Environmental protection for wafer level and package level applications

A method includes the steps of fabricating one or more semiconductor devices on a semiconductor wafer and depositing one or more conformal organic environmental protection layers over the semiconductor wafer using a vapor deposition process. By depositing the one or more conformal organic environmental protection layers using a vapor deposition process, thin film conformal organic environmental protection layers may be provided that offer excellent protection against water and oxygen ingress, thus increasing the ruggedness and reliability of the resulting semiconductor die.

FIELD OF THE DISCLOSURE

The present disclosure relates to semiconductor die and integrated circuit packages including conformal organic protective films for protecting from environmental exposure.

BACKGROUND

Semiconductor die and integrated circuit packages are used in myriad applications. Often, these applications result in exposure of the semiconductor die and integrated circuit packages to environmental conditions such as high temperature, humidity, and the like. To prolong the lifetime of devices incorporating semiconductor die and integrated circuit packages, environmental protection is paramount. Specifically, protecting semiconductor die and integrated circuit packages from degradation due to moisture ingress is necessary for maintaining reliability of the devices.

Generally, environmental protection may be applied at the wafer level or the package level. State of the art wafer level environmental protection involves the application of one or more thin film inorganic environmental protection layers, as illustrated inFIGS. 1A and 1B.FIG. 1Ashows a semiconductor wafer10, which is separated into a number of discrete semiconductor die12.FIG. 1Bshows a cross-sectional view of a portion of one of the semiconductor die12, which includes a substrate14, an active area16in a top portion of the substrate14, one or more intermediate layers18over the substrate14, one or more metallization layers20over the one or more intermediate layers18, and one or more inorganic environmental protection layers22over the one or more metallization layers. Those skilled in the art will appreciate that the active area16may include one or more implanted, diffused, or epitaxially grown regions, and that the one or more intermediate layers18and the one or more metallization layers20may be patterned to form any number of semiconductor devices in the semiconductor die12. For example, one or more implanted, diffused, or epitaxial regions in the active area16may interact with an intermediate layer18of oxide or nitride and one or more portions of a metallization layer20to form one or more transistors, one or more diodes, and the like.

Conventionally, the inorganic environmental protection layers22are applied via atomic layer deposition (ALD), and comprise oxides such as tantalum pentoxide (Ta2O4), aluminum oxide (Al2O3), or silicon nitride (Si3N4). While initially promising from an environmental protection perspective, these inorganic environmental protection layers22have proved inadequate in harsh environmental conditions. For example, when subjected to highly accelerated stress tests (HAST) in which the device is subject to 85% relative humidity at 130° C. for 96 hours under certain bias conditions or temperature humidity bias (THB) tests in which the device is subject to 85% relative humidity at 85° C. for 1000 hours under certain bias conditions, the device may fail due to moisture ingress and corrosion.

FIG. 2illustrates state of the art package level environmental protection. As shown, a semiconductor die24is attached to a package substrate26using a die attach28, and wire bonds30electrically connect the semiconductor die24to the package substrate26. A number of solder balls32may couple the package substrate26with a module (not shown), or other circuitry. An encapsulation layer34is usually provided over the semiconductor die24such that the semiconductor die24is completely encapsulated thereby.

Conventionally, the encapsulation layer34is an epoxy layer that is extruded or otherwise molded over the package. That is, the encapsulation layer34is not a thin film layer and is not provided via a vapor deposition process. While the encapsulation layer34of modern packages is quite good at preventing moisture ingress, providing environmental protection at the package level is much more cumbersome and results in a much larger device than when provided at the wafer level.

In light of the above, there is a need for improved environmental protection at both the wafer level and package level.

SUMMARY

The present disclosure relates to semiconductor die and integrated circuit packages including conformal organic protective films for protecting from environmental exposure. In one embodiment, a method includes the steps of fabricating one or more semiconductor devices on a semiconductor wafer and depositing one or more conformal organic environmental protection layers over the semiconductor wafer using a vapor deposition process. By depositing the one or more conformal organic environmental protection layers using a vapor deposition process, thin film conformal organic environmental protection layers may be provided that offer excellent protection against water and oxygen ingress, thus increasing the ruggedness and reliability of the resulting semiconductor die.

In one embodiment, the one or more conformal organic environmental protection layers are liquid crystal polymer layers. Specifically, the one or more conformal organic environmental protection layers may be p-Biphenyl Benzoic Acid.

