External gettering method and device

Abstract

Disclosed embodiments include external gettering provided by electronic packaging. An external gettering element for a semiconductor substrate, which may be incorporated as part of an electronic packaging for the structure, is disclosed. Semiconductor structures and stacked semiconductor structures including an external gettering element are also disclosed. An encapsulation mold compound providing external gettering is also disclosed. Methods of fabricating such devices are also disclosed.

Claims

1. A semiconductor wafer comprising: a substrate having a device section for forming semiconductor devices and a backside section; a first gettering material directly interfacing with said backside section, said first gettering material for forming a denude zone at said device section; and an external gettering element separate from said first gettering material and directly interfacing with said backside section, said external gettering element comprising (i) a second gettering material for forming said denude zone at said device section and (ii) an adhesive material, wherein said second gettering material is integrated with said adhesive material.

2. The semiconductor wafer of claim 1, wherein said adhesive material is a die attach film.

3. The semiconductor wafer of claim 1, wherein said adhesive material is configured to adhere said external gettering element to said backside section of said substrate.

4. The semiconductor wafer of claim 1, wherein said external gettering element is imbued with particular polarities or quantities of ions in order to attract ions or contaminants within said substrate toward said backside section.

5. A stacked semiconductor structure including a plurality of wafers, said structure comprising: a first substrate having a first device section designated for forming semiconductor devices and a first backside section; a second substrate having a second device section designated for forming semiconductor devices and a second backside section facing said first backside section of said first substrate; a first gettering material directly interfacing with said second backside section, said first gettering material for forming a denude zone in said second device section; and an external gettering element separate from said first gettering material and directly interfacing with said first backside section and/or said second backside section, said external gettering element comprising (i) a second gettering material for forming a denude zone in said first device section and/or said second device section and (ii) an adhesive material, wherein said second gettering material is integrated with said adhesive material.

6. The stacked semiconductor structure of claim 5, wherein said adhesive material adheres said first substrate and said second substrate.

7. The stacked semiconductor structure of claim 6, wherein said adhesive material is a die attach film.

8. The stacked semiconductor structure of claim 5, wherein said external gettering element is adhered to said second backside section by said adhesive material.

9. The stacked semiconductor structure of claim 8, further comprising a third gettering material, wherein said third gettering material is adhered to said first backside section.

10. The stacked semiconductor structure of claim 5, wherein said external gettering element is imbued with particular polarities or quantities of ions in order to attract ions or contaminants within said second substrate toward said second backside section.

11. The stacked semiconductor structure of claim 7, wherein said adhesive material is a dual-sided die attach film.

12. The stacked semiconductor structure of claim 10, wherein: said external gettering element is a first substrate, a first polymeric material, a first ceramic material, a first silicon material, or a first epoxy-based material.

13. The stacked semiconductor structure of claim 10, wherein said ions include oxide ions, silicon ions, carbide ions, and/or copper ions.

14. The stacked semiconductor structure of claim 5, wherein said external gettering element further directly interfaces with said first backside section.

15. The semiconductor wafer of claim 4, wherein said external gettering element is a substrate, a polymeric material, a ceramic material, or an epoxy-based material.

16. The semiconductor wafer of claim 4, wherein said ions include oxide ions and/or carbide ions.

17. The semiconductor wafer of claim 4, wherein said ions include copper ions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a semiconductor device with conventional intrinsic gettering;

(2) FIG. 2 is a cross-sectional view of a semiconductor device with conventional intrinsic gettering subject to grinding and/or thinning processes;

(3) FIGS. 3A-3B are cross-sectional views of a semiconductor device with conventional extrinsic gettering;

(4) FIG. 4 is a cross-sectional view of a semiconductor device with conventional extrinsic gettering subject to stress relief processes;

(5) FIG. 5 is a cross-sectional view of a semiconductor device including an external gettering element according to a first embodiment described herein;

(6) FIG. 6A is a cross-sectional view of a semiconductor device including an external gettering element according to a second embodiment described herein;

(7) FIG. 6B is a cross-sectional view of a semiconductor device including an external gettering element according to a third embodiment described herein;

(8) FIG. 7 is a cross-sectional view of a semiconductor device including an external gettering element according to a fourth embodiment described herein;

(9) FIG. 8A is a cross-sectional view of a semiconductor device including an external gettering element according to a fifth embodiment described herein;

(10) FIG. 8B is a cross-sectional view of a semiconductor device including an external gettering element according to a sixth embodiment described herein;

(11) FIG. 9 is a flowchart illustrating steps of a fabrication process for a semiconductor device including an external gettering element;

(12) FIG. 10 is a cross-sectional view of a semiconductor device including an encapsulation mold compound providing external gettering according to a seventh embodiment described herein;

(13) FIG. 11 is a flowchart illustrating steps of a fabrication process for a semiconductor device including an encapsulation mold compound providing external gettering.

