IT201800007967A1 - METHOD OF MANUFACTURING A REDISTRIBUTION LAYER, REDISTRIBUTION LAYER AND INTEGRATED CIRCUIT INCLUDING THE REDISTRIBUTION LAYER - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

"METHOD OF MANUFACTURING A REDISTRIBUTION LAYER, REDISTRIBUTION LAYER AND INTEGRATED CIRCUIT INCLUDING THE REDISTRIBUTION LAYER"

The present invention relates to a manufacturing method of a redistribution layer, a redistribution layer and an integrated circuit including the redistribution layer. Specifically, the redistribution layer is a copper (Cu) redistribution layer with a nickel-palladium (NiPd) finish.

As is known, integrated circuits (IC) consist of several superimposed layers made with semiconductor, insulating and conductive materials, typically defined by photolithography.

In a first phase (front end of line, FEOL) of an integrated circuit manufacturing process, individual devices such as transistors, diodes, resistors and capacitors, among others, are configured on the surface of a wafer.

In a second phase (back end of line, BEOL) the individual devices are interconnected by conductive metal lines. In particular, due to the complexity of modern IC configurations and the high density of individual devices, the back end of line process, BEOL, involves fabricating several stacked layers of metal, electrically insulated from each other by dielectric layers. ; ways through the dielectric layers allow you to connect any metal layer to the metal layers below and / or above the other.

In a third step of the IC manufacturing process, a redistribution layer (RDL) is configured on top of the last metal interconnect layer. As is known, the redistribution layer is an additional metal layer used to route the input / output pads to other positions on the chip area, allowing a simpler chip-to-chip union.

Figure 1 schematically shows a cross-sectional view of a portion of an IC 1 including a redistribution layer 2 according to the prior art. In particular, IC 1 is represented in a spatial coordinate system defined by three x, y, z axes orthogonal to each other and the cross-sectional view is taken on an xz plane, defined by the x axis and the z axis. In the following part, thicknesses, depths and heights are understood as measured along the z axis, and the meanings of "top" and "bottom", "above" and "below" are defined with reference to the direction of the z axis.

IC 1 includes an interconnection layer 3, consisting of conductive material; the redistribution layer 2 includes a dielectric layer 4 which extends above the interconnection layer 3 and a first passivation layer 6 which extends above the dielectric layer 4.

The redistribution layer 2 further comprises a barrier region 8, which extends over a top surface 6a of the first passivation layer 6 and through the entire depth of the first passivation layer 6 and of the dielectric layer 4, so as to be in contact with the interconnection layer 3.

The redistribution layer 2 further comprises a conductive region 10, which extends on top of the barrier region 8. In particular, in a top view of the IC 1, the conductive region 10 extends only within the area defined by the barrier region 8. Consequently, the conductive region 10 is not in contact with the first passivation layer 6.

Furthermore, the thickness of the barrier region 8 is less than the sum of the thicknesses of the dielectric layer 4 and of the first passivation layer 6. Consequently, a part of the conductive region 10 extends below the top surface 6a of the first passivation layer. passivation 6. In other words, the barrier region 8 and the conductive region 10 form a path through the dielectric layer 4 and the first passivation layer 6, providing a conductive path from the interconnection layer 3 to the top surface 6a of the first layer passivation 6.

The redistribution layer 2 further comprises a first coating region 12, which extends above the first passivation layer 6, around the conductive region 10 and the barrier region 8 and above the conductive region 10. The first region of coating 12 is in contact with the top surface 6a of the first passivation layer 6, of the conductive region 10 and of the barrier region 8. In other words, the first coating region 12 completely covers the portions of the barrier region 8 and of the conductive region 10 extending above the top surface 6a of the first passivation layer 6.

The redistribution layer 2 further comprises a second coating region 14, which extends above the first passivation layer 6, around the first coating region 12 and above the first coating region 12. The second coating region 14 is in contact with the first passivation layer 6 and the first coating region 12. In other words, the second coating region 14 completely covers the first coating region 12.

The redistribution layer 2 further comprises a second passivation layer 16 (e.g. polyamide, PBO, epoxy, etc.), which extends above the first passivation layer 6 and around the second coating region 14.

In particular, a convenient choice of conductive materials for the redistribution layer 2 is such that the conductive region 10 is made of copper (Cu), the first coating region 12 is made of nickel (Ni) and the second coating region 14 is made of palladium (Pd).

In particular, the choice of nickel and palladium as finishing pile on the conductive region 10 is due to its well-known advantages over aluminum as a bonding surface for copper wires, for example in terms of bonding window, shear strength , damage to the pitch and reliability.

