Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, and various signal processing circuits.
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual images for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The structure of semiconductor material allows the material's electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed operations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support, electrical interconnect, and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly, can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
One approach to achieving smaller semiconductor devices is the wafer level chip scale package (WLCSP). A conventional semiconductor wafer typically contains a plurality of semiconductor die separated by a saw street. An interconnect structure can be formed over the surface of the semiconductor wafer. The semiconductor wafer is processed by applying polymers, such as polyimide (PI) or polybenzoxazole (PBO), and redistribution layers to the wafer prior to singulation into WLCSP. PI has a typical curing temperature of 380 degrees Celsius (° C.) and PBO has a typical curing temperature of 300° C. PI and PBO are unsuitable for using in manufacturing processes with temperature tolerances lower than, for example, 300° C. After singulation of the semiconductor wafer into WLCSP, the bare silicon of the semiconductor die is exposed on the remaining sidewalls and back side. The fragile nature of exposed silicon in WLCSP devices is a concern in surface mount technology (SMT) assembly processes. The semiconductor die is subject to damage or degradation if a portion of the semiconductor die is exposed to external elements, particularly when surface mounting the die. For example, the semiconductor die can be damaged or degraded during handling or by exposure to light. Damage to the exposed silicon remains a problem for WLCSP and for advanced node products with fragile dielectric layers. Semiconductor die are also subject to damage during singulation of semiconductor wafers through the silicon or semiconductor material and into individual WLCSP. Singulation through semiconductor material can cause cracking or chipping of the semiconductor die. Testing of singulated WLCSP involves high cost and long testing time due to the handling of individual packages.
An important aspect of semiconductor manufacturing is high yield and corresponding low cost. The yield of a WLCSP process is limited by the nature of processing an incoming semiconductor wafer, which typically contains a number of semiconductor die having defects. In a WLCSP process, the defective semiconductor die are processed together with the functional semiconductor die on the semiconductor wafer. After processing and singulation into WLCSP, the WLCSP containing defective semiconductor die are discarded. Thus, the number of functional semiconductor die on the incoming semiconductor wafer limits the achievable yield from a WLCSP process. For example, an incoming wafer with 15% defective semiconductor die results in a maximum yield of 85% of functional WLCSP. Thus, the wafer-level processing of WLCSP inherently includes waste in processing defective semiconductor die, which increases the unit cost of manufacturing WLCSPs.
Semiconductor wafers are fabricated having various diameters and semiconductor die sizes and quantities. Semiconductor packaging equipment is typically developed according to each particular incoming semiconductor wafer size or semiconductor die quantity or size. For example, a 200 millimeter (mm) wafer is processed using 200 mm equipment, and a 300 mm wafer is processed using 300 mm equipment. Equipment for packaging semiconductor devices is limited in processing capability to the specific semiconductor wafer size or semiconductor die quantity and size for which the equipment is designed. As incoming semiconductor wafer sizes and semiconductor die sizes change, additional investment in manufacturing equipment is necessary. For example, smaller semiconductor die typically also have smaller, more advanced nodes. WLCSP processes are limited in the size of semiconductor die and node technology that can be processed into a WLCSP. In particular, advanced node semiconductor die may fall outside the design limits of WLCSP. When the design limits of WLCSP are exceeded, the design is conventionally changed over to a different package type, such as leadframe-based or substrate-based package types. A change to the fundamental design of the package may have a substantial impact on device footprint, form factor, and performance characteristics. Significant re-design of a package, such as changing to a different package type, also increases overall cost of manufacturing the semiconductor device. Investment in equipment for a specific size of semiconductor die, size of semiconductor wafer, or quantity of semiconductor die creates capital investment risk for semiconductor device manufacturers. As incoming semiconductor wafer sizes change, wafer-specific equipment becomes obsolete. Similarly, carriers and equipment designed for specific sizes and quantities of semiconductor die can become obsolete, because the carriers are limited in capability to handle different sizes and quantities of semiconductor die. Constant development and implementation of different equipment to accommodate changing wafer and die sizes increases the cost of manufacturing semiconductor devices.