Method to reduce the moisture content in an organic low dielectric constant material

(1) Field of the Invention

The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to reduce the moisture content in an organic, low dielectric constant, (low k), layer, used to passivate metal interconnect structures.

(2) Description of Prior Art

The use of more conductive metal interconnect structures, comprised of low resistivity metals such as copper, has resulted in decreases in performance degrading RC delays, when compared to counterparts fabricated with more resistive aluminum, or tungsten interconnect structures. In addition the use of low dielectric constant, (low k), materials. have allowed the capacitance value of RC delays to be significantly reduced. Inorganic spin on glass, (SOG), layers, such as silicon oxyfluoride, (Si x OF y ), or fluorinated silicate glass, (FSG), layers, with dielectric constants as low as 3.4, have been used to replace silicon oxide layers, exhibiting higher dielectric constants, and thus presented higher capacitance values, than FSG layers. Other low k materials, such as an organic layer of poly arylene ether, (PAE), featuring a dielectric constant between about 2.6 to 2.8, is also an attractive low k material, to be used in combination with copper interconnect structures, to result in the desired reductions in RC delay. However when using low k materials such as PAE, or other low k organic materials, the moisture absorbed by the low k organic material, if not reduced, can result in deleterious effects, such as loss of adhesion of the low k material, to overlying, and underlying layers, as well as corrosion of adjacent metal materials, such as copper interconnect structures.

This invention will describe a process for reducing the moisture content in organic low k materials, even if the low k organic material were exposed to the atmosphere for a period of time as great as three months. A high density plasma, (HDP), nitrogen treatment, or other nitrogen type treatments, are used to reduce the moisture in low k materials, without degrading the low k value of this material. The nitrogen treatment can be applied to PAE layers, as well as other organic, low k materials, such as FLARE, (Fluorinated polyARlene Ether polymers), HOSP, (Hydrido Organo Siloxane Polymer), LOSP, (Low Organic Siloxane Polymer). Prior art such as Chen et al, in U.S. Pat No. 5,866,945, as well as Ouellet, in U.S. Pat. No. 5,270,267, describe methods for treating SOG layers, in hydrogen, to restore dangling bonds, and to remove moisture from the SOG layer. However these prior arts do not described the key feature of this present invention in which an organic low k material, such as PAE, is treated in a nitrogen ambient, to reduce the moisture content in the organic low k material, even after the organic low k material had been exposed to the atmosphere for as long as three months.

It is an object of this invention to form a low k layer, overlying, and between, metal interconnect structures.

It is another object of this invention to use an organic material, with a dielectric constant below 2.8, for the low k layer.

It is still another object of this invention to perform a procedure, in a nitrogen ambient, to reduce the moisture content in the organic low k dielectric layer, even when the organic low k layer had been exposed to the atmosphere up to three months.

In accordance with the present invention a method of forming an organic low k layer, located overlying, and between, metal interconnect structures, is described. After formation of metal interconnect structures, overlying, and contacting, conductive regions, such as lower level metal interconnect structures, or active device regions, in a semiconductor structure, an organic layer, such as poly arylene ether, (PAE), with a dielectric constant of less than 2.8, is applied on the underlying metal interconnect structures. A nitrogen treatment, performed in either a high density plasma, (HDP), tool, or in conventional furnaces, is used to reduce the moisture content of the organic low k layer. The nitrogen treatment is effective in reducing the moisture content of organic low k layers, even for the case in which the organic low k layer had been exposed to the environment for a time period of up to three months.

The object and other advantages of this invention are best described in the preferred embodiment with reference to the attached drawings that include:

FIG. 1, which schematically, in cross-sectional style, shows metal structures prior to application of an organic low k layer.

FIG. 2, which schematically, in cross-sectional style, shows an organic low k layer on underlying metal structures, comprised with included water molecules.

FIG. 3, which schematically, in cross-sectional style, shows an organic low k layer, with removed water molecules after a high density plasma nitrogen treatment.

