Patent Publication Number: US-2023136036-A1

Title: Controlled degradation of a stimuli-responsive polymer film

Description:
INCORPORATION BY REFERENCE 
     A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in its entirety and for all purposes. 
    
    
     BACKGROUND 
     As semiconductor devices continue to scale down to smaller sizes, higher aspect ratio structures are used to achieve the desired device performance. The fabrication of semiconductor devices involves multiple iterations of processes such as material deposition, planarization, feature patterning, feature etching, and feature cleaning. The drive towards higher aspect ratio structures creates processing challenges for many of these traditional fabrication steps. Wet processes such as etch and clean, which may make up greater than 25% of the overall process flow, are particularly challenging on high aspect ratio (HAR) features due to the capillary forces that are generated during drying. The strength of these capillary forces depends on the surface tension and contact angle of the etch, clean, or rinse fluids that are being dried, as well as the feature spacing and aspect ratio. If the forces generated during drying are too high, then the high aspect ratio features will collapse onto each other and stiction may occur. Feature collapse and stiction will severely degrade the device yield. 
     The background description provided herein is for the purposes of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     SUMMARY 
     Removing a stimuli responsive polymer (SRP) from a substrate includes controlled degradation. In certain embodiments of the methods described herein, removing an SRP includes exposure to two reactants that react to form an acid or base that can trigger the degradation of the SRP. The exposure occurs sequentially to provide more precise top down control. In some embodiments, the methods involve diffusing a compound, or a reactant that reacts to form a compound, only to a top portion of the SRP. The top portion is then degraded and removed, leaving the remaining SRP intact. The exposure and removal cycles are repeated. 
     One aspect of the disclosure relates to a method including: providing to a chamber a high aspect ratio (HAR) structure having a stimulus responsive polymer (SRP) in a high aspect ratio gap formed between features of the HAR structure, the high aspect ratio gap having a total thickness T total ; and performing one or more cycles of removing the SRP from the gap including, each cycle including:
     (a) pulsing a first reactant to the chamber such that the first reactant diffuses into the gap only to a depth less than T total ,   (b) after (a), purging the chamber,   (c) after (b), pulsing a second reactant to the chamber such that the second reactant diffuses into the gap only to a depth less than T total ;   (d) reacting the first reactant and the second reactant to form a compound that degrades the SRP;   (e) degrading a thickness of SRP that is less than T total ; and   (f) removing the degraded SRP.   

     In some embodiments, the SRP includes a poly(phthalaldehyde) or a derivative thereof as a homopolymer or as one of the polymers of a copolymer. In some embodiments, the SRP includes a poly(aldehyde) or a derivative thereof as a homopolymer or as one of the polymers of a copolymer. 
     In some embodiments, the first or second reactant is water vapor. In some such embodiments, the other of the first or second reactant is ammonia or a gaseous oxide that reacts with the water vapor to an acidic or basic species. Examples of gaseous oxides include nitrogen dioxide, sulfur dioxide, and carbon dioxide. 
     In some embodiments, a target diffusion depth in (a) and (c) is the same. In some embodiments, a target diffusion depth in (a) and (c) is different. In some embodiments, the reaction in (d) is uncatalyzed. In some embodiments, the compound is an acid or base. Examples include sulfurous acid, nitric acid, carbonic acid, and ammonium hydroxide. 
     Another aspect of the disclosure relates to a method including: providing to a chamber a high aspect ratio (HAR) structure having a stimulus responsive polymer (SRP) in a high aspect ratio gap formed between features of the HAR structure, the SRP film having a total thickness T total ; and performing one or more cycles of removing the SRP from the gap including, each cycle including:
     (a) pulsing first reactant to the chamber such that the first reactant diffuses into the gap to a depth D first   reactant ,   (b) after (a), purging the chamber,   (c) after (b), pulsing a second reactant to the chamber such that the second reactant diffuses into the gap only to a depth D second   reactant , wherein D second   reactant  is less than D first   reactant ,   (d) reacting the first reactant and the second reactant to form a compound that degrades the SRP;   (e) degrading the SRP to a depth D second   reactant  ; and   (f) removing the degraded SRP.   