A known disadvantage of the redistribution layer 2 according to the prior art is due to a problem of the manufacturing method typically used, which involves a reduction growth of nickel on copper, to form the first coating region 12 around and above the region conductive 10. Typically, at the end of this phase, the first coating region 12 is not completely in contact with the top surface 6a of the first passivation layer 6 and a small empty space of the order of a few nanometers may be present between the first coating region 12 and the first passivation layer 6.

As a result, the nickel surface is not completely sealed, remaining exposed to environmental conditions. As is known, in the presence of high temperature and high humidity, the nickel surface can be damaged by corrosion processes. Furthermore, it is known that high electric fields can lead to the formation of dendritic structures capable of electromigrating giving rise to short circuits between the two nickel lines, ultimately leading to a failure of the IC.

The object of the present invention is to provide a method of manufacturing a redistribution layer, a redistribution layer and an integrated circuit including the redistribution layer, to overcome the problems previously illustrated. In particular, one of the objects of the present invention is to completely seal the nickel surface in a copper redistribution layer with a Ni / Pd finish.

According to the present invention, a method of manufacturing a redistribution layer, a redistribution layer and an integrated circuit including the redistribution layer, as defined in the appended claims, are provided.

For a better understanding of the present invention, preferred embodiments thereof are now described, purely by way of non-limiting example and with reference to the attached drawings, in which:

Figure 1 is a cross-sectional view of a portion of an integrated circuit including a redistribution layer according to the prior art;

Figure 2 is a cross-sectional view of a portion of an integrated circuit including a redistribution layer according to an embodiment of the present invention;

- Figure 3 is a cross-sectional view of another portion of the integrated circuit of Figure 2, including the portion of Figure 2;

Figures 4A to 4I are cross-sectional views of the respective steps of a manufacturing method of the redistribution layer of Figure 2;

- Figure 5 is a cross-sectional view of a portion of an integrated circuit including a redistribution layer according to another embodiment of the present invention; And

Figures 6A to 6F are cross-sectional views of the respective steps of a manufacturing method of the redistribution layer of Figure 5.

Figure 2 schematically shows a cross-sectional view of a portion of an IC 21 including a redistribution layer 22 according to an embodiment of the present invention. In particular, the IC 21 of figure 2 is represented in a spatial coordinate system defined by three axes x, y, z orthogonal to each other and the cross-sectional view is taken on an xz plane, defined by the x axis and by the z axis.

IC 21 includes an interconnection layer 23, made with a conductive material, such as aluminum or copper. In particular, the interconnection layer 23 is the last metal line of the BEOL of IC 21.

The redistribution layer 22 comprises a dielectric layer 24 which extends above the interconnect layer 23 and a first passivation layer 26 which extends above the dielectric layer 24.

In the following part, the expression "insulating layer" refers to the stack consisting of the dielectric layer 24 and the first passivation layer 26.

In particular, the dielectric layer 24 consists of an insulating material, such as silicon dioxide (SiO2) and has a thickness ranging for example between 900 nm and 1200 nm.

In particular, the first passivation layer 26 is made with an insulating material, such as silicon nitride (Si3N4) and has a thickness ranging for example between 500 nm and 650 nm. The first passivation layer 26 is delimited by a top surface 26a and a bottom surface 26b, the bottom surface 26b being in contact with the dielectric layer 24.

The redistribution layer 22 further comprises a barrier region 28. A first portion of the barrier region 28 extends above the top surface 26a of the first passivation layer 26; a second portion of the barrier region 28, in contact with the first portion, extends below the top surface 26a of the first passivation layer 26 and through the entire depth of the first passivation layer 26 and the dielectric layer 24, so as to be in contact with the interconnection layer 23.

The redistribution layer 22 further comprises a conductive region 30, which extends on top of the barrier region 28. In particular, in a top view of the IC 21, not shown in the figures, the conductive region 30 extends only across 'interior of the area defined by the barrier region 28. Consequently, the conductive region 30 is not in contact with the first passivation layer 26. In the following part, the term "conductive body" refers to the cell composed of the region of barrier 28 and from the conductive region 30.

Furthermore, the thickness of the barrier region 28 is less than the combined thickness of the dielectric layer 24 and the first passivation layer 26. Consequently, a portion of the conductive region 30 extends below the top surface 26a of the first passivation layer. 26. In other words, the barrier region 28 and the conductive region 30 form a path through the dielectric layer 24 and the first passivation layer 26, providing a conductive path from the interconnect layer 23 to the top surface 26a of the first passivation layer. passivation 26, which further extends above the top surface 26a of the first passivation layer 26.

In particular, the barrier region 28 is constituted by conductive material, such as titanium (Ti), or titaniotungsten (TiW) or titanium nitride (TiN) and has a thickness comprised for example between 270 nm and 330 nm.

