PLASMA PROCESS EMPLOYING MULTIPLE ZONE GAS DISTRIBUTION FOR IMPROVED UNIFORMITY OF CRITICAL DIMENSION BIAS
A passivation species precursor gas is furnished to an inner zone at a first flow rate, while flowing an etchant species precursor gas an annular intermediate zone at a second flow rate. Radial distribution of etch rate is controlled by the ratio of the first and second flow rates. The radial distribution of etch critical dimension bias on the wafer is controlled by flow rate of passivation gas to the wafer edge.
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This application claims the benefit of U.S. Provisional Application Ser. No. 61/126,600, filed May 5, 2008.
BACKGROUNDIn plasma processing of semiconductor wafers, precise feature profile control has become increasingly important during gate etching as the critical dimensions of semiconductor devices continue to scale down below 45 nm. For example, the integrity and critical dimension (CD) control of the hardmask during gate mask definition is critical in gate etch applications. For example, for a polysilicon gate, the hardmask layer overlying the polysilicon layer can be silicon nitride. For etching of the silicon nitride hardmask layer, the CD of greatest criticality is the mask length at the bottom of the hardmask. Likewise, for etching of the polysilicon gate, the CD of greatest criticality is the gate length at the bottom of the polysilicon gate. This length typically defines the all-important channel length of the transistor during later process steps. Therefore, during definition (etching) of the hardmask or of the polysilicon gate, it is important to minimize discrepancy between the required CD and the CD obtained at the end of the etch step. It is also important to minimize the variation in the CD bias, the difference between the CD as defined by the mask and the final CD after the etch process. Finally, it is important to minimize the CD bias microloading, which is the difference between the CD bias in regions in which the discrete circuit features are dense or closely spaced and the CD bias in regions in which the discrete circuit features are isolated or widely spaced apart.
Various conventional techniques have been used to meet these requirements. For instance, trial-and-error techniques have been used for determining the optimum gas flow rates for the various gas species in the reactor, the optimum ion energy (determined mainly by RF bias power on the wafer) and the optimum ion density (determined mainly by RF source power on the coil antenna). The foregoing process parameters affect not only CD, CD bias and CD bias microloading but also affect other performance parameters, such as etch rate and etch rate uniformity. It may not be possible to set the process parameters to meet the required performance parameters such as etch rate and at the same time optimize CD and minimize CD bias and CD bias microloading. As a result, the process window, e.g., the allowable ranges of process parameters such as chamber pressure, gas flow rates, ion energy and ion density, may be unduly narrow to satisfy all requirements.
A current problem is that CD bias is non-uniform, decreasing near the wafer edge. This problem is becoming more acute as device feature sizes are scaled down to 32 nm and smaller. Part of this problem is the sharp drop in CD bias at the wafer edge. We believe that this sharp drop is due to the lack of etch passivation species to passivate etch by-products. The amount of passivation species affects etch profile tapering and sidewall etch rate in high aspect ratio openings. Typically, the greater the amount of passivation gas present, the greater the etch profile tapering. What is desired is the etch profile or etch profile tapering be uniform across the wafer. This will promote a uniform distribution of CD bias. Because of the lack of passivation gas at the wafer edge, the etch profile taper is small at the wafer edge and large elsewhere.
SUMMARYA method is provided for etching a surface on a workpiece. The method includes flowing a first process gas mixture including an etchant species precursor gas and a passivation species precursor gas to an annular inner zone of gas dispersers in the ceiling at a first flow rate, while flowing a second process gas mixture including an etchant species precursor gas and a passivation species precursor gas to an annular intermediate zone of gas dispersers in the ceiling surrounding the inner zone at a second flow rate. The method further includes flowing a process gas constituting predominantly or exclusively a passivation species precursor gas to an annular outer zone of gas dispersers in the ceiling surrounding the intermediate zone at a third flow rate. Radial distribution of etch rate across the entirety of the wafer is controlled by controlling the ratio of the first and second flow rates. The radial distribution of etch critical dimension bias on the wafer is controlled by controlling the third flow rate.
