CN115290214A

CN115290214A - In-situ wired wafer film temperature sensor

Info

Publication number: CN115290214A
Application number: CN202210786821.7A
Authority: CN
Inventors: 夏子奂
Original assignee: Shanghai Gnd Etech Co ltd
Current assignee: Shanghai Gnd Etech Co ltd
Priority date: 2022-07-04
Filing date: 2022-07-04
Publication date: 2022-11-04

Abstract

The invention provides an in-situ wafer film temperature sensor which is used for measuring the temperature of a wafer (1) and is characterized by at least comprising a film temperature sensor (2), a film lead (3) and leads, wherein the film temperature sensor (2) is connected with the film lead (3), the film lead (3) is connected with the leads, and at least the film temperature sensor (2) and the film lead (3) are arranged on the wafer (1). The sensor provided by the invention is integrally attached to the wafer, is firmly fixed, and does not have the lead shaking phenomenon of the conventional wafer temperature measuring sensor.

Description

In-situ wired wafer film temperature sensor

Technical Field

The invention belongs to the field of semiconductor equipment, particularly belongs to the technical field of semiconductor wafer detection and temperature measurement, relates to a wafer temperature sensor, and particularly relates to an in-situ wired wafer film temperature sensor which can be used for measuring the temperature distribution of a semiconductor processing machine in a vacuum chamber.

Background

In semiconductor manufacturing processes, such as photolithography (Litho), dry etching (Dryetch), ion implantation (Implant), doping (Diffusion), lift-off (Dry strip), cleaning (Wet clean), photo-masking (Mask), chemical Vapor Deposition (CVD), physical Vapor Deposition (PVD), chemical Mechanical Polishing (CMP), and the like, all process steps require stringent temperature measurement and control.

An In situ wafer temperature sensor (In situ wafer temperature sensor) is used for measuring physical quantities such as temperature and the like In real working environment including the actual working process of a reaction cavity In the actual working process of a chip processing and manufacturing process, and is an indispensable system calibration tool In the manufacturing and production processes of semiconductor equipment.

Existing in-situ wired wafer thermometry sensors, as described in patents US6190040 and US6915589, include temperature sensors on the wafer, connecting leads, lead fasteners, vacuum pass-through bands, and interfaces. The temperature sensor such as thermocouple and thermal resistor is used as temperature measuring element or embedded in the blind hole of the wafer, or directly adhered to the wafer through high temperature resistant adhesive. Each temperature sensor needs to be led out by an independent lead wire, and one end of the wafer is pressed on the wafer by a metal fixing piece. The lead wires of the sensor are manufactured by hands, time is consumed for manufacturing under the condition that the number of temperature measurement points is large, and the lead wires are easy to overlap. The two ends of the lead are fixed, the middle of the lead is suspended, the lead is easy to shake, and if the lead shields a temperature measuring point, the accuracy of temperature measurement is greatly influenced in the process of using heat radiation heating. According to the production process requirements of semiconductor processing and manufacturing, the in-situ wafer temperature measuring sensor can be subjected to high-temperature or low-temperature treatment, an adhesive adhered to a wafer is easy to fall off, the bonding strength of the temperature sensor and the tensile strength of a lead are poor, and the temperature sensor is easy to be pulled and fall off manually during use.

Aiming at the quality problem and the cost problem of the existing in-situ wired wafer temperature measuring sensor, a brand new in-situ wired wafer temperature measuring sensor is required to be provided.

Disclosure of Invention

In order to solve the quality problem of an in-situ wired wafer temperature sensor in the prior art, the invention provides a novel in-situ wired wafer temperature sensor which is used for measuring the temperature of a wafer 1 and is characterized by at least comprising a film temperature sensor 2, a film lead 3 and a lead, wherein the film temperature sensor 2 is connected with the film lead 3, the film lead 3 is connected with the lead, and at least the film temperature sensor 2 and the film lead 3 are arranged on the wafer 1.

Preferably, at least the thin film temperature sensor 2 and the thin film lead 3 are disposed in a groove on the wafer 1.

Preferably, a part of the lead is disposed in a groove on the wafer 1, and the other end of the lead protrudes out of the wafer 1.

Preferably, at least a portion of the recess is covered with a cover sheet.

