JP6021131B2 - Etching method and etching apparatus - Google Patents

Description

  The present invention relates to an etching method and an etching apparatus. More specifically, the present invention relates to an etching method and an etching apparatus for dry etching Si single crystal, Si polycrystal, amorphous silicon, and the like.

  Etching techniques are performed at various steps in the manufacture of semiconductor devices. For example, an electrode forming process in a MOS device, a surface roughening process in a solar cell, a sacrificial layer etching process in MEMS, and the like can be given. As described above, the etching technique for silicon is applied to various technical fields.

Etching types include wet etching and dry etching. Dry etching includes reactive ion etching that generates ions and radicals using plasma. For example, Patent Document 1 discloses a technique for dry-etching polycrystalline Si by converting a mixed gas of SF ₆ gas and chlorine gas into plasma.

Further, dry etching includes chemical dry etching that does not use plasma. For example, Patent Document 2 discloses a technique of chemically dry etching a silicon substrate using XeF ₂ gas (see paragraph [0002] and the like of Patent Document 2).

JP 2002-367957 A JP 2000-21849 A

  By the way, when a gate electrode is formed by reactive ion etching in a MOS device manufacturing process, ion damage remains around the electrode. In the plasma generation region when etching a large area substrate, the plasma density is locally high. That is, a location having a high plasma density and a location having a low plasma density are generated with respect to the wafer. Therefore, it is difficult to uniformly etch the wafer plane. In addition, in order to use an etching method using plasma, it is of course necessary to provide a plasma generator in the facility. For this reason, the facilities are likely to be complicated and large. And equipment becomes expensive.

On the other hand, the gas used in chemical dry etching without using plasma is often not easy to handle. In the first place, these gases have a very high reactivity. For example, XeF ₂ gas is corrosive and toxic, has a boiling point as high as 114 ° C., and is not easy to handle. Xenon (Xe) is rare. Therefore, the gas itself becomes expensive. In addition, ClF ₃ may be used as an etching gas. ClF ₃ gas has combustion support, corrosivity, and toxicity. ClF ₃ gas is also expensive.

  The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide an etching method and an etching apparatus capable of performing dry etching on Si crystal or the like using a gas that is easy to handle and can be obtained relatively inexpensively without using a plasma generator. It is.

The etching method in the first aspect is a method of chemically dry-etching the Si member. The pressure of the mixed gas containing F ₂ and NO ₂ is in the range of 10 Pa to 10,000 Pa and the mixed gas is led to the Si member without being in a plasma state, and the temperature of the Si member is in the range of −20 ° C. to 500 ° C. Temperature. Then, the Si member is etched under this condition.

  This etching method is a method for dry-etching Si crystals such as Si single crystal and Si polycrystal, amorphous silicon, silicon nitride film, and silicon carbide film. Further, this method is a gas etching method, and the supplied gas is not put into a plasma state. Therefore, unlike plasma etching in which the plasma density locally increases in the plasma generation region, uniform etching can be performed on the wafer. That is, it is suitable for etching a large-diameter silicon wafer. Furthermore, etching can be performed using a relatively inexpensive gas. And the shape of the recessed part produced by etching also changes. Therefore, by suitably selecting the temperature range, it can be applied to various processes such as a roughening process of a solar cell, processing without plasma damage in a semiconductor device, and a sacrificial layer etching process of MEMS. Further, there is no need to provide an expensive plasma generator.

In the etching method according to the second aspect, the pressure of the mixed gas containing F ₂ and NO ₂ is guided to the Si member within a range of 100 Pa to 1000 Pa, and the temperature of the Si member is a temperature within a range of 180 ° C. to 500 ° C. And Thereby, highly accurate processing can be performed.

In the etching method in the third aspect, at least F atoms are generated by causing at least the reaction of F ₂ + NO ₂ → F + FNO ₂ to react with the Si member.

In the etching method in the fourth aspect, the distance from the mixing location where F ₂ and NO ₂ are mixed to the Si member is in the range of 5 mm to 70 mm. The distance of the F ₂ and NO ₂ from the mixing point for mixing to Si member refers to the distance from the mixing point for mixing F ₂ and NO ₂ to the nearest point of the Si component.

In the etching method according to the fifth aspect, the pressure of the mixed gas containing F ₂ and NO is set in the range of 100 Pa to 1000 Pa, and the mixed gas is guided to the Si member without being in a plasma state, and the temperature of the Si member is set to 60 ° C. The temperature is higher and within a range of 180 ° C. or lower. Then, a flat recess is formed by etching the Si member. In this case, the etching rate is sufficiently slow. Therefore, it is possible to carry out etching with relatively high accuracy. For example, it can be applied when processing a gate electrode of a semiconductor element. It can also be applied to remove a damage layer generated in the vicinity of the gate of the MOSFET.

In the etching method in the sixth aspect, the pressure of the mixed gas containing F ₂ and NO is set in the range of 100 Pa to 1000 Pa, and the mixed gas is led to the Si member without being in a plasma state, and the temperature of the Si member is set to 180 ° C. The temperature is higher and within a range of 500 ° C. or lower. And the recessed part which has a gentle curved surface is formed by etching Si member. For example, it can be applied when forming a MEMS.

The etching apparatus in the seventh aspect includes a reaction chamber for etching a Si member, a first gas supply unit for supplying a first gas containing F ₂ gas to the reaction chamber, and NO _{2 in} the reaction chamber. And a second gas supply unit for supplying a second gas including the gas. In this etching apparatus, the internal pressure of the reaction chamber is set in the range of 10 Pa to 10,000 Pa.

  In the etching apparatus according to the eighth aspect, the internal pressure of the reaction chamber is in the range of 100 Pa to 1000 Pa.

In the etching apparatus according to the ninth aspect, in the reaction chamber, at least a reaction of F ₂ + NO ₂ → F + FNO ₂ is caused and at least F atoms and the Si member are reacted.

In the etching apparatus according to the tenth aspect, the distance from the mixing location where F ₂ and NO ₂ are mixed to the Si member is in the range of 5 mm to 70 mm.

  According to the present invention, there is provided an etching method and an etching apparatus that can perform dry etching on Si crystal or the like using a gas that is easy to handle and can be obtained relatively inexpensively without using a plasma generator.

