BACKGROUND

The present invention relates, in general, to removing contaminants More specifically, the present invention relates to a method and apparatus for removing contaminants from a semiconductor object through sublimable particles

Semiconductor encapsulation molds are typically used to encapsulate semiconductor packages This is typically accomplished by transfer molding thermosetting plastic compositions to form the semiconductor packages In addition to traditional epoxy resins, new resin compositions, named 'green compounds', have been introduced as alternatives The green compounds are chosen over the traditional resins, as they do not contain halogens and are eco- fnendly In comparison to the traditional resins, the green compounds are stickier, and cause sticking to the mold surface and staining of packages so formed This leads to the formation of stresses in the internal parts of the molded packages during ejection from the mold surface This, in turn, reduces the strength of the molded package This eventually gives rise to quality and reliability issues, such as chip crack, micro crack, moisture seepage, etc In order to achieve higher molding quality, the encapsulation molds are required to be cleaned frequently to get rid of the oxidized release agents and any other contaminants Moreover, the frequency of cleaning required for the green compound is more than thrice that for the traditional resins

Various techniques, such as scraping, media blasting, melamine cleaning, rubber cleaning, plasma cleaning, laser cleaning and chemical cleaning, have been employed for removing contaminants from a base surface of a mold However, each of these techniques suffers from one or more disadvantages Some of these techniques are not very delicate and can often cause damage to the base surface In other cases, thin flashes and burrs are left on the base surface, thereby creating defects in the mold In certain techniques, the mold has to be taken out from a machine on which the mold was mounted, and has to be disassembled and cleaned part-by-part Removing and remounting the mold back onto the machine take a lot of time and fine tuning, thereby leading to wastage of time Some of these techniques involve spillage of media particles that needs to be removed properly from various parts of the mold, so that the mold can be assembled precisely Any leftover particle may cause inaccurate assembling of the parts, thereby damaging the mold when put to use Most of these techniques produce a huge amount of waste products that are not eco-friendly Disposal of these waste products is another hassle. Some of these techniques include an outgassing process, which produces fumes that pollute semiconductor materials being used for molding and a clean work environment.

In light of the foregoing discussion, there is a need for a method and apparatus for removing contaminants from a semiconductor object that does not damage the semiconductor object, can be performed inline, reduces the time required to clean, and reduces ecologically unfriendly waste.

SUMMARY

An object of the present invention is to provide a method and apparatus for removing contaminants from at least one portion of a semiconductor object.

Another object of the present invention is to provide a method and apparatus for removing contaminants from at least one portion of a semiconductor object that does not damage the semiconductor object.

Yet another object of the present invention is to provide a method and apparatus for removing contaminants from at least one portion of a semiconductor object that can be performed inline, thereby reducing the time required to clean.

Still another object of the present invention is to provide a method and apparatus for removing contaminants from at least one portion of a semiconductor object that reduces ecologically unfriendly waste.

Embodiments of the present invention provide a method and apparatus for removing contaminants from at least one portion of a semiconductor object. The apparatus includes a nozzle positioned at a preset position with respect to the portion of the semiconductor object, and a blasting unit for blasting solid particles of a material that sublimes instantaneously at a predefined temperature and/or pressure over the portion, through the nozzle. On impact, the particles sublime instantaneously, transforming into a gas, and remove the contaminants from the portion of the semiconductor object.

In accordance with an embodiment of the present invention, the apparatus includes a blasting-unit regulator for controlling at least one of: the size and/or shape of the particles, a flow rate at which the particles are blasted, and a material-to-carrier ratio of the amount of the material to the amount of a carrier.

In an embodiment of the present invention, the apparatus includes a nozzle-control unit. The nozzle-control unit is used to set a position and/or movement of the nozzle. The nozzle- control unit controls the movement of the nozzle in an automated manner. The nozzle-control unit positions the nozzle at the preset position in an automated manner.

In an embodiment of the present invention, the apparatus also includes a cleaning enclosure within which the particles are blasted over the portion, to avoid spillage of contaminants removed from the portion through blasting and to contain the level of noise generated during blasting.