So that the manner in which the above recited embodiments of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
DETAILED DESCRIPTIONIn embodiments described below, the gas distribution apparatus within the ceiling 104 may distribute process gases in three gas distribution zones that receive process gas from three independent gas supply lines 141, 142, 143. These three zones are, in one embodiment, annular concentric zones including inner, middle and outer zones. The gas mixtures and flow rates in each of the lines 141, 142, 143 may be independently controlled. For example, each line 141, 142, 143 may be supplied with process gas from a respective gas source 144, 145, 146. As will be described below, the gas supply lines 141, 142, 143 supply process gas for injection in respective inner, middle and outer gas injection zones below the ceiling. The gas furnished by the gas supplies 144 and 145 to the inner and middle gas injection zones is, in one embodiment, a mixture of an etch species precursor gas and a passivation species precursor gas, and etch rate distribution across the wafer may be controlled by the ratio of the flow rates from the gas supplies 144, 145. Gas furnished by the gas supply 146 to the outer gas injection zone may be a pure or nearly pure passivation species precursor gas, and radial distribution of CD bias or etch profile taper may be controlled by varying the gas flow rate from the gas supply 146. This latter adjustment is independent or nearly independent of the adjustment of the etch rate distribution. Typically, the CD bias distribution is non-uniform because it decreases near the wafer edge, and uniformity is achieved by increasing the passivation species precursor gas flow rate to the outer gas injection zone. In this way, two etch performance parameters, namely (a) distribution of etch rate and (b) distribution of CD bias, are controlled simultaneously and nearly independently of one another in the reactor of
The ceiling 104 in one embodiment includes a showerhead orifice plate 150 having an array of gas injection orifices 152 extending through it. In the illustrated embodiment of
In the illustrated embodiment, the lid 160 consists of an equal path length manifold 162 whose top surface 162b contacts the hub 170. Referring to
In the illustrated embodiment of
Referring again to
Referring yet again to
In accordance with one feature, the array of channels 180, 190, 200 in the bottom surface 162a of the EPLM manifold 162 are configured so that the distances traveled within the EPLM 162 by process gas to different orifices within inner zone 154 are uniform. In the illustrated embodiment, the distances traveled within the EPLM 162 by process gas to different orifices 152 within the middle zone 156 are uniform. In this same embodiment, the distances traveled within the EPLM 162 by process gas to different orifices 152 within the outer zone 158 are uniform. Another feature is that the arc distances subtended by the various equal path length channels within the EPLM are all not more than fractions of a circle, which prevents or minimized inductive coupling to the gases therein.
Referring to
As shown in
The radial translation layer 164 may have its plural middle zone axial channels 230 tilted at a second acute angle B relative to the axis of symmetry. In the illustrated embodiment, each middle zone axial channel 230 may have a first end 231 open at the top surface 162b and facing the middle concentric hub channel 172. Each middle zone axial channel 230 further may have a second end in registration with one of the middle zone gas inlets 199 of the EPLM 162. In this manner, eight middle zone axial channels 230 may provide gas flow from the middle hub channel 172 to the eight middle zone gas inlets 199 of the EPLM 162.
The radial translation layer 164 may have its plural outer zone axial channels 240 tilted at a third acute angle C relative to the axis of symmetry. Each outer zone axial channel 240 has a first end 241 open at the top surface 162b and facing the outer concentric hub channel 173. Each outer zone axial channel 240 further may have a second end in registration with one of the outer zone gas inlets 209 of the EPLM 162. In this manner, eight outer zone axial channels 240 may provide gas flow from the outer hub channel 173 to the eight outer zone gas inlets 209 of the EPLM 162.
The first, second and third acute angles A, B, C may be progressively smaller to accommodate the different radial locations of the inner zone gas inlets 186, the middle zone gas inlets 199 and the outer zone gas inlets 209. In the implementation of
In the illustrated embodiment of
In the illustrated embodiment of
In the illustrated embodiment of
In the illustrated embodiment of
Referring to
The process may be applied to etching a silicon nitride or silicon oxide hard mask prior to a gate etch step. In this case the etchant species precursor may be CF4 and the passivation species precursor may be CHF3. In general, the etchant species precursor gas is a fluorocarbon (i.e., a species containing no hydrogen) while the passivation species precursor gas is a fluoro-hydrocarbon (i.e., a species containing a significant proportion of hydrogen). More generally, the etchant species precursor gas contains a high proportion of fluorine and a low proportion (less than a few percent atomic ratio) or zero amount of hydrogen, while a significant fraction (20% atomic ratio) of the passivation species is hydrogen. The gas mixtures flowed to the inner and middle zones may be identical, while their flow rates are different and independently controlled.
The etch critical dimension (CD) bias and the etch profile taper tend to be less at the wafer edge. In order to improve uniformity of radial distribution of either or both the CD bias and the etch profile tapering, the third gas flow rate (the flow rate of the pure passivation species precursor gas to the outer zone of gas dispersers) is increased until the nonuniformity in distribution of CD bias or profile taper has been minimized. An overcorrection that raises the CD bias or etch profile taper at the wafer edge above the average value across the wafer requires a corresponding reduction in the pure passivation species precursor gas in outer zone of gas dispersers.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims
1. A method for etching a surface on a workpiece, comprising:
- applying RF plasma source power at first and second independently controlled power levels to respective inner and outer coil antennas overlying the ceiling;
- flowing a first process gas mixture comprising an etchant species precursor gas and a passivation species precursor gas to an annular inner zone of gas dispersers in the ceiling at a first flow rate;
- flowing a second process gas mixture comprising an etchant species precursor gas and a passivation species precursor gas to an annular intermediate zone of gas dispersers in the ceiling surrounding the inner zone at a second flow rate;
- flowing a process gas constituting predominantly or exclusively a passivation species precursor gas to an annular outer zone of gas dispersers in the ceiling surrounding the intermediate zone at a third flow rate;
- controlling radial distribution of etch rate across the entirety of the wafer by (a) controlling the ratio of the first and second power levels in the inner and outer coil antennas and (b) controlling the ratio of the first and second flow rates; and
- controlling radial distribution of etch critical dimension bias on the wafer by controlling said third flow rate.