It is a figure which shows schematic structure of the etching apparatus which concerns on 1st Embodiment. It is a figure which shows the structure of the periphery of the reaction chamber of the etching apparatus which concerns on 1st Embodiment. It is a cross-sectional photograph by the electron microscope of the silicon substrate which etched with the etching method which concerns on 1st Embodiment. It is the electron micrograph which compared the temperature dependence about the etching method which concerns on 1st Embodiment. It is a graph showing the energy change in the reaction of F _{2 +} NO ₂ by molecular orbital method calculation. The three-dimensional structure of NO ₂ is a diagram schematically showing. The reaction of NO ₂ and F ₂ is a diagram schematically showing. The reaction between the three-dimensional structure and NO and F ₂ of the NO is a diagram schematically showing. It is a figure which shows schematic structure of the etching apparatus which concerns on 2nd Embodiment. It is FIG. (1) which shows the structure of the gas supply unit of the etching apparatus which concerns on 2nd Embodiment. It is FIG. (2) which shows the structure of the gas supply unit of the etching apparatus which concerns on 2nd Embodiment. It is a figure which shows the cross-section of the partition of the etching apparatus which concerns on 2nd Embodiment. It is a figure which shows schematic structure of the etching apparatus which concerns on 3rd Embodiment. It is a figure which shows the structure of the gas supply unit of the etching apparatus which concerns on 3rd Embodiment. It is a figure which shows schematic structure of the etching apparatus which concerns on 4th Embodiment. It is a figure which shows the structure of the gas supply unit of the etching apparatus which concerns on 4th Embodiment. It is a figure which shows the cross-section of the partition of the etching apparatus which concerns on 4th Embodiment. It is a figure which shows schematic structure of the etching apparatus which concerns on 5th Embodiment. 4 is an electron micrograph showing a cross section of a silicon substrate when etching is performed at a pressure of 600 Pa and a substrate temperature of 27 ° C. for 5 minutes. 4 is an electron micrograph showing a cross section of a silicon substrate when etching is performed at a pressure of 600 Pa and a substrate temperature of 110 ° C. for 5 minutes. 4 is an electron micrograph showing a cross section of a silicon substrate when etching is performed at a pressure of 600 Pa and a substrate temperature of 300 ° C. for 5 minutes. It is an electron micrograph which compares the cross section of a silicon substrate in the case of performing etching by making substrate temperature into different temperature. It is a graph which shows the relationship between a substrate temperature and an etching rate. It is an electron micrograph which compares the surface of a silicon substrate in the case where etching is carried out with different substrate temperatures. It is a graph showing the relationship between the flow rate ratio and the etching rate of the NO gas to the flow rate of F ₂ gas. It is a graph showing the relationship between the mean square roughness of the bottom surface of the silicon substrate ratio and the etching of the flow rate of NO gas to the flow rate of F ₂ gas. It is an electron micrograph showing a cross section of a silicon substrate etched by changing the ratio of the flow rate of NO gas to the flow rate of F ₂ gas. It is the electron micrograph (the 1) which shows the bottom face of the silicon substrate etched by changing the ratio of the flow rate of NO gas to the flow rate of F ₂ gas. It is an electron micrograph (the 2) which shows the bottom face of the silicon substrate etched by changing the ratio of the flow rate of NO gas to the flow rate of F ₂ gas. It is an electron micrograph (the 3) which shows the bottom face of the silicon substrate etched by changing the ratio of the flow rate of NO gas to the flow rate of F ₂ gas. It is an electron micrograph (the 4) which shows the bottom face of the silicon substrate etched by changing the ratio of the flow rate of NO gas to the flow rate of F ₂ gas. It is an electron micrograph which compares the cross section of a silicon substrate in the case of implementing etching by making the inside of a reaction chamber into different pressure. It is an electron micrograph (the 1) which shows the case where the sacrificial layer of MEMS is etched. It is an electron micrograph (the 2) which shows the case where the sacrificial layer of MEMS is etched. It is a graph which shows the relationship between the frequency | count of collision of a particle | grain, and an etching rate. When using a and F ₂ and NO ₂ in the case of using the F ₂ and NO as an electron micrograph comparing etched portions with. For the case of using the a F ₂ and NO ₂ in the case of using the F ₂ and NO is a graph showing the temperature dependency of the etching rate. It is a graph which shows the reflectance of the silicon substrate roughened by the etching. It is a figure for demonstrating the effect which improves the light intake efficiency in the surface roughened by the etching.

  Hereinafter, specific embodiments will be described with reference to the drawings, taking as an example an etching method and an etching apparatus capable of performing chemical dry etching on Si crystal or the like.

(First embodiment)
This embodiment is characterized in that the Si member is etched by reacting F atoms generated by the reaction of F ₂ + NO ₂ → F + FNO ₂ with the Si member. Here, the Si member is made of a material including Si single crystal, Si polycrystal, amorphous silicon, a silicon nitride film, and a silicon carbide film. The Si member is used as a semiconductor, an electronic element such as a MOS or a solar cell, or a mechanical component such as a MEMS.

1. Etching Apparatus FIG. 1 is a schematic configuration diagram showing an outline of an entire etching apparatus 100 of the present embodiment. The etching apparatus 100 includes a first gas supply unit 111, a second gas supply unit 112, a third gas supply unit 113, mass flow controllers 121, 122, 123, pressure adjustment valves 131, 132, and a gas It has a mixing chamber 140 and a reaction chamber 150. In addition, it has a gas discharge part for discharging gas and various valves. Note that the etching apparatus 100 does not have a plasma generator.

The first gas supply unit 111 is for supplying a first gas containing F ₂ gas to the reaction chamber 150. The first gas is a mixed gas of F ₂ gas and Ar gas. The mixing ratio of F ₂ gas in this mixed gas is 5% by volume. The first gas is supplied by a low pressure gas pipe.

The second gas supply unit 112 is for supplying a _second gas containing NO ₂ gas to the reaction chamber 150. The second gas is NO ₂ gas. The second gas is supplied through a low pressure gas pipe.

The third gas supply unit 113 is for mixing Ar gas with the second gas. Therefore, after this mixing, the second gas is a mixed gas of NO ₂ gas and Ar gas. These gases are supplied by low-pressure gas pipes.

The mass flow controller 121 is for controlling the flow rate of the first gas including the F ₂ gas supplied from the first gas supply unit 111. The mass flow controller 122 is for controlling the flow rate of the second gas including the NO ₂ gas supplied from the second gas supply unit 112. The mass flow controller 123 is for controlling the flow rate of Ar gas supplied from the third gas supply unit 113.

  The pressure adjustment valve 131 is for adjusting the pressure of the gas delivered to the gas mixing chamber 140. The pressure adjustment valve 132 is for adjusting the pressure of the gas delivered to the gas discharge unit.

The gas mixing chamber 140 is for mixing the first gas containing F ₂ gas and the _second gas containing NO ₂ gas. Therefore, the gas mixing chamber 140 is disposed at a position upstream of the gas flow from the reaction chamber 150. Examples of the material of the gas mixing chamber 140 include heat resistant glass, a quartz tube, and a stainless tube. The temperature and pressure inside the gas mixing chamber 140 are almost the same as those in the reaction chamber 150. In the gas mixing chamber 140, F atoms are generated according to a reaction formula described later.

  The reaction chamber 150 is for etching the Si member with the mixed gas generated in the gas mixing chamber 140. Examples of the material of the reaction chamber 150 include heat resistant glass, a quartz tube, and a stainless tube. Details of the reaction chamber 150 will be described later.

2. Reaction Chamber As shown in FIG. 2, the reaction chamber 150 includes a mounting table 151 and a heater 152. The mounting table 151 is a table for mounting the Si member S1 to be etched. In addition, a thermometer is attached to the mounting table 151. Thereby, the temperature of Si member S1 can be measured now. The heater 152 is for heating the Si member S1. By feeding back the temperature of the Si member S1, the heater 152 can keep the temperature of the Si member S1 substantially constant.

  Moreover, the etching apparatus 100 has the voltage application part 160, as shown in FIG. The voltage application unit 160 is for supplying electric power to the heater 152. The reaction chamber 150 is provided with a pressure gauge 170. The pressure gauge 170 is for measuring the internal pressure of the reaction chamber 150. The reaction chamber 150 is provided with a dry pump 180.

3. 3. Chemical reaction occurring in gas mixing chamber and reaction chamber 3-1. Reaction in Gas Mixing Chamber Here, the chemical reaction that occurs in the gas mixing chamber 140 will be described. In the gas mixing chamber 140, chemical reactions of the following formulas (1) and (2) occur.
F ₂ + NO ₂ → F + FNO ₂ (1)
F + NO ₂ → FNO ₂ (2)
Reaction rate constant of formula (1): k1
Reaction rate constant of formula (2): k2

As described above, by mixing the F ₂ gas and the NO ₂ gas, F atoms are generated as shown in the equation (1). Then, as shown in equation (2), the generated F atoms recombine with NO _2, F atoms decreases. Therefore, the concentration of F atoms varies depending on which of these reactions is dominant.