Preferably, the thickness of the cover sheet is smaller than the depth of the groove.

Preferably, the cover plate is covered with high-temperature glue for assisting in fixing the cover plate.

Preferably, the cover plate is made of the same material as the wafer 1.

Preferably, the grooves on the wafer 1 are generated in any one of the following ways:

-dry etching;

-wet etching;

-laser grooving; or

-precision machining processes.

Preferably, the sensor provided by the invention further comprises a connector 4, the film lead 3 is connected with the connector 4, and the connector 4 is connected with the lead.

Preferably, the thin film temperature sensor 2 is a thermocouple or a thermistor.

Preferably, the thin film temperature sensor 2 is formed by performing a deposition operation on the wafer by using physical vapor deposition or chemical vapor deposition.

Preferably, the leads include a high temperature lead and a low temperature lead, and the low temperature lead is positioned on the side far away from the wafer 1.

Preferably, the high-temperature lead is platinum rhodium, nickel chromium or nickel aluminum alloy.

Preferably, an insulating layer made of a ceramic or quartz sleeve or a fiber tube is arranged outside the high-temperature lead.

Preferably, the low-temperature lead is a copper wire, an enameled wire, a cable or a shielded wire.

Preferably, the lead further comprises an interface, one end of the interface is connected with the low-temperature lead, and the other end of the interface is used for being connected with the outside to transmit temperature information.

Preferably, the lead further comprises a vacuum through-band, the vacuum through-band is located between the high-temperature lead and the low-temperature lead, and the high-temperature lead and the low-temperature lead are connected after penetrating through the vacuum through-band respectively.

Preferably, the vacuum through-belt thickness is no greater than 0.2mm.

Preferably, the vacuum pass-through band is composed of polyimide.

Preferably, the film lead 3 is a metal wire deposited on the wafer by vacuum coating.

Preferably, the material of the thin film wire 3 is gold, copper or silver.

Preferably, the sensor provided by the present invention further comprises at least one insulating layer, wherein the insulating layer is disposed in the groove, and at least the thin film temperature sensor 2 and the thin film lead 3 are disposed on the insulating layer.

Preferably, a protective layer or an insulating layer is deposited at least above the thin film temperature sensor 2 and the thin film wire 3.

Preferably, the connector includes a thin lead for connecting at least the film lead 3 and a protective paste.

Compared with the existing scheme, the wafer temperature sensor provided by the invention has the advantages that the thin film device and the lead wire are used for replacing the sensor and the lead wire on the wafer, the sensor provided by the invention is integrally attached to the wafer and is firmly fixed, and the lead wire shaking phenomenon of the existing wafer temperature sensor can be avoided. By the technical mode provided by the invention, the film deposition process is mature, the manufacturing is convenient and the cost is low.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIGS. 1A and 1B illustrate a schematic top view and a schematic side view, respectively, of an in-situ wired wafer thin film temperature sensor, according to an embodiment of the present invention;

FIG. 2 shows a schematic view of a thin film temperature sensor and leads in the connector area, according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a reticle for fabricating a thin film temperature sensor and leads according to one embodiment of the present invention;

FIG. 4 shows a schematic diagram of a thin film thermocouple and a thin film thermal resistor, according to an embodiment of the present invention.

Description of reference numerals:

1. a wafer;

2. a thin film temperature sensor;

3. a film lead;

4. a connector;

5. a high temperature lead;

6. a vacuum through-pass band;

7. a low temperature lead;

8. a connecting port;

9. an insulating layer;

10. a protective layer;

21. a thin film thermocouple positive electrode;

22. a thin film thermocouple cathode;

23. a temperature measuring point of a thin film thermocouple;

24. a thin film thermal resistance; 41. a thin lead; 42. an adhesive; 101. a sensor mask; 102. and (5) lead wire masking.

