Terahertz GaAs Schottky diode chip substrate replacement method and heterogeneous chip

Abstract

The present invention provides a terahertz GaAs Schottky diode chip substrate replacement method and heterogeneous chip, belonging to the field of semiconductor technology, including preparing an epitaxial wafer; making a basic structure of a Schottky diode; thinning the epitaxial wafer; applying a low-dielectric glue of a preset thickness on the back of the thinned epitaxial wafer to form a low-dielectric constant substrate; bonding a temporary protective substrate on the surface of the low-dielectric constant substrate; removing the temporary grinding substrate on the front of the epitaxial wafer; anode-cathode isolation etching; primary curing of the low-dielectric constant substrate; removing the temporary protective substrate on the surface of the low-dielectric constant substrate; secondary curing of the low-dielectric constant substrate to complete chip production. The terahertz GaAs Schottky diode chip substrate replacement method provided by the present invention can directly manufacture heterogeneous substrates less than 10 microns, without thinning the substrate after heterogeneous replacement, and directly applying glue and curing to form the substrate, which is easy to manufacture and has easy-to-control process parameters.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a terahertz GaAs Schottky diode chip substrate replacement method and a heterogeneous chip prepared based on the method. Background Art

[0002] The terahertz (THz) frequency range of 0.1THz to 10THz in the electromagnetic spectrum marks the transition from macroscopic electronics to microscopic photonics. Due to its unique properties, such as short wavelength, high transmittance, and wide bandwidth, not found in other bands, it holds significant application value in security imaging, communications, biomedicine, military, and space technology. THz technology has rapidly developed in recent years as an emerging interdisciplinary field and a research hotspot, offering enormous potential in electronics, information technology, life sciences, national defense, aerospace, and other fields. THz band applications are garnering increasing attention.

[0003] THz diode frequency doubling / mixing circuits utilize the nonlinear characteristics of diode semiconductor devices. The frequency multiplier uses them to generate harmonics of the fundamental signal and extract the corresponding order harmonics to obtain a radio frequency source with a frequency that is a multiple of the fundamental frequency; the mixer uses them to perform frequency shifting and filter frequency selection. These circuits form the basis for the application of terahertz technology.

[0004] In a classic terahertz circuit, a GaAs Schottky diode chip is flip-chip bonded to a quartz chip using conductive silver glue, and the quartz circuit is then bonded to the cavity using conductive silver glue, forming a classic terahertz circuit (hybrid integrated circuit) application module.

[0005] The circuit structure of this traditional hybrid integrated circuit (IC) terahertz Schottky diode has two significant drawbacks: As terahertz application frequencies increase, the difficulty of terahertz diode chip removal and handling becomes increasingly complex; and as the frequency increases, the diode's GaAs substrate increasingly affects terahertz circuit performance. To address these issues, the MASTER (Method of Adhesion by Spin-on-dielectric Temperature Enhanced Reflow) technology was developed. Its core concept is to fabricate the diode chip and peripheral circuitry on a GaAs wafer substrate, then grind off the substrate and glue it onto a quartz substrate to create a quartz substrate—essentially a substrate replacement. The quartz substrate is then sliced to create the circuitry.

[0006] This technology actually involves bonding the diode chip epitaxial structure wafer to a quartz substrate to replace the substrate. Its advantage is that it reduces the parasitic capacitance of the circuit and improves the performance of the terahertz circuit. Its difficulties mainly lie in two points: one is the thinning and processing of the quartz substrate. Because the circuit operating frequency is in the terahertz band, the high frequency quartz substrate must be very thin, even to more than ten microns, which poses a challenge to the thinning and processing of quartz; the second is the use of wafer bonding technology, which requires expensive wafer bonding equipment and strict process environment control to ensure the adhesion between the quartz substrate and the GaAs epitaxial structure. The specific process operation is difficult to control. Summary of the Invention

[0007] The embodiments of the present invention provide a terahertz GaAs Schottky diode chip substrate replacement method and a heterogeneous chip, which replaces a high-dielectric-constant GaAs single crystal substrate with a low-dielectric-constant substrate. This can reduce the difficulty of quartz thinning, reduce the parasitic capacitance of the Schottky diode, increase the cutoff frequency of the Schottky diode, and improve the repeatability of terahertz circuit manufacturing and the accuracy of circuit simulation. At the same time, the substrate is directly coated with a low-dielectric liquid material instead of solid quartz, eliminating the wafer bonding process between the semiconductor and the quartz substrate, and improving the accuracy of controlling the substrate thickness below 10 microns.

