Patent Application
20150183131
The present invention relates generally to cutting or dicing of semiconductor wafers and, more particularly, to a saw blade for cutting semiconductor wafers.
Semiconductor dies or integrated circuits are fabricated on wafers of silicon, for example, by a thin film formation technique, photolithography, impurity implantation technique, and so forth. After the integrated circuits are formed, the wafer is diced to cut or separate the individual circuits by cutting the wafer in both transverse and longitudinal directions along scribe lines. Dicing of a semiconductor wafer is usually done using a mechanical saw with a rotary dicing blade that can slice through a wafer mounted on a chuck table. While often referred to as “sawing,” the process generally uses an abrading process in which a circular blade composed of abrasive materials embedded in a binder matrix rotates at high speeds to grind away the wafer material. The cutting region of a dicing blade commonly consists of diamond grit embedded in a thin aluminium matrix, although other suitable materials exist. Blade thicknesses can vary but typically are between 15 and 140 microns. During the cutting process, cracks can develop in the wafer.
One known method for reducing the incidence of cracks employs a two-step process, partially cutting the wafer with a diamond blade to form grooves and then cutting through the remaining part of the wafer with a smaller-width resin blade. However, a two-step process reduces throughput.
Another undesirable effect that can take place during the cutting process is chipping of the upper and lower surfaces of the wafer. Chipping can occur when silicon particles loosen from the wafer between the rotating blade and the wafer being cut. In fact, one of the main defects that impacts integrated circuit assembly yield is “top side” (or upper surface) chipping of the dies, which occurs during the sawing (or cutting) process.
The occurrence of chipping can be reduced by operating at reduced dicing blade rotational speeds but this has the disadvantage of reducing throughput. One known method for reducing chipping is to use a dicing blade having an inner layer containing a first set of dicing particles and an outer layer containing a second set of dicing particles overlying the inner layer. The second set of dicing particles has a mean particle size that is smaller than a mean particle size of the first set and the inner layer extends beyond the outer layer to the outermost periphery of the blade. However, this blade design is not a practical solution for comparatively thick wafers with comparatively narrow scribe lines.
Thus, it would be advantageous to be able to cut or dice semiconductor wafers without chipping or cracking the dies and without reducing throughput.
The invention, together with objects and advantages thereof, may best be understood by reference to the following description of preferred embodiments together with the accompanying drawings in which:
The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practised. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the invention. In the drawings, like numerals are used to indicate like elements throughout. Furthermore, terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that module, circuit, device components, structures and method steps that comprises a list of elements or steps does not include only those elements but may include other elements or steps not expressly listed or inherent to such module, circuit, device components or steps. An element or step proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements or steps that comprises the element or step.
In one embodiment, the present invention provides a dicing blade having a blade edge comprising a first set of dicing particles and a stepped protuberance extending beyond the blade edge and comprising a second set of dicing particles having a mean particle size that is larger than a mean particle size of the first set of dicing particles.
In another embodiment, the present invention provides a dicing blade comprising two disks each having inner faces that are bonded together, each disk having an annular recess formed in its inner face. The annular recesses contain a first layer of dicing particles that extend a first distance beyond the periphery of the disk, and a second layer of dicing particles overlaying the first layer and extending a second distance beyond the periphery of the disk, where the second distance is greater than the first distance. A mean size of the dicing particles of the second layer is larger than a mean size of the dicing particles of the first layer.
In yet another embodiment, the present invention provides a method of manufacturing a dicing blade, comprising: (a) forming an annular recess in an inner face of a disk, (b) forming a first layer of dicing particles in the recess, (c) forming a second layer of dicing particles over the first layer and over a peripheral region of the disk, where a mean size of the dicing particles forming the second layer is large than a mean size of the dicing particles forming the first layer, (d) removing a part of the disk that includes the peripheral region of the disk to expose part of the first and second layers, and (e) bonding together the inner faces of the two disks formed in accordance with steps (a) to (d).
Referring now to
In one embodiment, the protuberance 103 is rectangular in profile and is stepped, which provides a sharp, step decrease in blade thickness. In an alternative embodiment, the transition between the thicknesses is provided by a bevelled edge. The corners of the protuberance 103 are rounded, and the length of the protuberance 103 is comparable with a desired total cut depth into a silicon wafer work piece 104 to be diced. In one example, the length of the protuberance 103 is two thirds of the silicon wafer work piece thickness plus 23 per cent of the thickness of adhesive dicing tape 105 to which the silicon wafer work piece 104 may be affixed. The thickness of the protuberance 103 is dictated by the width of a scribe line (not shown) in the silicon wafer work piece 104 and also by the wafer thickness for a step cut. A wider scribe width and a thicker wafer will dictate a greater thickness of the protuberance 103. A comparatively thick protuberance 103 can result in good stability during cutting. For example, for a 60 micron scribe line width, the thickness of the protuberance 103 is in a range 15-20 microns. Other widths of the protuberance 103 are possible, however.
In one embodiment, the widths of shoulders 106, 107 of the blade edge 102 located on either side of the protuberance 103 are equal. In one example, the width of the shoulders 106, 107 is 25 per cent of the thickness of the protuberance 103. The thickness of the blade 100 is, to some extent, dictated by scribe line width and work piece 104 thickness. In one example, the length of the blade edge 102 (that is from the point at which the blade edge 102 extends from the hub 101 to the step change in thickness at the start of the protuberance 103) is one third of the silicon wafer work piece 104 thickness.
With reference now to
Referring now to
Advantageously, with the ability to remove blemishes and topside chipping, the saw process speed may be faster compared with known arrangements thereby resulting in high throughput. Furthermore, the blade 100 may achieve the same outcome as a two-step process (i.e., cut then polish) but using just a single blade in a single cutting operation, thereby achieving improved throughput. Advantageously, the step change in blade thickness permits, in one operation, the cutting and the upper surface polishing of comparatively thick wafers having comparatively narrow scribe lines.
A method of manufacturing a dicing blade will now be described with reference to
Each hub half 400 then undergoes an electro-forming process in which nickel including fine dicing particles is electro-formed into the recess 401 to form a first layer 501 (see
In a next step (see
In a next step, (see
In a next step, (see
The description of the preferred embodiments of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or to limit the invention to the forms disclosed. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment disclosed, but covers modifications within the spirit and scope of the present invention as defined by the appended claims.
