Patent Grant
7477388
The disclosed invention relates to the use of electromagnetic radiation to investigate samples, and more particularly to the placing of an electromagnetic radiation absorbing and/or scattering and/or reflecting, (in a direction not parallel to electromagnetic radiation provided by an ellipsometer or polarimeter system which is reflected from the sample surface), mask adjacent to a sample, which mask allows electromagnetic radiation to access the sample over only a limited area determined by angle of incidence, sample thickness mask setoff from the sample surface, and ambient, surface film(s) and substrate refractive indices.
It is known in ellipsometry and polarimetry to impinge electromagnetic radiation onto a sample at an oblique angle, and collect electromagnetic radiation which reflects from the sample, then via detected change in the polarization state determine properties of the sample. Ellipsometer and Polarimeter Systems sequentially comprise a Source of a beam electromagnetic radiation, a Polarizer element, optionally a compensator element, a sample system, optionally a compensator element, an Analyzer element and a Detector System. It is noted that presence of at least one compensator is a distinguishing factor between ellipsometer and polarimeter systems.
The elements identified as a source of electromagnetic radiation, the polarizer and the sequentially first optional compensator can be considered to form, as a group, a Polarization State Generator (ie. PSG), and the sequentially second optional compensator, analyzer and detector can be considered, as a group, to form a Polarization State Detector (ie. PSD).
A problem which occurs in practicing ellipsometry or polarimetry, where a sample being investigated is not effectively infinitely thick, is that detected electromagnetic radiation which reflects from a sample includes components which reflect not only from the actual sample surface, and perhaps interfaces between thin films thereupon, but also from the back side of the substrate. Said reflection from the substrate backside confuses interpretation of the results, and while such can be accounted for in a mathematical model of the sample, it is often preferable to block said backside reflections and avoid the confusing effects thereof.
One approach to preventing backside reflections is to physically roughen the backside, however this approach alters the sample. The invention disclosed herein provides a simple approach to avoiding the effect of backside reflections without requiring sample modification.
With the present invention in mind a Search was conducted for patents that disclose means for blocking backside reflections from entering a detector. Patent Application No. 2002/0113200 A1 was identified as an aperture 103A is disclosed which can be placed near a detector to block entry of one of two beams from different sources. U.S. Pat. No. 3,799,679 to Simko is disclosed as an iris (38) is present near a detector which can be adjusted to block entry of backside reflection thereinto. Patents to Meeks, U.S. Pat. Nos. 6,130,749, 6,198,533 and 6,392,749 are disclosed for the presence of a hole 2022 in an integrating sphere near, but not atop a sample. U.S. Pat. No. 6,088,092 to Chen et al. is disclosed as it applies a spatial filter (28) to block backside reflection entry into a detector. U.S. Pat. No. 6,088,104 to Peterson is disclosed as a blocking element (B) is present which can be used to block electromagnetic radiation entry to a detector. U.S. Pat. No. 6,097,482 to Smith et al. is disclosed as it applies baffles to block light entry to a detector. U.S. Pat. No. 6,166,808 to Greve is disclosed as it describes use of an aperture near a detector to block backside reflections entry to a detector. A U.S. Pat. No. 3,857,637 to Obenredder, was identified by the Examiner in prosecution of the Parent application hereto, Ser. No, 10/731,202. It is noted that the opaque element (35) therein is shown in FIG. 3 thereof to be offset from contact with the top surface (29) of the sample glass (21). Further, in Col. 6, Lines 45-51 of the 637 patent it is stated that . . . an opaque member (35) such as a metal washer may be positioned adjacent the top surface (see FIGS. 2 and 3). In the instance where the washer is used, it would be advantageously positioned in the return tube (107) to shield the detector surface from the beam reflected from the bottom surface of the glass. However, said 637 patent does not identify or suggest applying such a mask in Ellipsometer and the like systems.
U.S. Pat. No. 5,298,974 to Chandley describes an apparatus for determining the surface topology of an article. FIG. 2 thereof suggests that a Mask-like element with a silt (5) therein can be placed into direct contact with a flat transparent article for the purpose of blocking reflections of an electromagnetic beam from the surface thereof other than those from the surface of the article. Said 974 patent does not identify or suggest applying such a mask in Ellipsometer and the like systems.
