Systems and methods for modifying features in a semi-conductor device

Systems and methods for modifying features of a semiconductor device. The systems and methods of the invention modify features of a semiconductor device according to the amount of exposure dose of light to which a common reticle field of a semiconductor device is exposed. A mask, or a thin film provided on a mask, having sub-resolutions provided thereon determines the amount of exposure dose to which various parts of the reticle field is exposed during the exposure. As a result, different features within the same reticle field can exhibit different dimensions even though exposed to the same exposure dose.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to systems and methods for modifying features in a semi-conductor device to enhance semi-conductor chip performance. More specifically, the invention relates to systems and methods that modify features within a common reticle field using a common exposure dose.

2. Related Art

Critical Dimension (CD) control, especially for FET transistor gate level or semiconductor devices are becoming more and more important as technology requirements are becoming more stringent. Using current lithographic techniques, including Optical Proximity Correction (OPC), model building and masks are increasingly difficult and expensive to build. Moreover, inherent variabilities in mask manufacturing processes exist that can exhibit themselves in inconsistent dimensions from device to device, or from region to region in a single device. Methods and systems rendering modifications to features already imparted to a device would thus prove a meaningful asset to the industry.

There are currently many sources for systematically varying linewidth features, for example, within a common reticle field of semiconductor devices. Exposure control, for example, results in the same doses of light being applied to resist throughout a full reticle field in current practices. Such dosing tends to increase or decrease all linewidths in the reticle field to the same degree however. Lower chip performance tends to occur as a result. Moreover, other means to vary or adjust linewidths, other features, or critical dimensions differently with a common reticle field tend to be more complex or more costly to implement than is ideally preferred.

More recently, as set forth in co-pending U.S. patent application Ser. No. 10/906,846 (IBM Ref.: BUR920040189US1), of common assignment herewith, double exposure techniques have been developed using a low transmission mask. In such double exposure techniques, different semiconductor features are modified at selected areas within the common reticle field by a second exposure dose that is transmitted to the photoresist through the low transmission mask. The modifications tend to be binary according to the features of the low transmission mask, wherein modified areas of the photoresist have been exposed to the dose through the low transmission mask and non-modified areas of photoresist are not exposed to the dose. While this technique tends to improve chip performance by modifying features within a common field, at least one additional mask and exposure would be required to vary features further within the common reticle field. Moreover, other systems and methods for modifying features within a common reticle field tend to be more complex or more costly, or both, than is preferred.

In view of the above, a need exists for systems and methods that modify features within a common reticle field during a common exposure dose in a simple and cost effective manner.

SUMMARY OF THE INVENTION

The systems and methods of the invention modify features of a semiconductor device according to the amount of exposure dose of light to which a common reticle field of a semiconductor device is exposed. A mask, or a thin film provided on a mask, having sub-resolution features provided thereon determines the amount of exposure dose to which various parts of the reticle field is exposed during the exposure. The features are modified during the same exposure dose. As a result, different features within the same reticle field can exhibit a change in dimension even though exposed to the same exposure dose.

In a preferred embodiment of the systems and methods of the invention, varied features are imparted to the reticle field of a semiconductor device using two exposure doses. According to the preferred embodiment, a substrate is provided with a gate conductive material and a photoresist is applied thereto. The photoresist is subjected to a first exposure dose through a main mask yielding a first pattern to photoresist of the semiconductor device. The first pattern is generally a standard pattern of features. Thereafter, and prior to developing the photoresist, the first mask is replaced with a second mask, and a second exposure dose is applied through the second mask to the photoresist. The second mask is a low transmission mask having sub-resolution features provided thereon. Different patterns in the sub-resolution features modify different portions of the exposed photoresist differently within the same reticle field during the second exposure dose. The patterns in the sub-resolution features may vary from continuously solid portions, spaced apart solid portions, open portions, holed or dotted portions, slotted portions or combinations thereof. The pattern imparted onto the photoresist of the semiconductor device can thus increase or decrease as a result of the exposure dose applied, depending on whether the photoresist is positive or negative, respectively.