In the past, it was strongly recognized that k2 was sufficiently larger than k1. That is, it was thought that F atoms were hardly produced (DD Ebbing and SD Gammon, General Chemistry, Brooks / Cole Pub. Co; 9th Enhanced ed. P555.). Therefore, it has never been thought that etching can be performed by mixing F ₂ gas and NO ₂ gas.

In this embodiment, as will be described later, F ₂ gas and NO ₂ gas are mixed under low pressure. The mean free path of each particle under low pressure is longer than the mean free path of each particle under high pressure. In the present embodiment, the gas mixture containing at least F ₂ and NO ₂ is continuously supplied to the gas mixing chamber 140. Therefore, it is considered that a certain number of F atoms generated by the reaction of the formula (1) may exist in the gas mixing chamber 140.

3-2. Reaction in the reaction chamber The reaction of the above formulas (1) and (2) also occurs in the reaction chamber 150. Then, the Si member S <b> 1 is etched using F atoms that may exist in a certain number inside the reaction chamber 150. At this time, the particles that contribute to the reaction of the Si member S1 with the Si atoms are not limited to the F atoms. However, it is considered that F atoms mainly contribute to etching.

4). Etching method 4-1. Pattern Formation Step First, a mask pattern is formed on the Si member S1. For example, in the case of manufacturing a power device, a mask is arranged at a location where a trench is not formed. An example of the material of the mask is SiO ₂ .

4-2. Gas Supply Process The etching method according to this embodiment will be described. First, the Si member S <b> 1 is mounted on the mounting table 151 of the reaction chamber 150. Next, the reaction chamber 150 is evacuated to lower the internal pressure of the reaction chamber 150. At the same time, the heater 152 is heated to the set value. Then, the first gas is supplied from the first gas supply unit 111, the second gas is supplied from the second gas supply unit 112, and the Ar gas is supplied from the third gas supply unit 113.

4-3. Etching Particle Generation Step Then, F atoms are generated by the reaction shown in the above formula (1). Other particles are also generated. These reactions mainly occur in the gas mixing chamber 140. At this time, F ₂ , NO ₂ , F, FNO ₂ , and Ar may exist in the mixed gas in the gas mixing chamber 140. In the reaction chamber 150, the same reaction can continue and the same particles can exist.

4-4. Etching Step Next, the mixed gas is introduced into the Si member S <b> 1 inside the reaction chamber 150. Then, the F atoms react with the Si member S1. Thereby, the etching of the Si member S1 proceeds. Thereby, the part of the Si member S1 that is not covered with the mask is removed. Here, the pressure inside the reaction chamber 150 is in the range of 10 Pa to 10,000 Pa. Further, the pressure inside the reaction chamber 150 is preferably in the range of 100 Pa to 1000 Pa. The pressure inside the reaction chamber 150 is the total pressure of the mixed gas that occupies the inside of the reaction chamber 150. Therefore, if Ar gas is supplied, the pressure is also included. And the temperature of Si member S1 shall be in the range of -20 degreeC or more and 500 degrees C or less. Within this pressure and temperature range, the gas mixture remains a gas. The mixed gas is not brought into a plasma state.

4-5. Other Steps Other steps may also be performed.

5. Experiment A (Possibility of F ₂ + NO ₂ etching)
5-1. Si member In this experiment, a silicon substrate was used as the Si member S1. The size of this silicon substrate was 6 mm wide and 15 mm long. The silicon substrate is a p-type semiconductor. The electrical resistivity was 10 Ωcm.

5-2. Experimental conditions 109.1 sccm of a mixed gas in which F ₂ gas was mixed with Ar gas at a volume ratio of 5% was supplied. As a result, 5.4 sccm of F ₂ gas is supplied to the reaction chamber. On the other hand, NO ₂ was supplied to the reaction chamber by 10 sccm. The pressure inside the reaction chamber was 600 Pa. The temperature of the silicon substrate was 300 ° C. Etching was performed for 5 minutes. The opening width set by the mask was 8 μm. The distance between the gas mixing chamber and the reaction chamber was 20 mm.

5-3. Experimental Results FIG. 3 is a photomicrograph of the silicon substrate taken with an electron microscope. The depth of the concave portion cut by etching was 0.75 μm. The etching rate was 0.15 μm / min. As shown in FIG. 3, the Si member can be finely processed.

6). Experiment B (temperature dependence of F ₂ + NO ₂ )
The experiment was performed under the same experimental conditions as the above-described Experiment A except for the temperature of the silicon substrate. FIG. 4A is an enlarged view of a part of FIG. 3 described above. FIG. 4B is a diagram showing a case where the temperature of the silicon substrate is 180 ° C. Conditions other than the temperature of the silicon substrate in FIG. 4B are the same as those in FIG. Even when the temperature of the silicon substrate is 180 ° C., etching can be performed. When the temperature of the silicon substrate was 180 ° C., the etching rate was about 20 nm / min.

7). Reactivity of F ₂ and NO ₂ 7-1. Molecular Orbital Calculation Here, in order to investigate the reactivity between F ₂ and NO ₂ , calculation was performed using the molecular orbital method. For this purpose, the Gaussian program (B3LYP / 6-311 + G (d)) was used. FIG. 5 is a graph showing the results. The horizontal axis of FIG. 5 is a reaction step. The vertical axis in FIG. 5 is energy.

In FIG. 5, the chemical reaction (see formula (1)) in which F ₂ and NO ₂ react and F and FNO ₂ are generated gradually proceeds from the left side to the right side in FIG. It shows how it is. That is, FIG. 5 shows, by energy calculation, a picture in which one F atom (f1) in the F ₂ molecule is taken into NO ₂ and the other F atom (f2) is released.

5 includes a left region R1 in FIG. 5 and a right region R2 in FIG. The region R1 is a region in which the horizontal axis (Reaction Steps) in FIG. The region R2 is a region where the horizontal axis (Reaction Steps) in FIG. Region R1 shows the energy change in the process in which one F atom (f1) of the F ₂ molecule is taken into NO ₂ . Region R2 shows the energy change in the process in which one F atom (f1) of the F ₂ molecule is taken into NO ₂ and then the other F atom (f2) is released from FNO ₂ . Therefore, different calculations are performed in the region R1 and the region R2.

First, calculation in the region R1 will be described. In the region R1, the coordinates of the NO ₂ molecule are fixed. Then, with the position of the N atom as the origin, the distance between one F atom (f1) in the F ₂ molecule and the N atom (origin) is taken as a variation parameter. Then, the distance between the F atom (f1) and the N atom is changed from 3 cm (when the horizontal axis (Reaction Steps) in FIG. 5 is 0) to 0.1 m increments, and the energy of the entire system (NO ₂ + F ₂ ) Calculate In the calculation in each case, the molecular structure of NO ₂ + F ₂ was changed, and the minimum value of energy in the system was plotted as the value on the vertical axis in FIG.

When the energy of the entire system takes the minimum value, F ₂ F atoms of the molecule (f1) suggesting that bound to the N atom of the NO ₂ molecules.

  Next, calculation in the region R2 will be described. In the region R2, it is assumed that the F atom (f1) is bonded to the N atom. Therefore, in this region R2, the distance between the N atom and the F atom (f1) remains constant. Then, under this bonding state, the coordinates of the remaining F atoms (f2) are moved. Therefore, in the region R2, the distance between the F atom (f2) and the F atom (f1) is a variation parameter. Then, as in the case of the region R1, the molecular structure was changed, and the minimum value of energy in the system was plotted as the value on the vertical axis in FIG.

  As described above, in the region R1 in FIG. 5, the distance between the N atom and the F atom (f1) is closer by 0.1 mm as the value of the horizontal axis (Reaction Steps) is larger. On the other hand, in the region R2 of FIG. 5, the distance between the F atom (f1) and the F atom (f2) is increased by 0.1 mm as the value of the reaction step (Reaction Steps) increases.

