This invention relates to a method and apparatus for shaping thin films on in-process semiconductor substrates. More particularly, this invention relates to a method and apparatus for shaping thin films in the near-edge regions of in-process semiconductor substrates employing plasma techniques.
Future trends in integrated circuit (IC) manufacturing processes require manufacturing engineers to become more attentive to the root causes of contamination. An emerging awareness, within the IC manufacturing engineering community, has recognized the substrate's edge exclusion area and edge surfaces as source locations of contamination. Contamination problems originating in these edge areas are the result of poorly adhering films that partially delaminate and break loose from the surface. These loose film fragments, or flakes, if they migrate towards the center of the wafer where active devices are being constructed, can become killer defects.
There is also a problem with existing remedies (Edge Bead Removal or EBR) for the flaking films. Traditional EBR methods are time consuming and expensive. Additionally, these EBR processes produce large volumes of hazardous waste. Finally, EBR processes yield topography near the edge that is not readily cleanable and traps particles.
Accordingly, it is an object of the invention to enable the use of relatively simple techniques for removing flaking films during the processing of a wafer.
It is another object of the invention to control the film shape on a processed wafer.
It is another object of the invention to provide an economical technique for shaping the edge of a wafer during processing.
Briefly, the invention provides an apparatus and method for shaping a thin film on a wafer.
The apparatus of the invention employs a rotatable chuck for holding a wafer, a housing having a slot for receiving an edge of a wafer on the chuck, at least one plasma source mounted on the housing for generating a flow of reactive gas and a channel in the housing communicating with the plasma source to direct the flow of reactive gas toward the edge of the wafer in the slot of the housing.
In addition, an exhaust plenum is disposed within the housing for receiving the reactive gas and an exhaust line communicates with and extends from the exhaust plenum for expelling reactive gas from the plenum.
Still further, there is at least one additional channel in the housing radially within the first channel for directing a flow of diluent/quenching gas onto the wafer; and at least one exhaust channel in the housing between this additional channel and the first channel for exhausting the diluent/quenching gas and reactive gas therefrom.
Generally, the housing is of semi-circular shape to receive a major portion of the wafer on the chuck in the slot but may be of any other suitable shape.
The apparatus may also be constructed with multiple sets of the inlet channels and exhaust channel and a plurality of plasma sources, for example, three plasma sources spaced circumferentially of the housing, for selectively etching of a polymer on a wafer, etching of silicon dioxide on a wafer and depositing an encapsulating silicon dioxide layer on a wafer.
The method of the invention comprises the steps of mounting a wafer having a thin film on a rotatable chuck; directing a flow of diluent/quenching gas onto the wafer in a radially outward direction; exhausting the flow of diluent/quenching gas from the wafer downstream of the flow of diluent/quenching gas; directing a flow of reactive gases towards the wafer radially outward of the diluent/quenching gas to react with the wafer; and rotating the wafer relative to the flow of reactive gas to remove film fragments from the edge of the wafer or to deposit material on the wafer.
During rotation, the wafer is moved in a rectilinear direction relative to the flow of reactive gas to allow removal of material from the thin film normally on the wafer while shaping the thin film to a predetermined shape. Thereafter, a second flow of reactive gases can be directed towards the wafer radially outward of the diluent/quenching gas to react with the wafer to deposit material thereon while the wafer is rotated to deposit a thin protective film of the material on the shaped thin film on the wafer.
The processing capability enabled by the method and apparatus described herein addresses both removal of the flaking films and control of the film shape that remains after processing. The film shaping capability allows for the use of conventional cleaning processes without particle trapping. Further, the process can also encapsulate the freshly processed surface with a thin film that prevents future flaking.
