SMALL MOLECULE FILMS FOR SACRIFICIAL BRACING, SURFACE PROTECTION, AND QUEUE-TIME MANAGEMENT

Abstract

The present disclosure relates to methods of forming a film including small molecules. Such methods can optionally include removing such small molecules, such as by way of sublimation, evaporation, or conversion to a more volatile form.

Claims

1. A method comprising: forming a film comprising small molecules on a surface of a substrate to protect the surface, thereby providing a protected surface.

2. The method of claim 1, further comprising: storing the protected surface in ambient conditions; and removing the small molecules from the surface of the substrate.

3. The method of claim 1, wherein said forming a film comprises a vapor comprising the small molecules or a solution comprising the small molecules.

4. The method of claim 2, wherein said removing the small molecules comprises inducing sublimation or evaporation of the small molecules.

5. The method of claim 1, further comprising, prior to said removing the small molecules, bringing the substrate into a chamber with pressure less than atmospheric pressure.

6. The method of claim 1, further comprising, prior to said removing the small molecules, converting the small molecules to a more volatile form.

7. The method of claim 1, further comprising converting the small molecules on the surface of the substrate to a less volatile form prior to said storing the protected surface in ambient conditions.

8. The method of claim 7, wherein said converting the small molecules to a less volatile form comprises photoisomerization.

9. The method of claim 7, wherein said converting the small molecules to a less volatile form comprises photodimerization.

10. The method of claim 7, wherein said converting the small molecules to a less volatile form comprises a Diels-Alder reaction.

11. The method of claim 1, wherein said converting the small molecules comprises providing a compound comprising one of formulas (Ia), (IIa), (IIIa), (IVa), (Va), and (VIII).

12. The method of claim 1, wherein the film is formed in a process chamber in which the substrate was immediately previously processed.

13. The method of claim 1, wherein at least one of the small molecules comprises a compound comprising one of formulas (I), (II), (III), (IV), (V), (VI), and (VII).

14. A method comprising: forming a film comprising small molecules on a surface of a substrate including high aspect ratio (HAR) structures, wherein the film can fill the HAR structures or form within the HAR structures; and exposing the substrate to a stimulus to induce sublimation of the small molecules.

15. (canceled)

16. The method of claim 14, wherein the substrate including the HAR structures further comprises a first solvent, and wherein said forming the film comprises: displacing the first solvent with a solution including small molecules and drying the substrate to form a solid film of small molecules.

17. The method of claim 14, wherein the small molecules are characterized by having a vapor pressure of less than about 76 mTorr at room temperature.

18. The method of claim 14, wherein the small molecules are solid at room temperature and atmospheric pressure.

19. The method of claim 14, wherein the small molecules have a vapor pressure of at least 10 Torr and no melting point at temperature less than about 400° C.

20. The method of claim 14, wherein the small molecules are fused aromatic rings.

21. The method of claim 20, wherein the small molecules are anthracene or naphthalene.

22. The method of claim 14, wherein at least one of the small molecules comprises a compound comprising one of formulas (I), (II), (III), (IV), (V), (VI), and (VII).

23. A processing tool comprising one or more semiconductor substrate processing chambers connected under vacuum; and a controller comprising instructions for forming a film comprising small molecules on a surface of a substrate to protect the surface and exposing the substrate to a stimulus to induce sublimation of the small molecules.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0063] FIG. 1 is a functional block diagram of an example of a substrate processing system including multiple substrate processing tools and a storage buffer according to the present disclosure.

[0064] FIG. 2 is a flow diagram showing certain operations in an example of a method for protection of an environmentally sensitive surface of a substrate.

[0065] FIG. 3 is a flow diagram showing certain operations in another example of a method for protection of an environmentally sensitive surface of a substrate.

[0066] FIG. 4 is a schematic showing an example of a substrate including a surface to be protected.

[0067] FIG. 5 is a flow diagram showing certain operations in an example of a method for bracing HAR structures using a film of small molecules.

[0068] FIG. 6 is a flow diagram showing certain operations in another example of a method for bracing HAR structures using a film of small molecules.

DETAILED DESCRIPTION

[0069] Provided are small molecule films for surface protection and queue-time management and related methods. Also provided herein small molecule films for sacrificial bracing of high aspect ratio (HAR) structures and related methods.

[0070] As used herein, the term small molecule refers to molecules having a size of 1000 daltons (grams/mole) or less or dimerized versions of these molecules. In particular embodiments, the small molecule can have a size of 500 daltons or less or be dimerized versions of these molecules.