As shown in FIG. 5, F ₂ and NO ₂ react to generate F atoms and FNO _2, and energy of 0.95 eV is generated. That is, the reaction of formula (1) is an exothermic reaction. And since there is almost no energy change in the region R2, the detachment of F atoms from FNO ₂ is a small part of the surplus energy of about 0.95 eV generated when F ₂ is bound to NO _2. It is only consumed and considered to be easily done.

7-2. Difference between NO ₂ and NO Here, NO will be described for comparison. F ₂ and NO cause the reaction shown in the following formula.
F ₂ + NO → F + FNO (3)
Reaction rate constant of formula (3): k3

And the calculation as shown in FIG. 5 was performed also for NO. As a result, the bond energy of FF was 1.8 eV. The binding energy of F-NO was 2.3 eV. The binding energy of F-NO ₂ was 2.4 eV. Thus, the bond energy of F—NO ₂ is almost the same as the bond energy of F—NO. In addition, the tendency to easily release F atoms is similar. However, when F ₂ and NO ₂ are actually reacted, the concentration of F atoms is smaller than when F ₂ and NO are reacted.

Conventionally, the following interpretation has been made. That is, it was thought that this is because the reaction rate constant k2 of the formula (2) is large. That is, most of the F atoms become FNO ₂ due to the recombination reaction of the formula (2), and as a result, the concentration of F atoms decreases. Therefore, by supplying the F2 and NO ₂ in the chamber, it is was thought to be extremely difficult to carry out etching.

However, the present inventors considered that the reaction rate constant k1 is small due to the difference in steric structure between NO and NO _{2 as} shown below.

FIG. 6 shows the three-dimensional structure of NO ₂ . As shown in FIG. 6, in NO ₂ , two O atoms are bonded to the N atom at a slight angle. This bond angle is 134.3 °. When the F ₂ molecule collides from the direction indicated by the arrow J1 in FIG. 6, causing the reaction of equation (1). When F ₂ molecules collide from the directions indicated by arrows J2 and J3 in FIG. 6, the reaction of formula (1) does not occur. FIG. 7 schematically shows the reaction between NO ₂ and F ₂ .

FIG. 8 schematically shows a reaction between the three-dimensional structure of NO and F ₂ . As shown in FIG. 8, N atoms and O atoms are linearly arranged in NO. When the F ₂ molecule collides from the direction indicated by the arrow in FIG. 8, causing the reaction of equation (3). As shown in FIG. 8, NO has a larger solid angle causing the reaction than NO ₂ . Therefore, the wave function of N atoms and the wave function of F atoms are more likely to overlap in the case of NO.

Thus, the reactivity with F ₂ is greatly different between NO ₂ and NO. The inventors thought that the cause of the difference was not due to the recombination reaction of the F atom according to the formula (2) as conventionally considered, but to the three-dimensional shape of NO ₂ . In other words, the reaction rate constant k2 of the equation (2) is large in the steady state, but in the non-equilibrium state as in this embodiment in which the gas flow continues to flow and new F ₂ and NO ₂ are always supplied. I guess it's not that big. From this, it can be inferred that F atoms can be generated by reacting F ₂ and NO ₂ without using plasma.

7-3. Etchability As described above, the reaction rate constant k2 of the recombination reaction (formula (2)) is not necessarily large when new F ₂ and NO ₂ are constantly supplied. And under low pressure, the mean free path is longer than under high pressure. For these two reasons, in the etching method using the etching apparatus 100 of this embodiment, F ₂ and NO ₂ are reacted to generate F atoms to such an extent that etching is possible. This is something that could not be considered in the past.

8). Modification 8-1. Gas Mixing Chamber In this embodiment, the gas mixing chamber 140 is provided in the etching apparatus 100. However, the gas mixing chamber 140 may not be provided. If there is a space where the first gas and the second gas are mixed before being supplied to the etching target portion of the Si member, the etching can be performed.

8-2. No third gas supply unit The third gas supply unit 113 may be omitted. A mixed gas of NO ₂ gas and Ar gas may be put in the second gas supply unit 112. Even in that case, the gas supplied to the gas mixing chamber 140 is the same. As long as the pressure of the first gas and the pressure of the second gas are the same, there is no need for Ar gas.

8-3. Cooling device In this embodiment, the reaction chamber 150 is provided with the heater 152. However, a cooling device may be provided instead of or together with the heater 152. This is because the etching can be performed under the condition where the Si member is at a low temperature.

8-4. Mask Pattern In this embodiment, a mask made of SiO ₂ is prepared. However, it is not necessary to form such a mask when roughening the surface of the solar cell. In this way, a mask may not be required.

8-5. Etching rate In the present embodiment, the pressure inside the reaction chamber 150 is set in the range of 10 Pa to 10,000 Pa, and the temperature of the Si member S1 is set in the range of −20 ° C. to 500 ° C. Here, when the pressure inside the reaction chamber 150 is 1000 Pa or less and the temperature of the Si member S1 is 300 ° C. or less, the etching rate is slower than that of the present embodiment. For example, it is about several nm / min. Therefore, for example, the pressure inside the reaction chamber 150 may be set in the range of 100 Pa to 1000 Pa, and the temperature of the Si member S1 may be set in the range of 180 ° C. to 500 ° C. In particular, the temperature of the Si member S1 is preferably in the range of 180 ° C. or higher and 300 ° C. or lower.

8-6. Generation of F _{2 In} the present embodiment, the first gas containing F ₂ is supplied. However, a source containing at least IF ₃ , IF ₅ , IF ₇ , and XeF ₂ may be heated to generate F ₂ gas. Further, F ₂ may be generated by electrolysis from a liquid containing HF. That is, in that case, the first gas supply unit 111 has an F ₂ generation unit.

9. Summary of this embodiment As described in detail above, the etching method according to this embodiment uses the Si member as a mixed gas obtained by mixing the first gas containing F ₂ and the second gas containing NO ₂ . It is a method that leads to the surface. Moreover, the pressure of the atmosphere at the time of etching is in the range of 10 Pa to 10,000 Pa, which is sufficiently smaller than the atmospheric pressure. Therefore, it is considered that the lifetime and concentration of F atoms used for etching are sufficient. Therefore, an etching method and an etching apparatus capable of performing high-accuracy low-speed etching on a Si member using an inexpensive gas that is relatively easily available without using plasma have been realized.

This embodiment is merely an example. Therefore, naturally, various improvements and modifications can be made without departing from the scope of the invention. For example, the inert gas mixed with F ₂ or the like is not limited to Ar gas. For example, He, Ne, Xe, and Kr can be used. N ₂ may also be used. Two or more kinds of these inert gases may be used.

(Second Embodiment)
A second embodiment will be described. This embodiment is different from the first embodiment only in the configuration of the etching apparatus. Therefore, the differences will be mainly described. That is, the description common to the etching apparatus 100 of the first embodiment is omitted.

1. Etching Device FIG. 9 is a diagram showing a schematic configuration of an etching device 200 of the present embodiment. As shown in FIG. 9, the etching apparatus 200 includes a first gas supply unit 111, a second gas supply unit 112, mass flow controllers 121 and 122, a gas supply unit 230, a gas mixing chamber 240, and a reaction. Chamber 250.

The gas supply unit 230 is for supplying the first gas containing F ₂ and the second gas containing NO ₂ to the gas mixing chamber 240. The gas supply unit 230 has a two-stage configuration. FIG. 10 shows the first stage 231 and FIG. 11 shows the second stage 232. The first stage 231 in FIG. 10 supplies the first gas to the gas mixing chamber 240. The second stage 232 in FIG. 11 supplies the second gas to the gas mixing chamber 240.

