Method for etching gallium oxide by ICP (Inductively Coupled Plasma)

Abstract

The invention belongs to the technical field of ICP (Inductively Coupled Plasma) etching, and relates to a method for etching gallium oxide by ICP, which comprises the following steps of: placing a gallium oxide sample with a PR mask on a wafer in an ICP etching chamber, introducing a first gas halide and a second gas halide into the front surface of the gallium oxide sample until the interior of the etching chamber is in a stable state, and removing the first gas halide and the second gas halide from the front surface of the gallium oxide sample; continuously introducing each gas and starting radio frequency to carry out etching treatment to obtain etched gallium oxide; the first gas halide comprises boron trichloride, and the second gas halide comprises any one or a combination of at least two of hydrogen bromide, chlorine and trifluoromethane. According to the method, pollution caused by the metal mask to gallium oxide etching can be avoided, the etching roughness can be reduced, the gallium oxide etching perpendicularity can be improved, the bottom of the etched gallium oxide achieves a fillet effect, and compared with a conventional etching method, the selection ratio of gallium oxide to PR is also obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of ICP etching technology and relates to a method for ICP etching gallium oxide. Background Technology

[0002] In today's semiconductor manufacturing field, high bandgap materials offer numerous advantages such as higher breakdown voltage, smaller device size, and lower energy conversion, making them a popular research material. For example, SiC devices have become a hot research topic. Compared to SiC, gallium oxide (GaO) materials offer many disruptive advantages, including a high bandgap and high breakdown voltage, low fabrication cost, high efficiency, and no need for complex epitaxy.

[0003] However, gallium oxide also faces challenges in ICP dry etching because the Ga-O bond energy is >374 kJ / mol, while the Si-Si bond energy is only 222 kJ / mol. Bond energy affects the selectivity of the mask material and the etching rate during dry etching, which in turn directly influences the etching angle. Slow etching rate and poor selectivity directly lead to poor gallium oxide morphology angles. Current technologies generally use chlorine-based gases to etch gallium oxide, but the GaCl3 generated during etching tends to adhere to the sidewalls and is difficult to volatilize, also resulting in a poor etching angle. Furthermore, when using chlorine-based gases for etching, Ar is used as a bombardment source to remove the generated byproducts, but this also creates high ion bombardment on the substrate surface, leading to decreased roughness and consequently increased leakage current in the device.

[0004] CN111180314A discloses a process improvement method for gallium oxide-based field-effect transistors. The process improvement method includes: forming a buffer layer stack structure on the front side of a gallium oxide substrate; thinning and polishing the back side of the gallium oxide substrate to ensure that the thickness and surface roughness of the gallium oxide substrate meet preset requirements; removing the buffer layer stack structure; forming a Ti / Ni alloy mask layer on the polished surface of the gallium oxide substrate by magnetron sputtering; photolithographic etching the mask layer; and forming a heat dissipation metal layer on the back side of the gallium oxide substrate.

[0005] CN114743873A discloses a gallium oxide diode device and its fabrication method. The method includes: cleaning a gallium oxide epitaxial layer and depositing a dielectric layer on top of the epitaxial layer; spin-coating photoresist on top of the dielectric layer and heating the photoresist to reflow it and form a slope; etching the photoresist and dielectric layer to remove the photoresist; using the dielectric layer as a mask, etching the gallium oxide epitaxial layer and dielectric layer; spin-coating photoresist on top of the dielectric layer plane; covering the gallium oxide diode device with a metal mask and removing the photoresist and dielectric layer; sputtering P-NiO material to form a P-NiO layer and stripping the metal mask; and electron beam evaporation of the metal to obtain a cathode and an anode.

