Methods, apparatuses, and substrate assembly structures for fabricating microelectronic components using mechanical and chemical-mechanical planarization processes

Methods, apparatuses and substrate assembly structures for mechanical and chemical-mechanical planarizing processes used in the manufacturing microelectronic-device substrate assemblies. One aspect of the invention is directed toward a method for planarizing a microelectronic-device substrate assembly by removing material from a surface of the substrate assembly, detecting a first change in drag force between the substrate assembly and a polishing pad indicating that the substrate surface is planar, and identifying a second change in drag force between the substrate assembly and the polishing pad indicating that the planar substrate surface is at the endpoint elevation. After the second change in drag force is identified, the planarization process is stopped. The first change in drag force between the substrate assembly and the planarizing medium is preferably detected by measuring a first change in the electrical current through a drive motor driving a substrate holder carrying the substrate assembly and/or a table carrying the polishing pad. The second change in drag force between the substrate assembly and the polishing pad may be identified by detecting a second change in the drive motor current or measuring a second change in the temperature of the planarizing solution or the polishing pad.

TECHNICAL FIELD

The present invention relates to fabricating components of microelectronic devices using mechanical and/or chemical-mechanical planarizing processes. More specifically, the present invention relates to methods, apparatuses and substrate assembly structures for identifying the endpoint in mechanical and/or chemical-mechanical planarization of microelectronic substrate assemblies.

BACKGROUND OF THE INVENTION

Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic substrates.FIG. 1schematically illustrates a planarizing machine10with a platen or table20, a carrier assembly30over the table20, a polishing pad40on the table20, and a planarizing fluid44on the polishing pad40. The planarizing machine10may also have an under-pad25between the platen20and the polishing pad40. In many planarizing machines, a drive assembly26rotates (arrow A) and/or reciprocates (arrow B) the platen20to move the polishing pad40during planarization.

The carrier assembly30controls and protects a substrate12during planarization. The carrier assembly30typically has a substrate holder32that holds the substrate12via suction, and a pad34in the substrate holder32that supports the backside of the substrate12. A drive assembly36of the carrier assembly30typically rotates and/or translates the substrate holder32(arrows C1and D, respectively). The substrate holder32, however, may be a weighted, free-floating disk (not shown) that slides over the polishing pad40.

The combination of the polishing pad40and the planarizing fluid44generally define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate12. The polishing pad40can be a conventional non-abrasive polishing pad without abrasive particles composed of a polymeric material (e.g., polyurethane), or it can be an abrasive polishing pad with abrasive particles fixedly bonded to a suspension material. In a typical application, the planarizing fluid44may be a CMP slurry with abrasive particles and chemicals for use with a conventional nonabrasive polishing pad. In other applications for use with an abrasive polishing pad, the planarizing fluid44is generally a “clean” chemical solution without abrasive particles.

To planarize the substrate12with the planarizing machine10, the carrier assembly30presses the substrate12against a planarizing surface42of the polishing pad40in the presence of the planarizing fluid44(arrow C2). The platen20and/or the substrate holder32then move relative to one another to translate the substrate12across the planarizing surface42. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate12.

CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects, and other components, many substrate assemblies develop large “step heights” that create a highly topographic substrate surface. To enable the fabrication of integrated circuits with high densities of components, it is necessary to produce a planar substrate surface at several stages of processing the substrate assembly because non-planar substrate surfaces significantly increase the difficulty of forming sub-micron features or photo-patterns to within a tolerance of approximately 0.1 μm. Thus, CMP processes should typically transform a highly topographical substrate surface into a highly uniform, planar substrate surface (e.g., a “blanket surface”).

