JP3860080B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
[Field of the Invention]
The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device used for a power supply circuit.
[0002]
[Prior art]
A power semiconductor device such as a diode used for rectification in a power supply circuit generally has electrodes formed on both the first main surface and the second main surface of a silicon chip. The manufacturing method of such a power semiconductor device is as follows. FIG. 4 is a cross-sectional view showing an outline of a method for manufacturing a power semiconductor device, wherein (a), (b), (c), and (d) each show a manufacturing process. In FIG. 4, 50 is a silicon wafer, 51a, 51b and 51c are silicon chips, 52 is a first main surface, 53 is a second main surface, 54a, 54b and 54c, and 55, 55a, 55b and 55c are electrodes. Indicates.
[0003]
That is, as shown in FIG. 4A, after impurities are diffused inside the silicon wafer 50 to form a conductive region, electrodes 54a to 54c are formed on the first main surface 52. Next, as shown in (b), the second main surface 53 is ground to make the silicon wafer 50 thinner. Then, as shown in (c), an electrode 55 is formed on the second main surface. Next, as shown in (d), the silicon chips 51a to 51c are diced.
[0004]
Incidentally, there are two types of states of the interface between bonded silicon and metal, ohmic contact and Schottky contact. The ohmic contact is so small that the contact resistance between silicon and metal is negligible. In contrast, a Schottky contact has a Schottky barrier, which causes a voltage drop between silicon and metal, affecting the forward characteristics of the device. Therefore, as described above, the second main surface 53 is roughened by grinding or polishing, thereby generating a work-affected layer on the silicon surface to form a recombination center on the silicon surface, thereby generating a Schottky barrier. I try not to let you. For example, it is known that when the silicon wafer 50 is ground with a grindstone of around # 360 to sufficiently roughen the silicon surface, generation of a Schottky barrier can be prevented to a considerable extent.
[0005]
However, the rougher the surface of silicon, the smaller the voltage drop between silicon and metal, but there is a problem that the strength of the silicon chip decreases. When the strength of the silicon chip is reduced, the yield in the manufacturing process of the semiconductor device after grinding is reduced. When the silicon wafer 50 is ground with, for example, a # 2000 or more grindstone to relatively reduce the roughness of the silicon surface, the strength of the silicon chip can be maintained sufficiently, but conversely, a Schottky barrier is generated and the semiconductor device The forward characteristics of the are reduced.
[0006]
[Problems to be solved by the invention]
In order to solve the above-mentioned problems, the present invention provides a semiconductor device having both forward characteristics when ground with a # 360 or more grindstone and strength of a semiconductor chip when ground with a # 2000 or more grindstone and a method for manufacturing the same. It is intended to provide.
[0007]
[Means for Solving the Problems]
As means for solving the above problems, the present invention provides an electrode formed on a first main surface of a semiconductor substrate, another electrode formed on a second main surface of the semiconductor substrate, In the method of manufacturing a semiconductor device in which the impurity concentration in the vicinity of the surface of the second main surface is about 3E ¹⁸ / cm ³ or more, the second main surface is ground using a # 1500 to # 2000 grindstone, A step of setting the roughness of the surface of the second main surface to a range of 0.003 μm to 0.005 μm in arithmetic mean roughness Ra and 0.01 μm to 0.03 μm in maximum height Ry; 2 is etched with an etchant containing hydrofluoric acid, nitric acid and sulfuric acid, and the surface roughness of the second main surface is 0.05 μm or more and 0.3 μm or less in terms of arithmetic average roughness Ra, the maximum height Ry is in the range of 0.3 μm to 1.3 μm. And a process.
[0008]
Therefore, the method of manufacturing a semiconductor device according to the present invention can make the surface of the semiconductor substrate relatively uniform and sufficiently rough and remove the crushed layer formed in the grinding step. Therefore, a Schottky barrier can be prevented from being generated between the surface of the semiconductor substrate and the metal, and the strength of the semiconductor chip can be sufficiently ensured.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for manufacturing a semiconductor device according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a cross-sectional view showing an example in which the method for manufacturing a semiconductor device according to the embodiment of the present invention is applied to manufacture of a diode. In FIG. 2, 10 is a substrate layer, 11 is an epitaxial layer, 12 is a first main surface, 13 is a second main surface, 14 is a rough surface, 15 is a P-type impurity diffusion region, 16 is a silicon oxide film, 17 is a passivation film, 18 and 19 are electrode films, and 50 is a silicon wafer. In addition, although the following example shows what applied the manufacturing method of the semiconductor device which concerns on this embodiment to manufacture of a diode, process (a) before and after the process (b) which applied embodiment And (c) are also described.
[0010]
In this example, a silicon wafer 50 formed by laminating the epitaxial layer 11 on the substrate layer 10 is used. Further, the impurity concentration in the vicinity of the second main surface of the substrate layer 10 is, for example, 1E ¹⁹ / cm ³ which is a preferable concentration for a rectifying diode.
