This application is related to (TS01-376), filed on Nov. 30, 2001, Ser. No. 10/002,986, and to (TS01-463), filed on Dec. 5, 2001, Ser. No. 10/005,806, assigned to Common Assignee
(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to particular chemistries for negative photoresist.
(2) Description of the Prior Art
Integrated semiconductor devices comprise electronic circuits of sub-micron and deep sub-micron dimensions and are typically created in or on the surface of a silicon substrate. The creation of semiconductor devices is supported by sophisticated and interacting, mutually supporting disciplines.
Device features are transposed from a mask onto a semiconductor surface using photolithographic imaging processes. Since this exposure depends on the transfer of photo energy from a source to a target surface, it is to be expected that, for target features that are created in very close proximity to each other, the transfer of photo energy interacts for very closely spaced device features, most commonly interconnect lines or contact holes having sub-micron spacing between adjacent lines.
A common measure for the occurrence of such interaction are applications where the Critical Dimensions (CD) of the layout of the Integrated Circuit (IC) approach the resolution limit of the lithography equipment. For such applications, proximity effects begin to influence the manner in which mask images are transferred to target surfaces. This interaction imposes limitations on the proximity of adjacent device features, these limitations are referred to as Critical Dimensions (CD) of a design and device layout.
Related application (TS01-376), filed on Nov. 30, 2001, Ser. No. 10/002,986, addresses problems and limitations that are encountered when creating openings on a semiconductor surface such as the surface of a layer of photoresist or the surface of a semiconductor substrate. This application provides two masks. The first mask, referred to as the packed mask, comprises the desired contact holes, which are part of the creation of a semiconductor device. To the packed mask are added padding holes in order to increase and condense the hole density of the packed mask. The second mask, referred to as the unpacking mask, comprises openings at the same locations as the locations of the padding holes of the first mask, the openings provided in the second mask have slightly larger dimensions than the padding holes of the first mask. A first exposure is made using the packed mask, a second exposure of the same surface area is made using the unpacking mask. The unpacking mask is used to selectively cover the padding contact holes, resulting in the final image. Two types of unpacking masks can be used, a first type having unpacking holes that surround the desired hole pattern, a second type having unpacking holes that align with the desired hole pattern.
Related application (TS01-463), filed on Dec. 5, 2001, Ser. No. 10/005,806 provides a method of creating contact holes using a packing and unpacking procedure, further applying a phase-shift mask. The Depth Of Focus (DOF) and Mask Error Factor (MEF) of closely packed holes can be improved using Alternating Phase Shifting Mask (Alt PSM) for the exposure of the holes. However, the Alt PSM is dependent on hole density or hole separation and is less effective where holes are relatively further separated from each other. In order to improve DOF and MEF performance for the creation of holes, the application adds extra holes to a given pattern of contact holes on the surface of a first mask, thus densifying the pattern of holes on the first mask and therefore reducing the range of the hole-diameter to hole separation ratio. The pattern of added holes is alternating in phase with the pattern of desired holes. The added holes will be filled up using a second mask.
U.S. Pat. No. 5,573,634 (Ham) shows a contact hole process using a double exposure photoresist process.
U.S. Pat. No. 5,308,741 (Kemp) shows a double exposure process with mask shifting and phase shifting.
U.S. Pat. No. 5,432,b44 (Shimizu) shows a double exposure process with a phase shift masks (PSM).
U.S. Pat. No. 5,017,461 (Abe), U.S. Pat. No. 5,998,092 (McCulloch et al.) U.S. Pat. No. 5,648,196 (Frechet et al.) and U.S. Pat. No. 5,532,113 (Frechet et al.) are related patents.
A principle objective of the invention is to provide optimized use of photoresist coating for packing-and-unpacking methods of photoresist exposure.
Another objective of the invention is to provide use of photoresist coating for packing-and-unpacking methods of photoresist exposure that allow optimum pattern density of the created pattern.
In accordance with the objectives of the invention a new water soluble negative photoresist is provided for packing-and-unpacking (PAU) processing steps.
a through 1c show the application of an Alt PSM of regularly packed holes and an unpacking mask to designate the unwanted holes for back fill.
a through 2d show Packing and Unpacking (PAU) with two coatings of photoresist.
