Patent Description:
Electronic probe cards are widely used by semiconductor manufacturers to characterize thousands of chips or dies at the wafer level. Commercially available electronic probe cards typically include vertical metallic needles that are designed to make contact with the dies at specific locations to supply input electrical signals to the devices under test on the dies and then probe out the output signals.

With the introduction of complementary metal oxide (CMOS) sensors, light emitting diodes (LEDs), optical detectors, and other miniaturized optical devices, optoelectronic probe cards have been developed to characterize and test the functionally and the performance of these devices on the wafer level. For example, optoelectronic probe cards have been used to test photodiodes on the wafer level, in which the light beam is injected vertically via a fiber coil and at the same time the electronic probe senses the output electrical signal from the photodiode under test. The same technique has also been used to characterize an array of LEDS using an array of lenses and an array of optical waveguides. On-wafer micro-mirrors have also been characterized by injecting and receiving the optical light vertically.

In addition, on-wafer measurements of devices (e.g., optical circuits and planar light-wave circuits (PLCs)) that include optical components requiring light to propagate parallel to the wafer have been performed utilizing testing equipment that injects the light horizontally in-plane. However, such optical testing devices that access the wafer from a side of the wafer with horizontal light coupling cannot be easily integrated into traditional electronic probe cards. Document <CIT> discloses an apparatus for testing integrated circuit dies of a wafer, wherein separate, additional mirror structures are fabricated into the wafer for each die under test, and wherein the test head provides optical test signals in an out-of-plane direction towards the scribe mirrors. Document <CIT> discloses an optical source on a probe substrate that also provides an optical signal in an out-of-plane direction towards the DUT.

Various aspects of the disclosure provide an integrated optical probe card and a system for performing wafer testing of optical micro-electro-mechanical systems (MEMS) structures with an in-plane optical axis. On-wafer optical screening of optical MEMS structures may be performed utilizing one or more micro-optical bench components to redirect light between an out-of-plane direction that is perpendicular to the in-plane optical axis to an in-plane direction that is parallel to the in-plane optical axis to enable testing of the optical MEMS structures with vertical injection of the light. Such a configuration enables the optical probe card to be assembled on one or more electronic needles of an electronic probe card.

The micro-optical bench component(s) is integrated with the optical probe card. As embodiment not encompassed by the claims but for illustration purpose only, the micro-optical bench component(s) may be fabricated on the wafer containing the optical MEMS structures. For example, the micro-optical bench component(s) may be fabricated in the dicing streets of the wafer.

The present invention is directed to an integrated optical probe card for batch testing optical MEMS structures as defined by the appended claims <NUM> to <NUM>. The integrated optical probe card includes a source configured to generate an input beam and to provide the input beam towards an optical MEMS structure, where optical MEMS structure includes an in-plane optical axis and the input beam propagates in an out-of-plane direction perpendicular to the in-plane optical axis. The integrated optical probe card further includes a detector optically coupled to receive an output beam from the optical MEMS structure, where the output beam propagates in the out-of-plane direction. The integrated optical probe card further includes a micro-optical bench component optically coupled to redirect the input beam and the output beam between the out-of-plane direction and an in-plane direction that includes the in-plane optical axis of the optical MEMS structure.

It is also disclosed as embodiment not encompassed by the claims but for illustration purpose only, a wafer including a plurality of dies under test, each including a respective one of a plurality of optical MEMS structures that includes an in-plane optical axis. The wafer further includes a plurality of micro-prisms fabricated within a plurality of dicing streets between the plurality of dies under test. Each of the micro-prisms includes at least one of a first surface or a second surface. The first surface may be configured to receive an input beam from an optical probe card propagating in an out-of-plane direction perpendicular to the in-plane optical axis and to redirect the input beam from the out-of-plane direction to an in-plane direction including the in-plane optical axis towards the optical probe card. The second surface may be configured to receive an output beam from the optical MEMS structure propagating in the in-plane direction and to redirect the output beam from the in-plane direction to the out-of-plane direction towards the optical probe card.

The present invention is also directed to a system for performing wafer testing, as defined by the appended claim <NUM>. The system includes a wafer including a plurality of dies under test, each including a respective one of a plurality of optical MEMS structures having an in-plane optical axis. The system further includes an optical probe card as described above.