Detailed Description

The technical problem to be solved by the present invention is to provide a thin film type in-situ wafer temperature sensor, which is to directly fabricate a temperature sensor and a sensor lead on a wafer by using a thin film deposition method, and the wafer has no suspended lead, thereby avoiding the risk that the lead shields a heat source, and elements are pulled and fall off. Compared with the traditional sensor, the thin film type temperature sensor has smaller size, thickness of only a few microns, smaller heat capacity and quicker temperature response; the existing wafer temperature sensor is provided with a plurality of leads and fixing pieces which are thicker than the wafer, and the thickness of the film type wafer temperature sensor is nearly the same as that of the wafer, so that the wafer temperature sensor is suitable for a semiconductor processing cavity and can more truly measure the in-situ wafer temperature in a compact process cavity.

Fig. 1A and 1B together illustrate a schematic diagram of an in-situ wired wafer film temperature sensor, wherein fig. 1A is a top view and fig. 1B is a side view. For convenience of expression, the corresponding description and identification of the two figures are provided to facilitate understanding of the position relationship and the structural relationship. Preferably, the in-situ wafer film temperature sensor provided by the invention comprises a wafer 1, a film temperature sensor 2, a film lead 3, a connector 4 and a lead. The leads preferably may comprise any one or more of the high temperature leads 5, vacuum passbands 6, low temperature leads 7 and interfaces 8, and further those skilled in the art will appreciate that any selection and combination of the above-described high temperature leads 5, vacuum passbands 6, low temperature leads 7 and interfaces 8 may be made as required by particular circumstances and remain within the scope of the present invention. It is further understood by those skilled in the art that the leads are not identified in a schematic manner in fig. 1A and 1B, wherein a combination of a high temperature lead 5, a vacuum feedthrough 6, a low temperature lead 7, and an interface 8 may preferably be understood as the leads to facilitate understanding by those skilled in the art.

The wafer 1 may be a single crystal silicon wafer, a sapphire wafer, a quartz wafer, a ceramic wafer, or the like, as a raw material for semiconductor processing. The size of the wafer 1 may also vary from 1 to 12 inches depending on the embodiment. The shape of the wafer 1 may be circular or square according to different embodiments. Further, as understood by those skilled in the art, preferably the wafer 1 is the object to be measured, and the thin film temperature sensor 2 is preferably used to measure the temperature of the wafer 1.

The thin film temperature sensor 2 may be a Resistance Type (RTD) or a Thermocouple (TC) according to various embodiments, wherein the resistance type thin film temperature sensor 2 may be divided into a Negative Temperature Coefficient (NTC) thermistor and a Positive Temperature Coefficient (PTC) platinum resistor. According to different embodiments, the types of the thermocouples can be selected from S, R, B, N, K, E, J, T and the like, and the types of K, R and B are preferred. The thermal resistance is preferably a platinum thermal resistance Pt100 or Pt1000. According to various embodiments, the thermocouple or the thermistor may use a vacuum coating method, such as Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD), to deposit a corresponding material on the wafer, such as ni-cr and ni-al for the K-type thermocouple and platinum for the pt thermistor.

The number of the thin film temperature sensors 2 may be 5 as shown in fig. 1A, or may be other numbers, such as 1,9,34, etc. The distribution of the thin-film temperature sensors 2 may be arranged according to different embodiments, and this is within the scope of the present invention.

The thin film lead 3 is preferably a metal wire deposited on the wafer by vacuum deposition, and according to different embodiments, a conductive material such as gold, copper, silver, or the like, or a material corresponding to a thermocouple, such as a K-type thermocouple made of nichrome or nickel-aluminum alloy, may be used to connect the thin film temperature sensor 2 and the connector 4.

Preferably, the connector 4 is used for connecting the film lead 3 and the wafer external lead.

The high-temperature lead 5 is used for connecting the thin film lead 3 on the wafer in a high-temperature environment, and can be made of high-temperature-resistant metal such as thermocouple homogeneous material platinum rhodium, nickel chromium and nickel aluminum alloy, and the outer insulating layer can be a ceramic or quartz sleeve or a fiber tube.

The vacuum pass-through band 6 is intended to pass an O-ring on a vacuum chamber, in a preferred embodiment with a thickness <0.2mm, further preferred with a thickness of 0.1mm. The selected material is Polyimide (PI). The structure may be a flexible printed circuit board, or a sandwich structure using the form of PI tape-lead-PI tape. For equipment machines which have no vacuum requirement and can directly work in the atmospheric environment, a vacuum through-pass band is not needed.