In accordance with the invention, an in-process semiconductor substrate (wafer) is held in place on a platen (e.g., using vacuum). The platen is sufficiently smaller, in diameter, than the wafer, allowing access to all of the edge surfaces of the wafer. The platen is attached to a spindle, which, in-turn, is connected to a rotational electromechanical system. The electromechanical system enables computer control of the rotational movement of the wafer during processing. Further, the entire platen assembly is mounted on a 3-axis (X, Y, Z) linear electromechanical positioning device. Plasma sources, similar to one described in U.S. Pat. No. 5,961,772, are located in proximity to the edge surfaces of the wafer. The gaseous output-flow from the plasma source (the flame) is directed to impinge on the edge surfaces by means of gas flow hardware design and electromechanical positioning devices (X, Y and Z wafer motion axes).
Proper selection of the input gases will determine the nature of the processing performed on the wafer. Certain gas mixtures will cause material on the wafer to react with the constituents in the flame such that the reaction by-products are volatile at the operating pressure. In such cases, the process is subtractive and is commonly referred to as etching. Other input gas mixtures will cause flame constituents to react with each other to deposit material onto the wafer. In such cases, the process is additive and is commonly referred to as chemical vapor deposition (CVD).
The dwell time of the reactive gas flow on any one location of the wafer's edge surfaces shall be controlled via the computer controlled, electro-mechanical positioning devices. For shaping the local topography using an etching process, the flame shall be commanded to dwell for longer times on areas where large material removal is desired and dwell shorter times on areas where less material removal is desired. For CVD processes, the flame shall be commanded to dwell longer times where thicker films are desired and shorter times where thinner films are desired.
For both etching and CVD processes, it will be important for the boundary between the processed area and the unprocessed area to be sharply defined. For this purpose, a flow of diluent and/or quenching gas shall be provided. The diluent and/or quenching gas flow is oriented to inhibit the diffusion of reactive gases from affecting areas on the wafer not intended for processing. Further, adjustable exhaust ports will be employed to direct the reactive gas flow away from the areas not intended for processing. These and other objects and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
a illustrates a part cross-sectional view of a wafer having flaking film fragments in a peripheral edge region;
b illustrates the wafer of
c illustrates the wafer of
d illustrates the wafer of
e illustrates the wafer of
f illustrates the wafer of
a illustrates a part cross-sectional view of a wafer having flaking film fragments in a peripheral edge region;
b illustrates a part cross-sectional view of the wafer of
c illustrates the wafer of
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring to
In accordance with the prior art technique, the wafer 10 is provided with a thin film coating 11 of any suitable material. As indicated, fragment flakes 12 may break away in the form of thin film flakes. Subsequently, as indicated in
Referring to
Referring to
Referring to
Referring to
Referring to
As illustrated three sets of plasma sources, 17 (including 17t, 17e, and 17b), 17′ (including 17t′, 17e′, and 17b′) and 17″ (including 17t″, 17e″ and 17b″), quenching gas lines, 19 (including 19t and 19b), 19′ (including 19t′ and 19b′) and 19″ (including 19t″ and 19b″) and exhaust conductance control valves 21 (including 21t and 21b), 21′ (including 21t′ and 21b′) 21″ (including 21t″ and 21b″) and 24, 24′ and 24″ may be arranged around the housing, 18, as shown. In this arrangement each set can operate independently with respect to process chemistry. For example, one set can perform etching of polymers, as indicated by 17t′, 17e′, 17b′, 19t′, 19b′, 21t′, 21b′ and 24′, while another set performs etching of SiO2, as indicated by items, 17t, 17e, 17b, 19t, 19b, 21t, 21b and 24, while a third set, as indicated by items 17t″, 17e″, 17b″, 19t″, 19b, 21t″, 21b″ and 24″ deposits an encapsulating SiO2 layer.
Examples of processes are shown in Table 1. The first column contains the input gases. The second column contains the active output species. The third column contains the type of process performed and the fourth column contains the thin film addressed by the process.