[0006] The above method uses a metal mask to etch gallium oxide. Although the metal mask can provide a very high selectivity for gallium oxide etching, the metal is difficult to process in subsequent processes. Wet stripping will produce a certain amount of residue, while dry removal requires strong ion bombardment, which will cause damage to the surface of gallium oxide. Summary of the Invention

[0007] The purpose of this invention is to provide a method for ICP etching of gallium oxide. The etching method described in this invention can avoid the contamination caused by metal masks during gallium oxide etching and reduce etching roughness. While significantly improving the verticality of gallium oxide etching, it also achieves a rounded corner effect at the bottom of the etched gallium oxide. Compared with conventional etching methods, the selectivity ratio of gallium oxide to PR is also significantly improved.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] In a first aspect, the present invention provides a method for ICP etching of gallium oxide, the method comprising the following steps:

[0010] A gallium oxide sample with a PR mask is placed on a wafer in an ICP etching chamber. A first gas halide and a second gas halide are introduced into the front side of the gallium oxide sample until the etching chamber is in a stable state. Then, the gases are continuously introduced and radio frequency is turned on to perform etching to obtain etched gallium oxide.

[0011] Wherein, the first gaseous halide includes boron trichloride, and the second gaseous halide includes any one or a combination of at least two of hydrogen bromide, chlorine, or trifluoromethane. Typical but non-limiting combinations include combinations of hydrogen bromide and chlorine, combinations of hydrogen bromide and trifluoromethane, or combinations of chlorine and trifluoromethane.

[0012] This invention uses PR as a mask for gallium oxide samples to avoid the metal contamination problems associated with using metal masks. However, using PR masks results in a relatively low selectivity between gallium oxide and PR. This invention uses boron trichloride (BCl3) and another gaseous halide as the process gas for etching gallium oxide. BCl3 forms a plasma state in an inductively coupled plasma, where (BCl3) is generated. 3+The ion clusters possess oxyphilic properties, capable of removing O from Ga₂O₃ and disrupting the Ga-O bond. The halogen gas in the second gas halide can react with metallic gallium to form the corresponding salt, and HBr, with its large molecular weight, can bombard the surface of Ga₂O₃, thus increasing the etching rate. A protective gas is introduced on the back side. The method described in this invention not only eliminates metal residue after etching, but also produces gallium oxide sidewalls with a vertical morphology and a smooth, rounded bottom. After optimization, the selectivity ratio of gallium oxide to PR can be significantly improved, solving the problems of poor etching morphology and slow etching rate caused by using PR masks.

[0013] This invention uses boron trichloride and another gaseous halide, such as hydrogen bromide, as process gases to etch gallium oxide. The etching reaction equation is as follows:

[0014] 2Ga + 6Cl• → 2GaCl3;

[0015] (BCl) 3+ ) Ion group + O•→ B2O3 + 4Cl•↑;

[0016] Utilize (BCl3) + Gallium oxide is etched using (ionic groups) and the reaction of Ga with Cl ions.

[0017] Br - +Ga→GaBr3↑;

[0018] The pressure inside the dry etching chamber is 0~100mt, which is a low-pressure state. The boiling point of GaBr3 can be reduced to below the room temperature boiling point. GaBr3 has a relatively low boiling point and has a certain sidewall protection capability.

[0019] Preferably, before placing the gallium oxide sample onto the wafer in the ICP etching chamber, oxygen is introduced into the etching chamber for cleaning, and the temperature of the hot plate is controlled at -10℃ to 70℃, for example: -10℃, 0℃, 10℃, 50℃ or 70℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0020] Preferably, the flow rate of the first gaseous halide is 50 sccm to 150 sccm, for example: 50 sccm, 80 sccm, 100 sccm, 120 sccm or 150 sccm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the flow rate of the second gaseous halide is 50 sccm to 150 sccm, for example: 50 sccm, 80 sccm, 100 sccm, 120 sccm or 150 sccm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the second gaseous halide is hydrogen bromide.

