HF is also included in the supplied gas. When this is considered, each reaction of Formula 11-Formula 14 can be rewritten as follows.
[Case 2]
(Oxidation process)
Si + 2O ₃ → SiO ₂ + 2O ₂ (Formula 11b)
(HF generation process)
COF ₂ + H ₂ O → CO ₂ + 2HF (Formula 12b)
(Hydrofluoric acid dissolution process)
2HF + 4HF + 2HF + 4H ₂ O → 4HF ₂ ⁻ + 4H ₃ O ⁺ (formula 13b)
(Etching process)
SiO ₂ + 4HF ₂ ⁻ + 4H ₃ O ⁺ → SiF ₄ + H ₂ O + 4H ₂ O + H ₂ O + 4HF
(Formula 14b)
2HF in the first term on the left side of Equation 13b corresponds to HF in the supply gas from the plasma space 26. HF in the supply gas is dissolved in the hydrofluoric acid condensed phase from the interface between the hydrofluoric acid condensed phase and the air layer on the surface of the silicon film 91. Note that 4HF in the second term on the left side of Equation 13b corresponds to the one generated by the etching reaction (5th term on the right side in Equation 14b), and 2HF in the third term on the left side of Equation 13b is the COF in the supply gas. _This corresponds to that generated by the HF reaction of No. 2 (the second term on the right side of Formula 12b).
Further, a part of H ₂ O generated by the etching reaction (Formula 14b) (the second term on the right side of Formula 14b) is used for the HF reaction of COF ₂ (the second term on the left side of Formula 12b). A part (3rd term on the right side of Formula 14b) is used for a new etching reaction (Formula 14b) via hydrofluoric acid dissolution (4th term on the left side of Formula 13b).

The reaction of the formula 11b~14b are chain reaction acting positive feedback that of _{H 2} O in mediating. This chain reaction can be controlled by adjusting the substrate temperature within a range of 50 ° C. or less to increase or decrease the amount of H ₂ O present on the silicon film surface. Since the amount of water added in the water addition step is small, the amount of H ₂ O on the silicon film surface is also small, and the silicon film surface always shows a dry tendency. Therefore, the amount of H ₂ O on the surface of the silicon film can be sufficiently controlled by adjusting the temperature to 50 ° C. or lower, and as a result, the growth of the condensed phase can be reliably suppressed. Also, H _{2 O} amount is less evaporable amount of the silicon film surface, extra generating of H _{2 O} by HF in the feed gas (fourth term on the right-hand side of Equation 14b), thereby the silicon film surface H ₂ O An amount can be ensured to maintain the reaction.
In addition, since HF is present in the supply gas, it is possible to reliably obtain H ₂ O for converting COF ₂ to HF at the start of processing.

The formulas 11b to 14b are summarized as follows.
Si + 2O ₃ + COF ₂ + 2HF → SiF ₄ + 2O ₂ + CO ₂ + H ₂ O (Formula 15b)
In Formula 15b, the number of hydrogen atoms (H) contributing to the reaction is two in 2HF in the fourth term on the left side, and the number of fluorine atoms (F) is _two in COF ₂ in the third term on the left side and the left side Two in 2HF in the fourth term, a total of four. Therefore, the ratio (F) / (H) of the number of hydrogen atoms (H) and the number of fluorine atoms (F) contributing to the reaction is (F) / (H) = 2.
The ratio (F) / (H) is preferably such that (F) / (H)> 1.5.

