Crack stop formation in integrated circuit chip manufacture

Abstract: A simplified crack stop formation compatible with shallow fuse etch processes which are utilized for modern low-cost redundancy designs using upper level metal fuses. A modified last level metallization (LLM) etch according to the invention allows a high-productivity single step bondpad/fuse/crack stop etch. The stack of metal films formed at the edge of the dicing channel is readily removed with a modified LLM etch prior to dicing causing the insulator films covering the dicing channel to be physically separated from the insulators coating the electrically active chip areas. The separation prevents cracks that could propagate through the insulators of the dicing channel in to the active chip.

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to the manufacture of integrated circuit chips (or microelectronic devices) and, more particularly, to the formation of crack stops which separate the dielectric films on a semiconductor substrate. BACKGROUND OF THE INVENTION Multiple integrated circuits (ICs) are formed on a semiconductor wafer and then separated into chips by dicing the wafer. During chip dicing, sometimes cracking of dielectric films on the semiconductor substrates occurs. The cracks propagate over long distances into the active chip area causing reliability problems. Therefore, a crack stop is usually formed by interruption of the dielectric film. Thus, cracks which are possibly created during chip dicing cannot penetrate the chip area. For a high-productivity process, the crack stop formation has to be combined with already existing processes. Usually, a combined bondpad/fuse/crack stop etch is employed. The fuse etch requires a well defined etch into the dielectric films (passivation and interlevel dielectrics). For fuses lying close to the substrate level (e.g., polysilicon or polycide fuses), the deep fuse etch usually reaches lower level metallizations which consist of different material than the upper metallization. Thus, a subsequent etch (for example, a hydrogenperoxide wet etch) is capable of removing a lower level metallization (such as tungsten) selectively from the upper level metallization (such as aluminum) which is already opened at the bondpads. As a result, a crack stop can easily be formed by a combined bondpad/fuse/crack stop etch by simply adding a selective wet etch of the lower metallization. However, for advanced design of fuses lying on upper metallization levels, the fuse etch is not deep enough to reach lower metallization levels with a different material. Therefore, other strategies for the crack stop formation have to be considered. From EP-A- 605 806 it is known to provide a crack stop formed by creating and metallizing a groove and selectively etching out the metal in the groove after the final passivation. DISCLOSURE OF THE INVENTION According to the invention, two approaches are used to form a crack stop, each approach avoiding a dedicated crack stop pattern and etch step for high-productivity manufacturing of integrated circuits. In both approaches, a metal stack at least up to the metallization level which will be completely opened during the fuse etch is created along the crack stop line. This includes also contact and via levels which have to be preformed as connected lines. It is essential that there is no continuity of the dielectric films between dicing and chip area. The first approach used to form a crack stop leaves the metal stack as it is. Due to the different physical properties of metals compared to dielectric films, the crack cannot penetrate through the metal line. The second approach requires a last level metallization (LLM) patterning by etching, such as reactive ion etching (RIE). During LLM etching, the LLM will be etched off at the crack stop line. Then, the underlying contacted metallization levels consisting of the same metallurgy can be etched by a slightly prolonged modified LLM etch. The following combined bondpad/fuse/crack stop etch results in further removal of interlevel dielectric films. Thus, lower level metallization of different metallurgy is opened which can be optionally removed by a subsequent etch process working selectively with respect to LLM metallurgy (bondpad). Thus a simplified crack stop formation is provided which is compatible with shallow fuse etch processes which are utilized for modern low-cost redundancy designs using upper level metal fuses. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention will now be described with reference to the drawings, in which: Figure 1 is a cross-sectional view schematically showing a complete metal stack including last level metallurgy in a semiconductor wafer structure according to the invention; and Figure 2 is a cross-sectional view schematically showing the result of a modified last level metallurgy etch and fuse etch of the metal stack of Figure 1. DETAILED DESCRIPTION OF THE INVENTION Referring now to Figure 1, there is shown a complete metal stack, before last level metallurgy (LLM) etch. This example shows contacts to substrate (CS), three metallization levels (M0, M1, M2) and two via levels (C1, C2). The metal stack is formed at least up to the metallization level which will be completely opened during the fuse etch along the crack stop line. The LLM is represented here by metallization M2 and may be, for example, aluminum or an aluminum alloy. The via level C2 and the metallization level M1 just below the LLM metallization M2 are the same or similar metallurgy, in this example, aluminum or aluminum alloy. The metal stack includes also contact and via levels which have to be preformed as connected lines. This lower level metallurgy is represented by the levels CS, M0 and C1 and may include, for example, a chemical vapour deposition (CVD) tungsten. Representative compositions of the various levels shown in Figure 1 are listed below: M2/C2 Ti/AlCu/TiN M1 Ti/TiN/AlCu/Ti/TiN C1 Ti/TiN/CVD W M0 Ti/TiN/CVD W CS Ti/TiN/CVD W Metallizations M1 and M2 may also be composed of multiple layers of refractory films and other aluminum alloys. The first approach to crack stop formation according to the invention leaves the metal stack as it is, as generally illustrated in Figure 1. Due to the different physical properties of metals compared to dielectric films, the crack cannot penetrate through the metal line. The second approach is illustrated in Figure 2 and requires a last level metallization (LLM) patterning by etching, such as reactive ion etching (RIE). The LLM contact (M2/C2) to the underlying metallization (M1) is etched off at the crack stop line. Then, the underlying contacted metallization levels consisting of the same metallurgy (M1) can be etched by a slightly prolonged modified LLM etch, resulting in the dashed line of Figure 2. At this point in the process, a partial metal stack (C1/M0/CS) remains and serves as the crack stop. The process can be taken further with a combined bondpad/fuse/crack stop etch resulting in further removal of interlevel dielectric films, as illustrated by the full line in Figure 2. Thus, the lower level metallization (C1/M0/CS) of different composition is opened which can be removed by a subsequent etch process working selectively to the LLM metallurgy (bondpad). The modified LLM etch according to the invention allows a high-productivity single step bondpad/fuse/crack stop etch. The remaining stack of metal films formed at the edge of the dicing channel may be readily removed after the modified LLM etch prior to dicing causing the insulator films covering the dicing channel to be physically separated from the insulators coating the electrically active chip areas. The separation prevents cracks that could propagate through the insulators in the dicing channel into active chip area.