[0023] This invention utilizes hydrogen bromide as the second gas halide, which significantly improves the etching selectivity. If conventional chlorine is used, in actual testing, its use leads to a decrease in photoresist selectivity; the higher the proportion of chlorine in the process gas, the lower the selectivity, resulting in the final etched morphology of Ga2O3 not achieving a perpendicular angle. This is mainly because Cl2 continuously consumes carbon in the photoresist during etching, leading to a decrease in selectivity. While trifluoromethane provides sidewall protection, it also deposits on the bottom of the Ga2O3. Its use requires higher down-frequency power for bottom deposit removal, which also leads to photoresist consumption during etching, further reducing selectivity.

[0024] Preferably, the method further includes:

[0025] While introducing the first and second gas halide gases, a protective gas is introduced to the back of the gallium oxide sample for cooling.

[0026] Preferably, the frontal pressure of the gallium oxide sample is 2 mtorr to 60 mtorr, for example: 2 mtorr, 5 mtorr, 10 mtorr, 30 mtorr or 60 mtorr, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the back pressure of the gallium oxide sample is 1 torr to 10 torr, for example: 1 torr, 2 torr, 5 torr, 8 torr or 10 torr, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the radio frequency power of the etching process is 50W to 2000W, for example: 50W, 100W, 500W, 1000W or 2000W, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the lower radio frequency power of the etching process is 10W~100W, for example: 10W, 20W, 50W, 80W or 100W, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the etching time is 800s to 1000s, for example: 800s, 850s, 900s, 950s or 1000s, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The etching method described in this invention can avoid the contamination caused by the metal mask to gallium oxide etching and reduce the etching roughness. While greatly improving the verticality of gallium oxide etching, it can also achieve the effect of rounded corners at the bottom of gallium oxide after etching. Compared with conventional etching methods, the selection ratio of gallium oxide to PR is also significantly improved.

[0033] (2) Improved etching rate: Metal masks require etching of the Ni layer. After using PR masks, hard mask etching is not required, and the overall etching time is reduced by about 30%.

[0034] (3) Etching angle improvement: Through the optimization test of the process Recipe, the sidewall angle after etching was improved from 70° to 89°.

[0035] (4) Cost reduction: Metal masks require etching of the Ni layer. By eliminating the use of metal masks, the number of process steps and the frequency of chamber cleaning are reduced, thereby reducing costs and improving equipment utilization. Attached Figure Description

[0036] Figure 1 This is a SEM image of the etched gallium oxide sample provided in Embodiment 1 of the present invention.

[0037] Figure 2 This is a magnified SEM image of the etched gallium oxide sample provided in Embodiment 1 of the present invention.

[0038] Figure 3 This is a roughness test image of a gallium oxide sample before etching within a range of 1.5 × 1.5 μm, provided in Example 1 of this invention.

[0039] Figure 4 This is a roughness test diagram of a gallium oxide sample before etching within a 5×5μm range provided in Embodiment 1 of the present invention.

[0040] Figure 5 This is a roughness test image of the etched gallium oxide sample within a range of 1.5 × 1.5 μm provided in Example 1 of the present invention.

[0041] Figure 6 This is a roughness test diagram of the etched gallium oxide sample within a 5×5μm range provided in Embodiment 1 of the present invention. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0043] In the gallium oxide samples with PR masks used in the embodiments and comparative examples of the present invention, the PR mask thickness is 2.153 μm, the angle between the gallium oxide sidewall and the bottom horizontal line is 69.85°, and the gallium oxide pattern is a grid pattern with a spacing of 1.984 μm and a width of 2.103 μm.

[0044] Example 1

[0045] This embodiment provides a method for ICP etching of gallium oxide, the method comprising the following steps:

[0046] After cleaning the etching chamber with oxygen in the ICP chamber, the wafer is placed on the hot plate inside the etching chamber, and the temperature of the hot plate is controlled at 60°C. A gallium oxide sample with a PR mask is placed on the wafer. Boron trichloride and hydrogen bromide are introduced into the front side of the gallium oxide sample with the PR mask at a flow rate of 100 sccm and a pressure of 8 mtorr. Helium gas is introduced into the back side of the gallium oxide sample with the PR mask for cooling, and the pressure is set to 8 torr. After 8 seconds, the gas flow rate is kept constant, and an upper RF power of 700W and a lower RF power of 60W are applied for a duration of 900 seconds to complete the etching.