  As shown in FIG. 10, the first stage 231 has a gas inlet 233 and a plurality of gas outlets 235. The plurality of gas ejection ports 235 are arranged discretely in a ring shape. Each gas outlet 235 opens toward the center of the gas mixing chamber 240. As long as it opens toward the inner side of the gas mixing chamber 240, it does not necessarily have to go to the center.

  As shown in FIG. 11, the second stage 232 has a gas introduction port 234 and a plurality of gas ejection ports 236. The plurality of gas ejection ports 236 are discretely arranged in a ring shape. Each gas outlet 236 opens toward the center of the gas mixing chamber 240. As long as it opens toward the inner side of the gas mixing chamber 240, it does not necessarily have to go to the center.

  The gas mixing chamber 240 is for generating F atoms by being supplied with the first gas and the second gas from the gas supply unit 230. The gas mixing chamber 240 is also provided with an exhaust port 245 for discharging the gas inside the gas mixing chamber 240.

  A partition wall 254 is provided between the gas mixing chamber 250 and the reaction chamber 250. The partition 254 is a perforated plate provided with a large number of through holes 254a, as shown in FIG. The through hole 254a has a tapered shape. That is, in the through hole 254a, the hole diameter increases from the gas mixing chamber 240 toward the reaction chamber 250. From these through holes 254a, F atoms and the like are sprayed onto the Si member. Thus, the partition 254 is a rectifying plate that rectifies the flow of F atoms or the like.

  The reaction chamber 250 has a mounting table 251 and an exhaust port 255. The partition wall 254 serving as a current plate is disposed at a position upstream of the gas flow from the mounting table 251. The reaction chamber 250 includes the heater 152 and the pressure gauge 170 shown in FIG. The exhaust port 255 is for exhausting gas from the reaction chamber 250.

2. Modification 2-1. Gas Supply Unit In the present embodiment, the gas supply unit 230 has a two-stage structure including a first gas ejection part 233 and a second gas ejection part 234. However, a configuration in which these are further repeatedly provided may be employed. For example, it is a four-stage gas supply unit. Of course, the structure of 6 steps | paragraphs or more may be sufficient.

(Third embodiment)
A third embodiment will be described. This embodiment is different from the second embodiment only in the configuration of the etching apparatus. Therefore, the differences will be mainly described. That is, the description common to the etching apparatus 200 of the second embodiment is omitted.

1. Etching Device FIG. 13 is a diagram showing a schematic configuration of an etching device 300 of the present embodiment. As shown in FIG. 13, the etching apparatus 300 includes a first gas supply unit 111, a second gas supply unit 112, mass flow controllers 121 and 122, a gas supply unit 330, a gas mixing chamber 340, a reaction Chamber 350.

The gas supply unit 330 is for supplying a first gas containing F ₂ and a second gas containing NO ₂ to the gas mixing chamber 340. As shown in FIG. 14, the gas supply unit 330 has gas inlets 331 and 332, a first chamber 333, a second chamber 334, and jet outlets 335 and 336.

  The first chamber 333 is a region to which the first gas supplied from the introduction port 331 is supplied. The second chamber 334 is a region to which the second gas supplied from the introduction port 332 is supplied. The first chamber 333 communicates with the gas mixing chamber 340 through a tapered jet port 335. The second chamber 334 communicates with the gas mixing chamber 340 through the jet port 336. For this reason, the first gas and the second gas are mixed with each other while being sprayed downward in FIGS. 13 and 14.

(Fourth embodiment)
A fourth embodiment will be described. This embodiment is different from the third embodiment only in the configuration of the etching apparatus. Therefore, the differences will be mainly described. That is, the description common to the etching apparatus 300 of the third embodiment is omitted.

1. Etching Device FIG. 15 is a diagram showing a schematic configuration of an etching device 400 of this embodiment. As shown in FIG. 15, the etching apparatus 400 includes a first gas supply unit 111, a second gas supply unit 112, mass flow controllers 121 and 122, a gas supply unit 430, a gas mixing chamber 440, a reaction A chamber 450 and a partition wall 460 are provided.

The gas supply unit 430 is for supplying the first gas containing F ₂ to the gas mixing chamber 340. As shown in FIG. 16, the gas supply unit 430 has a gas inlet 431, a gas chamber 432, and a jet outlet 433. The gas chamber 432 communicates with the gas mixing chamber 440 through the jet port 433. The jet nozzle 433 has a tapered shape.

  As shown in FIG. 17, the partition wall 460 is disposed at a position between the gas mixing chamber 440 and the reaction chamber 450. The partition wall 460 includes a flow path 461, an introduction port 462, a gas chamber 463, and a jet port 464. The channel 461 is for supplying the first gas to the gas mixing chamber 440. The gas chamber 463 is for supplying the second gas to the gas mixing chamber 440.

(Fifth embodiment)
A fifth embodiment will be described. This embodiment differs from the fourth embodiment only in the configuration of the etching apparatus. Therefore, the differences will be mainly described. That is, the description common to the etching apparatus 400 of the fourth embodiment is omitted.

1. Etching Device FIG. 18 is a diagram showing a schematic configuration of an etching device 500 of the present embodiment. As shown in FIG. 18, the etching apparatus 500 includes a first gas supply unit 111, a second gas supply unit 112, mass flow controllers 121 and 122, a gas supply unit 570, and a reaction chamber 550. doing.

  The gas supply unit 570 is for supplying the first gas and the second gas separately to the reaction chamber 550. The gas supply unit 570 has a torch shape. The gas supply unit 570 includes a first gas chamber 571 and a second gas chamber 572. The first gas chamber 571 is for injecting the first gas toward the reaction chamber 550. The shape of the opening 571a of the first gas chamber 571 is circular. The second gas chamber 572 is for injecting the second gas toward the reaction chamber 550. The shape of the opening 572a of the second gas chamber 572 is a ring shape. The opening 572a is disposed so as to surround the opening 571a.

  For this reason, the second gas is injected so as to surround the first gas. Then, the first gas and the second gas are mixed in the reaction chamber 550. And the chemical reaction shown in Formula (1) etc. arises. The opening widths of the openings 571a and 572a are narrow to some extent. Therefore, the mixed gas is irradiated toward a local portion inside the reaction chamber 550.

2. Field of Use The etching apparatus 500 of this embodiment can be used for local etching of Si members. Therefore, the mounting table 551 is preferably configured to be able to move such as translation and rotation.

(Sixth embodiment)
A cleaning apparatus according to the sixth embodiment will be described. The cleaning apparatus of this embodiment uses the etching apparatus 500 of the fifth embodiment as a cleaning apparatus. Therefore, the configuration of the apparatus is the same as that of the etching apparatus 500.

  Here, when a film of Si polycrystal or the like is formed by chemical vapor deposition, gas may circulate on the back surface of the wafer and adhere to the periphery of the wafer, which may greatly hinder the subsequent process. In order to remove the Si polycrystal on the back surface of the wafer, wet etching is often performed. However, in this case, many washing steps and waste liquid treatment are necessary.

  Therefore, in this embodiment, the back surface of the wafer is chemically dry etched using the etching apparatus 500.

  In addition, it is possible to remove the coating of the Si member formed on the parts of the apparatus for producing the Si member.

  Further, it can be used for cleaning a silicon substrate. Furthermore, by making the opening 571a into a ring shape and increasing the diameter of the openings 571a and 572a, the back surface of the silicon substrate can be cleaned without turning the silicon substrate over.

(Seventh embodiment)
A seventh embodiment will be described. In the first embodiment, a mixed gas of F ₂ and NO ₂ is used as the etching gas. In this embodiment, a mixed gas of F ₂ and NO is used as the etching gas. Therefore, differences from the first embodiment will be described. Note that the etching apparatuses 100, 200, 300, 400, and 500 described in the first to fifth embodiments may be used when performing the etching of the present embodiment. Then, instead of supplying NO ₂ gas, NO gas may be supplied.

