Thin-film fatigue test piece and thin-film fatigue test method

Abstract

To provide a thin film fatigue test piece and a thin film fatigue test method capable of easily and efficiently performing a test in fatigue strength evaluation of a thin film.MEANS FOR SOLVING THE PROBLEM: In a thin-film fatigue test piece, a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film are sequentially deposited on an upper surface of a semiconductor substrate. A part of the semiconductor substrate is hollowed out in a square or rectangular shape up to the first silicon oxide film to form a base test piece having a diaphragm shape. An evaluation film is deposited on the second silicon oxide film of the base test piece and patterned, and a breaking part, wiring, and a wiring pad are disposed, the breaking part is disposed substantially at the center of one of four sides of an end part of the diaphragm, and the wiring is disposed so as to pass through the vicinity of a corner of the diaphragm.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a thin film fatigue test piece and a thin film fatigue test method for a film used in a semiconductor chip.

Background Art

[0002] In the thin film used in a semiconductor chip, a resin covering the semiconductor chip, a repeated external force from wire bonding, or a repeated thermal load caused by a difference in the linear expansion coefficient of the films constituting the chip is applied. When designing the strength of the thin film against these repeated external forces, first, it is necessary to know the fatigue strength of the thin film. When the thickness of the thin film is several micrometers or more, since the thin film is self-supporting, a dumbbell test piece can be manufactured and a fatigue test with a repeated load can be performed. However, when the thickness of the thin film is less than several micrometers (especially less than 1 micrometer), since it is not self-supporting, a test piece or apparatus subjected to special processing is required.

[0003] As a method for evaluating the fatigue strength of a non-self-supporting thin film, for example, the method described in Patent Document 1 is known. In this method, a silicon oxide film, silicon, and an evaluation thin film are deposited on a silicon substrate, and a test piece is manufactured by etching from the back surface or the front surface. Also, in the test method, a forced displacement is applied to the test piece by an actuator, and the displacement is measured with a laser microscope. (Paragraphs

[0013] ,

[0014] )

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The strength of the thin film varies greatly depending on the manufacturing apparatus and manufacturing conditions. In order to easily determine the manufacturing conditions for a higher-strength thin film, a method is required that simplifies the production of test pieces and further simplifies the test apparatus so that multiple tests can be performed at once, rather than using complex test pieces as described above.

[0006] An object of the present invention is to provide a thin film fatigue test piece and a thin film fatigue test method that can be easily and efficiently tested in the evaluation of the fatigue strength of a thin film.

Means for Solving the Problems

[0007] The thin film fatigue test piece of the present invention has a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film sequentially deposited on the upper surface of a semiconductor substrate. A part of the semiconductor substrate is punched out to a square or rectangular shape up to the first silicon oxide film to form a base test piece having a diaphragm shape. The evaluation film is deposited and patterned on the second silicon oxide film of the base test piece, and a fracture part, wiring, and wiring pads are arranged. The fracture part is arranged substantially at the center of one of the four sides at the end of the diaphragm, and the wiring is arranged so as to pass near the corners of the diaphragm.

[0008] Alternatively, the thin film fatigue test piece of the present invention has a first silicon oxide film, a first silicon nitride film, a second silicon oxide film, a second silicon nitride film, and a third silicon oxide film sequentially deposited on the upper surface of a semiconductor substrate. A part of the semiconductor substrate is punched out to a square or rectangular shape up to the first silicon oxide film to form a base test piece having a diaphragm shape. The evaluation film is deposited and patterned on the second silicon oxide film of the base test piece, and a fracture part, wiring, and wiring pads are arranged. The fracture part is arranged substantially at the center of one of the four sides at the end of the diaphragm, and the wiring is arranged so as to pass near the corners of the diaphragm.

[0009] Alternatively, in the thin-film fatigue test method of the present invention, a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film are sequentially deposited on the upper surface of a semiconductor substrate. A part of the semiconductor substrate is cut out in a square or rectangular shape up to the first silicon oxide film to form a base test piece having a diaphragm shape. An evaluation film is deposited and patterned on the second silicon oxide film of the base test piece, and a fracture part, wirings, and wiring pads are arranged. The fracture part is arranged substantially at the center of one of the four sides at the end of the diaphragm, and the wirings are arranged so as to pass near the corners of the diaphragm. A thin-film fatigue test piece is used, and repeated air pressure is applied from the upper surface of the diaphragm to perform a fatigue test on the evaluation film.