[0008] To achieve the above objectives, in a first aspect, the present invention adopts a technical solution of providing a terahertz GaAs Schottky diode chip substrate replacement method, comprising:

[0009] preparing epitaxial wafers;

[0010] Making a Schottky contact as an anode and an ohmic contact as a cathode on the epitaxial wafer;

[0011] Bonding a temporary polishing substrate to the front of the epitaxial wafer to serve as a temporary substrate for thinning the epitaxial wafer;

[0012] Applying a low dielectric constant adhesive of a preset thickness on the back of the thinned epitaxial wafer to form a low dielectric constant substrate;

[0013] bonding a temporary protective substrate to the surface of the low dielectric constant substrate;

[0014] Using the temporary protective substrate as a temporary substrate, removing the temporary polishing substrate on the front side of the epitaxial wafer;

[0015] Anode-cathode isolation corrosion;

[0016] curing the low dielectric constant substrate once;

[0017] removing the temporary protective substrate from the surface of the low dielectric constant substrate;

[0018] The low dielectric constant substrate is secondary cured to complete the chip fabrication.

[0019] In combination with the first aspect, in a possible implementation, the low-dielectric adhesive is SOG-coated glass adhesive, or BCB adhesive, or polyimide adhesive.

[0020] In combination with the first aspect, in a possible implementation, the thickness of the low-dielectric glue is determined by the number of rotations according to the viscosity of the glue, and the substrate replacement is completed by curing the glue.

[0021] In combination with the first aspect, in a possible implementation, the thickness of the low-dielectric glue is 4-6 microns.

[0022] In combination with the first aspect, in a possible implementation, curing the low dielectric constant substrate includes placing the epitaxial wafer in a nitrogen oven and curing for t hours.

[0023] In combination with the first aspect, in a possible implementation, the primary curing temperature is 250° C.-300° C., and the curing time t is 1.5-3 hours.

[0024] In combination with the first aspect, in a possible implementation, the temperature of the secondary curing is 300° C.-350° C., and the curing time t is 1.5-3 hours.

[0025] In combination with the first aspect, in a possible implementation, a low-temperature adhesive is used to bond the temporary polishing plate substrate.

[0026] In combination with the first aspect, in a possible implementation, the temporary protective substrate is bonded with a high-temperature resistant adhesive.

[0027] The terahertz GaAs Schottky diode chip substrate replacement method provided by the present invention has the following advantages compared with the prior art: (1) the present invention uses the original chip circuit substrate as a basis, replaces the high-dielectric-constant GaAs single crystal substrate of the chip circuit with a low-dielectric-constant substrate, and forms a low-dielectric substrate structure of the terahertz circuit. When the low-dielectric-constant substrate structure is applied to the terahertz circuit, the parasitic capacitance of the Schottky diode can be reduced, and the cutoff frequency of the Schottky diode can be increased.

[0028] (2) Since the diode structure and its surrounding matching and filtering circuits are all manufactured by photolithography, the structural size deviation can be controlled within 1 micron, which improves the repeatability of terahertz circuit manufacturing and the accuracy of circuit simulation.

[0029] (3) Compared with the MASTER technology, the substrate is directly coated with liquid low dielectric constant glue and then solidified to replace solid quartz, eliminating the wafer bonding process between the semiconductor and the quartz substrate. At the same time, the control of the substrate thickness below 10 microns is more precise.

[0030] The substrate replacement method provided by the present invention can directly manufacture a substrate less than 10 microns without thinning the quartz substrate, and the substrate is formed by directly applying glue and curing. The manufacture is easy and the process environment is easy to control.