     In some embodiments, the SRP includes a poly(phthalaldehyde) or a derivative thereof as a homopolymer or as one of the polymers of a copolymer. In some embodiments, the SRP includes a poly(aldehyde) or a derivative thereof as a homopolymer or as one of the polymers of a copolymer. 
     In some embodiments, the first or second reactant is water vapor. In some such embodiments, the other of the first or second reactant is ammonia or a gaseous oxide that reacts with the water vapor to an acidic or basic species. Examples of gaseous oxides include nitrogen dioxide, sulfur dioxide, and carbon dioxide. 
     In some embodiments, D first   reactant  is equal to T total  such that the first reactant is diffused through the total thickness of the SRP film in a single cycle. In some embodiments, D first reactant  is less than T total  and multiple cycles are performed. In some embodiments, the reaction in (d) is uncatalyzed. In some embodiments, the compound is an acid or base. Examples include sulfurous acid, nitric acid, carbonic acid, and ammonium hydroxide. 
     Another aspect of the disclosure relates to a method including:
     providing a substrate having a stimulus responsive polymer (SRP) thereon;   performing multiple removal cycles, each cycle including:   exposing only a top portion of the SRP to a compound capable of degrading the SRP to thereby degrade the top portion of the SRP; and   removing only the top portion of the SRP.   

     In some embodiments, the SRP is provided without a catalyst. In some embodiments, exposing the top portion of the SRP to a compound includes pulsing the compound in vapor phase into a chamber housing the substrate. Examples of compounds include hydrogen bromide (HBr), hydrogen chloride (HCl), hydrogen fluoride (HF), hydrogen iodide (HI), nitric acid (HNO3), formic acid (CH 2 O 2 ), acetic acid (CH 3 COOH), formonitrile (HCN), or ammonia (NH 3 ), and methyl or ethyl amine gas. 
     In some embodiments, exposing the top portion of the SRP includes sequential pulsing of a first reactant and a second reactant, wherein the first reactant and the second reactant react to from the compound. In some such embodiments, the first reactant and second reactant react in the top portion of the SRP film. In some embodiments, exposing the top portion of the SRP includes a first pulse of a first reactant followed by multiple sequential pulses of a second reactant, wherein the first reactant and the second reactant react to form the compound. In some embodiments, sequential pulses are separated by inert gas purges. 
     In some embodiments, the SRP includes a poly(phthalaldehyde) or a derivative thereof as a homopolymer or as one of the polymers of a copolymer. In some embodiments, the SRP includes a poly(aldehyde) or a derivative thereof as a homopolymer or as one of the polymers of a copolymer. 
     In some embodiments, the SRP is provided between features of high aspect ratio (HAR) structures. In some embodiments, the SRP is provided as a protective coating on substrate. 
     These and other aspects are discussed below with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS.  1 A and  1 B  are flow diagrams showing certain operations in examples semiconductor fabrication processes that use stimulus response polymers (SRPs). 
         FIG.  2 A  shows a side cross-sectional view of an example of a high aspect ratio (HAR) structure in which enough of the SRP is removed in a single removal that the structure features collapse. 
         FIG.  2 B  shows a side cross-sectional view of an example of a high aspect ratio (HAR) structure in which the SRP removal is controlled to prevent collapse. 
         FIGS.  3  and  4    are process flow diagrams showing examples of methods of controlled exposure to degrade an SRP. 
         FIG.  5    shows sequences of side cross-sectional views of removing SRP from HAR structures according to various embodiments of the method of  FIG.  4   . 
         FIG.  6    is process flow diagrams showing an example of a method of controlled exposure to degrade an SRP. 
         FIG.  7    shows sequences of side cross-sectional views of removing SRP from HAR structures according to various embodiments of the method of  FIG.  6   . 
         FIG.  8    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. 
     
    
    