[0047] SEM images of the etched gallium oxide sample are shown below. Figure 1-2 As shown, by Figure 1-2 It can be seen that the etching method described in this application has a high etching verticality, and the bottom of the etched gallium oxide achieves a rounded corner effect.

[0048] The roughness side views of the gallium oxide sample before and after etching are shown below. Figure 3-6 As shown, by Figure 3-6 As can be seen, the roughness of the sample is significantly improved after etching by the method described in this invention.

[0049] Example 2

[0050] This embodiment provides a method for ICP etching of gallium oxide, the method comprising the following steps:

[0051] After cleaning the etching chamber with oxygen in the ICP chamber, the wafer is placed on the hot plate inside the etching chamber, and the temperature of the hot plate is controlled at -10℃. A gallium oxide sample with a PR mask is placed on the wafer. Boron trichloride and hydrogen bromide are introduced into the front side of the gallium oxide sample with the PR mask at flow rates of 150 sccm and 100 mtorr, respectively, with a pressure of 8 mtorr. Helium gas is introduced into the back side of the gallium oxide sample with the PR mask for cooling, with a pressure of 8 torr. After 6 seconds, the gas flow rates are kept constant, and an upper RF power of 1000W and a lower RF power of 60W are applied for 1000 seconds to complete the etching.

[0052] Example 3

[0053] This embodiment provides a method for ICP etching of gallium oxide, the method comprising the following steps:

[0054] After cleaning the etching chamber with oxygen in the ICP chamber, the wafer is placed on the hot plate inside the etching chamber, and the temperature of the hot plate is controlled at 70°C. A gallium oxide sample with a PR mask is placed on the wafer. Boron trichloride and hydrogen bromide are introduced into the front side of the gallium oxide sample with the PR mask at flow rates of 50 sccm and 150 mtorr, respectively, with a pressure of 6 mtorr. Helium gas is introduced into the back side of the gallium oxide sample with the PR mask for cooling, with a pressure of 8 torr. After 10 seconds, the gas flow rates are kept constant, and an upper RF power of 2000 W and a lower RF power of 100 W are applied for 800 seconds to complete the etching.

[0055] Example 4

[0056] The only difference between this embodiment and Embodiment 1 is that hydrogen bromide is replaced with chlorine gas; all other conditions and parameters are exactly the same as in Embodiment 1.

[0057] Example 5

[0058] The only difference between this embodiment and Example 1 is that hydrogen bromide is replaced with trifluoromethane; all other conditions and parameters are exactly the same as in Example 1.

[0059] Example 6

[0060] The only difference between this embodiment and Embodiment 1 is that the upper radio frequency power is 20W, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0061] Example 7

[0062] The only difference between this embodiment and Embodiment 1 is that the upper radio frequency power is 3000W, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0063] Example 8

[0064] The only difference between this embodiment and Embodiment 1 is that the lower radio frequency power is 5W; all other conditions and parameters are exactly the same as in Embodiment 1.

[0065] Example 9

[0066] The only difference between this embodiment and Embodiment 1 is that the lower radio frequency power is 150W; all other conditions and parameters are exactly the same as in Embodiment 1.

[0067] Example 10

[0068] The only difference between this embodiment and Embodiment 1 is that the frontal pressure of the gallium oxide sample with the PR mask is 1 mtorr; all other conditions and parameters are exactly the same as in Embodiment 1.

[0069] Example 11

[0070] The only difference between this embodiment and Embodiment 1 is that the frontal pressure of the gallium oxide sample with the PR mask is 80 mtorr; all other conditions and parameters are exactly the same as in Embodiment 1.