[0031] In a second aspect, an embodiment of the present invention further provides a heterogeneous chip, which is prepared using the terahertz GaAs Schottky diode chip substrate replacement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic structural diagram of a conventional GaAs epitaxial structure provided in an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of the basic structure of a Schottky diode on the front side of an epitaxial wafer provided in an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of the structure of a wafer after substrate thinning and removal provided by an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of the structure for applying low dielectric adhesive according to an embodiment of the present invention;

[0036] Figure 5 A schematic diagram of a structure in which a temporary protective substrate is provided on the surface of a low-dielectric adhesive according to an embodiment of the present invention;

[0037] Figure 6 A schematic diagram of the structure for removing the temporary protective substrate on the front side of an epitaxial wafer provided in an embodiment of the present invention;

[0038] Figure 7 A schematic diagram of the structure of anode-cathode corrosion isolation provided by an embodiment of the present invention;

[0039] Figure 8 A schematic diagram of the structure of a chip after cutting provided by an embodiment of the present invention;

[0040] Description of reference numerals:

[0041] 1. GaAs semi-insulating single crystal substrate; 2. AlGaAs etch stop layer; 3. GaAs layer; 4. N + GaAs layer; 5, N - GaAs layer; 6. cathode; 7. anode air bridge; 8. anode; 9. temporary grinding plate substrate; 10. low dielectric constant substrate; 11. temporary protective substrate. DETAILED DESCRIPTION

[0042] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0043] The present invention adopts a diode chip circuit basic structure to be manufactured on a GaAs wafer substrate, and then the substrate is ground off, leaving the diode chip and peripheral circuit on an extremely thin GaAs epitaxial layer (thickness of several microns); a liquid low-dielectric adhesive, such as SOG (spin-on-glass) glass adhesive, or BCB adhesive, or PMGI polyimide adhesive is directly coated on the GaAs epitaxial layer. The thickness of the adhesive is determined by the viscosity of the adhesive and the number of rotations, and the substrate replacement is completed by curing the adhesive.

[0044] The present invention adopts a liquid glue coating method, which is applied to the back side of the wafer with the GaAs substrate removed (its device structure is manufactured on the front side of the wafer) by spin coating. The thickness of the glue is controlled by the number of rotations. After reaching the required thickness, the liquid glue is solidified and transformed by heating, thereby realizing the substrate replacement of the terahertz chip circuit.

[0045] The present invention provides a method for replacing a terahertz GaAs Schottky diode chip substrate, and the specific embodiments are as follows:

[0046] Example 1

[0047] Please also refer to Figures 1 to 8 The method for replacing the substrate of a terahertz GaAs Schottky diode chip provided by the present invention is now described. The method for replacing the substrate of a terahertz GaAs Schottky diode chip comprises the following steps:

[0048] Step 1: Wafer basic structure: Use GaAs conventional epitaxial structure design, as shown in the attached Figure 1 .

[0049] The present invention adopts conventional GaAs epitaxial structure to make GaAs diode device, such as Figure 1 As shown, from bottom to top, there is a GaAs semi-insulating single crystal substrate 1, on which is grown an AlGaAs etch stop layer 2 with a thickness of 1000 angstroms, and on which are grown an N+GaAs layer 4 and an N-GaAs layer 5. The semiconductor growth method described above uses conventional MBE technology or MOCVD technology to prepare epitaxial wafers for semiconductor devices.

[0050] Step 2: Fabrication of the basic structure of the Schottky diode: Using conventional technology to fabricate the basic structure of the GaAs diode on the epitaxial wafer above, such as the anode metal, cathode metal structure and anode air bridge 7, the anode structure is a Schottky contact, and is prepared using Ti / Pt / Au or Pd / Ti / Au or other reasonable metal structures; the cathode 6 structure is an ohmic contact, and is prepared using AuGeNi alloy or other reasonable metal structures, as shown in the attached figure. Figure 2 shown.

