JP4323303B2 - Substrate manufacturing method - Google Patents

Description

The present invention relates to a substrate manufacturing method suitable for high-density three-dimensional mounting or wiring in which silicon IC chips or the like are stacked. More specifically, in order to electrically connect the front and back surfaces of the substrate on which the wiring is formed, a substrate (through wiring substrate) having a wiring that penetrates and electrically connects the front and back surfaces of the substrate passes through the front and back surfaces. The present invention relates to a method of manufacturing a substrate that can advantageously prevent the conductive material (metal) filled in the hole to be dropped from the hole, that is, the through wiring portion, and thereby improve the durability of the through wiring substrate.

  In recent years, high-density mounting of a system using a three-dimensional stacked element in which silicon substrates are stacked in a three-dimensional direction is being studied with the aim of further increasing the speed, function, size, and weight of semiconductor devices such as CPUs, memories, and sensors. . As one means for realizing such high-density mounting, it has been proposed to penetrate the silicon substrate in the thickness direction and to be electrically connected, that is, to form a through wiring. The advantages of high-density mounting using through wiring are as follows. First, since the silicon substrate is made of the same material as the functional element, the use of such a silicon substrate as a substrate material for three-dimensional wiring not only can reduce distortion due to thermal shrinkage, but also has excellent thermal conductivity. Also, it is advantageous for mounting elements (for example, CPU, laser diode, etc.) that generate intense heat. In addition, even when it is desired to increase the effective area of the detection unit as much as possible, such as a single non-stacked silicon device, such as an image sensor, the package size can be greatly reduced by taking out the terminal on the back surface of the chip through the through wiring There is.

  For example, Patent Document 1 discloses a silicon substrate on which the through wiring as described above is formed. In this patent document 1, a deep-reactive ion etching (hereinafter simply referred to as “DRIE”) method, a wet etching method, a micro drill machining method, or the like is applied to a substrate such as silicon or gallium arsenide (GaAs). A through hole or a non-through hole is formed by the following, and then the substrate on which the through hole or the non-through hole is formed is immersed in a molten metal tank under reduced pressure so that the molten metal is filled in the through hole or the non-through hole. After that, a substrate on which through wiring is formed by cooling and solidifying is disclosed.

Such a through wiring substrate is shown in a sectional view in FIG. As shown in FIG. 3 (a), the silicon substrate 31 having through holes formed by the DRIE method, as shown in the vicinity of the through holes, has an electrical insulating layer 32 formed on the front and back surfaces and through holes of the silicon substrate by a thermal oxidation method. The through-hole 33 is formed by filling the through-hole in which the electrical insulating layer 32 is formed with metal. On the back surface of the silicon substrate, as shown in FIG. 4B, external wiring 34 connected to the through wiring is provided with a fixed substrate 35 made of glass or the like as necessary.
JP 2003-168859 A

  As disclosed in Patent Document 1, in a conventional through wiring substrate, a hole formed so as to penetrate from one surface of the substrate to the other surface has a diameter in a plane perpendicular to the thickness direction of the substrate, It has a cylindrical shape that is substantially the same as the opening diameter of the hole in the surface of the substrate over the thickness direction of the substrate. That is, in the cross section in the thickness direction of the substrate, the diameter of the through hole in the vicinity of the surface portion and the diameter in the vicinity of the central portion in the thickness direction are substantially the same.

  By filling the substrate having such a through-hole shape with a conductive material, a through wiring that conducts the front and back surfaces of the substrate is formed. The metal filled in the through-hole is used for the substrate. It has poor wettability with materials such as silicon and glass, and it is not chemically or attractively coupled (intermolecular force, Coulomb force) to the substrate in a solidified state after filling. Therefore, due to the large difference in thermal expansion coefficient between the substrate and the filling metal, depending on the temperature change during use of the substrate, etc., the wiring metal filled in the through hole is below the melting point of the metal. There was also a case of trying to drop out from the through hole. As a result, there is a risk that the through wiring may have poor conduction.