[0071] Substrate surfaces may be exposed to ambient conditions during semiconductor fabrication. Many of the substrate surfaces are sensitive to modification due to ambient or environmental exposure. The surface changes that occur can adversely impact a subsequent process and/or degrade device performance. These exposure phenomena may be referred to herein as queue time effects.

[0072] A sacrificial protection layer including a film of small molecules may be applied after processing and prior to exposure to ambient conditions during transfer or storage. In some examples, the substrates may be exposed to ambient conditions during transfer to and/or storage in a storage buffer or other location. In other examples, the substrates may be exposed to ambient conditions during transfer from one substrate processing chamber or tool to another substrate processing chamber or tool.

[0073] After storage and/or transfer and prior to additional substrate processing, the sacrificial protective layer is removed by sublimation and/or, with a short period as a liquid, evaporation. In some examples, removal of the sacrificial protective layer is performed in a substrate processing tool and then other processes are performed on the substrate in the same substrate processing tool without exposure to ambient conditions. In some examples, a single substrate has the sacrificial protection layer applied and removed a plurality of times during substrate processing.

[0074] Referring now to FIG. 1, a substrate processing system 100 includes one or more substrate processing tools 102 (substrate processing tools 102-1 and 102-2 are shown for illustration purposes) and substrate buffer 130 or other substrate storage. Each of the substrate processing tools 102-1 and 102-2 includes a plurality of processing chambers 104-1, 104-2, . . . and 104-M (collectively processing chambers 104) (where M is an integer greater than one). For example only, each of the processing chambers 104 may be configured to perform a substrate treatment. In some examples, the substrates may be loaded into one of the processing chambers 104, processed, and then moved to one or more other ones of the processing chambers 104 and/or removed from the substrate processing tool 100 (e.g., if all perform the same treatment).

[0075] Substrates to be processed are loaded into the substrate processing tools 102-1 and 102-2 via ports of a loading station of an atmosphere-to-vacuum (ATV) transfer module 108. In some examples, the ATV transfer module 108 includes an equipment front end module (EFEM). The substrates are then transferred into one or more of the processing chambers 104. For example, a transfer robot 112 is arranged to transfer substrates from loading stations 116 to load locks 120. A vacuum transfer robot 124 of a vacuum transfer module 128 is arranged to transfer substrates from the load locks 120 to the various processing chambers 104.

[0076] After processing in one or more of the substrate processing tools 102-1 and 102-2, the substrates may be transported outside of a vacuum environment. For example, the substrates may be moved to a location for storage (such as the substrate buffer 130). In other examples, the substrates may be moved directly from the substrate processing tool to another substrate processing tool for further processing or from the storage buffer 130 to another substrate processing tool for further processing.

[0077] Exposure of the substrate to ambient conditions may cause defects or otherwise adversely impact downstream processing. Systems and methods according to the present disclosure are used to add the sacrificial protective layer to the substrate prior to exposure to ambient conditions. In some examples, the sacrificial protective layer is applied in the substrate processing tool prior to transferring the substrate to the substrate buffer for storage or to another substrate processing tool. In other examples, the sacrificial protective layer is applied in another processing chamber (not associated with the substrate processing tool).

[0078] Prior to performing another treatment on the substrate, the sacrificial protective layer is removed. For example, the substrate may be transferred to the substrate processing tool 102-2 after a period of storage in the storage buffer 130 or after processing in the substrate processing tool 102-1. The sacrificial protective layer may be removed in one of the processing chambers in the substrate processing tool 102-2, another processing chamber (not associated with the substrate processing tool 102-2). In some embodiments, the sacrificial protective layer is removed in a load lock 120.

[0079] In some examples, the sacrificial protective layer is applied by a processing chamber in the same substrate processing tool (that performed substrate treatment) prior to exposure to ambient conditions. Since the substrate processing tool operates at vacuum, exposure of the substrate to ambient conditions is prevented.

[0080] In some examples, the sacrificial layer is deposited after a wet clean process. In this case, oxides and residues may be removed by the wet clean process and the sacrificial layer is deposited in sequence prior to drying the wafer. In some examples, this process is not done under vacuum and is done without any exposure of the dry pristine surface to the ambient.

[0081] In other examples, the substrate is transported from the substrate processing tool to another processing chamber located outside of the substrate processing tool that adds the sacrificial protective layer. Using this approach limits or reduces the period of exposure of the substrate to ambient conditions. Exposure is limited to a brief period of transport from the substrate processing tool to the processing chamber where the sacrificial protective layer is applied. Storage of the substrate may be performed for longer periods without additional exposure to ambient conditions.

