Capacitively loaded mems filter with aluminum nitride dielectric and method of manufacture
By employing aluminum nitride dielectric in capacitively loaded filters and combining magnetron sputtering and photolithography etching processes, the challenges of process compatibility and thickness control in existing technologies have been solved, enabling the production of miniaturized, high-performance RF filters and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NO 55 INST CHINA ELECTRONIC SCI & TECHNOLOGYGROUP CO LTD
- Filing Date
- 2023-07-26
- Publication Date
- 2026-08-04
AI Technical Summary
Existing capacitor-loaded filters generally use silicon nitride or silicon oxide as the capacitor dielectric. The high growth temperature leads to poor process compatibility, the thickness of the capacitor dielectric is difficult to control precisely, and the patterning is difficult, resulting in poor uniformity of filter performance.
Aluminum nitride is used as the capacitor dielectric. The aluminum nitride dielectric layer is deposited by magnetron sputtering and patterned by photolithography and wet etching processes. This allows for precise control of the dielectric thickness and pattern size, simplifies the process flow, and reduces costs.
This has resulted in RF filters that are small in size, have low loss, and exhibit good performance uniformity, thereby reducing manufacturing costs and improving economic efficiency.
Smart Images
Figure CN116864954B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to capacitor-loaded filters, and more particularly to a silicon-based capacitor-loaded filter using aluminum nitride as the dielectric. Background Technology
[0002] Filters are the most important filtering components in communication systems, and their size, cost, and integration are crucial considerations in system design. Traditional LC filters and microstrip filters are large and have weak out-of-band rejection capabilities, while cavity and dielectric filters are difficult to miniaturize. Silicon-based filters utilize Micro-electro-mechanical systems (MEMS) technology, a high-precision multilayer three-dimensional microfabrication technique. Using MEMS technology to fabricate filters achieves micrometer-level processing precision, resulting in filters with significant advantages in size, loss, selectivity, and consistency, meeting the requirements of the millimeter-wave band. Using a high-resistivity silicon substrate reduces high-frequency losses in transmission lines, giving the filter advantages such as small size, low loss, and high quality factor. Comb-line filter resonators, with one end short-circuited and the other open-circuited, are widely used in RF circuits. When a capacitor is applied to ground at the open-circuit end, the size of the resonator is significantly reduced. Existing capacitor-loaded filters generally use silicon nitride or silicon oxide as the capacitor dielectric, but the high growth temperature leads to poor process compatibility, and the difficulty in precisely controlling the dielectric thickness results in poor filter performance uniformity. On the other hand, silicon nitride and silicon oxide are more difficult to pattern, which also leads to a decrease in the uniformity of filter performance. Summary of the Invention
[0003] The purpose of this invention is to provide a small-sized, simple-to-manufacture aluminum nitride-based capacitor-loaded MEMS filter and its manufacturing method.
[0004] The technical solution for achieving the objective of this invention is as follows: Firstly, this invention provides a method for fabricating a capacitively loaded MEMS filter using aluminum nitride as the dielectric, comprising:
[0005] Step 1: Provide a silicon substrate;
[0006] Step 2: Form a lower electrode metal layer on the silicon substrate and pattern the lower electrode metal layer.
[0007] Step 3: Deposit a capacitor dielectric layer on the patterned capacitor lower electrode metal layer and pattern it;
[0008] Step 4: Coat the silicon substrate with photoresist, expose and develop it, then etch the silicon substrate to form silicon holes;
[0009] Step 5: Thin the back of the silicon substrate to expose silicon vias and form through-silicon vias;
[0010] Step 6: Form a metal adhesion layer and a seed layer on the front and back sides of the silicon substrate, on the surface of the capacitor dielectric layer, and inside the silicon via;
[0011] Step 7: Coat the front side of the silicon substrate and the capacitor dielectric layer with photoresist. After exposure and development, form a second metal layer in the developed area on the front side of the silicon substrate, namely the upper electrode of the capacitor, the filter resonator, the through-silicon via and the back side of the silicon substrate. Remove the photoresist and remove the adhesion layer and seed layer outside the pattern of the second metal layer on the front side.
[0012] Secondly, the present invention also provides a capacitor-loaded MEMS filter with aluminum nitride as the dielectric, prepared based on the method described in the first aspect.