     DETAILED DESCRIPTION 
     Stimuli responsive polymers (SRPs) may be used in semiconductor fabrication processes for sacrificial bracing of high aspect ratio (HAR) structures. Low ceiling temperature SRPs can be spontaneously removed when exposed to stimuli such as mildly elevated temperatures or acidic vapors, avoiding aggressive wet or dry removal chemistries that may harm the substrate surface. These SRPs can also be used for surface protection from airborne molecular contaminants and queue-time extension. 
     As indicated above, in many embodiments, the SRPs are low ceiling temperature (T c ) polymers. T c  is the equilibrium temperature between a polymer and its monomers. As used herein, the term low T c  refers to T c  values below a removal temperature. In some embodiments, the T c  is below room temperature, such that the polymers are thermodynamically unstable at room temperature. Instead, the low T c  polymer is kinetically trapped to allow prolonged storage at room temperature. In some examples, the stable storage period is on the order of months or years. Low T c  polymers will rapidly de-polymerize to its monomer constituents if an end-group or main chain bond is broken. Thus, the polymer de-polymerizes in response to stimuli such as ultraviolet (UV) light, heat, or an acidic/basic catalyst or compound. The monomer products are volatile and leave or can be easily removed from the surface and chamber. 
     While in some embodiments, the T c  is below room temperature, in the context of semiconductor processing, low T c  may also refer to ceiling temperatures that are higher than room temperature. For example, removal temperatures of up to 400° C. may be used, meaning that the ceiling temperature is below 400° C., with the polymer kinetically trapped below the ceiling temperature. 
     In some embodiments of the methods described herein, removing an SRP includes controlled degradation by diffusing a compound, or a reactant that reacts to form a compound, only to a top portion of the SRP. The top portion is then degraded and removed, leaving the remaining SRP intact. The exposure and removal cycles are repeated. 
     In some embodiments of the methods described herein, removing SRPs includes exposure to two reactants that react to form an acid or base that can trigger the degradation of the SRP. The exposure occurs sequentially to provide more precise top down control. A first reactant may be provided in gaseous form and diffuses into the SRP. Pressure, temperature, flow rate, and exposure time may be controlled to modulate the depth of diffusion. The first reactant is then purged, and the second reactant is provided in gaseous form to diffuse into the SRP. Pressure, temperature, flow rate, and exposure time may be controlled to modulate the depth of diffusion. A reaction occurs only to the depth and extent that the first and second reactants are both present in the SRP. Thus, all or only a portion of the SRP is degraded and removed in a cycle. 
     The methods described above allow removal of the SRP at lower temperatures than using heat by itself as a stimulus. This can be advantageous for avoiding the formation of non-volatile carbonaceous species (char). Further, the methods allowed controlled removal without adding non-volatile catalysts, dyes, or other additives to the film. Eliminating low volatility additives and char results in a significant reduction or elimination of residues upon SRP removal. 
     Examples of processes that involve the use of sacrificial SRPs are described below with reference to  FIGS.  1 A and  1 B , with further details of the removal process provided with reference to  FIGS.  2 - 7   . Turning to  FIG.  1 A , an example of a method for bracing HAR structures using an SRP is shown. First at an operation  101 , 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  101  may be a transitional solvent if the prior solvent is not chemically compatible with the SRP solution. 
     Next in an operation  103 , the solvent is displaced with a solution that includes a stimuli responsive polymer (SRP). The substrate is then dried in an operation  105 . The SRP solidifies as the liquid portion solution is removed and the SRP fills the HAR structures. A mechanical brace forms in the HAR structures to prevent collapse of the structures due to capillary forces that are generated during solvent drying. The fill may include one or more additional components. Such additional components may include stabilizers, surfactants, and/or plasticizers. 
     The substrate is then exposed to a stimulus to degrade all of or only the top portion of the SRP in an operation  107 . As described further below, operation  107  may involve controlled exposure to a compound or to two reactants that react to form a compound that degrades the SRP. The stimulus is any compound that scissions bonds of the SRP to degrade it. In some embodiments, the compound is a relatively strong acid or base. Volatile monomers or fragments from the degraded polymer can then be removed from the structure in an operation  109 . If SRP is still present, operations  107  and  109  are repeated one or more times to remove all the SRP in an operation  111 . The amount of SRP removed in each repetition may be the same or different. 