1. 1. Chemical reaction occurring in gas mixing chamber and reaction chamber 1-1. Reaction in Gas Mixing Chamber Here, the chemical reaction that occurs in the gas mixing chamber 140 will be described. In the gas mixing chamber 140, chemical reactions of the following formulas (3) and (4) occur.
F ₂ + NO → F + FNO (3)
F + NO → FNO (4)
Reaction rate constant of formula (3): k3 (cm ³ / molecules −s)
Reaction rate constant of formula (4): k4 (cm ³ / molecules −s)

As described above, when the F ₂ gas and the NO gas are mixed, F atoms are generated as shown in the equation (3). And as shown in Formula (4), the produced | generated F atom recombines with NO and F atom reduces. Therefore, the concentration of F atoms varies depending on which of these reactions is dominant. That is, it is not always clear what value the F atom concentration is.

Conventionally, k3 and k4 were considered to be approximately the same as shown below (Kolb, CE; J. Chem. Phys. 1976, 64, 3087-3090.).
k3 ≒ k4
= 7.04 × 10 ⁻¹³ exp (−1150 / T) (5)
T: Temperature (K)
Therefore, although F atoms are generated by mixing F ₂ gas and NO gas, they are recombined with NO. Therefore, it has been considered that the concentration of F atoms is not so high. That is, it was thought that it was not so suitable for performing etching.

In this embodiment, as will be described later, F ₂ gas and NO gas are mixed under low pressure. The mean free path of each particle under low pressure is longer than the mean free path of each particle under high pressure. In the present embodiment, the gas mixture containing at least F ₂ and NO is continuously supplied to the gas mixing chamber 140. For this reason, it is considered that a certain number of F atoms generated by the reaction of the formula (3) may exist in the gas mixing chamber 140.

1-2. Reactions in the reaction chamber The reactions of the above formulas (3) and (4) also occur in the reaction chamber 150. Then, the Si member S <b> 1 is etched using F atoms that may exist in a certain number inside the reaction chamber 150. At this time, the particles that contribute to the reaction of the Si member S1 with the Si atoms are not limited to the F atoms. However, it is considered that F atoms mainly contribute to etching.

2. Etching method 2-1. Pattern Formation Step First, a mask pattern is formed on the Si member S1. For example, in the case of manufacturing a semiconductor device, a mask is arranged at a location where a trench is not formed. An example of the material of the mask is SiO ₂ .

2-2. Gas Supply Process The etching method according to this embodiment will be described. First, the Si member S <b> 1 is mounted on the mounting table 151 of the reaction chamber 150. Next, the reaction chamber 150 is evacuated to lower the internal pressure of the reaction chamber 150. At the same time, the heater 152 is heated to the set value. Then, the first gas is supplied from the first gas supply unit 111, the second gas is supplied from the second gas supply unit 112, and the Ar gas is supplied from the third gas supply unit 113.

2-3. Etching Particle Generation Step Then, F atoms are generated by the reaction shown in the above formula (3). Other particles are also generated. These reactions mainly occur in the gas mixing chamber 140. At this time, F ₂ , NO, F, FNO, Ar, these ions, electrons, and other particles may exist in the mixed gas in the gas mixing chamber 140. In the reaction chamber 150, the same reaction occurs and the same particles may exist.

2-4. Etching Step Next, the mixed gas is introduced into the Si member S <b> 1 inside the reaction chamber 150. Then, the F atoms react with the Si member S1. Thereby, the etching of the Si member S1 proceeds. Thereby, the part of the Si member S1 that is not covered with the mask is removed. Here, the pressure inside the reaction chamber 150 is in the range of 10 Pa to 10,000 Pa. Further, the pressure inside the reaction chamber 150 is preferably in the range of 100 Pa to 1000 Pa. The pressure inside the reaction chamber 150 is the total pressure of the mixed gas that occupies the inside of the reaction chamber 150. Therefore, if Ar gas is supplied, the pressure is also included. And the temperature of Si member S1 shall be in the range of -20 degreeC or more and 500 degrees C or less. Within this pressure and temperature range, the gas mixture remains a gas. The mixed gas is not brought into a plasma state.

2-5. Other Steps Other steps may also be performed.

3. Experiment C (F ₂ + NO temperature dependence)
3-1. Si member In this experiment, a silicon substrate was used as the Si member S1. The size of this silicon substrate was 6 mm wide and 15 mm long. The silicon substrate is a p-type semiconductor. The electrical resistivity was 10 Ωcm.

3-2. Experimental conditions In this experiment, etching was performed under the experimental conditions shown in Table 1. 109.1 sccm of a mixed gas in which F ₂ gas was mixed with Ar gas at a volume ratio of 5% was supplied. As a result, 2.7 sccm of F ₂ gas is supplied to the reaction chamber. On the other hand, NO was supplied to the reaction chamber by 5 sccm. The pressure inside the reaction chamber was 600 Pa. Etching was performed for 5 minutes. The opening width set by the mask made of SiO ₂ was 8 μm square. The distance between the gas mixing chamber and the reaction chamber was 20 mm. In this experiment, etching was performed under the above conditions by changing the temperature of the silicon substrate.

[Table 1]
F ₂ gas 2.7sccm
NO gas 5sccm
Internal pressure of reaction chamber (total pressure) 600Pa
Etching time 5 minutes Mask opening width 8μm square Substrate temperature 27 ℃ ~ 300 ℃

3-3. Experimental results 3-3-1. Etching Shape FIGS. 19 to 22 are photomicrographs showing a cross section of a silicon substrate etched in this experiment. A scanning electron microscope (SEM) was used as a microscope.

  FIG. 19 is a scanning micrograph showing a cross section when the substrate temperature is 27 ° C. As shown in FIG. 19, in this case, a recess having a relatively deep and rough shape was formed. The etching rate at this time is about 5 μm / min. The aspect ratio was about 3.

  FIG. 20 is a scanning micrograph showing a cross section when the substrate temperature is 110 ° C. As shown in FIG. 20, in this case, a flat recess was formed. The etching rate is about 0.7 μm / min. The aspect ratio was almost 1.

  FIG. 21 is a scanning micrograph showing a cross section when the substrate temperature is 300.degree. As shown in FIG. 21, in this case, a concave portion having a gentle concave surface was formed. Further, crystal plane orientation was observed.

  As shown in FIG. 22, the silicon substrate could be etched when the substrate temperature was in the range of 27 ° C. to 300 ° C. Moreover, the cross-sectional shape of etching differs depending on the substrate temperature. As shown in FIG. 22, when the substrate temperature was 27.degree. C., 40.degree. C., 50.degree. C., and 60.degree. C., a relatively deep and rough recess was formed. Thus, when the substrate temperature is in the range of 20 ° C. or higher and 60 ° C. or lower, a rough concave portion is formed. Therefore, it is suitable for roughening a wide area.

  As shown in FIG. 22, when the substrate temperatures were 65 ° C., 85 ° C., 110 ° C., and 180 ° C., flat concave portions were formed. When the substrate temperature is higher than 60 ° C. and lower than or equal to 180 ° C., a flat recess is formed.

  As shown in FIG. 22, when the substrate temperatures were 230 ° C. and 300 ° C., a concave portion having a gentle concave surface was formed. When the substrate temperature is higher than 180 ° C. and not higher than 500 ° C., a concave portion having a gentle concave surface is formed.

3-3-2. Etching Rate FIG. 23 shows the etching rate. The horizontal axis in FIG. 23 is 1000 times the reciprocal of the temperature. The information in FIG. 23 indicates the temperature corresponding to the value on the horizontal axis. The vertical axis in FIG. 23 is the etching rate. As shown in FIG. 23, the etching rate is fast in the temperature region T1 where rough etching is performed near room temperature. As the substrate temperature rises, the etching rate decreases, and takes a minimum value when the substrate temperature is about 60 ° C. In a region where the substrate temperature is higher than 60 ° C., the etching rate tends to be faster as the substrate temperature is higher.