In the competitive semiconductor industry, it is also highly desirable to maximize the yield of operable devices as quickly as possible. One factor of CMP processing that affects the yield of operable devices is the ability to accurately stop CMP processing at a desired endpoint. In a typical CMP process, the desired endpoint is reached when the surface of the substrate is highly planar and/or when enough material has been removed from the substrate assembly to form discrete components of the integrated circuits (e.g., shallow-trench-isolation structures, contacts, damascene lines, etc.). Accurately endpointing CMP processing is important for maintaining a high yield because: (1) subsequent processing may not be possible if the surface is not sufficiently planar; and/or (2) the integrated circuits may not operate if the discrete components are not accurately formed. For example, if the substrate is “under-planarized,” shallow-trench-isolation structures may not be adequately isolated from one another. Conversely, if the substrate assembly is “over-polished,” “dishing” can occur in shallow-trench-isolation structures that can cause current-leakage paths or parasitic capacitance. Extreme cases of over-polishing can even destroy sections of the substrate assembly. Thus, it is highly desirable to stop CMP processing at the desired endpoint.

One drawback of CMP processing is that it is difficult to determine when the substrate surface is both planar and at the desired endpoint elevation in the substrate assembly. In one conventional method for determining the endpoint of CMP processing, the planarizing period of one substrate assembly in a run is estimated using the polishing rate of previous substrate assemblies in the run and the thickness of material that is to be removed from the particular substrate assembly. The estimated planarizing period for the particular substrate assembly, however, may not be accurate because the polishing rate may change from one substrate assembly to another. Thus, this method may not accurately planarize all of the substrate assemblies in a run to the desired endpoint.

In another method for determining the endpoint of CMP processing, the substrate assembly is removed from the pad and the substrate carrier, and then a measuring device measures a change in thickness of the substrate assembly. Removing the substrate assembly from the pad and substrate carrier, however, is time-consuming and may damage the substrate assembly. Thus, this method generally reduces the throughput and yield of CMP processing.

In still another method for determining the endpoint of CMP processing, a portion of the substrate assembly is moved beyond the edge of the pad, and an interferometer directs a beam of light directly onto the exposed portion of the substrate assembly to measure a change in thickness of a transparent layer. The substrate assembly, however, may not be in the same reference position each time it overhangs the pad. For example, because the edge of the pad is compressible, the substrate assembly may not be at the same elevation for each measurement. Thus, this method may inaccurately measure the change in thickness of the substrate assembly.

In yet another method for determining the endpoint of CMP processing, U.S. Pat. Nos. 5,036,015 and 5,069,002, which are herein incorporated by reference, disclose detecting the planar endpoint by sensing a change in friction between a wafer and the polishing medium. Such a change of friction may be produced by a different coefficient of friction at the wafer surface as one material (e.g., an oxide) is removed from the wafer to expose another material (e.g., a metal film). More specifically, U.S. Pat. Nos. 5,036,015 and 5,069,002 disclose detecting the change in friction by measuring the change in electrical current through the drive motor for the platen and/or substrate holder.

Although the endpoint detection technique disclosed in U.S. Pat. Nos. 5,036,015 and 5,069,002 is an improvement over the previous endpointing methods, the increase in current through the drive motors may not accurately indicate the endpoint of a substrate. The detection of a single change in friction at the interface between the different materials may only indicate that at least a portion of the substrate surface is at the level of the interface. Other portions of the substrate surface, however, may be above or below the interface level and/or the interface level itself may not be planar. The apparatus and methods disclosed in U.S. Pat. Nos. 5,036,015 and 5,069,002 may accordingly indicate that at least a portion of the substrate surface is at the endpoint elevation, but they do not necessarily indicate that the substrate surface is planar. Thus, the apparatus and methods of U.S. Pat. Nos. 5,036,015 and 5,069,002 may not indicate that the substrate surface is both planar and at the endpoint elevation.

SUMMARY OF THE INVENTION

The present invention relates to mechanical and chemical-mechanical planarizing processes for manufacturing microelectronic-device substrate assemblies. One aspect of the invention is directed toward a method for planarizing a microelectronic-device substrate assembly by removing material from a surface of the substrate assembly, detecting a first change in drag force between the substrate assembly and a polishing pad indicating that the substrate surface is at least substantially planar, and identifying a second change in drag force between the substrate assembly and the polishing pad indicating that the planar substrate surface is at least substantially at the endpoint elevation. After the second change in drag force is identified, the planarization process is stopped.