     The number of repetitions is such that bracing remaining after each cycle of operation  107  and  109  can withstand the capillary forces without collapsing.  FIGS.  2 A and  2 B , which show HAR structures having SRP films of thickness T total , illustrate schematically the difference between too few and enough cycles.  FIG.  2 A  shows a side cross-sectional view of an example of a HAR structure in which too much of the SRP is removed in a single removal. The high aspect ratio features collapse. In  FIG.  2 B , by contrast, the structure remains intact. 
     SRPs may also be used in the semiconductor fabrication processes for transient protection of a sensitive surface of substrate. This in turn can extend available queue time between fabrication steps. During semiconductor fabrication, many surfaces are sensitive to airborne molecular contaminants (AMCs) in the surrounding environment. Queue time can lead to exposure to the AMCs and unwanted interactions such as oxidation, corrosion, and halogenation.  FIG.  1 B  shows an example of a method for protection of a sensitive surface of a substrate. At operation  121 , a substrate including an environmentally 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 copper, cobalt, titanium, titanium nitride, tungsten or molybdenum, and/or other structures and materials. 
     The surface is then coated with a solution including an SRP in an operation  123 . The substrate is then dried in an operation  125 , forming a protective coating including SRP on the sensitive substrate. The substrate can then be stored in ambient conditions in an operation  127 . When ready for further processing, the substrate is exposed to a stimulus that degrades all or a top portion of the SRP in an operation  129 . As described further below, operation  129  may involve controlled exposure to a compound or to two reactants that react to form a compound that degrades the SRP. The stimulus is any compound that scissions bonds of the SRP to degrade it. In some embodiments, the compound is a relatively strong acid or base. Volatile monomers or fragments from the degraded polymer can then be removed from the structure in an operation  131 . If SRP is still present, operations  129  and  131  are repeated one or more times to fully remove the SRP in an operation  133 . The amount of removed in each repetition may be the same or different. 
       FIGS.  1 A and  1 B  are flow diagrams showing certain operations in examples semiconductor fabrication processes that use SRPs, though the methods described herein are not limited to particular applications but may be used with any application in which SRPs are removed from any surface. The thickness of an SRP film before any removal may be expressed as a total thickness (T total ). If the thickness varies across a surface, T total  is the maximum thickness. In certain embodiments of the methods described herein, an amount of SRP that is removed at any one removal operation is less than T total , i.e., the SRP is removed portion by portion in multiple removal cycles. In other embodiments, all of the SRP may be removed in a cycle. 
     In some embodiments, the SRP is directly exposed to pulses of a vapor phase compound (e.g., a base or acid) that can degrade the SRP. For example, hydrogen bromide (HBr), hydrogen chloride (HCl), hydrogen fluoride (HF), hydrogen iodide (HI), nitric acid (HNO3), formic acid (CH 2 O 2 ), acetic acid (CH 3 COOH), formonitrile (HCN), or ammonia (NH 3 ), various methyl or ethyl amines gas or vapor may be used. In some examples, when HBr vapor is used, the substrate is maintained at a pressure in a range from 5 mT to 5000 mT and a temperature in a range from 0° C. to 100° C. In some examples, the substrate is maintained at a pressure in a range from 750 mT to 1500 mT and a temperature in a range from 35° C. to 70° C. In some examples, the temperature of the substrate is maintained at a pressure of 1000 mT and a temperature of 60° C. The amount of acidic vapor or vapor of other compound is controlled to limit the diffusion.  FIG.  3    is a process flow diagram showing an example of a method of controlled exposure to a compound to degrade the SRP. A substrate is provided with SRP film in an operation  301 . Examples of apparatus that the substrate may be provided to are described below with reference to  FIG.  8   . In some embodiments, operation  301  involves providing the substrate to a processing chamber. In other embodiments, the substrate is in the chamber from a previous processing operation. The SRP may be provided in a variety of forms - for example, in a gap between features of a structure or as blanket film on all or part of a substrate. 
     A compound is pulsed into the chamber in an operation  303 . The partial pressure of the vapor and/or the pulse time can be controlled to control the overall exposure to the vapor and the diffusion depth. The chamber can be purged in an operation  305 . Purging can involve evacuating the chamber and/or flowing inert gas to be swept out through the chamber. Such a gas may be, for example, continuously flowing including during operation  303  or may be itself pulsed into the chamber. During operation  305  volatilized monomer or SRP fragment may be pumped or purged out of the chamber. Operations  303  and  305  are repeated until the SRP is removed in an operation  307 . 
