A through-wafer electrical signal communication apparatus and method utilize a semiconductor substrate having first and surfaces and a continuous peripheral edge. The first surface supports active integrated circuit components. An electromagnetic waveguide supports data communication through the semiconductor substrate. The waveguide has an electrically conductive waveguide boundary structure surrounding a waveguide interior region formed by a portion of the semiconductor substrate. The waveguide is sized and configured to propagate electromagnetic waves of selected wavelength and propagation mode from a first waveguide end to a second waveguide end. A signal launching structure radiates electromagnetic waves into the first waveguide end. A signal pickup structure receives electromagnetic waves from the second waveguide end. The apparatus and method may utilize one or more of the waveguides. The waveguides may include a real waveguide, one or more virtual waveguide formed using light energy, and/or a hybrid waveguide comprising real and virtual waveguide structures.

BACKGROUND

The present disclosure relates to semiconductor devices. More particularly, the disclosure concerns through-wafer data communication.

2. Description of the Prior Art

By way of background, semiconductor through-wafer signal communication has been proposed using optical and electrical signal carrying techniques. Applications include through-wafer communication of data signals, clock signals or other information. The optical technique passes signal information through the wafer using modulated light. A disadvantage of this approach is that optical signal processing is required to modulate and demodulate the optical carrier. The electrical technique communicates signal information electrically using metal vias extending through the wafer. A disadvantage of this approach is that the semiconductor wafer can be disturbed or damaged by such structures.

SUMMARY

A through-wafer electrical signal communication apparatus and method utilize a semiconductor substrate having a first surface, a second surface and a continuous peripheral edge. The first surface is an active device surface supporting active integrated circuit components and the second surface is a back surface. An electromagnetic waveguide supports electrical signal communication through the semiconductor substrate between the first and second surfaces. The waveguide has an electrically conductive waveguide boundary structure surrounding a waveguide interior region formed by a portion of the semiconductor substrate. The waveguide is sized and configured to propagate electromagnetic waves of selected wavelength and propagation mode from a first waveguide end to a second waveguide end. A signal launching structure is configured to radiate electromagnetic waves into the first waveguide end. A signal pickup structure is configured to receive electromagnetic waves from the second waveguide end. The apparatus and method may utilize one or more of the waveguides. The waveguides may include a real waveguide formed using an electrically conductive material, one or more virtual waveguides formed using light energy, and/or a hybrid waveguide comprising real and virtual waveguide structures.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Introduction

Turning now to the Drawings, which are not necessarily to scale,FIG. 1illustrates a semiconductor substrate4that may be used to construct an apparatus supporting through-wafer electrical signal communication. The semiconductor substrate4may be a wafer or a die that has been cut from a wafer. It has a first surface6and an opposing second surface8that together define the substrate's thickness dimension. A continuous peripheral edge10defines a perimeter of the semiconductor substrate4. The first surface6is an active device surface that supports active integrated circuit components12. The second surface8is a back surface that may or may not include active components. The semiconductor substrate4may be formed from any suitable semiconductor material of a type that is conventionally used for integrated circuit devices, including but not limited to silicon, germanium, gallium-arsenide and other semiconductor materials. The semiconductor substrate4may be fabricated for use in many different kinds of apparatus, including but not limited to CPUs (Central Processing Units), information processing devices, memory devices, communication devices, and other device types that can process, store, generate, consume, use, communicate and/or otherwise manipulate information (including data and/or instructions). According to example embodiments described in more detail below, some or all of the information manipulated by the active integrated circuit components of the semiconductor substrate4may be communicated from one surface (6or8) of the semiconductor substrate4to the other. Such information may include digital information, analog information, or both. When such information is communicated through the semiconductor substrate4, it may be referred to generically as signal information.

Turning now toFIG. 2, the ability to communicate electrical signal information through the semiconductor substrate4may be provided by an electromagnetic waveguide20. As used herein, electrical signal communication refers to communication using sub-light frequency electromagnetic energy. As will be described in the context of example embodiments hereinafter, the waveguide20may extend through the semiconductor substrate4between the first surface6and the second surface8, e.g., along the axis representing the substrate's thickness dimension. The waveguide20includes an electrically conductive waveguide boundary structure22that surrounds a waveguide interior region24comprising all or a portion of the semiconductor substrate4.