In particular, the conductive region 30 is made of conductive material, such as copper (Cu) and has a thickness ranging for example between 8 μm and 12 μm.

The redistribution layer 22 further comprises a first coating region 32, which extends above the conductive region 30 and around the conductive region 30, at the side walls of the portion of the conductive region 30 above the top surface 26a of the first passivation layer 26.

In particular, the first coating region 32 is made of conductive material, such as nickel (Ni) and has a thickness ranging for example between 1 μm and 1.8 μm.

According to an aspect of the present description, the first coating region 32 is not in contact with the first passivation layer 26. In particular, the portion of the first coating region 32 which extends around the side walls of the conductive region 30 has a surface 32a facing directly towards the top surface 26a of the first passivation layer 26 and substantially parallel to the top surface 26a of the first passivation layer 26, at a distance Hgap from the top surface 26a of the first passivation layer 26, said distance being included for example between 10 nm and 50 nm, said distance being measured along the z axis.

The redistribution layer 22 further comprises a second coating region 34, which extends above the first passivation layer 26, around the first coating region 32 and above the first coating region 32. The second coating region 34 is in contact with the first passivation layer 26 and the first coating region 32. In other words, the second coating region 34 completely covers the first coating region 32.

In particular, the second coating region 34 is made of conductive material, such as palladium (Pd) and has a thickness comprised, for example, between 0.2 μm and 0.5 μm.

According to an aspect of the present invention, the second coating region 34 extends between the first passivation layer 26 and the first coating region 32, filling an empty space having a height Hgap between the first passivation region 26 and the first region 32. In other words, the second coating region 34 completely seals the first coating region 32. Consequently, unlike the case of the redistribution layer 2 of Figure 1 according to the prior art, the first coating region 32 is not exposed to environmental conditions, preventing the risk of corrosion. Therefore, the redistribution layer 22 of Figure 2 according to the present embodiment has an improved reliability compared to the prior art, especially in conditions of high temperature and high humidity.

The redistribution layer 22 further comprises a second passivation layer 36, which extends above the first passivation layer 26 and around the second coating region 34. In particular, the second passivation layer 36 is made of an insulating material , such as polyimide, PBO, epoxy, etc.

Figure 3 schematically shows a cross-sectional view of another portion of the IC 21, including the portion of Figure 2, corresponding to the area within the dashed lines in Figure 3. Elements already shown in the view of Figure 2 are designated by the same reference numerals and are not further described.

Figure 3 shows that the barrier region, the conductive region, the first coating region and the second coating region are respectively part of a barrier layer 38, a conductive layer 40, a first coating layer 42 and a second layer 44. The second passivation layer 36 extends over the second coating layer 44. In addition, the second passivation layer 36 may include an opening 46 which partially exposes the second coating layer 44, to allow for a joining by wire by means of a wire 48, for example made of copper.

As is evident from Figure 3, based on the routing conformation of the interconnection layers and the redistribution layer 22 of the IC 21, a cross section of the IC 21 may include areas in which the barrier layer 38 and the conductive layer 40 do not form a path through the first passivation layer 26 and the dielectric layer 24 to reach the interconnection layer 23. In any case, there is always a gap having a height Hgap between the first coating layer 42 and the first layer of passivation 26, said empty space has been filled by the second coating layer 44.

In addition, IC 21 also includes metal interconnection layers, insulating layers and vias included in the BEOL that extend below the interconnection layer 23 and indicated as a whole with the reference number 50.

Figures 4A to 4I schematically show a cross-sectional view of the steps of a manufacturing method of a redistribution layer according to an embodiment of the present invention; in particular, the method of Figures 4A to 4I is a method of manufacturing the redistribution layer 22 of Figure 2. The redistribution layer is represented in a system of spatial coordinates defined by the three axes x, y, z orthogonal to each other and the cross-sectional view is taken on an xz plane, defined by the x axis and the z axis.

Referring to Figure 4A, a wafer 60 is provided, including an interconnect layer 63. In particular, the interconnect layer 63 is the outermost metallization layer of the back end of line of an integrated circuit. The lower layers of the integrated circuit are not shown in Figures 4A to 4I.

A dielectric layer 64 is formed above the interconnection layer 63. In particular, the dielectric layer 64 is constituted by an insulating material, such as silicon dioxide (SiO2) and has a thickness comprised for example between 900 nm and 1200 nm.

A first passivation layer 66 is formed above the dielectric layer 64. In particular, the first passivation layer 66 is made of an insulating material, such as silicon nitride (Si3N4) and has a thickness ranging for example between 500 nm and 650 nm. In the following part, the expression "insulating layer" refers to the stack composed of the dielectric layer 64 and the first passivation layer 66.