[0051] Step 3: Remove the GaAs semi-insulating single crystal substrate. Figure 3 Conventional techniques were used to thin the epitaxial wafer by attaching its front surface to a sapphire substrate. Conventional low-temperature wax was used for bonding, and the sapphire substrate served as a temporary polishing substrate. Mechanical thinning and chemical selective etching were then used to completely remove the GaAs semi-insulating substrate and the AlGaAs etch stop layer.

[0052] Step 4: Applying low dielectric constant substrate 10 material: Use glue coating equipment to apply SOG glue on the epitaxial wafer with the substrate removed. The glue thickness is 5 microns or 5.5 microns. Figure 4 .

[0053] Step 5: Protective process of low dielectric constant substrate 10, as shown in the attached Figure 5 Temporarily adhere the epitaxial wafer, which has undergone substrate replacement, to a sapphire substrate using a high-temperature resistant adhesive. The sapphire substrate serves as a temporary protective base plate 11. The high-temperature resistant adhesive should be suitable for both self-bonding and bonding high-temperature resistant materials such as metal, ceramics, glass, fiberglass, asbestos, and graphite. High-temperature resistant adhesives come in two main categories: organic and inorganic. Any adhesive suitable for bonding can be used.

[0054] Step 6, temporary substrate removal of the grinding plate: Use conventional methods to remove the temporary grinding plate substrate 9, as shown in the attached Figure 6 shown.

[0055] Step 7, anode 8 and cathode 6 isolation corrosion: clean the sticky wax, and then use conventional semiconductor technology to etch and isolate the anode 8 and cathode 6, as shown in the attached Figure 7 shown.

[0056] Step 8: Primary curing of SOG adhesive: Place the wafer obtained above in a nitrogen oven at 250°C for 2 hours. The temperature can also be 260°C, 280°C, or 300°C. The primary curing time can be 1.5 hours, 2 hours, or 2.5 hours.

[0057] Step 9, chip cutting: use conventional semiconductor chip cutting process to cut, the cutting depth is greater than 5 microns, and then use organic solvent to remove the temporary protective substrate 11, as shown in the attached Figure 8 .

[0058] Step 10: Secondary curing of the SOG glue to form a low dielectric constant substrate 10: Place the wafer in a 300°C nitrogen oven for 2 hours of curing to complete chip manufacturing. The secondary curing temperature can be higher than the primary curing temperature. For example, 260°C, 280°C, 300°C, 350°C, etc. can be selected without limitation. The secondary curing time can be 1.5 hours, 2 hours, or 2.5 hours without limitation. The secondary curing time can be the same as or different from the primary curing time.

[0059] The low dielectric constant substrate 10 is formed into a heterogeneous substrate by coating and curing a liquid glue. Its thickness and other process parameters can be directly controlled without thinning the heterogeneous substrate. It is directly coated and cured, and its thickness is easy to control.

[0060] Example 2

[0061] Use PMGI polyimide glue to replace the substrate

[0062] The difference from Example 1 lies in step 4: coating of a low dielectric constant low dielectric glue material: using glue coating equipment, coating PMGI glue on the wafer from which the substrate has been removed, with a thickness of 5 microns.

[0063] Example 3

[0064] Substrate replacement using coated BCB glue

[0065] The difference from the first embodiment lies in step 4: coating of the low dielectric constant substrate 10 material: using a coating device, coating the wafer from which the substrate has been removed with BCB glue, with a thickness of 4.5 μm.

[0066] Compared with the prior art, the terahertz GaAs Schottky diode chip substrate replacement method provided in this embodiment has the following advantages:

[0067] (1) The present invention takes the original chip circuit substrate as the basis and replaces the high dielectric constant GaAs single crystal substrate of the chip circuit with a low dielectric constant substrate, thereby realizing a low dielectric substrate structure of the terahertz circuit. When the low dielectric constant substrate structure is applied to the terahertz circuit, it can reduce the parasitic capacitance of the Schottky diode and increase the cutoff frequency of the Schottky diode.