[0013] Compared with existing technologies, the significant advantages of this invention are as follows: The method for fabricating an RF filter and the RF filter of this invention involve forming a lower metal electrode layer on a silicon substrate and patterning the lower metal electrode layer. Then, an aluminum nitride dielectric layer and silicon dioxide are deposited on the patterned lower electrode metal layer. Photoresist is coated and patterned on the silicon dioxide surface. The exposed silicon dioxide pattern is removed, the photoresist is removed, and the patterned silicon dioxide is used as a mask to pattern the aluminum nitride. The silicon dioxide is then removed, thus achieving the patterning of the aluminum nitride. The aluminum nitride is fabricated using a magnetron sputtering process, which allows for precise thickness control, stable film quality, and precise control of dielectric constant and pattern size. A second metal layer is fabricated through a patterned electroplating process, serving simultaneously as the upper electrode metal of the capacitor, the metal of the filter resonator, the TSV via, and the back-side grounding metal of the silicon substrate. This significantly simplifies the process flow, reduces process steps, lowers the fabrication cost of the RF filter, and improves economic efficiency. Attached Figure Description
[0014] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:
[0015] Figure 1 This is a schematic diagram of the structure of the radio frequency filter in an embodiment of the present invention;
[0016] Figure 2 This is a schematic diagram of the cross-sectional structure of the radio frequency filter in an embodiment of the present invention;
[0017] Figures 3(a)-3(f) This is a schematic diagram of the manufacturing process of the radio frequency filter in an embodiment of the present invention.
[0018] Explanation of reference numerals in the attached figures
[0019] 100: Radio frequency filter;
[0020] 110: Silicon substrate;
[0021] 120: Aluminum nitride as the lower electrode of the capacitor;
[0022] 130: Molybdenum metal, the lower electrode of the capacitor;
[0023] 140: Aluminum nitride capacitor dielectric layer;
[0024] 160: Silicon TSV via;
[0025] 170: Upper electrode of capacitor
[0026] 180: Filter resonator;
[0027] 190: Metal layer on the back of the filter. Detailed Implementation
[0028] like Figure 1 , Figure 2 As shown, the radio frequency filter of the present invention includes a silicon substrate, an aluminum nitride and molybdenum metal forming a lower electrode of a capacitor, an aluminum nitride capacitor dielectric layer, a TSV via, an Au resonator, an Au capacitor upper electrode, and Au inside the TSV via and grounded Au on the back side of the silicon substrate. The radio frequency filter is fabricated through the following steps:
[0029] Step 1: Provide a silicon substrate;
[0030] Step 2: Form a lower electrode metal layer on the silicon substrate and pattern the metal electrode layer;
[0031] Step 3: Deposit an aluminum nitride dielectric layer and silicon dioxide on the patterned lower electrode metal layer, coat the silicon dioxide surface with photoresist and pattern it, remove the exposed silicon dioxide pattern, remove the photoresist, use the patterned silicon dioxide as a mask to pattern the aluminum nitride, remove the silicon dioxide, and realize the patterning of aluminum nitride.
[0032] Step 4: Coat the silicon substrate with photoresist, expose and develop it, and then etch the silicon substrate to form silicon holes;
[0033] Step 5: Perform a thinning operation on the back side of the silicon substrate to expose silicon vias and form through-silicon vias;
[0034] Step 6: Form a metal adhesion layer and a seed layer on the front and back surfaces of the silicon substrate, on the surface of the aluminum nitride dielectric layer, and inside the silicon vias;
[0035] Step 7: Coat the front side of the silicon substrate and the aluminum nitride dielectric layer with photoresist. After exposure and development, form a second metal layer in the developed area on the front side of the silicon substrate, namely the upper electrode of the capacitor, the filter resonator, the through-silicon via and the back side of the silicon substrate. Remove the photoresist and remove the seed layer outside the pattern of the second metal layer on the front side.
[0036] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0037] refer to Figure 1 and Figure 2 As shown, a first aspect of the present invention relates to a method for manufacturing a radio frequency filter 100, the method comprising:
[0038] As shown in Figure 3(a), a silicon substrate 110 is provided, and aluminum nitride 120 and molybdenum 130 are deposited on the silicon substrate 110 as capacitor lower electrodes.
[0039] Specifically, in this step, the substrate material is high-resistivity silicon, typically with a resistivity ≥10000 Ω·cm. Aluminum nitride 120 and molybdenum 130 are fabricated using magnetron sputtering, with aluminum nitride thickness ranging from 10 to 50 nanometers and molybdenum thickness ranging from 100 to 600 nanometers.
[0040] As shown in Figure 3(b), the lower electrode layer of the capacitor is patterned on the silicon substrate.
[0041] Specifically, in this step, for example, photoresist is coated onto the surface of the lower electrode of the capacitor, and after exposure and development, a pattern of the lower electrode of the capacitor is formed. A dry etching process is used to remove the molybdenum and aluminum nitride outside the pattern masked by the photoresist, and then an organic solvent is used to remove the photoresist to form the metal lower electrode patterns 120 and 130.
[0042] As shown in Figure 3(c), aluminum nitride dielectric layer and silicon oxide masking layer are deposited on the surface of the metal lower electrode patterns 120 and 130 and the silicon substrate 110 using thin film deposition technology. The silicon oxide masking layer is patterned using photolithography and wet etching processes. The photoresist is removed using an organic solvent. Using silicon oxide as a mask, the aluminum nitride dielectric layer is patterned using wet etching, and then the silicon oxide masking layer is removed using wet etching to form capacitor dielectric layer pattern 140.
