1. Field of the Invention
The embodiments of the invention generally relate to semiconductor transistors and more particularly relate to a method that utilizes a hard mask in combination with a photoresist mask during the source/drain impurity implantation processing to eliminate undesirable damage to the source/drain regions when the hard mask is removed.
2. Description of the Related Art
Complimentary metal oxide semiconductor (CMOS) transistors utilize transistors that have opposite types of characteristics depending upon the dopants used. These opposite type transistors are commonly referred to as positive-type (P-type) and negative-type (N-type) transistors.
When implanting impurities for the source/drain regions, an organic photoresist can be patterned to provide an implant block mask that protects one type of transistor while the impurities are implanted into the opposite type transistor. However, the process of removing this photoresist may damage the source/drain regions. More specifically, dopant loss during stripping of the implant block mask resist is a problem, especially as scaled devices require shallower and highly doped junction formation. The problem is most serious for the S/D (source and drain) extension implantation. The loss of the dopant from the extension implanted area under the spacer causes a severe degradation in series resistance of the field effect transistor (FET) device because there is no silicide formed under the spacer.
When an organic photoresist is used as the implant block mask, a “crust” layer is formed by heavy ion bombardment during the ion implantation. The crust layer is a highly polymerized carbon rich compound which is not easily etched without a strong oxidizing etch such as O2RIE or high temperature wet S/P (sulfuric acid and hydrogen peroxide). However, these strong oxidizing etches oxidize the exposed implanted silicon substrate and, as a result, a significant amount of the dopant can be lost.
In view of these issues, disclosed herein is a method of manufacturing an integrated circuit structure that uses a combination of a hard mask and a photoresist in order to reduce damage to implanted impurities. The method implants a first-type of channel implant in a first area of a substrate and implants a second-type of channel implant in a second area of the substrate to form the well regions of different transistors. A shallow trench isolation region is formed in the substrate between the first-type of channel implant and the second-type of channel implant. The method also forms gates above the well regions by forming at least one first gate conductor above the first area of the substrate and at least one second gate conductor above the second area of the substrate. The gate formation process includes any necessary gate oxides, gate caps, etc.
Rather than forming conventional organic photoresists to accomplish source and drain doping, the present embodiments form a first hard mask over the first gate conductor(s), the second gate conductor(s), and the substrate. The first hard mask comprises an oxide, a nitride, etc. Then, a first organic photoresist is patterned over the first hard mask so as to leave the first organic photoresist on areas of the first hard mask that are above the first area of the substrate. The method then removes the portions of the first hard mask that are not protected by the first organic photoresist to leave the first hard mask on the first area of the substrate and not on the second area of the substrate.
Once the first organic photoresist has been used to pattern the first hard mask, the method removes the first organic photoresist and implants second-type impurities in the second area of the substrate to form second source and drain regions (e.g., source drain extensions) adjacent the second gate conductor. The method then grows second spacers on the second gate conductor and implants additional second-type impurities in the second area of the substrate to form additional second source and drain regions adjacent the second source and drain extensions.
The first hard mask is then removed using a wet etching process. Then, the method forms a second hard mask over the first gate conductor(s), the second gate conductor(s), and the substrate. As with the first hard mask, the second hard mask comprises an oxide, a nitride, etc. For example, the first hard mask and the second hard mask can comprise silicon nitride (Si3N4), compositions of SiGeOx such that Ge more than 60% (but less than 100%) relative to Si, etc. The method also patterns a second organic photoresist over the second hard mask, to leave the organic photoresist on areas of the second hard mask that are above the second area of the substrate. The method similarly removes portions of the second hard mask not protected by the organic photoresist to leave the second hard mask on the second area of the substrate and not on the first area of the substrate.
As with the first doping process, the method then removes the second organic photoresist and implants first-type impurities in the first area of the substrate to form first source and drain regions (e.g., source and drain extensions) adjacent the first gate conductor. First spacers are then grown on the first gate conductor and additional first-type impurities are implanted in the first area of the substrate to form additional first source and drain regions adjacent the first source and drain extensions.
After performing such a doping process, the method removes the second hard mask using a wet etching process and then silicides the first gate conductor, the first source and drain regions, the first source and drain extensions, the second gate conductor, the second source and drain regions, and the second source and drain extensions.
The first-type of channel implant, the first gate conductor, the first source and drain extensions, and the first source and drain regions combine to form a first-type transistor. The second-type of channel implant, the second gate conductor, the second source and drain extensions, and the second source and drain regions combine to form a second-type transistor.