[0082] Subsequently, the sacrificial protective layer may be removed prior to further processing. In some examples, the sacrificial protective layer is removed in another substrate processing tool under vacuum conditions prior to substrate treatment in processing chambers of the same substrate processing tool. In other examples, the substrate is transported to a processing chamber that removes the sacrificial protective layer and then to the substrate processing tool for further processing. This approach also limits exposure to ambient conditions between the processing chamber and the substrate processing tool or other environment.

[0083] In one example, the sacrificial protective layer is formed immediately after etch, deposition, or other process by exposing the substrate to a small molecule vapor that condenses on the surface to form a film. This can be performed directly inside the tool in which the etch or deposition occurred (e.g., substrate processing tool 102-1) and may occur in the same processing chamber in which the etch or deposition occurred. The substrate is then taken to the next tool for processing (e.g., substrate processing tool 102-2). Once the substrate is again no longer exposed to ambient conditions (for example by bringing the substrate under vacuum or an atmosphere purged with an inert gas) vacuum and stimuli are applied to induce the film to degrade and be removed from the substrate. This may take place for example inside of the load lock (e.g., load lock 120) or inside of the next processing chamber (e.g., processing chamber 104-1),

[0084] FIG. 2 shows an example of a method for protection of an environmentally sensitive surface of a substrate. At operation 201, a substrate including a sensitive surface is provided. The surface may be a planar surface or include one or more pillars, holes, and trenches, including HAR structures. Examples of substrate surfaces that can be sensitive to environmental queue time effects include silicon, silicon germanium, and germanium structures such as fins and nanowires, metal surfaces including but not limited to tungsten or molybdenum, and/or other structures and materials.

[0085] A film including small molecules is then formed on the substrate in an operation 203. In some embodiments, this may involve exposing the surface to a vapor including the small molecules such that they condense on the surface to form the film. In some embodiments, this may involve spin-coating a solution including the small molecules in an appropriate solvent, and then removing the solvent. Non-limiting methodologies of forming a film include vapor-based deposition, such as chemical vapor deposition; and solvent-based deposition, such as spin-coating, drop-casting, or solvent-casting. As described further below, in some embodiments, after operation 203, a stimulus may be applied to convert the molecule to a less volatile form for stability.

[0086] The film formed in operation 203 may be the sacrificial protective layer described above with reference to FIG. 1. The substrate can then be stored in ambient conditions in an operation 205. When ready for further processing, the substrate is exposed to a stimulus, such as heat and/or light, that induces sublimation or evaporation in an operation 207. As described further below, in some embodiments, prior to or as part of operation 207, a stimulus may be applied to convert the molecule to a more volatile form for easy removal.

[0087] The small molecules may have relatively low vapor pressure at room temperature; in some embodiments, it less than about 1×10.sup.−4 atm or less than about 76 mTorr. The small molecules are solid at atmospheric pressure and room temperature (about 20° C.-25° C.). The small molecules are further characterized by having a vapor pressure of at least 10 Torr at a temperature higher than 20° C. below about 400° C. Examples of such small molecules include fused aromatic rings such as naphthalene and anthracene.

[0088] The film of small molecules may have a non-negligible vapor pressure once on the substrate, potentially contaminating the loading stations or other storage units, or contaminating the wafer backside during queue time. Thus, a chemical or physical switch may be incorporated into the molecule such that once on the substrate, it becomes significantly less volatile than in its initial form and is locked into place. FIG. 3 shows another example of a method for protection of an environmentally sensitive surface of a substrate. Operations 301 and 303 are performed as described above with respect to operations 201 and 203 of FIG. 2. Then, in an operation 304, the small molecules are converted to a less volatile form. In some other embodiments, the film may be formed with the less volatile form such that operation 304 is not performed, or not performed while the molecules are on the substrate surface. The substrate in then stored in ambient conditions in an operation 305. Once ready for the next processing operation, the molecules are converted to the more volatile form in an operation 306. The substrate is then exposed to a stimulus to induce sublimation or evaporation of the small molecules in an operation 307. Operation 306 may be part of or overlap with operation 307.

[0089] Operations 304 and 306 involve exposure to appropriate stimulus including radiation, heat, or exposure to a particular compound under appropriate conditions. For example, in some embodiments, operations 304 and 306 involves exposing the film to light at specific wavelength. In some embodiments, operation 304 involves a mixture of chemicals supplied under specific conditions to form the less volatile form. Examples of reversible chemical reactions that may be performed in operation 304 include photoisomerization of a molecule such as stilbene from trans to cis, photodimerization, and a combination reaction such as a Diels-Alder reaction.

