LED alignment points for semiconductor die

Post-manufacturing analysis of a semiconductor device is enhanced via a method and system that use a light emitting diode (LED) formed in a semiconductor die during its manufacture. According to an example embodiment of the present invention, a LED is formed within a semiconductor die having a circuit side opposite a back side. A conductor is formed that extends from the LED to the back side of the die, and is coupled to a terminal formed on the back side. The LED is activated via the terminal and used to align the die for analysis. By forming a LED within the semiconductor die during its manufacture, post manufacturing analysis is enhanced by the alignment capabilities provided by the readily activated LED.

FIELD OF THE INVENTION
 The present invention relates generally to semiconductor devices and their
 fabrication and, more particularly, to semiconductor devices and their
 manufacture involving techniques for aligning an integrated circuit for
 analysis.
 BACKGROUND OF THE INVENTION
 The semiconductor industry has recently experienced technological advances
 that have permitted dramatic increases in circuit density and complexity,
 and equally dramatic decreases in power consumption and package sizes.
 Present semiconductor technology now permits single-chip microprocessors
 with many millions of transistors, operating at speeds of hundreds of
 millions of instructions per second to be packaged in relatively small,
 air-cooled semiconductor device packages. A by-product of such
 high-density and high functionality in semiconductor devices has been the
 demand for increased numbers of external electrical connections to be
 present on the exterior of the die and on the exterior of the
 semiconductor packages which receive the die, for connecting the packaged
 device to external systems, such as a printed circuit board.
 As the manufacturing processes for semiconductor devices and integrated
 circuits increase in difficulty, methods for testing and debugging these
 devices become increasingly important. Not only is it important to ensure
 that individual chips are functional, it is also important to ensure that
 batches of chips perform consistently. In addition, the ability to detect
 a defective manufacturing process early is helpful for reducing the number
 of defective devices manufactured.
 Traditionally, integrated circuit dies have been tested using methods
 including accessing circuitry or devices within the die. In order to
 access portions of circuitry in the integrated circuit die it is sometimes
 necessary to align the die with equipment such as a milling device, a test
 fixture, or other test equipment. For example, in flip-chip type dies,
 transistors and other circuitry are located in a very thin
 epitaxially-grown silicon layer in a circuit side of the die. The circuit
 side of the die is arranged facedown on a package substrate. This
 orientation provides many operational advantages. However, due to the
 face-down orientation of the circuit side of the die, the transistors and
 other circuitry near the circuit side are not readily accessible for
 testing, modification, or other purposes. Therefore, access to the
 transistors and circuitry near the circuit side is from the back side of
 the chip. Such back side access often requires milling through the back
 side and probing certain circuit elements. The milling and probing
 processes may potentially damage elements in the integrated circuit if not
 properly aligned. The difficulty, cost, and destructive aspects of
 existing methods for testing integrated circuits are impediments to the
 growth and improvement of semiconductor technologies. To access the
 backside circuitry, it is necessary to align the circuit with a CAD
 layout. This is done with alignment markers; however, alignment markers
 are not visible through silicon from the backside with most tools without
 substantial thinning.
 SUMMARY OF THE INVENTION
 The present invention is directed to a method for manufacturing and
 analyzing a semiconductor die that improves the ability to align the die
 for post-manufacturing testing. The present invention is exemplified in a
 number of implementations and applications, some of which are summarized
 below.
 According to an example embodiment of the present invention, a
 semiconductor die having a light-emitting diode (LED) is formed. The
 semiconductor die has a circuit side opposite a back side. A terminal is
 formed in the back side, and a conductor is formed extending from the
 terminal and toward the circuit side. A LED is formed within the
 semiconductor die and coupled to the conductor. The LED is activated via
 the terminal and used for aligning the die for analysis. The activated LED
 provides a detectable reference point from which to align the die for
 analysis, such as for milling or testing defective dies.
 According to another example embodiment of the present invention, a system
 is arranged to analyze a semiconductor die having a LED formed within the
 die and a conductor coupled to the LED and extending to a terminal on the
 surface of the die. A power source is coupled to the terminal to activate
 the LED via the conductor. A radiation detection device is arranged to
 detect radiation emitted from the activated LED. Using the detected
 radiation, the die is aligned in a test fixture. The system further
 includes test equipment arranged to analyze the die once it has been
 aligned.
 The above summary of the present invention is not intended to describe each
 illustrated embodiment or every implementation of the present invention.
 The figures and detailed description which follow more particularly
 exemplify these embodiments.