Another Published Application is WO 2005/088272A1 by Nanofilm Technologie. This publication is likely the best art found, and discloses blocking electromagnetic radiation backside reflections from a sample by a Mask which is offset from the surface of said sample, in an ellipsometer system. Also, U.S. Pat. No. 3,857,637 describes use of a mask offset from a sample in a non-ellipsometric setting and was cited by the Examiner in prosecution of the Parent application Ser. No. 10/731,202, which it is noted, in contrast, Claims a mask placed directly on the surface of a sample.
In addition, with the present invention in mind, it is further disclosed that Co-Pending application Ser. No. 11/288,785 from which this application is a CIP, is included herein by reference.
Even in view of the known prior art, need remains for a simple to practice method for avoiding effects of sample backside reflections which does not require sample, or investigating system alteration.
As described in Parent application Ser. No. 10/731,202, the disclosed invention is basically a method of investigating a sample system (SS) which typically comprises at least one thin film (TF) on the surface of a substrate (SUB), using a beam of electromagnetic radiation (EMI) which impinges thereupon at an oblique angle of incidence (O). Said method eliminates the effects of reflection from the backside (BS) of said substrate (SUB) in a beam of electromagnetic radiation (EMR) which reflects from the surface (SUR) of the substrate (SUB), or at least one thin film (TF) thereon.
One recitation of the present invention method provides that it is a method of investigating a sample which comprises a sample system (SS) having:
providing an ellipsometer or polarimeter comprising:
Another recitation of the present invention method of investigating a sample system (SS) having:
providing an ellipsometer or polarimeter comprising:
The just recited method can be applied where said at least one thin film comprises a plurality of thin films and wherein (T′″) is a composite thin film (TF) thickness and wherein (O″) is an effective oblique angle at which the beam of electromagnetic radiation which is reflected from the backside (BS) of said substrate makes in said thin film (TF), at the interface between said substrate (SUB) and said composite thin film (TF).
Another recitation of the present invention method of investigating a sample which comprises a substrate (SUB) having:
providing an ellipsometer or polarimeter comprising:
It is noted that said sample (SS) can be a composite comprising a thin film (TF) on the surface of a substrate (SUB).
In any of the foregoing methods the hole (H) in the mask can be of a shape selected from the group of:
Continuing, a present invention system for investigating a sample (SS) having:
A present invention method of investigating a sample (SS) which comprises a substrate (SUB), said sample system (SS) having:
providing a mask (M) comprising top and bottom sides, there being detector means (BDETS) on said bottom side thereof;
placing the bottom side of said mask (M) adjacent to said front side (FS) of said sample system (SS), said mask (M) having a hole (H) therein with an effective diameter (D) which is related to the thickness (T) of the substrate by the equation:
D>=2T′ TAN(θ); and
D<=T′ Tan(θ)+2T Tan(θ′)+T′ Tan(θ);
where T′ is the combined thickness of the mask and its offset (T″) from the surface of said sample (SS) and (O) is said oblique angle of incidence at which said beam of electromagnetic radiation (EMI) impinges upon said front side (BS) of said substrate (SUB), and where (T) is the thickness of said substrate (SUB) and (θ′) is an oblique angle of incidence at which said beam of electromagnetic radiation (EMI) impinges upon said back side (BS) of said substrate (SUB). Said method proceeds with the causing of an incident beam of electromagnetic radiation (EMI) of cross sectional diameter (BW) to impinge upon the surface (SUR) of the front side (FS) of said substrate (SUB) at an oblique angle of incidence (θ), such that said incident electromagnetic beam (EMI) reflects from the surface (SUR) of said front side (FS) of said substrate (SUB) as reflected electromagnetic beam (EMR) and enters a detector (DET), said reflected electromagnetic beam (EMR) having no component therein which reflected from the back side (BS) of said sample system (SS) as a result of being blocked by said mask (M). Components of electromagnetic radiation reflected from the backside (BS) of said sample system (SS) enter said detector means (BDETS) on said bottom side of said mask (M). Said method further comprises:
causing at least one selection from the group comprising:
The invention will be better understood by reference to the Detailed Description Section of the Specification, in conjunction with the Drawings.
