Long-distance air bridge capable of preventing bridge floor from sinking and preparation method of long-distance air bridge

Abstract

The invention relates to a long-distance air bridge for preventing depression of a bridge floor and a preparation method thereof, and the method comprises the steps: enabling GaAs layers and InGaP layers to be alternately arranged for multiple times to form a first layer to an Nth layer, and enabling an Al < x > Ga < 1-x > As layer to be arranged below the Nth layer; depositing a first photoresist layer on the first layer, performing exposure / development, and etching the first layer to form a first mesa; etching the second layer and then removing the first photoresist layer; coating a second photoresist layer, performing exposure / development, etching the third layer to form a second mesa, and etching the fourth layer to remove the second photoresist layer; sequentially forming a third table-board to an a-th table-board according to the same operation; and coating an (a + 1) th photoresist layer on the outer side of the a-th table top, performing exposure / development, performing metal evaporation, removing metal and the (a + 1) th photoresist layer on the outer side of the a-th table top, and sequentially and completely etching the first layer and the Nth layer below the air bridge to complete the air bridge manufacturing process. According to the invention, a long-span air bridge structure is realized, and a window of an etching process is larger.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a long-distance air bridge for preventing bridge surface depressions and its preparation method. Background Technology

[0002] In the fields of microelectromechanical systems (MEMS), semiconductor devices, and high-frequency integrated circuits, air-bridge structures are widely used as a key interconnect technology to achieve low-capacitance, low-loss electrical connections between different components. A typical fabrication process for this structure is as follows:

[0003] First, a photolithographically patternable sacrificial layer material, namely the first pier photoresist, is coated onto the substrate, such as... Figure 1 Subsequently, the graphic areas of the bridge piers are defined on the photoresist layer through exposure and development processes. Next, a high-temperature baking process is performed to cause the remaining photoresist material to reflow, thereby forming a bridge pier structure with the desired arch shape. Afterward, metal evaporation is performed on the entire structural surface to form a bridge deck metal layer covering the arch sacrificial layer, such as... Figure 2 Finally, the underlying sacrificial photoresist layer is removed using specific removal processes (such as solvent dissolution, plasma ashing, etc.), releasing the suspended metal bridge surface, thus completing the fabrication of the air bridge. Figure 3 In existing technologies, the large span of the bridge deck can cause a depression in the light obstruction in the central area after baking, and this trend becomes more pronounced with larger spans; for example... Figure 4 As shown; however, the high-temperature baking of photoresist may result in incomplete removal; if the baking temperature is insufficient, an arc-shaped morphology cannot be formed; the larger the span, the more obvious the deformation of the photoresist, which to some extent restricts the long span of the air bridge. Summary of the Invention

[0004] The purpose of this invention is to provide a long-distance air bridge that prevents bridge surface depression and its preparation method. This invention can improve the problem of deformation of transconductor photoresist over long distances, realize the air bridge structure with long span, and at the same time, the etching process window is larger and the process tolerance is higher.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a long-distance air bridge to prevent bridge deck dents, comprising the following steps:

[0006] Step S1: Al layers are alternately set multiple times, forming layers 1 through N from top to bottom. The first and Nth layers are both GaAs layers, and Al is placed below the Nth layer. × Ga 1-x As layer;

[0007] Step S2: Deposit a first photoresist layer on the first layer and expose / develop it. Then, wet etch the first layer to form a first mesa for a time of Tg1. Wet etch the second layer for a time of Tp1 to remove the first photoresist layer.

[0008] Step S3: Continue to coat the second photoresist layer and perform exposure / development. Use wet etching to etch the third layer for a time of Tg2. Form the second mesa on both sides of the first mesa. Use wet etching to etch the fourth layer for a time of Tp2. Remove the second photoresist layer.

[0009] Step S4: Following the operations in step S2, form the third platform to the a-th platform in sequence;

[0010] Step S5: Coat the (a+1)th photoresist layer on the outer side of the (a)th mesa and expose / develop it. Then perform metal evaporation to remove the metal on the outer side of the (a)th mesa and the (a+1)th photoresist layer, thus completing the air bridge metal deposition.

[0011] Step S6: Completely etch the first and Nth layers below the air bridge in sequence to complete the air bridge process.