[0090] In a specific example, operation 304 involves the dimerization of anthracene, which requires UV light to go forward (e.g., UV light above 300 nm, which can promote photo-cycloaddition to promote dimerization). It is reversible in operation 306 with the trigger of heat or additional UV light of a higher energy, such as UV light below 300 nm (e.g., which can reverse the photo-cycloaddition reaction, thus producing monomers).

##STR00001##

[0091] In some embodiments, operation 304 involves a Diels-Alder reaction:

##STR00002##

[0092] For example, cyclopentadiene reacts spontaneously at room temperature to yield dicyclopentadiene, and reverts back to cyclopentadiene at temperatures above approximately 125° C. Addition of heat can thermally reverse the cycloaddition reaction, thereby producing the initial reactants. As discussed above, in some embodiments, operation 304 may be omitted with operation 306 performed to form cyclopentadiene.

##STR00003##

[0093] Other photodimerization, photopolymerization, photoisomerization, and Diels-Alder reactions can be employed with small molecules useful for conducting such reactions, as described herein.

[0094] Photodimerization and photopolymerization can include, for instance, optionally substituted anthracene or optionally substituted naphthalene. Optional substitutions for such compounds can include alkyl, alkenyl, alkynyl, aryl, heterocyclyl, cyano, nitro, amino, aminoalkyl, azido, azidoalkyl, hydroxyl, hydroxyalkyl, halo, haloalkyl, carboxyl (—CO.sub.2H), carboxyalkyl, carboxyaldehyde (—C(O)H), alkoxy, aryloxy, alkanoyl (e.g., —C(O)—R, in which R is alkyl), aryloyl (e.g., —C(O)—R, in which R is aryl), alkanoyloxy (e.g., —O—C(O)—R, in which R is alkyl), aryloyloxy (e.g., —O—C(O)—R, in which R is aryl), alkoxycarbonyl (e.g., —C(O)—OR, in which R is alkyl), aryloxycarbonyl (e.g., —C(O)—OR, in which R is aryl), and/or oxo.

[0095] In one embodiment, the small molecule is a compound including formula (I):

##STR00004##

or a salt thereof, in which each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, optionally substituted amino, azido, hydroxyl, halo, carboxyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, and/or optionally substituted aryloyl. In some instances, the small molecule can undergo photodimerization to provide a dimer including formula (Ia):

##STR00005##

in which each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 can be any described herein for formula (I). The photodimerization reaction can also result in a dimer that is a structural isomer of formula (Ia), such as a positional isomer in which the position of substituents R.sup.1, R.sup.2, R.sup.3, and R.sup.4 can differ based on the alignment of the monomer (formula (I)) during photodimerization.

[0096] In another embodiment, the small molecule is a compound including formula (II):

##STR00006##

or a salt thereof, in which each of R.sup.1 and R.sup.2 is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, optionally substituted amino, azido, hydroxyl, halo, carboxyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, and/or optionally substituted aryloyl. In some instances, the small molecule can undergo photodimerization to provide a dimer including formula (IIa):

##STR00007##

in which each of R.sup.1 and R.sup.2 can be any described herein for formula (II). The photodimerization reaction can also result in a dimer that is a structural isomer of formula (IIa), such as a positional isomer in which the position of substituents R.sup.1 and R.sup.2 can differ based on the alignment of the monomer (formula (II)) during photodimerization.

[0097] Photoisomerization, as well as photodimerization and photopolymerization reactions, can be employed with stilbene or derivatives thereof. Optional substitutions for such compounds can include alkyl, alkenyl, alkynyl, aryl, heterocyclyl, cyano, nitro, amino, aminoalkyl, azido, azidoalkyl, hydroxyl, hydroxyalkyl, halo, haloalkyl, carboxyl, carboxyalkyl, carboxyaldehyde, alkoxy, aryloxy, alkanoyl, aryloyl, alkanoyloxy, aryloyloxy, alkoxycarbonyl, aryloxycarbonyl, and/or oxo.

[0098] In one embodiment, the small molecule is a compound including formula (III):

##STR00008##

or a salt thereof, in which R.sup.1 is H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, azido, hydroxyl, halo, carboxyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkoxycarbonyl, or optionally substituted aryloxycarbonyl; and Ar1 is optionally substituted with one or more of the following: optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, amino, optionally substituted aminoalkyl, azido, optionally substituted azidoalkyl, hydroxyl, optionally substituted hydroxyalkyl, halo, optionally substituted haloalkyl, carboxyl, optionally substituted carboxyalkyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkanoyloxy, optionally substituted aryloyloxy, optionally substituted alkoxycarbonyl, and/or optionally substituted aryloxycarbonyl.