     As indicated above, in some embodiments, the SRP is exposed to reactants sequentially in each cycle. This can provide additional control over the process and may be implemented in various ways. In some embodiments, diffusion of both reactants is tightly controlled. This can provide additional control over removal process as the film will only degrade to a depth where both reactants are present. Thus, if one of the two reactants diffuses more than targeted, diffusion of the other reactant can still control the amount of film removed.  FIG.  4    shows an example of a process flow that may be used in accordance with embodiments. A substrate is provided with SRP film in an operation  401 , as described above with respect to operation  301  in  FIG.  3   . At this stage, prior to removal, the SRP film has a thickness T total . A first reactant is pulsed into the chamber in an operation  403 . The substrate temperature and the partial pressure of the vapor and/or the pulse time can be controlled to control the overall exposure to the vapor and the diffusion depth. As a result of operation  403 , the first reactant diffuses through a top portion of the SRP film. The chamber can be purged in an operation  405 . Purging can involve evacuating the chamber and/or flowing inert gas to be swept out through the chamber. Such a gas may be, for example, continuously flowing including during operation  403  or may be itself pulsed into the chamber. A second reactant is then pulsed in operation  407 . Like in operation  403 , the substrate temperature and partial pressure of the vapor and/or pulse time can be controlled to limit the diffusion depth. The first reactant and the second reactant react to form a compound that itself reacts with the SRP to scission its bonds. The SRP is degraded to the depth that both reactants diffused. The chamber can be purged in an operation  409  as described above. During operation  409  volatilized monomer or SRP fragment may be pumped or purged out of the chamber. Operations  403 - 409  are repeated until the SRP is removed in an operation  411 . In some embodiments, operation  411  may not be performed. For example, in a surface protection application where bracing HAR features is not a concern, a single cycle may be sufficient to remove the SRP. In such cases, the reactants may be diffused throughout the entire thickness of the film in operations  403  and  407 . 
     In the example of  FIG.  4   , the target diffusion depth of each reactant may be the same or different.  FIG.  5    shows examples of different embodiments. First, at  501 , a sequence of side cross-sectional views of a HAR structure filled with SRP is shown. The sequence shows two cycles of SRP removal according in an example of a method according to  FIG.  4    in which each reactant is targeted to diffuse to the same depth. A first pulse of reactant 1 (R1) results in diffusion to a depth D1 followed by a first pulse of reactant 2 (R2) that results in diffusion to D1. The reactants react, forming a compound that degrades the SRP to D1. The degraded SRP is removed leaving the gap unfilled to D1. The cycle repeats removing SRP to a depth D2. The cycles can continue until the SRP is removed. 
     At  503 , another sequence of side cross-sectional views of a HAR gap filled with SRP is shown. The sequence shows two cycles of SRP removal according in an example of a method according to  FIG.  4    in which each reactant is targeted to diffuse to a depth beyond the diffusion depth of the previous reactant pulse. A first pulse of reactant 1 (R1) results in diffusion to a depth D1 followed by a first pulse of reactant 2 (R2) that results in diffusion to D2. The reactants react, forming a compound that degrades the SRP to D1, and leaves unreacted reactant R2 to a depth D2. The degraded SRP is removed leaving the gap unfilled to D1 with unreacted reactant R2 present in the SRP to D2. The next reactant pulse R1 is done to a target depth D3. The reactants react, forming a compound that degrades the SRP to D2, and leaves unreacted reactant R1 to a depth D3. The degraded SRP is removed leaving the gap unfilled to D2 with unreacted reactant R1 present in the SRP to D3. The next reactant pulse R2 is done to a target depth D4. The reactants react, forming a compound that degrades the SRP to D3, and leaves unreacted reactant R2 to a depth D4. The cycles can continue until the SRP is removed. As can be seen by comparing sequence  503  to sequence  501 , allowing each pulse of reactant to diffuse further into the SRP than the previous reactant pulse can reduce the number of cycles, though each pulse may take longer. 
     In some embodiments, the SRP is exposed to a first reactant, which is allowed to diffuse throughout all of or a first portion of the SRP, followed by multiple pulses of the second reactant, each of which results in diffusion of the second reactant and SRP degradation in only a top portion of the SRP.  FIG.  6    shows an example of a process flow that may be used in accordance with embodiments. 