<FIG> illustrates an example of an optical micro-electro-mechanical systems (MEMS) structure <NUM> that may be fabricated on a wafer. The optical MEMS structure <NUM> shown in <FIG> may be, for example, an interferometer fabricated in a semiconductor substrate <NUM> of the wafer. The semiconductor substrate <NUM> may be, for example, a silicon-on-insulator (SOI) wafer that includes a device layer <NUM>, a handle layer <NUM>, and a buried oxide (BOX) layer <NUM> sandwiched between the device layer <NUM> and the handle layer <NUM>. Various components of the MEMS interferometer, such as mirrors <NUM> and <NUM>, a MEMS actuator <NUM>, and other optical components may be defined using a single lithographic step and etched in the device layer <NUM> using a highly anisotropic process until the etch stop (BOX) layer <NUM> is reached. Any moveable parts, such as a moveable mirror <NUM> and the MEMS actuator <NUM> may be released by selectively removing the BOX layer <NUM> underneath the moveable parts.

<FIG> illustrates an example of a system <NUM> including a wafer <NUM> and an optical probe card <NUM>, according to some aspects of the disclosure. The wafer <NUM> includes a plurality of die <NUM>, each having a respective optical MEMS structures <NUM> fabricated thereon. The optical MEMS structures <NUM> may be similar to the MEMS interferometer shown in <FIG> or may be any other type of optical MEMS device having an in-plane optical axis. As used herein, the term "in-plane" refers to a propagation direction of light that is parallel to the wafer <NUM>.

As can be seen in <FIG>, the wafer <NUM> includes the semiconductor substrate <NUM> comprised of the device layer <NUM>, handle layer <NUM>, and BOX layer <NUM>. The optical MEMS structures <NUM> are defined in the device layer <NUM> and are separated from one another by respective dicing streets <NUM> in the wafer <NUM>. The dicing streets <NUM> define the area between the dies <NUM> through which the wafer <NUM> may be sliced to divide the wafer <NUM> into the respective dies <NUM>.

In various aspects of the disclosure, one or more micro-optical bench components <NUM> may also be fabricated in the device layer <NUM> within each of the plurality of dicing streets <NUM> on the wafer <NUM>. In the example shown in <FIG>, the micro-optical bench components <NUM> include micro-prisms with forty-five degree inclined surfaces. However, it should be understood that the micro-optical bench components <NUM> may include other or additional components. Examples of micro-optical bench components <NUM> include, but are not limited to, micro-prisms, micro-mirrors, micro-lenses, and/or micro-beam splitters.

The micro-optical bench components <NUM> may be fabricated, for example, from the silicon material in the device layer <NUM>, and may be metallized or coated with another reflective material on the forty-five degree inclined surfaces to improve the optical coupling. The micro-optical bench components <NUM> are designed for testing (DFT) using wafer level testing via the optical probe card <NUM>. Since the micro-optical bench components <NUM> are fabricated in the dicing streets <NUM>, the die area on the wafer <NUM> may be maximized. Thus, after the on-wafer testing, the dies <NUM> may be diced, thereby removing the micro-optical bench components <NUM>.

The optical probe <NUM> includes a source <NUM> (light source), a detector <NUM> and at least one optical fiber <NUM> (two of which are illustrated in <FIG>). The source <NUM> may include a broadband light source or narrow-band light source. For example, the source <NUM> may include one or more wideband thermal radiation sources or a quantum source with an array of light emitting devices that cover a wavelength of interest. The detector <NUM> may include, for example, a detector array or a single pixel detector. The optical fibers <NUM> may include, for example, single core fibers, dual core fibers, or fiber bundles.

The source <NUM> is configured to generate an input beam of light and to direct the input beam via an input optical fiber <NUM> towards an input micro-optical bench component <NUM> on the wafer <NUM> located adjacent to an input of an optical MEMS structure <NUM> on a die <NUM> under test. As shown in <FIG>, the input fiber <NUM> directs the input beam to propagate in an out-of-plane direction with respect to a plane of the wafer <NUM>. As used herein, the term "out-of-plane" refers to a propagation direction of light that is perpendicular to the wafer <NUM>. Since the optical MEMS structure <NUM> under test has an in-plane optical axis that is perpendicular to the out-of-plane propagation direction of the input beam from the input optical fiber <NUM>, the input micro-optical bench component <NUM> is configured to redirect the input beam from the out-of-plane direction to an in-plane direction that is parallel to the wafer <NUM> and that includes the in-plane optical axis of the optical MEMS structure <NUM> under test. The input micro-optical bench component <NUM> may then direct the input beam to the optical MEMS structure <NUM> under test for propagation inside the optical MEMS structure <NUM>. The input beam may propagate in-plane inside the optical MEMS structure <NUM> utilizing free space propagation or waveguide/guided propagation.