Then, Figure 4B, a trench 67 is formed through the first passivation layer 66 and the dielectric layer 64, to expose a surface of the interconnection layer 63. For example, the trench 67 is formed by convenient photolithography and etching steps. dry of a known type, applied at the exposed surface of the first passivation layer 66.

Hence, Figure 4C, a barrier layer 68 is formed on top of the first passivation layer 66, for example by physical vapor deposition (PVD). The barrier layer 68 partially fills the trench 67, covering the previously exposed side walls of the dielectric layer 64 and of the first passivation layer 66 and the previously exposed surface of the interconnection layer 63.

In particular, the barrier layer 68 consists of conductive material, such as titanium (Ti), or titaniotungsten (TiW) or titanium nitride (TiN). Furthermore, the thickness of the barrier layer 68 is lower than the combined thickness of the dielectric layer 64 and of the first passivation layer 66 and in particular is comprised for example between 270 nm and 330 nm. Then, a seed layer 69 is formed on top of the barrier layer 68, partially filling the trench 67. For example, the seed layer 69 is deposited by PVD.

In particular, the seed layer 69 is made of conductive material, such as copper (Cu) and has a thickness comprised, for example, between 180 nm and 220 nm, so that the trench 67 is only partially filled by the seed layer 69.

Then, Figure 4D, a photolithographic mask 70 'is applied on the exposed surface of the seed layer 69. In particular, the conformation of the photolithographic mask 70' is designed considering that the openings in the mask define areas where a layer will be formed in one step of the manufacturing method.

In particular, figure 4D shows an opening 70 "of the photolithographic mask 70 ', the opening 70" being centered on the partially filled trench 67 so that the trench 67 is not covered by the photolithographic mask 70'.

Therefore, Figure 4E, a conductive layer 70 is formed above the portions of the seed layer 69 not covered by the photolithographic mask 70 '. The thickness of the conductive layer 70 is high enough to completely fill the trench 67 and to partially fill the opening 70 "of the photolithographic mask 70 '.

In particular, the conductive layer 70 is made of the same conductive material as the seed layer 69, such as copper (Cu) and has a thickness ranging for example between 8 μm and 12 μm.

In particular, the conductive layer 70 is formed by electrodeposition. Then, the photolithographic mask 70 'is removed by a wet removal process, exposing the portions of the seed layer 69 not covered by the conductive layer 70.

Then, figure 4F, said exposed portions of the seed layer 69, not covered by the conductive layer 70, are removed for example by wet chemical etching, until the portions of the barrier layer 68 underlying them are exposed. Therefore, the remaining portions of the seed layer 69, covered by the conductive layer 70, together with the conductive layer 70, form the conductive region 30 of the redistribution layer 22 of Figure 2.

Then, the exposed portions of the barrier layer 68 are removed, for example by wet chemical etching, until the portions of the first passivation layer 66 below are exposed, without affecting the portions of the barrier layer 68 below the conductive layer 70. , for example using standard photolithography techniques. Consequently, the barrier region 28 of the redistribution layer 22 of Figure 2 is formed.

Then, Figure 4G, a first coating layer 72 is formed by electroless deposition, at the exposed surfaces of the barrier layer 68 and the conductive layer 70. Therefore, the first coating layer 72 completely covers the layer conductive 70 and the barrier layer 68 and is in contact with the partially exposed surface of the first passivation layer 66 indicated by the reference number 66a. In particular, the first coating layer 72 is in contact with the exposed surface 66a of the first passivation layer 66 at a bottom surface 72a of the first coating layer 72.

In particular, the first coating layer 72 is made of a conductive material, such as nickel (Ni) and has a thickness comprised for example between 1 μm and 1.8 μm.

Then, figure 4H, a heat treatment is applied on the wafer 60 to create a gap 73 between said surface 66a of the first passivation layer 66 and the bottom surface of the first coating layer 72. In particular, the gap 73 has the height Hgap in the range from 10 to 50 nm.

According to an aspect of the present invention, the heat treatment comprises a first step of raising the temperature of the wafer 60 from room temperature to an elevated temperature. The ambient temperature is comprised, for example, between 20 ° C and 25 ° C; the elevated temperature is comprised, for example, between 245 ° C and 255 ° C. In particular, the temperature increase occurs during a first time interval, for example between 10 s and 60 s.

Then, in a second step, after the first step of the heat treatment, the wafer is kept at the elevated temperature for a second time interval comprised, for example, between 30 s and 180 s.

Then, in a third step, after the second step of the heat treatment, the temperature of the wafer 60 decreased from the elevated temperature to the room temperature in a third time interval, which lasts no more than 180 s.