     A substrate is provided with SRP film in an operation  601 , as described above with respect to operation  301  in  FIG.  3   . A first reactant is pulsed into the chamber in an operation  603 . The substrate temperature and partial pressure of the vapor and/or the pulse time can be controlled to control the overall exposure to the vapor and the diffusion depth. As a result of operation  603 , the first reactant diffuses through the SRP film to a target diffusion depth. In some embodiments, the target diffusion depth may be the entire depth of the SRP film, i.e., T total . In other embodiments, it may be less than the entire depth, e.g., half T total , one quarter of the T total , etc. The chamber can be purged in an operation  605 . Purging can involve evacuating the chamber and/or flowing inert gas to be swept out through the chamber. Such a gas may be, for example, continuously flowing including during operation  603  or may be itself pulsed into the chamber. A second reactant is then pulsed in operation  607 . In operation  607 , the target diffusion depth is less than that for the first reactant in operation  603 . For example, if the first reactant diffused throughout the entire depth or half the entire depth in operation  603 , the target diffusion depth in operation  607  may be one-fifth or one-fourth of the depth. The first reactant and the second reactant react to form a compound that itself reacts with the SRP to scissions its bonds. The SRP is degraded only to the depth that the second reactant diffused. Thus, the second reactant diffusion depth controls the overall removal rate. The chamber can be purged in an operation  609  as described above. During operation  609  volatilized monomer or SRP fragment may be pumped or purged out of the chamber. In an operation  611 , operations  607  and  609  are repeated until the first reactant is consumed. In embodiments in which the first reactant diffuses through the entire film, the SRP may be completely removed after operation  611 . In other embodiments, in an operation  613 , operations 603-611 may be repeated one or more times until the SRP is completely removed. 
       FIG.  7    shows examples of different embodiments according to the method described in  FIG.  6   . First, at  701 , a sequence of side cross-sectional views of a HAR structure filled with SRP is shown. The sequence shows multiple cycles of SRP removal according in an example of a method according to  FIG.  6    in which the first reactant is targeted to diffuse to entire depth of the SRP. A first pulse of reactant 2 (R2) results in diffusion to a depth D1. The reactants react, forming a compound that degrades the SRP to D1. The degraded SRP is removed leaving the gap unfilled to D1. The R2 - removal cycle repeats removing SRP to a depth D2. The cycles can continue until the SRP is removed. 
     At  703 , another sequence of side cross-sectional views of a HAR structure filled with SRP is shown. The sequence shows multiple cycles of SRP removal according in an example of a method according to  FIG.  6    in which the first reactant is targeted to diffuse to half the depth of the SRP. A first pulse of reactant 2 (R2) results in diffusion to a depth D1. The reactants react, forming a compound that degrades the SRP to D1. The degraded SRP is removed leaving the gap unfilled to D1. The R2 - removal cycle repeats removing SRP to a depth D2. The cycles can continue until the SRP is removed from half the gap depth. Reactant 1 is then pulsed again to diffuse to the bottom of the gap. The R2 - removal cycles can then be repeated (not shown) until the film is completely removed. 
     Stimulus Compounds and Reactants 
     Examples of compounds that may be used to degrade SRPs includes acids (e.g., having a pKa of less than 7, and in some embodiments less than 4, or less than 2) and bases (e.g., having a pKb of less than 7, and in some embodiments, less than 4 or less than 2). 
     Examples of reactants which can be pulsed to in an alternate fashion to produce compounds which are effective to scission SRPs include SO 2  (sulfur dioxide) and water (H 2 O) which react to form sulfurous acid (H 2 SO 3 ), nitrogen dioxide (NO 2 ) and water to form nitric acid (HNO 3 ), carbon dioxide (CO 2 ) and water to form carbonic acid (H 2 CO 3 ), and ammonia (NH 3 ) and water to form ammonium hydroxide (NH 4 OH). Other oxides may react with water or another reactant to form acids or bases. 
     In some embodiments, reactants that form hydrogen bonds (e.g., H 2 O or NH 3 ) may be used as the first reactant in a scheme such as shown in  FIGS.  6  and  7   . This is because hydrogen bonding may be useful for having the reactant adsorb in the film once diffused. 
     According to various embodiments, the reaction may be catalyzed or uncatalyzed. In some embodiments, a catalyst (e.g., a thermally activated catalyst) may be provided in the SRP, delivered with a reactant, or introduced as a separate pulse. However, in many embodiments, the reaction is uncatalyzed such that SRP is provided free of catalysts. This can facilitate SRP removal. 
     In some embodiments, the reaction is byproduct-free. 
     SRPs 
     Example of SRPs are provided below. However, the methods described herein may be used with any SRPs. In some embodiments, the SRPs are copolymers including poly(aldehydes). In particular embodiments, they may be self-immolative polymers as described in U.S. Pat. Publication No. 2018/0155483, which was published on Jun. 7, 2018 and which is hereby incorporated herein by reference in its entirety. Examples of copolymers in that reference include those of Formula I: 
     