The instant invention applies to the use of two photolithographic exposure masks. The first exposure mask is a packed exposure mask, which comprises holes with a single hole-to-separation ratio. This ratio may typically be a ratio of 1:1 but is not limited to this and can be extended to include any ratio that is within the effective range of the Alt PSM. The second mask, the unpacking mask, comprises holes that are slightly larger than the holes in the packed mask. The holes provided in the unpacking mask have a slightly larger diameter than the holes in the packed mask, the holes provided in the unpacking mask center on the desired holes. As a first processing step in creating a hole pattern, the packed mask is used to delineate both types of holes. After this exposure has been completed, the unpacking mask is used to selectively cover the padding holes, resulting in a final image.
In using PAU with two photoresist coatings, see
For the application of the second photoresist coating it may be required, in order to maintain the image created in the first coating of photoresist, to harden and/or cross link the first layer of photoresist. For this purpose two layers of photoresist can be used for the formation of the first coating of photoresist, the bottom layer of these two layers of photoresist is first cross linked after which an imaging layer of photoresist is coating over the surface of the cross linked layer of photoresist. The imaging layer preferably comprises elements that form a non-volatile compound, such as silicon, during Reactive Ion Etch (RIE) of oxide or oxide containing layers. The imaging layer is then delineated by applying O2 RIE etching and serves as the first layer of photoresist.
For the second layer of photoresist that is required for the procedure of using PAU with two photoresist coatings, either positive or negative photoresist can be used.
If a positive photoresist is used for the second layer of photoresist, a light-field unpacking mask based on the padding holes results in coverage of the padding holes and a dark-field unpacking mask based on the desired holes results in coverage of the background.
If a negative photoresist is used for the second layer of photoresist, a dark-field unpacking mask based on the padding holes exposes the second layer of photoresist at the padding holes to make them insoluble in the resist developer, resulting in coverage of the padding holes. Alternatively, a light-field unpacking mask based on the desired holes exposes the negative second layer of photoresist in all areas except where the desired holes are located and results in coverage of the background.
The above described process will now be further highlighted using
Referring specifically to
a through 2d show Packing and Unpacking (PAU) with two coatings of photoresist, as follows:
The specific and preferred selection of the photoresist that is used for layers 22 and 26 of
For the first layer 22 of photoresist, the preferred resist is a positive resist such as I-line resist and KrF resist and ArF resist and F2 resist and EUV resist. This resist is exposed for the packed mask and developed. For the second layer 26 of photoresist, the preferred resist of the invention is a water soluble negative resist. The second layer 26 of photoresist is coated on the delineated first layer 22 of photoresist image without affecting this first delineated layer 22 of photoresist, hence the second layer 26 of photoresist is preferred to comprise a water soluble negative resist. After the second layer 25 of negative photoresist has been deposited, the second layer photolithographic mask is used to expose the second layer 26 of photoresist, using water to develop this layer and create the pattern of layer 26 that is shown in cross sections of
The advantages of using water soluble photoresist for the second layer 26,
The invention can be summarized as follows:
Of these latter elements, the following details can be provided.
1. a base polymer such as polyvinylacetal has the chemical composition of:
with n having a value between 0 and about 4.
2. a photo-active compound comprising OCH3, CF3SO3 and S(CH3)2
3. of the ethyleneurea, the structure is unknown due to the mixture of various alkyl groups.
Further detail relating to the preferred materials of the invention is provided following.
Base polymer: preferred: water soluble polymers
The invention, of applying a water soluble negative-tone photoresist for creating closely spaced contact holes, can be summarized as follows:
Alternately, the invention can be summarized as follows:
Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the spirit of the invention. It is therefore intended to include within the invention all such variations and modifications which fall within the scope of the appended claims and equivalents thereof.
Number | Name | Date | Kind |
---|---|---|---|
5017461 | Abe | May 1991 | A |
5308741 | Kemp | May 1994 | A |
5376483 | Rolfson | Dec 1994 | A |
5432044 | Shimizu | Jul 1995 | A |
5532113 | Fréchet et al. | Jul 1996 | A |
5573634 | Ham | Nov 1996 | A |
5648196 | Fréchet et al. | Jul 1997 | A |
5998092 | McCulloch et al. | Dec 1999 | A |
6664011 | Lin et al. | Dec 2003 | B2 |
6800415 | Lu et al. | Oct 2004 | B2 |
6905621 | Ho et al. | Jun 2005 | B2 |
20030104319 | Lin et al. | Jun 2003 | A1 |
20050106493 | Ho et al. | May 2005 | A1 |
Number | Date | Country | |
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20040234897 A1 | Nov 2004 | US |