[0099] In some instances, the small molecule can undergo photodimerization to provide a dimer including formula (IIIa):

##STR00009##

[0100] in which each of R.sup.1 and Ar1, independently, can be any described herein for formula (III). The photodimerization reaction can also result in a dimer that is a structural isomer of formula (IIIa), such as a positional isomer in which the position of substituents R.sup.1 and Ar1 can differ based on the alignment of the monomer (formula (III)) during photodimerization.

[0101] In another instance, the small molecule is a compound including formula (IV):

##STR00010##

or a salt thereof, in which each R.sup.1 is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, azido, hydroxyl, halo, carboxyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkoxycarbonyl, or optionally substituted aryloxycarbonyl; and Ar1 is optionally substituted with one or more of the following: optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, amino, optionally substituted aminoalkyl, azido, optionally substituted azidoalkyl, hydroxyl, optionally substituted hydroxyalkyl, halo, optionally substituted haloalkyl, carboxyl, optionally substituted carboxyalkyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkanoyloxy, optionally substituted aryloyloxy, optionally substituted alkoxycarbonyl, and/or optionally substituted aryloxycarbonyl.

[0102] In some instances, the small molecule can undergo photopolymerization to provide a polymer including formula (IVa):

##STR00011##

in which each of R.sup.1 and Ar1, independently, can be any described herein for formula (IV) and in which n is from 1 to 10,000. The photopolymerization reaction can also result in a polymer that is a structural isomer of formula (IVa), such as a positional isomer in which the position of substituents R.sup.1 and Ar1 can differ based on the alignment of the monomer (formula (IV)) during photopolymerization.

[0103] In yet another instance, the small molecule is a compound including formula (V):

##STR00012##

or a salt thereof, in which Z is an optionally substituted aryl, optionally substituted heteroaryl, or optionally substituted heterocyclyl; and each of Ar1 and Ar2 is, independently, optionally substituted with one or more of the following: optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, amino, optionally substituted aminoalkyl, azido, optionally substituted azidoalkyl, hydroxyl, optionally substituted hydroxyalkyl, halo, optionally substituted haloalkyl, carboxyl, optionally substituted carboxyalkyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkanoyloxy, optionally substituted aryloyloxy, optionally substituted alkoxycarbonyl, and/or optionally substituted aryloxycarbonyl.

[0104] In some instances, the small molecule can undergo photopolymerization to provide a polymer including formula (Va):

##STR00013##

in which each of Z, Ar1, and Ar2, independently, can be any described herein for formula (V) and in which n is from 1 to 10,000. The photopolymerization reaction can also result in a polymer that is a structural isomer of formula (Va), such as a positional isomer in which the position of substituents Z, Ar1, and Ar2 can differ based on the alignment of the monomers (formula (V)) during photopolymerization.

[0105] Diels-Alder reactions may be performed by employing a diene (or a diyne) and a dienophile (or a diynophile) to provide a cyclic derivative. Non-limiting dienes include a cyclic or acyclic compound having two or more double bonds, such as those having a 4π electron system, including an optionally substituted 1,3-unsaturated compound (e.g., optionally substituted 1,3-butadiene, optionally substituted cyclopentadiene, optionally substituted cyclohexadiene, optionally substituted furan, optionally substituted thiofuran, or optionally substituted imine) or an optionally substituted benzene. Non-limiting diynes include a cyclic or acyclic compound having two or more triple bonds, such as an optionally substituted 1,3-butadiyne. Non-limiting dienophiles, heterodienophiles, and diynophiles having a 2π electron system include an optionally substituted alkene, optionally substituted alkyne, optionally substituted ketone, optionally substituted aldehyde, optionally substituted heteroalkene, optionally substituted imine, optionally substituted benzene, optionally substituted cycloalkene, and optionally substituted cycloheteroalkene.

[0106] The cyclic derivative can include, e.g., an optionally substituted cycloalkene (e.g., optionally substituted cyclohexene or optionally substituted 1,4-cyclohexadiene), optionally substituted dihydropyran (e.g., optionally substituted 3,6-dihydro-2H-pyran), optionally substituted tetrahydropyridine (e.g., optionally substituted 1,2,3,6-tetrahydropyridine), optionally substituted benzene, optionally substituted dihydronaphthalene, optionally substituted norbornene, optionally substituted heteronorbornene, optionally substituted benzonorbornene, optionally substituted heterocycle, optionally substituted carbocycle, or optionally substituted dicyclopentadiene.