The method of forming an organic low k layer, and of reducing the moisture content in the organic low k layer, will now be described in detail. FIG. 1, schematically shows conductive regions 2 , embedded in insulator layer 1 . Conductive regions 2 , can be metal interconnect structures, comprised of a metal layer chosen from a group that includes an aluminum based material, an aluminum layer, or a tungsten layer. Conductive regions 2 , can also be metal plug structures, again comprised of either tungsten or aluminum, overlying and contacting, an underlying, lower metal interconnect structure, (not shown in the drawings), or overlying and contacting an active device region, in a semiconductor substrate, (not shown in the drawings) Insulator layer 1 , can be a silicon oxide layer, or a borophosphosilicate glass layer. Metal interconnect structures 3 , comprised of a metal chosen from a group that includes copper, aluminum-copper, or tungsten, is formed overlying and contacting conductive regions 2 . Metal interconnect structures 3 , are formed via deposition of the metal layer, via plasma vapor deposition, (PVD), procedures, to a thickness between about 2000 to 12000 Angstroms, followed by patterning of the metal layer, via conventional photolithographic and reactive ion etching, (RIE), procedures, using Cl 2 or SF 6 as an etchant. The photoresist shape, used as a mask for definition of metal interconnect structures 3 , is then removed via plasma oxygen ashing and careful wet cleans.

An organic low k layer 4 a, is next applied, via spin on procedures, resulting in organic low k layer 4 a, located on, and located between metal interconnect structures 3 . To obtain the desired low k, needed for reduction in capacitance, and thus increases in performance, the low k organic layer is chosen from a groups that includes: PAE, (Poly Arylene Ether), FLARE, (Fluorinated Arylene Ether), HOSP, (Hydrido Organo Siloxane Polymer), and LOSP, (Low Organic Siloxane Polymer), all with a dielectric constant below 2.8. The organic low k layer 4 a, is this case comprised of PAE, shown schematically in FIG. 2, is applied to a thickness between about 3000 to 10000 Angstroms, exhibiting a dielectric constant between about 2.6 to 2.8. A post application, curing procedure, performed at a temperature between about 350 to 450° C., in a nitrogen ambient, for a time between about 30 to 120 min, is used to remove solvents, incorporated in PAE layer 4 a, during the application procedure. However there exists a propensity for organic low k layers, to absorb moisture from the environment. Water molecules 5 , are shown schematically, throughout organic low k layer 4 a. The level of water absorbed in PAE layer 4 a, increases with the amount of time PAE layer 4 a, is exposed to air. Therefore if a tool needed for a subsequent procedure, is down for maintenance or repair, or if samples, with exposed PAE surfaces are awaiting an engineering change, involving the creation of a new photolithographic design, the level of moisture absorbed into the exposed organic low k layer, can be great enough to adversely influence the yield and reliability of the devices using the organic low k layers. For example excess moisture in organic low k layer 4 a, can result in a loss of adhesion between the organic low k layer, and underlying, or overlying materials. The excess moisture, in organic low k layer 4 a, can also result in oxidation of, or corrosion of, metal interconnect structures 3 .

A method of removing water molecules 5 , or reducing the moisture content of organic low k layer 4 a, comprised in this case with PAE, is next addressed. A nitrogen treatment, performed using either high density plasma, (HDP), procedures, or performed using other type procedures in a nitrogen ambient, are performed at a temperature between about 350 to 450° C., for a time between about 0.5 to 2.0 min, using a power between about 250 to 1000 watts, and a pressure between about 50 to 200 mtorr. The HDP treatment removes water molecules from organic low k layer 4 a, resulting in organic low k layer 4 b, without the absorbed water molecules 5 . This is schematically shown in FIG. 3 . The extended nitrogen treatment does not change the dielectric constant, for the organic low k layer, as evidenced by the dielectric constant of PAE layer 4 b, still between about 2.6 to 2.8, after a 2 min. treatment, HDP nitrogen treatment. This nitrogen treatment is successful in reducing the moisture content, in organic low k layers, even after the organic low k layer was left exposed to the environment for a period of time as long as three months.

While this invention has been particularly shown and described with reference to, the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of this invention.