In one embodiment, the vapor deposition process may be a low pressure, plasma-enhanced chemical vapor deposition (LP-PECVD) process. In another embodiment, the vapor deposition process may be a molecular vapor deposition (MVD) process. In yet another embodiment, the vapor deposition process may be a molecular layer deposition (MLD) process.

In one embodiment, the semiconductor wafer comprises one of gallium nitride (GaN) and gallium arsenide (GaAs). Generally, gallium nitride and gallium arsenide devices are high power (e.g., rated for a blocking voltage greater than 30V) devices that often suffer from reliability problems due to environmental exposure. Providing the conformal organic environmental protection layers significantly increases the ruggedness and reliability of the resulting semiconductor die for these high power devices.

DETAILED DESCRIPTION

FIG. 3shows a cross-sectional view of a portion of a semiconductor die36according to one embodiment of the present disclosure. As shown, the semiconductor die36includes a substrate38, an active area40in a top portion of the substrate38, one or more intermediate layers42over the substrate38, one or more metallization layers44over the one or more intermediate layers42, and one or more conformal organic environmental protection layers46over the one or more metallization layers44. Those skilled in the art will appreciate that the active area40may include one or more implanted, diffused, or epitaxially grown regions, and that the one or more intermediate layers42and the one or more metallization layers44may be patterned to form any number of semiconductor devices in the semiconductor die36. For example, one or more implanted, diffused, or epitaxial regions in the active area40may interact with an intermediate layer42of oxide and one or more portions of a metallization layer44to form one or more transistors, one or more diodes, or the like.

In some embodiments, the substrate38may comprise gallium nitride (GaN) or gallium arsenide (GaAs). Generally, semiconductor die comprising gallium nitride and gallium arsenide are relatively high-power devices (e.g., rated for blocking voltages greater than 30V). Those skilled in the art will appreciate that as the power handling capability of a device increases, so does the potential for damage of the device due to environmental exposure. Accordingly, the one or more conformal organic environmental protection layers46are provided to provide a barrier against moisture ingress. Notably, the one or more conformal organic environmental protection layers46are thin-film layers deposited by a vapor deposition process such as low pressure, plasma-enhanced chemical vapor deposition (LP-PECVD), molecular vapor deposition (MVD), or molecular layer deposition (MLD). In some embodiments, each of the one or more conformal organic environmental protection layers46may thus be less than 10,000 Å, less than 5,000 Å, less than 4,000 Å, less than 3,000 Å, less than 2,000 Å, and less than 1,000 Å. In one embodiment, the one or more conformal organic environmental protection layers46comprise a liquid crystal polymer (LCP). For example, the one or more conformal organic environmental protection layers46may comprise p-Biphenyl Benzoic Acid. Organic materials such as liquid crystal polymers have very dense polymer carbon-nitrogen (C—N) structures and no oxygen vacancy diffusion at elevated temperatures. Accordingly, these materials provide excellent moisture barriers. Further, these materials are usable at very high frequencies (e.g., up to 110 GHz).

Organic materials such as liquid crystal polymers significantly outperform their inorganic counterparts (e.g., oxides) in terms of water and oxygen permeability and temperature stability. Generally, liquid crystal polymers are second only to ceramics in these terms, and inorganic materials significantly lag behind.

While organic materials such as liquid crystal polymers have been previously used, for example, as package substrates, these applications did not contemplate their use as thin-film environmental protection layers applied via a vapor deposition process (i.e., CVD, MVD, or MLD as discussed above). Rather, conventional applications for working with organic materials such as liquid crystal polymers have been limited to, for example, molding and extrusion. These conventional applications for organic materials did not provide a process by which a thin film layer of said organic materials could be applied, for example, over a semiconductor wafer as shown inFIG. 3.

The conformal organic environmental protection layers46may allow the semiconductor die36to pass a highly accelerated stress test (HAST) in which the device is subject to 85% relative humidity at 130° C. for 96 hours under certain bias conditions or temperature humidity bias (THB) tests in which the device is subject to 85% relative humidity at 85° C. for 1000 hours under certain bias conditions. This may hold true even for high power (e.g., rated for blocking voltages greater than 30V) devices as discussed above. Since the environmental protection is provided at the wafer level rather than the package level, the size added due to packaging may be eliminated or reduced, thereby reducing the size of a device incorporating the semiconductor die36.