[0071] Example 12

[0072] The only difference between this embodiment and Embodiment 1 is that the back pressure of the gallium oxide sample with the PR mask is 0.5 torr; all other conditions and parameters are exactly the same as in Embodiment 1.

[0073] Example 13

[0074] The only difference between this embodiment and Embodiment 1 is that the back pressure of the gallium oxide sample with the PR mask is 15 torr; all other conditions and parameters are exactly the same as in Embodiment 1.

[0075] Comparative Example 1

[0076] The only difference between this comparative example and Example 1 is that hydrogen bromide is not introduced; all other conditions and parameters are exactly the same as in Example 1.

[0077] Comparative Example 2

[0078] The only difference between this comparative example and Example 1 is that boron trichloride is not introduced; all other conditions and parameters are exactly the same as in Example 1.

[0079] Comparative Example 3

[0080] The difference between this comparative example and Example 1 is that metallic Ni is used as a mask, and the Ni layer is first etched to expose the Ga2O3 layer. Other conditions and parameters are exactly the same as in Example 1.

[0081] Performance testing:

[0082] The roughness and perpendicularity of the samples obtained after etching in the examples and comparative examples were tested. The perpendicularity is the angle between the sidewall of the etched channel and the bottom horizontal line (the difference between the two sides is taken). The closer the angle is to 90°, the better the perpendicularity. A lower roughness Ra value indicates better roughness and higher device performance. "NA" indicates that the value cannot be measured. The test results are shown in Table 1.

[0083] Table 1

[0084]

[0085] As can be seen from Table 1, and from Examples 1-3, the ICP etching method for gallium oxide described in this invention has high etching selectivity and can meet the conditions of bottom rounded corners, sidewall perpendicularity, and low bottom roughness of the etched gallium oxide sample.

[0086] Comparing Examples 1 and 4-5, it can be seen that the type of the second gas halide affects the etching effect during the ICP etching of gallium oxide described in this invention. According to the test results, chlorine was used to replace hydrogen bromide gas. The results showed that the selectivity ratio of Ga2O3:PR decreased from 3:1 to 1.4:1, and the etching effect was significantly reduced. Although the selectivity ratio was improved to some extent when trifluoromethane replaced hydrogen bromide gas, the sidewall angle was still smaller than that in Example 1. The reason is that trifluoromethane, as a sidewall protection gas, can improve the sidewall protection capability to a certain extent, but its sidewall protection capability is weaker than that of hydrogen bromide gas.

[0087] Comparing Examples 1 and 6-7, it can be seen that during the ICP etching of gallium oxide described in this invention, the up-frequency power affects the etching effect. Controlling the up-frequency power between 50W and 2000W results in a better etching effect. If the up-frequency power is too low, the plasma concentration generated in the chamber is low and insufficient to etch the Ga2O3 material on the surface. If the up-frequency power is too high, the high plasma concentration can significantly improve the etching rate of the sample, but at the same time, the large amount of RF energy obtained causes the temperature of the sample surface to rise, resulting in a decrease in the Ga2O3:PR selectivity.

[0088] A comparison of Examples 1 and 8-9 shows that during the ICP etching of gallium oxide described in this invention, the lower radio frequency (RF) power affects the etching effect. Controlling the RF power between 10W and 100W results in a better etching effect. If the RF power is too low, the plasma generated in the chamber will not have sufficient downward traction force. At this time, the etching reaction is mainly a chemical reaction. However, the bond energy in Ga2O3 is relatively high, and relying solely on chemical reactions will lead to a significant decrease in the etching rate. If the RF power is too high, the energy obtained by the plasma will increase, and the ions in it will continuously bombard the sample surface, causing the sample temperature to rise. The PR material is more sensitive to temperature than Ga2O3, which will lead to a significant decrease in the sample selectivity. Furthermore, excessive PR consumption can easily cause insufficient etching angle.