It is therefore a primary purpose and/or objective of the disclosed invention to, in the context of ellipsometer and polarimeter systems, teach a simple system, and method of its application to block reflections from the backside of a sample from reaching a detector, which reflections result from a beam of electromagnetic radiation impinging upon said sample surface at an oblique angle.
It is a further primary purpose and/or objective of the disclosed invention to teach a simple system, and method of its application which enable separate detection of reflections that result from a beam of electromagnetic radiation impinging upon said sample surface at an oblique angle, and which reflect from either the front or back side.
Additional purposes and/or objectives of the disclosed invention will become apparent from a reading of the Specification and Claims.
a demonstrates a system containing a sample for practicing the disclosed invention including a Mask with Hole (H) present therein.
b and 2c show what are to be considered functionally equivalent Hole (H) shapes.
a shows the relationship between the thickness (T) of a sample and the diameter (D) of the hole in the mask (M) placed in contact with the sample surface necessary to block reflections from the backside (BS) of the substrate (SUB).
b shows the relationship between the thickness (T) of a sample including at least one thin film (TF) on the surface thereof, and the diameter (D) of the hole in the mask (M) placed in contact with the thin film surface necessary to block reflections from the backside (BS) of the substrate (SUB).
a shows a sample similar to that in
b shows a sample similar to that in
a demonstrates a sample as in
b demonstrates a sample as in
a and 6b shows that the mask (M) can include backside reflection detector elements (BDETS).
Turning now to the Drawings, there is shown in
The elements identified as (LS), (P) and (C) can be considered to form, as a group, a Polarization State Generator (PSG), and the components (C′), (A) and (DET) can be considered, as a group, to form a Polarization State Detector (PSD).
Turning now to
a shows the relationship between the thickness (T) of the sample and the diameter (D) of the hole in the mask (M) necessary to block reflections from the backside (BS) of the substrate (SUB). Also indicated are indices of refraction, (n0), (n1) and (n2) for the ambient, thin film (TF) and substrate (SUB) respectively. Formulas which relate the thin film (TF) thickness (T) to the effective diameter of the hole (H) are also shown in
D<=2T TAN(θ′); and
n0′ SIN(θ)=n2 Sin(θ′);
where n0′ is a composite refractive index based on (n0) and any present thin films, exemplified by (n1) in
b is similar to
It is also noted that while there is usually some thin film present on any substrate, there need not be any thin film(s) present on the substrate for the described technique to be applicable. That is, the surface of a substrate per se. can be investigated through a mask (M).
a shows a sample similar to that in
D>=2T′ TAN(θ); and
D<=T′ Tan(θ)+2T Tan(θ′)+T′ Tan(θ);
where T′ is the combined thickness of the mask and its offset (T″) from the surface of said sample (SS) and (O) is said oblique angle of incidence at which said beam of electromagnetic radiation (EMI) impinges upon said front side (BS) of said substrate (SUB), and where (T) is the thickness of said substrate (SUB) and (θ′) is an oblique angle of incidence at which said beam of electromagnetic radiation (EMI) impinges upon said back side (BS) of said substrate (SUB).
b shows a sample similar to that in
D>=2T′ TAN(θ); and
D<=T′ Tan(θ)+2T′″ Tan(θ″)+2T Tan(θ′)+T″ Tan(θ);
where (T′) comprises the combined thickness said mask (M) and its offset (T″) from the surface of said at least one thin film (TF) and (θ) is the oblique angle of incidence at which said beam of electromagnetic radiation (EMI) impinges upon said surface (SUR) of said thin film (TF), and where (T) is the thickness of said substrate (SUB) and (θ′) is an oblique angle of incidence at which said beam of electromagnetic radiation (EMI) impinges upon said back side of said sample, and where T′″ is the thickness of the at least one thin film (TF) and (θ″) is an oblique angle at which the beam of electromagnetic radiation which is reflected from the backside (BS) of said substrate makes in said thin film (TF), at the interface between said substrate (SUB) and thin film (TF).