While the invention is amenable to various modifications and alternative
 forms, specifics thereof have been shown by way of example in the drawings
 and will be described in detail. It should be understood, however, that
 the intention is not necessarily to limit the invention to the particular
 embodiments described. On the contrary, the intention is to cover all
 modifications, equivalents, and alternatives falling within the spirit and
 scope of the invention as defined by the appended claims.
 DETAILED DESCRIPTION
 The present invention is believed to be applicable to a variety of
 different types of semiconductor devices, and the invention has been found
 to be particularly suited for flip-chips and other types of integrated
 circuit dies requiring or benefiting from alignment for post-manufacturing
 analysis. While the present invention is not necessarily limited to such
 devices, various aspects of the invention may be appreciated through a
 discussion of various examples using this context.
 According to an example embodiment of the present invention, a
 semiconductor die is manufactured with a LED formed within the die. The
 LED is connected to a terminal via a conductor. When a power supply is
 connected to the terminal, the LED is powered and emits radiation. The
 radiation can be detected and used to align the die. For example, the
 position of the LED can be pre-determined on a circuit layout. By
 detecting the radiation, the location of the LED is found. Using the
 location of the LED as a reference point, the die can be aligned with a
 circuit layout and other circuitry or devices within the die can be
 determined. Identifying the location of circuitry or devices within the
 die is useful for post-manufacturing analysis, such as aligning for
 milling the device, forming probes and making contact to a portion of
 circuitry within the device, or aligning for exciting portions of the
 device for analysis.
 One example manner in which to create the LED is by forming a p-n junction
 using a III-V compound such as Gallium-arsenide. In an essential reversion
 of the creation of electron-hole pairs, energy is released when an
 electron recombines with a hole. More specifically, when an electron drops
 into a hole in the p-n junction, a photon of energy is generated. Using
 the Gallium-arsenide diode, the photon radiation generated during
 recombination is detectable for alignment. Another way is to forward bias
 a Si p-n junction.
 According to a more particular example embodiment of the present invention,
 FIGS. 1-4 show a portion 100 of a semiconductor die being fabricated. In
 FIG. 1, back side substrate 110 has been formed and a terminal 115 is
 formed in the substrate 110 at the surface 111. Once the terminal 115 is
 formed, additional substrate is formed to complete the back side and a
 conductor 220 is formed in the back side, coupled to the terminal 115, and
 extending away from the back side surface 111 of the die. Trench isolation
 340 and LED 330 are formed, and the conductor 220 is coupled to the LED
 330. In FIG. 4, the circuit side 450 is formed to complete the fabrication
 of the portion of die.
 The LED in the die of FIGS. 1-4 can be activated via a power source coupled
 to the terminal. FIG. 5 shows a system 500 for powering an LED formed in a
 semiconductor die, such as in FIGS. 1-4, and using the LED for alignment
 purposes, according to another example embodiment of the present
 invention. The die 510 is arranged in a test fixture 560. A power source
 540 is coupled to LED 525 within the die via a terminal 515 on the back
 side of the die and a conductor 520. Radiation 530 is emitted from the LED
 in response to the power source 540 and is detected at radiation detection
 device 550. A camera or a microscope capable of detecting IR or visible
 light can be used to detect the radiation 530. Using the detected
 radiation, the position of the LED is determined and the die is aligned
 for analysis. In another implementation, a computer arrangement 570 is
 coupled to the detection device 550 and arranged to use the detected
 radiation to align the die.
 According to another example embodiment of the present invention, LEDs are
 formed in more than one location in a semiconductor die. The LEDs are
 powered and used for alignment. By using more than one LED, alignment of
 the die can be achieved in a more accurate manner than with a single LED.
 For example, FIG. 6 shows an overview 600 of a semiconductor die 610. Four
 terminals 615, 616, 617, and 618 are located in the comer regions of the
 die 610. Each terminal is connected via a conductor to LEDs 625, 626, 627,
 and 628, respectively. When the terminals are coupled to a power source
 and the LEDs are activated, the radiation from the LEDs can be detected
 and used to align the die 610.
 While the present invention has been described with reference to several
 particular example embodiments, those skilled in the art will recognize
 that many changes may be made thereto without departing from the spirit
 and scope of the present invention, which is set forth in the following
 claims.