[0089] A comparison of Examples 1 and 10-11 shows that during the ICP etching of gallium oxide described in this invention, the front pressure of the gallium oxide sample of the PR mask affects the etching effect. Controlling the front pressure of the gallium oxide sample of the PR mask between 2 mtorr and 60 mtorr results in a better etching effect. If the front pressure of the gallium oxide sample of the PR mask is too low, the process gas in the chamber is removed by the vacuum system, resulting in insufficient plasma and a significant decrease in the etching rate. If the front pressure of the gallium oxide sample of the PR mask is too high, the excessively high chamber pressure reduces the mean free path of the plasma in the chamber, i.e., significantly reduces the ion bombardment intensity. Therefore, the resulting etching reaction is mainly a chemical reaction, leading to a decrease in the etching rate.

[0090] A comparison of Examples 1 and 12-13 shows that during the ICP etching of gallium oxide described in this invention, the back pressure of the gallium oxide sample of the PR mask affects the etching effect. Controlling the back pressure of the gallium oxide sample of the PR mask at 1 mtorr~10 mtorr results in a better etching effect. If the back pressure of the gallium oxide sample of the PR mask is too low, the reduced back pressure will significantly decrease the back cooling function of the wafer, resulting in the inability to quickly transfer the temperature of the sample surface, causing the wafer temperature to run away uncontrollably, increasing PR loss and decreasing selectivity. If the back pressure of the gallium oxide sample of the PR mask is too high, the helium loss on the back side is large, and the gas overflows from the edge of the wafer, which cannot effectively dissipate heat from the wafer surface, leading to temperature runaway on the wafer surface, increased wafer surface temperature, greater PR loss, and decreased selectivity.

[0091] A comparison of Example 1 and Comparative Example 1 shows that, without the use of hydrogen bromide, the selectivity of the sample decreases, the etching angle is insufficient, and the etching rate decreases.

[0092] Comparing Example 1 and Comparative Example 2, it can be seen that the selectivity of Ga2O3 is improved to a certain extent without the use of boron trichloride, but the etching rate is significantly reduced, and the etching angle of the sample is also reduced compared with Example 1.

[0093] As can be seen from the comparison between Example 1 and Comparative Example 3, the gallium oxide sample using PR as a mask in this invention avoids the metal contamination problem caused by using metal masks, while achieving better etching effect and a higher gallium oxide to PR selectivity ratio. This solves the problems of poor etching morphology and slow etching rate caused by using PR masks.

[0094] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method of etching gallium oxide by ICP, characterized by, The method comprises the following steps: The method comprises the following steps: The method comprises the following steps:

2. The method of claim 1, wherein, The first gas halide comprises boron trichloride, and the second gas halide comprises any one or a combination of at least two of hydrogen bromide, chlorine and trifluoromethane.

3. The method of claim 1, wherein, Before the gallium oxide sample with the PR mask is placed on the wafer in the ICP etching chamber, oxygen is introduced into the etching chamber for cleaning treatment, and the temperature of the hot plate is controlled to be-10 DEG C to 70 DEG C.

4. The method of claim 1, wherein, The flow rate of the first gas halide is 50sccm to 150sccm.

5. The method of claim 1, wherein, The flow rate of the second gas halide is 50sccm to 150sccm.

6. The method of claim 1, wherein, The method further comprises: while the first gas halide and the second gas halide are introduced, a protective gas is introduced into the back of the gallium oxide sample for cooling.

7. The method of claim 1, wherein, The front surface pressure of the gallium oxide sample is 2mtorr to 60mtorr.

8. The method of claim 1, wherein, The back surface pressure of the gallium oxide sample is 1torr to 10torr.

9. The method of claim 1, wherein, The upper radio frequency power of the etching treatment is 50W to 2000W.

10. The method of claim 1, wherein, The lower radio frequency power of the etching treatment is 10W to 100W. The etching treatment time is 800s to 1000s.

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