Polishing pad with window and method for manufacturing the same

Abstract

The present invention discloses a polishing pad with a window, and a method for manufacturing the same, in which the polishing pad is not deformed and the polishing slurry does not leak into the gap between the window and the polishing pad because a heat sealing method and a vibration sealing method are not used in the process of inserting and attaching the window to the polishing pad. The polishing pad with a window includes a polishing layer having a first perforation formed in the thickness direction, a window inserted and fixed in the first perforation of the polishing layer, a lower support layer located below the polishing layer and the window, and having a second perforation for irradiating an optical beam formed on the lower side of the window with a width narrower than that of the first perforation or the window, an adhesive layer that mediates the bonding between the polishing layer and the lower support layer, has the same area as the lower support layer, overlaps partially with but does not contact an edge portion of the window, and an adhesive sealant located between the window and the adhesive layer.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0083351 filed on July 6, 2022, and all the contents disclosed in the literature of the Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a windowed polishing pad used for chemically and mechanically planarizing a semiconductor wafer and a method for manufacturing the same. More specifically, in the process of inserting and attaching a window to a polishing pad, since a thermal fusion method and a vibration fusion method are not applied, the polishing pad is not deformed and polishing slurry does not leak into the gap between the window and the polishing pad. The present invention relates to a windowed polishing pad and a method for manufacturing the same.

Background Art

[0003] A chemical mechanical planarization / polishing (hereinafter referred to as CMP) process is a process introduced for global planarization of semiconductor elements. Particularly, due to the trend of increasing the diameter, increasing the integration level, reducing the line width, and multi-layerizing the wiring structure of semiconductor wafers, it has emerged as a more important process.

[0004] In such a CMP process, the polishing rate and flatness are important, which are determined by the process conditions of the polishing apparatus and the consumable members, namely, the polishing slurry and the polishing pad. Among these, the polishing slurry functions to chemically remove the wafer film quality through the chemical components in the slurry solution. And the polishing pad serves to uniformly disperse the polishing slurry on the wafer while in contact with the surface of the wafer, and at the same time physically remove the wafer film quality through the polishing particles contained in the slurry solution and the protrusions located on the surface of the polishing pad.

[0005] Furthermore, in recent CMP processes, polishing pads are used that are inserted and mounted up to a window to detect the end point of wafer polishing. This detection is performed by transmitting an optical beam, such as a laser beam, through the window in the polishing pad, allowing for analysis of the wafer thickness during the polishing process.

[0006] Figure 1 is a schematic diagram of a side cross-section of a conventional polishing pad equipped with a window. As shown in Figure 1, a conventional polishing pad equipped with a window includes a polishing layer (10) with perforations formed in the thickness direction, a window (20) inserted and fixed into the perforations of the polishing layer (10), a lower support layer (30) located below the polishing layer (10) and the window (20), with an opening (22) for transmitting an optical beam formed on the lower side of the window (20) that is narrower than the window (20), and an adhesive layer (40) that joins the polishing layer (10), the window (20), and the lower support layer (30).

[0007] Thus, in a typical polishing pad equipped with a window, a portion of the adhesive layer (40) interposed between a portion of the lower surface of the window (20) and the lower support layer (30) is used to attach the window (20) within the polishing pad. The adhesive layer (40) is formed by applying a hot-melt adhesive (for example, with a melting point of 90°C to 130°C) between a portion of the lower surface of the window (20) and the lower support layer (30), and then forming it by heat fusion.

[0008] However, when a heat-sealing method is used to attach the window (20) to the polishing pad in this way, high-temperature thermal energy is transferred to the polishing layer (10) of the polishing pad, causing dimensional deformation problems such as the polishing pad shrinking or expanding. In addition, because there is no separate sealing means, the polishing slurry inevitably leaks out below the lower support layer (30) during the CMP process, sequentially penetrating into the gap between the polishing layer (10) and the window (20) and the gap between the window (20) and the adhesive layer (40) or the lower support layer (30). In other words, the CMP process is a harsh process in which physical and chemical external forces are applied in a high-temperature and high-humidity environment, so the window (20) shrinks and expands repeatedly during the CMP process, which can cause the adhesive layer (40) to separate or gaps to form, resulting in leakage of the polishing slurry. Therefore, the adhesive layer (40) alone has limitations in preventing leakage of the polishing slurry.