[0012] Furthermore, the volume ratio of the components in the etching solution used for wet etching of GaAs layers in the first to Nth layers is ammonia:hydrogen peroxide:water = 1:1.5:10, and the volume ratio of the components in the etching solution used for wet etching of InGaP layers in the first to Nth layers is HCl:H3PO4 = 4:1.

[0013] Furthermore, NMP solvent was used to remove the first photoresist layer to the (a+1)th photoresist layer.

[0014] Furthermore, the metal used for metal vapor deposition in step S5 is Ti, Pt, Au, Ti or Au.

[0015] Furthermore, in step S4, the etching time for wet etching of the GaAs layer is sequentially from Tg3 to Tgn, and the etching time for wet etching of the InGaP layer is sequentially from Tp2 to Tpn.

[0016] Furthermore, in step S6, the etching times for the first layer, the second layer to the (N-2)th layer, the (N-1)th layer, and the Nth layer are Tg1, Tp1 to Tgn-1, Tpn-1, and Tgn, respectively.

[0017] A long-distance air bridge to prevent bridge deck denting, the air bridge includes piers and a bridge body, with piers connected to both ends of the bridge body, the bridge body including a top bridge deck and a stepped bridge deck, the stepped bridge deck connecting both sides of the top bridge deck.

[0018] Furthermore, the angle between the connecting sections between the steps in the stepped bridge deck and the horizontal plane is 30° to 55°.

[0019] Beneficial effects of the present invention: The present invention utilizes GaAs, InGaP, and Al x Ga 1-x As the substrate material, an air bridge surface is formed by etching the substrate, replacing the role of photoresist and improving the problem of photoresist deformation over long spans, thus realizing a long-span air bridge structure. Using the substrate as the bridge surface structure allows the air bridge surface formed by metal evaporation to replicate the flat substrate interface, achieving an air bridge structure with no appearance depressions and controllable height to ground. The bridge surface material is the substrate material, and wet etching is used in the air bridge formation process, effectively avoiding the removal difficulties caused by high-temperature baking of photoresist, optimizing the process flow, and improving quality and yield. In addition, this invention uses an external epitaxial method, which allows for a larger etching process window and higher process tolerance, ensuring that the air bridge height strictly matches the design value, and eliminating deviations from the design dimensions caused by minor changes in etching rate, etching solution temperature, etc.

[0020] The process is simple, and the bridge deck fabrication is straightforward. Furthermore, this application addresses the shortcomings of the previous application, "A Manufacturing Method for a Long-Span Air Bridge": the lack of an etching stop layer, a small process window, and susceptibility to over-etching due to fluctuations in etching rate, etching tank temperature, and etching time. Figure 18 As shown, compared with the applicant's previous application for "A Process Method for Manufacturing a Long-Distance Span Air Bridge", this method does not additionally coat a fifth photoresist layer, but instead uses AlGaAs with a high Al content as the final etching termination layer. This allows for full-surface etching without patterning, simplifying the process and saving materials. Using AlGaAs with a high Al content as the final etching termination layer improves upon the previous patent application's "A Process Method for Manufacturing a Long-Distance Span Air Bridge" where the etching process of the fifth photoresist layer could potentially etch into the metal, causing structural abnormalities. Attached Figure Description

[0021] Figure 1 A schematic diagram of coating photoresist on bridge piers using existing manufacturing methods;

[0022] Figure 2 A schematic diagram of the bridge deck metal formed by metal vapor deposition using existing manufacturing methods;

[0023] Figure 3 A schematic diagram of a bridge deck metal manufactured using existing methods;

[0024] Figure 4 This is a schematic diagram showing a dent that appears after baking using existing manufacturing methods.

[0025] Figure 5 This is a schematic diagram of the deposition of the first photoresist layer using the process method of the present invention.

[0026] Figure 6 A schematic diagram showing the formation of the first mesa using the process method of the present invention;

[0027] Figure 7 This is a schematic diagram of removing the first photoresist layer using the process method of the present invention;

[0028] Figure 8 This is a schematic diagram of the coating of the second photoresist layer using the process method of the present invention;

[0029] Figure 9 This is a schematic diagram illustrating the formation of the second mesa using the process method of the present invention;

[0030] Figure 10 This is a schematic diagram of removing the second photoresist layer using the process method of the present invention.

