Radio frequency semiconductor device and method of manufacturing radio frequency semiconductor device

Abstract

The invention relates to a radio frequency semiconductor device and a method of manufacturing a radio frequency semiconductor device. In accordance with an example of the present invention, an RF semiconductor device for processing a radio frequency (RF) signal in an operating frequency range includes a semiconductor chip including a first surface, a second surface, a sidewall, and an active chip region. The first and second surfaces extend in a lateral direction and the sidewalls extend in a vertical direction. A metal layer outside the active chip region faces the second surface of the semiconductor chip. The thickness of the metal layer is lower than the skin depth corresponding to the operating frequency range.

Description

Technical Field

[0001] The present disclosure relates to radio frequency semiconductor devices, and in particular to radio frequency semiconductor devices having metal layers. In addition, the present disclosure relates to methods of manufacturing such devices. Background Art

[0002] In the field of advanced driver assistance systems (ADAS), radio frequency (RF) semiconductor devices play a vital role. In order to improve the performance and functions of RF semiconductor devices, more and more functions are packaged into components with small packages, resulting in electromagnetic interference (EMI) coupling between the circuit and other components of the RF semiconductor devices. As RF semiconductor devices become smaller and more tightly packaged, they are also more susceptible to EMI.

[0003] Therefore, it is an object of the present application to provide a concept for an RF semiconductor device which reduces electromagnetic interference in the RF semiconductor device. This object is solved by an RF semiconductor device according to claim 1 and a method of manufacturing a RF semiconductor device according to claim 20 . Summary of the invention

[0004] According to an example of the present invention, an RF semiconductor device for processing a radio frequency (RF) signal within an operating frequency range includes a semiconductor chip, the semiconductor chip including a first surface, a second surface, a sidewall, and an active chip area. The first surface and the second surface extend in a lateral direction and the sidewall extends in a vertical direction. A metal layer is provided outside the active chip area, wherein the metal layer faces the second surface of the semiconductor chip, wherein the thickness of the metal layer is lower than a skin depth corresponding to the operating frequency range.

[0005] According to an example of the present invention, a method for manufacturing an RF semiconductor device for processing a radio frequency (RF) signal within an operating frequency range includes:

[0006] A semiconductor chip is provided, the semiconductor chip comprising a first surface, a second surface, a sidewall and an active chip area, the first surface and the second surface extending in a lateral direction and the sidewall extending in a vertical direction,

[0007] A metal layer is provided outside the active chip area, wherein the metal layer faces the second surface of the semiconductor chip, wherein a thickness of the metal layer is below a skin depth corresponding to an operating frequency range.

[0008] Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present disclosure is illustrated in the accompanying drawings by way of example and not limitation, wherein the same reference numerals represent similar or identical elements. The elements in the accompanying drawings are not necessarily scaled to scale with each other. The features of the various illustrated examples may be combined unless they are mutually exclusive.

[0010] Figure 1 A cross-sectional view of an RF semiconductor device is shown, wherein a metal layer is arranged over a semiconductor die.

[0011] Figure 2 A cross-sectional view of an RF semiconductor device is shown, wherein a plurality of metal layers are arranged over a semiconductor die.

[0012] Figure 3 A cross-sectional view of an RF semiconductor device is shown in which a metal layer extends beyond the semiconductor die.

[0013] Figure 4 A cross-sectional view of an RF semiconductor device is shown wherein multiple metal layers extend beyond the semiconductor die.

[0014] Figure 5 A cross-sectional view of an RF semiconductor device is shown in which one metal layer extends up to the semiconductor die and another metal layer extends beyond the semiconductor die.

[0015] Figure 6 A cross-sectional view of an RF semiconductor device is shown in which one metal layer extends up to the semiconductor die and multiple metal layers extend beyond the semiconductor die.

[0016] Figure 7 A cross-sectional view of an RF semiconductor device is shown in which one plurality of metal layers extends up to a semiconductor die and another plurality of metal layers extends beyond the semiconductor die.

[0017] Figure 8 A cross-sectional view of an RF semiconductor device is shown, wherein an antenna is arranged between gaps in a metal layer.

[0018] Fig. 8A A cross-sectional view of an RF semiconductor device is shown, wherein a metal layer is arranged below a redistribution layer.

[0019] Fig. 9 A cross-sectional view of an RF semiconductor device is shown, wherein a metal layer is arranged on a housing.

[0020] Fig.10 A cross-sectional view of an RF semiconductor device is shown, wherein a metal layer is arranged between a housing lid and a semiconductor die.

[0021] Fig.11 Experimental measurements of reflection, transmission, and absorption of a metal layer are shown. DETAILED DESCRIPTION

[0022] In the following description, directional terms, such as "top", "bottom", "upper", "lower", "front", "back", etc., are used with reference to the orientation of the figures being described. The components of the present disclosure can be positioned in a number of different orientations, and the directional terms are used for illustrative purposes and are by no means limiting.

[0023] In addition, to the extent that the terms "including," "having," "with," or other variations thereof are used in the detailed description or claims, these terms are intended to be inclusive in a manner similar to the term "comprising." The terms "coupled" and "connected," and their derivatives, may be used. It should be understood that these terms may be used to indicate that two elements cooperate or interact with each other, whether they are in direct physical or electrical contact, or they are not in direct contact with each other; intermediate elements or layers may be provided between "bonded," "attached," or "connected" elements.