[0009] Therefore, if a window can be installed within the polishing pad while preventing dimensional deformation of the polishing pad and leakage of the polishing slurry below the lower support layer, it is predicted to be a new driving force in polishing semiconductor wafers. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, the object of the present invention is to provide a polishing pad with a window and a method for manufacturing the same, in which the polishing pad does not deform because heat fusion and vibration fusion methods are not applied during the process of inserting and attaching the window to the polishing pad, and polishing slurry does not leak into the gap between the window and the polishing pad. [Means for solving the problem]

[0011] To achieve the above objective, the present invention provides a polishing layer having first perforations formed in the thickness direction, a window inserted and fixed into the first perforations of the polishing layer, a lower support layer located below the polishing layer and the window, with second perforations formed on the lower side of the window to irradiate an optical beam, with a width narrower than the first perforations or the window, an adhesive layer mediating the joining of the polishing layer and the lower support layer, having the same area as the lower support layer, partially overlapping but not in contact with the edge portion of the window, and an adhesive sealant located between the window and the adhesive layer, wherein the adhesive sealant is a cyanoacrylic resin and polyurethane compounds The present invention provides a polishing pad with a window, characterized in that the adhesive is formed by the curing of a liquid adhesive containing [a specific substance].

[0012] Furthermore, the present invention comprises the steps of: a) forming a first perforation that penetrates in the thickness direction at one end of a polishing member; b) attaching a support member to the lower surface of the polishing member with a first adhesive to form a structure in which a lower support layer, an adhesive layer, and a polishing layer are sequentially laminated; c) perforating the lower support layer and adhesive layer in the area corresponding to the first perforation of the polishing layer with a width narrower than the first perforation to form a second perforation that penetrates both the first perforation and the polishing layer; d) applying a second adhesive to the upper surface of the adhesive layer exposed to the outside on the side of the first perforation, and then inserting a window into the first perforation; and e) pressing the window inserted into the first perforation so that it is fixed with the second adhesive, wherein the second adhesive is a cyanoacrylic resin. and polyurethane compounds The present invention provides a method for manufacturing a polishing pad with a window, characterized by including the following: [Effects of the Invention]

[0013] The polishing pad with a window and its manufacturing method according to the present invention have the advantage that, since heat fusion and vibration fusion methods are not applied in the process of inserting and attaching the window to the polishing pad, the polishing pad does not deform and the polishing slurry does not leak into the gap between the window and the polishing pad. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram of a side cross-section of a conventional polishing pad with a window. [Figure 2] Figure 2 is a schematic diagram of a side cross-section of a windowed polishing pad according to one embodiment of the present invention. [Figure 3] Figure 3 shows the sequential manufacturing process of a windowed polishing pad according to one embodiment of the present invention. [Modes for carrying out the invention]

[0015] The present invention will be described in detail below with reference to the attached drawings. Figure 2 is a schematic cross-sectional view of a windowed polishing pad according to one embodiment of the present invention. As shown in Figure 2, the polishing pad with a window according to the present invention includes a polishing layer (110) having a first perforation (112) formed in the thickness direction, a window (120) inserted and fixed into the first perforation (112) of the polishing layer (110), a lower support layer (130) located below the polishing layer (110) and the window (120), with a second perforation (122) formed on the lower side of the window (120) for irradiating an optical beam, having a width narrower than the first perforation (112) or the window (120), an adhesive layer (140) mediating the joining of the polishing layer (110) and the lower support layer (130), having the same area as the lower support layer (130), partially overlapping but not in contact with the edge portion of the window (120), and an adhesive sealant (150) located between the window (120) and the adhesive layer (140).

[0016] Due to the trend towards larger diameters, higher integration, finer line widths, and multi-layer wiring structures in semiconductor wafers, the chemical and mechanical planarization / polishing (CMP) process, introduced for the global planarization of semiconductor devices, requires careful consideration of polishing speed and degree of planarization. These are determined by the process conditions of the polishing equipment and the consumable components, namely the polishing slurry and polishing pad. The polishing pad, in particular, plays a crucial role in uniformly dispersing the polishing slurry onto the wafer surface while in contact with it, and simultaneously physically removing the wafer film through the polishing particles contained in the slurry solution and protrusions on the surface of the polishing pad. Recently, it has become possible to attach a window to such a polishing pad, transmit an optical beam through it to detect the end point of the wafer polishing process, and analyze the wafer thickness during the polishing process.