In particular, while the heat treatment is applied, the wafer 60 is kept in a nitrogen atmosphere (N2) at a pressure between 1.0 and 5.0 Torr.

The Applicant has verified that by applying the above described heat treatment to the wafer 60, it is possible to conveniently modify some mechanical properties of the barrier layer 68, of the conductive layer 70 and of the first coating layer 72. In particular, the coefficient of thermal expansion and the modulus Young's are modified with the heat treatment, and the residual stress of said layers is modified, determining, at the end of the heat treatment, the formation of the empty space 73.

Then, Figure 4I, a second coating layer 74 is formed by reduction deposition, at the exposed surfaces of the first coating layer 72. In particular, the second coating layer 74 grows from the first coating layer 72, which extends over the first cladding layer 72, around the side walls of the first cladding layer 72 and into the gap between the first cladding layer 72 and the surface 66a of the first passivating layer 66. Therefore, the second coating layer 74 completely seals the first coating layer 72 and the barrier layer 68 and is in contact with the surface 66a of the first passivation layer 66. Consequently, the first coating layer 72 is not exposed to the environment.

In particular, the second coating layer 74 is made of conductive material, such as palladium (Pd) and has a thickness ranging for example between 0.2 μm and 0.5 μm.

Hence, a second passivation layer is formed above the first passivation layer 26 and around the second coating region 94. In particular, the second passivation layer is made of an insulating material, such as polyimide. Therefore, the redistribution layer 22 of Figure 2 is obtained.

Figure 5 schematically shows a cross-sectional view of a portion of an IC 81 including a redistribution layer 82 according to another embodiment of the present invention; the elements in common with the IC 21 and the redistribution layer 22 of Figure 2 are designated by the same reference numbers are not further described.

The redistribution layer 82 differs from the redistribution layer 22 of Figure 2 due to the presence of spacers 86. In particular, the redistribution layer 82 comprises spacers 86 which extend above and in contact with the top surface 26a of the first passivation layer 26.

In particular, the spacers 86 are made of insulating material, such as silicon dioxide (SiO2) or silicon nitride (Si3N4) and have a thickness Hgap2 comprised for example between 10 nm and 100 nm.

The redistribution layer 82 further includes a barrier region 88, which extends over the spacers 86 and through the entire depth of the first passivation layer 26 and the dielectric layer 24, so as to be in contact with the interconnection 23.

The redistribution layer 82 further comprises a conductive region 90, which extends on top of the barrier region 88. In particular, in a top view of the IC 81, not shown in the figures, the conductive region 90 extends only across the 'interior of the area defined by the barrier region 88. Consequently, the conductive region 90 is not in contact with the first passivation layer 26. In the following part, the term "conductive body" refers to the cell composed of the region of barrier 88 and from the conductive region 90.

Furthermore, the thickness of the barrier region 88 is less than the combined thickness of the dielectric layer 24 and the first passivation layer 26. Consequently, a portion of the conductive region 90 extends below the top surface 26a of the first passivation layer. 26. In other words, the barrier region 88 and the conductive region 90 form a path through the dielectric layer 24 and the first passivation layer 26, providing a conductive path from the interconnect layer 23 to the top surface 26a of the first passivation layer. passivation 26.

In particular, the barrier region 88 is made of conductive material, such as titanium (Ti) or titaniotungsten (TiW) or titanium nitride (TiN) and has a thickness comprised for example between 270 nm and 330 nm.

In particular, the conductive region 90 is made of conductive material, such as copper (Cu) and has a thickness ranging for example between 8 μm and 12 μm.

The redistribution layer 82 further includes a first coating region 92, which extends above the conductive region 90 and around the conductive region 90, at the side walls of the portion of the conductive region 90 above the top surface 26a of the first passivation layer 26. In other words, the first coating region 92 covers the surface of the conductive region 90 not already covered by the barrier region 88.

In particular, the first coating region 92 is made of conductive material, such as nickel (Ni) and has a thickness ranging for example between 1 μm and 1.8 μm.

According to an aspect of the present description, the first coating region 92 is not in contact with the first passivation layer 26. In particular, the portion of the first coating region 92 extending around the side walls of the conductive region 90 has a surface 92a facing directly towards the top surface 26a of the first passivation layer 26 and substantially parallel to the top surface 26a of the first passivation layer 26, at a distance Hgap2 from the top surface 26a of the first passivation layer 26 being equivalent to the height Hgap2 of the spacers 86, said distance Hgap2 being measured along the z axis.

The redistribution layer 22 further comprises a second coating region 94, which extends above the first passivation layer 26, around the first coating region 92 and above the first coating region 92. The second coating region 94 is in contact with the first passivation layer 26 and the first coating region 92. In other words, the second coating region 94 completely covers the first coating region 92.