[0024] Embodiments described herein provide a new concept for absorbing RF signals in an RF semiconductor device including a semiconductor die. The new concept is based on the following discovery: if the thickness of a metal layer provided in the RF semiconductor device is selected to correspond to at most 50% of the skin depth of the operating frequency range of the RF semiconductor device, improved channel-to-channel isolation in the RF semiconductor device can be obtained. The semiconductor die is encapsulated by a low-loss molding compound, through which the RF signal propagates without any significant attenuation. Typically, a metal sheet is provided in the RF semiconductor device to shield the RF semiconductor device from RF signals. Within the RF semiconductor device, the shielding causes the RF signal at the metal sheet to be reflected into the RF semiconductor device. The reflected RF signal can easily pass through the low-loss molding compound and couple the RF channel in the RF semiconductor device. This coupling may degrade the performance of the RF semiconductor device.

[0025] Even if the thickness of the metal sheet is equal to or greater than the skin depth, almost all of the RF signal will be reflected at the metal sheet, and only a negligible portion of the RF signal will be absorbed by the metal sheet.

[0026] The new concept proposed in this paper solves the problem of reducing coupling between RF channels by considering the thickness of the metal layer arranged above the semiconductor die. By reducing the thickness of the metal layer to below the skin depth at the corresponding operating frequency, the absorption of the RF signal can exceed the reflection of the RF signal at the metal sheet. In other words, the amount of RF signal absorbed by the metal sheet can be greater than the amount of RF signal reflected at the metal layer. This increases the channel-to-channel isolation in the RF semiconductor device. In addition, the amount of metal used to manufacture the metal sheet can also be reduced. Figure 1A cross-sectional view of a radio frequency (RF) semiconductor device 100 is shown. The RF semiconductor device 100 has a semiconductor chip 102, which is configured to operate in a predetermined frequency range (such as a millimeter wave frequency range), for example, in a first frequency range from 1 GHz to 500 GHz or in a second frequency range from 60 GHz to 90 GHz or 70 GHz to 140 GHz. In some examples, the semiconductor chip 102 may correspond to a radar chip and may be used as a transmitter, a receiver, a sensor, a detector, etc. In other examples, the semiconductor chip may be a 5G or 6G communication chip, a high data transmission communication system, a wireless backhaul system for a secure human body scanning system. The RF signal or multiple RF signals refers to an RF signal or multiple RF signals within the operating frequency range.

[0027] The semiconductor chip 102 has a first surface 104, a second surface 106 opposite to the first surface 104, and a sidewall 108. The first surface 104 and the second surface 106 may be referred to as a first main surface and a second main surface. The first surface 104 and the second surface 106 extend in a lateral direction and the sidewall 108 extends in a vertical direction. An active chip region with transistors and other circuit elements is provided in the semiconductor chip 102. The active chip region may be capable of generating and analyzing RF signals and other signals. In some examples, the active chip region may also be referred to as an RF chip circuit device.

[0028] The first surface 104 of the semiconductor chip 102 is arranged on the first side 112 of the redistribution layer 110, and electrical contacts are established between the semiconductor chip 102 and the conductive structures of the redistribution layer 110. For example, the electrical contacts may be formed by bonding pads, which may be made of aluminum and / or copper. This allows RF signals to be transmitted from the semiconductor chip 102 to the electrical contacts and / or vice versa. Figure 1 In an implementation of , the RF semiconductor device 100 may correspond to a wafer level package.

[0029] The semiconductor chip 102 may have a thickness selected in the range of 100 μm to 1000 μm, wherein the thickness is measured between the first surface 104 and the second surface 106 of the semiconductor chip 102. In some examples, the semiconductor chip 102 may have a thickness selected in the range of 50 μm to 400 μm. In some examples, the thickness of the semiconductor chip 102 may also be measured between the first side 112 of the redistribution layer 110 and the second surface 106 of the semiconductor chip 102. The redistribution layer 110 may have one or more conductive structures in the form of metal lines or metal planes, which are parallel to the first surface 104 of the semiconductor chip 102. The conductive structures guide the current in the RF semiconductor device 100 and are electrically isolated from each other by dielectric materials. The conductive structures may be made of aluminum, copper, or a copper alloy. The dielectric material may include an oxide or a nitride.

[0030] The redistribution layer 110 has a second side 120 opposite to the first side 112. A plurality of first solder balls 122 are arranged on the second side 120 of the redistribution layer 110. Thus, the redistribution layer 110 establishes electrical connections between the plurality of first solder balls 122 and the semiconductor chip 102. Figure 1 A printed circuit board (PCB) not shown in the figure can be electrically and mechanically mounted to the plurality of first solder balls 122. The plurality of first solder balls 122 may include at least one of Sn, Ag, or Cu. Each of the plurality of first solder balls 122 may have a diameter in a range between 200 μm and 400 μm and a pitch in a range between 400 μm and 600 μm. In some examples, a flip chip BGA (ball grid array) or a wire bonded BGA may be used to establish electrical and mechanical connections to the PCB.

[0031] The metal layer 114 is disposed above the semiconductor chip 102 and outside the active chip area. The metal layer 114 has a top surface 114a and a bottom surface 114b that are opposite to each other. The bottom surface 114b of the metal layer 114 faces the second surface 106 of the semiconductor chip 102. The metal layer 114 can have a smooth or rough top surface 114a and a bottom surface 114b, however, the thickness of the metal layer 114 is always lower than the skin depth of the metal layer 114 in the corresponding operating frequency range, wherein the thickness of the metal layer 114 is measured in the vertical direction between the top surface 114a and the bottom surface 114b. In some examples, the thickness is selected so that the thickness of the metal layer 114 is along the extension of the metal layer 114 and is always lower than the skin depth.

