Placement of absorbing material in a semiconductor device

A semiconductor device includes a hermetically sealed housing having a top member and a bottom member. The bottom member includes a recess. A semiconductor die is enclosed within the housing. Absorbing material is positioned in the recess under the semiconductor die. A porous film is positioned between the semiconductor die and the absorbing material.

BACKGROUND

Semiconductor devices are widely used today in many electronic applications, such as televisions, children's toys, and computers. Manufacturers of semiconductor devices are working with new materials, new processes, and new technologies daily to develop new semiconductor devices that are a fraction of the size of their ancestors. The smaller the size of the semiconductor device, the smaller the electronic application can be designed. The smaller the size of the electronic application, the more likely consumers are to use the electronics in every day life. This is very evident from the evolution of the computer from the large, slow information processing computers of the 1980's to the fast handheld devices of today.

A typical semiconductor device is manufactured from a number of components including a semiconductor die or “chip” that has been fabricated according to traditional film deposition, masking, etching, and doping processes, a hermetically sealed housing, an absorbing material, such as a getter and/or desiccant material, and strands of wire to connect the die to pins on the housing. Typically, the die is placed in one half of the housing and the strands of wire are connected from the die to the pins on the housing that will provided a means for communicating between the die and the electronic application. Once the die has been seated in the housing, and the strands of wire properly connected, the top half of the housing may be secured to the bottom half of the housing to seal the die within the housing and protect the die from outside contaminants and moisture. While hermetically sealing the die prevents new contaminants from reaching the die, the sealing process does not rid the housing of contaminants that may already be trapped in the housing or contaminants that may be caused by a welding process used to seal the two halves of the housing.

Typically, absorbing material has been added to the device package as a means of absorbing and holding the contaminants and/or moisture present in the housing after the housing has been hermetically sealed. The absorbing material is generally located on the lid of the housing. While the positioning of the absorbing material on the lid of the housing has adequately absorbed contaminants in past devices, new electronic applications are requiring smaller semiconductor devices with the ability to process more information at increasing speeds than the past devices. Further, many semiconductor devices function optically and require a glass window in the top half of the housing to access the die optically. The requirements for smaller device designs require that the glass top half of the housing be recessed to accommodate the desiccant material. This has the effect of either reducing the functional optical die area or increasing the overall package size to regain functionality.

The embodiments described hereinafter were developed in light of this situation and the drawbacks associated with existing systems.

DETAILED DESCRIPTION

A semiconductor device having absorbing material, such as a getter and/or desiccant material, positioned under a semiconductor die is provided to aid in the design and manufacturing of smaller semiconductor devices. A semiconductor device includes a semiconductor die manufactured by film deposition, masking, etching, and doping processes that are known in the art, a hermetically sealed housing, and absorbing material. The semiconductor device is assembled according to traditional processes of bonding the die to a lower portion of the housing, electrically connecting the die to the housing, and hermetically sealing the die to prevent contaminants from penetrating the housing and damaging the functional characteristics of the die. The absorbing material is positioned under the die to allow for a reduction in the size of the device while allowing for sufficient absorbing material capacity to maintain the internal operating environment of the device as well as ensuring that the absorbing material will not interfere with the operation of the device.

In an exemplary embodiment,FIGS. 1,2A, and2B illustrate a semiconductor device10that is comprised of a housing12, such as a ceramic pin grid array (CPGA) housing, having a bottom member14and a top member16, a semiconductor die18, and absorbing material20, such as a getter and/or desiccant material. As illustrated byFIGS. 2A and 2B, die18is typically bonded with bonding material pads26, such as solder or epoxy, to bottom member14and electrically connected to housing12by wire strands22. Wire strands22are further connected to pins24on housing12so that die18may communicate with any electronic application.

