JP6871550B2 - Etching device - Google Patents

Description

The technical field of the present specification relates to an etching apparatus for etching a group III nitride semiconductor.

Group III nitride semiconductors represented by GaN are applied to LEDs, for example. In addition, group III nitride semiconductors have high dielectric breakdown strength, high heat resistance, and high-speed operability. Therefore, it is expected to be applied as a power device.

When applying a group III nitride semiconductor to a power device, the group III nitride semiconductor may be etched. One example is the case of forming a trench in a group III nitride semiconductor. Therefore, techniques for etching group III nitride semiconductors have been developed. For example, Patent Document 1 discloses a technique for performing dry etching using a gas containing _{Cl 2} at a substrate temperature of 200 ° C. or higher and 600 ° C. or lower.

Japanese Unexamined Patent Publication No. 2014-45049

However, in the technique of Patent Document 1, the group III nitride semiconductor may be overetched. That is, the group III nitride semiconductor under the mask becomes thin. In this case, the mechanical strength of the narrow portion is weak. In addition, the electric field may be concentrated in the narrow portion. Therefore, it is preferable to suppress overetching of the group III nitride semiconductor.

The technique described in the present specification has been made to solve the problems of the above-mentioned conventional techniques. The problem is to provide an etching apparatus capable of suppressing overetching of a group III nitride semiconductor.

The etching apparatus according to the first aspect includes a processing chamber for etching the group III nitride semiconductor, a substrate holding unit for holding the group III nitride semiconductor, and a gas supply unit for supplying the first gas to the inside of the processing chamber. It has a plasma generating unit that converts the first gas into plasma, and a first potential applying unit that applies a high frequency potential to the substrate holding unit. The first gas is a chlorine-based mixed gas containing _{Cl 2} and B _{Cl 3.} The first potential applying portion applies a bias having a smaller absolute value to the substrate holding portion as the volume ratio of _{BCl 3 in the first gas is larger.} The first potential applying portion is
Vpp ≤ -1200 · X + 480
Vpp ≧ -1200 ・ X + 290
0.01 ≤ X ≤ 0.4
Vpp: Bias (V)
X: A bias is applied to the substrate holding portion so as to satisfy the volume ratio of _{BCl 3 in the first gas.}

In this etching apparatus, the first potential applying portion applies a bias to the substrate holding portion, which has a smaller absolute value as the volume ratio of _{BCl 3 in the first gas is larger.} Therefore, there is almost no risk of overetching the group III nitride semiconductor directly under the mask. That is, the width of the group III nitride semiconductor directly under the mask is almost the same as the width of the mask.

In the present specification, an etching apparatus for suppressing overetching of a group III nitride semiconductor is provided.

It is a figure which shows the schematic structure of the etching apparatus of 1st Embodiment. It is a figure which shows typically the behavior of Cl- ion. It is a figure which shows typically the behavior of Cl radical. It is a scanning micrograph (No. 1) which shows the cross section of the etched GaN substrate. It is a scanning micrograph (No. 2) which shows the cross section of the etched GaN substrate. It is a graph which shows the surface roughness of the GaN substrate with respect to the volume ratio of _{BCl 3 in} the 1st gas. It is a graph which shows the photoluminescence intensity with respect to the volume ratio of _{BCl 3 in} the 1st gas. 6 is a graph showing the relationship between the volume ratio of _{BCl 3 in} the first gas and the bias Vpp.

Hereinafter, a specific embodiment will be described with reference to the drawings, taking an etching apparatus as an example.

(First Embodiment)
1. 1. Etching apparatus FIG. 1 is a diagram showing a schematic configuration of an etching apparatus 1000 of the first embodiment. The etching apparatus 1000 includes a processing chamber 1001, a susceptor 1100, a susceptor support portion 1110, a heating portion 1120, a SiC plate 1130, a first potential applying portion 1200, a first matching unit 1210, and a plasma generating portion. It has a 1300, a second potential applying unit 1400, a second matching unit 1410, a gas supply unit 1500, a gas supply pipe 1510, a shower plate 1600, an exhaust port 1700, and a spare chamber 1800.