In the example shown in <FIG>, another micro-optical bench component <NUM> is located adjacent to an output of the optical MEMS structure <NUM> under test to receive an output beam propagating parallel to the wafer <NUM> (e.g., in an in-plane direction). The output micro-optical bench component <NUM> is configured to redirect the output beam from the in-plane direction to the out-of-plane direction towards an output optical fiber <NUM>. The output optical fiber <NUM> then directs the output beam towards the detector <NUM>. Thus, each of the micro-optical bench components <NUM> is optically coupled to redirect the input beam and the output beam between the out-of-plane direction and the in-plane direction that includes the in-plane optical axis of the optical MEMS structure <NUM> to facilitate in-plane (horizontal) wafer level testing of dies <NUM>.

<FIG> is a diagram illustrating another example of a testing system <NUM> in which the micro-optical bench components <NUM> are fabricated on the wafer <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, the backside of the wafer <NUM> is etched in the dicing streets <NUM> to enable backside testing of the dies <NUM> by the optical probe card <NUM>. In addition, the micro-optical bench components (micro-prisms) <NUM> are not metallized, thus facilitating the use of total internal reflection at the forty-five degree inclined interfaces of the micro-prisms to redirect the input and output beams between the out-of-plane direction and the in-plane direction.

<FIG> is a diagram illustrating another example of a testing system in which the micro-optical bench components <NUM> are fabricated on the wafer <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, the optical probe card <NUM> includes only a single optical port used for both transmitting and receiving the optical input/output beams. In this example, the optical probe card <NUM> includes a single optical fiber <NUM> optically coupled to a directional coupler <NUM> that directs the input beam from the source <NUM> to the optical fiber <NUM>, which may then direct the input beam <NUM> towards a micro-optical bench component <NUM> associated with a die <NUM> under test. The directional coupler <NUM> further directs the reflection signal (output beam) received by the optical fiber <NUM> from the micro-optical bench component <NUM> towards the detector <NUM>. In some examples, the source <NUM> and coupler <NUM> may each be wideband, thus enabling wave front division couplers and/or free space couplers or beam splitters to be utilized as the directional coupler <NUM>.

Thus, with this configuration, only a single micro-optical bench component (micro-prism) <NUM> may need to be fabricated in each of the dicing streets <NUM>. The single input/output port, single core optical fiber <NUM>, and directional coupler <NUM> configuration of the optical probe card <NUM> may also be utilized in embodiments in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, such as any of the embodiments shown in <FIG>.

<FIG> is a diagram illustrating another example of a testing system <NUM> in which the micro-optical bench components <NUM> are fabricated on the wafer <NUM>, according to some aspects of the disclosure. As in the example shown in <FIG>, the optical probe card <NUM> includes a single input/output port, along with a single optical fiber <NUM>. However, in the example shown in <FIG>, the optical fiber <NUM> may be a dual core fiber or a fiber bundle. The dual core fiber <NUM> may include two adjacent fiber cores, one that serves as the input and is optically coupled to the source <NUM> and one that serves as the output and is optically coupled to the detector <NUM>. The fiber bundle <NUM> may include multiple adjacent cores, some of which serve as the input and are optically coupled to the source, and others that serve as the output and are optically coupled to the detector <NUM>. Thus, the dual core optical fiber or fiber bundle <NUM> may include separate input and output fiber ports, each connected to the source <NUM> and detector <NUM>, respectively. The dual core/fiber bundle configuration of the optical fiber <NUM> of the optical probe card <NUM> may also be utilized in embodiments in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, such as any of the embodiments shown in <FIG>.

<FIG> is a diagram illustrating an example of a testing system <NUM> in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, according to some aspects of the disclosure. The optical probe card <NUM> includes two optical fibers <NUM>, each cleaved with a respective cleaving angle of forty-five degrees, thereby employing total internal reflection from the forty-five degree cleaved glass interface to redirect the input and output beams between the out-of-plane direction and the in-plane direction. Thus, the micro-optical bench components <NUM> are formed at the cleaved glass interface of the optical fibers <NUM>.