[0031] Figure 11 This is a schematic diagram of the coating of the third photoresist layer using the process method of the present invention;

[0032] Figure 12 This is a schematic diagram illustrating the formation of the third mesa using the process method of the present invention;

[0033] Figure 13 This is a schematic diagram of removing the third photoresist layer using the process method of the present invention.

[0034] Figure 14 This is a schematic diagram of the fourth photoresist layer being coated using the process method of the present invention;

[0035] Figure 15 This is a schematic diagram of metal vapor deposition using the process method of the present invention;

[0036] Figure 16 This is a schematic diagram of removing the metal and fourth photoresist layer on the outer side of the third mesa using the process method of the present invention.

[0037] Figure 17 This is a schematic diagram illustrating the removal of the first to fifth layers of material beneath the metal using the process method of this invention;

[0038] Figure 18 This is a schematic diagram of over-etching using the old method.

[0039] Among them: 101, first layer; 102, second layer; 103, third layer; 104, fourth layer; 105, fifth layer; 106, Al x Ga 1-x1. As layer, 2. First photoresist layer, 3. First platform, 4. Second photoresist layer, 5. Second platform, 6. Third photoresist layer, 7. Third platform, 8. Fourth photoresist layer, 9. Metal, 11. Pier, 12. Bridge body, 121. Top bridge deck, 122. Stepped bridge deck. Detailed Implementation

[0040] The invention will now be further described with reference to the accompanying drawings.

[0041] Please see Figures 1 to 18 The present invention provides an embodiment: a method for preparing a long-distance air bridge to prevent bridge deck dents, comprising the following steps:

[0042] Step S1: Al layers are alternately set multiple times, forming layers 101 to N from top to bottom. Both layer 101 and layer N are GaAs layers, and Al is placed below layer N. × Ga 1-x As layer 106; Al x Ga 1-x When the Al content in As is high (typically x>0.5), AlGaAs will form a dense, inert aluminum oxide (Al2O3) passivation layer in the etchant for GaAs (such as a citric acid-based solution), thereby almost stopping the etching process, wherein x is preferably 0.6.

[0043] Step S2: Deposit the first photoresist layer 2 on the first layer 101 and expose / develop it. Then, use wet etching to form the first mesa 3 for a time of Tg1. Use wet etching to etch the second layer 102 for a time of Tp1 to remove the first photoresist layer 2.

[0044] Step S3: Continue to coat the second photoresist layer 4 and perform exposure / development. Use wet etching to etch the third layer 103 for a time of Tg2. Form the second mesa 5 on both sides of the first mesa 3. Use wet etching to etch the fourth layer 104 for a time of Tp2. Remove the second photoresist layer 4.

[0045] Step S4: Following the operations in step S2, form the third platform 7 to the a-th platform in sequence;

[0046] Step S5: Coat the (a+1)th photoresist layer on the outer side of the a-th mesa and expose / develop it. Then perform metal 9 evaporation to remove the metal 9 and the (a+1)th photoresist layer on the outer side of the a-th mesa, thus completing the deposition of the air bridge metal 9.

[0047] Step S6: Completely etch the first layer 101 and the Nth layer below the air bridge in sequence to complete the air bridge process.

[0048] Please continue reading. Figures 1 to 18 As shown, in one embodiment of the present invention, the volume ratio of the components in the etching solution used for wet etching of GaAs layers in the first layer 101 to the Nth layer is ammonia:hydrogen peroxide:water = 1:1.5:10, and the volume ratio of the components in the etching solution used for wet etching of InGaP layers in the first layer 101 to the Nth layer is HCl:H3PO4 = 4:1.

[0049] Please continue reading. Figures 1 to 18 As shown, in one embodiment of the present invention, the removal of the first photoresist layer 2 to the a+1th photoresist layer is carried out using NMP solvent.

[0050] Please continue reading. Figures 1 to 18 As shown, in one embodiment of the present invention, the metal 9 deposited in step S5 is Ti, Pt, Au, Ti or Au.

[0051] Please continue reading. Figures 1 to 18 As shown, in one embodiment of the present invention, the etching time for wet etching of the GaAs layer in step S4 is sequentially from Tg3 to Tgn, and the etching time for wet etching of the InGaP layer is sequentially from Tp2 to Tpn.