In an embodiment of the present invention, the apparatus further includes a vacuum hose connected with a vacuum pump. The vacuum hose sucks contaminants removed from the portion through blasting, to dispose the contaminants without any spillage. In addition, the vacuum so created vents out the gas formed after sublimation.

In accordance with an embodiment of the present invention, the semiconductor object is a semiconductor manufacturing unit, and the method is performed inline with the semiconductor manufacturing unit. This, in turn, reduces the time required to clean. A semiconductor manufacturing unit may, for example, be an assemblage of machinery parts used to manufacture semiconductor devices. In accordance with another embodiment of the present invention, the semiconductor object is a semiconductor device. The semiconductor device may, for example, be in a bare, assembled or encapsulated form.

On impact, the particles transfer their kinetic energy to the contaminants, thereby knocking the contaminants off the portion of the semiconductor object. In addition, instantaneous sublimation of these particles produces a micro-thermal shock, thereby cracking and delaminating the contaminants. Moreover, the sudden increase in the volume of the particles from the solid phase to the gaseous phase produces a micro explosion, which knocks the contaminants off the portion of the semiconductor object. The complete process of removal of contaminants occurs at a micro level, and does not damage the semiconductor object.

As the particles sublime instantaneously, no waste products are produced. In addition, the contaminants are sucked through the vacuum hose, which avoids any spillage. This reduces ecologically unfriendly waste. BRIEF DESCRIPTION OF THE DRAWINGS

FIG 1 is a flow diagram illustrating a method for removing contaminants from at least one portion of a semiconductor object, in accordance with an embodiment of the present invention,

FIG 2 is a flow diagram illustrating a method for removing contaminants from at least one portion of a semiconductor object, in accordance with another embodiment of the present invention,

FIG 3 is a schematic diagram illustrating a portion of an apparatus for removing contaminants from at least one portion of a semiconductor object, in accordance with an embodiment of the present invention,

FIG 4 is a perspective view of the apparatus, in accordance with an embodiment of the present invention,

FIG 5 is a perspective view of a portion of the apparatus, in accordance with an embodiment of the present invention,

FIG 6a is a cross-sectional view illustrating a position of a nozzle with respect to the portion of the semiconductor object, in accordance with an embodiment of the present invention,

FIG 6b is a cross-sectional view illustrating another position of the nozzle with respect to the portion of the semiconductor object, in accordance with an embodiment of the present invention, and

FIG 7 is a top view illustrating the movement of the nozzle across the semiconductor object, in accordance with an embodiment of the present invention

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a method and apparatus for removing contaminants from at least one portion of a semiconductor object In the description herein for embodiments of the present invention, numerous specific details are provided, such as examples of components and/or mechanisms, to provide a thorough understanding of embodiments of the present invention One skilled in the relevant art will recognize, however, that an embodiment of the present invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not specifically shown or described in detail to avoid obscuring aspects of the embodiments of the present invention.

A nozzle is positioned at a preset position with respect to the portion of the semiconductor object. Solid particles of a material that sublimes instantaneously at a predefined temperature and/or pressure are blasted over the portion, through the nozzle. On impact, the particles remove the contaminants from the portion of the semiconductor object.

FIG. 1 is a flow diagram illustrating a method for removing contaminants from at least one portion of a semiconductor object, in accordance with an embodiment of the present invention. The method is illustrated as a collection of steps in a logical flow diagram, which represents a sequence of steps that can be implemented in hardware, software, or a combination thereof.

At step 102, a nozzle is positioned at a preset position with respect to the portion of the semiconductor object. A nozzle is defined as a projecting outlet through which any form of matter passes. The nozzle may be of any shape or size. The nozzle may, for example, be cylindrical, conical, bell-shaped, convergent-divergent or annular in shape. The nozzle may, for example, be elliptical, circular or polygonal in cross-section.

At step 104, solid particles of a material that sublimes instantaneously at a predefined temperature and/or pressure are blasted over the portion, through the nozzle. Examples of the material include, but are not limited to, solid carbon dioxide (often referred as dry ice), solid iodine, camphor and solid naphthalene. Sublimation of a material is a transition of the material from the solid phase to the gaseous phase with no intermediate liquid phase. For a particular material, sublimation occurs at temperatures and/or pressures beyond the triple point of that material. Consider, for example, that dry ice is used for blasting at step 104. The triple point of dry ice is 216.55 Kelvin (i.e., - 55.6 degree Celsius) and 517 kilo Pascal (i.e., 5.1 atmosphere). Therefore, dry ice sublimes instantaneously under normal atmospheric conditions. Therefore, the predefined temperature and/or pressure can be selected based on the triple point of the material being used for blasting at step 104.