In particular, the second coating region 94 is made of conductive material, such as palladium (Pd) and has a thickness comprised for example between 0.2 μm and 0.5 μm.

According to an aspect of the present invention, the second coating region 94 extends between the first passivation layer 26 and the first coating region 92, filling an empty space between the first passivation region 26 and the first coating region 92. In other terms, the second coating region 94 completely seals the first coating region 92. Consequently, as in the case of the redistribution layer 22 of figure 2, the first coating region 92 is not exposed to environmental conditions, thus preventing the risk of corrosion. Therefore, the redistribution layer 82 according to the present embodiment has greater reliability than the prior art, especially in conditions of high temperature and high humidity.

Figures 6A to 6F schematically show a cross-sectional view of the steps of a manufacturing method of a redistribution layer according to an embodiment of the present invention; in particular, the method of Figures 6A to 6F is a manufacturing method of the redistribution layer 82 of Figure 5. The redistribution layer is represented in a system of spatial coordinates defined by three axes x, y, z orthogonal to each other and the cross-sectional view is taken on an xz plane, defined by the x axis and the z axis.

Referring to Figure 6A, a wafer 100 is provided, including an interconnect layer 103. In particular, the interconnect layer 103 is the outermost metallization layer on the back end of line of an integrated circuit. The lower layers of the integrated circuit are not shown in Figures 6A to 6F.

A dielectric layer 104 is formed above the interconnection layer 103. In particular, the dielectric layer 104 is made of an insulating material, such as silicon dioxide (SiO2) and has a thickness comprised for example between 90 nm and 1200 nm.

A first passivation layer 106 is formed above the dielectric layer 104. In particular, the first passivation layer 106 is made of an insulating material, such as silicon nitride (Si3N4) and has a thickness ranging for example between 500 nm and 650 nm. In the following part, the expression "insulating layer" will be used to refer to the stack consisting of the dielectric layer 104 and the first passivation layer 106.

A spacer layer 105 is formed on top of the first passivation layer 106. In particular, the spacer layer 105 is made of an insulating material, such as silicon dioxide (SiO2) or silicon nitride (Si3N4).

According to an aspect of the present disclosure, the spacer layer 105 is used as a sacrificial layer, being partially chemically etched in a subsequent step of the manufacturing method. For this reason, preferably, the spacer layer 105 has a high selectivity in terms of chemical etching with respect to the first passivation layer 106. Consequently, the choice of the material used for the spacer layer 105 depends on the material used for the first passivation layer 106. For example, if the first passivation layer 106 is made of Si3N4, the spacer layer 105 will preferably be made of SiO2 or Si3N4 with a high chemical etching rate. As is known, Si3N4 with a higher chemical attack rate can be obtained by depositing the spacer layer 105 at a lower temperature than that used to deposit the first passivation layer 104. In particular, the spacer layer 105 has the thickness Hgap2 in the range from 10 to 100 nm.

Then, Figure 6B, a trench 107 is formed through the dielectric layer 104 and the first passivation layer 106, until a surface of the interconnection layer 103 is exposed. For example, the trench 107 is formed by photolithography and etching steps dry dry systems of known type, in correspondence with the exposed surface of the spacing layer 105.

Hence, a barrier layer 108 is formed on top of the spacer layer 105, for example by PVD. The barrier layer 108 partially fills the trench 107, covering the previously exposed side walls of the spacer layer 105, the first passivation layer 106 and the dielectric layer 104 and covering the previously exposed surface of the interconnect layer 103.

In particular, the barrier layer 108 is made of conductive material, such as titanium (Ti), titaniotungsten (TiW) or titanium nitride (TiN). Furthermore, the thickness of the barrier layer 108 is lower than the combined thickness of the dielectric layer 104, of the first passivation layer 106 and of the spacing layer 105 and in particular is comprised for example between 270 nm and 330 nm. Then, a seed layer 109 is formed on top of the barrier layer 108, partially filling the trench 107. For example, the seed layer 109 is deposited by PVD.

In particular, the seed layer 109 is made of conductive material, such as copper (Cu) and has a thickness comprised for example between 180 nm and 220 nm so that the trench 107 is only partially filled by the seed layer 109.

Then, a photolithographic mask (not shown in the figures) is applied to the exposed surface of the seed layer 109. In particular, the conformation of the photolithographic mask is designed considering that the openings in the mask define areas where a layer will be formed at a later stage the manufacturing method.

In particular, the photolithographic mask has an opening at the partially filled trench 107.

