Method of making a semiconductor device by converting a hydrophobic surface of a dielectric layer to a hydrophilic surface

[0002] The present invention relates to a method of making semiconductor devices, in particular, those that include a dielectric layer that has a hydrophobic surface when initially deposited.

[0003] Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal layers and between metal lines on each layer, capacitance increases. To address this problem, insulating materials that have a relatively low dielectric constant are being used in place of silicon dioxide to form the dielectric layer that separates the metal lines.

[0004] Certain materials that may be used to form low k dielectric layers (e.g., carbon doped oxides) are hydrophobic. Their hydrophobic nature renders it difficult to clean their surfaces, and to bond such materials to other layers. In addition, materials that are coated onto a hydrophobic dielectric layer may lack desirable thickness uniformity.

[0005] To prevent the hydrophobic character of a carbon doped oxide (or other type of hydrophobic dielectric layer) from adversely impacting a process for making semiconductor devices, a hard mask (e.g., one comprising silicon nitride) may be formed on the dielectric layer's surface prior to depositing other materials on that layer. Forming such a hard mask on such a dielectric layer increases the cost of the process for making the devices. In addition, using such a hard mask may increase the dielectric constant of the overall insulating layer (i.e., the combination of the hydrophobic dielectric layer and the hard mask), when compared to an insulating layer that includes the dielectric layer only. As an alternative to forming a hard mask on a hydrophobic dielectric layer to address this issue, certain wet chemicals may be used to modify the dielectric layer's surface chemistry. Because, however, such chemicals are relatively expensive, their use (like adding a hard mask) increases the cost of the process.

[0006] Accordingly, there is a need for an improved process for making a semiconductor device that includes a hydrophobic dielectric layer. There is a need for such a process that converts a hydrophobic surface of such a layer to a hydrophilic one in a relatively inexpensive and unobtrusive manner, enabling improved adhesion characteristics and facilitating surface cleaning. The method of the present invention provides such a process.

[0007] FIGS. 1a-1drepresent cross-sections of structures that may result after certain steps are used to make a semiconductor device in a process that may benefit from application of the method of the present invention.

[0008] FIG. 2 provides a schematic representation of a CVD chamber for depositing a dielectric layer.

[0009] FIGS. 3a-3crepresent cross-sections of structures that may result after certain steps are used to make a semiconductor device in a second process that may benefit from application of the method of the present invention.

[0010] FIGS. 4a-4erepresent cross-sections of structures that may result after certain steps are used to make a semiconductor device in a third process that may benefit from application of the method of the present invention.

[0011] FIG. 5 represents a cross-section of a structure that includes a dielectric layer that has a hydrophobic surface when initially deposited on a substrate, to which the method of the present invention may be applied.

[0012] A method is described for converting a hydrophobic surface of a dielectric layer to a hydrophilic surface. That method comprises forming a dielectric layer on a substrate, then operating a plasma enhanced chemical vapor deposition (“PECVD”) reactor to generate a plasma that converts the surface of that layer from a hydrophobic surface to a hydrophilic surface. In a preferred embodiment of the present invention, the reactor is first operated to form the dielectric layer on the substrate. It is then operated to generate the plasma that converts the surface of that layer from a hydrophobic surface to a hydrophilic surface while the substrate remains in situ inside the reactor.

[0013] In the following description, a number of details are set forth to provide a thorough understanding of the present invention. It will be apparent to those skilled in the art, however, that the invention may be practiced in many ways other than those expressly described here. The invention is thus not limited by the specific details disclosed below.

[0014] The method of the present invention may be used in many contexts. For example, this method may be used when making a semiconductor device that includes a carbon doped oxide containing dielectric layer, e.g., being applied to convert a hydrophobic surface of such a dielectric layer into a hydrophilic surface—which can better adhere to materials that are coated onto it and which can be more easily cleaned. FIGS. 1a-1drepresent cross-sections of structures that may be formed when making a semiconductor device using the method of the present invention. FIG. 1arepresents a structure that includes substrate 100 upon which is formed a first conductive layer 101. First conductive layer 101 is covered by barrier layer 102, which in turn is covered by hydrophobic dielectric layer 103—which may comprise a carbon doped oxide.

[0015] Substrate 100 may be any surface, generated when making an integrated circuit, upon which a conductive layer may be formed. Substrate 100 may include, for example, active and passive devices that are formed on a silicon wafer such as transistors, capacitors, resistors, diffused junctions, gate electrodes, local interconnects, etc . . . . Substrate 100 also may include insulating materials that separate such active and passive devices from the conductive layer or layers that are formed on top of them, and may include previously formed conductive layers.