The processing chamber 1001 is a reaction chamber for etching the group III nitride semiconductor of the substrate S1. The substrate S1 has a group III nitride semiconductor. The processing chamber 1001 has a susceptor 1100 that supports the substrate S1, a susceptor support portion 1110, a SiC plate 1130, a plasma generating portion 1300, a shower plate 1600, and an exhaust port 1700.

The susceptor 1100 is a substrate holding portion for supporting the substrate S1 having a group III nitride semiconductor. The material of the susceptor 1100 is, for example, SiC. Further, the carbon material may be coated with SiC. The susceptor support portion 1110 is a support base for supporting the susceptor 1100. The heating unit 1120 is for heating the susceptor 1100. The heating unit 1120 heats the substrate S1 via the susceptor 1100.

The first potential applying unit 1200 is for applying a high frequency potential to the susceptor 1100. Therefore, the first potential applying unit 1200 can apply the potential to the substrate S1 via the susceptor 1100. The frequency of the high frequency potential in the first potential applying unit 1200 is, for example, 13.56 MHz. Of course, the frequency may be other than this. The first matching device 1210 is arranged between the first potential applying portion 1200 and the susceptor 1100. That is, the first potential applying unit 1200 is connected to the susceptor 1100 via the first matching device 1210.

The plasma generation unit 1300 is for generating plasma at a position facing the susceptor 1100 inside the processing chamber 1001. The plasma generation unit 1300 converts the first gas, which will be described later, into plasma. The plasma generation unit 1300 is an ICP unit that generates inductively coupled plasma (ICP).

The second potential applying unit 1400 is for applying a high frequency potential to the plasma generating unit 1300. The frequency of the high frequency potential in the second potential applying unit 1400 is, for example, 27.12 MHz. Of course, the frequency may be other than this. The second matching unit 1410 is arranged between the second potential applying unit 1400 and the plasma generating unit 1300. That is, the second potential applying unit 1400 is connected to the plasma generating unit 1300 via the second matching device 1410.

The gas supply unit 1500 is for supplying the first gas to the inside of the processing chamber 1001. Here, the first gas is a mixed gas of _{Cl 2} and B _{Cl 3.} The gas supply pipe 1510 is a flow path for connecting the gas supply unit 1500 and the processing chamber 1001. The gas supply unit 1500 supplies the first gas to the spare chamber 1800. After that, the first gas passes from the spare chamber 1800 through the shower plate 1600 and reaches the location of the plasma generating unit 1300. The shower plate 1600 is a straightening vane that rectifies the first gas. The exhaust port 1700 is for discharging gas from the processing chamber 1001.

2. Etching method The etching apparatus 1000 of the first embodiment is used. First, the substrate S1 is arranged on the susceptor 1100 of the etching apparatus 1000. Next, the etching apparatus 1000 is evacuated. Then, the gas supply unit 1500 supplies the first gas, which is a mixed gas of _{Cl 2} and BCl _{3, to the inside of the processing chamber 1001.} Then, the first potential applying unit 1200 applies a high frequency bias Vpp to the susceptor 1100. The second potential applying unit 1400 applies a high frequency potential to the plasma generating unit 1300. As a result, the plasma generating unit 1300 generates plasma inside the processing chamber 1001. Then, the first gas is turned into plasma, and a plasma product is generated from the plasma generation region. Plasma products include ions and radicals derived from B and Cl, and ultraviolet light. Then, such ions and radicals etch the group III nitride semiconductor of the substrate S1.

2-1. Etching condition 1
The etching conditions are shown in Table 1. The gas supply unit 1500 supplies the first gas to the inside of the processing chamber 1001. Here, the first gas is a chlorine-based mixed gas. More specifically, the first gas is a mixed gas of _{Cl 2} and BCl _{3. The volume ratio of BCl 3} to the first gas is 0.01 or more and 0.4 or less. Here, _{the volume ratio of BCl 3} to the first gas is the same as the flow rate ratio of _{BCl 3} to the first gas introduced into the treatment chamber 1001. The internal pressure of the processing chamber 1001 is 1 Pa or more and 10 Pa or less. When the internal pressure of the processing chamber 1001 is within this range, the plasma generated by the plasma generating unit 1300 is inductively coupled plasma. The bias Vpp is 0 V or more and 468 V or less. The frequency of the bias Vpp is about 1 MHz or more and 100 MHz or less. The output of the plasma generating unit 1300 is about 200 W or more and 800 W or less. The substrate temperature is 300 ° C. or higher and 500 ° C. or lower.