Claims: A semiconductor wafer structure comprising: a plurality of integrated circuit areas formed on the wafer from a plurality of metallization and dielectric levels for dicing into individual integrated circuit chips; and a metal stack line defining a crack stop line between said integrated circuit areas and dicing channel areas, said metal stack line being formed from an upper level metallization (M1, C2, M2) including a last level metallization (M2) and an underlying level of metallization (M1) connected by a via level metallization (C2), the underlying metallization and the via metallization having the same or similar composition as the last level metallization (M2), wherein said upper level metallization is etchable to open fuses formed elsewhere in said wafer structure, and a lower level metallization (CS, MO, C1) reaching from the wafer to said upper level metallization, said lower level metallization (CS, MO, C1) including a lower metallization level (MO), a contact level (CS) and a via level (C1), said contact and via levels being preformed as connected lines, said lower level metallization being in contact with said upper level metallization and wherein the composition of the lower level metallization is different from the composition of the upper level metallization and is selectively etchable with respect to the upper level metallization. The semiconductor wafer structure of claim 1 wherein said upper level metallization comprises aluminium or an aluminium alloy and said lower level metallization comprises tungsten. A method of forming a crack stop in a semiconductor wafer structure as claimed in claim 1 or claim 2 comprising the steps of: patterning by etching the last level metallization (M2) and via level metallization (C2) to the underlying level of metallization (M1) in a combined etch to open fuses elsewhere in said wafer structure; and further etching the underlying level of metallization (M1) at the crack stop line by a prolonged etch used in patterning the last level metallization, whereby a partial metal stack remains and serves as said crack stop. A method as claimed in claim 3 in which said lower level metallization is revealed by said prolonged etch, further comprising the step of selectively etching said lower level metallization along said crack stop line to form a separation serving as a crack stop between said integrated circuit areas and dicing channel areas on the wafer structure.

Inventors: MITWALSKY ALEXANDER, RYAN JAMES GARDNER, MITWALSKY, ALEXANDER, RYAN, JAMES, GARDNER
Applicants: IBM, SIEMENS AG, INTERNATIONAL BUSINESS MACHINES CORPORATION, SIEMENS AKTIENGESELLSCHAFT
Application year: 1997
Main classification: H01L23
IPC codes: H01L23, H01L21