DETAILED DESCRIPTION

(14) In the following detailed description, reference is made to various embodiments of the invention. These embodiments are described with sufficient detail to enable those skilled in the art to practice them. It is to be understood that other embodiments may be employed, and that various structural, logical and electrical changes may be made. In addition, reference is made to various processes including multiple steps. It should be understood that these steps need not be performed in the order that they are listed, unless specifically stated as such.

(15) The term substrate used in the following description may include any supporting structure including, but not limited to, a semiconductor substrate that has an exposed substrate surface. A semiconductor substrate should be understood to include silicon, silicon-on-insulator (SOI), silicon-on-sapphire (SOS), doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures, including those made of semiconductors other than silicon. The substrate, as well as devices formed therein, may be formed of any appropriate materials known in the art. When reference is made to a semiconductor substrate or wafer in the following description, previous process steps may have been utilized to form regions or junctions in or over the base semiconductor or foundation.

(16) In embodiments described below, external gettering is applied to semiconductor devices using electronic packaging. For example, in certain embodiments an external gettering element is applied to a backside of a semiconductor substrate. The external gettering element may be integrated with or arranged by electronic packaging that is typically used when fabricating a semiconductor device using the semiconductor substrate. For example, the external gettering element may be integrated with, or adhered by, an adhesive material that is applied to an already-polished backside of a substrate. In other embodiments described below, an encapsulation mold compound embedded with one or more additives may be formed around the semiconductor substrate.

(17) FIG. 5 is a cross-sectional view of a semiconductor device including external gettering according to a first embodiment. FIG. 5 illustrates a bulk substrate 101, including a device section 211 and an internal gettering section 212. As shown in FIG. 5, bulk substrate 101 includes contaminants 102. It should be understood that, while an internal gettering section 212 is shown, embodiments need not include any internal gettering within substrate 101.

(18) Bulk substrate 101 in FIG. 5 has already been subjected to a thinning process, such as a backside grinding process, and stress relief processes, such as DP, MCP, or CMP processes described above, in order to achieve a desired thickness and to maintain the die strength of substrate 101. Accordingly, bulk substrate 101 includes a stress relieved backside 215, as described above with regard to FIG. 4.

(19) As shown in FIG. 5, an external gettering element 520 is applied to stress relieved backside 215. In the embodiment shown in FIG. 5, external gettering element 520 includes a gettering material that is integrated into an adhesive material. The adhesive material may be a type of adhesive material typically employed as part of the electrical packaging used during fabrication of semiconductor devices. For example, external gettering element 520 may be integrated into a die attach film (DAF), which is then applied to stress relieved backside 215. Examples of DAF products known in the industry that may be appropriate for integration with a gettering material include Nitto Denko's EM-550H-P, Lintec Corp.'s LE4424, and Henkel Corp.'s ATB-130, to name but a few.

(20) The gettering material of external gettering element 520 may be, for example, a substrate or other polymeric, ceramic, silicon, or epoxy-based material, or any material compliant with electronic packaging, which has been imbued with ions of different polarities or quantity. The ions used to imbue the gettering material of external gettering element 520 may be organic and/or inorganic additives, for example, oxide ions, silicon ions, carbide ions, or other types of ions that can be used to imbue gettering materials. The polarity and quantity of ions that may be imbued in the gettering material of external gettering element 520 may be highly situational and/or device dependent, and accordingly it should be understood that any appropriately ion-imbued material may be used. For example, gettering materials for varying purposes may have one of multiple different concentration levels, such as a high, medium, or low concentration level.

(21) In a preferred embodiment, a gettering material may be soaked in an organic ion solution, such as a Copper (Cu) ion solution, until a high concentration level is reached. The ion concentration level of the material may then be measured by conventional methods, such as by using the ICP-AES method that is commonly known in the art.

(22) When the gettering material is integrated into a DAF, as shown in the external gettering element 520, the external gettering element 520 may be adhered directly to stress relieved backside layer 215. External gettering element 520 provides external gettering, attracting and/or trapping mobile metals or ions contaminants 102 in the substrate 101 towards the backside 215 of substrate 101 and away from device section 211. Accordingly, external gettering element 520 provides for the performance benefits of gettering, while maintaining the strengthening benefits of stress relief techniques.