[Table 1]
Internal pressure 1 Pa or more 10 Pa or less _{Volume ratio of BCl 3} 0.01 or more 0.4 or less Bias 0 V or more 468 V or less

2-2. Etching condition 2
_{The larger the volume ratio of BCl 3} to the first gas, the smaller the absolute value of the bias Vpp applied to the susceptor 1100 by the first potential applying unit 1200.

The first potential applying unit 1200 applies a bias Vpp satisfying the following equation to the susceptor 1100.
Vpp ≤ -1200 · X + 480 ……… (1)
Vpp ≧ -1200 ・ X + 290 ……… (2)
0.01 ≤ X ≤ 0.4
Vpp: Bias (V)
X: Volume ratio of _{BCl 3} to the first gas

In this case, the group III nitride semiconductor is preferably etched. There is almost no risk of overetching group III nitride semiconductors.

2-3. Etching condition 3
It is more preferable that the gas supply unit 1500 makes _{the volume ratio of BCl 3 in} the first gas 2% or more and 30% or less. That is, the first gas supplied by the gas supply unit 1500 satisfies the following equation.
0.02 ≤ X ≤ 0.3

In this case, the group III nitride semiconductor is more preferably etched. There is almost no risk of overetching group III nitride semiconductors.

3. 3. Relationship between plasma product and bias Here, the relationship between plasma product and bias will be described. Among the plasma products, ions and radicals will be described. It explained ^- Cl on behalf of the ions. Cl radicals will be described on behalf of radicals.

3-1. Ion Behavior FIG. 2 is a diagram schematically showing the behavior of ^Cl-ions. Cl ^- ions are negatively charged. Therefore, the bias Vpp ^{accelerates Cl-} ions toward the substrate S1. That is, the Cl ^- ion moves in the direction of arrow K1 in FIG. Therefore, Cl ^- ions etch the group III nitride semiconductor of the substrate S1 mainly in the longitudinal direction. Here, the vertical direction is a direction perpendicular to the plate surface of the substrate S1.

3-2. Radical Behavior FIG. 3 is a diagram schematically showing the behavior of Cl radicals. Cl radicals are electrically neutral. Therefore, it is not affected by the surrounding electric field. Therefore, Cl radicals move radially regardless of the bias Vpp. That is, the Cl radical moves in the direction of arrow K2 in FIG. Therefore, the Cl radical etches the group III nitride semiconductor of the substrate S1 not only in the vertical direction but also in the horizontal direction. Here, the lateral direction is a direction parallel to the plate surface of the substrate S1. Therefore, it is considered that this radical is involved in the overetching of the group III nitride semiconductor.

3-3. Bias and Etching In this embodiment, the bias Vpp is adjusted according to the state of the plasma product generated in the plasma generation region. This adjusts the balance between the ions and radicals that reach the substrate S1. This prevents the width of the group III nitride semiconductor directly under the mask from becoming narrow.

3-4. Action of BCl ₃ Also, in etching, _{B of BCl 3} may bond with the group III nitride semiconductor on the side surface of the recess of the group III nitride semiconductor. Then, it is possible that B suppresses overetching on the surface of the group III nitride semiconductor. Therefore, it is considered that the bias Vpp may be reduced as the flow rate of _{BCl 3 increases. This is because it is considered that B of BCl 3} suppresses the side etching of the group III nitride semiconductor even if the bias Vpp is reduced and the contribution of radicals is increased. Alternatively, it is considered that the larger the flow rate of _{BCl 3,} ^{the more Cl-ions are generated.} Therefore, it is considered that it is not necessary to increase the bias Vpp so much.

4. Effect of the present embodiment The etching apparatus 1000 of the present embodiment can etch a group III nitride semiconductor while suppressing overetching. That is, the width of the mask and the width of the group III nitride semiconductor below the mask are almost equal.