[0068] (2) Since the diode structure and its surrounding matching and filtering circuits are all manufactured by photolithography, the structural size deviation can be controlled within 1 micron, which improves the repeatability of terahertz circuit manufacturing and the accuracy of circuit simulation.

[0069] (3) Compared with the MASTER technology, the substrate is directly coated with low-dielectric material instead of solid quartz, eliminating the wafer bonding process between the semiconductor and the quartz substrate, and at the same time, the control of the substrate thickness below 10 microns is more precise.

[0070] The substrate replacement method provided by the present invention can directly prepare a low dielectric constant substrate with a thickness of less than 10 microns without thinning the quartz substrate. The substrate is formed by directly applying glue and curing. The production is easy and the process environment is easy to control.

[0071] Based on the same inventive concept, embodiments of the present application also provide a heterogeneous chip fabricated using the aforementioned terahertz GaAs Schottky diode chip substrate replacement method. By using a thin-film heterogeneous substrate formed by curing a low-dielectric liquid adhesive instead of solid quartz, a novel heterogeneous chip is constructed. The resulting heterogeneous chip's structural dimensional deviation can be controlled to within 1 micron, improving the repeatability of terahertz circuit fabrication and the accuracy of circuit simulations. This reduces the parasitic capacitance of the Schottky diode and increases its cutoff frequency.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for replacing a terahertz GaAs Schottky diode chip substrate, characterized in that: include: preparing epitaxial wafers; Making a Schottky contact as an anode (8) and an ohmic contact as a cathode (6) on the epitaxial wafer; A temporary grinding plate substrate (9) is bonded to the front of the epitaxial wafer to serve as a temporary substrate for thinning the epitaxial wafer; Applying a low dielectric constant adhesive of a preset thickness on the back of the thinned epitaxial wafer to form a low dielectric constant substrate (10); Bonding a temporary protective substrate (11) on the surface of the low dielectric constant substrate (10); Using the temporary protective substrate as a temporary substrate, removing the temporary polishing substrate (9) on the front side of the epitaxial wafer; Anode-cathode isolation corrosion; curing the low dielectric constant substrate (10) once; removing the temporary protective substrate (11) from the surface of the low dielectric constant substrate (10); The low dielectric constant substrate (10) is cured for a secondary step to complete the production of the chip.

2. The method for replacing a terahertz GaAs Schottky diode chip substrate according to claim 1, wherein: The low dielectric glue is SOG coated glass glue, or BCB glue, or polyimide glue.

3. The method for replacing a terahertz GaAs Schottky diode chip substrate according to claim 1, wherein: The thickness of the low-dielectric glue is determined according to the viscosity of the glue and the number of rotations, and the substrate replacement is completed by curing the glue.

4. The method for replacing a terahertz GaAs Schottky diode chip substrate according to claim 1 or 2, wherein: The thickness of the low dielectric glue is 4-6 microns.

5. The method for replacing a terahertz GaAs Schottky diode chip substrate according to claim 1, wherein: Curing the low dielectric constant substrate (10) comprises placing the epitaxial wafer into a nitrogen oven and curing for t hours.

6. The method for replacing the substrate of a terahertz GaAs Schottky diode chip according to claim 5, wherein: The primary curing temperature is 250° C.-300° C., and the curing time t is 1.5-3 hours.

7. The method for replacing a terahertz GaAs Schottky diode chip substrate according to claim 5, wherein: The temperature of the secondary curing is 300° C.-350° C., and the curing time t is 1.5-3 hours.

8. The method for replacing a terahertz GaAs Schottky diode chip substrate according to claim 1, wherein: The temporary grinding plate substrate (9) is bonded by using a low-temperature adhesive.

9. The method for replacing a terahertz GaAs Schottky diode chip substrate according to claim 1, wherein: The temporary protective substrate (11) is bonded with a high temperature resistant adhesive.

10. A heterogeneous chip, characterized in that: The terahertz GaAs Schottky diode chip is prepared by using the substrate replacement method according to any one of claims 1 to 9.

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