The wet etching process used to remove the first and second hard masks is selective to the substrate, the first-type impurities, and the second-type impurities. Therefore, the wet etching process does not damage the substrate, the first source and drain extensions, the second source and drain extensions, the first source and drain regions, or the second source and drain regions.
As mentioned above, the first and second hard mask can comprise silicon nitride (Si3N4), SiGeOx with Ge at least 60% relative to Si) etc.; however, the first hard mask and the second hard mask can be formed by growing a silicon oxide (SiO2) liner on the first gate conductor, the second gate conductor, and the substrate; and depositing a germanium (Ge) layer on the silicon oxide liner. Alternatively, the first hard mask and second hard mask can be formed by depositing a silicon nitride (Si3N4) liner on the first gate conductor, the second gate conductor, and the substrate followed by growing a silicon dioxide (SiO2) layer on the silicon nitride liner.
Therefore, as shown above, instead of using an organic photoresist as an implant blocking mask, an inorganic hard mask material is used as the blocking mask. The hard mask material is chosen so that, after the implantation, the material can be easily removed selectively to the implanted silicon substrate without causing any damage to the implanted source/drain regions or their extensions.
The embodiments of the invention will be better understood from the following detailed description with reference to the drawings, which are not necessarily drawing to scale and in which
The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description.
Disclosed herein is a method of manufacturing an integrated circuit structure that uses a combination of a hard mask and a photoresist in order to reduce damage to implanted impurities. As shown in flowchart form in
The method also forms gates above the well regions by forming at least one first gate conductor above the first area of the substrate and at least one second gate conductor above the second area of the substrate in item 106. The gate formation process includes any necessary gate oxides, gate caps, etc.
Rather than forming conventional organic photoresists to accomplish source and drain doping, the present embodiments form a first hard mask over the first gate conductor(s), the second gate conductor(s), and the substrate in item 108. The first hard mask comprises an oxide, a nitride, etc. Then, a first organic photoresist is patterned over the first hard mask (110) so as to leave the first organic photoresist on areas of the first hard mask that are above the first area of the substrate. The method then removes the portions of the first hard mask that are not protected by the first organic photoresist (112) to leave the first hard mask on the first area of the substrate and not on the second area of the substrate.
Once the first organic photoresist has been used to pattern the first hard mask, the method removes the first organic photoresist (114) and implants second-type impurities in the second area of the substrate (116) to form second source and drain regions (e.g., source drain extensions) adjacent the second gate conductor. The method then grows second spacers on the second gate conductor (118) and implants additional second-type impurities in the second area of the substrate (120) to form additional second source and drain regions adjacent the second source and drain extensions.
The first hard mask is then removed using a wet etching process in item 122. Then, the method forms a second hard mask over the first gate conductor(s), the second gate conductor(s), and the substrate in item 124. As with the first hard mask, the second hard mask comprises an oxide, a nitride, etc. For example, the first hard mask and the second hard mask can comprise silicon nitride (Si3N4), SiGeOx with Ge at least 60% relative to Si) etc.
The method also patterns a second organic photoresist over the second hard mask in item 126, to leave the organic photoresist on areas of the second hard mask that are above the second area of the substrate. The method similarly removes portions of the second hard mask not protected by the organic photoresist (128) to leave the second hard mask on the second area of the substrate and not on the first area of the substrate.
As with the first doping process, the method then removes the second organic photoresist (130) and implants first-type impurities in the first area of the substrate (132) to form first source and drain regions (e.g., source and drain extensions) adjacent the first gate conductor. First spacers are then grown on the first gate conductor (134) and additional first-type impurities are implanted in the first area of the substrate (136) to form additional first source and drain regions adjacent the first source and drain extensions.
After performing such a doping process, the method removes the second hard mask using a wet etching process (138) and then silicides the first gate conductor, the first source and drain regions, the first source and drain extensions, the second gate conductor, the second source and drain regions, and the second source and drain extensions in item 140.
A shallow trench isolation region 224 is formed in the substrate 200 between the first-type of channel implant 202 and the second-type of channel implant 204. The method also forms gates above the well regions by forming at least one first gate conductor 218 above the first area 252 of the substrate 200 and at least one second gate conductor 216 above the second area 250 of the substrate 200. The gate conductors mentioned herein can comprise polysilicon, metals, metal alloys, or any other conductor. The gate formation process includes any necessary gate oxides 226, 228, gate caps, etc.