A typical sequence of events to shape an SiO2 thin film on the top surface of a wafer followed by an SiO2 CVD encapsulation process as depicted in
1. A well-centered wafer, 10, is placed on the vacuum wafer platen, 16.
2. The vacuum wafer platen is moved in X, Y and Z axes such that the wafer is centered within the slot, 22, and the edge portion of the wafer is located immediately adjacent to diluent/quenching gas supply channels 19t and 19b.
3. Diluent/quenching gas flow rate setpoints are sent to the mass flow controllers (MFC) 25t and 25b and the diluent/quenching gas shutoff valves 26t and 26b are commanded to open. Gas begins to flow down diluent/quenching gas supply channels 19t and 19b and impinges on the edge of the wafer 10.
4. Fine exhaust channel conductance control valve, 21t, is commanded open to a predefined position. (Conductance control valve 21b is not opened. This allows the diluent/quenching gas flow from channel 19b to protect the backside of the wafer 10 from unwanted diffusion of reactive gases).
5. Process gas flow rate setpoints are sent to the process input gas MFCs (not shown) and process input gas shutoff valve 27t is commanded to open. Process input gases He, O2 and CF4 begin to flow through channel 30t.
6. The conductance control valve 24 of housing exhaust plenum 23 is commanded to a pre-defined position.
7. A forward power setpoint is sent to the RF power supply 29t and the RF power is commanded on. A plasma is formed inside the plasma source 17t and reactive gases begin to flow through channel 30t into the housing exhaust plenum 23 and out through the conductance control valve 24 to the exhaust system (not shown).
8. The impedance matching network, 28t, tunes the load impedance to match the output impedance of the RF power supply 29t. The control system (not shown) compares the magnitude of the power reflected back to power supply 29t to a pre-defined threshold value. The control system (not shown) decides to halt the process or continue based upon the reflected power comparison. A successful comparison signifies formation of a stable plasma inside plasma source 17t.
9. Assuming the decision is to continue, the vacuum wafer platen 16 is commanded to begin rotating at a predefined angular velocity.
10. The vacuum wafer platen 16 is commanded to move in the X, Y and Z axes, positioning the edge surfaces into the reactive gas stream flowing from reactive gas channel 30t.
11. The shaping of the thin films is controlled by the dynamics of the vacuum wafer platen's, 16, motion as follows:
12. Referring to
SiO2+F4→SiF4+O2
As the process effluent, SiF4+O2 is produced, the exhaust plenum 23 directs the effluent flow towards the exhaust system (not shown) under control of the conductance control valve 24. Continued movement of the wafer in the positive X axis brings the main portion of the coating 11 into contact with the reactive gas flowing through channel 30t and the above chemical reaction proceeds to remove a portion of coating 11. When the preprogrammed edge exclusion limit is reached the vacuum wafer platen 16 is commanded to reverse direction and move in a smoothly decelerating motion until it it arrives back at its starting position. The described motion will yield an SiO2 removal profile that, when applied to the thin film shape 11 and 12 depicted in
13. Once the thin film removal shaping is complete the RF power supply 29t is commanded off.
14. The process input gas shutoff valve 27t is closed.
15. The diluent/quenching gas shutoff valves 26t and 26b are closed.
16. The diluent/quenching gas supply channel conductance control valve 21t is closed.
17. The housing exhaust plenum's conductance control valve 24 is closed.
Depending on the application, certain metal films may have become exposed during the oxide removal step. To prevent these metal films from flaking, an encapsulating SiO2 thin film 15 can be deposited as follows:
19. Fine exhaust channel conductance control valve 21t″ is commanded open to a predefined position. (Conductance control valve 21b″ is not opened. This allows the diluent/quenching gas flow from channel 19b″ to protect the backside of the wafer 10 from unwanted diffusion of reactive gases).
20. Process gas flow rate setpoints are sent to the process input gas MFCs (not shown) and process input gas shutoff valve 27t″ is commanded to open. Process input gases He, TEOS and O3 begin to flow through channel 30t″.