In an exemplary operation, the source <NUM> may generate an input beam and direct the input beam via the input optical fiber <NUM> towards the cleaved glass interface <NUM> of the input optical fiber <NUM> positioned adjacent to an input of an optical MEMS structure <NUM> under test. The cleaved glass interface of the input optical fiber <NUM> functions as the input micro-optical bench component <NUM> that is optically coupled to redirect the input beam from the out-of-plane direction to the in-plane direction towards the input of the optical MEMS structure <NUM> under test. The cleaved glass interface of the output optical fiber <NUM> positioned adjacent to an output of the optical MEMS structure <NUM> under test functions as the output micro-optical bench component <NUM> to receive the output beam propagating in the in-plane direction and to redirect the output beam from the in-plane direction to the out-of-plane direction towards the detector <NUM>.

<FIG> is a diagram illustrating another example of a testing system in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, the cleaved surfaces of the input and output optical fibers <NUM> are coated with a respective reflective coating <NUM> (e.g., a dielectric or metallic coating). Thus, instead of using total internal reflection, the coated surfaces <NUM> of each of the cleaved optical fibers <NUM> function as the micro-optical bench components <NUM> to redirect the input and output beam between the out-of-plane direction and the in-plane direction.

<FIG> is a diagram illustrating another example of a testing system <NUM> in which the micro-optical bench components are integrated on the optical probe card <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, each of the input and output optical fibers <NUM> includes a respective integrated grin lens <NUM> to enhance the coupling efficiency of the input and output beams to and from the optical MEMS structure <NUM> under test by reducing diffraction loss.

<FIG> is a diagram illustrating another example of a testing system <NUM> in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, the micro-optical bench components <NUM> include micro-prisms <NUM>, each having a forty-five degree angled surface <NUM> that is metallized or coated with another reflective material. Each of the micro-prisms <NUM> is mounted on the body of the optical probe card <NUM> and aligned with the input/output optical fibers <NUM>.

In an exemplary operation, the source <NUM> may generate an input beam and direct the input beam via the input optical fiber <NUM> towards an input micro-prism <NUM> positioned adjacent to an input of an optical MEMS structure <NUM> under test. The input micro-prism <NUM> is optically coupled to redirect the input beam from the out-of-plane direction to the in-plane direction towards the input of the optical MEMS structure <NUM> under test. An output micro-prism <NUM> positioned adjacent to an output of the optical MEMS structure <NUM> under test is optically coupled to receive the output beam propagating in the in-plane direction and to redirect the output beam from the in-plane direction to the out-of-plane direction towards the output optical fiber <NUM> and detector <NUM>.

<FIG> is a diagram illustrating another example of a testing system <NUM> including micro-optical bench components <NUM> integrated on the optical probe card <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, the micro-optical bench components <NUM> include micro-prisms <NUM>, each having a metallized curved surface <NUM>. In some examples, the curved surfaces <NUM> may be designed to enhance the optical coupling efficiency of the optical probe card <NUM> by focusing the input beam into the optical MEMS structure <NUM> under test and focusing the output beam towards the output optical fiber <NUM>.

<FIG> is a diagram illustrating another example of a testing system <NUM> in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, each of the input and output optical fibers <NUM> are lensed fibers including respective lenses <NUM>. The integrated lenses <NUM> on the optical fibers <NUM> may be, for example, cylinder lenses, ball lenses, or grin lenses. In some examples, the lensed optical fibers <NUM> may be designed to enhance the optical coupling efficiency of the optical probe card <NUM> by focusing the input beam into the optical MEMS structure <NUM> under test via the input micro-prism <NUM> and focusing the output beam received from the output micro-prism <NUM> towards the detector <NUM>.

<FIG> is a diagram illustrating another example of a testing system <NUM> in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, the micro-optical bench components <NUM> include micro-prisms <NUM>, each having a forty-five degree angled surface <NUM> that is not metallized to enable each of the micro-prisms to utilize total internal reflection within the micro-prisms <NUM> to redirect the input and output beams between the out-of-plane direction and the in-plane direction. Each of the micro-prisms <NUM> is mounted on the body of the optical probe card <NUM> and aligned with the input/output optical fibers <NUM>.