In another embodiment of the systems and methods of the invention, the modified features within a common reticle field are achieved using a single exposure dose applied through a single mask. The semiconductor device is prepared as before to have the gate conductive material and photoresist applied thereon. The mask is provided with a chrome side and a non-chrome side, as known in the art. The chrome side of the mask includes a main pattern. The non-chrome side includes a low transmission thin film with sub-resolution features arranged therein. The sub-resolution features provided within the thin film can have various patterns, such as continuously solid portions, spaced apart solid portions, holed or dotted portions, slotted portions or combinations thereof. Features of varied dimensions are thus imparted to the photoresist through the sub-resolution features of the single mask's thin film during the same exposure dose.

By varying the exposure dose in selected regions of a semiconductor device according to the systems and methods of the invention, the semiconductor device may be adjusted or “tuned” to better achieve the intended linewidth, spacing or other critical dimensions for the device. Such adjustments or “tuning” of the semiconductor device as the device is manufactured tends to enhance performance of the device. Further, systematic issues, such as mask ACLV, pattern density, voltage drop, or other design issues can be minimized.

The above and other features of the invention, including various novel details of construction and combinations of parts, will now be more particularly described with reference to the accompanying drawings and claims. It will be understood that the various exemplary embodiments of the invention described herein are shown by way of illustration only and not as a limitation thereof. The principles and features of this invention may be employed in various alternative embodiments without departing from the scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates a semiconductor device1, such as a wafer, having a photoresist material2coated thereon in conventional manner. The artisan will appreciate that, prior to application of the photoresist, the semiconductor device is prepared and primed to enhance adhesion of the photoresist to the semiconductor device in a uniform thickness with minimal, or ideally no, particulate contamination as is practiced in the art.

The photoresist is an organic compound that experiences a change in solubility in a developer solution when exposed to ultraviolet (UV) light according to the systems and methods of the invention. The photoresist can be a positive photoresist, whereby unmasked regions of photoresist exposed to UV light are rendered more soluble and easily washed away by the developer solution. The non-exposed or masked portions of positive photoresist thus remain on the semiconductor device as the patterned features. Alternatively, the photoresist can be a negative photoresist, whereby unmasked regions of the photoresist exposed to UV light become cross-linked and hardened, i.e., less soluble. Masked portions of the negative photoresist thus remain more soluble and are able to be subsequently etched away, leaving only those less soluble hardened portions of the photoresist as the patterned features on the semiconductor device. Features initially patterned onto the photoresist are thus more easily increased when negative photoresist is used as additional cross-linking and hardening of initial features may be achieved using a second mask that increases the amount of negative photoresist exposed to UV light. The systems and methods of the invention are thus generally described herein using positive photoresist, although the artisan should readily appreciate that, in view of the above, negative photoresist could as well be used to modify features of a semiconductor device.

FIG. 2aillustrates a low transmission mask10for use with the semiconductor device1ofFIG. 1, for example, after the photoresist2has been subjected to a first exposure dose through a first mask (not shown). The first mask and exposure dose creates a first pattern of standard features on the photoresist2in conventional manner. The features resulting from the first exposure dose through the main mask may then be tested to determine whether the given features would provide optimal semiconductor performance. Such performance may be characterized as a predetermined range within which the features are ideally within. If the features are determined by testing to be beyond the acceptable range, then a second mask10may be built to modify the features resulting from the main mask by subjecting the photoresist2to a second exposure dose.

Referring still toFIG. 2a, the second mask10is independently built to comprise a chrome side10aand a non-chrome side10bas is common in the art. The chrome side10a, however, is patterned with sub-resolution features11(i.e., and, as is clearly illustrated inFIG. 2a, only sub-resolution features) that permit various amounts of UV light to be transmitted through the mask10and to the photoresist2on the semiconductor device1. The sub-resolution features11permit the second, or adjusting, dose to be averaged over the pattern, which minimizes line roughness. The second mask10may also be imaged out of focus to farther minimize line roughness. Minimizing line roughness in this manner tends to provide more subtle transitions between the patterned regions on a device. The sub-resolution features11of the mask10are shown inFIG. 2aas comprising a continuousty solid portion11a, a group of dotted or holed portions11b, and a group of spaced apart solid portions11c. Of course, as the artisan should readily appreciate, other configurations and portions of sub-resolution features may comprise the mask10according to the systems and methods of the invention.