21. The conductance control valve 24″ of the housing exhaust plenum 23 is commanded to a pre-defined position.
22. A forward power setpoint is sent to the RF power supply 29t″ and the RF power is commanded on. A plasma is formed inside the plasma source 17t″ and reactive gases begin to flow through channel 30t″ into the housing exhaust plenum 23 and out through the conductance control valve 24″ to the exhaust system (not shown).
23. The impedance matching network 28t″ tunes the load impedance to match the output impedance of the RF power supply 29t″. The control system (not shown) compares the magnitude of the power reflected back to power supply 29t″ to a pre-defined threshold value. The control system (not shown) decides to halt the process or continue based upon the reflected power comparison. A successful comparison signifies formation of a stable plasma inside plasma source 17t″.
24. Assuming the decision is to continue, the vacuum wafer platen 16 is commanded to begin rotating at a predefined angular velocity.
25. The vacuum wafer platen 16 is commanded to move in the X, Y and Z axes, positioning the edge surfaces into the reactive gas stream flowing from reactive gas channel 30t″.
26. The shaping of the thin film deposition is controlled by the dynamics of the motion of the vacuum wafer platen 16 as follows:
27. From the starting position the wafer 10 is moved in the X and Y direction such that the net direction vector is pointing in the direction of the plasma source 17t″. A smoothly accelerating motion is employed. As the edge of the wafer moves beneath reactive gas channel 30t″ the SiO2 thin film begins to deposit on the wafer, 10, surface according to the following chemical equation:
Si(OC2H5)+8O3→SiO2+10H2O+8CO2
As the process effluent, 10H2O+8CO2, is produced, the exhaust plenum 23 directs the flow towards the exhaust system (not shown) under control of the conductance control valve 24″. Continued movement of the wafer brings more of the previously etched thin film 11 into contact with the reactive gas flow and the above chemical reaction continues depositing the thin film 15. When the pre-programmed edge exclusion limit is reached the vacuum wafer platen 16 is commanded to reverse direction and move in a smoothly decelerating motion until it arrives back at its starting position. The described motion will yield an SiO2 thin film deposition profile that, when applied to the thin film shape 11 depicted in
28. Once the thin film deposition shaping is complete the RF power supply 29t″ is commanded off.
29. The process input gas shutoff valve 27t″ is closed.
30. The diluent/quenching gas shutoff valves 26t″ and 26b″ are closed.
31. The diluent/quenching gas supply channel conductance control valve 21t″ is closed.
33. With the processing sequence complete, the wafer 10 can be removed from the vacuum wafer platen 16.
The shape of the etched surface can be nearly anything. The limiting factors are the spatial frequency capabilities of the reactive gas footprint shape and the servo system dynamic response. Other shapes of interest might include convex or concave shapes or shapes that intersect the wafer top surface plane further in from the edge.
The protective thin film 15 may be of any suitable thickness. Typically, the film 15 is thin enough such that none of the layer of film 15 extends above the plane of the remaining film 11 and thick enough to be mechanically strong enough to weather the stresses exerted by the film 11 the protective film 15 is covering. For example, a thickness of 0.1 to 0.3 um should be sufficient. The thickness of the layer of film 15 may also be varied in the same way the etching process profile is varied, via a spatial variation of the reactive gas footprint dwell time.
The invention thus provides an apparatus and method of shaping thin films in the regions of in-process semiconductor substrates that are economical and relatively simple and efficient.
The invention also provides a method that allows flakes to be readily removed from a semiconductor substrate and the edge region of the processed substrate to be contoured to a desired shape.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
This application is a divisional of U.S. patent application Ser. No. 10/401,074 filed on Mar. 27, 2003, which claims the benefit of Provisional Application 60/376,154, filed Apr. 26, 2002. The disclosures of the above applications are incorporated herein by reference.
Number | Date | Country | |
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60376154 | Apr 2002 | US |
Number | Date | Country | |
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Parent | 10401074 | Mar 2003 | US |
Child | 11131611 | May 2005 | US |