[0032] As described below, the skin depth of the metal layer depends on the resistivity of the metal layer and the frequency of the RF signal.The skin depth of the metal layer 114 refers to the skin depth of the metal layer 114 at a bulk resistivity value and where the bulk resistivity value is constant.

[0033] In some examples, the thickness of the metal layer 114 may be 1% to 10% of the skin depth of the metal layer 114 at the corresponding operating frequency. Alternatively, the thickness of the metal layer may be between 10% and 30% or between 30% and 50% of the skin depth of the metal layer 114 at the corresponding operating frequency. Specifically, the thickness of the metal layer 114 may be at most 50% of the skin depth of the metal layer 114 at the corresponding operating frequency. In some examples, the thickness of the metal layer 114 may be less than 10% of the skin depth of the metal layer 114 at the corresponding operating frequency. Therefore, the absorption of the RF signal may exceed the reflection of the RF signal at the metal sheet. In some examples, when the thickness of the metal layer is less than 5% of the skin depth of the metal layer, the absorption may be greater than 50% and the reflection may be less than 20% (described later). In other words, the amount of RF signal absorbed by the metal sheet may be greater than the amount of RF signal reflected at the metal layer. This may increase channel-to-channel isolation in RF semiconductor devices. In addition, the amount of metal used to manufacture the metal sheet may also be reduced.

[0034] The metal layer 114 can absorb RF signals from the RF chip circuit device and thereby reduce interference between RF chip circuit device components, such as interference from one channel to another channel. In other words, the metal layer 114 reduces the RF signal reflected back to the RF chip circuit device and thus improves RF characteristics, such as channel-to-channel isolation of the RF semiconductor device 100. The metal layer 114 can also absorb RF signals from external elements and provide RF shielding for the RF semiconductor device 100 to isolate from external elements.

[0035] Optimal performance of the RF semiconductor device 100 may be achieved by selecting the relative thickness of the metal layer 114 to be below the skin depth as described below, which thickness depends on the operating frequency of the RF semiconductor device 100 .

[0036] The improvement of the absorption characteristics of the metal layer is based on the skin depth effect, where the skin depth refers to the depth to which the RF signal can penetrate the metal layer. When the RF signal passes through the metal layer, it tends to be distributed within the metal layer, so that the RF signal density is the largest near the surface of the metal layer and decreases exponentially with the increase of the depth of the metal layer. The skin depth depends on the frequency of the RF signal and the characteristics of the metal layer. The calculation formula of the skin depth δ is:

[0037]

[0038] Wherein, f is the frequency of the RF signal, p is the resistivity of the metal layer and μ is the magnetic permeability of the metal layer.

[0039] When the metal layer has a thickness exceeding the mm range (especially exceeding 1 mm), the metal layer behaves as a bulk metal. For example, the mean free path of electrons can be several hundred nanometers and the thickness of the metal layer is greater than the skin depth. In addition, the optical and electrical properties of the metal layer are constant and cannot be tuned. Optical properties mean reflection, transmission or absorption, etc. Electrical properties mean resistivity, mean free path of electrons or electron density, etc. Bulk metals have low resistivity and high electron density and therefore almost all RF signals are reflected on bulk metals.

[0040] When the thickness of the metal layer 114 is lower than the skin depth, i.e., less than 100 nm, the optical and electrical properties are no longer constant, but depend on the thickness of the metal layer. This is due to the grain size effect and quantum confinement caused by the thickness reduction. For example, when the thickness of the metal layer 114 is reduced in a nonlinear manner, the resistivity of the metal layer 114 increases relative to the bulk resistivity value. The mean free path of the electrons in the metal layer 114 becomes comparable to or smaller than the thickness of the metal layer 114, which enhances surface scattering. Due to the high resistivity and enhanced surface scattering, the RF signal penetrating the metal layer 114 is scattered by the metal layer 114. Therefore, the RF signal may eventually be absorbed by the metal layer 114 instead of being reflected.

[0041] In the RF semiconductor device 100, the metal layer 114 includes a metal or a metal alloy, such as Au, Al, CuTi, Ta, Ti, Ru, PtMn, TaN, TiN, Co 90 Fe 10 、Ni 80 Fe 20 、Ni 60 Cr 40 , but not limited to the above examples. The metal layer may have a thickness between 1 nm and 150 nm to achieve maximum absorption in a first frequency range from 1 GHz to 500 GHz. Taking ruthenium as an example, a thickness between 2.5 nm and 10 nm may be selected to maximize absorption in a second frequency range from 60 GHz to 90 GHz.

[0042] With the introduction of the metal layer 114 on the semiconductor chip 102, a new concept is introduced that allows for efficient, economical and configurable absorption concepts of RF signals for RF semiconductor devices. In particular, the metal layer 114 is appropriately selected and furthermore the thickness of the metal layer 114 corresponds to the operating frequency range of the RF semiconductor device 100. The metal layer 114 can be deposited on the semiconductor device 102 using techniques such as sputtering deposition or vapor deposition (PVD), evaporation, electrochemical deposition (ECD), electroless deposition (ED), ALD, metal film lamination, etc. The new concept is low-cost and highly flexible, because the requirements of various RF semiconductor devices can be adapted by changing the thickness of the metal layer 114, thereby achieving the adjustment of the absorption characteristics. In particular, the thickness change required to adapt the absorption characteristics is in the nanometer or micrometer range, which does not actually affect the device size in the millimeter range, and does not require any additional steps or materials. This makes the concept particularly suitable for upcoming technologies and chip scaling with more and more functions integrated, because the absorption can be easily changed and adjusted, for example, to take into account the required operating frequency, the size or design of the RF semiconductor device, the routing of the RF lines within the RF semiconductor device, or the type of packaging used. The concept can be used for single-chip RF devices or multi-chip RF devices in which multiple semiconductor chips are arranged above each other in the semiconductor device or arranged laterally to each other in the semiconductor device. The metal layer 114 can extend completely over an area of ​​the second main surface of the semiconductor chip 102, or at least extend to a large part of the second main surface of the semiconductor chip 102. In other examples, the metal layer 114 can be arranged to extend only over a specific semiconductor chip area of ​​particular interest.