[0043] As shown in Figure 3(d), a TSV pattern is formed on the surface of the silicon substrate 110 using a photolithography patterning process, and a dry etching process is used to etch the silicon substrate to form TSV holes.
[0044] As shown in Figure 3(e), a thinning process is performed on the back side of the silicon substrate 110 to expose TSV holes and form TSV vias 160.
[0045] As shown in Figure 3(f), an adhesion layer and a seed layer are fabricated on the front and back sides of the silicon substrate using magnetron sputtering. A capacitor top electrode pattern 170 and a filter resonator pattern 180 are formed using photolithography. Electroplating is then used to form the capacitor top electrode 170, the filter resonator 180, the metal inside the TSV via, and the back-side ground metal 190. The photoresist is removed using an organic solvent, and the adhesion layer and seed layer outside the capacitor top electrode pattern and the filter resonator pattern are removed using a dry or wet process, thus forming a complete filter product.
[0046] In summary, this invention discloses a low-loss silicon-based filter and its fabrication method. The RF filter fabrication method and the RF filter of this invention employ magnetron sputtering to fabricate the lower electrode and dielectric layer of the capacitor, resulting in high film quality and precise thickness control. A second metal layer is fabricated using a patterned electroplating process, serving simultaneously as the upper electrode metal of the capacitor, the filter resonator metal, the TSV via, and the back-side grounding metal of the silicon substrate. This significantly simplifies the process flow, reduces the number of process steps, lowers the fabrication cost of the RF filter, and improves economic efficiency.
[0047] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.
Claims
1. A method for fabricating a capacitively loaded MEMS filter using aluminum nitride as the dielectric, characterized in that, include: Step 1: Provide a silicon substrate; Step 2: Form a lower electrode metal layer on the silicon substrate and pattern the lower electrode metal layer. Step 3: Deposit a capacitor dielectric layer on the patterned capacitor lower electrode metal layer and pattern it. Specifically, deposit an aluminum nitride dielectric layer and silicon dioxide on the patterned capacitor lower electrode metal layer, coat the silicon dioxide surface with photoresist and pattern it, remove the exposed silicon dioxide pattern, remove the photoresist, use the patterned silicon dioxide as a mask to pattern the aluminum nitride, remove the silicon dioxide, and realize the patterning of aluminum nitride. Step 4: Coat the silicon substrate with photoresist, expose and develop it, then etch the silicon substrate to form silicon holes; Step 5: Thin the back of the silicon substrate to expose silicon vias and form through-silicon vias; Step 6: Form a metal adhesion layer and a seed layer on the front and back sides of the silicon substrate, on the surface of the capacitor dielectric layer, and inside the silicon via; Step 7: Coat the front side of the silicon substrate and the capacitor dielectric layer with photoresist. After exposure and development, form a second metal layer in the developed area on the front side of the silicon substrate, namely the upper electrode of the capacitor, the filter resonator, the through-silicon via and the back side of the silicon substrate. Remove the photoresist and remove the adhesion layer and seed layer outside the pattern of the second metal layer on the front side.
2. The method according to claim 1, characterized in that, In step 1, the provided silicon substrate is high-resistivity silicon with a resistivity of 3000-10000 Ω•cm.
3. The method according to claim 1, characterized in that, In step 2, the lower electrode metal layer of the capacitor is a two-layer composite material, consisting of aluminum nitride and molybdenum from bottom to top.
4. The method according to claim 3, characterized in that, Aluminum nitride and molybdenum were prepared by magnetron sputtering. The thickness of aluminum nitride ranged from 10 to 50 nanometers, and the thickness of molybdenum ranged from 100 to 600 nanometers.
5. The method according to claim 1, characterized in that, The capacitor dielectric layer material is aluminum nitride, and the preparation method is magnetron sputtering, with a thickness ranging from 100 to 1000 nanometers.
6. The method according to claim 1, characterized in that, The metal adhesion layer and seed layer are one of Ti / TiW / Au, TiW / Au, and Cr / Au.
7. The method according to claim 1, characterized in that, In step 7, the photoresist is a negative photoresist.
8. The method according to claim 1, characterized in that, After development, the areas on the front side of the silicon substrate, namely the capacitor electrode, filter resonator, through-silicon via, and the metal layer on the back side of the silicon substrate, are grown into a gold layer of standard thickness, with a thickness of 2-5 micrometers, through an electroplating process.
9. A capacitively loaded MEMS filter using aluminum nitride as the dielectric, characterized in that, The filter is manufactured using the filter manufacturing method described in any one of claims 1 to 8.