The removal of material from the substrate surface generally involves pressing the substrate surface against a polishing pad and imparting relative motion between the substrate surface and the polishing pad. The first change in drag force between the substrate assembly and the polishing pad is preferably detected by measuring a first change in the electrical current through a drive motor driving a substrate holder carrying the substrate assembly and/or a table carrying the polishing pad. The first change in drag force may alternatively be detected by measuring a first change in temperature of the planarizing solution or the polishing pad. The second change in drag force between the substrate assembly and the polishing pad may be identified by detecting a second change in the drive motor current, or measuring a second in the temperature of the planarizing solution or the polishing pad. The first change in drag force indicates that the substrate surface is at least substantially planar, and the second change in drag force indicates that the planar substrate surface is at least substantially at the endpoint elevation. After the second change in drag force between the substrate assembly and the polishing pad is identified, the act of stopping removal of material from the substrate surface generally involves removing the substrate assembly from the polishing pad and/or terminating the relative motion between the substrate assembly and the polishing pad.

In one particular aspect of the invention, the second change in drag force between the substrate assembly and the planarizing medium is accentuated from the drag force when the substrate surface is planar by constructing a substrate assembly including an endpoint indicator having a first coefficient of friction at an endpoint elevation and a cover layer having a second coefficient of friction over the endpoint indicator. For example, the endpoint indicator is preferably fabricated by plasma deposition of a silicon nitride layer at the endpoint elevation, and the cover layer is preferably formed by depositing a high density plasma oxide layer over the plasma silicon nitride layer. Alternatively, the endpoint indicator can be fabricated by depositing either a silicon carbide layer or a boron nitride layer at the endpoint elevation.

In each of these more particular aspects of the invention, the first change in drag force can be detected by measuring an increase in the electrical current through the drive motor of the table from a start current to a planarity current indicating that the substrate surface is planar and located in the high density plasma oxide layer. Additionally, the second change in drag force can be identified by measuring a decrease in the electrical current through the drive motor from the planarity current to an endpoint current because each of the plasma silicon nitride, boron nitride and silicon carbide endpoint indicators has a significantly lower coefficient of friction than the high density plasma oxide layer. Accordingly, many aspects of the invention involve first detecting that a planar surface has been formed on the substrate assembly by detecting a first change in the table current, and then identifying that the particular endpoint of the substrate assembly has been reached by subsequently identifying a second change in the table current. Other aspects of the invention also involve modifying the surface of the endpoint indicator to accentuate the difference in drag force between the substrate assembly and the polishing pad at the endpoint elevation.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure describes substrate assembly structures, apparatuses and methods for mechanical and/or chemical-mechanical planarization of microelectronic-device substrate assemblies. Many specific details of certain embodiments of the invention are set forth in the following description, and inFIGS. 2–9, to provide a thorough understanding of the embodiments described herein. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the invention may be practiced without several of the details described in the following description. For example, even though many aspects of the present invention are described below in the context of constructing shallow-trench-isolation (STI) structures, the invention is also applicable to constructing other structures and components in the manufacturing of microelectronic devices.

FIG. 2is a partial schematic cross-sectional view of one stage in a method for constructing an STI structure on a microelectronic-device substrate assembly100in accordance with one embodiment of the invention. The substrate assembly100has a substrate110, a thin oxide layer120formed over the substrate110, and an elevation indicator or endpoint indicator130formed over the oxide layer120. In the fabrication of STI structures and other components for integrated circuits in semiconductor devices, the substrate110is preferably a single crystal silicon wafer. The substrate110can alternatively be a glass substrate for a baseplate of a field emission display, or any other suitable type of substrate for other types of microelectronic devices. When the substrate110is composed of silicon, the oxide layer120is preferably a thin layer of silicon dioxide grown by oxidizing the surface of the substrate110. The oxide layer120, for example, generally has a thickness of approximately 100 Å to define a pad oxide layer.