The low-temperature lead 7 is used in a low-temperature environment or outside a vacuum cavity, and can be a copper wire, an enameled wire, a cable, a shielded wire and the like according to different embodiments.

Interface 8 is used for connecting the host computer to transmit temperature signal, can adopt DB, SCSI,2pin interface, LEMO interface etc. according to different embodiments.

Fig. 2 shows a schematic representation of the film temperature sensor 2 and the leads 3 in the region of the connector 4.

In a preferred embodiment, the film temperature sensor 2 is connected to the lead 3, and the lead 3 is connected to the lead 5 through a thin lead 41. The thin wires 41 may be gold wires or aluminum wires, and the film wires 3 and the wafer outer wires 5 may be connected using an ultrasonic bonding machine. Preferably, a protective adhesive 42 is applied to the connection site, and a refractory ceramic adhesive or the like may be used according to various embodiments.

Optionally, an insulating layer 9, such as SiO2, siN, is deposited between the wafer 1 and the temperature sensor 2 and the film leads 3 for electrical insulation between the wafer and the temperature sensor and the film leads.

Optionally, a protective layer 10 is deposited on the temperature sensor 1 and the film lead 2 for protecting the temperature sensor and the film lead. The protective layer 10 may be made of the same material as the insulating layer 9 or the same material as the wafer 1.

Further, the thin film temperature sensor 2 and the thin film lead 3 can be manufactured by using a photolithography process, for example, a layer of photoresist is firstly spin-coated on a wafer, an optical mask is used for shielding the unexposed position, the area where the sensor and the lead are required to be manufactured is exposed and baked, the photoresist is removed after development, the thin film sensor and the lead material are deposited by using a vacuum coating method, and finally the residual photoresist is removed.

The hollow mask plate can also be directly attached to the wafer for vacuum coating. FIG. 3 shows a schematic diagram of a reticle used to fabricate a thin film temperature sensor and leads, as an example. The sensor mask 101 and the lead mask 102 are respectively provided with pattern notches of a thin film sensor and a thin film lead, the sensor mask and the lead mask are respectively arranged on a wafer 1 before vacuum coating, materials to be evaporated penetrate through the mask hollowed pattern notches to be deposited on the wafer in a PVD or CVD mode, and the positions without notches prevent the thin films from being deposited on the wafer 1.

FIG. 4 illustrates, as an example, two schematic views of a thin film temperature sensor, a thin film thermocouple and a thin film thermistor. The thin-film thermocouple is composed of a thin-film thermocouple positive electrode 21 and a thin-film thermocouple negative electrode 22. In the manufacturing process, the positive/negative electrode film material can be firstly deposited through the mask plate, then the other electrode material is deposited, and the two films are mutually overlapped at the temperature measuring point to form the film thermocouple temperature measuring point 23. The film leads 3 are connected to the positive and negative electrodes, and the same material as the positive and negative electrodes is used. The film lead wire and the film thermocouple can be manufactured simultaneously, namely, a positive/negative electrode film material is deposited through a mask plate printed with the shapes of the positive/negative electrodes of the thermocouple and the lead wire of the same level, and then another electrode film material is deposited through a mask plate printed with the shape of the other electrode.

The thin film heat resistor 24 is made of an extremely fine metal thin film, and a platinum heat resistor Pt100 or Pt1000 can be used. The film lead 3 can be made of conductive materials such as gold, copper and silver, and is connected with two ends of the film thermal resistor 24 through 4 wires to form a 4-wire thermal resistor testing mode, so that high-precision testing can be realized.

Those skilled in the art will appreciate that in a preferred embodiment, the wafer may be pre-grooved with the film temperature sensors and film leads embedded therein, optionally covered with a cover sheet of the same material as the wafer. The thickness of the cover plate is slightly thinner than that of the groove, and the surface of the wafer is almost the same as the original wafer surface after the cover plate is fixed by high-temperature glue.

The wafer may be pre-grooved at the connector location and the connectors may be embedded therein. The leads can be led out from the side of the wafer.

The grooving can be dry etching or wet etching, laser grooving or precision machining.

In yet another variation, the thin film temperature sensor and thin film leads, etc. are directly glued or bonded to the surface of the wafer, which is within the scope of the present invention. Preferably, in such a variation, both the film temperature sensor and the film lead are attached to the surface of the wafer.