5. Modification 5-1. The rare gas or nitrogen gas gas supply unit 1500 supplies a first gas which is a chlorine-based mixed gas. The first gas is a mixed gas of _{Cl 2} and B _{Cl 3.} The gas supply unit 1500 may supply the inside of the processing chamber 1001 with a second gas obtained by mixing the first gas with a gas containing at least one of a nitrogen gas and a rare gas. However, the volume ratio X occupied by the BCl ₃ is the volume of BCl ₃ in the total volume of Cl ₂ and BCl _3.

5-2. Position of plasma generating unit In the present embodiment, the plasma generating unit 1300 is located inside the processing chamber 1001. The plasma generation unit 1300 may be arranged inside a separate chamber outside the processing chamber 1001. However, it is preferable that the plasma generating unit 1300 is arranged at a position not so far from the susceptor 1100 on which the substrate S1 is arranged.

5-3. Types of plasma generating unit In this embodiment, the plasma generating unit 1300 is an ICP unit. However, another plasma generator may be used as the plasma generator 1300. For example, the plasma generator 1300 may be either a capacitively coupled plasma (CCP), an electron cyclotron resonance plasma (ECR), a helicon wave excited plasma (HWP), or a microwave excited surface wave plasma (SWP). There may be.

5-4. Susceptor The susceptor 1100 may be rotatable.

5-5. Combination You may freely combine the above modified examples.

6. Summary of the present embodiment The etching apparatus 1000 of the present embodiment adjusts the high frequency potential applied to the susceptor 1100 by the first potential applying unit 1200. A first gas, which is a mixed gas of _{Cl 2} and B _{Cl 3} , is supplied as a plasma gas. Then, the bias applied by the first potential applying unit 1200 is adjusted according to the volume ratio of _{BCl 3 in} the first gas. As a result, the etching apparatus 1000 can prevent the width of the group III nitride semiconductor directly under the mask from being narrowed.

1. 1. Experiment 1 (without overetching)
FIG. 4 is a scanning micrograph (No. 1) showing a cross section of the etched GaN substrate. A GaN substrate on which a mask had been formed was used as the substrate. The substrate temperature was 400 ° C. The output of the plasma generator was 400 W. The bias frequency was 3.2 MHz. The bias Vpp was 228V. The volume ratio of BCl _{3 in the supplied gas was 0.1.} The internal pressure of the processing chamber 1001 was 5 Pa. The etching time was 30 seconds. In this case, the conditional expressions (1) and (2) are satisfied.

As shown in FIG. 4, in this case, the width of the mask and the width of the GaN in the lower layer of the mask are almost equal.

2. Experiment 2 (when there is overetching)
FIG. 5 is a scanning micrograph (No. 2) showing a cross section of the etched GaN substrate. A GaN substrate on which a mask had been formed was used as the substrate. The substrate temperature was 400 ° C. The output of the plasma generator was 400 W. The bias frequency was 3.2 MHz. The bias Vpp was 228V. The only gas supplied was chlorine gas. The internal pressure of the processing chamber 1001 was 5 Pa. The etching time was 10 minutes. In this case, the conditional expressions (1) and (2) are not satisfied.

As shown in FIG. 5, in this case, the GaN in the layer below the mask is overetched. That is, the width of a part of the GaN in the layer below the mask is smaller than the width of the mask.

3. 3. Experiment 3 (surface roughness)
FIG. 6 is a graph showing the surface roughness of the GaN substrate with respect to the volume ratio of _{BCl 3 to the first gas.} The horizontal axis of FIG. 6 is the volume ratio of _{BCl 3 to the supplied gas.} The vertical axis of FIG. 6 is the surface roughness of the GaN substrate. A GaN substrate on which a mask had been formed was used as the substrate. The substrate temperature was 400 ° C. The output of the plasma generator was 400 W. The bias frequency was 3.2 MHz. The bias Vpp was 230V. The internal pressure of the processing chamber 1001 was 5 Pa. The etching time was 1 minute.