The waveguide20is sized and configured to propagate electromagnetic waves of selected wavelength and propagation mode from a first waveguide end26to a second waveguide end28, with the waveguide interior region including the bulk material of the semiconductor substrate4.FIG. 3Aillustrates an embodiment in which the waveguide20is of circular cross-section.FIG. 3Billustrates an embodiment in which the waveguide20is of rectangular cross-section. Other shapes could potentially also be used. As is known in the art, increasing a waveguide's cross-sectional area allows longer wavelengths to be propagated, and visa versa. It is contemplated that the waveguide20may be readily designed to handle signals as low as several GHz into the THz range, which is suitable for high-speed digital devices. It will be appreciated that losses through the waveguide20(both conductor and dielectric) may need to be accounted for, but should be tolerable insofar as the distance through the semiconductor substrate4will usually be small due to the substrate's low thickness.

A signal launching structure30is configured to radiate electromagnetic energy into the first waveguide end26. A signal pickup structure32is configured to receive electromagnetic energy from the second waveguide end28. The structures30and32may be provided by conventional antenna launch and pickup stubs, respectively. It should be noted thatFIG. 2illustrates a configuration wherein the first waveguide end26and the signal launching structure30are situated at the active device surface6of the semiconductor substrate4, and the second waveguide end28and the signal pickup structure32are situated at the back surface8. This is for purposes of example only and it is to be understood that a reverse configuration may also be used.

First Example Embodiment

Turning now toFIG. 4, an apparatus40with through-wafer electrical signal communication capability is shown. The apparatus40is constructed from the semiconductor substrate4ofFIG. 1and further includes the waveguide20ofFIG. 2embodied as a real waveguide20A. The real waveguide20A includes a real waveguide boundary structure22A formed by an electrically conductive material that surrounds the semiconductor peripheral edge10. For example, the electrically conductive material may comprise an electrically conductive (e.g., metal) sleeve in which the semiconductor substrate4is situated. The conductive sleeve may either short the substrate peripheral edge10or an insulation layer could be added to electrically isolate the semiconductor substrate4from the conductive sleeve. Alternatively, the electrically conductive material may comprise an electrically conductive (e.g., metallization) coating applied to the substrate peripheral edge10, or to an insulation layer surrounding the peripheral edge if electrical isolation is desired. The remaining components of the real waveguide20A are as described above in connection withFIG. 2, as shown by the use of corresponding reference numbers appended with the letter “A.” Thus, the real waveguide20A includes a waveguide interior region24A, a first waveguide end26A and a second waveguide end28A. In addition, the apparatus40includes a signal launching structure30A and a signal pickup structure32A.

A desired signal propagation mode of the waveguide20A (e.g., TE, TM, hybrid modes, etc.) can be excited in the usual manner employing the launching structure30A. The signal information is extracted at the pickup structure32A following transmission through the waveguide. The electromagnetic signal carried by the waveguide20A will be of a frequency greater than the waveguide's cutoff frequency. The waveguide's cutoff frequency will be a function of the material set and the waveguide geometry, all of which may be selected using known waveguide design principles. It will be appreciated that the geometry of the real waveguide20A will be dictated by the shape and cross-sectional area of the semiconductor substrate4, and consequently the waveguide size may be somewhat large. However, the wavelength cutoff may be suitable for propagating a clock signal. For example, the real waveguide20A, which encompasses the entire bulk phase of the semiconductor substrate4, may be used for clock distribution with minimal clock skew across the whole active device surface6. In addition, higher frequency harmonics may also be propagated for data communication. Thus, the real waveguide20A may be used for communicating a clock signal or a data signal. It could also be operated in a multiplexed mode (e.g., WDM) to carry one or more data and/or clock signals. The length of the waveguide20A may be controlled by lapping the semiconductor substrate4to control its thickness.

Although not shown, through-wafer communication of digital information (as opposed to analog information) may be handled by using an digital-analog converter to convert the information to analog form upstream of the launching structure30A. An analog-digital converter may then be placed downstream of the pickup structure32A to convert the information back to digital form.