More specifically, in another preferred embodiment, the in-situ wafer film temperature sensor provided by the invention comprises a wafer, a film temperature sensor, a film lead, a connector and a lead. The leads may comprise any one or more of high temperature leads, vacuum feedthrough bands, low temperature leads, and interfaces.

The wafer is a substrate for bearing a sensor, is an object to be measured in temperature and is also a wafer manufactured by semiconductor processing, and the wafer is made of monocrystalline silicon wafers, sapphire wafers, quartz wafers and ceramic wafers. Ranging in size from 1 to 12 inches. The shape is circular and square.

The thin film temperature sensor is a device for measuring the temperature of a wafer, and may be a Thermocouple (TC) or a thermal Resistor (RTD), which may be further classified as a Negative Temperature Coefficient (NTC) thermistor or a Positive Temperature Coefficient (PTC) platinum thermistor. The types of the thermocouples can be selected from S, R, B, N, K, E, J, T and the like, and the types of K, R and B are preferred. The thermal resistance is preferably a platinum thermal resistance Pt100 or Pt1000. The thermocouple or the thermal resistor can use a vacuum coating method, such as Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD), and corresponding materials are deposited on the wafer, such as Ni-Cr and Ni-Al alloy used for a K-type thermocouple and platinum used for a platinum thermal resistor.

The film lead is a metal wire deposited on the wafer in a vacuum coating mode, can be made of conductive materials such as gold, copper and silver or materials with the corresponding model of a thermocouple, and is used for connecting the temperature sensor and the connector.

Optionally, an insulating layer, such as SiO, is deposited between the wafer and the temperature sensor and thin film wire ₂ SiN is used for electrical insulation between the wafer and the temperature sensor and the thin film wire.

Optionally, a protective layer or an insulating layer is deposited above the temperature sensor and the film lead for protecting the temperature sensor and the film lead.

The connector is used for connecting the film lead and the wafer outer lead, and the inner part of the connector optionally comprises a thin lead and protective glue. The thin wires may be gold or aluminum wires, and the thin film wires and the wafer outer wires may be connected using an ultrasonic bonding machine.

The high-temperature lead is used for connecting a thin film lead on a wafer in a high-temperature environment, can be made of high-temperature-resistant metal such as thermocouple homogeneous materials of platinum rhodium, nickel chromium and nickel aluminum alloy, and the outer insulating layer can be a ceramic or quartz sleeve or a fiber tube.

The vacuum through belt is used for passing through an O-shaped sealing ring on a vacuum cavity, and the thickness of the vacuum through belt is less than 0.2mm, and preferably 0.1mm. The selected material is Polyimide (PI). The structure can be a flexible printed circuit board, or a sandwich structure using the form of PI tape-lead-PI tape. For equipment machines which have no vacuum requirement and can directly work in the atmospheric environment, a vacuum through-pass band is not needed.

The low-temperature lead is used outside a low-temperature environment or a vacuum cavity and can be a copper wire, an enameled wire, a cable and a shielding wire.

The interface is used for connecting the host computer to transmit temperature signal, can be DB, SCSI,2pin interface, LEMO interface etc..

In a preferred embodiment, optionally, a groove can be formed in the wafer in advance at the position of the film temperature sensor and the film lead, the sensor and the lead are embedded in the groove, and a cover sheet made of the same material as the wafer is optionally covered above the groove. The thickness of the cover plate is slightly thinner than that of the groove, and the surface of the wafer is almost the same as the original wafer after being fixed by high-temperature glue.

In a preferred embodiment, the wafer may optionally be pre-grooved at the connector location, with the connectors embedded therein. The leads can be led out from the side of the wafer.