(23) Stacked semiconductor packages, such as wafer-on-wafer packages and other forms of three-dimensional semiconductor packaging, can provide increased spatial efficiency for devices utilizing semiconductor technology. FIGS. 6A and 6B show two such examples of a stacked package including the external gettering concept described above.

(24) FIG. 6A is a cross-sectional view of a semiconductor device including external gettering according to a second embodiment. FIG. 6A shows one such example of a stacked package, including a first wafer with a first semiconductor substrate 101, device layer 211, and intrinsic gettering layer 212, and a second wafer with a second semiconductor substrate 301, device layer 311, and intrinsic gettering layer 312. It should be understood that, while internal gettering sections 212, 312 are shown in substrates 101, 301, embodiments need not include any internal gettering.

(25) The respective backsides of substrates 101 and 301 are adhered by an external gettering element 525 that is integrated into a dual-sided adhesive, such as a dual-sided DAF product known in the industry, including, for example, Nitto Denko's EM 55011-P. As shown in FIG. 6, external gettering element 525 provides external gettering to both substrates 101, 301, pulling contaminants 102 towards the respective backsides and away from the respective device sections 211, 311.

(26) FIG. 6B is a cross-sectional view of a semiconductor device including external gettering according to a third embodiment. FIG. 6B shows another such example of a stacked package, including similar elements to those described above with regard to FIG. 6A. In FIG. 6B, however, device layer 311 of substrate 301 is adhered to the backside of substrate 101 by the external gettering element 525 that is integrated into a dual-sided adhesive. Device layer 311 of substrate 301 may be provided extrinsic gettering by a separate external gettering element 526, which may be, for example, a single or dual-sided adhesive with an integrated gettering material. Alternatively, the external gettering element at the backside of substrate 301 may be a separate external gettering element adhered by an adhesive material.

(27) FIG. 7 is a cross-sectional view of a semiconductor device including external gettering according to a fourth embodiment. In FIG. 7, the external gettering element includes a stand-alone layer of gettering material 636, separate from an adhesive material 630, which is applied on the stress-relieved backside of substrate 101. Gettering material 636 may be, for example, a substrate or other polymeric, ceramic, silicon, or epoxy-based material, or any material compliant with electronic packaging, which has been imbued with ions of different polarities or quantity. Adhesive material 630, which may be, for example, a conventional DAF or another known adhesive or laminate, holds the gettering material in place on the backside of substrate 101.

(28) The concept described above with regard to FIG. 7 may also be applied to form a stacked package. FIG. 8A is a cross-sectional view of a semiconductor device including external gettering according to a fifth embodiment. FIG. 8A shows one such example of a stacked package, including a first wafer with a first bulk substrate 101, device layer 211, and intrinsic gettering layer 212, and a second bulk substrate 301, device layer 311, and intrinsic gettering layer 312. The respective backsides of substrates 101 and 301 are adhered by a dual-sided adhesive 630, such as a dual-sided DAF product known in the industry. Dual-sided adhesive 630 also laminates external gettering elements 636, 646 to the stress-relieved backside of substrate 101. External gettering elements 636, 646 are stand-alone layers of gettering material that are not integrated into the adhesive 630, similar to the gettering material described above with regard to FIG. 7. External gettering elements 636, 646 have been imbued with ions of different polarities or quantity, in order to provide appropriate external gettering to the respective substrates 101, 301 by pulling contaminants 102 towards the respective backsides and away from the respective device sections 211, 311. It should be understood that, while multiple external gettering elements 636, 646 are shown in FIG. 8, in other embodiments, a single external gettering element may be adhered to a backside of one of substrates 101 and 301.

(29) FIG. 8B is a cross-sectional view of a semiconductor device including external gettering according to a sixth embodiment. FIG. 8B shows another such example of a stacked package, including similar elements to those described above with regard to FIG. 8A. In FIG. 8B, however, device layer 311 of substrate 301 is adhered to the backside of substrate 101 by the adhesive 630, and external gettering element 646 is omitted. Device layer 311 of substrate 301 may be provided extrinsic gettering by a separate external gettering element 637, which may be, for example, adhered to the backside of substrate 301 by a separate adhesive 631. Alternatively, the external gettering element at the backside of substrate 301 may be integrated into an adhesive.

(30) FIG. 9 is a flowchart illustrating steps of a fabrication process 900 for a semiconductor device including an external gettering element. Process 900 may be used to fabricate one or more of the embodiments described above with regard to FIGS. 5-8.

