The present invention relates to the field of manufacturing of integrated circuits and more specifically to using sloped sidewalls in resist and dielectric layer openings to improve the deposition quality of conductors or interconnections.
The continued shrinking of integrated circuit switching devices has resulted in the geometries of electrically conductive interconnects also being reduced, as well as the reduction of bonding pad passivation openings, causing problems with step coverage of subsequent metalization deposition.
Current passivation processes create steep sidewalls. This can cause step coverage issues for subsequent metalization steps. Step coverage problems can occur due to the directional nature of the deposition process, resulting in a shadowing effect or a Damascene-type application of metals or conductors to the bond pad area. One solution is to control the heating during the metalization process which results in surface diffusion. Another solution is to rotate the substrate during metalization will reduce the shadowing effect. These two approaches to solving the step coverage problem results in improvements, but still does not produce a continuously uniform film.
When one or more conductive compounds or metals are formed, the steeply sloped sidewall geometry of the band pad opening 121 causes a non-uniform or discontinuous deposition profile. As illustrated in
Described is a method that forms a sloped sidewall profile in a bond pad opening that will facilitate and improve the uniformity of a conductive layer that is deposited over and within the bond pad opening. The sloped sidewall used in conjunction with a metalization or conductor deposition process results in a continuous and uniform thickness. By using a sloped sidewall angle opening over the bond pad, a shadowing or Damascene effect during a metalization or deposition process is reduced or eliminated.
First, a bond pad is formed on a silicon substrate followed by the formation of a dielectric layer over the bond pad and the silicon substrate. The dielectric material formed over the bond pad is normally a non-conductive material such as a nitride, an oxide, or an oxy-nitride. The dielectric layer may be composed of a single or multiple layers of dielectric materials. The typical thickness of the dielectric layer may be up to several microns (um).
In one embodiment, as show in
In
A curved and sloped sidewall in the dielectric material opening to the bond pad may be formed using a straight sidewall profile in the resist mask, followed by using an isotropic etch process that undercuts the photoresist opening. This method will produce a curved sidewall in the dielectric layer over the bond pad opening.
In one embodiment of the invention, a sloped sidewall is formed in a photoresist opening by heating the patterned resist to or beyond the photoresist glass transition temperature (Tg). The photoresist material will reflow, and the sidewall angle of the photoresist opening may be controlled to vary the sidewall angle of the photoresist opening. The resist opening sloped sidewall is used to subsequently expose and form a sloped opening to a bond pad. A sloping sidewall may be formed over any dielectric or dielectric substitute that may benefit from having a sloping sidewall angle.
A variety of standard resist materials may be used, such as an I-Line resist, however, the invention is applicable to any chemically amplified (CAR) or non-chemically amplified resist material, such as I-line, g-line, ArF, EUV, or resists sensitive to 248 nm, 193 nm, or 157 nm light sources. Typical 193 nm resists include acrlyate, methacrylate and other hybrids. Also, the geometry size does not particularly matter, and it is possible to implement the process using 248 nm geometries or smaller.
In
In one embodiment, the patterned resist is heated by heating the underlying substrate from the non-photoresist side of the wafer. Heat is transferred through the wafer/substrate and begins heating the photoresist mask from the substrate side of the photoresist layer. The patterned photoresist layer that is in contact with the underlying substrate reaches or exceeds the glass transition temperature and begins to reflow. In this embodiment, an I-Line resist material, sensitive to 365 nm, is used and heated to 165 degrees Centigrade for 60 seconds. However, in other embodiments, the method works with other resist material such as I-line and ArF, other resists that are also sensitive to 248 nm or 193 nm, and materials sensitive to other light sources.
The temperature of the reflow step is dependant on the glass transition temperature (Tg) of the material, but typical processing conditions are 160 to 180 degrees Centigrade for 60 to 90 seconds on a proximity bake hot plate. This range would be also be relevant for other I-line, ArF, chemically amplified resists (CAR), and DUV (deep ultra-violet) resists. Generally, using temperatures that are higher over the chosen material's Tg will result in sidewalls that are more sloped or have a shallower angle. General ranges that will enable sloped sidewalls in resist openings are 140C to 175 degrees Centigrade and time ranges of 50 to 90 seconds.
In general, the I-line and ArF resists have higher glass transition temperatures (Tg) than other 248 nm sensitive resists and would use the higher end of the temperature range described above. Other resist materials with sensitivities in the 248 nm or 193 nm wavelengths could also be used, with the temperature and time parameters depending on the glass transition temperature (Tg) of the resist polymer.
Also, there is a trade off between time and temperature. A process that uses higher temperatures for shorter time periods (e.g. 190C for 15 sec) may produce similar results as 165C for 60 seconds. Alternate temperature ranges for the reflow step may be necessary when using other classes of resist materials, but can be characterized and also used to create sloped resist openings. Further variations in the resist material, and temperature profile may also vary the slope angle of the photoresist sidewall profile, depending on the specific resist material and heating method that is used.
The substrate or wafer may also be heated by a variety of procedures including direct contact, heated gas, or irradiation. Another embodiment to achieve a sloped sidewall in a photoresist opening is implemented by heating the wafer from the resist side of the substrate. In this embodiment, the resist layer will form rounded corners on the top portion of the resist layer. The softening of the resist surface will propagate through the resist opening and form a sloped sidewall profile. Again, further variations in the resist material, temperatures, time, and temperature rise may vary the slope angle of the photoresist sidewall profile, depending on the specific resist material that is used in the process.
As described above and shown in
After the sloped profile in a photoresist opening has been formed, a subsequent etch process will then remove the dielectric material and create an opening to the bond pad. The etch process exposes the bond pad and also approximately transfers the slope profile of the resist to the dielectric material formed over the bond pad. Similar to the slope profile of the resist layer, the opening in the dielectric material will be wider at its upper portion in comparison to its lower portion where the bond pad will be exposed.
In one embodiment, the etch process is tailored to balance the etch selectivity of the resist in comparison to the dielectric layer to transfer the photoresist sloped profile to the dielectric layer. The etch process should be selective as to etch the dielectric material below the patterned resist at a rate approximately equal to or faster in comparison to the rate of removing the resist material.
As illustrated in
In one embodiment, the etch process comprises the use of a generic plasma dielectric etch, including some optimization of the power and gas flows to vary the slope in the etched dielectric opening.
In
An angle of the sloped dielectric sidewall is preferred at approximately 45 degrees, for example within the range of 40 to 50 degrees, to improve the uniformity of metal deposition. However, the profile angle may be controlled to maintain a higher angle, for example, to accommodate a higher density of bond pad openings. Also, the metalization critical angle varies with both the materials used and the chosen deposition process. The critical angle will be related to the sloped profile angle of the bond pad opening, but alternate embodiments exists outside of the dielectric slope angle range of 40 to 50 degrees. A shallow slope angle in the dielectric sidewall profile will successfully facilitate a subsequent etch metalization or conductor deposition, however, steeper angles in the photoresist sidewall may also improve a subsequent conductor deposition or metalization process.
The sloped profile of the dielectric opening that exposes the bond pad is now ready for a subsequent metalization process. As shown in
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art. In other instances well known semiconductor fabrication processes, techniques, materials, equipment, etc., have not been set forth in particular detail in order to not unnecessarily obscure the present invention.