Still referring toFIG. 2a, the solid portion11aof the sub-resolution feature11generally precludes the transmission of UV light to the photoresist2. The main pattern imparted to the photoresist2by the first mask is thus retained where the second mask10has continuously solid portions11aoverlying that region of the main pattern. Of course, where the continuously solid portion11asub-resolution feature of the second mask is larger than the main pattern already imparted to the photoresist2and the photoresist is a positive photoresist, then that region of the main pattern is decreased when the second exposure dose occurs due to the breaking of links and increased solubility of the photoresist2subjected to the second exposure dose.

Likewise, the holed or dotted portions11bor spaced solid portions11cof the sub-resolution features11generally permit varying amounts of UV light to be transmitted therethrough to the main patterned photoresist2. Where the mask10has such openings or spaced portions thorugh which a second exposure dose of UV light may be transmitted to the photoresist, the main pattern of the photoresist2is altered to correspond to the sub-resolution features11of the second mask10. As before, where positive photoresist is used, subjecting more of the main patterned photoresist to UV light through the second exposure dose tends to decrease the feature dimensions on the photoresist. The features resulting from the second exposure dose, thus are modifications to the first imparted main pattern of features and are effectively a second pattern of features imparted to the photoresist.

Because the amount of UV light transmitted through the sub-resolution features of the second mask can vary from none to all, the second pattern of features can impart different changes in dimensions to different regions of the photoresist during the same second exposure dose. Small adjustments or “tuning” of linewidths, spacing or other critical dimensions of the pattern of features on the photoresist of the semiconductor device can be achieved as a result.

FIG. 2billustrates a top view of the second mask10ofFIG. 2awith the sub-resolution features imparted thereon. The features imparted to the underlying photoresist2(not shown inFIG. 2b) through the mask10thus generally correspond to the sub-resolution features11a-11cof the mask10. As shown inFIG. 2b, the mask10has a continuously solid portion11a, dotted or holed portions11b, and spaced apart solid portions12c. Of course, the artisan will readily appreciate that the features imparted to the semiconductor device1may be altered by varying the sub-resolution features11formed on the mask10as described above. The standard features first imparted to the photoresist by the first mask may have been smaller or larger than the second pattern of features eventually imparted to the photoresist2of the semiconductor device1through the second mask10as shown inFIG. 2b. Of course, patterning modifications could have been accomplished using a negative photoresist as well.

As is evident fromFIGS. 2a&2bin particular, use of the second mask10and the sub-resolution features11provided thereon permits varying amounts of UV light to be transmitted to different regions of the underlying photoresist during the same exposure dose of UV light. The pattern of features first imparted onto the semiconductor device1from the main mask, may thus be modified to achieve intended linewidths, spacing or other critical dimensions of the semiconductor device.

FIG. 2cillustrates a semiconductor device1with resist2thereon prior to a second exposure.FIG. 2don the other hand, illustrates a semiconductor device1with resist2thereon after a second exposure.

FIG. 3illustrates a flowchart of one method of modifying features on a semiconductor device using a mask similar to the mask10ofFIG. 2aaccording to one embodiment of the systems and methods of the invention. Understood in the method set forth in the flowchart ofFIG. 3is that the a conventionally cleaned and primed semiconductor device1, such as a wafer, is provided prior to applying the photoresist in Step100ofFIG. 3. Thereafter, in Step110, a first mask is provided over the photoresist. The first mask provides the main pattern of features, which tend to be standard features, as discussed above. Then, in Step120, a first exposure dose of UV light is applied to the photoresist through the first mask. The intended standard first pattern of features is thus imparted to the photoresist. After removal of the first mask, Step130provides a second mask over the photoresist. The second mask has the sub-resolution features, for example as discussed above with respect toFIGS. 2a&2b. Next, in Step140, a second exposure of UV light is transmitted to the photoresist through the second mask and sub-resolutions provided thereon. The second exposure dose of UV light helps to achieve intended linewidths, spacing, or other critical dimensions in the photoresist of the semiconductor device. Thereafter, the process according to the systems and methods of the invention end, wherein it is understood that the semiconductor device with modified features is then hard-baked and further processed in conventional manner.

FIGS. 4a-5illustrate a second embodiment of modifying features on a semiconductor device1according to the systems and methods of the invention. The semiconductor device1has a photoresist material2coated thereon in conventional manner, the semiconductor device having been cleaned and primed to enhance adhesion of the photoresist to the semiconductor device as practiced in the art. The photoresist can be positive or negative photoresist.