  Such a tendency suggests that the concentration of F atoms depends on the temperature inside the reaction chamber 150. Note that the temperature inside the reaction chamber 150 is substantially equal to the temperature of the silicon substrate. In addition, it is considered that in the reaction chamber 150, other particles such as FNO function as an etchant in addition to F atoms.

  In the temperature region T1, a concave portion having a rough shape is formed. Therefore, it is suitable for roughening a wide area. For example, it can be applied to roughening the surface of a solar cell. In the temperature region T2, a flat concave portion can be formed. Also, the etching rate is sufficiently slow. Therefore, it is possible to carry out etching with relatively high accuracy. For example, it can be applied when forming a trench of a semiconductor element. It can also be applied to remove a damage layer generated in the vicinity of the gate of the MOSFET. In the temperature region T2, a concave portion having a gentle concave surface can be formed. For example, it can be applied when forming a MEMS.

  Table 2 summarizes the temperature, the value of 1000 / T shown on the horizontal axis of FIG. 23, and the etching rate. Here, the etching rate is a value in a direction perpendicular to the plate surface of the silicon substrate.

[Table 2]
Temperature 1000 / T Etching rate (vertical direction)
(° C) (K ^-1 ) (μm / min)
27 3.3 4.37
40 3.2 2.60
51 3.1 1.21
60 3.0 0.72
85 2.8 0.50
110 2.6 0.68
180 2.2 1.34
230 2.0 1.88
300 1.7 2.77

  FIG. 24 shows the surface state of the silicon substrate when the substrate temperature is 27 ° C. and when the substrate temperature is 230 ° C.

3-3-3. Comparative Example Etching is performed on the silicon substrate in either case of supplying only F ₂ gas (Comparative Example 1) or supplying only NO gas (Comparative Example 2) under the conditions shown in Table 1. There wasn't. The substrate temperature in these cases was room temperature.

4). Experiment D (F ₂ + NO flow rate dependence)
4-1. Si member The same silicon substrate as used in Experiment C was used.

4-2. Experimental conditions Experiments were performed under the experimental conditions shown in Table 3. The substrate temperature was 27 ° C. Then, the ratio of the supply amount of F ₂ gas and the supply amount of NO gas was changed by changing the supply amount of NO gas from 0 sccm to 8 sccm. Conditions other than these are the same as in Experiment C shown in Table 1.

[Table 3]
F ₂ gas 2.7sccm
NO gas 0-8sccm
Internal pressure of reaction chamber (total pressure) 600Pa
Etching time 5 minutes Mask opening width 15μm square Substrate temperature 27 ℃

4-3. Experimental Results The experimental results are shown in FIG. The horizontal axis of FIG. 25 is the ratio of the NO gas flow rate to the F ₂ gas flow rate. The vertical axis in FIG. 25 is the etching rate. As shown in the graph of FIG. 25, the etching rate was fast when the ratio of the flow rate of NO gas to the flow rate of F ₂ gas was in the range of 1.0 to 2.0. The value of the etching rate within this range was about 5 μm / min. In other words, suitable etching can be performed within this range. Note that the silicon substrate could not be etched when NO gas was not supplied (0 sccm).

FIG. 26 is a graph showing the relationship between the flow rate ratio of F ₂ and NO and the roughness of the etched surface. The horizontal axis of FIG. 26 is the ratio of the NO gas flow rate to the F ₂ gas flow rate. The vertical axis | shaft of FIG. 26 is the mean square roughness (nm) of an etching location. As shown in FIG. 26, as the supply amount of NO is increased, the roughness of the etched portion tends to be rough. The maximum value is obtained when the ratio of the flow rate of NO gas to the flow rate of F ₂ gas is 1.5. The mean square roughness at that time is about 12 nm. When the supply amount of NO is further increased, the roughness value of the etched portion decreases. In addition, the broken line in FIG. 26 has shown the calculated value of F atom.

  FIG. 27 is a scanning micrograph showing a cross section of the etched silicon substrate. A case where the flow rate of NO is 1 sccm (C1) and a case where the flow rate of NO is 4 sccm (C2) are shown. When the flow rate of NO was 4 sccm, three different types of etch pits H1, H2, and H3 shown in Table 4 could be observed. FIG. 28 shows how a plurality of types of etch pits are formed. FIG. 28 is a scanning photomicrograph (C3) showing the bottom surface of the etched silicon substrate. The flow rate of NO is 4 sccm.

  FIG. 29 is a scanning micrograph (C4) showing the bottom surface of the silicon substrate when the flow rate of NO is 1 sccm. In this case, etch pits H1 and H3 are mainly generated. FIG. 30 is a scanning micrograph (C5) showing the bottom surface of the silicon substrate when the flow rate of NO is 3 sccm. In this case, a number of etch pits H2 are formed in addition to the etch pits H1 and H3. FIG. 31 is a scanning micrograph (C6) showing the bottom surface of the silicon substrate when the flow rate of NO is 8 sccm. In this case, the etch pit H1 is expressed, but the etch pits H2 and H3 are lost.

[Table 4]
Etch pit type Pit diameter H1 50 nm to 100 nm H2 300 nm to 600 nm H3 2 μm to 5 μm

5. Experiment E (F ₂ + NO pressure dependence)
5-1. Si member The same silicon substrate as used in Experiment C was used.

5-2. Experimental conditions Experiments were performed under the experimental conditions shown in Table 5. Further, a mixed gas in which F ₂ gas was mixed with Ar gas at a volume ratio of 10% was supplied. As shown in Table 5, the substrate temperature was 27 ° C. The etching time was 5 minutes. The opening width of the mask was 8 μm square. Under these conditions, etching was performed with the internal pressure of the reaction chamber being 200 Pa, 400 Pa, 600 Pa, and 800 Pa.

[Table 5]
F ₂ gas 5.4sccm
NO gas 16sccm
Internal pressure of reaction chamber (total pressure) 100Pa-1000Pa
Etching time 5 minutes Mask opening width 8μm square Substrate temperature 27 ℃

5-3. Experimental Results FIG. 32 shows the results. FIG. 32A is a scanning micrograph at 200 Pa. FIG. 32B is a scanning micrograph at 400 Pa. FIG. 32C is a scanning photomicrograph at 600 Pa. FIG. 32 (d) is a scanning photomicrograph at 800 Pa. FIG. 32 (e) is a scanning photomicrograph obtained by enlarging FIG. 32 (a). FIG. 32F is an enlarged scanning micrograph of FIG. 32B. FIG. 32G is an enlarged scanning micrograph of FIG.

  As shown in FIG. 32, a hemispherical recess was formed by etching. In addition, the larger the pressure in the reaction chamber, the larger the size of the recess produced by etching. That is, the higher the pressure, the higher the etching rate. Also, the higher the pressure, the finer the surface roughness of the inner surface of the etched recess.

6). Experiment F (etching of sacrificial layer of MEMS)
FIG. 33A is a scanning photomicrograph when the sacrificial layer of MEMS is etched. FIG. 33 (b) is an enlarged photograph of FIG. 33 (a). As shown in FIG. 33A, the sacrificial layer of the MEMS having a fine structure could be suitably etched.

  FIG. 34 (a) is a scanning photomicrograph when the sacrificial layer of MEMS is etched. FIG. 34 (b) is an enlarged photograph of FIG. 34 (a). The temperature of the MEMS at this time was 27 ° C. As described above, the etching can be suitably performed even at substantially normal temperature.