The solid particles of the material may be of any shape and/or size. The solid particles may, for example, be in the form of grains, pellets, or powder. The solid particles are pressurized and accelerated with an incoming high-pressured carrier, to create a blast stream through the nozzle. A carrier is a medium through which the solid particles are carried through the nozzle to contaminated portions of the semiconductor object. Compressed air may, for example, be used as the carrier.

On impact, the solid particles of the material transfer their kinetic energy to the contaminants, thereby knocking the contaminants off the portion of the semiconductor object. In addition, instantaneous sublimation of these particles produces a micro-thermal shock, thereby cracking and delaminating the contaminants. The extent of cracking and delaminating of the contaminants depends on the thermal conductivity of the contaminants. Moreover, the sudden increase in the volume of the particles from the solid phase to the gaseous phase produces a micro explosion, which knocks the contaminants off the portion of the semiconductor object.

In accordance with an embodiment of the present invention, the semiconductor object is a semiconductor manufacturing unit. A semiconductor manufacturing unit may, for example, be an assemblage of various machinery parts used to manufacture semiconductor devices. Examples of the portion of the semiconductor manufacturing unit include, but are not limited to, semiconductor encapsulation molds, press tools, Integrated Circuit (IC) test probes, trim/form punches/dies, ball attach tools, and other tools in electronics industry where resin, solder, tin or other contaminants are deposited. Steps 102-104 may be performed inline with the semiconductor manufacturing unit, i.e., the various machinery parts of the semiconductor manufacturing unit need not be disassembled to perform steps 102-104. Steps 102-104 may also be performed offline.

In accordance with another embodiment of the present invention, the semiconductor object is a semiconductor device. Contaminants, such as resin, solder, tin, glue, oil, grease and dirt, may be removed from the semiconductor device. Examples of such semiconductor devices include, but are not limited to, semiconductor IC chips, Printed Circuit Boards (PCBs), semiconductor wafers, and flat panel displays. The semiconductor device may, for example, be in a bare, assembled or encapsulated form.

FIG. 2 is a flow diagram illustrating a method for removing contaminants from at least one portion of a semiconductor object, in accordance with another embodiment of the present invention. The method is illustrated as a collection of steps in a logical flow diagram, which represents a sequence of steps that can be implemented in hardware, software, or a combination thereof.

At step 202, the position and/or movement of a nozzle is set with respect to the portion of the semiconductor object. In an example, the position and/or movement of the nozzle may be set by using one or more pre-programmable instructions. For example, the position of the nozzle may be set at a distance from the portion of the semiconductor object. The movement of the nozzle may be set in a horizontal and/or vertical direction, based on the surface and shape of the portion of the semiconductor object. In addition, the movement of the nozzle may be set to cover the entire semiconductor object.

At step 204, one or more blasting parameters are set. The blasting parameters may, for example, include the shape and/or size of solid particles of a material that sublimes instantaneously at a predefined temperature and/or pressure, a flow rate at which the solid particles are to be blasted, and a material-to-carrier ratio. The material-to-carrier ratio is defined as the ratio of the amount of the material to the amount of the carrier. Details of these blasting parameters have been provided in conjunction with FIG. 4.

At step 206, the nozzle is positioned at the position preset at step 202. In accordance with an embodiment of the present invention, the position of the nozzle may be regulated in an automated manner. In accordance with another embodiment of the present invention, the position of the nozzle may be regulated manually.

At step 208, the movement of the nozzle is controlled, as per the movement preset at step 202. In accordance with an embodiment of the present invention, the movement of the nozzle may be controlled in an automated manner. For example, the nozzle can be mounted on a series of motorized axes, thereby covering the entire portion to be cleaned. In accordance with another embodiment of the present invention, the movement of the nozzle may be controlled manually.