[0107] The diene, diyne, dienophile, diynophile, and cyclic derivative can include one or more optional substitutions, such as any described herein for alkyl and aryl. In other embodiments, optional substitutions for such compounds include alkyl, alkenyl, alkynyl, aryl, heterocyclyl, cyano, nitro, amino, aminoalkyl, azido, azidoalkyl, hydroxyl, hydroxyalkyl, halo, haloalkyl, carboxyl, carboxyalkyl, carboxyaldehyde, alkoxy, aryloxy, alkanoyl, aryloyl, alkanoyloxy, aryloyloxy, alkoxycarbonyl, aryloxycarbonyl, oxo, trialkylsilyl (e.g., —SiR.sub.3, in which R is alkyl as defined herein), or trialkylsilyloxy (e.g., —OSiR.sub.3, in which R is alkyl as defined herein).

[0108] A non-limiting Diels-Alder reaction includes the following:

##STR00014##

in which a first small molecule including formula (VI) is reacted with a second small molecule including formula (VII) to provide a cyclic derivative having formula (VIII).

[0109] In one embodiment, the small molecule is a compound including formula (VI):

##STR00015##

or a salt thereof, in which

[0110] Xa is ═CR.sup.aR.sup.b, ═NR.sup.a, ═O, or ═S, in which ═ indicates a bivalent moiety;

[0111] Xb is ═CR.sup.a— or ═N—, in which use of ═ with — indicates a trivalent moiety;

[0112] each of R.sup.1, R.sup.2, R.sup.5, R.sup.a, and R.sup.b is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, azido, hydroxyl, halo, carboxyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkoxycarbonyl, optionally substituted aryloxycarbonyl, optionally substituted trialkylsilyl, or optionally substituted trialkylsilyloxy; and

[0113] wherein Xa and R.sup.5 can optionally be taken together to be ═CR.sub.a—Xc-, in which Xc is —O—, —S—, —NR.sup.a—, —C(O)O—, or optionally substituted alkylene (e.g., —CR.sup.aR.sup.b— or —CR.sup.a1R.sup.b1CR.sup.a2R.sup.b2—, in which R.sup.a, R.sup.a1, R.sup.a2, R.sup.b, R.sup.b1, and R.sup.b2 are any described herein for R.sup.a or R.sup.b).

[0114] In particular embodiments, small molecule is a compound including formula (VIa) or (VIb):

##STR00016##

or a salt thereof, in which each of Xb, Xc, R.sup.1, R.sup.2, R.sup.5, R.sup.a, and R.sup.b can be any described herein for formula (VI).

[0115] In another embodiment, the small molecule is a compound including formula (VII):

##STR00017##

or a salt thereof, in which

[0116] Ya is ═CR.sup.aR.sup.b, ═NR.sup.a, ═O, or ═S, in which ═ indicates a bivalent moiety;

[0117] each of R.sup.3, R.sup.4, R.sup.a, R.sup.a1, R.sup.a2, R.sup.a3, and R.sup.b is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, azido, hydroxyl, halo, carboxyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkoxycarbonyl, or optionally substituted aryloxycarbonyl; and

[0118] wherein Ya and R.sup.4 can optionally be taken together to be ═CR.sup.a1—CR.sup.a2═CR.sup.a3—Xc-, in which Xc is —O—, —S—, —NR.sup.a—, —C(O)O—, or optionally substituted alkylene (e.g., —CR.sup.aR.sup.b— or —CR.sup.a1R.sup.b1CR.sup.a2R.sup.b2—, in which R.sup.a, R.sup.a1, R.sup.a2, R.sup.b, R.sup.b1, and R.sup.b2 are any described herein for R.sup.a or R.sup.b).

[0119] In particular embodiments, the small molecule is a compound including one of formulas (VIIa)-(VIId):

##STR00018##

or a salt thereof, in which each of Xc, R.sup.3, R.sup.4, R.sup.a, R.sub.a1, R.sup.a2, R.sup.a3, and R.sup.b can be any described herein for formula (VII).