Rather than forming conventional organic photoresists to accomplish source and drain doping, the present embodiments form a first hard mask 230 over the first gate conductor 218(s), the second gate conductor 216(s), and the substrate 200. The hard masks mentioned herein comprise an oxide, a nitride, etc., and can be applied using any suitable process such as spin-on processing, etc. For example, the hard masks mentioned herein can comprise a material such as SixGeI-xO2, (where x from 1 to 0) which can be removed by a diluted HF or COR; or can comprise SixGeI-x (where x from 0 to 0.6) which can be removed by a diluted H2O2/HF mixture after the ion implantation.
Then, a first organic photoresist 232 is patterned over the first hard mask 230 so as to leave the first organic photoresist 232 on areas of the first hard mask 230 that are above the first area 252 of the substrate 200. The photoresist masks mentioned herein can comprise any commonly known photoresist masks, such as organic photoresists that are exposed to a pattern of light and developed to allow openings to form in the mask.
Referring now to
As shown in
As shown in
The first hard mask 230 is then removed using a wet etching process. As mentioned above, the hard masks utilized herein can be removed by using diluted HF, COR, H2O2/HF, etc., mixtures after the ion implantation. Such wet etching process aggressively attacks the hard mask material, but has almost no affect on the silicon substrate. Therefore, such wet etching processes are considered to be highly selective to the hard mask material. Because of the high selectivity of the wet etch of the hard mask to the implanted substrate 200, the dopant and the silicon substrate loss are minimized. In other words, because the embodiments herein remove the organic material of the photoresist 232 before the ion implantation process is performed, no hard crust material is formed (as mentioned above, a crust may occur if the organic photoresists 232 were left in place). Since no hard crust layer is formed, aggressive material removal processing is not necessary with the embodiments herein, which allows the source/drain implantations and their extensions to remain relatively unaffected within the substrate.
As shown in
As mentioned above, the first and second hard mask 240 can comprise, for example, silicon nitride (Si3N4), SiGeOx with Ge at least 60% relative to Si) etc.; however, the first hard mask 230 and the second hard mask 240 can be formed by growing a silicon oxide (SiO2) liner on the first gate conductor 218, the second gate conductor 216, and the substrate 200; and depositing a germanium (Ge) layer on the silicon oxide liner. Alternatively, the first hard mask 230 and second hard mask 240 can be formed by depositing a silicon nitride (Si3N4) liner on the first gate conductor 218, the second gate conductor 216, and the substrate 200 followed by growing a silicon dioxide (SiO2) layer on the silicon nitride liner.
As shown in
As with the first doping process, the method then removes the second organic photoresist 238 and implants first-type impurities 242 in the first area 252 of the substrate 200 to form first source and drain regions (e.g., source and drain extensions 208) adjacent the first gate conductor 218, as shown in
Again, the wet etching process used to remove the first and second hard masks 230, 240 is selective to the substrate 200, the first-type impurities 242, 244, and the second-type impurities 234, 236. Therefore, the wet etching process does not damage the substrate 200, the first source and drain extensions 208, the second source and drain extensions 206, the first source and drain regions 212, or the second source and drain regions 210. Once again, since no hard crust layer is formed, aggressive material removal processing is not necessary with the embodiments herein, which allows the source/drain implantations and their extensions to remain relatively unaffected within the substrate.
As shown in
The first-type of channel implant 202, the first gate conductor 218, the first source and drain extensions 208, and the first source and drain regions 212 combine to form a first-type transistor 256. The second-type of channel implant 204, the second gate conductor 216, the second source and drain extensions 206, and the second source and drain regions 210 combine to form a second-type transistor 254 that is complementary to the first transistor 256. The second-type impurities comprises any positive-type impurity (P-type impurity, e.g., phosphorus (P), arsenic (As), antimony (Sb) etc.) and the first-type impurity comprises any negative-type impurity (N-type impurity, e.g., boron, indium, etc.). In addition to the methods discussed herein, and any other methodologies can be utilized to form the various transistors mentioned here, such as those discussed in U.S. Pat. No. 7,491,598 (incorporated herein by reference).
Therefore, as shown above, instead of using an organic photoresist as an implant blocking mask, an inorganic hard mask material is used as the blocking mask. The hard mask material is chosen so that, after the implantation, the material can be easily removed selectively to the implanted silicon substrate without causing any damage to the implanted source/drain regions or their extensions.
The resulting integrated circuit chip can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.
It should be understood that the corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. Additionally, it should be understood that the above-description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. Well-known components and processing techniques are omitted in the above-description so as to not unnecessarily obscure the embodiments of the invention.
Finally, it should also be understood that the terminology used in the above-description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. For example, as used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, as used herein, the terms “comprises”, “comprising,” and/or “incorporating” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.