Second Example Embodiment

Turning now toFIGS. 5-7, another apparatus50with through-wafer electrical signal communication capability is shown. The apparatus50is constructed from the semiconductor substrate4ofFIG. 1and further includes the waveguide20ofFIG. 2embodied as a virtual waveguide20B. The virtual waveguide20B includes a virtual waveguide boundary structure22B surrounding a virtual waveguide interior region24B. The virtual waveguide boundary structure22B is formed by an electrically conductive region of the semiconductor substrate4. This region comprises free semiconductor charge carriers that have been excited into a conduction band by incident light52emitted by a light source54(seeFIG. 7). The incident light52changes the index of refraction within the electrically conductive region of the semiconductor substrate4(relative to the electromagnetic signal being propagated). This produces a dielectric waveguide whose wave containment properties are determined by the index of diffraction differential and whose effective size for purposes of determining the waveguide cutoff frequency can be determined by mode field diameter analysis. For such waveguides, the index of refraction behavior is given by is given by Snell's Law;
n1sin θ1=n2sin θ2,
where n1is the index of refraction corresponding to the waveguide core (interior region24B), and n2is the index of refraction corresponding to the waveguide ‘cladding’ phase (boundary structure22B). In a preferred embodiment, n1>n2. Based on typical values for the index of refraction delta between excited free carriers (in usual concentrations) in bulk silicon and bulk silicon without free carrier excitation, the critical angle (of incidence) to achieve total internal signal reflection in the virtual waveguide20B would be greater than approximately 40 degrees.

The incident light52may be emitted by the light source54onto either the active device surface6or the back surface8of the semiconductor substrate4in a selected pattern at a selected wavelength. In the embodiment ofFIGS. 5-7, the light source54is on the back surface8because this area is not normally covered with active components. If desired, however, the light source54could be placed on the active device surface6.

The incident light52emitted by the light source54may be collimated and can be shaped to define a desired waveguide configuration (e.g., cylindrical, rectangular) by placing a shaping pattern56(seeFIGS. 6 and 7) between the light source54and the semiconductor substrate4. The shaping pattern56includes an inner mask56A that blocks an interior portion of the incident light52. Only a portion52A of the incident light that strikes the semiconductor substrate outside inner mask56A creates the virtual waveguide boundary structure22B. To help control the virtual waveguide boundary structure thickness, an optional second mask56B may also be used. It will be seen inFIG. 6that the inner mask56A is circular in shape and that the outer mask56B is annular in shape. This produces the illustrated cylindrical geometry of the virtual waveguide30B. It will be appreciated that other mask shapes may be used to provide other virtual waveguide geometries.

The frequency of the incident light52required to excite the free-carriers of the semiconductor material into the conduction band may be of a specific monochromatic or near monochromatic wavelength (coherent or non-coherent) corresponding to the absorption band of the free-carriers in the semiconductor substrate4. This will depend on the semiconductor material and its doping characteristics. The light should be non-reactive to the substrate material in the region of the virtual waveguide boundary structure22B. The light transmission characteristics of semiconductor materials are well known. By way of example, it is known that light wavelengths between 1100-1300 nm (infrared light) are non-reactive to silicon semiconductor material and even low power levels will excite free carriers of doped silicon substrate material into the conduction band. Note that the substrate material is considered to be doped because CMOS and other integrated circuit devices are typically fabricated from p-type or n-type silicon (or other semiconductor material) such that the semiconductor substrate material will normally be intrinsically doped. It is therefore contemplated that the incident light52will excite free-carrier dopants in the semiconductor substrate4as opposed to producing phonon-assisted excitation of the bulk semiconductor phase.

One or more infrared light emitting diodes or other light emitting device(s) producing infrared light in the desired wavelength range may be used as the light source54, depending on the desired optical power level. The light source54may be fabricated in any desired manner. In some cases, fiber optic elements or other light alignment structures may be used to collimate the incident light52. To determine the optical power requirements, the light absorption coefficient for the free-carrier dopants in the semiconductor substrate material may be calculated using the Drude equation:
α=(kfc)n,pλ2ρn,p,
where kfcis absorption coefficient for the specific free carriers (fc) under consideration, n and p represent the n-type and p-type silicon, λ is wavelength and ρ is the free carrier density.