Hence, Figure 6C, a conductive layer 110 is formed over the portions of the seed layer 109 not covered by the photolithographic mask. In particular, the thickness of the conductive layer 110 is sufficiently high to completely fill the trench 107.

In particular, the conductive layer 110 is made of the same conductive material as the seed layer 109, such as copper (Cu) and has a thickness ranging for example between 8 μm and 12 μm.

In particular, the conductive layer 110 is formed by electrodeposition. Then, the photolithographic mask is removed by a wet removal process, exposing portions of the seed layer 109 not covered by the conductive layer 110.

Then, said exposed portions of the seed layer 109, not covered by the conductive layer 110, are removed, for example by wet chemical etching, until the portions of the barrier layer 108 below are exposed. Therefore, the remaining portions of the seed layer 109, covered by the conductive layer 110, together with the conductive layer 110, form the conductive region 90 of the redistribution layer 82 of Figure 5.

Then, the exposed portions of the barrier layer 108 are removed, for example by wet chemical etching, until the underlying portions of the spacing layer 105 are exposed, without affecting the portions of the barrier layer 108 below the conductive layer 110. Consequently, the barrier region 88 of the redistribution layer 82 of Figure 5 is formed.

Then, Figure 6D, a first coating layer 112 is formed by reduction deposition, at the exposed surfaces of the barrier layer 108 and the conductive layer 110. Thus, the first coating layer 112 completely covers the conductive layer 110 and the barrier layer 108 and is in contact with the partially exposed surface of the spacing layer 105. In particular, the first covering layer 112 is in contact with the spacing layer 105 at a bottom surface 112a of the first covering layer 112.

In particular, the first coating layer 112 is made of conductive material, such as nickel (Ni) and has a thickness comprised for example between 1 μm and 1.8 μm.

Then, Figure 6E, the spacer layer 105 is partially etched chemically to create a gap 113 between a top surface 106a of the first passivation layer 106 and the first coating region 112, the top surface 106a being in contact with the remaining portions of the spacing layer 105. In particular, the empty space 113 has the height Hgap2 in the range from 10 to 100 nm.

In particular, the spacer layer 105 is etched chemically by wet chemical etching, using chemicals that selectively remove the spacer layer 105 with respect to the first coating layer 112, the barrier layer 108 and the first passivation layer 106.

For example, the wafer 100 can be immersed in a hydrofluoric acid (HF) bath in a buffered hydrofluoric (BHF) bath if the spacer layer 105 is made of silicon dioxide or silicon nitride with a high chemical attack rate, in so that the spacer layer 105 is etched chemically at a speed greater than that of the surrounding layers.

In particular, the etching step proceeds at least until the empty space 113 is completely formed, so that the remaining portions of the spacer layer 105 do not extend between the first passivation layer 106 and the first coating layer 112 In other words, at the end of the chemical etching step of Figure 6E, the bottom surface 112a of the first coating layer 112, facing directly towards the top surface 106a of the first passivation layer 106, is not in direct contact with the spacer layer 105.

Then, Figure 6F, a second coating layer 114 is formed by reduction deposition at the exposed surfaces of the first coating layer 112. In particular, the second coating layer 114 grows from said surfaces of the first coating layer 112 , extending above the first cladding layer 112, around the side walls of the first cladding layer 112 and within the void space between the first cladding layer 112 and the top surface 106a of the first passivating layer 106. Therefore, , the second coating layer 114 completely seals the first coating layer 112 and is in contact with the top surface 106a of the first passivation layer 106. Consequently, the first coating layer 112 is not exposed to the environment.

In particular, the second coating layer 114 is made of conductive material, such as palladium (Pd) and has a thickness ranging for example between 0.2 μm and 0.5 μm.

Hence, a second passivation layer is formed above the first passivation layer 106 and around the second coating region 114. In particular, the second passivation layer is made of an insulating material such as polyimide. Therefore, the redistribution layer 82 of Figure 5 is obtained.

The advantages of the invention described above, according to the various embodiments, clearly emerge from the previous description.

In particular, since the first coating region is completely sealed by the second coating region, it is possible to use materials for the first coating region that are subject to corrosion when exposed to the environment, without compromising the reliability of the redistribution layer.

Complete sealing of the conductive material can also improve the electromigration performance of the device.

Finally, it is clear that modifications and variations can be made to what has been described and illustrated herein, without departing in this way from the scope of protection of the present invention, as defined in the attached claims.