At step 210, the solid particles are blasted over the portion through the nozzle. As described earlier, sublimation occurs at temperatures and/or pressures beyond the triple point of the material. Therefore, the predefined temperature and/or pressure can be selected based on the triple point of the material being used for blasting at step 210. In case of dry ice, step 210 can be carried out at normal room temperatures and atmospheric conditions.

On impact, the solid particles of the material transfer their kinetic energy to the contaminants, thereby knocking the contaminants off the portion of the semiconductor object. In addition, instantaneous sublimation of these particles produces a micro-thermal shock, thereby cracking and delaminating the contaminants. Moreover, the sudden increase in the volume of the particles from the solid phase to the gaseous phase produces a micro explosion, which knocks the contaminants off the portion of the semiconductor object. At step 212, contaminants removed from the portion of the semiconductor object through blasting are sucked, to avoid any spillage.

It should be noted here that steps 202-212 are only illustrative and other alternatives can also be provided where steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein. For example, steps 208 and 210 may be performed simultaneously.

FIG. 3 is a schematic diagram illustrating a portion of an apparatus for removing contaminants from at least one portion 302 of a semiconductor object, in accordance with an embodiment of the present invention. FIG. 3 shows portion 302 of the semiconductor object, contaminants 304 formed over portion 302, a nozzle 306, a nozzle-control unit 308, and solid particle 310 of a material that sublimes instantaneously at a predefined temperature and/or pressure.

Nozzle 306 is positioned at a preset position with respect to portion 302 of the semiconductor object. Nozzle-control unit 308 is used to set the position and/or movement of nozzle 306. Nozzle-control unit 308 positions nozzle 306 at the preset position, and controls the movement of nozzle 306 in an automated manner, in accordance with an embodiment of the present invention. In accordance with another embodiment of the present invention, the position and/or movement of nozzle 306 are controlled manually.

Nozzle 306 is coupled to a blasting unit (not shown in FIG. 3). Solid particles 310 are blasted over portion 302, through nozzle 306, using the blasting unit. On impact, solid particles 310 sublime instantaneously, and remove contaminants 304 from portion 302 of the semiconductor object.

FIG. 4 is a perspective view of an apparatus 400 for removing contaminants from at least one portion of a semiconductor object, in accordance with an embodiment of the present invention. Apparatus 400 includes a nozzle (not shown in FIG. 4), a nozzle-control unit (not shown in FIG. 4), a blasting unit 402, a blasting-unit regulator 404, a cleaning enclosure 406, a support frame 408, a vacuum pump (not shown in FIG. 4), and a vacuum hose 410. With reference to FIG. 4, the semiconductor object includes an encapsulation mold, shown as an upper half 412a and a lower half 412b. In an embodiment of the present invention, the semiconductor object includes multiple encapsulation molds. Cleaning enclosure 406 encloses the inner molding portions of the encapsulation mold. Cleaning enclosure 406 has a height slightly smaller than the gap between upper half 412a and lower half 412b (often referred as the daylight of the encapsulation mold). The shape and size of cleaning enclosure 406 may be chosen depending on machine constraints and work environment of apparatus 400. Cleaning enclosure 406 may, for example, be made of any suitable material, such as aluminum, steel, leather, rubber and plastic.

Cleaning enclosure 406 has an inlet (not shown in FIG. 4) for allowing movement of the nozzle across various portions of the encapsulation mold. Support frame 408 provides support to cleaning enclosure 406.

Blasting-unit regulator 404 includes a plurality of regulators, such as a shape and size regulator to control the shape and/or size of solid particles of a suitable material, a flow-rate regulator to control the flow rate of the solid particles, a ratio regulator to control the material-to- carrier ratio, and other regulators for power supply, etc. The flow rate of the solid particles is set using the flow-rate regulator. The desired flow rate of the solid particles may vary according to the shape and size of the encapsulation mold, the shape and size of the solid particles, and the material-to-carrier ratio.

The solid particles are blasted over the portion of the encapsulation mold, through the nozzle, within cleaning enclosure 406. The solid particles sublime instantaneously, transforming into a gas, thereby leaving no waste product. Contaminants removed from the portion of the encapsulation mold are contained within cleaning enclosure 406, thereby avoiding any spillage. In addition, cleaning enclosure 406 contains the level of noise generated during the process of blasting.