FIG. 4is a flow chart illustrating a method for providing environmental protection at the wafer level according to one embodiment of the present disclosure. The process begins with a semiconductor wafer (step100). First, one or more semiconductor devices are fabricated on the semiconductor wafer (step102). Those skilled in the art will appreciate that this may involve implanting an active area in the semiconductor wafer, providing one or more intermediate layers over the semiconductor wafer, providing one or more metallization layers over the one or more intermediate layers and/or the semiconductor wafer, and the like. Next, one or more conformal organic environmental protection layers are deposited over the semiconductor wafer using a vapor deposition process (step104). As discussed above, the vapor deposition process may be a low pressure, plasma-enhanced chemical vapor deposition process (LP-PECVD), a molecular vapor deposition (MVD) process, or a molecular layer deposition (MLD) process. The one or more conformal organic environmental protection layers are thin-film layers that may comprise a liquid crystal polymer such as p-Biphenyl Benzoic Acid, and may be less than 10,000 Å thick. The one or more conformal organic environmental protection layers may then be patterned (step106). This may involve masking and etching the one or more conformal organic environmental protection layers. For example, plasma etching or the like may be used to pattern the one or more conformal organic environmental protection layers. Patterning of the one or more conformal organic environmental protection layers may be done, for example, to expose one or more contact pads formed by one or more metallization layers for allowing connection to the semiconductor devices in the semiconductor die. Finally, the semiconductor wafer may be singulated into a number of semiconductor die (step108).

In addition to being used at the wafer level, the use of vapor deposited organic environmental protection layers may also be provided at the package level as illustrated inFIG. 5. As shown, a semiconductor die48is attached to a package substrate50using a die attach52, and wire bonds54electrically connect the semiconductor die48to the package substrate50. A number of solder balls56may couple the package substrate50with a module (not shown), or other circuitry. One or more conformal organic environmental protection layers58are provided over the semiconductor die48and the package substrate50. In some embodiments, an encapsulation layer60is provided over the one or more conformal organic environmental protection layers58.

As discussed above, the conformal organic environmental protection layers58may be thin-film layers deposited by a vapor deposition process such as low pressure, plasma-enhanced chemical vapor deposition (LP-PECVD) or molecular vapor deposition (MVD). In some embodiments, each of the one or more conformal organic environmental protection layers58may thus be less than 5,000 Å, less than 4,000 Å, less than 3,000 Å, less than 2,000 Å, and less than 1,000 Å. In one embodiment, the one or more conformal organic environmental protection layers58comprise a liquid crystal polymer (LCP). For example, the one or more conformal organic environmental protection layers58may comprise p-Biphenyl Benzoic Acid. The semiconductor die48may comprise gallium nitride (GaN) or gallium arsenide (GaAs), and further may be a high power (e.g., rated for blocking voltages greater than 30V) device. The one or more conformal organic environmental protection layers58may further decrease moisture ingress in the package and thus increase the ruggedness and reliability thereof. Providing the one or more conformal organic environmental protection layers58may provide the additional benefit of preventing dendritic growth of metals (i.e whiskers) most notably silver and tin used in die or solder bump attachment, as the one or more conformal organic environmental protection layers58act as an inhibitor of said metal dendrides.

FIG. 6is a flow chart illustrating a method for providing environmental protection at the package level according to one embodiment of the present disclosure. First, an integrated circuit package is fabricated (step200). Those skilled in the art will appreciate that this may involve, for example, providing a package substrate or other package base and mounting one or more semiconductor die thereto (both mechanically and electrically). Next, one or more conformal organic environmental protection layers are deposited over the semiconductor die and package (step202). As discussed above, the vapor deposition process may be a low pressure, plasma-enhanced chemical vapor deposition process (LP-PECVD) or a molecular vapor deposition (MVD) process. The one or more environmental protection layers are thin-film layers that may comprise a liquid crystal polymer such as p-Biphenyl Benzoic Acid, and may be less than 5,000 Å thick. The one or more environmental protection layers may then be patterned (step204). This may involve masking and etching the one or more environmental protection layers. For example, plasma etching or the like may be used to pattern the one or more environmental protection layers. Patterning the one or more conformal organic environmental protection layers may, for example, provide access to one or more contact pads for the package.