[0043] The new concept introduced in the present application is also very suitable for fan-out type packaging, in which the RF signal is located in the fan-out area and is significantly affected by interference from other RF signals, and the new concept will be described in the following description for examples. In these examples, the metal layer 114 can extend in the entire fan-out area or in most of the fan-out area or in part of the fan-out area.

[0044] In some examples, the thickness of semiconductor chip 102 can be within a quarter wavelength of the RF signal. This configuration provides the additional advantage that the RF signal reflected at second surface 106 will have a 180° phase shift relative to the RF signal originating from the RF chip circuitry and / or first surface 104, and will therefore disappear from destructive interference within semiconductor chip 102, and thereby further reduce interference among RF chip circuitry components.

[0045] In some examples, at least one antenna may be configured on second surface 106 of semiconductor chip 102 such that the at least one antenna is exposed and separated from metal layer 114 by a gap. Furthermore, metal layer 114 may reduce interference between the at least one antenna.

[0046] Figure 2 An example of an RF semiconductor device 200 is shown, which may include Figure 1 The metal layer 114 is the first metal layer of a plurality of metal layers 216 (e.g., a stack of metal layers 216), wherein each of the plurality of metal layers 216 includes a top surface 216a and a bottom surface 216b opposite to its respective top surface 216a. The plurality of metal layers 216 are arranged between the first surface 104 and the second surface 106 of the semiconductor chip 102, wherein the bottom surface 216b of each of the plurality of metal layers 216 faces the second surface 106. The thickness of each of the plurality of metal layers 216 is lower than the skin depth corresponding to the operating frequency range of the semiconductor device 200, wherein the thickness of each of the plurality of metal layers 216 is measured between its respective top surface 216a and bottom surface 216b. Therefore, each of the plurality of metal layers 216 provides the same characteristics and features as the above-described metal layer 114 to improve RF characteristics and reduce EMI. The material between each metal layer in the plurality of metal layers 216 may be a non-metal material or a dielectric material, such as a molding compound, silicon, or silicon dioxide.

[0047] Each metal layer in the plurality of metal layers 216 may be separated by a distance within a quarter wavelength of the operating frequency range or a distance outside a quarter wavelength of the operating frequency range. The quarter wavelength spacing between the plurality of metal layers 216 further improves the RF characteristics because the RF signal reflected at each metal layer in the plurality of metal layers 216 will have a 180° phase shift relative to the RF signal reflected at the adjacent metal layer in the plurality of metal layers 216, and thus the RF signal will disappear due to destructive interference. The RF semiconductor device 200 combines the absorption, transmission, and reflection properties of the plurality of metal layers 216.

[0048] In some examples, each metal layer in the plurality of metal layers 216 may be composed of the same metal or different metals. When the plurality of metal layers 216 are composed of different metals, RF signals of various frequencies may be absorbed.

[0049] Figure 3 An example of an RF semiconductor device 300 is shown, which may include Figure 1The RF semiconductor device 300 is a fan-out package including a fan-out region. For example, the fan-out package can be manufactured by an eWLB (embedded wafer level ball grid array) process or other fan-out wafer level packaging technology.

[0050] The RF semiconductor device 300 includes a molding compound 302. The molding compound 302 completely or at least partially covers the second surface 106 and completely or at least partially covers the sidewalls 108 of the semiconductor chip 102 and a first portion of the first side 112 of the redistribution layer 110 that is not covered by the semiconductor chip 102. The molding compound 302 includes an outer surface of the RF semiconductor device, wherein the outer surface has a top side 304 and a sidewall 308. The top side 304 faces the second surface 106 of the semiconductor chip 102 and the fan-out region and extends beyond the second surface 106 of the semiconductor chip 102 and the fan-out region, and the sidewalls 308 of the RF semiconductor device face the sidewalls 108 of the semiconductor chip 102. The molding compound 302 may be a low-loss molding compound having low-loss characteristics in the operating frequency range of the RF semiconductor device 300. At least the first region of the molding compound 302 may have a thickness in the range of 20 μm to 1000 μm, wherein the thickness of the first region is measured in a vertical direction between the top side 304 of the RF semiconductor device 300 and the first side 112 of the redistribution layer 110. In other words, at least the first region is located in the fan-out region of the RF semiconductor device 300.

[0051] The low loss characteristics of the molding compound 302 reduce the attenuation of the RF signal to be processed in the fan-out region of the RF semiconductor device 300, and make the fan-out region susceptible to interference by the RF signal. In order to improve the RF signal interference in such a case, a first metal layer 314 is provided on the top side 304 of the RF semiconductor device 300, wherein the first metal layer 314 faces the second surface 106 of the semiconductor chip 102 and the fan-out region and / or the sidewall 308 of the RF semiconductor device 300. The first metal layer 314 also faces the fan-out region and can absorb the RF signal in the fan-out region, and thus improves the channel-to-channel isolation in the fan-out region and other parts of the RF semiconductor device 300. In some examples, the first metal layer 314 can be directly provided and contact the top side 304 and / or the sidewall 308 of the RF semiconductor device 300. The first metal layer 314 has the same functions and features as the metal layer 114 of the RF semiconductor device 100.