Die18is manufactured by methods known in the art that generally involve transforming a silicon wafer by a number of film deposition, masking, etching, and doping steps into an operational die such as a microprocessor chip or microelectromechanical (MEMS) chip. Typically, the processes required to manufacture semiconductor die18must be completed in an extremely clean environment. The clean environment is required to prevent impurities from penetrating die18and damaging the functional characteristics of die18. Once the die manufacturing process has been completed, die18is often in a fragile state. A hermetically sealed housing12is used to protect die18from any impurities that could be introduced in any electronic application. The hermetic seal may be created by solder reflow, seam welding, or laser welding, for example. Once sealed, housing12cannot be opened again to rid the interior of vapor and other contaminants, which may have been introduced before or during the sealing process. Therefore, absorbing material20is activated and sealed in housing12with die18to “soak-up” or absorb the water vapor and any other potentially harmful contaminants that may damage die18. Absorbing material20not only initially absorbs the vapor and contaminants; it also holds the vapor and contaminants for the life of device10.

Referring now toFIG. 2A, an exemplary semiconductor device10is illustrated that includes absorbing material20positioned in a recess28of bottom member14according to an embodiment. Absorbing material20may be bonded to bottom member14to secure absorbing material20in housing12. The positioning of absorbing material20in this manner allows for a variety of semiconductor device design options, such as reducing the size of device10and/or the addition of functional features to device10. Also, particular exemplary devices10may have a top member16that includes a window or aperture30to allow semiconductor device10to be employed in applications requiring the optical operation of die18. One example of employing device10optically is in the projection of images in display, digital projector, or other imaging systems. Positioning absorbing material20underneath die18removes absorbing material20from top member16, thereby allowing the size of top member16to be reduced while maintaining an optical path through window30. Thus, in both instances, the overall size of device10may be reduced without having to decrease the size of die18and risk the loss of functionality or having to decrease the size of the absorbing material and sacrifice the internal environment of housing12.

Absorbing material20may also be bonded to the underside of semiconductor die18prior to the die being bonded to bottom member14as illustrated inFIG. 2B. The bonding of absorbing material20will not interfere with the functional operation of die18. The process of bonding absorbing material20to die18offers manufacturers another possible means of securing absorbing material20in semiconductor device10while at the same time allowing for a decrease in the package size of device10and maintaining the internal environment of housing12.

FIG. 3illustrates another exemplary embodiment. In this particular embodiment, absorbing material20is positioned underneath die18, between die bonding material pads26, and bonded to bottom member14. However, bottom member14does not include a recess to seat absorbing material20, therefore, the overall thickness of housing12may not be decreased as it was inFIGS. 2A and 2Bwhere recess28was employed. Housing12may require the added thickness of bottom member14because of the environment that device18may be employed. Device18may be employed in environments that realize temperature extremes and the thickness of housing12may be required to protect die18. The positioning of absorbing material20under die18still allows for the use of device10in applications requiring optical operation while maintaining the volume and/or surface area of absorbing material to ensure the internal environment of housing12. Also, absorbing material20may also be bonded to die18as discussed previously (see e.g.FIG. 2B) to provide further manufacturing options.

In the exemplary embodiment illustrated inFIG. 4, absorbing material20may be introduced into device10by depositing the absorbing material into an aperture32of bottom member14. This particular embodiment increases the manufacturing flexibility even further for a particular semiconductor device by allowing die18to be positioned and sealed within housing12prior to the introduction of absorbing material20. Absorbing material20is positioned underneath die18as described in the previous embodiments to allow for the reduction in size of device10as well as the optical operation of device10. In this particular embodiment, a porous material34, such as porous silicon or ceramic film, is positioned between die18and absorbing material20. Porous material34may be employed to allow absorbing material to communicate with the internal environment in applications where absorbing material20may not contact die18. Contaminants trapped within housing12are allowed to pass through porous material34to be absorbed by absorbing material20in the manner described above. Alternatively, porous material34may be omitted and absorbing material20may be positioned in direct contact with die18(similar toFIG. 2B) so that contaminants pass directly to the absorbing material. A cap36may be used to seal absorbing material20within housing12and hermetically seal device10. Cap36may be formed by depositing a metal film, such as for example aluminum, titanium, or tungsten, into aperture32.

