Patent Publication Number: US-2006005337-A1

Title: Cleaning member and cleaning method of substrate processing equipment

Description:
FIELD OF THE INVENTION  
      The present invention relates to a cleaning member for cleaning a substrate processing equipment and a cleaning method of a substrate processing equipment using the same.  
     BACKGROUND ART  
      In various substrate processing equipment which dislike foreign matter, such as production apparatus and inspection apparatus of semiconductors, flat panel displays, printed wiring boards, and the like, substrates are carried while physically being brought into contact with respective carrying systems. In that case, when foreign matter is attached to a substrate or carrying system, it stains the succeeding substrates one by one, so that it is necessary to perform a cleaning treatment by periodically stopping the apparatus. Therefore, there was a problem of reducing the working ratio and requiring considerable labor.  
      For the purpose of solving this problem, there have been proposed a method wherein foreign matter attached to the inside of a substrate processing equipment is cleaned and removed by carrying an adhesive material-fixed substrate as a cleaning member into the above apparatus (cf. Patent Document 1) and a method wherein foreign matter attached to the backside of a substrate is removed by carrying a plate-like member (cf. Patent Document 2).  
      Of these, in the latter method of carrying a plate-like member, the member can be carried into a substrate processing equipment without troubles but the method is inferior in essential removing ability for foreign matter.  
      To the contrary, the above method of carrying an adhesive material-fixed substrate exhibits a superior removing ability for foreign matter and thus is an effective method for avoiding the above reduction of the working ratio and considerable labor. However, in this method, the adhesive material and the contacting parts of the apparatus strongly adhere to each other and are sometimes not peeled off and thus there is a possibility that the substrate cannot be securely carried. Therefore, the removing ability for foreign matter and the carrying ability have been coordinated by reducing an adhesive force as far as possible (cf. Patent Document 3). 
          [Patent Document 1] JP-A-10-154686     [Patent Document 2] JP-A-11-87458     [Patent Document 3] JP-A-11-121242        

     SUMMARY OF THE INVENTION  
      The temperature of the chuck table in the objective substrate processing equipment to be cleaned changes within a wide range of room temperature to a high temperature depending on the kind of substrate processing. Therefore, a cleaning member capable of being used within a wide temperature range is ideal.  
      However, in the case of a conventional cleaning member, it is necessary to lower the temperature of a chuck table having a high temperature to room temperature at its cleaning. This is because the cleaning member is thermoplastic and hence its adhesive strength increases with a decrease of its elastic modulus under a high temperature atmosphere even if it is non-adhesive at room temperature. Therefore, it is a problem that it takes a lot of time to regulate the temperature of the chuck-table (temperature lowering/temperature elevation) and hence working ratio is reduced.  
      In view of such circumstances, an object of the invention is to provide a cleaning member capable of securely removing foreign matter attached to the chuck table of a substrate processing equipment, which does not adhere to the chuck table, maintains a good carrying ability, and exhibits an excellent removing ability for foreign matter even when the temperature of the chuck table is from room temperature to a high temperature (25 to 200° C.)  
      As a results of intensive studies for achieving the aforementioned object, the present inventors have found that a cleaning member having a cleaning layer which is non-adhesive within a wide temperature range of room temperature to a high temperature and exhibits a tensile elastic modulus (Young&#39;s modulus) of a specific value or less can be well carried into a substrate processing equipment within a wide temperature range of room temperature to a high temperature without causing inconveniences such as adhesion as before even when the temperature of the chuck table having a high temperature is not lowered to room temperature and also the foreign matter attached to the inside of the apparatus can be removed conveniently and securely by carrying the member, and thus they have accomplished the invention.  
      The invention has been accomplished based on such a finding.  
      Namely, the invention relates to a cleaning member comprising a cleaning layer which is non-adhesive at the temperature range of 25 to 200° C. and has a tensile elastic modulus (Young&#39;s modulus) of 3,000 MPa or less, and in particular, relates to the cleaning member having the above constitution, wherein the tensile elastic modulus (Young&#39;s modulus) of the cleaning layer is 100 MPa or less.  
      Moreover, the invention can provide the cleaning member having the above constitution, which is a cleaning sheet having the cleaning layer, the cleaning member having the above constitution, which is a carrying member with a cleaning function having the cleaning layer on the carrying member, the cleaning member having the above constitution, wherein the carrying member with a cleaning function comprises the above cleaning sheet provided on the carrying member through an adhesive layer, and the cleaning member having the above constitution, wherein the above carrying member with a cleaning function comprises the cleaning layer directly provided on the carrying member.  