Note that while not shown in
a demonstrates a scenario as in
b demonstrates a sample as in
a and 6b show that the mask (M) can include backside reflection detector elements (BDETS), which can comprise solid state detector elements or the ends of light fibers, for instance, which conduct collected electromagnetic radiation to separate detectors, (not shown).
It is to be understood that as regards the Masking aspect of the present invention, any mask which blocks backside reflections from entering a detector of electromagnetic radiation reflected from the front side of a sample is within the scope of the disclosed invention. Masks can be made of material which is absorbing and/or scattering and/or reflecting of electromagnetic radiation, if in a direction not parallel to the electromagnetic radiation reflected from the substrate surface.
Finally, as regards masks (M) comprising any the hole (H) geometry which are offset from the top surface of a sample by a distance (T″), (see
Having hereby disclosed the subject matter of the present invention, it should be obvious that many modifications, substitutions, and variations of the present invention are possible in view of the teachings. It is therefore to be understood that the invention may be practiced other than as specifically described, and should be limited in its breadth and scope only by the Claims.
This application is a CIP of application Ser. No. 10/731,202 Filed Dec. 10, 2003; now abandoned and Claims Benefit of Provisional Application Ser. No. 60/452,673 Filed Mar. 10, 2003 therevia. This application is further a CIP of application Ser. No. 11/288,785 Filed Nov. 30, 2005 now U.S. Pat. No. 7,385,698, and therevia of application Ser. No. 11/098,669 Filed Apr. 2, 2005 now U.S. Pat. No. 7,239,391, and therevia of the following: Ser. No. 10/238,241, Filed Sep. 10, 2002, (now U.S. Pat. No. 6,937,341);Ser. No. 10/194,881, Filed Jul. 15, 2002, (now U.S. Pat. No. 6,940,595);Ser. No. 09/756,515, Filed Jan. 9, 2001, (U.S. Pat. No. 6,455,853);Ser. No. 09/916,836, Filed Jul. 27, 2001, (now U.S. Pat. No. 6,636,309); and via application Ser. No. 11/098,669, Claims benefit of Provisional Application Ser. No. 60/639,097 Filed Dec. 27, 2004).
| Number | Name | Date | Kind |
|---|---|---|---|
| 3799679 | Simtco | Mar 1974 | A |
| 3857637 | Obenredder | Dec 1974 | A |
| 5235457 | Lichtman et al. | Aug 1993 | A |
| 5298974 | Chandley | Mar 1994 | A |
| 5510892 | Mitzutani et al. | Apr 1996 | A |
| 6088092 | Chen et al. | Jul 2000 | A |
| 6088104 | Peterson | Jul 2000 | A |
| 6097482 | Smith et al. | Aug 2000 | A |
| 6130749 | Meeks | Oct 2000 | A |
| 6166808 | Greve | Dec 2000 | A |
| 6198533 | Meeks | Mar 2001 | B1 |
| 6275291 | Abraham et al. | Aug 2001 | B1 |
| 6392749 | Meeks | May 2002 | B1 |
| 20020113200 | Hajjar et al. | Aug 2002 | A1 |
| Number | Date | Country |
|---|---|---|
| 0481649 | Apr 1992 | EP |
| WO 9624034 | Aug 1996 | WO |
| WO 2005088272 | Sep 2005 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 60452673 | Mar 2003 | US | |
| 60639097 | Dec 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10731202 | Dec 2003 | US |
| Child | 11439491 | US | |
| Parent | 11288785 | Nov 2005 | US |
| Child | 10731202 | US | |
| Parent | 11098669 | Apr 2005 | US |
| Child | 11288785 | US | |
| Parent | 10238241 | Sep 2002 | US |
| Child | 11098669 | US | |
| Parent | 10194881 | Jul 2002 | US |
| Child | 10238241 | US | |
| Parent | 09756515 | Jan 2001 | US |
| Child | 10194881 | US | |
| Parent | 09916836 | Jul 2001 | US |
| Child | 09756515 | US |