[0052] In some examples, the thickness of at least the first region of mold compound 302 measured in the fan-out region may be within a quarter wavelength of an operating frequency of RF semiconductor device 300. RF signals reflected at top side 304 will have a 180° phase shift relative to RF signals reflected from second surface 106 of semiconductor chip 102 or from first side 112 of redistribution layer 110 and thus the RF signals will disappear from destructive interference within RF semiconductor device 300.

[0053] In some examples, the thickness of at least the first region of the molding compound 302 can be different than a quarter wavelength of the operating frequency range.

[0054] The molding compound 302 may be an epoxy resin, a filled epoxy resin, a glass fiber filled epoxy resin, a thermosetting polymer, a thermoplastic polymer, or an elastomeric polymer, but is not limited to the above examples.

[0055] Figure 4 An example of an RF semiconductor device 400 is shown, which may include Figure 2 The RF semiconductor device 200 and Figure 3 The first metal layer 314 is a metal layer in the plurality of metal layers 416, and the plurality of metal layers 416 have the same Figure 2 The plurality of metal layers 216 may have the same features, functions, and thicknesses. In one example, the plurality of metal layers 416 may be spaced apart by a quarter wavelength of the operating frequency, as described above with respect to the plurality of metal layers 216.

[0056] A plurality of metal layers 416 may be arranged on the top side 304 of the RF semiconductor device 400, wherein a bottom surface 414b of each metal layer in the plurality of metal layers 416 faces the second surface 106 of the semiconductor chip 102 and the fan-out region and extends beyond the second surface 106 of the semiconductor chip 102 and the fan-out region. The material between each metal layer in the plurality of metal layers 416 may be a non-metallic material or a dielectric material, such as a molding compound, silicon, or silicon dioxide. In some examples, each metal layer in the plurality of metal layers 416 may be composed of a different metal so that RF signals of various frequencies may be absorbed.

[0057] Figure 5 An example of an RF semiconductor device 500 is shown, which may include Figure 3 In addition to the first metal layer 314 extending over the top side 304 of the RF semiconductor device 500, the RF semiconductor device 500 also includes a second metal layer 514, which is similar to the metal layer 114 disposed over the second surface 106 of the semiconductor chip 102 described above. The second metal layer 514 has the same Figure 1The first metal layer 314 on the top side 304 of the RF semiconductor device 500 absorbs RF signals in the molding compound 302 and the fan-out region, while the second metal layer 514 on the second surface 106 of the semiconductor chip 102 absorbs RF signals within the semiconductor chip 102. The RF signal propagating in the RF semiconductor device 500 may be scattered between the first metal layer 314 and the second metal layer 514 and eventually disappear.

[0058] Figure 6 An example of an RF semiconductor device 600 is shown, which may include Figure 4 In addition to the plurality of metal layers 416, the RF semiconductor device 600 also includes a second metal layer 614, which is similar to the metal layer 114 disposed on the second surface 106 of the semiconductor chip 102. The second metal layer 614 has the same Figure 1 The metal layer 114 has the same functions and characteristics.

[0059] Figure 7 An example of an RF semiconductor device 700 is shown, which may include Figure 6 Some or all of the features of the RF semiconductor device 600. Figure 7 A second plurality of metal layers 716 is provided, which includes the second metal layer 514. The second plurality of metal layers 716 are arranged between the first surface 104 and the second surface 106 of the semiconductor chip 102. The second plurality of metal layers 716 have Figure 2 The multiple metal layers 216 have the same functions and characteristics.

[0060] Figure 8 An example of an RF semiconductor device 800 is shown, which may include Figure 3 Some or all of the features of the RF semiconductor device 300. Figure 8 , the first metal layer 314 is shown to include at least one recess 802. The at least one recess 802 may be a groove, a trench, a notch, or the like.

[0061] In some examples, the at least one recess 802 can be configured to accommodate an antenna 804 disposed on the top side 304 of the RF semiconductor device 800. The at least one antenna 804 can be configured to have the same horizontal height as the bottom surface 314b of the first metal layer 314. The at least one antenna 804 is separated from the first metal layer 314 in a lateral direction by a gap between the first metal layer 314 and the at least one antenna 804. The first metal layer 314 can absorb RF signals and thus can reduce and tune interference originating from the at least one antenna 804 or between a plurality of at least one antennas.

[0062] Fig. 8AAn example of an RF semiconductor device 800A is shown, which may include Figure 8 The RF semiconductor device 800A differs from the RF semiconductor device 800 in the location of the first metal layer 314 and the location of the at least one antenna 804. Fig. 8A , the first metal layer 314 and at least one antenna 804 are arranged on the second side 120 of the redistribution layer 110. The first metal layer 314 is arranged near the at least one antenna 804 in the fan-out region, wherein the first metal layer 314 can absorb RF signals and reduce interference originating from the at least one antenna 804 in the fan-out region.

[0063] In the RF semiconductor device described in the previous example, the heat sink may be mounted on the top side 304 of the RF semiconductor device 800. A thermal interface material may be arranged between the top side 304 of the RF semiconductor device and the heat sink. The thermal interface material may include, for example, a gap filler pad, a dispensable gap filler, a phase change material, and have a thermal conductivity in the range of 1 W / mK to 20 W / mK.