Referring toFIG. 4a, a high transmission mask20for use with the semiconductor device1ofFIG. 1, for example, is illustrated. The high transmission mask20is comprised of a chrome side20aand a non-chrome side20bin conventional manner. A first or main pattern of standard features21(i.e., implicitly intended as comprising, or consisting of, only lithographically resolvable features) is provided on the chrome side20aof the mask20, and a second pattern of features is provided by a thin film22having sub-resolution features23(and as is clearly illustrated inFIG. 4a, only sub-resolution features) on the non-chrome side20bof the mask20. When the mask20is aligned over the photoresist2of the semiconductor device1and subjected to an exposure dose of UV light, the first pattern of standard features21that would be imparted to the photoresist2are modified by the transmission of light through the sub-resolution features23of the mask20. The first pattern of features are thus modified to correspond to the adjustments provided thereto by the second pattern of features through the sub-resolution features of the thin film23. Thereafter, any soluble photoresist is rinsed away in the case of positive photoresist, or etched away in the case of negative photoresist. The first pattern of features can thus be made to increase or decrease in dimensions according to the UV light transmitted thereto through the sub-resolution features23of the thin film of the mask20. The thin film23may be moly silicide, for example, to block all or a percentage, such as 5%, of the UV light transmitted from the exposure dose. The thin film is thus applied to the non-chrome side of the mask20in a substantially uniform thickness of approximately 25 Angstroms, for example, although other thicknesses or materials could be used to vary the transmissivity qualities of the thin film, as the artisan should appreciate.

FIG. 4billustrates a view of a semiconductor device1with features imparted thereon the photoresist2, which is understood to be positive photoresist in this instance. The features imparted to the photoresist2inFIG. 4bgenerally correspond to the first pattern of main features prior to a second exposure.FIG. 4c, on the other hand, illustrates a view of a semiconductor device as modified by the second pattern of features through the sub-resolution features23of the mask20ofFIG. 4aafter a second exposure, for example. As shown inFIGS. 4band4c, the photoresist2of the semiconductor device1has a pattern of features corresponding to the masked portions of the positive photoresist2. Where the sub-resolution features23provided additional masking beyond that evident in the chrome side of the mask20, the solid feature of the positive photoresist is increased. Where the sub-resolution features23of the thin film was holed or dotted, for example, to allow UV light to transmit therethrough and onto the photoresist, corresponding portions of soluble photoresist, such as small circular portions of soluble photoresist, are eventually rinsed away after the second exposure. Of course, the artisan will appreciate that other modification patterns, including those accomplished using negative photoresist, are available as well in the discretion of the artisan. In this manner, adjustments to the first main pattern of features may be accomplished using a single exposure dose of UV light.

FIG. 5illustrates a flowchart of a method of modifying features on a semiconductor device using a mask having a thin film as inFIG. 4aaccording to a second embodiment of the systems and methods of the invention. Understood in the method set forth in the flowchart ofFIG. 5is that a conventionally cleaned and primed semiconductor device, such as a wafer, is provided prior to applying the photoresist in step1000ofFIG. 5. Thereafter, in Step1100a mask is provided over the photoresist. The mask provides a first main pattern of features on a chrome side thereof, and a thin film having sub-resolution features providing a second pattern of features on a non-chrome side thereof. The second pattern of features modifies the first pattern of features when subjected to an exposure dose of UV light. Then, in Step1200an exposure dose of UV light is applied to the photoresist through the mask. That UV light transmitted through the sub-resolution features of the mask modify the first pattern of features to achieve intended linewidth, spacing or other critical dimensions in the photoresist of the semiconductor device, wherein it is understood that any soluble photoresist is thereafter rinsed or etched away, and the semiconductor device with modified features is then hard-baked and further processed in conventional manner. Positive or negative photoresist may be used with the second embodiment of the systems and methods of the invention.

The various exemplary embodiments of the invention as described hereinabove do not limit different embodiments of the present invention. The material described herein is not limited to the materials, designs, or shapes referenced herein for illustrative purposes only, and may comprise various other materials, designs or shapes suitable for the systems and procedures described herein as should be appreciated by one of ordinary skill in the art.