Next, a case where CF ₃ OH is generated as a fluorine-based intermediate gas in the plasma space 26 will be described. In this case, the following reaction occurs.
[Case 3]
(Oxidation process)
Si + 2O ₃ → SiO ₂ + 2O ₂ (Formula 11c)
(COF ₂ production process)
CF ₃ OH + H ₂ O → COF ₂ + HF + H ₂ O (Formula 12-1c)
(HF generation process)
COF ₂ + H ₂ O → CO ₂ + 2HF (Formula 12-2c)
(Hydrofluoric acid dissolution process)
HF + HF + 4HF + 2HF + 4H ₂ O → 4HF ₂ ⁻ + 4H ₃ O ⁺ (formula 13c)
(Etching process)
SiO ₂ + 4HF ₂ ⁻ + 4H ₃ O ⁺ → SiF ₄ + 2H ₂ O + 4H ₂ O + 4HF
(Formula 14c)
(Overall reaction)
Si + 2O ₃ + CF ₃ OH + HF → SiF ₄ + 2O ₂ + CO ₂ + H ₂ O
(Formula 15c)
As shown in Formula 12-1c, CF ₃ OH is unstable and decomposes into COF ₂ and HF. Therefore, after this decomposition, the same reaction as in case 2 occurs (formulas 11c, 12-2c, 13c, 14c).
In Formula 15c, the number of hydrogen atoms (H) contributing to the reaction is 2 in total, one in CF ₃ OH in the third term on the left side and one in HF in the fourth term on the left side, and the number of fluorine atoms ( F) is a total of four in three in CF ₃ OH in the third term on the left side and one in HF in the fourth term on the left side. Therefore, the ratio (F) / (H) of the number of hydrogen atoms (H) and the number of fluorine atoms (F) contributing to the reaction is (F) / (H) = 2.
In case 3 as well, the reaction can be controlled by adjusting the amount of H ₂ O on the surface of the silicon film by manipulating the substrate temperature.

Next, another embodiment of the present invention will be described.
As shown in FIG. 2, the ozonizer 12 is omitted in the second embodiment of the present invention. Instead, the supply path 13 from the oxygen supply unit 11 is joined to the fluorine-based gas path between the humidifier 22 and the plasma head 23.
Note that the supply path 13 may be merged with the fluorine-based gas path upstream of the humidifier 22.

Thus, O ₂ from the oxygen supply unit 11 is mixed with the low dew point CF ₄ from the humidifier 22 (mixing step). The mixing ratio of O ₂ to CF ₄ is preferably 5 to 20 vol%.

This mixed gas is introduced into the plasma space 26 of the plasma head 23 and turned into plasma, and a fluorine-based reactive gas such as COF ₂ is generated from CF ₄ and an oxidizing gas such as O ₃ is generated from O _2. (Plasma process). Therefore, the generation part of the fluorine-based reactive gas and the generation part of the oxidizing gas can be made common, and the configuration can be simplified.
These generated gases are blown out from the blowing path 27 and blown onto the substrate 90 (blowing process), and the silicon film 92 is etched by the same reaction process as in the first embodiment.

The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the first embodiment, fluorine gas such as COF ₂ from the plasma head 23 and ozone from the ozonizer 12 may not be mixed and supplied to the silicon film surface from different outlets. .
The oxidizing gas may be generated using an oxygen plasma discharge device different from the plasma head 23 for the fluorine-based gas in place of the ozonizer 12.
After the oxidizing gas is sprayed, fluorine reactive gas such as COF ₂ may be sprayed.