The endpoint indicator130is fabricated on the oxide layer120so that a top surface132of the endpoint indicator130is located at a desired endpoint elevation for subsequent CMP processing of the substrate assembly100. The endpoint indicator130is composed of a material that has a first coefficient of friction, such as a material having either a very high or a very low coefficient of friction. For example, low frictional coefficient endpoint indicators can be composed of silicon carbide, boron nitride, or plasma deposited silicon nitride. Suitable deposition techniques for the plasma deposited silicon nitride include plasma vapor deposition techniques that are known in the semiconductor device fabrication arts. After the endpoint indicator130has been formed, the trenches for the STI structures are formed.

FIGS. 3 and 4are partial schematic cross-sectional views of subsequent stages of the method for constructing an STI structure on the substrate assembly100.FIG. 3illustrates the substrate assembly100after a plurality of trenches112have been etched in the substrate10and an oxide liner122has been grown in each of the trenches112. The trenches112are formed by photopatterning a layer of resist (not shown) on the endpoint indicator130, and then etching through the endpoint indicator130, the oxide layer120, and a portion of the substrate10. The oxide liner122is then formed by oxidizing the exposed silicon in the trenches112to grow a thin layer of silicon dioxide in the trenches that connects with the silicon dioxide of the oxide layer120. Isolated pads of the endpoint indicator130are then left on the oxide layer120between the trenches112.

Referring toFIG. 4, the material for the STI structures is provided by depositing a cover layer124over the endpoint indicator130and into the trenches112. The cover layer124has a second coefficient of friction that is different from the first coefficient of friction of the endpoint indicators130. For example, when the cover has a relatively high coefficient of friction, the endpoint indicator130is selected from a material having a low coefficient of friction. Alternatively, the top surfaces132of the endpoint indicator130can be treated to impart a high or low coefficient of friction to the endpoint indicator130. The cover layer124is preferably formed by depositing silicon dioxide using a high density plasma process. The high density plasma (HDP) silicon dioxide combines with the silicon dioxide liner122(FIG. 3) and the oxide layer120to form an integral cover layer124of silicon dioxide. The HDP silicon dioxide has a higher coefficient of friction than boron nitride, silicon carbide, or plasma deposited silicon nitride used as the endpoint indicator130. At this point of fabricating the STI structures, the substrate assembly100is now ready to be planarized to remove excess material of the cover layer124from the substrate assembly100.

FIGS. 5A and 5Bare partial schematic cross-sectional views illustrating subsequent stages of the method for constructing an STI structure involving mechanical and/or chemical-mechanical planarization of the substrate assembly100. Referring toFIG. 5A, the substrate assembly100is inverted and attached to a backing pad34in a substrate holder32so that the substrate assembly100is positioned over a polishing pad40on a table20. The table20, substrate holder32, backing pad34, and polishing pad40can be similar to those described above with respect toFIG. 1. The substrate holder32then presses the cover layer124against the polishing pad40, and the substrate holder32and/or the polishing pad40move to translate the substrate assembly100across the polishing pad40in the presence of a planarizing solution (not shown). After a period of time, a planar substrate surface127is formed at an intermediate elevation in the cover layer124. The substrate surface127, more particularly, becomes planar at an elevation spaced apart from the top surfaces132of the endpoint indicators130.

Referring toFIG. 5B, the substrate assembly100is further planarized until the substrate surface127of the cover layer124is coplanar with exposed top surfaces132of the endpoint indicators130. At this point of the planarizing stage, it is important to accurately stop removing material from both the endpoint indicators130and the cover layer124to prevent over-polishing or under-polishing of the substrate assembly100.