[0017] However, conventional polishing pads equipped with windows suffer from dimensional deformation problems, such as shrinkage or expansion of the polishing pad, because the windows are attached by heat fusion or vibration fusion. In addition, conventional polishing pads equipped with windows do not have a separate sealing means, so polishing slurry leaks into the gap between the window and the polishing pad facing it during the CMP process. Therefore, the applicant has invented a polishing pad with a window that prevents both the dimensional deformation problem of the polishing pad and the leakage problem of polishing slurry.

[0018] First, the polishing layer (110) may be a foam having micropores. The foam may contain one or more resins selected from the group consisting of polyurethane resins, polyester resins, polyamide resins, acrylic resins, polycarbonate resins, polyolefin resins, and epoxy resins, and it is desirable to construct the polishing layer (110) with a foam containing polyurethane resin, i.e., a polyurethane foam. The average diameter of the pores in the polishing layer (110) or foam may be 5 to 100 μm, and the porosity of the polishing layer (110) or foam may be 20 to 70 volume%, but is not limited to these values.

[0019] The surface of the polishing layer (110) may have an uneven structure in which convex portions and concave portions are alternately patterned in order to achieve the original purpose of the polishing layer (serving as a flow channel for the polishing slurry), or grooves having a pitch, width, depth, etc. of a specific shape may be formed at specific positions. Further, the thickness of the polishing layer (110) may be, for example, 1.5 to 2.5 mm, but there is no particular limitation on the thickness as it may vary depending on the thickness of the object to be polished (semiconductor wafer) or process conditions, etc.

[0020] In such a polishing layer (110), a first through hole (or a first punched area, 112) is formed in the thickness direction. There is no particular limitation on the shape of the first through hole (112), and circular, elliptical, square, and polygonal shapes can be exemplified based on the planar shape (the shape seen from above). Further, there is no particular limitation on the size (area or volume) of the first through hole (112), and it may be formed in any size as long as the transmission of an optical beam is possible. Also, there is no particular limitation on the position of the first through hole (112), and it may be anywhere in the polishing layer (110) as long as the thickness of the wafer can be measured through the optical beam.

[0021] Next, the window (120) is inserted and fixed into the first through hole (112) of the polishing layer (110). The upper surface position in the inserted and fixed state may be the same as the upper surface position of the polishing layer (110), or may be lower than the upper surface position of the polishing layer (110) (that is, in the latter case, the portion where the window is inserted may be recessed). On the other hand, when the window (120) protrudes from the polishing layer (110), not only may it affect the polishing of the wafer, but scratches or cracks may occur on the upper surface of the window (120), making it difficult for the optical beam to pass through. Therefore, it is not desirable to configure the window (120) to protrude from the polishing layer (110).

[0022] The window (120) may include a normal one used as a material for a window for a polishing pad in the art. However, it is desirable in terms of transmittance and reliability of detecting the polishing end point to apply the window for a polishing pad disclosed in Korean Patent Application No. 10-2022-0008594 (Title of the Invention: Method for Manufacturing a Window for a Polishing Pad and a Window for a Polishing Pad Manufactured by this Method) filed by the applicant on January 20, 2022. In addition, in order to prevent the polishing slurry from leaking to the lower part of the window (120), it may also be desirable to apply a non-foamed body without pores as the material of the window (120).

[0023] And since the window (120) must be inserted into the first perforation (112) of the polishing layer (110) described above, it must have the same area as the first perforation (112) or a smaller area. However, when the area of the window (120) is the same as the area of the first perforation (112), the insertion into the first perforation (112) is not smooth and may damage the polishing layer (110) or the window (120) itself. Therefore, it may be desirable that the area of the window (120) is slightly smaller than the area of the first perforation (112).