[0016] Conductive layer 101 may be made from materials conventionally used to form conductive layers for semiconductor devices. Barrier layer 102 serves to prevent an unacceptable amount of the material included in conductive layer 101 from diffusing into dielectric layer 103. Barrier layer 102 also acts as an etch stop to prevent a subsequent via etch step from exposing conductive layer 101 to subsequent cleaning steps. Barrier layer 102 preferably is made from silicon nitride or silicon carbide, but may also comprise other structures that can serve such functions, e.g., a cobalt or tungsten shunt, as is well known to those skilled in the art.

[0017] The structure shown in FIG. 1amay be generated using conventional process steps, as will be apparent to those of ordinary skill in the art. As part of such a conventional process for forming that structure, a PECVD reactor, e.g., PECVD reactor 200 represented by FIG. 2, may be used to form dielectric layer 103 on barrier layer 102 to generate that structure. Because the surface of dielectric layer 103 is hydrophobic, it has poor adhesion qualities and is difficult to clean. By applying the method of the present invention to that surface, however, it may be converted to a hydrophilic surface that may bond better to photoresist and be easier to clean.

[0018] In one embodiment of the present invention, while the FIG. 1astructure remains in situ inside the reactor, that reactor may be operated to generate a plasma that converts the surface of dielectric layer 103 from a hydrophobic surface to a hydrophilic surface. Although preferably retaining the wafer in situ inside the reactor when forming the dielectric layer and converting its surface to a hydrophilic surface, those skilled in the art will appreciate that these steps can be performed separately, e.g., by first forming dielectric layer 103 on barrier layer 102, then placing the resulting structure into a PECVD reactor to convert its surface to a hydrophilic surface.

[0019] To generate the plasma that converts the surface of layer 103 to a hydrophilic surface, a gas that is selected from the group consisting of oxygen, nitrogen, argon, hydrogen, xenon, krypton, nitrous oxide, carbon monoxide, and carbon dioxide may be introduced into reactor 200 in the conventional manner. Alternatively, a mixture of helium and one of these gases may be introduced into reactor 200, or two or more of these gases (with or without helium) may be fed into the reactor. This gas, or gases, may be introduced into reactor 200 at conventional temperatures and pressures. Optimal operating conditions may, of course, depend upon the composition of the gas streams fed into the reactor, the type of reactor used, and the desired properties for the surface of dielectric layer 103. In a preferred embodiment, a plasma is then struck at RF power of between about 100 and about 3,000 watts. Any commercially viable frequency, e.g., 13.56 MHz, 27 MHz, microwave frequencies, etc. . . . , may be used to generate the plasma. The surface of layer 103 is preferably exposed to that plasma for at least about 0.5 seconds and for less than about 20 seconds.

[0020] Exposing dielectric layer 103 to such a plasma can convert its surface from a hydrophobic surface to a hydrophilic one. The depth of that modified surface can be controlled by changing the RF power, reactor pressure, gas stream composition, susceptor temperature, and/or exposure duration. Optimal operating conditions and gas stream makeup will depend upon the desired properties for the surface of layer 103.

[0021] After converting the surface of dielectric layer 103 to a hydrophilic surface, photoresist layer 130 may be deposited onto it, and patterned, to generate the structure represented by FIG. 1b. Because of the hydrophilic nature of the surface of layer 103, photoresist layer 130 may bond to that surface in a satisfactory manner—without requiring a hard mask to be formed on layer 103 prior to forming photoresist layer 130. Via 107 may then be etched, followed by removing the photoresist, generating the structure shown in FIG. 1c. At this stage of the process, via 107 and the surface of dielectric layer 103 must be cleaned. Because the surface of layer 103 is now hydrophilic, it may be cleaned in the conventional manner, without first requiring its surface chemistry to be modified with wet chemicals. Following that cleaning step, conventional process steps are used to remove part of barrier layer 102 and to fill via 107 with a conductive material. A chemical mechanical polishing (“CMP”) step may then be applied to remove excess material to form second conductive layer 105, creating the FIG. 1dstructure.