[0011]
First, as shown in FIG. 2A, after a silicon oxide film 16 and a passivation film 17 are formed, a metal is deposited on the first main surface 12 side of the silicon wafer 50 to form an electrode film 18. Further, after a photoresist film (not shown) is formed in a pattern corresponding to the shape of the electrode in a photographic process, unnecessary portions of the electrode film 18 are removed to form a predetermined pattern.
[0012]
Next, as shown in FIG. 2B, the second main surface 13 of the silicon wafer 50 is ground to make the surface a rough surface 14, and further wet-etched. This process is a part according to this embodiment, and will be described in detail later. Then, as shown in FIG. 2C, a metal is deposited on the second main surface 13 of the silicon wafer 50 to form an electrode film 19.
[0013]
Note that each step shown in FIG. 2 is merely an example, and portions other than the step shown in FIG. 2B can be replaced with other steps. In addition, the process according to this embodiment can be applied to the manufacturing process of other semiconductor devices such as MOSFETs and IGBTs other than diodes.
[0014]
Further, the process of FIG. 2B will be described in detail. FIG. 1 is a flowchart of a method for manufacturing a semiconductor device according to an embodiment of the present invention. S1 in FIG. 1 corresponds to FIG. 2A, and S2 and S3 correspond to FIG. 2B.
[0015]
When the process shown in S1 is finished, as shown in S2, the second main surface 13 of the silicon wafer 50 is ground with a grindstone having a count of # 1500 to 2000. By this grinding, the second main surface 13 has an arithmetic average roughness Ra in the range of 0.003 to 0.005 μm and a maximum height Ry in the range of 0.01 to 0.03 μm.
[0016]
Next, as shown in S3, the second main surface 13 of the silicon wafer 50 is etched with an etchant containing hydrofluoric acid, nitric acid and sulfuric acid. By this etching, the roughness of the surface of the second main surface is set in a range of 0.05 μm to 0.3 μm in arithmetic mean roughness Ra and 0.3 μm to 1.3 μm in maximum height Ry.
[0017]
The advantages of the manufacturing method shown in S2 and S3 in FIG. 1 are due to the reason described below. FIG. 3 is a graph showing the results of experiments on the relationship between the roughness and strength of the surface of a silicon wafer. FIG. 3 shows a sample of a second main surface of a silicon wafer of the same type as a sample, which is ground, polished after grinding, ground and etched, and etched. This is a comparison of the strengths of various types of processing. In addition, about each intensity | strength, a silicon wafer is mounted | worn to a tension compression test machine so that the 2nd main surface side may contact | connect a bending strength jig | tool, and the bending strength of a silicon wafer is pressed from the 1st main surface side. Is measuring. In addition, the thickness of the sample after each processing was set to the same 300 μm. Further, in this experiment, the etching process was performed by etching about 2 μm using an etching solution containing hydrofluoric acid, nitric acid and sulfuric acid. In addition, those that were ground and polished, and those that were ground and etched were ground with a # 2000 grindstone. In this case, the roughness (maximum height Ry) of the second main surface was approximately 0.7 to 0.8 after polishing or after etching.
[0018]
In addition, in the case of only grinding, an experiment was performed by changing the roughness (maximum height Ry) of the second main surface to various values for comparison purposes. Furthermore, as shown in FIG. 4, it was found that the strengths of those that were just grounded almost coincided with the curve represented by the alternate long and short dash line.
[0019]
When the roughness (maximum height Ry) of the second main surface is in the range of 0.7 to 0.8, those that have been ground and ground have a strength that is at least twice that of the ground surface. I understood. In addition, it was found that those that were etched after grinding and those that were only etched had a strength that was nearly four times that of the one that was etched after grinding.
[0020]
Therefore, additional experiments were conducted on the etched parts after grinding, and the results were evaluated. The following conclusions were obtained. First, the roughness of the second main surface of the silicon wafer is almost the same as when Ry is 0.7 to 0.8 if the maximum height Ry is in the range of 0.3 μm to 1.3 μm. It was found that the strength of In addition, when the forward characteristics of the ohmic contact in this range were evaluated, it was found that it was equivalent to the case where only grinding with a # 360 or so grindstone.
In addition, when the maximum height Ry exceeded 1.3 μm, a bending strength was clearly inferior. In addition, when the maximum height Ry was less than 0.3 μm, it was discovered that the electrode film did not adhere and the ohmic contact was not sufficiently formed.
[0021]
Secondly, in order to set the roughness of the second main surface of the silicon wafer in the range of 0.3 μm or more and 1.3 μm or less at the maximum height Ry, it is assumed that etching is performed using the above-described etching solution. In this case, it has been found that grinding may be performed using a # 1500 to # 2000 grindstone. In addition, when the maximum height Ry is in the range of 0.3 μm to 1.3 μm, the arithmetic average roughness Ra of the second main surface of the silicon wafer is in the range of 0.05 μm to 0.3 μm. I also understood that.