Referring to the embodiments shown in fig. 1A, 1B, 2, 3 and 4, it is understood by those skilled in the art that, in a variation, the wafer 1 may be referred to as an object to be measured, i.e., the thin film temperature sensor provided by the present invention is used to measure the object to be measured, and preferably, the components such as the thin film temperature sensor are disposed in the object to be measured in the manner provided by the present invention. In the above description of the embodiments of the present invention, the object to be measured is replaced by the wafer 1 for convenience of description, but all objects to be measured may be applied to the solution provided by the present invention, which does not affect the protection scope of the present invention.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims

1. The in-situ wafer film temperature sensor is used for measuring the temperature of a wafer (1) and is characterized by at least comprising a film temperature sensor (2), a film lead (3) and a lead, wherein the film temperature sensor (2) is connected with the film lead (3), the film lead (3) is connected with the lead, and at least the film temperature sensor (2) and the film lead (3) are arranged on the wafer (1).

2. The sensor according to claim 1, characterized in that at least the thin film temperature sensor (2), thin film leads (3) are arranged in a recess on the wafer (1).

3. A sensor according to claim 2, characterized in that a part of the leads is arranged in a recess on the wafer (1), the other end of the leads extending out of the wafer (1).

4. A sensor according to claim 2 or 3, wherein at least a portion of the recess is covered with a cover.

5. The sensor of claim 4, wherein the thickness of the cover sheet is less than the depth of the groove.

6. The sensor of claim 5, wherein the cover sheet is covered with a high temperature glue to assist in securing the cover sheet.

7. Sensor according to claim 5 or 6, characterized in that the cover plate is of the same material as the wafer (1).

8. The sensor according to claim 2 or 3 or 5 or 6, characterized in that the grooves on the wafer (1) are produced in any of the following ways:

-dry etching;

-wet etching;

-laser grooving; or

-precision machining processes.

9. The sensor of claim 1 or 2 or 3 or 5 or 6, further comprising a connector (4), wherein the film lead (3) is connected to the connector (4), and wherein the connector (4) is connected to the lead.

10. The sensor according to claim 1 or 2 or 3 or 5 or 6, characterized in that the thin film temperature sensor (2) is a thermocouple or a thermal resistor.

11. The sensor according to claim 9, wherein the thin film temperature sensor (2) is formed by performing a deposition operation on the wafer using physical vapor deposition or chemical vapor deposition.

12. The sensor according to claim 1 or 2 or 3 or 5 or 6 or 11, characterized in that the leads comprise high temperature leads and low temperature leads, the low temperature leads being located at a side remote from the wafer (1).

13. The sensor of claim 12, wherein the high temperature lead is platinum rhodium, nickel chromium, or nickel aluminum alloy.

14. The sensor of claim 13, wherein the high temperature lead is externally provided with an insulating layer made of a sleeve or a fiber tube made of ceramic or quartz.

15. The sensor of claim 13 or 14, wherein the low temperature lead is a copper wire, a lacquered wire, a cable or a shielded wire.

16. The sensor of claim 12, wherein the lead further comprises an interface, one end of the interface is connected to the low temperature lead, and the other end of the interface is used for connecting to the outside to transmit temperature information.

17. The sensor of claim 13 or 14 or 16, wherein the lead further comprises a vacuum pass-through band, the vacuum pass-through band is located between the high temperature lead and the low temperature lead, and the high temperature lead and the low temperature lead are respectively connected after passing through the vacuum pass-through band.

18. The sensor of claim 17, wherein the vacuum feedthrough strip has a thickness of no more than 0.2mm.

19. The sensor of claim 18, wherein the vacuum pass-through band is comprised of polyimide.

20. A sensor according to claim 1 or 2 or 3 or 5 or 6 or 11 or 13 or 14 or 16 or 18 or 19, wherein the thin film leads (3) are metal wires deposited on the wafer by vacuum coating.

21. A sensor according to claim 20, characterized in that the material of the thin-film wire (3) is gold, copper or silver.

22. A sensor according to claim 2 or 3 or 5 or 6 or 11 or 13 or 14 or 16 or 18 or 19 or 21, characterized by at least one insulating layer, which is arranged in the recess and on which at least the thin-film temperature sensor (2) and the thin-film leads (3) are arranged.

23. A sensor according to claim 22, characterized in that a protective or insulating layer is deposited at least above the thin-film temperature sensor (2) and the thin-film wire leads (3).

24. A sensor according to claim 1 or 2 or 3 or 5 or 6 or 11 or 13 or 14 or 16 or 18 or 19 or 21 or 23, characterized in that the connector comprises a thin wire at least for connecting the film wire (3) and a protective glue.