[0052] Please continue reading. Figures 1 to 18 As shown, in one embodiment of the present invention, the etching times of the first layer 101, the second layer 102 to the (N-2)th layer, the (N-1)th layer, and the Nth layer in step S6 are Tg1, Tp1 to Tgn-1, Tpn-1, and Tgn, respectively.

[0053] Please see Figure 17 The present invention provides another embodiment: a long-distance air bridge to prevent bridge deck denting, the air bridge including piers 11 and bridge body 12, both ends of the bridge body 12 are connected to piers 11, the bridge body 12 includes a top bridge surface 121 and a stepped bridge surface 122, the stepped bridge surface 122 is connected to both sides of the top bridge surface 121.

[0054] Please continue reading. Figure 17 As shown, in one embodiment of the present invention, the angle between the connecting segments between the stepped surfaces of the stepped bridge surface 122 and the horizontal plane is 30° to 55°.

[0055] Taking gallium arsenide as an example as a substrate material, the approach is similar for other materials.

[0056] 1) From top to bottom, the order is GaAs / InGaP / GaAs / InGaP / GaAs / Al x Ga 1-x As(x is preferably 0.6), and the thickness of each layer is preferably...

[0057] Deposit the first photoresist layer 2, with a thickness greater than After exposure / development, as Figure 5 As shown;

[0058] 2) Wet etching process:

[0059] a) The etching of GaAs (first layer 101) uses an etching solution with a volume ratio of ammonia:hydrogen peroxide:water = 1:1.5:10. Since InGaP (second layer 102) serves as the etching termination layer, the etching rate is [not specified]. For example, theoretically the etching time is 20s, but it can be longer in this case, such as 40s, and the process window is larger; in this embodiment, for the convenience of subsequent explanation, the GaAs etching time is Tg1.

[0060] b) The etching of InGaP (second layer 102) uses an etching solution volume ratio of HCl:H3PO4 = 4:1. Similarly, because the underlying GaAs (third layer 103) acts as an etching stagnation layer, the etching time at this point can be longer. The etching time is Tp1, forming the first mesa 3, as follows. Figure 6 As shown,

[0061] c. Remove the first photoresist layer 2, such as Figure 7 As shown; the photoresist layer is generally removed using NMP solvent, and the same solvent is used for photoresist removal in the following cases;

[0062] d. Apply a second photoresist, such as Figure 8 As shown, GaAs (third layer 103) and InGaP (fourth layer 104) are etched using the same principle to form the second mesa 5, as shown. Figure 9 As shown; remove the second photoresist layer 4, as... Figure 10 As shown;

[0063] The etching time for GaAs etching is Tg2.

[0064] The InGaP etching time is Tp2;

[0065] e. Coating with a third photoresist, such as Figure 11 As shown, GaAs and InGaP are etched using the same principle to form the third mesa 7, as... Figure 12 As shown; remove the third photoresist layer 6, as... Figure 13 As shown;

[0066] The etching time for GaAs is Tg3;

[0067] This embodiment takes the air bridge span formed by three platforms as an example. Platforms can be added according to design requirements and the required air bridge span.

[0068] f. Coat the fourth photoresist 8 with a thickness greater than 1.2µm (this thickness can be adjusted according to the depth of the platform; for example, 1.2µm here needs to be greater than the total depth of the three platforms in this embodiment). After exposure / development, the morphology is as shown below. Figure 14 As shown;

[0069] For metal 9 deposition, the commonly used metal 9 structure is Ti / Pt / Au / Ti / Au, with a total thickness typically ranging from 2 to 4 μm, which can be adjusted according to design requirements. Figure 15 As shown;

[0070] After removing metal 9 and photoresist by NMP, as follows: Figure 16 As shown, air bridge metal 9 deposition was completed;

[0071] g. Using the etching solution described above for etching GaAs and InGaP, sequentially etch away the first layer 101 to the fifth layer 105 GaAs / InGaP / GaAs / InGaP / GaAs to complete the fabrication of the air bridge; the etching sequence can be Tg1 / Tp1 / Tg2 / Tp2 / Tg3, resulting in an air bridge as shown in the image. Figure 17 As shown.