[0022] The method of the present invention may be applied to other processes for forming semiconductor devices. FIGS. 3a-3crepresent structures that may be formed when making a semiconductor device that includes a dual damascene interconnect. To make such a device, a second layer of photoresist is deposited onto the structure shown in FIG. 1c, then patterned to produce photoresist layer 336, which defines the trench that will be etched into dielectric layer 303—which may comprise a carbon doped oxide. FIG. 3arepresents the resulting structure. When the surface of dielectric layer 303 has been previously converted to a hydrophilic surface, using the technique described above, photoresist layer 336 will bond to layer 303 in an acceptable fashion.

[0023] After forming photoresist layer 336, trench 306 may be etched into dielectric layer 303, as shown in FIG. 3b. Trench 306, via 307, and the surface of layer 303 are then cleaned. Because that surface has been converted into a hydrophilic surface, it may be adequately cleaned using standard cleaning steps. Part of barrier layer 302 is then removed, followed by filling trench 306 and via 307 with a conductive material, then applying a CMP step to remove excess material to form conductive layer 305—generating the FIG. 3cstructure.

[0024] Still another process for making a semiconductor device, which may benefit from use of the method of the present invention, is illustrated in FIGS. 4a-4e. In that process, via 407 is filled with sacrificial light absorbing material (“SLAM”) 408 to create the structure shown in FIG. 4a. That SLAM may comprise a dyed spin-on-polymer (“SOP”) or dyed spin-on-glass (“SOG”) that has dry etch properties similar to those of dielectric layer 403, which may comprise a carbon doped oxide, and light absorbing properties that enable the substrate to absorb light during lithography. SLAM 408 may be spin coated onto the FIG. 1cstructure in the conventional manner.

[0025] By filling via 407 with SLAM 408, substrate reflection that occurs during trench lithography—which could adversely affect dual damascene via and trench formation—may be reduced or eliminated. In addition, filling via 407 with SLAM 408 may eliminate the need to use etch chemistry to etch the trench that is highly selective to dielectric layer 403 over barrier layer 402, to ensure that the trench etch step will not etch through barrier layer 402. When the surface of dielectric layer 403 has been previously converted to a hydrophilic surface, using the method of the present invention, SLAM 408 will bond to layer 403 in an acceptable fashion. Another benefit of the present invention, when applied in this context, is that converting dielectric layer 403's surface to a hydrophilic surface may improve the thickness uniformity of SLAM 408.

[0026] A second layer of photoresist may then be deposited onto SLAM 408, then patterned to produce photoresist layer 436, which defines the trench that will be etched into dielectric layer 403, as shown in FIG. 4b. Trench 406 is then etched into dielectric layer 403 to produce the FIG. 4cstructure. Following that trench etch step, the remaining portions of photoresist layer 436 and remaining portions 409 of the SLAM must be removed. Photoresist 436 may be removed using a conventional photoresist ashing process, or, alternatively, by exposing it to a plasma generated from a forming gas—e.g., a gas that includes up to about 5% hydrogen in nitrogen, helium and/or argon.

[0027] After removing the photoresist, remaining portions 409 of the SLAM must be removed, along with any residues resulting from the photoresist removal step. Because the surface of dielectric layer 403 has been converted into a hydrophilic surface, the remaining portions of the SLAM may be removed, and via 407 and trench 406 cleaned, using a standard wet etch step. Part of barrier layer 402 may then be removed to generate the structure represented by FIG. 4d. Filling trench 406 and via 407 with a conductive material, then applying a CMP step to remove excess material to form conductive layer 405, generates the FIG. 4estructure.

[0028] The process of the present invention provides a convenient and inexpensive way to convert a hydrophobic surface of a dielectric layer into a hydrophilic surface, which can improve that surface's adhesion properties and make it easier to clean. Although the foregoing description has demonstrated how certain processes for making semiconductor devices can benefit from the use of this method, the method of the present invention may be used in many other contexts. In this respect, FIG. 5 represents a cross-section of a structure that includes hydrophobic dielectric layer 500 deposited on substrate 501. The method of the present invention may be applied to convert a hydrophobic surface of dielectric layer 500 to a hydrophilic surface, regardless of how substrate 501 is constituted, regardless of the type of hydrophobic material that makes up dielectric layer 500, and regardless of the application to which the structure shown in FIG. 5 is employed.

[0029] Although the foregoing description has specified certain steps, materials, and equipment that may be used in the above described method for converting a hydrophobic surface of a dielectric layer to a hydrophilic surface, those skilled in the art will appreciate that many modifications and substitutions may be made. Accordingly, it is intended that all such modifications, alterations, substitutions and additions be considered to fall within the spirit and scope of the invention as defined by the appended claims.