      Furthermore, the invention can provide a cleaning method of a substrate processing equipment, which comprises carrying the cleaning member having each of the above constitutions into the substrate processing equipment, and a substrate processing equipment cleaned by the cleaning method.  
      Thus, in the invention, by using a cleaning member having a cleaning layer which is non-adhesive at the temperature range of 25 to 200° C. and has a tensile elastic modulus (Young&#39;s modulus) of 3,000 MPa or less, in particular, 100 MPa or less, the cleaning member can be well carried into a substrate processing equipment within a wide temperature range of room temperature to a high temperature and also foreign matter attached to the inside of the apparatus can be removed conveniently and securely. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      In the invention, the cleaning layer should be non-adhesive at the temperature range of 25 to 200° C. and should have a tensile elastic modulus (Young&#39;s modulus) of 3,000 MPa or less, or desirably, a tensile elastic modulus (Young&#39;s modulus) is in the range of preferably 100 MPa or less, more preferably 1 to 100 MPa, particularly preferably 10 to 90 MPa.  
      When the cleaning layer is thus non-adhesive at a wide temperature range of room temperature to a high temperature, the inconvenience that the layer adheres the chuck table can be avoided and a good carrying ability can be maintained even when the temperature of the chuck table of the substrate processing equipment is in a high temperature state.  
      Moreover, when the tensile elastic modulus (Young&#39;s modulus) is 3,000 MPa or less, in particular, 100 MPa or less, foreign matter can be efficiently removed and a high removing ability of foreign matter is obtained by an anchoring effect through sufficient sinking of foreign matter into the cleaning layer. The tensile elastic modulus (Young&#39;s modulus) was measured in accordance with a test method JIS K7127.  
      In the invention, such a cleaning layer is not particularly limited in its material component as far as it exhibits the above properties but, for example, polytetrafluoroethylene-based, perfluoroalkoxy-based, fluorinated ethylene propylene-based, polyether ether ketone-based, polysulfone-based, polyethersulfone-based, Nylon-based, polyacetal-based, epoxy-based, polycarbonate-based, cyclic polyolefin-based, aramide-based, polydimethylsiloxane-based, and polyimide-based polymeric materials are preferably used.  
      In particular, polytetrafluoroethylene-based polymeric materials are most suitable. Namely, this kind of materials have a high bond energy, are excellent in heat resistance, exhibit extremely small changes of physical properties toward temperature variation, and maintain stable physical properties within a wide temperature range owing to the electron-withdrawing property of fluorine. Moreover, the elastic modulus can be freely controlled by stretching conditions. Furthermore, since the surface free energy is small, the materials exhibit non-adhesiveness within a wide temperature range.  
      The cleaning member of the invention may be a cleaning sheet having such a cleaning layer or may be a carrying member with a cleaning function having such a cleaning layer on the carrying member.  
      In the case that the cleaning member is a cleaning sheet, it may be one obtained by shaping the above cleaning layer alone into a film or may have a constitution wherein a heat-resistant support such as a polyester film or a polyamide film is used and the above cleaning layer is formed on the support by coating on the support by a commacoat process, a fountain process, a gravure process, or the like. In these embodiments, the above function can be exhibited when the thickness of the cleaning layer is 5 μm or more but the thickness is particularly preferably from 10 to 50 μm.  
      Moreover, in the case that the cleaning member is a carrying member with a cleaning function, it may have a constitution wherein the above cleaning sheet is provided on the carrying member through an adhesive layer or a constitution wherein the cleaning layer is directly provided on the carrying member.  
      In the former constitution, an adhesive layer may be formed beforehand on the above cleaning sheet to be employed to prepare a cleaning sheet with an adhesive layer, which is then attached onto the carrying member utilizing the above adhesive layer. Moreover, in the latter constitution, a cleaning layer may be formed on the carrying member by direct coating of a cleaning layer-forming material by a spin-coating process, a spray process, or the like.  
      Furthermore, it is also possible to prepare a carrying member with a cleaning function by transferring and laminating, onto the carrying member, the above cleaning layer coated on the support.  
      In the former constitution, it is desirable that the adhesive layer has a 180° peel adhesive strength toward the silicon wafer (mirror side) of 0.01 to 10 N/10 mm width, preferably 0.05 to 5 N/10 mm width. When the adhesive strength is too high, there is a risk that the cleaning sheet may be torn at the time when the sheet is peeled off and removed from the carrying member. The thickness of the adhesive layer is not particularly limited but is usually from 5 to 100 μm, preferably from about 10 to 50 μm.  