  FIG. 4 is a sectional view showing a conventional example of a through hole provided in a substrate. FIG. 5A shows an example in which the through hole h is formed in a cylindrical shape on the substrate 31a. FIG. 4B shows an example of a shape in which the through hole h has a portion having a small hole diameter on the surface of the substrate 31b. The through hole having such a shape is formed by etching when performing deep etching by the DRIE method. It is formed when the etching is finished when the formed hole reaches the other surface from one surface. FIG. 6C shows an example in which the through hole h has a shape in which the hole diameter decreases linearly from one surface to the other surface of the substrate 31c. For example, when deep etching is performed by the DRIE method, the pressure condition is changed. Formed when fluctuated. FIG. 4D shows an example in which the through hole h has a step in the vicinity of the center thereof. After forming a through hole by etching using a small diameter etching mask, the large diameter etching mask is used. This is formed when deep etching is performed in the through hole up to the center in the thickness direction of the substrate 31d. In the conventional through holes shown in FIG. 4, after filling with metal, as shown in FIGS. 5A to 5D, in the through hole shape of a rectangular cross section (FIG. 5A), There is a possibility that the filled metal may fall off from both sides of the substrate, and in the through hole shape shown in FIGS. 5B to 5D, the filled metal may fall off from one side of the substrate.

  Penetration wiring boards are likely to be used in environments where the temperature changes drastically, such as automobiles, and because they may be used for higher integration of devices with high heat generation such as power elements, Even when it fluctuates, it is required that the wiring metal does not fall out of the through hole.

Therefore, the present invention advantageously solves the above-mentioned problem, and by adding a device to the shape of the through hole provided in the substrate, the wiring metal filled in the through hole is dropped from the through hole. The purpose of the present invention is to propose a method of manufacturing a substrate that can prevent

According to the substrate manufacturing method of the present invention, in the substrate manufacturing method for forming a through hole to be filled with a conductive material , an insulating layer is formed on the surface of the substrate, and an opening is formed on one surface of the insulating layer. A step of forming a through hole reaching the other insulating layer by a DRIE method with respect to the opening, and etching is continuously performed after the through hole is formed, and a substrate surface is formed in the vicinity of the other insulating layer . compared to a pore size of the portion where the pore diameter is expanded, characterized in that it comprises a step of forming on the substrate.

In the substrate obtained by the present invention, the through-hole formed in the substrate has a larger hole diameter than the hole diameter on both sides in the thickness direction excluding the substrate surface . For the holes formed in the substrate for wiring in this way, a portion that has a diameter that is different from the hole diameter on the front and back surfaces of the substrate by having a portion that is larger than the hole diameter on the substrate surface in the thickness direction of the substrate. Becomes a locking part of the conductive material filled in the hole and restricts the movement of the conductive material, so that the conductive material forming the through-wiring falls out of the hole even if the environmental temperature changes Can be prevented.

In addition, a conductive material filled into a substrate with holes that have the above-mentioned shape, and a substrate in which wiring is formed in the thickness direction of the substrate, prevents the filled conductive material from falling off regardless of fluctuations in the environmental temperature. Therefore, a substrate with high wiring reliability can be obtained.

Further, the present invention is a conductive material on the occasion for forming a through hole to be filled, a step of forming a step of forming an insulating layer on the surface of the substrate, an opening on one surface of the insulating layer, A step of forming a through hole reaching the other insulating layer by the DRIE method with respect to the opening, and etching is continuously performed after the formation of the through hole, and this is compared with the hole diameter of the substrate surface in the vicinity of the other insulating layer. Forming a portion having an enlarged hole diameter on the substrate, thereby providing at least one portion where the hole diameter in the cross section in the thickness direction of the substrate is larger than the hole diameter on the substrate surface. The board | substrate used as the hole shape which has can be manufactured easily.

1 shows an example of a substrate thus obtained in this invention in a main part cross-sectional view. In the substrate shown in FIG. 1 (a), an insulating layer 12 of SiO2 is formed on the surface of a substrate 11 made of silicon. And the through-hole which goes to the other surface from one surface of this board | substrate is formed, and the penetration wiring 13 is formed by filling this through-hole with a conductive material (metal). Further, on one surface of the substrate 11, an I / O pad 14 serving as an external wiring is provided together with a fixed substrate 15 made of glass or the like so as to be connected to the through wiring 13. The shape of the through hole in the substrate shown in FIG. 1A is as shown in the radial direction of the through hole in a region inside the portion in contact with the I / O pad 14 in the cross section in the thickness direction of the substrate. It has an enlarged part.