       
         
         
             
             
         
       
     
      wherein R is substituted or unsubstituted C 1 -C 20  alkyl, C 1 -C 20  alkoxyl, C 2- C 20  alkenyl, C 2 -C 20  alkynyl, C 6 -C 10  heteroaryl, C 3 -C 10  cycloalkyl, C 3 -C 10  cycloalkenyl, C 3 -C 10  heterocycloalkyl, or C 3 -C 10  heterocycloalkenyl; and, when substituted, R is substituted with C 1 -C 20  alkyl, C 1 -C 20  alkoxy, C 2 -C 20  alkenyl, C 2 -C 20  alkynyl, C 6 -C 10  aryl, C 6 -C 10  heteroaryl, aldehyde, amino, sulfonic acid, sulfinic acid, fluoroacid, phosphonic acid, ether, halide, hydroxy, ketone, nitro, cyano, azido, silyl, sulfonyl, sulfinyl, or thiol. 
     In particular embodiments, the SRPs are cyclic copolymers of the phthalaldehyde monomer with a second aldehyde such as ethanal, propanal, or butanal. Examples of such copolymers are given in U.S. Pat. Publication No. 2018/015548 as Formula II: 
     
       
         
         
             
             
         
       
     
     Specific examples in U.S. Pat. Publication No. 2018/015548 include copolymers of PHA and one or more of acetaldehyde, propanal, butanal, pentanal, hexanal, heptanal, octanal, nonanal, decanal, undecanal, propenal, butenal, pentenal, hexenal, heptenal, octenal, nonenal, decenal, undecenal, and any combination thereof. 
     The SRPs may also be any appropriate linear or cyclic copolymer including the pure phthalaldehyde homopolymer. It also may be a homopolymer of poly(phthalaldehyde) derivatives such as poly(4,5-dichlorophthalaldehyde). 
     Apparatus 
     The removal processes described may be implemented in a chamber which may be part of a substrate processing system. The substrate processing system may further include one or more additional substrate processing tools used to process substrates including deposition of SRPs and upstream and downstream processing. Referring now to  FIG.  8   , a substrate processing system  800  includes one or more substrate processing tools  802  (substrate processing tools  802   a  and  802   b  are shown for illustration purposes) and substrate buffer  830  or other substrate storage. Each of the substrate processing tools  802   a  and  802   b  includes a plurality of processing chambers  804   a ,  804   b ,  804   c , etc. (collectively processing chambers  804 ). For example only, each of the processing chambers  804  may be configured to perform a substrate treatment. In some examples, the substrates may be loaded into one of the processing chambers  804 , processed, and then moved to one or more other ones of the processing chambers  804  and/or removed from the substrate processing tool  800  (e.g., if all perform the same treatment). 
     Substrates to be processed are loaded into the substrate processing tools  802   a  and  802   b  via ports of a loading station of an atmosphere-to-vacuum (ATV) transfer module  808 . In some examples, the ATV transfer module  708  includes an equipment front end module (EFEM). The substrates are then transferred into one or more of the processing chambers  804 . For example, a transfer robot  812  is arranged to transfer substrates from loading stations  816  to load locks  820 . A vacuum transfer robot  824  of a vacuum transfer module  828  is arranged to transfer substrates from the load locks  820  to the various processing chambers  804 . 
     After processing in one or more of the substrate processing tools  802   a  and  802   b , 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  830 ). 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  830  to another substrate processing tool for further processing. 
     Exposure of the substrate to ambient conditions may cause defects or otherwise adversely impact downstream processing. A sacrificial protective layer including an SRP can be added 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). 
     Prior to performing another treatment on the substrate, the sacrificial protective layer is removed as described herein. For example, the substrate may be transferred to the substrate processing tool  802   b  after a period of storage in the storage buffer  830  or after processing in the substrate processing tool  802   a . The sacrificial protective layer may be removed in one of the processing chambers in the substrate processing tool  802   b , or another processing chamber (not associated with the substrate processing tool  802   b ). In some embodiments, the sacrificial protective layer is removed in a load lock  820 . 
     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. 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 or immediately after 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. 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. 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. 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  802   a ) 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  802   b ). 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 compounds, and in some cases, other stimuli, as described above are applied to induce the film to degrade and be removed from the substrate. This may take place inside of a processing chamber as described above (e.g., process chamber  804   a  of substrate processing chamber  802   b ). 
     In various embodiments, a system controller is employed to control process conditions during processing including during the SRP removal. The controller will typically include one or more memory devices and one or more processors. A processor may include a CPU or computer, analog and/or digital input/output connections, stepper motor controller boards, etc. 
     The controller may control all the activities of a removal apparatus. The system controller executes system control software, including sets of instructions for controlling the timing, mixture of gases, chamber pressure, chamber temperature, wafer temperature, wafer chuck or pedestal position, plasma power, and other parameters of a particular process. Other computer programs stored on memory devices associated with the controller may be employed in some embodiments. 