      Such an adhesive layer is not particularly limited in material constitution and any of usual adhesives such as acrylic and rubber-based ones can be used. Of these, as acrylic adhesives, those containing as a main polymer an acrylic polymer wherein a component having a weight average molecular weight of 100,000 or less is contained in an amount of 10% by weight or less is particularly preferably used. The above acrylic polymer can be synthesized by polymerizing a monomer mixture containing a (meth)acrylic acid alkyl ester as a main monomer and other copolymerizable monomer(s) added as required.  
      In the case that the cleaning member of the invention is the carrying member with a cleaning function as mentioned above, the carrying member to be used is not particularly limited, and suitable one may be used in response to the kind of substrate processing equipment. Specific examples thereof include semiconductor wafer, and substrates for flat panel displays such as LCD and PDP, as well as substrates for compact disc, MR head, and the like.  
      In the invention, by carrying the cleaning member having the above constitution into a substrate processing equipment to thereby bring the member into contact with sites to be washed, such as chuck table, foreign matter attached to the inside of the above apparatus can be conveniently and securely removed without causing any trouble on carrying the member.  
      Namely, by using the cleaning member of the invention, both of the carrying ability and the removing ability of foreign matter can be easily achieved.  
      In the invention, the substrate processing equipment to be cleaned is not particularly limited as far as it possesses a high-temperature chuck table. Examples thereof include an exposure irradiation apparatus, a resist coating apparatus, a developing apparatus, an ashing apparatus, a dry etching apparatus, an ion injection apparatus, a PVD apparatus, a CVD apparatus, an appearance inspecting apparatus, a wafer prober, and the like.  
      In the invention, it can provide aforementioned each substrate processing equipment cleaned by the above method.  
     EXAMPLES  
      The following will describe the invention in more detail with reference to Examples of the invention. However, the invention is not limited only to the following Examples.  
      In this connection, the term “part(s)” as used in the following means part(s) by weight.  
     Example 1  
      As a cleaning layer, a polytetrafluoroethylene-based film having a thickness of 25 μm (manufactured by Mitsui Fluorochemical Co., Ltd.) was used. The tensile elastic modulus (Young&#39;s modulus) under atmospheres of 25° C., 100° C., and 200° C. was 87 MPa, 71 MPa, and 45 MPa, respectively. The tensile elastic modulus (Young&#39;s modulus) was measured in accordance with a test method JIS K7127 (test speed 50 mm/minute, test piece width 10 mm, initial chuck interval 10 mm). In addition, the 180° peel adhesive strength toward the silicon wafer (mirror side) (measured in accordance with JIS Z0237) under atmospheres of 25° C., 100° C., and 200° C. was 0 N/10 mm width in all cases.  
      Into a 500 mL-volume three-necked flask-type reactor equipped with a thermometer, a stirrer, a nitrogen-inlet tube, and a reflux condenser were introduced 73 parts of 2-ethylhexyl acrylate, 10 parts of n-butyl acrylate, 0.15 parts of N,N-dimethylacrylamide, 5-parts of acrylic acid, 0.15 part of 2,2′-azobisisobutyronitrile as a polymerization initiator, and 100 parts of ethyl acetate so that the total amounted to 200 g. The whole was mixed with introducing nitrogen gas for about 1 hour to replace internal air by nitrogen. Thereafter, the inner temperature was made 58° C. and the state was maintained for about 4 hours to effect polymerization, whereby an adhesive polymer solution was obtained.  
      Then, 3 parts of a polyisocyanate compound [trade name “Colonate L” manufactured by Nippon Polyurethane Industry Co., Ltd.] as a crosslinking agent was homogeneously mixed with 100 parts of the adhesive polymer solution thus obtained to prepare an adhesive solution A.  
      As a separator, there was used a long polyester film having a thickness of 38 μm, one surface of which was subjected to a peeling treatment with a silicone-based peeling agent. The above adhesive layer solution. A was applied on the peeled surface of the separator so that the thickness after drying became 15 μm. After drying, the above polytetrafluoroethylene-based film (thickness 25 μm) as a cleaning layer was laminated on the adhesive layer to prepare a cleaning sheet A.  
      After the separator at the adhesive layer side was peeled off, the cleaning sheet A was attached to the mirror side of an 8-inch silicon wafer, a carrying member, by means of a hand roller to prepare a carrying member A with a cleaning function. In this connection, the 180° peel adhesive strength of the above adhesive layer toward the silicon wafer (mirror side) was 1.5 N/10 mm width.  
      Evaluation for cleaning was performed as follows using a wafer prober [“UF200” manufactured by Tokyo Seimitsu Co., Ltd.], a wafer conduction test apparatus for semiconductor production (temperature variable range of chuck table: 25 to 200° C.).  