If desired, the apparatus50may be maintained at a controlled reduced temperature to stabilize the conduction band free-carriers in the bulk material of the semiconductor substrate4. This technique can be used to provide a desired index of refraction differential between the electrically conductive region of the waveguide boundary structure22B and adjacent portions of the semiconductor substrate that are not excited by the incident light52. Reducing the substrate temperature also increases the light transmission characteristics of the semiconductor substrate4for a given wavelength of the incident light52. Increasing the doping level of the semiconductor substrate material will increase conductivity.

The light source54may have a substantially constant optical output under operating conditions and may be turned-off when the waveguide20B is not required. Thus, the incident light requires no modulation. The pattern of conduction band free-carriers formed in the semiconductor substrate4by the incident light52constitutes the virtual waveguide boundary structure22B. The non-illuminated semiconductor material inside the virtual waveguide boundary structure represents the virtual waveguide interior region24B. The virtual waveguide20B can be excited into a desired propagation mode (e.g., TE, TM, hybrid modes, etc.) of an electromagnetic signal of frequency greater than the waveguide's cutoff frequency. Again, the waveguide's cutoff frequency will be a function of the material set and the waveguide geometry, as may be determined using known waveguide design principles. Excitation of the desired propagation mode may be performed in the usual manner.

The remaining components of the virtual waveguide20B are as described above in connection withFIG. 2, as shown by the use of corresponding reference numbers appended with the letter “B.” Thus, in addition to the waveguide boundary structure22B and the waveguide interior region24B, the virtual waveguide20B includes a first waveguide end26B and a second waveguide end28B. In addition, the apparatus50includes a signal launching structure30B and a signal pickup structure32B.

It will be appreciated that more than one of the virtual waveguides20B could be formed on the semiconductor substrate4. This would provide plural through-wafer signal pathways that could be used, for example, to provide plural data pathways or to provide multiple clock regions for distributed clocking with minimal clock skew across the active device surface6. Each virtual waveguide20B could have its own light source54. Alternatively, a single instance of the light source54could be used for all of the virtual waveguides. Other light source/waveguide combinations could also be used.

Third Example Embodiment

Turning now toFIG. 8, another apparatus60with through-wafer electrical signal communication capability is shown. The apparatus60is constructed from the semiconductor substrate4ofFIG. 1and further includes a virtual coaxial waveguide20C designed for TEM mode signal propagation. The virtual coaxial waveguide20C may be formed using the same technique used to make the virtual waveguide20B ofFIGS. 5-7. In this embodiment, a shaping pattern (not shown) patterns the incident light (not shown) to form an inner virtual propagation medium22C-1disposed within an outer virtual waveguide structure22C-2. A separation region24C of selected size lies between these two electrically conductive structures.

The remaining components of the virtual coaxial waveguide20C are as described above in connection withFIG. 2, as shown by the use of corresponding reference numbers appended with the letter “C.” Thus, in addition to the inner waveguide propagation medium22C-1and the outer waveguide boundary structure22C-2, the virtual coaxial waveguide20C includes a first waveguide end26C and a second waveguide end28C. In addition, the apparatus60includes a signal launching structure30C and a signal pickup structure32C.

Fourth Example Embodiment

Turning now toFIG. 9, another apparatus70with through-wafer electrical signal communication capability is shown. The apparatus70is constructed from the semiconductor substrate4ofFIG. 1and further includes a hybrid virtual/real coaxial waveguide20D designed for TEM mode signal propagation. The hybrid coaxial waveguide20D includes an inner virtual waveguide propagation medium22D-1disposed within an outer real waveguide structure22D-2. The inner virtual waveguide propagation medium22D-1may be formed using the same technique used to make the virtual waveguide20B ofFIGS. 5-7. The outer real waveguide boundary structure22D-2may be formed using the same technique used to make the real waveguide20A ofFIG. 4. A separation region24D lies between these two electrically conductive structures.

The remaining components of the hybrid coaxial waveguide20D are as described above in connection withFIG. 2, as shown by the use of corresponding reference numbers appended with the letter “D.” Thus, in addition to the inner waveguide propagation medium22D-1and the outer waveguide boundary structure22D-2, the hybrid coaxial waveguide20D includes a first waveguide end26D and a second waveguide end28D. In addition, the apparatus70includes a signal launching structure30D and a signal pickup structure32D.

Accordingly, a semiconductor through-wafer electrical signal-carrying apparatus and method have been disclosed. While various embodiments have been described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the invention. It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.