FIG. 5Cillustrates one embodiment for accurately endpointing the planarizing stage of the method for forming STI structures. The endpoint is determined by detecting a first change in drag force between the substrate assembly and the polishing pad indicating that the substrate surface127has become planar (FIG. 5A), and then identifying a second change in drag force caused by exposing the endpoint indicators130indicating that the planar substrate surface127is at the endpoint elevation (FIG. 5B).FIG. 5C, more particularly, illustrates an embodiment of the method in which: (1) the first and second changes in drag force are indicated by measuring a change in the electrical current through a drive motor driving the table20(FIG. 1) of the planarizing machine; and (2) the second coefficient of friction of the cover layer124is greater than the first coefficient of friction of the endpoint indicators130. The resulting current trace exhibits a start up current140, a first change in current142detecting the first change in drag force, a planarity current146, and a second change in current148identifying a second change in drag force.

Still referring toFIG. 5C, the start up current140remains relatively constant during a first stage A of the CMP process because the cover layer124is highly topographical (FIG. 4) and the surface area of the substrate assembly100contacting the polishing pad40remains relatively constant. The first change in current142increases rapidly in a second stage B of the CMP process because, as the substrate surface127becomes planar (FIG. 5B), the increase in surface area of the substrate assembly100contacting the polishing pad significantly increases the drag force between the substrate assembly100and the pad. Once the substrate surface127becomes planar, the table current remains substantially constant at the planarity current146in a third stage C of the CMP process. The second change in current148then decreases rapidly during a fourth stage D of the CMP process as the top surfaces132of the endpoint indicators132are exposed because the lower coefficient of friction of the endpoint indicators130reduces the drag force between the substrate assembly100and the polishing pad40. The planarizing process is terminated after the second change148in current occurs indicating that the top surfaces132of the endpoint indicators130are exposed across the face of the substrate assembly110(FIG. 5B).

FIGS. 6 and 7are partial schematic cross-sectional views illustrating subsequent processing of the substrate assembly100after the substrate assembly100has been planarized to form the STI structures. Referring toFIG. 6, the substrate assembly100is dipped in a buffered HF solution to remove a portion of the cover layer124between the endpoint indicators130. The upper surfaces127of the cover layer124are accordingly slightly below the exposed surfaces132of the endpoint indicators130.

FIG. 7illustrates the substrate assembly100after the endpoint indicators130have been removed and the cover layer124(FIG. 6) has been uniformly etched to form a plurality of STI structures128between active areas114of the substrate110. When the endpoint indicators130are formed from plasma silicon nitride, the endpoint indicators130are stripped from the substrate assembly100by dipping the substrate assembly100in a phosphoric acid dip. The cover layer124is then etched until the sections of the cover layer124that were previously under the endpoint indicators130(seeFIG. 6) are removed to expose the active areas114of the substrate110. The STI structures128filling the trenches112in the substrate110accordingly isolate active areas114of the substrate110from one another. As such, active features113can be constructed on the active areas114in accordance with known microelectronic-device fabrication processes. During the fabrication of such active features113and the associated contacts, the raised portions of the STI structures128are generally lowered to approximately the level of the substrate110(not shown).

The methods set forth above with respect toFIGS. 2–7enhance the yield of operable STI structures because the process for endpointing the planarizing stage accurately indicates both the planarity and the endpoint elevation of the substrate surface. Conventional planarizing and endpointing methods often produce surfaces with variances from the desired endpoint elevation of approximately ±200 Å because they do not detect whether the substrate surface is planar. In contrast to conventional endpointing methods, by first detecting that the substrate surface is planar and then identifying that the substrate surface is at the endpoint elevation in accordance with the methods set forth above with respect toFIGS. 2–7, the deviation in uniformity across the surface of the substrate assembly is generally approximately ±10 Å. Several embodiment of the endpointing process of the invention are thus expected to reduce problems associated with over-polishing or under-polishing the substrate assembly that can create current leakage paths or even destroy the integrated circuit components on substrate assemblies.