Advantages of the Invention

[0010] According to the present invention, in the evaluation of the fatigue strength of a thin film, it is possible to provide a thin-film fatigue test piece and a thin-film fatigue test method that can be tested simply and efficiently.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of the present invention will be described with appropriate reference to the drawings. However, the present invention is not limited to the embodiments taken up here, and combinations and improvements can be made as appropriate without changing the gist.

Example

[0013] FIGS. 1 and 2 are overall views of a thin-film fatigue test piece according to an embodiment. FIG. 1 shows two examples of wiring pads 8 and 9, and FIG. 2 shows four examples of wiring pads 8, 9, 10, and 11.

[0014] In FIG. 1, the wiring between the outline, wiring pad 8 and wiring pad 9 passes through the corner or vicinity of the diaphragm 5. That is, it passes through the four corners 7 or the vicinity of the diaphragm. When air pressure is applied from the upper surface of the test piece, a stress concentration portion 13 is generated in the evaluation film 4 at the diaphragm end portion 12. By repeating this, a fatigue test of the evaluation film 4 becomes possible.

[0015] Hereinafter, mainly, the example of FIG. 2 will be described in detail. The thin-film fatigue test piece is composed of a semiconductor substrate 1, a silicon oxide film 2, a silicon nitride film 3, an evaluation film 4, a diaphragm 5, an evaluation film break portion 6, four corners 7 of the diaphragm, a wiring pad 8, a wiring pad 9, a wiring pad 10, a wiring pad 11, and a diaphragm end portion 12.

[0016] FIG. 3 shows a cross section taken along line A-A of FIG. 2. Sequentially, the semiconductor substrate 1, the silicon oxide film 2, the silicon nitride film 3, and the evaluation film 4 are laminated.

[0017] Next, a method for fabricating the thin-film fatigue test piece of FIG. 2 will be described with reference to FIG. 4. In Step 1, a semiconductor substrate 1 is prepared. In Step 2, on its upper surface, a silicon oxide film 2 of 0.2 μm, a silicon nitride film 3 of 0.2 μm, and a silicon oxide film 2 of 0.2 μm are deposited in sequence. After that, in order to improve the density of the above three films, annealing is performed at a temperature of 800 °C or higher.

[0018] Thereafter, in Step 3, from the back surface of the semiconductor substrate 1, the semiconductor substrate 1 is removed into a square or rectangular shape with a liquid such as KOH to form a diaphragm 5. At this time, the silicon oxide film 2 on the semiconductor substrate 1 serves as an etching stopper because it is hardly removed by the KOH solution. The removal of the semiconductor substrate 1 may be performed by dry etching, but wet etching with KOH is better because it is easier to control the shape of the semiconductor substrate 1 and does not cost much. Up to this stage, it is formed on the wafer. Thereafter, it is cut into a desired shape by dicing to obtain a base test piece.

[0019] Thereafter, in Step 4, an evaluation film 4 is deposited and patterned on the uppermost silicon oxide film 2, and wirings (not shown) of the evaluation film 4, wiring pads 8, 9, 10, and 11 are fabricated. At this time, the evaluation film breaking part 6 made of the evaluation film 4 and the diaphragm end part 12 are fabricated on four sides, and one of these sides is arranged so as to come to approximately the center. Further, the wiring made of the evaluation film 4 passes through the corner or the vicinity of the diaphragm 5. It passes through the vicinity of the four corners 7 of the diaphragm and is connected to the wiring pads 8, 9, 10, and 11.

[0020] Next, the test method will be described with reference to FIGS. 5, 6, and 7. As shown in FIG. 5, a repeated air pressure as shown in FIG. 6 is applied from the upper surface of a test piece in which an evaluation film 4 is deposited and patterned on a base test piece, and a fatigue test of the evaluation film 4 is performed. As shown in FIG. 7, when air pressure is applied from the upper surface of the test piece, a stress concentration portion 13 is generated in the evaluation film 4 at the diaphragm end 12. By repeating this, a fatigue test of the evaluation film 4 becomes possible. FIG. 8 is a view when a repeated air pressure is applied to the above test piece and viewed from the upper surface of the test piece, and an evaluation film breakage portion 6 that becomes a crack appears in the evaluation film 4 at the diaphragm end 12.

[0021] Next, a crack evaluation method will be described. In this test, the four-terminal method is used. A current is passed through the wiring pads 8 and 9 which are the electrodes in FIG. 2, and voltage changes at both ends of the evaluation film breakage portion 6 are detected by the wiring pads 10 and 11. For external electrode leads from the wiring pads 8, 9, 10, and 11, as shown in FIG. 10, metal foil 14 is used, and connections to the wiring pads 8, 9, 10, and 11 are made with Ag paste.