  In this way, the through-hole has a portion that expands in the radial direction at a portion other than the surface portion of the substrate, in other words, a portion larger than the hole opening diameter (hole diameter) of the substrate surface. In the through wiring 13 formed by filling the hole with a conductive material and solidified, a portion enlarged in the radial direction becomes a locking portion between the through hole and the through wiring 13. Therefore, the metal that has been filled and solidified in the hole to form the through-wiring 13 without any gaps acts as a stopper even if there is no chemical or attractive bonding force between the substrate and the metal. Therefore, movement in any direction on both sides of the substrate is suppressed. As a result, it is possible to effectively prevent the filled metal from falling off.

  The material of the fixed substrate 15 can be appropriately selected depending on the application, such as silicon, glass, metal plate, resin, plastics, and the like.

  As the material of the I / O pad 14, a known material that can be used for an electrode, such as a typical element metal or a transition metal, can be used.

In FIG. (B) shows another example of the substrate thus obtained to the invention in a principal part cross-sectional view. The example in the figure is an example in the case where external wiring or a fixed substrate is not provided on one surface (lower surface) of the substrate.

In the example of FIG. 2B, an insulating layer 17 made of SiO ₂ is formed on the surface of a substrate 16 made of silicon. In addition, an insulating layer 18 made of SiO ₂ is formed at the center of the substrate 16 in the thickness direction. And the through-hole which goes to the other surface from one surface of this board | substrate is formed, and the penetration wiring 19 is formed by filling this through-hole with an electroconductive material (metal). And this through-hole has the part of the hole diameter expanded rather than the opening diameter of the surface in the thickness direction center part vicinity of a board | substrate. Then, when the through wiring 18 is formed by filling the through hole having such a shape with a conductive material (metal), the enlarged diameter portion of the hole becomes a locking portion, and FIG. Similarly to the example shown, it is possible to prevent the conductive material (metal) filled in the hole and solidified from dropping off from either side of the substrate.

  In the embodiment shown in FIGS. 1A and 1B, the relationship between the size of the portion where the hole diameter increases in the thickness direction of the substrate and the opening diameter of the holes on the substrate surface is as shown in FIG. 2 (a) and 2 (b) correspond to the substrates shown in FIGS. 1 (a) and 1 (b), respectively, and show the substrates in the previous stage of filling with metal.

  When the opening diameter on the substrate surface of the substrate in FIG. 2A is a, the diameter of the portion where the hole diameter is enlarged is b, and the width of the I / O pad is c, this relationship is satisfied so that the inequality a <b <c is satisfied. A portion where the hole diameter is enlarged is formed. 2 (b), where d is the opening diameter on one substrate surface, e is the diameter of the portion where the hole diameter is enlarged, and f is the opening diameter on the other substrate surface, d ≦ f <e or f ≦. A portion where the hole diameter is enlarged is formed so as to satisfy the relationship of d <e.

  The substrate having the shape shown in FIGS. 1A and 1B can be formed as follows. First, the substrate shown in FIG.

First, a silicon substrate 11 is prepared, and an insulating layer 12 of SiO ₂ is formed on the surface of the silicon substrate 11 by a thermal oxidation method or the like. Next, the I / O pad 14 and the fixed substrate 15 are provided on one surface of the silicon substrate 11. For example, glass, a silicon substrate, a metal plate, or the like can be used for the fixed substrate 15. Next, an opening is selectively formed in the other surface of the silicon substrate 11 to form a through hole in the SiO ₂ insulating layer 12 by photolithography. Next, deep etching is performed on the formed opening using the SiO ₂ insulating layer 12 as an etching mask to form a through hole in the silicon substrate 11. The DRIE method already described can be used for this deep etching. The DRIE method uses sulfur hexafluoride (SF ₆ ) as an etching gas, and alternately etches with high-density plasma and forms a passivation film on the sidewall (Bosch process), thereby deep-etching the silicon substrate. Is something that can be done.

When the silicon substrate is etched in the thickness direction during the deep etching by the DRIE method, the hole reaches from the surface where the opening is formed to the SiO ₂ insulating layer on the other surface. Here, in the case of forming the through hole in the conventional method, the etching is finished when the hole diameter of the portion in contact with the SiO ₂ insulating layer on the other surface becomes substantially the same as the hole opening diameter on one surface. (This is called "just etching"). On the other hand, when the substrate is manufactured according to the present invention, the etching is not completed even if the just etching is performed, and the etching is further continued (this is referred to as “over-etching”). Then, the etching in the thickness direction is suppressed by the SiO ₂ protective film, the inner silicon substrate portion than the SiO ₂ protective film is etched so as to enlarge the diameter of the through-hole. In this way, a portion having a diameter larger than the hole opening diameter on both surfaces of the substrate can be formed by overetching using the deep etching method.