[0064] Fig. 9 An example of an RF semiconductor device 900 is shown. The RF semiconductor device 900 includes an RF semiconductor device 906, a printed circuit board 904, and a housing 902. The RF semiconductor device 906 is Figure 3 The RF semiconductor device 300. The RF semiconductor device 906 is mechanically and electrically coupled to the printed circuit board 904 via a plurality of first solder balls 122. The RF semiconductor device 906 is surrounded by a housing 902, wherein the first metal layer 314 is arranged on a wall of the housing 902 facing the top side 304 of the RF semiconductor device 900. The housing 902 may be a metal or plastic housing. For locations where the antenna beam will radiate out of the radome housing, the material needs to be selected in such a way that the housing 902 is transparent.

[0065] Fig.10 An example of an RF semiconductor device 1000 is shown, which may include Figure 1 The RF semiconductor device 1000 includes some or all features of the RF semiconductor device 1000. The RF semiconductor device 1000 includes a plurality of second solder balls 1002, wherein the plurality of second solder balls 1002 face the plurality of first solder balls 122. In the lateral direction, the plurality of second solder balls 1002 extend beyond the plurality of first solder balls 122. The plurality of second solder balls 1002 may include the same material and may have the same or different diameter and pitch as the plurality of first solder balls 122. A substrate 1004 is sandwiched between the plurality of first solder balls 122 and the plurality of second solder balls 1002. The substrate 1004 may be composed of a laminate or FR4 or bismaleimide triazine material, wherein the substrate 1004 may include vertical interconnects or horizontal interconnects.

[0066] The RF semiconductor device 1000 further includes a lid 1006, wherein the lid 1006 is a hollow structure having a main surface 1006a and side legs 1006b. The side legs 1006b are perpendicular to the main surface 1006a. The lid 1006 is mounted on the semiconductor chip 102 so that the main surface 1006a faces the second surface 106 having the metal layer 114 and extends beyond the second surface 106 having the metal layer 114. The side legs 1006b are mounted on the substrate 1004 and face the sidewalls 108 of the semiconductor chip 102. The side legs 1006b can be mounted to the substrate using an adhesive. A thermal interface material layer 1010 is arranged between the metal layer 114 and a portion of the main surface 1006a of the lid 1006 to provide mechanical stability and thermal stability between the semiconductor chip 102 and the lid 1006. The lid 1006 can be composed of a metal material or a non-metal material and provides electrical shielding, heat distribution, and thermal mechanical stability in the RF semiconductor device 1000. The metallic material and the non-metallic material may include a thermally conductive material.

[0067] The underfill material 1008 completely covers each of the plurality of first solder balls 122 and partially covers the sidewalls 108 of the semiconductor chip 102 and portions of the substrate 1004. A cavity 1016 is formed between the periphery of the underfill compound 1008, the substrate 1004, and the lid 1006. The underfill material 1008 is a thermosetting epoxy resin that reduces thermal stress generated due to mismatch in thermal expansion coefficients between the substrate 1004 and the semiconductor chip 102.

[0068] In some examples, molding compound 302 can be disposed in cavity 1016. Cover 1006 can be a flat cover including only major surface 1006a. An adhesive layer can be disposed between major surface 1006a of cover 1006 and molding compound 302 to increase adhesion between cover 1006 and molding compound 302.

[0069] In all of the above examples, a metal layer having a thickness below the skin depth at the operating frequency is provided to improve the RF characteristics, in particular the absorption characteristics.

[0070] Fig.11 The thickness dependence of transmission (T), reflection (R) and absorption (A) of a metal layer 114 including ruthenium (Ru) at a single operating frequency of 60 GHz is shown. Fig.11, the metal layer 114 means the Ru layer. The Ru layer was deposited on the molding compound 302 during the measurement, and the thickness of the molding compound was 0.87 mm. As shown on the x-axis, the thickness of the Ru layer varied from 2.5 nm to 30 nm, and as shown on the y-axis, the transmission (T), reflection (R), and absorption (A) of the metal layer 114 were measured. The skin depth of the Ru layer is 580 nm, corresponding to a bulk resistivity value of 8 μΩcm. As described herein, electrical properties are related to thickness in the nm range. For example, when the thickness of the Ru layer changes from 30 nm to 4 nm, the resistivity of the Ru layer increases from ~10 μΩcm to more than 40 μΩcm.

[0071] exist Fig.11 In the thickness range of the Ru layer in the Ru layer, when the thickness of the metal layer is comparable to or less than the mean free path of electrons in the metal layer, some parts of the RF signal are absorbed by the Ru layer 114 due to grain size effects, enhanced surface scattering, etc. At room temperature and under the condition of bulk resistivity, the mean free path of electrons in the Ru body is less than 10nm. Specifically, when the thickness is less than 10nm, the absorptivity of the Ru layer, which is about 1.7% of the skin depth of the Ru layer, is higher than the reflectivity. The absorptivity can exceed 50% and the reflectivity can be less than 20%. This situation is very suitable for improving RF characteristics and EMI because the absorptivity is high and the reflectivity is low. As the thickness of Ru increases beyond 10nm thickness, the skin depth effect is no longer effective and therefore the reflectivity is higher than the absorptivity and transmittance.

[0072] The following examples are related to other aspects of the present disclosure:

[0073] Example 1 discloses an RF semiconductor device for processing a radio frequency (RF) signal within an operating frequency range, comprising:

[0074] A semiconductor chip comprising a first surface, a second surface, a sidewall and an active chip area, wherein the first surface and the second surface extend in a lateral direction and the sidewall extends in a vertical direction,

[0075] A metal layer is located outside the active chip area, wherein the metal layer faces the second surface of the semiconductor chip, wherein a thickness of the metal layer is lower than a skin depth corresponding to an operating frequency range.

[0076] Example 2 discloses the RF semiconductor device according to Example 1, wherein the metal layer is disposed on the second surface of the semiconductor chip.