[0022]
Third, after processing the silicon wafer, the arithmetic average roughness Ra of the second main surface of the silicon wafer is 0.05 μm or more and 0.3 μm or less, and the maximum height Ry is 0.3 μm or more and 1.3 μm or less. In order to be in the range, the roughness of the second main surface of the silicon wafer after grinding is 0.003 μm or more and 0.005 μm or less in arithmetic average roughness Ra, and 0.01 μm or more in maximum height Ry. It was found that it should be in the range of 0.03 μm or less. If the roughness after grinding is out of this range, problems such as longer etching time after grinding and a crush layer on the second main surface remain.
[0023]
Fourth, when the grinding conditions are the same and the above-mentioned etching solution is compared with another etching solution, the above-mentioned etching solution can remove the crushed layer on the second main surface caused by grinding in the shortest time. I understood. Note that it takes about 1 minute to about 10 minutes to remove the crushed layer on the second main surface ground with a # 1500 to 2000 grindstone with the above-described etching solution.
[0024]
Note that FIG. 4 shows that even when only etching is performed, the strength close to that obtained after grinding is obtained. However, in the case of processing only by etching, the time required for processing is several times longer than that after etching after grinding. Not right.
[0025]
As described above, when the method for manufacturing a semiconductor device according to the first embodiment of the present invention is applied, the forward characteristic of the ohmic contact with the electrode film formed on the second main surface of the silicon wafer is # It becomes the same as the forward characteristic when grinding with a grindstone of around 360. In addition, the strength of the silicon wafer has an advantage that it is equivalent to that obtained by grinding with a # 2000 or larger grindstone.
[0026]
In addition, although the above description has made the case where it applies to the process of manufacturing the diode of this invention as an example, it can apply preferably also to the process of manufacturing MOSFET, IGBT, etc. In that case, the impurity concentration in the vicinity of the second main surface of the substrate layer 10 may not be 1E ¹⁹ / cm ³ , but may be a preferable concentration of about 3E ¹⁸ / cm ³ or more.
[0027]
【The invention's effect】
As described above, according to the present invention, as a method for manufacturing a semiconductor device, the second main surface of a semiconductor substrate is ground using a # 1500 to # 2000 grindstone, and the surface roughness of the second main surface is determined. In the range of 0.003 μm to 0.005 μm in arithmetic mean roughness Ra and 0.01 μm to 0.03 μm in maximum height Ry, and the second main surface to hydrofluoric acid, nitric acid and Etching with an etching solution containing sulfuric acid, the roughness of the surface of the second main surface is 0.05 μm to 0.3 μm in arithmetic mean roughness Ra, and 0.3 μm to 1.3 μm in maximum height Ry. By introducing the following steps, a semiconductor device having both forward characteristics when grinding with a # 360 or grindstone and strength of a semiconductor chip when grinding with a grindstone of # 2000 or more is manufactured. Can wear. Therefore, the ohmic contact of the semiconductor device manufactured by this manufacturing method has a reliability equivalent to or higher than that of the prior art.
[Brief description of the drawings]
FIG. 1 is a flowchart of a method for manufacturing a semiconductor device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing an example in which a method for manufacturing a semiconductor device according to an embodiment of the present invention is applied to manufacture of a diode.
FIG. 3 is a graph showing the results of experiments on the relationship between the roughness and strength of the surface of a silicon wafer.
FIG. 4 is a cross-sectional view schematically showing a method for manufacturing a power semiconductor device.
[Brief description of symbols]
DESCRIPTION OF SYMBOLS 10 Substrate layer 11 Epitaxial layer 12 Silicon oxide film 13 Silicon oxide film 14 Photoresist film 15 P-type impurity diffusion region 16 Silicon oxide film 17 Passivation film 18 Electrode film 19 Electrode film 50 Silicon wafer 51a Silicon chip 51b Silicon chip 51c Silicon chip 52 1st main surface 53 2nd main surface 54a Electrode 54b Electrode 54c Electrode 55 Electrode 55a Electrode 55b Electrode 55c Electrode

Claims (2)

An electrode is formed on the first main surface of the semiconductor substrate, another electrode is formed on the second main surface of the semiconductor substrate, and the impurity concentration in the vicinity of the surface of the second main surface of the semiconductor substrate is 3E ^18. / Cm ³ or more in a method for manufacturing a semiconductor device,
The second main surface is ground using a # 1500 to # 2000 grindstone, and the surface roughness of the second main surface is 0.003 μm or more and 0.005 μm or less in terms of arithmetic average roughness Ra, maximum A step of adjusting the height Ry to a range of 0.01 μm or more and 0.03 μm or less;
The second main surface is etched with an etchant containing hydrofluoric acid, nitric acid and sulfuric acid, and the surface roughness of the second main surface is 0.05 μm or more and 0.3 μm or less in terms of arithmetic average roughness Ra, And a step of adjusting the maximum height Ry to a range of 0.3 μm or more and 1.3 μm or less. A semiconductor device manufactured using the method for manufacturing a semiconductor device according to claim 1.

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