<FIG> is a diagram illustrating another example of a testing system <NUM> in which the micro-optical bench components <NUM> are integrated on the optical probe card <NUM>, according to some aspects of the disclosure. In the example shown in <FIG>, the micro-optical bench components <NUM> include micro-prisms <NUM> fabricated with curved surfaces <NUM> that facilitate total internal reflection to enhance the optical coupling efficiency of the optical probe card by focusing the input beam into the optical MEMS structure <NUM> under test and focusing the output beam toward the output optical fiber <NUM>.

<FIG> is a diagram illustrating a perspective view of a portion of an integrated optical probe card <NUM>, according to some aspects of the disclosure. In particular, <FIG> illustrates a body <NUM> of the integrated optical probe card <NUM> including two adjacent optical metallized micro-prisms 900a and 900b fabricated therein, each having an inclination of forty-five degrees to redirect the input beam and the output beam between the out-of-plane direction and the in-plane direction. The integrated optical probe card <NUM> further includes two half-cylinders (grooves) 1400a and 1400b configured to receive input and output optical fibers, respectively (e.g., the input and output optical fibers may be inserted into the grooves 1400a and 1400b). The input and output optical fibers may then be connected to the source and detector, respectively, which may, in some examples, be integrated directly into the two grooves 1400a and 1400b. The integrated optical probe card <NUM> further includes at least one cross alignment mark <NUM>, which may be used to align the integrated optical probe card <NUM> when the integrated optical probe card is assembled on another device, such as an electronic probe card.

<FIG> is a diagram illustrating an example of an electronic probe card <NUM> including the integrated optical probe card <NUM>, according to some aspects of the disclosure. The electronic probe card includes a plurality of electronic needles <NUM> for contacting the dies under test at specific locations to supply input electrical signals and then probe out the output signals. The integrated optical probe card <NUM> may be attached to the body of the electronic probe card <NUM> at any place on the electronic probe card <NUM> and via any attachment mechanism. In the example shown in <FIG>, the integrated optical probe card <NUM> is integrated with the electronic probe card <NUM> on the electronic needles <NUM>. For example, the integrated optical probe card <NUM> may be assembled on one of the electronic needles <NUM> or on several of the electronic needles <NUM> (as shown in <FIG>) to provide additional support for the optical probe card <NUM>.

<FIG> is a flow chart illustrating an exemplary process <NUM> for on-wafer testing of optical MEMS structures with in-plane optical axes. The process begins at block <NUM>, where an input beam is generated by a source. At block <NUM>, the input beam may be directed towards an optical MEMS structure under test in an out-of-plane direction perpendicular to the in-plane optical axis of the optical MEMS structure under test.

At block <NUM>, the input beam may be redirected from the out-of-plane direction to an in-plane direction that includes the in-plane optical axis. For example, one or more micro-optical bench components may redirect the input beam to the in-plane direction for input to the optical MEMS structure under test. At block <NUM>, an output beam may be received from the optical MEMS structure under test in the in-plane direction. At block <NUM>, the output beam may be redirected from the in-plane direction to the out-of-plane direction towards a detector.

Additional elements, components, steps, and/or functions may also be added. The apparatus, devices, and/or components illustrated in <FIG> may be configured to perform the method, features, or steps described herein.

It is to be understood that the specific order or hierarchy of steps in the method disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the method may be rearranged. The process described herein presents elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.

Claim 1:
An integrated optical probe card for batch testing optical MEMS structures, comprising:
a source (<NUM>) configured to generate an input beam and to provide the input beam towards an optical MEMS structure (<NUM>), wherein the optical MEMS structure (<NUM>) comprises an in-plane optical axis;
a detector (<NUM>) optically coupled to receive an output beam from the optical MEMS structure (<NUM>);
characterized in that it further comprises a micro-optical bench component (<NUM>) integrated on the integrated optical probe card (<NUM>) and optically coupled to receive the input beam propagating from the source (<NUM>) and to redirect the input beam from an out-of-plane direction perpendicular to the in-plane optical axis to an in-plane direction comprising the in-plane optical axis of the optical MEMS structure (<NUM>) to inject the input beam into the optical MEMS structure (<NUM>) in the in-plane direction, wherein the micro-optical bench component (<NUM>) is further optically coupled to receive the output beam propagating in the in-plane direction from the optical MEMS structure (<NUM>) and to redirect the output beam from the in-plane direction to the out-of-plane direction for propagating towards the detector (<NUM>).