[0120] Reactions between two small molecules can provide a cyclic derivative, such as, e.g., a compound including formula (VIII):

##STR00019##

or a salt thereof, in which

[0121] each of Xa and Ya is, independently, ═CR.sup.aR.sup.b, ═NR.sup.a, ═O, or ═S, in which ═ indicates a bivalent moiety;

[0122] Xb is ═CR.sup.a— or ═N—, in which use of ═ with — indicates a trivalent moiety;

[0123] each of R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.a, R.sup.a1, R.sub.a2, R.sup.a3, and R.sup.b is, independently, H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocyclyl, cyano, nitro, azido, hydroxyl, halo, carboxyl, carboxyaldehyde, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkanoyl, optionally substituted aryloyl, optionally substituted alkoxycarbonyl, optionally substituted aryloxycarbonyl, optionally substituted trialkylsilyl, or optionally substituted trialkylsilyloxy; and

[0124] wherein Ya and R.sup.4 can optionally be taken together to be ═CR.sup.a1—CR.sup.a2═CR.sup.a3—Xc-, and

[0125] wherein Xa and R.sup.5 can optionally be taken together to be ═CR.sup.a—Xc-, in which Xc is —O—, —S—, —NR.sup.a—, —C(O)O—, or optionally substituted alkylene (e.g., —CR.sup.aR.sup.b— or —CR.sup.a1R.sup.b1CR.sup.a2R.sup.b2, in which R.sup.a, R.sup.a1, R.sup.a2, R.sup.b, R.sup.b1, and R.sup.b2 are any described herein for R.sup.a or R.sup.b).

[0126] In particular embodiments, the cyclic derivative is a compound including one of formulas (VIIIa)-(VIIIe):

##STR00020##

or a salt thereof, in which each of Xb, Xc, Ya, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.a, R.sup.a1, R.sup.a2, R.sup.a3, R.sup.b, R.sup.b1, and R.sup.b3 can be any described herein for formula (VIII). In particular instances, R.sup.b1 and R.sup.b3 are any described herein for R.sup.b in formula (VIII).

[0127] In some embodiments, the sacrificial protective layer including small molecules may be part of a multi-layer transient protective film. FIG. 4 shows an example of a substrate 401 including a surface to be protected. A multi-layer film including small molecule layer 403 and layer 405 is on the substrate surface and serves as a transient protective layer. For example, the multi-layer film may be implemented to protect surfaces as described above with respect to FIG. 2. In addition to the small molecule layer, the multi-layer film includes one or more cap layers that provide protection from unwanted oxidation, corrosion, or halogenation due to exposure to ambient conditions. In the example of FIG. 4, there is one cap layer 405, however additional cap layers of the same or different composition may be used. Examples of thicknesses may range from 2-1000 nm for a small molecule layer, and from a few nm's to several microns for the one or more cap layers. Thicknesses may depend on storage ambient and length of time, for example.

[0128] The cap layer 405 may be a high density material with little-to-no porosity or defects. It is deposited in a manner that does not degrade the small molecule material. Example deposition processes can include electron-beam evaporation, various sputtering processes, atomic layer deposition, and chemical vapor deposition. Example cap layers can include oxide films such as SiO.sub.x, SnO.sub.x, AlO.sub.x, TiO.sub.x, ZrO.sub.x, HfO.sub.x, and ZnO.sub.x, and nitride films such as SiN.sub.x wherein x is a number greater than 0. In some embodiments, the cap layer may be a polymer film.

[0129] The layer in contact with the environmentally sensitive surface generally contains the small molecules, which can be removed in a benign way with little residue left behind. To construct the film, the small molecule layer is first spin-coated or vapor deposited. Then one or more cap layers are subsequently deposited onto the small molecule layer. Vapor-phase, low temperature, non-plasma CVD techniques may be used to avoid small molecule degradation. Additionally, the cap layer may be spun cast on top of the small molecule film using a solvent that does not dissolve the small molecule layer. Multiple different types of films may be deposited multiple times in a repeated stack to optimize protection of the surface.

[0130] In some embodiments, a first cap layer may be deposited by a mild CVD process to protect the small molecule film followed by deposition by a harsher technique such as PECVD to grow faster, more robust films. The temperature of the substrate should generally be below a degradation temperature of the small molecule film throughout the entire process, or exceed it for no more than a few seconds.

[0131] Removing the one or more cap layers can involve using a plasma or solvent to degrade these layers, turning off the plasma or removing the solvent before the small molecule film itself is fully removed. The small molecule film can then be removed, leaving behind the clean surface of interest, which is protected from the harsh chemistries or conditions used to remove the cap layers.

[0132] In some embodiments, the cap layers may be peeled-off by attaching them with an adhesive to another substrate, while the first substrate remains chucked or affixed to some kind of holder. The whole assembly is then heated while being pulled apart. Since the heating may serve to degrade the small molecule material, this spot is where the two halves separate, leaving behind a clean substrate free of the protecting film, while the bulk of the protecting film remains attached by the adhesive to the second substrate.