      First, when a wafer carrying system before cleaning was checked on 12 apparatus of Apparatus A to L, foreign matter capable of discrimination on a visual level was observed on the chuck tables of all the apparatus. That is, 14 pieces were observed on Apparatus A, 15 pieces on Apparatus B, 15 pieces on Apparatus C, 16 pieces on Apparatus D, 14 pieces on Apparatus E, 13 pieces on Apparatus F, 13 pieces on Apparatus G, 15 pieces on Apparatus H, 13 pieces on Apparatus I, 12 pieces on Apparatus J, 15 pieces on Apparatus K, and 13 pieces on Apparatus L.  
      On Apparatus A, while the chuck table was maintained at the temperature of 200° C., the carrying member A with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the carrying member A with a cleaning function which came out of the apparatus, 14 pieces of foreign matter (14 pieces on the table) were trapped and thus it was understood that foreign matter could be securely trapped.  
      Moreover, on Apparatus B, after the temperature of the chuck table was lowered to room temperature (25° C.), the carrying member A with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the carrying member A with a cleaning function which came out of the apparatus, 15 pieces of foreign matter (15 pieces on the table) were trapped and thus it was understood that foreign matter could be securely trapped.  
     Example 2  
      A cleaning sheet B was prepared in the same manner as in Example 1 except that a polyethersulfone-based film having a thickness of 25 μm (“Sumilite FS-1300” manufactured by Sumitomo Bakelite Co., Ltd.) was used as a cleaning layer instead of the polytetrafluoroethylene-based film.  
      The tensile elastic modulus (Young&#39;s modulus) under atmospheres of 25° C., 100° C., and 200° C. were 2,034 MPa, 1,850 MPa, and 1,634 MPa, respectively. In addition, the 180° peel adhesive strength toward the silicon wafer (mirror side) under atmospheres of 25° C., 100° C., and 200° C. was 0 N/10 mm width in all cases.  
      Then, after the separator at the adhesive layer side was peeled off, the above cleaning sheet B was attached to the mirror side of an 8-inch silicon wafer, a carrying member, by means of a hand roller to prepare a carrying member B with a cleaning function.  
      On Apparatus C, while the chuck table was maintained at the temperature of 200° C., the carrying member B with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the carrying member B with a cleaning function which came out of the apparatus, 10 pieces of foreign matter (15 pieces on the table) were trapped and thus it was understood that foreign matter could be trapped.  
      Moreover, on Apparatus D, after the temperature of the chuck table was lowered to room temperature (25° C.), the carrying member B with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the carrying member B with a cleaning function which came out of the apparatus, 11 pieces of foreign matter (16 pieces on the table) were trapped and thus it was understood that foreign matter could be trapped.  
     Example 3  
      A polyethersulfone-based film having a thickness of 400 μm (“Sumilite FS-1300” manufactured by Sumitomo Bakelite Co., Ltd.) was used as a cleaning layer. This film was used as a cleaning sheet C and the sheet was singly punched into an 8-inch silicon wafer shape to prepare a cleaning member C.  
      On Apparatus E, while the chuck table was maintained at the temperature of 200° C., the cleaning member C was carried with bringing the cleaning layer come into the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the cleaning member C which came out of the apparatus, 9 pieces of foreign matter (14 pieces on the table) were trapped and thus it was understood that foreign matter could be trapped.  
      Moreover, on Apparatus F, after the temperature of the chuck table was lowered to room temperature (25° C.), the cleaning member C was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the cleaning member C which came out of the apparatus, 9 pieces of foreign matter (13 pieces on the table) were trapped and thus it was understood that foreign matter could be trapped.  
     Example 4  
      In NMP (N-methyl-2-pyrrolidone), 4,4′-diaminodiphenyl ether was reacted with pyromellitic dianhydride. The resin solution obtained after cooling was applied on the mirror side of an 8-inch silicon wafer, a carrying member, by means of a spin coater, followed by drying under heating at 100° C. for 10 minutes. It was subjected to a heat treatment at 280° C. for 2 hours under a nitrogen atmosphere to form a cleaning layer having a thickness of 20 μm, whereby a carrying member D with a cleaning function was prepared.  
      The tensile elastic modulus (Young&#39;s modulus) of the above cleaning layer under atmospheres of 25° C., 100° C., and 200° C. was 1,580 MPa, 1,210 MPa, and 920 MPa, respectively. In addition, the 180° peel adhesive strength toward the silicon wafer (mirror side) under atmospheres of 25° C., 100° C., and 200° C. was 0 N/10 mm width in all cases.  