[0072] The present invention has the following working principle: The present invention utilizes GaAs, InGaP, and Al × Ga 1-x As the substrate material, an air bridge surface is formed by etching the substrate, replacing the role of photoresist and improving the problem of photoresist deformation over long spans, thus realizing a long-span air bridge structure. Using the substrate as the bridge surface structure allows the air bridge surface formed by metal 9 vapor deposition to replicate the flat substrate interface, achieving an air bridge structure with no appearance depressions and controllable height to ground. The bridge surface material is the substrate material, and wet etching is used in the air bridge formation process, effectively avoiding the removal difficulties caused by high-temperature baking of photoresist, optimizing the process flow, and improving quality yield. In addition, this invention uses an external epitaxial method, which allows for a larger etching process window and higher process tolerance.

[0073] The above description is only a preferred embodiment of the present invention and should not be construed as a limitation of this application. All equivalent changes and modifications made in accordance with the scope of the patent application of the present invention should be covered by the present invention.

Claims

1. A method for the preparation of a long distance air bridge for the prevention of deck depressions, characterized in that, The method comprises the following steps: Step S1, the GaAs layer and the InGaP layer are alternately arranged multiple times to sequentially form a first layer to an Nth layer from top to bottom, the first layer and the Nth layer are both GaAs layers, and an Al x Ga 1-x As layer is arranged below the Nth layer; Step S2, depositing a first photoresist layer on the first layer, and performing exposure / development, then etching the first layer by wet etching to form a first mesa, and the etching time is Tg1; etching the second layer by wet etching, and the etching time is Tp1, and the first photoresist layer is removed; Step S3, continuing to coat a second photoresist layer, and performing exposure / development, then etching the third layer by wet etching, and the etching time is Tg2, so as to form a second mesa on both sides of the first mesa, and etching the fourth layer by wet etching, and the etching time is Tp2, and the second photoresist layer is removed; Step S4, sequentially forming a third mesa to an a-th mesa according to the operation in step S2; Step S5, coating an a+1-th photoresist layer on the outside of the a-th mesa, and performing exposure / development, then performing metal evaporation, and removing the metal on the outside of the a-th mesa and the a+1-th photoresist layer, so as to complete air bridge metal deposition; Step S6, sequentially etching the first layer and the Nth layer under the air bridge completely, and completing the air bridge process.

2. A method of making a long distance air bridge for preventing deck sagging according to claim 1, characterized in that: The volume ratio of components in the etching liquid for wet etching of the GaAs layer in the first layer to the Nth layer is ammonia water: hydrogen peroxide: water = 1:1.5:10, and the volume ratio of components in the etching liquid for wet etching of the InGaP layer in the first layer to the Nth layer is HCl: H3PO4 = 4:

1.

3. The method for preparing a long-distance air bridge to prevent bridge deck denting according to claim 1, characterized in that: The first photoresist layer to the a+1-th photoresist layer are all removed by using NMP solvent.

4. The method for preparing a long-distance air bridge to prevent bridge deck denting according to claim 1, characterized in that: The metal for metal evaporation in step S5 is Ti, Pt, Au, Ti or Au.

5. The method for preparing a long-distance air bridge to prevent bridge deck denting according to claim 1, characterized in that: The etching time for wet etching of the GaAs layer in step S4 is Tg3 to Tgn in sequence, and the etching time for wet etching of the InGaP layer is Tp2 to Tpn in sequence.

6. The method for preparing a long-distance air bridge to prevent bridge deck denting according to claim 1, characterized in that: The etching time of the first layer, the second layer to the N-2th layer, the N-1th layer and the Nth layer in step S6 is Tg1, Tp1 to Tgn-1, Tpn-1 and Tgn in sequence.

7. A long span air bridge for preventing the depression of a bridge deck, prepared by the method according to claim 1, characterized by: The air bridge comprises a pier and a bridge body, the two ends of the bridge body are connected with the piers, the bridge body comprises a top bridge surface and a stepped bridge surface, and the stepped bridge surface is connected on both sides of the top bridge surface.

8. A long distance air bridge for preventing depression of a bridge deck according to claim 7, characterized in that: The angle between the connecting section between the stepped surfaces in the stepped bridge surface and the horizontal plane is 30° to 55°.

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