(31) In step 901, a bulk semiconductor substrate is provided. The bulk semiconductor substrate may be, for example, a silicon substrate or other material, and may include an internal gettering section, as discussed above with regard to bulk substrate 101 (FIG. 5).

(32) In step 902, the bulk substrate is thinned. For example, the backside of the bulk substrate may be subjected to a backside grinding process, as described above, or to any appropriate thinning process known in the art.

(33) In step 903, the substrate is subjected to a stress relief process to polish the backside of the wafer and increase overall wafer strength. For example, dry polish (DP) techniques, such as mechano-chemical polishing (MCP) techniques, or chemical-mechanical polishing/planarization (CMP) techniques may be used. Alternatively, other techniques such as GDP, Poligrind, or other known polishing techniques may be used.

(34) In step 904, an external gettering element is applied to the stress-relieved backside of the substrate. The external gettering element may comprise a gettering material, such as a substrate or other polymeric, ceramic, silicon, or epoxy-based material, or any appropriately ion-imbued material. The ions used to imbue the gettering material of external gettering element may be, for example, organic or inorganic additives, such as oxide ions, silicon ions, carbide ions, or other types of ions that can be used to imbue gettering materials. The gettering material may be imbued with organic or inorganic ions through known processes, such as by soaking the gettering material in an ion solution.

(35) The external gettering element may be integrated into an adhesive material, as described above with regard to FIGS. 5-6. Alternatively, the external gettering element may be a stand-alone layer of gettering material, as described above with regard to FIGS. 7-8. If a stand-alone layer is used as the external gettering element, in step 905, an adhesive or laminate, such as a conventional single-sided or dual-sided DAF, may be applied to maintain the external gettering element on the backside of the substrate, and/or to provide adhesive for a multiple-die stacked semiconductor structure (see Step 907, supra) such as the stacked structure shown in FIG. 8. It should be understood that, if the gettering material is integrated into an adhesive material in step 904, then step 905 may optionally be omitted.

(36) In step 906, semiconductor devices are formed in the denude zone that is provided by the external gettering of the external gettering element. Formed semiconductor devices may include, for example, source and drain structures, gate structures, channel sections, and other structures known in the art. It should be understood that, if a stack semiconductor structure is formed (see Step 907, supra), then semiconductor devices may instead be formed in one or both substrates after the formation of the stack semiconductor structure.

(37) In step 907, a stack semiconductor structure can be formed, using the semiconductor substrate with applied external gettering element formed in steps 901-906. In one embodiment, the external gettering element is integrated into a dual-sided DAF, as described above with regard to FIG. 6. The dual-sided DAF may be used to attach a second semiconductor wafer. The second semiconductor wafer may receive the benefit of external gettering from the same external gettering element as the first wafer, and/or from a separate external gettering element. In another embodiment, a conventional dual-sided DAF may be used to attach the second semiconductor wafer, and may also be used to adhere a second external gettering element to the backside of the second semiconductor wafer, as described above with regard to FIG. 8.

(38) It should be understood that, while FIGS. 5 through 9 describe embodiments where an adhesive material is used with an external gettering element, the concept described herein is not so limited. For example, some configurations of semiconductor devices may not require adhesives, such as DAF, in their manufacture, and adding an adhesive to the manufacturing process may be undesirable. In addition, it may be desirable to provide gettering to semiconductor devices using more than one technique.

(39) FIG. 10 is a cross-sectional view of a semiconductor device including external gettering according to a fifth embodiment. FIG. 10 illustrates a bulk substrate 101 including a device section 711, an internal gettering section 212, and a backside section 715. As shown in FIG. 10, semiconductor devices formed in device section 711 are connected to external electronic connections 752 (which may be, for example, a ball grid array package that is well known in the art) via solder bumps 751.

(40) As shown in FIG. 10, bulk substrate 101 includes contaminants 102. It should be understood that, while an internal gettering section 212 is shown, embodiments need not include any internal gettering within substrate 101. In one embodiment, bulk substrate 101 in FIG. 10 may have already been subjected to a thinning process, such as a backside grinding process, and stress relief processes, such as DP, MCP, or CMP processes described above, in order to achieve a desired thickness and to maintain the die strength of substrate 101. In such an embodiment, backside section 715 is a stress relieved backside, as described above with regard to FIG. 4. Alternatively, substrate 101 may have been subjected to other thinning and/or polishing methods, or may not have been subjected to any thinning and/or polishing methods.

