In situ dry etching procedure to form a borderless contact hole

(1) Field of the Invention

The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to form a borderless contact hole to an underlying conductive region

(2) Description of Prior Art

The trend to micro-minituriaztion, or the ability to fabricate semiconductor devices with features smaller than 0.50 micrometers, has presented difficulties when attempting to form narrow diameter, deep contact holes in a dielectric layer, to expose underlying conductive regions. The use of photoresist as a mask for etching of a thick dielectric layer presents selectivity concerns in regards to a fast removal etch rate of the photoresist, in the dielectric layer etching ambient, therefore not allowing only the photoresist shape to be used as the etch mask. Increasing the thickness of the photoresist mask to accommodate the non-selectivity of the etch ambient only reduces the resolution needed to define deep, narrow diameter openings. The use of a hard mask layer, with increased etch rate selectivity to the material being etched, results in additional process cost as a result of the ex-situ removal of the photoresist shape, performed after the photoresist shape had been used to define the desired opening in the hard mask layer. In addition, ex situ removal of the hard mask layer, also results in unwanted additional process cost.

This invention will describe a process for defining a narrow diameter, contact hole opening, in a thick dielectric layer, featuring in situ removal of the defining photoresist shape, after transferring the desired contact hole shape to a hard mask insulator layer. The present invention will then teach a process in which the desired contact hole opening is in situ formed in the thick dielectric layer, followed by an in situ procedure which defines the desired opening in a bottom insulator stop layer, while removing the hard mask insulator layer from the top surface of the thick dielectric layer. This completely in situ, dry etch procedure, allows the attainment of a borderless contact to be realized. Prior art such as Chiang et al, in U.S. Pat. No. 5,922,515, describe a process for forming a deep contact hole in a dielectric layer, using a hard mask layer, however that prior art does not teach the complete in situ, selective dry etch procedure, described in the present invention featuring in situ removal of the hard mask insulator layer during definition of the contact hole opening in a bottom insulator stop layer.

It is an object of this invention to define a narrow diameter, deep contact hole opening, in a dielectric layer, using an in situ, dry etching procedure.

It is another object of this invention to initially define the desired contact hole opening in a hard mask insulator layer, using a photoresist shape as an etch mask, followed by the in situ removal of the defining photoresist shape.

It is still another object of this invention to use the hard mask as a etch mask to in situ define the desired contact hole opening in a dielectric layer, with the selective, in situ dry etching procedure terminating on an underlying stop layer.

It is still yet another object of this invention to in situ define a borderless contact hole opening in the stop layer, again using the hard mask insulator layer as an etch mask, exposing an underlying conductive region, and resulting in the in situ removal of the hard mask insulator layer from the top surface of the dielectric layer.

In accordance with the present invention an in situ, dry etch procedure, used to form a borderless contact hole opening in a dielectric layer, is described. After defining a desired contact hole opening in an overlying hard mask insulator layer, via a dry etching cycle using a photoresist shape as an etch mask, the photoresist shape is in situ removed. Another in situ, dry etch cycle is next used to selectively transfer the contact hole opening, defined in the overlying hard mask insulator layer, to a thick dielectric layer, with the selective dry etching procedure terminating at the appearance of an underlying insulator stop layer. Finally another in situ dry etching cycle is used to define the desired contact hole opening in the underlying insulator stop layer, exposing a portion of the top surface of a conductive region, resulting in a borderless contact hole opening. The dry etching cycle used for the opening of the insulator stop layer also results in the in situ removal of the exposed hard mask insulator layer.

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

FIGS. 1-5, which schematically, in cross-sectional style, show key stages of fabrication used to define a borderless contact hole opening, using in situ, dry etching procedures.

The method of forming a borderless contact hole opening, in a dielectric layer, using in situ dry etching procedures, will now be described in detail. FIG. 1, schematically shows conductive region 1 , which will be exposed at the conclusion of the borderless contact opening described in this invention. Conductive region 1 , can be a metal silicide layer, such as cobalt silicide, titanium silicide or nickel silicide, which had been formed on a polysilicon, or single crystalline feature. An Insulator layer 2 , such as silicon oxynitride, (SiON), or silicon nitride, (Si 3 N 4 ), is formed on conductive region 1 , at a thickness between about 200 to 600 Angstroms, via plasma enhanced chemical vapor deposition, (PECVD), procedures. Insulator layer 2 , will be used as a stop layer, when defining the narrow diameter contact hole in an overlying dielectric layer. An interlevel dielectric layer, (ILD), 3 , comprised of silicon oxide, or borophosphosilicate glass, (BPSG), using tetraethylorthosilicate, (TEOS), as a source, is next deposited to a thickness between about 5000 to 10000 Angstroms, via PECVD procedures. Insulator 4 a , again comprised of either silicon oxynitride or silicon nitride, is then deposited on ILD layer 3 , at a thickness between about 500 to 3000 Angstroms, again via use of PECVD procedures. Insulator layer 4 a , will serve as an anti-reflective coating, (ARC), layer, allowing optimum resolution of an overlying photoresist shape to be realized. In addition insulator layer 4 a , will serve as a hard mask, to allow the narrow diameter contact hole feature to be transferred to underlying ILD layer 3 , without the use of an overlying photoresist shape. Photoresist shape 5 , is then formed, to a thickness between about 4000 to 6000 Angstroms, featuring opening 6 a , obtained via conventional photolithographic exposure and development procedures, with opening 6 a , featuring a diameter between about 0.06 to 0.35 um. The results of these deposition and photolithographic procedures are schematically shown in FIG. 1 .