[0024] Subsequently, the lower support layer (130) is located below the polishing layer (110) and is positioned so as to also cover a part of the lower part of the window (120). It supports the polishing layer (110) and serves to absorb and disperse the impact applied to the polishing layer (110) instead. The lower support layer (130) may include, for example, but is not limited to, those selected from the group consisting of a non-woven fabric system impregnated with a polyurethane resin, a polyurethane foam system, and a suede system of a polyurethane resin. In addition, the thickness of the lower support layer (130) may be, for example, 0.4 to 1.5 mm, but there is no particular limitation on the thickness, as it may vary depending on the thickness of the polishing layer (110) or process conditions, etc.

[0025] A second perforation (or second perforation region, 122) for irradiating an optical beam is formed in the thickness direction of the lower support layer (130). Therefore, the second perforation (122) is formed below the region of the first perforation (112) or the window (120) with a narrower width so that the optical beam is irradiated and transmitted towards the window (120). That is, the second perforation (122) is formed below the first perforation (112), is formed with a smaller planar area than the first perforation (112), and is connected to the first perforation (112) and the second perforation (122) so that they penetrate each other. On the other hand, if the planar area of ​​the second perforation (122) is larger than or equal to the planar area of ​​the first perforation (112), the window (120) inserted into the first perforation (112) will not be fixed and will detach downwards. Therefore, the planar area of ​​the second perforation (122) must always be smaller than the planar area of ​​the first perforation (112) (i.e., the lower support layer also acts as a fastener to prevent the window from detaching). Furthermore, there are no particular restrictions on the shape of the second perforation (122), and examples include circular, elliptical, quadrilateral, and polygonal shapes based on the planar shape (shape viewed from above).

[0026] Next, the adhesive layer (140) mediates the joining of the polishing layer (110) and the lower support layer (130), and since it is located facing the entire upper surface of the lower support layer (130), it has the same area as the lower support layer (130). Therefore, like the lower support layer (130), the adhesive layer (140) partially overlaps with the edge portion of the window (120), but does not come into contact with it.

[0027] Such an adhesive layer (140) may contain, for example, one or more selected from the group consisting of polyurethane resins, polyester resins, ethylene-vinyl acetate resins, polyamide resins, and polyolefin resins, and it is preferable that it contains one or more of either polyurethane resins or polyester resins.

[0028] Finally, the adhesive sealant (150), which is a core component of the present invention, is located between the window (120) and the adhesive layer (140), and serves to bond them together while simultaneously preventing the slurry from penetrating and leaking into the interior and underside of the polishing pad during the polishing process.

[0029] On the other hand, as explained earlier, in order to insert the window (120) into the first perforation (112) of the polishing layer (110) without damage, the area of ​​the window (120) must be made smaller than the area of ​​the first perforation (112). As a result, a small gap is created between the wall surface of the first perforation (112) and the window (120). Therefore, in order to more fundamentally prevent slurry penetration and leakage, the adhesive sealant (150) can also be formed in the gap space formed between the wall surface of the first perforation (112) and the window (120). In this case, as shown in Figure 2, the adhesive sealant (150) can continue continuously from the gap space formed between the wall surface of the first perforation (112) and the window (120) to the space between the window (120) and the adhesive layer (140), forming a right-angle shape.

[0030] Such adhesive sealant (150) includes a cured liquid adhesive, for example, the liquid adhesive may contain one or more compounds selected from the group consisting of vinyl acetate compounds, polychloroprene compounds, polyurethane compounds, acrylate compounds such as cyanoacrylate, and epoxy compounds. The adhesive sealant (150) is characterized by being provided without thermal melting.

[0031] On the other hand, the polishing pad with a window according to the present invention further includes a tape layer (160) which is optionally attached to the entire lower surface of the lower support layer (130). The tape layer (160) is for adhesively fixing the polishing pad to the platen, and can be used without particular limitation as long as it can adhere and fix the polishing pad and the platen to each other, such as double-sided adhesive tape.

[0032] Next, a method for manufacturing a windowed polishing pad according to the present invention will be described. Figure 3 sequentially shows the manufacturing process of a windowed polishing pad according to one embodiment of the present invention. Referring to Figure 3, the method for manufacturing the windowed polishing pad is: a) forming a first perforation (112) that penetrates in the thickness direction at one end of the polishing member (110); b) attaching a support member (130) to the lower surface of the polishing member (110) with a first adhesive (140) to form a structure in which a lower support layer (130), an adhesive layer (140), and a polishing layer (110) are sequentially laminated; c) the lower support layer (130) and adhesive layer (140) in the region of the polishing layer (110) corresponding to the first perforation (112) The steps include: d) drilling a portion with a width narrower than the first drilling (112) to form a second drilling (122) that penetrates the first drilling (112) of the polishing layer (110); d) applying a second adhesive (150) to the upper surface of the adhesive layer (140) exposed to the outside on the first drilling (112) side, and then inserting the window (120) into the first drilling (112); and e) pressing the window (120) inserted into the first drilling (112) so that it is fixed via the second adhesive (150).