As shown in FIG. 6, the surface roughness when the mixed gas of _{Cl 2} and B _{Cl 3} is used is smaller than the surface roughness when only _{Cl 2 is used. When the volume ratio of BCl 3 to} the supplied gas is 0%, the surface roughness is 8 nm. _{When the volume ratio of BCl 3 to} the supplied gas is 10%, the surface roughness is the smallest at 1.5 nm. _{When the volume ratio of BCl 3 to} the mixed gas is 20%, the surface roughness is 4 nm. Therefore, under this condition, _{the volume ratio of BCl 3 to} the mixed gas is preferably about 10%. _{For example, the volume ratio of BCl 3} to the mixed gas is preferably 5% or more and 15% or less.

4. Experiment 4 (photoluminescence)
FIG. 7 is a graph showing the photoluminescence intensity with respect to the volume ratio of _{BCl 3 in the first gas.} The horizontal axis of FIG. 7 is the volume ratio of _{BCl 3 to the supplied gas.} The vertical axis of FIG. 7 is the photoluminescence intensity. A GaN substrate on which a mask had been formed was used as the substrate. The substrate temperature was 400 ° C. The output of the plasma generator was 400 W. The bias frequency was 3.2 MHz. The bias Vpp was 230V. The internal pressure of the processing chamber 1001 was 5 Pa. The etching time was 1 minute.

As shown in FIG. 7, the photoluminescence intensity was about 0.7 regardless of the volume ratio of _{BCl 3 to the supplied gas.}

5. Experiment 5 (bias)
In the case of 5-1.5 Pa FIG. 8 is a graph showing the relationship between the volume ratio of _{BCl 3 in the first gas and the bias Vpp.} The horizontal axis of FIG. 8 is the volume ratio of _{BCl 3 to the first gas.} The vertical axis of FIG. 8 is the bias Vpp. The internal pressure of the processing chamber 1001 at this time is 5 Pa.

In FIG. 8, the “◯” mark indicates that the horizontal etching rate with respect to the vertical etching rate is −15% or more and 15% or less. The "+" mark indicates that the horizontal etching rate relative to the vertical etching rate is greater than 15%. Here, when the horizontal etching rate with respect to the vertical etching rate is a positive value, overetching occurs. When the horizontal etching rate with respect to the vertical etching rate is a negative value, under-etching occurs. As shown in FIG. 8, the overetching is not so large inside the region R1. In the region R1, the horizontal etching rate with respect to the vertical etching rate is −15% or more and 15% or less. The region R1 is represented by the equations (1) and (2).

It is considered that the conditional expressions (1) and (2) can be applied when the internal pressure of the processing chamber 1001 is 1 Pa or more and 10 Pa or less.

1000 ... Etching device 1001 ... Processing chamber 1100 ... Scepter 1110 ... Scepter support part 1120 ... Heating part 1130 ... SiC plate 1200 ... First potential applying part 1210 ... First matching unit 1300 ... Plasma generating part 1400 ... Second potential Granting unit 1410 ... Second matching unit 1500 ... Gas supply unit 1510 ... Gas supply pipe 1600 ... Shower plate 1700 ... Exhaust port

Claims (3)

A processing room for etching group III nitride semiconductors,
A substrate holding portion for holding the group III nitride semiconductor and
A gas supply unit that supplies the first gas to the inside of the processing chamber,
A plasma generating unit that turns the first gas into plasma, and
A first potential applying portion that applies a high frequency potential to the substrate holding portion, and
Have,
The first gas is
It is a chlorine-based mixed gas containing Cl ₂ and BCl _{3, and is a mixed gas.}
The first potential applying portion is
The larger the volume ratio of _{BCl 3} to the first gas, the more.
A bias having a small absolute value is applied to the substrate holding portion.
The first potential applying portion is
Vpp ≤ -1200 · X + 480
Vpp ≧ -1200 ・ X + 290
0.01 ≤ X ≤ 0.4
Vpp: Bias (V)
X: An etching apparatus for applying a bias to the substrate holding portion so as to satisfy the volume ratio of _{BCl 3 in} the first gas. In the etching apparatus according to claim 1,
The gas supply unit
0.02 ≤ X ≤ 0.3
An etching apparatus for supplying the first gas to the inside of the processing chamber so as to satisfy the above conditions. In the etching apparatus according to claim 1 or 2.
The gas supply unit
An etching apparatus for supplying a second gas, which is a mixture of the first gas and a gas containing at least one of N _{2 and a rare gas, into the inside of the processing chamber.}

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