Claims (15)

CLAIMS 1. Method of manufacturing a redistribution layer (22) for an integrated circuit (21), comprising the steps of: - forming, on a wafer (60), an insulating layer (64, 66), a bottom surface of which is in contact with the wafer (60); - forming a conductive body (28, 30) above a top surface (66a), opposite the bottom surface, of the insulating layer (64, 66); - forming a first coating region (72) which extends around and on the conductive body (28, 30), in contact with the conductive body (28, 30), and having a bottom surface (72a) in contact with the top surface (66a) of the insulating layer (64, 66); - applying a heat treatment on the wafer (60) to modify a residual stress of the first coating region (72) so as to form a gap (73) between the bottom surface (72a) of the first coating region (72) and the top surface (66a) of the first passivation layer (66); - forming, after the heat treatment, a second coating region (74) around and above the first coating region (72), filling said empty space (73) and completely sealing the first coating region (72). Method according to claim 1, wherein the step of applying the heat treatment comprises: - increasing a temperature of the wafer (60) from a first temperature to a second temperature in a first time interval; - keeping the temperature of the wafer (60) stable at the second temperature for a second time interval after the first time interval; - reducing the temperature of the wafer (60) from the second temperature to the first temperature in a third time interval after the second time interval. Method according to claim 2, wherein the first temperature is between 20 ° C and 255 ° C, the second temperature is between 245 ° C and 255 ° C, the first time interval is between 10 s and 60 s , the second time interval is between 30 s and 180 s, and the third time interval does not last longer than 180 s. Method according to any one of the preceding claims, wherein the empty space (73) has a height (Hgap) between 10 nm and 50 nm, measured as the distance of the top surface (66a) of the insulating layer (64, 66 ) from the bottom surface (72a) of the first coating region (72) along an orthogonal direction to the top surface (66a) of the insulating layer (64, 66) and to the bottom surface (72a) of the first coating region (72 ). Method according to any one of the preceding claims, wherein the step of forming the first coating region (72) comprises coating the conductive body (28, 30) by reduction deposition of a conductive material, and the step of forming the second coating region (74) comprises coating the first coating region (72) by reduction deposition of a conductive material. Method according to any one of the preceding claims, wherein the step of forming the first coating region (72) comprises depositing a layer of nickel. Method according to any one of the preceding claims, wherein the step of forming the conductive body (28, 30) comprises growing or depositing a barrier layer (68) of titanium-tungsten above the top surface (66a) of the insulating layer (64, 66) and a conductive layer (70) of copper above the barrier layer (68). Method according to any one of the preceding claims, wherein the step of forming the insulating layer (64, 66) comprises depositing a dielectric layer (64) of silicon dioxide on the wafer (60) and a first passivation layer (66) of silicon nitride above the dielectric layer (64). Method according to any one of the preceding claims, wherein the wafer (60) comprises an interconnection layer (63), which extends below the insulating layer (64, 66), the method further comprising the step of forming a trench (67) extending from the top surface (66a) of the insulating layer (64, 66) to the interconnecting layer (63), the step of forming the conductive body (28, 30) comprising depositing conductive material (68, 70) in the trench (67) so as to form a direct conductive path between the interconnection layer (63) and the conductive body (28, 30 ). Method according to claim 9, further comprising the steps of: - forming a second passivation layer (36) extending around and over the second coating region (74); - form an opening (46) in the second passivation layer (36) to allow a union by wire (48) with the second coating region (74). 11. Redistribution layer (22) for an integrated circuit (21), comprising: - an insulating layer (24, 26) which extends over the integrated circuit (21); - a conductive body (28, 30) which extends above a surface (26a) of the insulating layer (24, 26); - a first coating region (32) extending around and above the conductive body (28, 30), in contact with the conductive body (28, 30) and at a distance (Hgap) from the surface (26a) of the insulating layer (24, 26); - a second cladding region (34) extending around and above the first cladding region (32), and extending between the first cladding region (32) and the insulating layer (24, 26), in contact with the first coating region (32) and with the conductive body (28, 30), completely sealing the first coating region (32). Redistribution layer (22) according to claim 11, wherein a portion of the first cladding region (32) extending around the side walls of the conductive body (28, 30) has a surface (32a) facing directly towards the surface (26a) of the insulating layer (24, 26) at a distance (Hgap) from the surface (26a) of the insulating layer (24, 26) between 10 nm and 50 nm. Redistribution layer (22) according to claim 11 or 12, wherein the conductive body (28, 30) comprises a copper layer, the first coating region (32) is made of nickel and the second coating region ( 34) is made of palladium. The redistribution layer (22) according to any one of claims 11 to 13, wherein the integrated circuit (21) comprises an interconnect layer (23) extending beneath the insulating layer (24, 26), and wherein the conductive body (28, 30) extends below the surface (26a) of the insulating layer (24, 26), through the entire depth of the insulating layer (24, 26), until it comes into contact with the interconnection layer (23). Integrated circuit (21) including a redistribution layer (22) according to any one of claims 11 to 14.