[0077] Example 3 discloses the RF semiconductor device according to Examples 1 and 2, wherein the thickness of the semiconductor chip is within a range of a quarter wavelength corresponding to an operating frequency range of the RF semiconductor device.

[0078] Example 4 discloses an RF semiconductor device according to Example 1 and Example 2, wherein the RF semiconductor device includes multiple metal layers, wherein the metal layer is the first metal layer among the multiple metal layers, wherein the multiple metal layers are arranged between a first surface and a second surface of a semiconductor chip, wherein the multiple metal layers are located outside an active chip area, and wherein a thickness of each of the multiple metal layers is lower than a skin depth corresponding to an operating frequency range of the semiconductor device.

[0079] Example 5 discloses an RF semiconductor device according to any of the preceding examples, wherein the semiconductor device further comprises a molding compound, wherein the molding compound covers at least a portion of the second surface and / or at least a portion of the sidewalls of the semiconductor chip.

[0080] Example 6 discloses an RF semiconductor device according to Example 5, wherein the RF semiconductor device includes a housing, wherein the metal layer is arranged between a wall of the housing and the second surface of the semiconductor chip.

[0081] Example 7 discloses an RF semiconductor device according to Example 5, wherein the metal layer is a first metal layer, wherein the first metal layer is disposed over a top side of the RF semiconductor device, facing the second surface of the semiconductor chip and / or a sidewall of the RF semiconductor device.

[0082] Example 8 discloses the RF semiconductor device according to Example 7, wherein a thickness of at least the first region of the molding compound is within a range of one quarter wavelength of an operating frequency of the RF semiconductor device.

[0083] Example 9 discloses an RF semiconductor device according to Example 7 or Example 8, wherein the first metal layer is a metal layer of a plurality of metal layers, wherein the plurality of metal layers are arranged between the second surface of the semiconductor chip and the top side of the RF semiconductor device, wherein the thickness of each of the plurality of metal layers is lower than a skin depth corresponding to an operating frequency range of the RF semiconductor device.

[0084] Example 10 discloses the RF semiconductor device according to Example 7, wherein the first metal layer includes at least one recess.

[0085] Example 11 discloses an RF semiconductor device according to Example 10, wherein the semiconductor device includes at least one antenna, wherein the at least one antenna is arranged in a recess of the metal layer, wherein the at least one antenna is separated from the metal layer by a gap.

[0086] Example 12 discloses the RF semiconductor device according to Example 11, wherein the first metal layer and the at least one antenna are arranged on the second side of the redistribution layer.

[0087] Example 13 discloses an RF semiconductor device according to Examples 7 to 9, wherein a second metal layer is disposed on a second surface of the semiconductor chip, wherein a thickness of the second metal layer is lower than a skin depth corresponding to an operating frequency range of the RF semiconductor device.

[0088] Example 14 discloses an RF semiconductor device according to Example 9, wherein the RF semiconductor device includes a second plurality of metal layers, wherein the second plurality of metal layers are arranged between the first surface and the second surface of the semiconductor chip, wherein the thickness of each of the plurality of metal layers is lower than a skin depth corresponding to an operating frequency range of the semiconductor device.

[0089] Example 15 discloses an RF semiconductor device according to Example 5, wherein the RF semiconductor device includes a housing, wherein the metal layer is arranged between a wall of the housing and the second surface of the semiconductor chip.

[0090] Example 16 discloses an RF semiconductor device according to any of the preceding examples, wherein the RF semiconductor device includes at least one of the following elements:

[0091] a plurality of first solder balls arranged between the first surface and the substrate and a plurality of second solder balls arranged between the plurality of first solder balls and the substrate,

[0092] an underfill compound completely covering the plurality of first solder balls, wherein the plurality of first solder balls are arranged between the first surface and the substrate and wherein the underfill compound partially covers a sidewall of the semiconductor chip; or

[0093] A cover is mounted on the second surface of the semiconductor chip, wherein the cover extends beyond the second surface of the semiconductor chip.

[0094] Example 17 discloses an RF semiconductor device according to any preceding example, wherein the thickness of the metal layer is in the range of 0.5 nm to 100 nm.

[0095] Example 18 discloses an RF semiconductor device according to any of the preceding examples, wherein the thickness of the metal layer is at most 50% of a skin depth corresponding to an operating frequency.

[0096] Example 19 discloses a method of manufacturing an RF semiconductor device for processing a radio frequency (RF) signal within an operating frequency range, comprising:

[0097] A semiconductor chip is provided, the semiconductor chip comprising a first surface, a second surface, a sidewall and an active chip area, the first surface and the second surface extending in a lateral direction and the sidewall extending in a vertical direction,

[0098] A metal layer is provided outside the active chip area, wherein the metal layer faces the second surface of the semiconductor chip, wherein a thickness of the metal layer is below a skin depth corresponding to an operating frequency range.

Claims

1. An RF semiconductor device (100) for processing a radio frequency (RF) signal within an operating frequency range, include: A semiconductor chip (102), the semiconductor chip (102) comprising a first surface (104), a second surface (106), a sidewall (108) and an active chip area, the first surface (104) and the second surface (106) extending in a lateral direction and the sidewall (108) extending in a vertical direction, A metal layer (114) is located outside the active chip area, wherein the metal layer (114) faces the second surface (106) of the semiconductor chip (102), wherein the thickness of the metal layer (114) is lower than a skin depth corresponding to the operating frequency range.

2. The RF semiconductor device (100) of claim 1, wherein the metal layer (114) is disposed on the second surface (106) of the semiconductor chip (102).