[0033] The steps of forming a first hole (112) in the polishing member (110) in step a) and forming a second hole (122) in the lower support layer (130) and the adhesive layer (140) in step c) can be performed by a press method using a cutting tool, but are not limited to this. On the other hand, it should be added that the polishing member is the same as the polishing layer (110) described above, and the above terminology was used considering that it is before the layer is formed.

[0034] Step b) above is the step of attaching the support member (130) to the lower surface of the polishing member (110) with the first adhesive (140). At this time, the first adhesive (140) can first be heated and melted separately (90°C to 130°C), then applied to one surface of the support member (130) and bonded to the lower surface of the polishing member (110), or the first adhesive (140) can be applied to one surface of the support member (130), then heated and melted, and then bonded to the lower surface of the polishing member (110). On the other hand, the support member is the same as the lower support layer (130), and it should be added that the above terminology was used considering that it is before the layer is formed.

[0035] The second adhesive is the same as the adhesive sealant (150) described above, and therefore the second adhesive (150) is a liquid adhesive. In step d), the second adhesive (150) is applied only to the upper surface of the adhesive layer (140) exposed to the outside on the first perforation (112) side, but in order to more fundamentally prevent slurry penetration and leakage, the second adhesive (150) can also be applied to the wall surface of the first perforation (112). The pressing in step e) can be carried out under temperature conditions of 10°C to 70°C, preferably 10°C to 40°C. Thus, the present invention completely eliminates the heat fusion method when attaching the window (120) to the polishing pad (i.e., the second adhesive is not heated and melted in steps d) to e), thereby preventing or minimizing dimensional deformation problems of the polishing pad (specifically, the polishing layer) compared to conventional methods of attaching the window using heat fusion or vibration fusion.

[0036] On the other hand, the method for manufacturing a polishing pad with a window according to the present invention further includes, if necessary, the step of attaching a tape (160) to the lower surface of the support member (130) (i.e., the surface to which the first adhesive is not applied). This may be done at any stage of the manufacturing method, but from the standpoint of convenience, it may be desirable to attach the tape (160) before step c) (i.e., the step of forming the second hole) is performed.

[0037] The present invention will be described in more detail below with reference to specific examples. The following examples are provided to facilitate understanding of the present invention, and the present invention is not limited thereto. [Examples]

[0038] Example 1: Manufacturing of a polishing pad with a window First, a first perforation (planar shape: rectangular, planar area: 20 mm x 60 mm) was formed at one end of a polishing member (thickness: 2 mm) made of polyurethane foam, penetrating in the thickness direction. Then, a support member (nonwoven fabric impregnated with polyurethane resin, thickness: 0.8 mm) was attached to the lower surface of the polishing member with a first adhesive (polyurethane resin), thereby manufacturing a structure in which a lower support layer, an adhesive layer, and a polishing layer were sequentially laminated (at this time, the first adhesive was melted at a temperature of 110°C to attach the polishing member and the support member).

[0039] Next, a second hole (planar shape: rectangular, planar area: 13 mm × 50 mm) was formed by drilling a hole with a narrower width than the first hole in the lower support layer and adhesive layer portion corresponding to the first hole in the polishing layer.

[0040] Next, a second adhesive (cyanoacrylic resin) was applied to the upper surface of the adhesive layer exposed to the outside of the first perforated side. Then, a window (non-foamed polyurethane material) was inserted into the first perforation, and finally, the window inserted into the first perforation was pressed together under a temperature of 30°C so that it was fixed with the second adhesive, thereby manufacturing a polishing pad with a window.

[0041] Comparative Example 1: Manufacturing of a polishing pad with a window A polishing pad with a window was manufactured in the same manner as in Example 1, except that the window was attached with the first adhesive without using the second adhesive, and the first adhesive was melted at a temperature of 110°C to attach the window.