     Typically, there will be a user interface associated with the controller. The user interface may include a display screen, graphical software displays of the apparatus and/or process conditions, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc. 
     System control logic may be configured in any suitable way. In general, the logic can be designed or configured in hardware and/or software. The instructions for controlling the drive circuitry may be hard coded or provided as software. The instructions may be provided by “programming.” Such programming is understood to include logic of any form, including hard coded logic in digital signal processors, application-specific integrated circuits, and other devices which have specific algorithms implemented as hardware. Programming is also understood to include software or firmware instructions that may be executed on a general purpose processor. System control software may be coded in any suitable computer readable programming language. 
     The computer program code for controlling the reactant pulses and purge gas flows and other processes in a process sequence can be written in any conventional computer readable programming language: for example, assembly language, C, C++, Pascal, Fortran, or others. Compiled object code or script is executed by the processor to perform the tasks identified in the program. Also as indicated, the program code may be hard coded. 
     The controller parameters relate to process conditions, such as, for example, process gas composition and flow rates, temperature, pressure, substrate temperature, and plasma power. These parameters are provided to the user in the form of a recipe and may be entered utilizing the user interface. 
     Signals for monitoring the process may be provided by analog and/or digital input connections of the system controller. The signals for controlling the process are output on the analog and digital output connections of the system. 
     The system software may be designed or configured in many ways. 
     For example, various chamber component subroutines or control objects may be written to control operation of the chamber components necessary to carry out the deposition processes in accordance with the disclosed embodiments. Examples of programs or sections of programs for this purpose include substrate positioning code, process gas control code, pressure control code, and heater control code. 
     In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can include semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and/or specific processing components (a wafer pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the “controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of processing gases, temperature settings (e.g., heating and/or cooling), pressure settings, vacuum settings, power settings, flow rate settings, fluid delivery settings, positional and operation settings, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system. 
     Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer. 
     The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. The parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus, as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber. 
     Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a PVD chamber or module, a CVD chamber or module, an ALD chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers. 
     As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or load ports in a semiconductor manufacturing factory. 
     The controller may include various programs. A substrate positioning program may include program code for controlling chamber components that are used to load the substrate onto a pedestal or chuck and to control the spacing between the substrate and other parts of the chamber such as a gas inlet and/or target. A process gas control program may include code for controlling gas composition, flow rates, pulse times, and optionally for flowing gas into the chamber. A pressure control program may include code for controlling the pressure in the chamber by regulating, e.g., a throttle valve in the exhaust system of the chamber. A heater control program may include code for controlling the current to a heating unit that is used to heat the substrate. Alternatively, the heater control program may control delivery of a heat transfer gas such as helium to the wafer chuck. A plasma power program may control plasma power. 
     Examples of chamber sensors that may be monitored during removal include mass flow controllers, pressure sensors such as manometers, and thermocouples located in the pedestal or chuck. Appropriately programmed feedback and control algorithms may be used with data from these sensors to maintain desired process conditions. 
     The foregoing describes implementation of disclosed embodiments in a single or multi-chamber semiconductor processing tool. The apparatus and process described herein may be used in conjunction with lithographic patterning tools or processes, for example, for the fabrication or manufacture of semiconductor devices, displays, LEDs, photovoltaic panels, and the like. Typically, though not necessarily, such tools/processes will be used or conducted together in a common fabrication facility. Lithographic patterning of a film typically comprises some or all of the following steps, each step provided with a number of possible tools: (1) application of photoresist on a workpiece, i.e., substrate, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or UV curing tool; (3) exposing the photoresist to visible or UV or x-ray light with a tool such as a wafer stepper; (4) developing the resist so as to selectively remove resist and thereby pattern it using a tool such as a wet bench; (5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) removing the resist using a tool such as an RF or microwave plasma resist stripper. 
     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.