[0133] Also provided herein methods of bracing HAR structures with films of small molecules. FIG. 5 is an example of a method for bracing HAR structures using a film of small molecules. First at an operation 501, a substrate including HAR structures with a solvent is provided. HAR structures are structures having high aspect ratios (ARs), e.g., at least 8, 10, 20, 30, 40, or 80. The substrate may be provided, for example, after a wet etch or cleaning operation and have solvent associated with the prior operation. In some embodiments, the solvent in operation 501 may be a transitional solvent if the prior solvent is not chemically compatible with the small molecule solution.

[0134] Next in an operation 503, the solvent is displaced with a solution that includes small molecules. The substrate is then dried in an operation 505. The small molecules precipitate out of solution, filling the HAR structures with a solid film and/or forming the solid film within the HAR structures. The small molecules function as a mechanical brace in the HAR structures to prevent collapse of the structures due to capillary forces that are generated during solvent drying. The substrate is then exposed to a stimulus, such light or heat, that induces sublimation of the film in an operation 507.

[0135] The small molecules have relatively low vapor pressure at room temperature; in some embodiments, it less than about 1×10.sup.−4 atm or less than about 76 mTorr. The small molecules are solid at atmospheric pressure and room temperature (about 20° C.-25° C.). The small molecules are further characterized by having a vapor pressure of at least 10 Torr at a temperature above about 20° C. but below about 400° C., without having a melting point below this temperature, such that there is no transition to liquid. Examples of such small molecules include fused aromatic rings such as naphthalene and anthracene.

[0136] The solution in operation 503 includes a solvent that dissolves the small organic molecule and is chemically compatible with the substrate and the solvent in operation 501. It may be optimized for substrate wetting and displacement.

[0137] FIG. 6 is another example of a method for bracing HAR structures using a film of small molecules. First at an operation 601, a substrate including HAR structures is provided. HAR structures are structures having high aspect ratios (ARs), e.g., at least 8, 10, 20, 30, 40, or 80. In other embodiments, the substrate may be provided, for example, after a wet etch or cleaning operation and have a first solvent associated with the prior operation. If this first solvent is not chemically compatible with the small molecules, then this first solvent may be a transitional solvent that is replaced by a second solvent.

[0138] Next, in operation 603, a film including small molecules is formed on the substrate. Such forming can include exposing the surface to a vapor including the small molecules such that they condense on the surface to form the film. In other embodiments, this may involve spin-coating a solution including the small molecules in an appropriate solvent, and then removing the solvent. Non-limiting methodologies of forming a film include vapor-based deposition, such as chemical vapor deposition; and solvent-based deposition, such as spin-coating, drop-casting, or solvent-casting.

[0139] In other embodiments, forming can include displacing a solvent (e.g., the first or second solvent) of the substrate with a solution that includes small molecules. This solution can include a further solvent (e.g., a third solvent) that dissolves the small organic molecule and is chemically compatible with the substrate and the first solvent (or the second solvent) employed with the HAR structures. The further solvent (e.g., the third solvent) may be optimized for substrate wetting and displacement. The substrate can then be dried. The small molecules precipitate out of solution, filling the HAR structures with a solid film.

[0140] Whether formed by vapor-based or solution-based deposition, the small molecules of the film function as a mechanical brace in the HAR structures to prevent collapse of the structures due to capillary forces that are generated during solvent drying. The substrate is then exposed to a stimulus, such light or heat, that induces sublimation of the film in an operation 605.

[0141] The small molecules can have relatively low vapor pressure at room temperature; in some embodiments, it less than about 1×10.sup.−4 atm or less than about 76 mTorr. The small molecules are solid at atmospheric pressure and room temperature (about 20° C.-25° C.). The small molecules are further characterized by having a vapor pressure of at least 10 Torr at a temperature above about 20° C. but below about 400° C., without having a melting point below this temperature, such that there is no transition to liquid. Examples of such small molecules include fused aromatic rings such as naphthalene and anthracene.

[0142] The methods described herein may provide one or more of the following advantages for sacrificial bracing of HAR structures. In some embodiments, relatively mild conditions may be used to remove the materials, preventing damage to the sensitive underlying surface and avoiding detectable residue. Because the materials can be sublimed at lower temperatures, high temperatures that may cause charred residues can be avoided. In some embodiments, processing may take place at room temperature. Because the small molecules form solid films at room temperature in some embodiments, the process window is larger than with, for example, freeze-drying processes. In some embodiments, the small molecules are easier to produce than polymers.

[0143] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.