Example 1 will be described.
Using the etching apparatus 1 shown in FIG. 1, the amorphous silicon coated on the glass substrate surface was etched. H ₂ O was added in an amount of dew point of 13.5 ° C. (water vapor partial pressure 1.55 kPa) in the humidifier 22 to CF ₄ 0.8 slm as a fluorine-based raw material. The flow rate ratio of this added H ₂ O to CF ₄ was 1.55 vol%. This low dew point CF ₄ was introduced into the interelectrode space 26 of the plasma head 23 and turned into plasma under atmospheric pressure. Plasma conditions were as follows.
Supply power: 0.165kW
Supply voltage: Vpp = 13kV
Electrode area: 35 cm ²
As a result of analyzing the gas components after being converted to plasma by a Fourier transform infrared spectrometer (FTIR), it was confirmed that HF was produced at 0.0057 slm and COF ₂ was produced at 0.0149 slm for 1 slm of CF ₄ .
Here, the ratio (F) / (H) of the number of fluorine atoms (F) and the number of hydrogen atoms (H) contained in 0.0057 mol of HF and 0.0149 mol of COF ₂ is:
(F) / (H) = (0.0149 × 2 + 0.0057) /0.0057=6.2
And the condition of (F) / (H)> 1.5 is satisfied.
Further, H ₂ O after plasma was hardly observed, and it was confirmed that it became 1/10 or less before plasma.
Separately, O ₂ 0.4 slm was supplied to the ozonizer 12 as a raw material for the oxidizing gas to obtain 8 vol% (ratio to O ₂ ), that is, 0.032 slm of O ₃ . O ₃ is required to be at least a value (0.01775 slm) that is a sum of at least the volume flow rate of COF ₂ (0.0149 slm) and half of the volume flow rate of HF (0.0057 slm), and about twice that is preferable. However, it can be said that the O ₃ flow rate obtained by the ozonizer 12 is substantially suitable.
The substrate temperature was 20 ° C., and the gas from the plasma head 23 and the gas from the ozonizer 12 were mixed and sprayed onto the substrate surface.
When the etching rate was measured, it was 45000 A / min, and a sufficiently large etching rate could be obtained.

In Example 2, the relationship between the substrate temperature, the amount of water added to the fluorine-based source gas, and the etching rate was examined. After adjusting the amount of H ₂ O added by the humidifier 22 to CF ₄ 0.5 slm, the plasma head 23 turned it into plasma. Plasma conditions were as follows.
Supply power: 0.165kW
Supply voltage: Vpp = 13kV
Electrode area: 35 cm ²
Further, 8 vol% (compared to O ₂ ratio) of O ₃ is made by Ozonizer 12 using O ₂ 0.5 slm, and this is mixed with the above-mentioned plasma gas and supplied to the glass substrate, and amorphous silicon on the surface The film was etched.
The substrate temperature was set to three types of 20 ° C., 40 ° C., and 60 ° C., and the etching rate under each temperature condition was measured. (Note that 60 ° C. is a conventional general substrate temperature and is a comparative example.)

The results are shown in FIG.
As can be seen from the figure, when the substrate temperature is 60 ° C. as in the prior art, the etching rate hardly changes even if the amount of water added to the fluorine-based source gas is increased.
On the other hand, when the substrate temperature is 20 ° C., the etching rate rises greatly from the vicinity of the water addition amount at which the dew point becomes 10 ° C., and the etching rate reaches a peak near the water addition amount at which the dew point becomes 20 ° C. It has been found that an etching rate sufficiently higher than the conventional one (when the substrate temperature is 60 ° C.) can be obtained up to the vicinity of the amount of water added at 40 ° C.
It has been found that even when the substrate temperature is 40 ° C., an etching rate sufficiently higher than the conventional one (when the substrate temperature is 60 ° C.) can be obtained in a water addition range with a dew point of 10 ° C. to 40 ° C.

  The present invention can be applied to etching a silicon film on the surface, for example, in the manufacture of a flat panel glass such as a semiconductor wafer or a liquid crystal.

1 is a schematic configuration diagram of an etching apparatus according to a first embodiment of the present invention. It is a schematic block diagram of the etching apparatus which concerns on 2nd Embodiment of this invention. Water amount to the fluorine-based material CF ₄ etching rate for (dew point display) is a graph showing the results of Example 1 were measured by changing the substrate temperature. It is a graph which shows the gas-liquid partition coefficient of ozone with respect to temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching apparatus 2 Substrate temperature control means 3 Conveyance means 4 Reactive gas supply system 10 Ozone supply system 11 Oxygen supply part 12 Ozonizer 13 Ozone supply path 20 Fluorine-type gas supply system 21 Fluorine-type raw material supply part 22 Humidifier 23 Plasma head 24 Electrode 25 Power supply 26 Plasma space 27 Blowout path 41 Suction path 42 Exhaust means 90 Substrate 91 Silicon film (processed object)