      On Apparatus G, while the chuck table was maintained at the temperature of 200° C., the carrying member D with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the carrying member D with a cleaning function which came out of the apparatus, 10 pieces of foreign matter (13 pieces on the table) were trapped and thus it was understood that foreign matter could be trapped.  
      Moreover, on Apparatus H, after the temperature of the chuck table was lowered to room temperature (25° C.), the carrying member D with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. Moreover, as a result of visual observation on the surface of the carrying member D with a cleaning function which came out of the apparatus, 11 pieces of foreign matter (15 pieces on the table) were trapped and thus it was understood that foreign matter could be trapped.  
     Comparative Example 1  
      A cleaning sheet E was prepared in the same manner as in Example 1 except that a thermoplastic polyurethane film having a thickness of 25 μm (“E-660” manufactured by Nippon Miractran Co., Ltd.) was used as a cleaning layer instead of the polytetrafluoroethylene-based film.  
      The tensile elastic modulus (Young&#39;s modulus) of the above cleaning layer under atmospheres of 25° C., 100° C., and 200° C. was 250 MPa, 45 MPa, and 11 MPa, respectively. The tensile elastic modulus (Young&#39;s modulus) was measured in accordance with a test method JIS K7127 (test speed 50 mm/minute, test piece width 10 mm, initial chuck interval 10 mm). In addition, the 180° peel adhesive strength toward the silicon wafer (mirror side) (measured in accordance with JIS Z0237) under atmospheres of 25° C., 100° C., and 200° C. was 0 N/10 mm width, 1.2 N/10 mm width, and 1.8 N/10 mm width, respectively.  
      Then, after the separator at the adhesive layer side was peeled off, the above cleaning sheet E was attached to the mirror side of an 8-inch silicon wafer, a carrying member, by means of a hand roller to prepare a carrying member E with a cleaning function.  
      On Apparatus I, while the chuck table was maintained at the temperature of 200° C., it was tried to carry the carrying member E with a cleaning function while the cleaning layer side was brought into contact with the carrying system, but the cleaning layer strongly adhered to the contacting site and the member could not be carried.  
      Moreover, on Apparatus J, after the temperature of the chuck table was lowered to room temperature (25° C.), the carrying member E with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. However, as a result of visual observation on the surface of the carrying member E with a cleaning function which came out of the apparatus, only 6 pieces of foreign matter (12 pieces on the table) were trapped and thus the trapping ability for foreign matter was not sufficient.  
     Comparative Example 2  
      A cleaning sheet F was prepared in the same manner as in Example 1 except that a polyimide film having a thickness of 25 μm (“Apical NPI” manufactured by Kaneka Corporation) was used as a cleaning layer instead of the polytetrafluoroethylene-based film.  
      The tensile elastic modulus (Young&#39;s modulus) of the above cleaning layer under atmospheres of 25° C., 100° C., and 200° C. was 4,100 MPa, 4,050 MPa, and 4,000 MPa, respectively. In addition, the 180° peel adhesive strength toward the silicon wafer (mirror side) under atmospheres of 25° C., 100° C., and 200° C. was 0 N/10 mm width in all cases.  
      Then, after the separator at the adhesive layer side was peeled off, the above cleaning sheet F was attached to the mirror side of an 8-inch silicon wafer, a carrying member, by means of a hand roller to prepare a carrying member F with a cleaning function.  
      On Apparatus K, while the chuck table was maintained at the temperature of 200° C., the carrying member F with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. In addition, as a result of visual observation on the surface of the carrying member F with a cleaning function which came out of the apparatus, only 5 pieces of foreign matter (15 pieces on the table) were trapped and thus the trapping ability for foreign matter was not sufficient.  
      Moreover, on Apparatus L, after the temperature of the chuck table was lowered to room temperature (25° C.), the carrying member F with a cleaning function was carried with bringing the cleaning layer side into contact with the carrying system, whereby the carrying system such as the chuck table was cleaned. As a result, any phenomenon that the cleaning layer strongly adhered to the contacting site was not observed and the member could be carried without problems. In addition, as a result of visual observation on the surface of the carrying member F with a cleaning function which came out of the apparatus, only 3 pieces of foreign matter (13 pieces on the table) were trapped and thus the trapping ability for foreign matter was not sufficient.  
      While the invention has been described in detail and with reference Lo specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.  
      This application is based on Japanese patent applications No. 2004-201260 filed on Jul. 8, 2004, and Japanese patent applications No. 2005-146522 filed on May 19, 2005, the entire contents thereof being hereby incorporated by reference.