FIG. 8is a diagram illustrating another embodiment of a process for endpointing the planarizing stage of processing a semiconductor assembly. In this embodiment, the start up current140, the first change in current142, and the planarity current146follow a trace similar to that described above with respect toFIG. 5C. The endpoint indicators130(FIGS. 2–5B) of this embodiment, however, have a higher coefficient of friction than the cover layer124(FIGS. 2–5B). Accordingly, the second change in current149increases from the planarity current146to an endpoint current at the end of the fourth stage D of the planarizing process. The difference in the coefficient of friction between the cover layer124and the endpoint indicators130can accordingly be selected such that the second change in drag force after the substrate surface127has become planar may accordingly increase or decrease with respect to the drag force when the substrate surface is planar.

In another embodiment (not shown), the slurry can be modified or selected to cause a decrease in drag force as the substrate surface127becomes planar such that the first change in drag force decreases during the second stage B (FIG. 5C) of the planarizing process. One suitable slurry for decreasing the drag force as the substrate surface127becomes planar is Klevesol, manufactured by Rodel Corporation. Thus, the first change in the table current may decrease from the start current.

In still another embodiment of the invention, the first and/or second coefficients of friction of the endpoint indicator130and/or the cover layer124can be modified to increase the difference between the first and second coefficients of friction. Referring toFIG. 5B, for example, a slurry (not shown) between the substrate assembly100and the polishing pad40can be modified or selected to react with the top surfaces132of the endpoint indicator130in a manner that either reduces or increases the first coefficient of friction of the top surfaces132of the endpoint indicator130. One particular embodiment adds surfactants and/or other chemicals to a slurry to increase or decrease the first coefficient of friction of the surface stratum of an endpoint indicator130. For example, a polyoxyethylene ether can be added to a slurry (e.g., Corrundum or ILD-1300 slurries manufactured by Rodel Corporation) to decrease the coefficient of friction at the surface of a silicon nitride endpoint indicator. This particular embodiment is accordingly particularly well suited for use with a cover layer composed of silicon dioxide because it increases the difference between the coefficients of friction between the reacted silicon nitride and the silicon dioxide.

In another embodiment, the top surfaces132of the endpoint indicator130can be modified using implantation, diffusion, deposition or other techniques to create a surface stratum of the endpoint indicator130having a desired coefficient of friction. Referring toFIGS. 2 and 3, for example, the surface of the endpoint indicator130can be treated to increase or decrease the difference in the coefficients of friction at the interface between the endpoint indicator130and the cover layer124(FIG. 4). One particular embodiment involves implanting boron, phosphor and/or carbon into a silicon nitride endpoint indicator to create a surface stratum having a lower coefficient of friction than the untreated silicon nitride. Another particular embodiment involves diffusing boron and/or phosphor into a polysilicon endpoint indicator to create a surface stratum having a different coefficient of friction than the polysilicon. Still another particular embodiment involves depositing a thin layer of silicon carbide or boron over a thermally deposited silicon nitride layer (e.g., Chemical Vapor Deposition) to produce a surface stratum having a lower coefficient of friction than the silicon nitride layer.

FIG. 9is a schematic cross-sectional view of a planarizing machine110in accordance with yet another embodiment of the invention in which the first and second changes in drag force can be monitored by measuring the temperature change of the slurry, the polishing pad and/or the substrate assembly. The planarizing machine110, for example, can have an infrared sensor170positioned over the polishing pad to measure the temperature changes of either the polishing pad40or the planarizing solution44on the polishing pad40. In alternative embodiments, the planarizing machine110can have a temperature sensor172touching the planarizing solution44on the pad40, or a temperature sensor174located in a flow of planarizing solution44off of the polishing pad40. In still another alternative embodiment, a temperature sensor176attached to the substrate holder32measures changes in the temperature of the substrate assembly100. In these embodiments, an increase in temperature indicates a corresponding increase in drag force between the substrate assembly100and the polishing pad40. Similarly, a decrease in temperature indicates a decrease in drag force. The changes in temperature are expected to follow traces similar to those shown inFIGS. 5C and 8, except that the axis labeled “Table Current” would represent the “Temperature.”