Claims (13)

In a method of etching a workpiece made of silicon,
By generating ozone as an oxidizing gas that can oxidize silicon, and by passing a gas containing fluorine-based raw material that is not reactive with silicon and water through a plasma space near atmospheric pressure separately from this ozone generation A fluorine-based reactive gas is generated, and the ozone and the fluorine-based reactive gas are sprayed on an object to be processed at a temperature of 10 ° C. to 50 ° C.,
The fluorine-based reactive gas includes a non-radical fluorine-based intermediate gas selected from COF ₂ , CF ₃ OH, and F ₂ , and the ratio of the number of fluorine atoms (F) to the number of hydrogen atoms (H) is (F) /(H)>1.5,
The fluorine-based intermediate gas reacts with water to generate HF as a fluorine-based etching gas having silicon oxide etching ability, and water is generated by etching reaction of silicon oxide with the fluorine-based etching gas. Etching method. The oxidizing gas is ozone;
The fluorine-based reactive gas includes COF ₂ as the fluorine-based intermediate gas and HF as the fluorine-based etching gas,
The etching method of claim 1, wherein the volumetric flow rate of ozone is greater than or equal to the sum of 1 and the volumetric flow rate of COF ₂ half the volumetric flow rate of HF.   The etching method according to claim 2, wherein a volume flow rate of the ozone is twice or more of the total. The etching method according to claim 1, wherein the fluorine-based intermediate gas is COF ₂ .   The etching method according to claim 1, wherein the oxidizing gas is obtained by passing oxygen gas through a plasma space near atmospheric pressure. That the fluorine reactive gas was obtained by passing a low dew point fluorine-based material gas dew point to the fluorine-based material is added an amount of water to be 10 ° C. to 40 ° C. in the plasma space in the vicinity of atmospheric pressure The etching method according to claim 1, wherein: In a method of etching a workpiece made of silicon,
A mixing step of mixing a fluorine raw material having no reactivity with silicon, an amount of water having a dew point of 10 ° C. to 40 ° C. with respect to the fluorine raw material, and obtaining a mixed gas;
A plasma process for generating a reactive gas by passing the mixed gas through a plasma space near atmospheric pressure;
A spraying step of spraying the reactive gas on an object to be processed at a temperature of 10 ° C. to 50 ° C .;
The ratio of oxygen in the mixed gas is 5 to 20 vol% with respect to the fluorine-based raw material,
The reactive gas is
(A) ozone as an oxidizing gas capable of oxidizing silicon;
(B) a non-radical fluorine-based intermediate gas selected from COF ₂ , CF ₃ OH, and F ₂ , and the ratio of the number of fluorine atoms (F) to the number of hydrogen atoms (H) is (F) / (H)> A fluorine-based reactive gas which is 1.5;
The fluorine-based intermediate gas reacts with water to generate HF as a fluorine-based etching gas having silicon oxide etching ability, and water is generated by the etching reaction of silicon oxide with the fluorine-based etching gas. Etching method characterized. The etching method according to claim 6, wherein the fluorine-based material is CF ₄ .   The etching method according to any one of claims 6 to 8, wherein the concentration of water after passing through the plasma space is 1/10 or less before passing through the plasma space.   The etching method according to claim 6, wherein the dew point is 10 ° C. to 20 ° C.   The etching method according to claim 1, wherein a temperature of the object to be processed is set to 10 ° C. to 30 ° C.   The etching method according to any one of claims 1 to 11, wherein the lower limit of the temperature range of the object to be processed is set to an indoor dew point instead of 10 ° C.   The etching method according to claim 1, wherein the temperature of the object to be processed is set to room temperature.

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