1. Technical Field
This disclosure relates to fuses for semiconductor devices and more particularly, to electrical fuses with characteristics to enhance the efficiency of fuse programming.
2. Description of the Related Art
In semiconductor devices, fuses are employed in a variety of applications. For example, fuses are employed to enable redundant elements to be employed in the case of failures encountered on the semiconductor device. One type of fuse includes an electrically programmable fuse. These fuses may include poly-silicide. Poly-silicide includes polycrystalline silicon and an overlayer of silicide, such as a metal silicide. The electrically programmable fuses typically include an appropriately shaped polysilicon layer that is silicided to obtain a poly-silicon/metal silicide stack structure.
Referring to FIG. 1, a layout (shape) of a fuse 10 is shown. Fuse 10 includes a fuse link 12, an anode 14 and a cathode 16. Current crowding takes place around a location 18 where the fuse link 12 abuts the cathode 16, when a bias is applied to set or program the fuse. The current crowding initiates electro-migration effects at the fuse link 12 resulting in further current crowding and finally for appropriate bias conditions, the poly-silicide line melts or the silicide agglomerates to result in an open circuit or a high resistance state (i.e., the fuse gets programmed) at the location 18. The effect of material migration due to, for example, electro-migration can be increased at the cathode-fuse link junction by increasing the ratio of Lcathode to Lfuse, as this encourages current crowding. In typical layouts, the thickness of the fuse link 12, the anode 14 and the cathode 16 are the same thickness because they are formed on the same level. Therefore, the lengths of Lcathode and Lfuse are determinative of the effective cross-sectional area of the fuse link/anode intersection. A polysilicon layer 20 and a suicide layer 22 as shown in FIG. 2 are provided at a uniform thickness for the fuse link 12, the anode 14 and the cathode 16. A nitride capping layer 24 is also provided over layers 20 and 22.
Typical electrically programmable fuses require current flow and voltage levels at an appropriate level for a requisite amount of time to program the fuse. Therefore, a need exists for an apparatus and method to initiate and aid mass transport processes near a fuse link/cathode intersection to reduce the programming current, voltage and time. These reductions are desirable for the electrical fuse technology to minimize energy consumption and the cost of programming fuses.
A fuse for semiconductor devices, in accordance with the present invention, includes a cathode formed from a first material, an anode formed from a second material and a fuse link connecting the cathode and the anode and formed from the second material. The second material is more susceptible to material migration than the first material when the fuse is electrically active such that material migration is enhanced in the second material.
In alternate embodiments, the first material may include polysilicon, and the second material may include a silicide. The second material may also include silicided polysilicon. The cathode preferably has a larger cross-sectional area than the fuse link. The first material and the second material between the cathode and the fuse link may provide an interface which is substantially perpendicular to a current flow direction through the fuse link. The second material preferably includes electromigration properties which are greater than the electromigration properties of the first material. The second material may include one of Al, Cu and Au. The first material may include one of W, Mo and TiN. The second material/first material preferably include pairs which include one of AI/W, Cu/TiN and Cu/W, respectively.
Another fuse for semiconductor devices, in accordance with the present invention, includes a conductive pattern formed on a substrate, the conductive pattern forming a cathode on a first end portion. A fuse link is connected to the cathode and an anode. The anode is formed on a second end portion of the conductive pattern. A material having a higher mass transport rate than material employed to form the conductive pattern is formed on the anode and the fuse link to provide a material migration susceptibility for the fuse link which is greater than the material migration susceptibility of the cathode such that when the fuse is electrically active material migration is enhanced in the fuse link.
In other embodiments, the material of the conductive pattern may include polysilicon. The material having a higher mass transport may include a silicide. The cathode and the fuse link may provide an interface which is substantially perpendicular to a current flow direction through the fuse link. The cathode preferably has a larger cross-sectional area than the fuse link.
Still another fuse for semiconductor devices, in accordance with the present invention, includes a polysilicon pattern formed on a substrate. The polysilicon pattern forms a cathode on a first end portion. A fuse link is connected to the cathode and an anode. The anode is formed on a second end portion of the polysilicon pattern. A silicide material is formed on the anode and the fuse link to provide an electromigration susceptibility for the fuse link which is greater than the electromigration susceptibility of the cathode, such that, when the fuse is electrically active, electromigration is enhanced in the fuse link.
In alternate embodiments, the cathode preferably has a larger cross-sectional area than the fuse link. The polysilicon of the cathode and the silicide of the fuse link may provide an interface which is substantially perpendicular to a current flow direction through the fuse link.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.