3. The RF semiconductor device (100) according to claim 1 and claim 2, wherein the thickness of the semiconductor chip (102) is within a range of a quarter wavelength corresponding to the operating frequency range of the RF semiconductor device (100).

4. The RF semiconductor device (200) according to claim 1 and claim 2, wherein the RF semiconductor device (400) comprises a plurality of metal layers (216), wherein the metal layer (114) is a first metal layer among the plurality of metal layers (216), wherein the plurality of metal layers (216) are arranged between the first surface (104) and the second surface (106) of the semiconductor chip (102), wherein the plurality of metal layers (216) are located outside the active chip area, wherein the thickness of each of the plurality of metal layers (216) is lower than a skin depth corresponding to the operating frequency range of the semiconductor device (200).

5. The RF semiconductor device (300) according to any of the preceding claims, wherein the semiconductor device (300) further comprises a molding compound (302), wherein the molding compound (302) covers at least a portion of the second surface (106) of the semiconductor chip (102) and / or at least a portion of the sidewall (108).

6. The RF semiconductor device (900) of claim 5, wherein the RF semiconductor device comprises a housing (902), wherein the metal layer (114) is arranged between a wall of the housing (902) and the second surface (106) of the semiconductor chip (102).

7. The RF semiconductor device (300, 500, 800) according to claim 5, wherein the metal layer (114) is a first metal layer (314), wherein the first metal layer (314) is arranged on the top side (304) of the RF semiconductor device (300, 500, 800), facing the second surface (106) of the semiconductor chip (102) and / or the side wall (308) of the RF semiconductor device (300, 500, 800).

8. The RF semiconductor device (300, 400, 500, 600, 700, 800) of claim 7, wherein a thickness of at least a first region of the molding compound (302) is within a range of a quarter wavelength of the operating frequency of the RF semiconductor device (300, 400, 500, 600, 700, 800).

9. The RF semiconductor device (400) according to claim 7 or claim 8, wherein the first metal layer (314) is a metal layer of a plurality of metal layers (416), wherein the plurality of metal layers (416) are arranged between the second surface (106) of the semiconductor chip (102) and the top side (304) of the RF semiconductor device (400), and wherein the thickness of each metal layer of the plurality of metal layers (416) is lower than the skin depth corresponding to the operating frequency range of the RF semiconductor device (400).

10. The RF semiconductor device (800) of claim 7, wherein the first metal layer (314) comprises at least one recess (802).

11. The RF semiconductor device (800) of claim 10, wherein the semiconductor device (1000) comprises at least one antenna (804), wherein the at least one antenna (804) is arranged in a recess (802) of the metal layer (114), wherein the at least one antenna (804) is separated from the metal layer (114) by a gap (806).

12. The RF semiconductor device (800A) of claim 11, wherein the first metal layer (314) and the at least one antenna are arranged on the second side (120) of the redistribution layer (110).

13. The RF semiconductor device (500, 600, 700) according to claim 7 to claim 9, wherein a second metal layer (514) is arranged on the second surface (106) of the semiconductor chip (102), wherein the thickness of the second metal layer (514) is lower than the skin depth corresponding to the operating frequency range of the RF semiconductor device (500, 600, 700).

14. The RF semiconductor device (700) according to claim 9, wherein the RF semiconductor device (700) comprises a second plurality of metal layers (716), wherein the second plurality of metal layers (716) are arranged between the first surface (104) and the second surface (106) of the semiconductor chip (102), wherein the thickness of each metal layer in the plurality of metal layers (716) is lower than the skin depth corresponding to the operating frequency range of the semiconductor device (700).

15. The RF semiconductor device according to any of the preceding claims, wherein the RF semiconductor device comprises a redistribution layer (110), wherein the redistribution layer (110) comprises a first side (112), wherein the first side (112) faces the first surface (104) of the semiconductor chip (102).

16. The RF semiconductor device of any one of the preceding claims, wherein a plurality of first solder balls (122) are arranged on a second side (120) of the redistribution layer (110) opposite to the first side (112).

17. The RF semiconductor device (1000) according to any one of the preceding claims, wherein the RF semiconductor device comprises at least one of the following elements: a plurality of first solder balls (122) arranged between the first surface (104) and the substrate (1004), and a plurality of second solder balls (1002) arranged between the plurality of first solder balls (122) and the substrate (1004), an underfill compound (1008) that completely covers the plurality of first solder balls (122), wherein the plurality of first solder balls (122) are arranged between the first surface (104) and the substrate (1004), and wherein the underfill compound (1008) partially covers the sidewall (108) of the semiconductor chip (102); or A cover (1006) is mounted on the second surface (106) of the semiconductor chip (102), wherein the cover (1006) extends beyond the second surface (106) of the semiconductor chip (102).

18. An RF semiconductor device according to any one of the preceding claims, wherein the thickness of the metal layer (114) is in the range of 0.5 nm to 100 nm.

19. An RF semiconductor device according to any one of the preceding claims, wherein the thickness of the metal layer (114) is at most 50% of the skin depth corresponding to the operating frequency.

20. A method of manufacturing an RF semiconductor device (100) for processing radio frequency (RF) signals within an operating frequency range, include: A semiconductor chip (102) is provided, the semiconductor chip (102) comprising a first surface (104), a second surface (106), a sidewall (108) and an active chip area, the first surface (104) and the second surface (106) extending in a lateral direction and the sidewall extending in a vertical direction, A metal layer (114) is provided outside the active chip area, wherein the metal layer (114) faces the second surface (106) of the semiconductor chip (102), wherein the thickness of the metal layer (114) is lower than a skin depth corresponding to the operating frequency range.

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