(41) Substrate 101 is surrounded by encapsulation mold compound 750. According to known processes in the art, an encapsulation mold compound 750 may be applied through an aperture in an encapsulation mold 753 into a cavity formed by the encapsulation mold 753. The encapsulation mold 753 is subsequently removed, leaving the encapsulation mold compound 750 surrounding substrate 101. The encapsulation mold compound may be composed of various plastics and/or resins, such as a molded epoxy compound.

(42) As described herein, in addition to providing physical, thermal, and/or electrical protection to semiconductor devices formed on substrate 101, at least a portion of encapsulation mold compound 750 may also be embedded with an additive in order to provide gettering to substrate 101. For example, encapsulation mold compound 750 may be embedded with organic and/or inorganic ions, such as those described above with regard to imbuing gettering material in FIGS. 5-9. The polarity and quantity of ions for the encapsulation mold compound may be highly situational and/or device dependent, and accordingly it should be understood that any appropriately embedded encapsulation mold compound may be used. As shown in FIG. 10, encapsulation mold compound 750 provides gettering to substrate 101, drawing contaminants 102 towards backside 715 and away from device section 711.

(43) FIG. 11 is a flowchart illustrating steps of a fabrication process 1100 for a semiconductor device including an encapsulation mold compound providing gettering. Process 1100 may be used to fabricate, for example, the embodiment described above with regard to FIG. 10.

(44) In step 1101, a bulk semiconductor substrate is provided. The bulk semiconductor substrate may be, for example, a silicon substrate or other material, and may include an internal gettering section, as discussed above with regard to bulk substrate 101 (FIG. 5).

(45) Optionally, in steps 1102 and 1103, the bulk substrate is thinned and polished, respectively. The thinning and/or polishing processes used in steps 1102 and 1103 may be those described above with regard to steps 902 and 903 of process 900 (FIG. 9). Alternatively, process 1100 may omit one or both of these steps.

(46) In step 1104, semiconductor devices are formed in at least one section of the bulk substrate. Formed semiconductor devices may include, for example, source and drain structures, gate structures, channel sections, and other structures known in the art. In step 1105, solder bumps or other conductive connections are formed in order to provide electrical connections between devices formed on the substrate and external electronic connections 752 (see Step 1107, infra).

(47) In step 1106, an encapsulation mold is provided surrounding the substrate. The encapsulation mold may include multiple pieces which foi in a cavity surrounding the substrate, and preferably includes at least one aperture for injecting encapsulation mold compound into the aperture.

(48) In step 1107, gettering encapsulation mold compound is applied, for example by injection into the cavity formed by the encapsulation mold compound. Gettering encapsulation mold compound may be composed of conventional encapsulation mold compound materials, such as a plastic, resin, or other epoxy mold compound, which are embedded with organic and/or inorganic additives, in order to provide gettering to substrate 101. In one embodiment, only a portion of the encapsulation mold compound includes the organic and/or inorganic additives to provide gettering at a location of the substrate (e.g., backside 715 in FIG. 10). In another embodiment, substantially the entire encapsulation mold compound is embedded with the organic and/or inorganic additives. The gettering encapsulation mold compound attracts contaminants and forms a denude zone on the at least one section of the bulk substrate where the semiconductor devices are formed (see step 1104, supra).

(49) After the gettering encapsulation mold compound is applied, the encapsulation mold may be removed. The encapsulation mold may be removed before or after completing fabrication of the semiconductor assembly, including step 1108 of process 1100 (infra).

(50) In step 1108, external electronic connections may optionally formed to provide external connections for the semiconductor devices and solder bumps. For example, the external electronic connections may be a ball grid array package as shown in FIG. 10, or other external electronic connections known in the art that may be used to form integrated circuits or other semiconductor device assemblies. The external electronic connections may be formed near the device region, for example connecting via solder bumps to the semiconductor devices in the device region, as shown in FIG. 10.

(51) It should be understood that while FIGS. 10 and 11 show the formation of a semiconductor device without an external gettering element as described above with regard to FIGS. 5 through 9, this need not be the case. For example, a semiconductor device including an external gettering element adhered to a backside of the substrate may be encapsulated by a gettering encapsulation mold compound.

(52) The above description and drawings are only to be considered illustrative of specific embodiments, which achieve the features and advantages described herein. Modification and substitutions to specific processes, process conditions, and structures can be made. For example, it should be understood that appropriate materials other than those specifically described in connection with the above embodiments may be used, and that the steps of the processes described above may be performed in a different order than the specific order in which they are described. Accordingly, the embodiments of the invention are not to be considered as being limited by the foregoing description and drawings, but only by the scope of the appended claims.