[0042] Experimental Example 1: Evaluation of the degree of dimensional deformation of polishing pads The dimensions of the polishing layer of the polishing pad manufactured in Example 1 and the dimensions of the polishing layer of the polishing pad manufactured in Comparative Example 1 were compared and contrasted, and the degree of deformation was measured compared to the dimensions before the window was installed. The results are shown in Table 1 below.

[0043] [Table 1]

[0044] As a result of the measurements, as shown in Table 1 above, the polishing pad (polishing layer) of Example 1, in which the window was attached without heat fusion, had the same dimensions as before the window was attached, confirming that there was no dimensional deformation of the polishing pad. On the other hand, the polishing pad (polishing layer) of Comparative Example 1, in which the window was attached by heat fusion, had expanded beyond the dimensions before the window was attached, confirming that expansion due to heat fusion had occurred.

[0045] Experimental Example 2: Evaluation of leakage in polishing slurry The polishing pads manufactured in Example 1 and Comparative Example 1 were respectively placed so that a semiconductor wafer was in contact with their surfaces. After injecting CMP slurry onto the wafers, the polishing pads were rotated, and it was observed whether the slurry leaked to the bottom of the polishing pads.

[0046] Observations revealed that when using the polishing pad of Example 1, in which an adhesive sealant (second adhesive) was positioned between the adhesive layer and the window, no leakage of slurry to the bottom of the polishing pad occurred at all. On the other hand, when using the polishing pad of Comparative Example 1, in which the adhesive layer and window were attached without the adhesive sealant (second adhesive), it was confirmed that slurry leaked to the bottom of the polishing pad. [Explanation of Symbols]

[0047] 10, 110: Polishing layer 112: 1st perforation 20, 120: Window 22, 122: 2nd perforation 30, 130: Lower support layer 40, 140: Adhesive layer 150: Adhesive sealant 160: Tape layer

Claims

1. A polished layer in which the first perforation is formed in the thickness direction, A window inserted and fixed into the first hole in the polishing layer, A lower support layer is located below the polishing layer and the window, and below the window, a second perforation for irradiating a light beam is formed with a width narrower than the first perforation or the window. An adhesive layer mediates the bonding between the polishing layer and the lower support layer, has the same area as the lower support layer, and partially overlaps with the edge portion of the window but does not come into contact with it. The system comprises an adhesive sealant located between the window and the adhesive layer, The aforementioned adhesive sealant is an adhesive formed by the curing of a liquid adhesive containing a cyanoacrylic resin and a polyurethane compound, characterized in that it is a polishing pad with a window.

2. The polishing pad with a window according to claim 1, characterized in that the adhesive sealant is also formed in the space between the wall surface of the first hole and the window.

3. The windowed polishing pad according to claim 2, characterized in that the adhesive sealant extends continuously from the separation space formed between the wall surface of the first hole and the window to the space between the window and the adhesive layer, and has a right-angle cross-section.

4. The windowed polishing pad according to claim 1, characterized in that the adhesive sealant is provided without being melted by heat.

5. a) A step of forming a first hole that penetrates through one end of the polishing member in the thickness direction, b) The step of attaching a support member to the lower surface of the polishing member with a first adhesive, thereby forming a structure in which a lower support layer, an adhesive layer, and a polishing layer are sequentially laminated, c) The step of drilling the lower support layer and the adhesive layer portion in the region corresponding to the first drilling in the polishing layer with a width narrower than the first drilling, thereby forming a second drilling that penetrates the first drilling in the polishing layer and the other drilling, d) After applying the second adhesive to the upper surface of the adhesive layer exposed to the outside on the first perforation side, insert the window into the first perforation, e) The step of pressing the window inserted into the first hole so that it is fixed with the second adhesive, A method for manufacturing a polishing pad with a window, characterized in that the second adhesive contains a cyanoacrylic resin and a polyurethane compound.

6. The method for manufacturing a windowed polishing pad according to claim 5, characterized in that the second adhesive is also applied to the wall surface of the first hole.

7. The method for manufacturing a windowed polishing pad according to claim 5, characterized in that the second adhesive is not heated or melted in step d) through step e).

Images