After over-etching, the portion of the SiO ₂ insulating layer corresponding to the bottom of the hole is removed to penetrate the hole, and then the SiO ₂ insulating layer is formed on the side surface of the through hole and the substrate surface by a thermal oxidation method or the like. Fill the through hole with metal. Through the steps as described above, the substrate shown in FIG. 1A is obtained.

Next, the substrate having the shape shown in FIG. 1B can be formed as follows. First, two silicon substrates 16 are prepared, and an insulating layer 17 of SiO ₂ is formed on the surface (both surfaces) of each of the silicon substrates 16 by a thermal oxidation method or the like. Next, these two silicon substrates 16 are bonded in the thickness direction. As this bonding method, for example, an anodic bonding method can be used. Next, openings are selectively formed in the SiO ₂ insulating layer 17 on both surfaces of the silicon substrate 16 by photolithography. Since this opening is for forming a through-hole, the openings on both sides are aligned with the position where the through-hole is formed. Next, using the SiO ₂ insulating layer 17 on the surface of the silicon substrate as an etching mask, deep etching is performed from the opening toward the center in the thickness direction. This deep etching can use the DRIE method.

Since the substrate to be etched is formed by bonding two silicon substrates having the SiO ₂ insulating layer formed on the surface as described above, the SiO ₂ insulating layer 18 when bonded is formed at the center in the thickness direction. Is present. Therefore, when etching is performed in the thickness direction of the substrate by this DRIE method and the hole reaches the SiO ₂ insulating layer in the central portion in the thickness direction, the presence of the SiO ₂ insulating layer 18 leads to the thickness direction beyond this. No holes are formed. If etching is continued in this state (overetching), the silicon substrate 16 portion in the vicinity of the SiO ₂ insulating layer 18 in the center in the thickness direction is etched so as to increase the diameter of the through hole. By performing such over-etching from the surface of both surfaces to the central portion in the thickness direction, a portion having a diameter larger than the hole opening diameter on both surfaces of the substrate can be formed in the central portion in the thickness direction.

After over-etching, the SiO ₂ insulating layer at the center in the thickness direction of the hole is removed to penetrate the hole, and then the SiO ₂ insulating layer is formed on the side surface of the through hole and the substrate surface by a thermal oxidation method or the like. Fill the through hole with metal. Through the steps as described above, the substrate shown in FIG. 1B is obtained.

In the example shown in FIG. 1 (b), although bonding two substrates, by bonding three or more substrates in the thickness direction, can also be obtained substrate follow the present invention.

  Another method for manufacturing a substrate having the shape shown in FIG. 1B is as follows. In short, this method is a method in which two silicon substrates are prepared, each silicon substrate is over-etched to form a through hole, and then the two silicon substrates are bonded.

First, two silicon substrates 16 are prepared, and an insulating layer 17 of SiO ₂ is formed on the surface (both surfaces) of each of the silicon substrates 16 by a thermal oxidation method or the like. Next, an opening is selectively formed in the SiO ₂ insulating layer 17 for each silicon substrate 16 by photolithography. This opening is for forming a through hole. Next, using the SiO ₂ insulating layer 17 on the surface of each silicon substrate as an etching mask, deep etching is performed in the thickness direction from the opening by, for example, the DRIE method.

Etching is continued even if the hole reaches the SiO ₂ insulating layer formed on the other surface by deep etching (over-etching). Thus, the silicon substrate portion inside the SiO ₂ protective film is etched so as to enlarge the diameter of the through-hole, in other words, compared to the hole opening diameter on both sides of the substrate by overetching using the deep etching method. A portion having a large diameter is formed.

After over-etching, the portion of the SiO ₂ insulating layer corresponding to the bottom of the hole is removed to penetrate the hole, and then the SiO ₂ insulating layer is formed on the side surface of the through hole and the substrate surface by a thermal oxidation method or the like.

  The two silicon substrates that have undergone such a process are joined with the positions of the through holes aligned. As this bonding method, for example, an anodic bonding method can be used. Next, the substrate shown in FIG. 1B is obtained by filling the through holes with metal.

  Utilizing deep etching by the DRIE method to form a hole-shaped through-hole having a portion where the hole diameter in the cross section in the thickness direction of the substrate is larger than the hole diameter on the substrate surface as shown in FIG. The preferable conditions for overetching that can be performed will be described.