2. The method of claim 1 wherein said surface of said workpiece comprises a silicon-containing hardmask thin film of one of (a) silicon nitride or (b) silicon oxide, and said etchant species precursor gas comprises a fluorocarbon while said passivation species precursor gas comprises a fluoro-hydrocarbon.
3. The method of claim 1 wherein said surface of said workpiece comprises a silicon-containing thin film, and said etchant species precursor gas comprises a fluorine and carbon compound containing a small or zero atomic fraction of hydrogen while said passivation species precursor gas comprises a fluorine and carbon compound containing a significant atomic fraction of hydrogen.
4. The method of claim 3 wherein said significant atomic fraction is at least ⅕th and said small atomic fraction is less than ⅕th.
5. The method of claim 1 wherein said first and second process gas mixtures are the same.
6. The method of claim 1 wherein:
- each of the annular zones of gas dispersers constitute gas dispersers arranged in respective circles at uniform intervals for each circle;
- each said flowing is performed so that the flow rate and pressure at all the gas dispersers within a given zone is uniform.
7. The method of claim 6 wherein each said flowing comprises flowing the gas through uniform path lengths to each of the gas dispersers within a given one of said zones.
8. The method of claim 1 wherein said controlling CD bias comprises increasing said third flow rate whenever CD bias near an edge of said workpiece is less than elsewhere on said workpiece, while controlling etch rate distribution across said workpiece independently of the distribution of said CD bias.
9. The method of claim 1 wherein said controlling CD bias comprises decreasing said third flow rate whenever CD bias near an edge of said workpiece is greater than elsewhere on said workpiece, while controlling etch rate distribution across said workpiece independently of the distribution of said CD bias.
10. The method of claim 1 wherein said controlling etch profile taper comprises increasing said third flow rate whenever etch profile taper near an edge of said workpiece is less than elsewhere on said workpiece, while controlling etch rate distribution across said workpiece independently of the distribution of said CD bias.
11. The method of claim 1 wherein said controlling etch profile taper comprises decreasing said third flow rate whenever etch profile taper near an edge of said workpiece is greater than elsewhere on said workpiece, while controlling etch rate distribution across said workpiece independently of the distribution of said CD bias.
12. A method for etching a surface on a workpiece, comprising:
- flowing a first process gas mixture comprising an etchant species precursor gas and a passivation species precursor gas to an annular inner zone of gas dispersers in the ceiling at a first flow rate;
- flowing a second process gas mixture comprising an etchant species precursor gas and a passivation species precursor gas to an annular intermediate zone of gas dispersers in the ceiling surrounding the inner zone at a second flow rate;
- flowing a process gas constituting predominantly or exclusively a passivation species precursor gas to an annular outer zone of gas dispersers in the ceiling surrounding the intermediate zone at a third flow rate;
- controlling radial distribution of etch rate across the entirety of the wafer by controlling the ratio of the first and second flow rates; and
- controlling radial distribution of etch critical dimension bias on the wafer by controlling said third flow rate.
13. The method of claim 12 wherein said surface of said workpiece comprises a silicon-containing hardmask thin film of one of (a) silicon nitride or (b) silicon oxide, and said etchant species precursor gas comprises a fluorocarbon while said passivation species precursor gas comprises a fluoro-hydrocarbon.
14. The method of claim 12 wherein said surface of said workpiece comprises a silicon-containing thin film, and said etchant species precursor gas comprises a fluorine and carbon compound containing a small or zero atomic fraction of hydrogen while said passivation species precursor gas comprises a fluorine and carbon compound containing a significant atomic fraction of hydrogen.
15. The method of claim 14 wherein said significant atomic fraction is at least ⅕th and said small atomic fraction is less than ⅕th.
Type: Application
Filed: Jun 20, 2008
Publication Date: Nov 5, 2009
Applicant: Applied Materials, Inc. (Santa Clara, CA)
Inventors: Dan Katz (San Jose, CA), David Palagashvili (Mountain View, CA), Brian K. Hatcher (San Jose, CA), Theodoros Panagopoulos (San Jose, CA), Valentin N. Todorow (Palo Alto, CA), Edward P. Hammond, IV (Hillsborough, CA), Alexander M. Paterson (San Jose, CA), Rodolfo P. Belen (San Francisco, CA)
Application Number: 12/143,146
International Classification: H01L 21/302 (20060101);