Vacuum hose 410 is connected with the vacuum pump, and is inserted in cleaning enclosure 406 for sucking the contaminants contained within cleaning enclosure 406. This ensures disposal of the contaminants, while avoiding any spillage. In addition, the vacuum so created in cleaning enclosure 406 vents out the gas formed after sublimation. For example, in case of dry ice, a solid particle of dry ice expands approximately 700 times in volume at the time of sublimation.

Apparatus 400 may also include a camera (not shown in FIG. 4) that captures the state of the surface of the encapsulation mold before and after blasting. This enables apparatus 400 and/or an operator of apparatus 400 to decide whether the pattern of cleaning requires any modification. The pattern of cleaning may, for example, be defined by the position and/or movement of the nozzle and other blasting parameters, such as the shape and/or size of the solid particles, the flow rate and the material-to-carrier ratio

Apparatus 400 is portable, and can be moved around a semiconductor manufacturing factory with ease In addition, apparatus 400 can be attached to any portion of the semiconductor manufacturing unit that requires cleaning For example, apparatus 400 may be used to clean die bond, wire bond, heating plate, flip chip, molds and presses, punches and dies, and test sockets and probes

FIG 5 is a perspective view of a portion of apparatus 400, in accordance with an embodiment of the present invention Cleaning enclosure 406 includes an inlet 502 for allowing movement of a nozzle 504 Nozzle 504 may, for example, move in a horizontal, vertical, diagonal or zigzag manner

FIG 6a is a cross-sectional view illustrating a position of nozzle 504 with respect to upper half 412a and lower half 412b of the encapsulation mold, in accordance with an embodiment of the present invention With reference to FIG 6a, nozzle 504 is positioned facing towards lower half 412b of the encapsulation mold, within cleaning enclosure 406

FIG 6b is a cross-sectional view illustrating another position of nozzle 504 with respect to upper half 412a and lower half 412b of the encapsulation mold, in accordance with an embodiment of the present invention With reference to FIG 6b, nozzle 504 is positioned facing towards upper half 412a of the encapsulation mold, within cleaning enclosure 406

It should be noted that nozzle 504 may also be designed to target both upper half 412a and lower half 412b at the same time Other suitable designs of nozzle 504 should be apparent to those skilled in the relevant art

FIG 7 is a top-view illustrating the movement of nozzle 504 across lower half 412b of the encapsulation mold, in accordance with an embodiment of the present invention With reference to FIG 7, the movement of nozzle 504 is set to repeat from right to left and then left to right horizontally, till entire lower half 412b of the encapsulation mold is cleaned

Embodiments of the present invention provide a method and apparatus for removing contaminants from at least one portion of a semiconductor object Solid particles of a material that sublimes instantaneously under normal atmospheric conditions are blasted over the portion of the semiconductor object On impact, the particles transfer their kinetic energy to the contaminants, thereby knocking the contaminants off the portion of the semiconductor object. In addition, instantaneous sublimation of these particles produces a micro-thermal shock, thereby cracking and delaminating the contaminants. Moreover, the sudden increase in the volume of the particles from the solid phase to the gaseous phase produces a micro explosion, which knocks the contaminants off the portion of the semiconductor object. The complete process of removal of contaminants occurs at a micro level, and therefore, does not damage the semiconductor object.

In accordance with an embodiment of the present invention, the semiconductor object is a semiconductor manufacturing unit, and the method is performed inline with the semiconductor manufacturing unit. This, in turn, reduces the time required to clean.

As the particles sublime instantaneously, no waste products are produced. In addition, a cleaning enclosure encloses the portion being cleaned, and therefore, avoids any spillage of the contaminants. The cleaning enclosure also contains the level of noise generated during blasting. The contaminants are also sucked through the vacuum hose, which ensures their disposal without any spillage. This reduces ecologically unfriendly waste.

This application may disclose several characteristic limitations that support any range within the disclosed features even though a precise feature limitation is not stated verbatim in the specification because the embodiments of the invention could be practiced throughout the disclosed features.