FIGS. 6A to 6C are cross-sectional views showing the process of manufacturing the substrate having the shape shown in FIG. As already described, the SiO ₂ insulating layer 12 is formed on the surface of the silicon substrate 11, and openings are selectively formed in the SiO ₂ insulating layer 12 (FIG. 6A). Let the thickness of this silicon substrate be t. Next, using the SiO ₂ insulating layer 12 as an etching mask, deep etching is performed on the formed opening by the DRIE method to form a through hole in the silicon substrate 11 (FIG. 6B). The diameter is a.Even if it is just etching, the etching is not finished, and further etching is continued (over etching), and the silicon substrate portion inside the SiO ₂ protective film is compared with the hole opening diameters on both sides of the substrate. A portion having a large diameter is formed (FIG. 6C), where the diameter of the widened portion is b and the width of the I / O pad is c.

The substrate thickness direction of the etching rate by DRIE method and E _1, the hole diameter of the hole bottom by etching, the etching time until the same as the hole diameter a of the opening (just etching time) and y _1, t = E ₁ the relationship of y ₁ is satisfied.

If this etching is continued, since the SiO ₂ insulating layer 12 is provided at the bottom of the hole, the etching in the thickness direction is stopped, and the hole side wall near the hole bottom is etched. Assuming that the etching rate in the side wall direction is E ₂ and the etching time (total etching time) from the start of etching to the diameter of the widened portion is b is y ₂ , b = E ₂ (y ₂ −y ₁ )> 0. Therefore, in order to obtain a substrate in which the diameter of the opening is b, y ₂ > y _1, that is, it is necessary to perform etching for a longer time than just etching, and b = E ₂ (y ₂ −y ₁ It is necessary to perform etching under conditions that satisfy>) 0.

Further, when the I / O pad 14 is connected to the metal filled in the through hole, the diameter b of the above-described widened portion must be smaller than the width c of the I / O pad 14. Therefore, it is necessary to satisfy the condition of c> b = E ₂ (y ₂ −y ₁ )> 0. From this inequality, the upper limit of the total etching time is determined. That is, it is important to perform the etching under conditions that satisfy y ₂ <c / E ₂ −t / E ₁ . E ₁ and E ₂ are values determined by the apparatus and etching conditions.

  The present invention is not limited to the above-described embodiments, and many variations are possible.

  For example, the opening shape of the through-hole, that is, the opening shape of the hole in the plan view of the substrate is not limited to a circle including an ellipse, but may be any shape such as a triangle, a quadrangle, or more polygons.

  Moreover, the board | substrate which provides a through-hole does not ask | require material if it is used as board | substrates, such as glass, ceramics, and a metal besides silicon | silicone.

  Moreover, the through hole was formed not only in a direction perpendicular to the substrate surface, but also in any direction forming an angle of 0 to 90 ° with respect to the substrate surface for use as an interposer or the like. The hole shape according to the invention can be applied to the holes.

  Moreover, as a method for filling the metal into the through hole, a molten metal suction method or a plating method is a typical method, and any of the above methods may be used when manufacturing the substrate of the present invention. Further, other conventionally known methods can also be used.

Further, the insulating layer formed on the surface of the silicon substrate is not limited to the SiO ₂ insulating layer, and for example, an insulating layer having a high dielectric constant such as a SiN layer can be used.

Is a fragmentary cross-sectional view showing an example of a substrate thus obtained to the present invention. Is a diagram illustrating the size of the through hole provided in the substrate thus obtained to the present invention. It is sectional drawing which shows the principal part of the conventional penetration wiring board. It is sectional drawing which shows the example of a shape of the conventional through-hole. It is sectional drawing explaining the drop-off example of the metal with which the conventional through-hole was filled. It is a figure explaining the manufacturing method of the board | substrate according to this invention.

Explanation of symbols

11 Substrate 12 Insulating layer 13 Through wiring 14 I / O pad 15 Fixed substrate

Claims (1)

In a method for manufacturing a substrate for forming a through hole to be filled with a conductive material,
Forming an insulating layer on the surface of the substrate; forming an opening in one surface of the insulating layer; forming a through hole reaching the other insulating layer by DRIE method in the opening; after hole formation, etching is carried out continuously, the portion where the pore size than the pore size of the substrate surface in the vicinity of the other insulating layer is expanded, characterized in that it comprises a step of forming on the substrate A method for manufacturing a substrate.

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