A first step of the in situ dry etching procedure is next addressed, resulting in the definition of opening 6 b , formed in insulator layer 4 a , using photoresist shape 5 , featuring small diameter opening 6 a , as an etch mask. This is schematically shown in FIG. 2 . Opening 6 b , in insulator layer 4 a , is formed via a dry etch, or anisotropic, reactive ion etching, (RIE), procedure, performed at a power between about 1000 to 1500 watts, at a pressure between about 50 to 100 mtorr, and using an etch ambient that is comprised with, between about 50 to 100 sccm of CF 4 , between about 5 to 20 sccm of O 2 , and between about 80 to 200 sccm of argon. The first step of the dry etch procedure is performed in a chamber in a dry etch tool, such as a reactive ion etching, (RIE), tool.

The first step of the in situ dry etching procedure is terminated at the appearance of ILD layer 3 , followed by the in situ removal of photoresist shape 5 , performed in the same chamber of the dry etch tool previously used for the first step of the in situ dry etching procedure. The in situ removal of photoresist shape 5 , is accomplished at a power between about 500 to 1000 watts, at a pressure between about 100 to 300 mtorr, and using an ambient comprised with; between about 50 to 100 sccm of O 2 , and between about 10 to 20 sccm of N 2 . The result of the in situ photoresist removal procedure is schematically shown in FIG. 3 .

A second step, of the in situ dry etch procedure is next used to selectively form opening 6 c , in ILD layer 3 . This is schematically shown in FIG. 4 . This in situ, selective, anisotropic RIE step, is performed using insulator layer, or hard mask layer 4 a , featuring opening 6 b , as an etch mask. The second step of the in situ dry etching procedure is performed at a power between about 1000 to 2000 watts, at a pressure between about 40 to 70 mtorr, and using an etch ambient comprised with; between about 5 to 16 sccm of C 4 F 8 , between about 50 to 400 sccm of CO, between about 100 to 500 sccm of argon, and between about 1 to 10 sccm of O 2 . The selectivity of etch rate ratio of ILD silicon oxide layer 3 , to hard mask, SiON layer 4 a , and to SiON stop layer 2 , is between about 20 to 50, to 1, allowing this second step of the in situ dry etch procedure to slow or terminate at the appearance of insulator stop layer 2 . In addition hard mask insulator layer 4 a , is only slightly etched, resulting in thinner, insulator layer, or hard mask insulator layer 4 b, shown schematically in FIG. 4 . The lower selectivity, or etch rate ratio, of ILD layer 3 , to photoresist, would have warranted a thicker photoresist shape to be used, if the photoresist shape were used to define opening 6 c , in ILD layer 3 . The ability to resolve the narrow diameter feature in a thicker photoresist layer, might not be easily attainable and therefore the use of hard mask insulator layer 4 a , as a defining mask is critical. The second step of the in situ dry etch procedure again is performed in the same dry etching chamber, and tool used for the previous procedures.

A third, and final step, of the in situ dry etch procedure is next addressed, to create the small diameter opening in insulator stop layer 2 . Hard mask insulator layer 4 b , is used as an etch mask allowing the third step of the in situ dry etch procedure to define opening 6 d , exposing the top surface of conductive region 1 . This is schematically shown in FIG. 5 . The third step of the dry etch procedure is performed at a power between about 300 to 500 watts, at a pressure between about 50 to 100 mtorr, and using an etch ambient comprised with; between about 20 to 60 sccm of CH 2 F 2 , between about 50 to 100 sccm of argon, and between about 10 to 20 sccm of O 2 . Since the removal rate of conductive region 1 , is small when exposed to this etch ambient, an over etch cycle is used to completely remove hard mask insulator layer 4 b . The use of the insulator stop layer for final definition of small diameter contact hole opening 6 d , results in a borderless contact hole, since misalignment can now be tolerated. The diameter of the small diameter contact hole opening, is identical to opening 6 a , in photoresist shape 5 , between about 0.06 to 0.35 um. The third step of this in situ dry etching procedure was again performed in the same RIE chamber and tool used for the previous dry etching steps.

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.