7). Experiment G (Number of collisions in F ₂ + NO)
FIG. 35 is a graph showing the relationship between the number of collisions of gas particles and the etching rate. Here, the mean free path and the number of collisions (n) were calculated from the internal pressure of the reaction chamber and the distance (d) from the gas mixing location to the silicon substrate. And the distance (d) used as the frequency | count of the collision and the etching rate at the time of a pressure were plotted.

7-1. Number of collisions and etching rate As shown in FIG. 35, in the region (I), the etching rate increases in proportion to the number of collisions n. In the region (II), the etching rate decreases by 1 / d ² . In region (III), the etching rate is significantly reduced.

  The present inventors consider the result of FIG. 35 as follows. In the region (I), it is considered that F atoms are increased by the reaction of the formula (3). In the region (II), the number of F atoms increased by repeated collisions is considered to decrease due to the reaction of the formula (4). In the region (III), since NO and FNO are adsorbed on the surface of Si, it is considered that etching of Si by F atoms is suppressed.

7-2. The internal pressure of the reaction chamber and the etching rate The internal pressure of the reaction chamber and the number of collisions are proportional. Therefore, the internal pressure of the reaction chamber when the distance from the gas mixing point is 30 mm is displayed in the upper part of FIG. As shown in FIG. 35, a certain amount of etching can be performed when the internal pressure of the reaction chamber is in the range of 100 Pa to 1000 Pa.

7-3. The distance from the gas mixing location and the etching rate The distance from the gas mixing location and the number of collisions are proportional. Therefore, the distance from the gas mixing point to the silicon substrate when the internal pressure of the reaction chamber is 600 Pa is displayed in the upper part of FIG. As shown in FIG. 35, a certain amount of etching can be performed when the distance from the gas mixing point is in the range of 5 mm to 70 mm. Moreover, it is more preferable that the distance from the gas mixing location is in the range of 5 mm to 50 mm.

8). Comparison of NO and NO ₂ Here, an experiment using NO as the second gas and an experiment using NO ₂ are compared. FIG. 36 is a photomicrograph comparing an etching site using NO and an etching site using NO ₂ at the same scale. 36A and 36B, the substrate temperature was 300 ° C., and the internal pressure of the reaction chamber was 600 Pa. As described above, the etching rate is greatly different between the case where NO is used as the second gas and the case where NO ₂ is used.

  FIG. 37 shows the relationship between the substrate temperature and the etching rate. When NO was used as the second gas, the etching could be carried out in a wide range where the substrate temperature was 20 ° C. or higher and 300 ° C. or lower.

On the other hand, when NO ₂ was used as the second gas, the etching could be carried out in the range where the substrate temperature was 180 ° C. or higher and 300 ° C. or lower. Thus, the etching rate when NO is used as the second gas is about 30 times the etching rate when NO ₂ is used.

9. Application Field As described above, in the temperature region T1 of FIG. 23, since rough etching can be performed, it is preferably applied to the roughening of the surface of the solar cell. For example, as shown in FIG. 38, the reflectance of the solar cell becomes very small due to the roughening of the present embodiment. Therefore, as shown in FIG. 39, some of the light reflected from the roughened surface can be incident again on the other roughened surface. Thereby, more light is absorbed into the solar cell. In summary, the light irradiated from the outside of the solar cell is absorbed more inside the solar cell on the roughened Si surface than the flat Si surface.

  In the temperature region T2 of FIG. 23, since flat and low-speed etching can be performed, it is preferably applied to remove a damaged layer near the gate of the semiconductor device by etching. In the temperature region T3 of FIG. 23, since a gentle concave surface can be formed, it is preferably used for manufacturing MEMS.

10. Modified Example The modified example described in the first embodiment can be similarly applied.

11 Summary of this Embodiment As described in detail above, the etching method according to this embodiment uses the surface of the Si member as a mixed gas in which a first gas containing F ₂ and a second gas containing NO are mixed. It is a way to lead to. Moreover, the pressure of the atmosphere at the time of etching is in the range of 10 Pa to 10,000 Pa, which is sufficiently smaller than the atmospheric pressure. Therefore, it is considered that the lifetime and concentration of F atoms used for etching are sufficient. Therefore, an etching method and an etching apparatus have been realized that can perform various etchings on the Si member using an inexpensive gas that is relatively easily available without using plasma.

This embodiment is merely an example. Therefore, naturally, various improvements and modifications can be made without departing from the scope of the invention. For example, the inert gas mixed with F ₂ or the like is not limited to Ar gas. For example, He, Ne, Xe, and Kr can be used. N ₂ may also be used. Two or more kinds of these inert gases may be used.

100, 200, 300, 400, 500 ... Etching apparatus 111 ... First gas supply unit 112 ... Second gas supply unit 113 ... Third gas supply unit 121, 122, 123 ... Mass flow controllers 131, 132 ... Pressure adjustment Valve 140 ... Gas mixing chamber 150 ... Reaction chamber 151 ... Mounting table 152 ... Heater 160 ... Voltage application unit 170 ... Pressure gauge S1 ... Si member

Claims (10)

In an etching method for dry etching a Si member,
The pressure of the mixed gas containing F ₂ and NO ₂ is set in the range of 10 Pa to 10,000 Pa and the mixed gas is led to the Si member without being in a plasma state,
The temperature of the Si member is a temperature within a range of −20 ° C. or more and 500 ° C. or less,
An etching method comprising etching the Si member. The etching method according to claim 1,
The pressure of the mixed gas containing F ₂ and NO ₂ is guided to the Si member within a range of 100 Pa to 1000 Pa,
An etching method, wherein the temperature of the Si member is set to a temperature within a range of 180 ° C. or higher and 500 ° C. or lower. In the etching method according to claim 1 or 2,
F ₂ + NO ₂ → F + FNO ₂
To generate at least F atoms,
An etching method comprising reacting F atoms with the Si member. In the etching method according to any one of claims 1 to 3,
An etching method, wherein a distance from a mixing location where F ₂ and NO ₂ are mixed to the Si member is in a range of 5 mm to 70 mm. In an etching method for dry etching a Si member,
The pressure of the mixed gas containing F ₂ and NO is set within a range of 100 Pa to 1000 Pa and the mixed gas is led to the Si member without being in a plasma state,
The temperature of the Si member is set to a temperature within a range higher than 60 ° C and lower than 180 ° C,
A flat recess is formed by etching the Si member. In an etching method for dry etching a Si member,
The pressure of the mixed gas containing F ₂ and NO is set within a range of 100 Pa to 1000 Pa and the mixed gas is led to the Si member without being in a plasma state,
The temperature of the Si member is set to a temperature within a range higher than 180 ° C. and 500 ° C. or lower,
An etching method, wherein a concave portion having a gentle curved surface is formed by etching the Si member. In an etching apparatus for dry etching a Si member,
A reaction chamber for etching the Si member;
A first gas supply unit for supplying a first gas containing F ₂ gas to the reaction chamber;
A second gas supply unit for supplying a _second gas containing NO ₂ gas to the reaction chamber;
Have
The internal pressure of the reaction chamber is in the range of 10 Pa to 10,000 Pa,
An etching apparatus characterized by not having a plasma generator. The etching apparatus according to claim 7, wherein
An etching apparatus characterized in that an internal pressure of the reaction chamber is in a range of 100 Pa to 1000 Pa. The etching apparatus according to claim 7 or 8,
In the reaction chamber,
F ₂ + NO ₂ → F + FNO ₂
An etching apparatus characterized by causing at least the above reaction and reacting at least F atoms with the Si member. In the etching apparatus according to any one of claims 7 to 9,
The distance from the mixing location where F ₂ and NO ₂ are mixed to the Si member is
An etching apparatus characterized by being in a range of 5 mm to 70 mm.