Semiconductor chip with linear expansion coefficients in direction parallel to sides of hexagonal semiconductor substrate and manufacturing method

#The present invention relates to a semiconductor chip, a semiconductor wafer, and a semiconductor chip manufacturing method. More particularly, the present invention relates to a semiconductor chip, a semiconductor wafer, and a semiconductor chip manufacturing method that use a hexagonal semiconductor having anisotropic mechanical properties in a direction parallel to a principal surface, such as silicon carbide or gallium nitride.

#In semiconductor devices, there has conventionally been used a silicon (Si) substrate. In recent years, wide-band gap semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) are attracting attention in the field of power semiconductor devices, and are being developed.

#Wide-band gap semiconductors are semiconductor materials with a high degree of hardness that are wider in band gap than Si. Research is conducted to put into practical use various semiconductor devices that make use of the physical properties of wide-band gap semiconductors, such as power elements, environmentally-resistant elements, high-temperature operating elements, and high-frequency elements. Application of the wide-band gap semiconductors to power elements, in particular, such as switching elements and rectifier elements, is attracting attention, because the power elements that use SiC or GaN have advantages including a significant reduction in power loss as compared to that of Si power elements.

#FIGS. 1(a) and 1(b) are plan views each illustrating a semiconductor wafer according to an embodiment of the present invention.

#FIGS. 2(a) and 2(b) are schematic plan views illustrating marks and directions of the semiconductor wafers of FIG. 1(a) and FIG. 1(b), respectively.

#FIG. 3 is a diagram illustrating a <11-20> direction and a <1-100> direction in a hexagonal semiconductor.

#In order to assess the reliability of an SiC device, the inventors of the present invention manufactured a 3.6 mm-square power semiconductor device 1010 having a MISFET structure by using, as a semiconductor wafer 1001, a 4H—SiC wafer whose principal surface is off-cut by approximately 4° from a (0001) plane toward a <11-20> direction as illustrated in FIG. 18(a). The symbol “-” attached in front of a numerical value of the Miller index herein represents a bar of the numerical value that follows. For example, the third index of the <11-20> orientation represents “2 bar”. The surface of the power semiconductor device is partially covered with a protective film which uses SiN. The semiconductor wafer 1001 was cut along scribe lines 1020x and 1020y to be broken into semiconductor chips each including the power semiconductor device 1010. The semiconductor chips were then assembled into packages under package assembly conditions A, B, and C which ensures a satisfactory reliability for MISFET structure power semiconductor elements made from Si. The packaged devices were tested by a temperature cycle test which is a common reliability assessment test and in which temperature is repeatedly raised and dropped between −65° C. and 150° C. For comparison, power semiconductor devices were similarly manufactured from Si, assembled into packages, and subjected to the temperature cycle test.

#The package assembly here includes steps of electrically connecting and fixing the semiconductor chip to a metal lead frame with solder or the like, forming an aluminum wire or the like between the lead frame and the semiconductor chip, and sealing the semiconductor chip with an epoxy-based resin material. In general, a polyimide-based material called junction coating resin (JCR) is applied before the power semiconductor element is sealed with resin in some cases.

#Herein, a component part that has a desired function as a device such as a MISFET or a diode is referred to as a power semiconductor element, whereas a component part that includes a power semiconductor element, a perimeter portion formed around the power semiconductor element, and a protective film that covers, at least partially, the power semiconductor element and the perimeter portion is referred to as a power semiconductor device. Pieces of a semiconductor wafer with a plurality of power semiconductor devices formed thereon which are obtained by dividing the semiconductor wafer along scribe lines are referred to as semiconductor chips. The semiconductor chips each include a semiconductor substrate which is a broken piece of the wafer. A structure in which a semiconductor chip is housed in a package is referred to as a semiconductor device.