FIG. 5illustrates another exemplary embodiment. In this particular embodiment, absorbing material20is positioned in a casing37that is bonded and sealed on the outside of housing12to bottom member14. Casing37may be manufactured from any metal such a kovar, steel, or aluminum. Bottom member14includes a port38that passes from an outside of bottom member14to the interior of device10. A hole40included in casing37is aligned with port38. Contaminants trapped in device10during manufacturing may exit a chamber42where die18is positioned through port38. Upon leaving chamber42, contaminants enter casing37and are absorbed by absorbing material20in the manner described above.

Placing absorbing material20into its own casing37also offers many advantages. In this particular embodiment, die18may be bonded into a recess of bottom member14as illustrated inFIG. 5. The placement of absorbing material20within its own casing37allows the overall surface area of the absorbing material to be increased providing for a greater area of contact and absorption of contaminants. Increasing the surface area of absorbing material20allows for higher pumping speed and capacity, which enables a higher vacuum and additional environmental control. This added control allows for a decrease in the overall thickness of absorbing material20, thereby contributing to minimizing the thickness of device10. This particular embodiment allows for a larger die size to be employed without increasing the overall size of device10, thereby increasing or at least maintaining the functionality of die10and increasing the number of possible uses of device18in electronic applications.

All the above exemplary embodiments may be manufactured in similar ways. The semiconductor die18may be manufactured according to the typical die manufacturing processes of depositing a number of films onto a silicon wafer, and processing the wafer through a number of masking and etching processes, and doping the wafer to achieve die18.FIG. 6illustrates an exemplary semiconductor device assembly process. Prior to bonding die18to bottom member14, absorbing material20is introduced into housing12as describedFIGS. 2A,2B, and3at step100. Absorbing material20may be deposited into recess28of bottom member14(seeFIG. 2A), onto the backside of die18(seeFIG. 2B) or onto a surface of bottom member14(seeFIG. 3). Next, absorbing material20is taken through a curing process at step110. In these particular embodiments, absorbing material is subjected to a temperature of about 320 degrees Celsius for 30 minutes. Die18is then positioned over absorbing material20and bonded or soldered to bottom member14of housing12at step120. Wire strands22are attached between die18and bottom member14at step130and top member16is positioned on bottom member14and housing12is hermetically sealed at step140to prevent further contaminants from entering device10and damaging the functional characteristics of die18.

FIG. 7illustrates the assembly process of device10shown inFIG. 4and involves a similar process to that ofFIGS. 2A,2B and3except that die18is sealed between bottom member14and top member16prior to depositing absorbing material20. Die18is positioned over aperture32and bonded to bottom member14at step200. Die18is wire bonded to bottom member14at step210. Top member16and bottom member14are bonded together at step220. Porous material34is deposited into aperture32at step230. Absorbing material20is introduced into device10through aperture32at step240and cured at step250. Aperture32is hermetically sealed with cap36at step260to prevent further contaminants from entering device10and damaging the functional characteristics of die18.

FIG. 8illustrates the assembly process of device10shown inFIG. 5and provides for the embedding of die18into bottom member14. Absorbing material20is deposited into its own casing37at step300and cured at step310. Semiconductor die18is bonded to bottom member14at step320and die18is then wire bonded to bottom layer14at step330. Next, Casing37is bonded to bottom member14so that hole40in casing37is aligned with port38in bottom member14at step340so that contaminants in chamber42may pass to absorbing material20. Housing12is then hermetically sealed between top member16and bottom member14at step350to prevent any contaminants from entering housing12and damaging device10.

The above-described system and methods provide significant advantages over known systems and methods. Specifically, the positioning of the absorbing material underneath the semiconductor die allows for the size of the semiconductor device package to be decreased without sacrificing functionality, thereby increasing the uses of the semiconductor devices in a wider variety of electronic applications. Also, the size of the absorbing material may be maintained so that the internal environment of the housing is not sacrificed, which, in turn ensures the functional integrity of the die.

While the present invention has been particularly shown and described with reference to the foregoing preferred embodiment, it should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiment is illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.