[0022] Since the change in voltage due to crack propagation is small, amplification by 10 to 1000 times may be performed using an amplifier. When it is completely broken, no voltage is generated, so this change may be determined as breakage, or it may be determined as breakage from the change in voltage. When breakage progresses from about 80% to 90% of the film thickness, the resistance rises rapidly, so this change may be determined as breakage.

[0023] Next, the operation and effect of this structure will be described. A sandwich structure of a silicon oxide film 2, a silicon nitride film 3, and a silicon oxide film 2 is formed on the semiconductor substrate 1. Generally, the silicon oxide film 2 has a compressive film stress. That is, it expands. On the other hand, the silicon nitride film 3 has a tensile film stress. That is, it contracts. With only the silicon oxide film 2, the film expands and wrinkles are generated in the diaphragm 5, so the silicon nitride film 3 that contracts is disposed on the silicon oxide film 2. In addition, since the metal film that becomes the evaluation film 4 is generally deposited on the silicon oxide film, the above three-layer sandwich structure is formed.

[0024] As shown in FIG. 9, this three-layer structure may also be a five-layer structure. That is, on the semiconductor substrate 1, there are a silicon oxide film 2, a silicon nitride film 3, a silicon oxide film 2, a silicon nitride film 3, and a silicon oxide film 2. By making it into five layers, there are two silicon nitride films, so wrinkles can be more effectively suppressed. A seven-layer structure may be implemented, but it has little effect on wrinkle suppression.

[0025] In the base test, since the silicon oxide film 2 and the silicon nitride film 3 are formed on the semiconductor substrate 1 and the semiconductor substrate 1 is partially removed from the back surface, the production is easier compared with the conventional method. Also, a base test piece was fabricated in advance, and the evaluation film 4 was deposited thereon. Since the base test piece is fabricated in advance, the production of the test piece for repeated pressurization only involves depositing and patterning the evaluation film 4, so the production of the test piece can be made even easier.

[0026] The evaluation film breaking part 6 was arranged approximately at the center of one side among the four sides of the diaphragm 5. Since the displacement of the diaphragm 5 is small when air pressure is applied at the four corners 7 of the diaphragm, they were arranged at almost the center where the displacement is the largest. Conversely, the wiring by the evaluation film 4 was located at the four corners 7 of the diaphragm or in the vicinity where the displacement of the diaphragm 5 is small when air pressure is applied. Thereby, high stress is generated in the evaluation film breaking part 6, but almost no stress is generated in the wiring of the evaluation film 4 at the four corners 7 of the diaphragm or in the vicinity. Therefore, it is possible to suppress the occurrence of cracks in the wiring of the evaluation film 4 at the four corners 7 of the diaphragm or in the vicinity.

[0027] In the background art section, it was described that when the thickness of the evaluation film 4 is several micrometers, the evaluation film 4 is self-supporting, so it is possible to conduct tests with a general tensile test. Therefore, this test piece and test method are effective for thin films with a thickness below the micrometer order that are not self-supporting.

[0028] The external force load on the test piece utilizes air pressure. Since the external force load can be simultaneously applied to a plurality of test pieces from a pressure source via a plurality of pneumatic regulators with different air pressures, tests can be conducted under multiple conditions at once. Therefore, it becomes possible to easily determine the manufacturing conditions for high-strength thin films.

[0029] According to this embodiment, since only a base test piece is prepared in advance and the evaluation film 4 is deposited and patterned thereon, the test piece can be easily fabricated. Also, the external force load on the test piece utilizes air pressure. Since the external force load can be simultaneously applied to a plurality of test pieces from a pressure source via a plurality of pneumatic regulators with different air pressures, tests can be conducted under multiple conditions at once. Therefore, it becomes possible to easily determine the manufacturing conditions for high-strength thin films.

[0030] Regarding a part of the configuration of the embodiment, addition, deletion, and substitution can be made without impairing the gist of the present invention.

Explanation of Reference Numerals

[0031] 1 ··· Semiconductor substrate 2 ··· Silicon oxide film 3 ··· Silicon nitride film 4 ··· Evaluation film 5 ··· Diaphragm 6 ··· Evaluation film fracture part 7 ··· Four corners of the diaphragm 8 ··· Wiring pad 9 ··· Wiring pad 10 ··· Wiring pad 11 ··· Wiring pad 12 ··· Diaphragm end 13 ··· Stress concentration part 14 ··· Metal foil

Claims

1. On the upper surface of a semiconductor substrate, a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film are deposited in sequence. A part of the semiconductor substrate is etched into a square or rectangular shape up to the first silicon oxide film to form a base test piece having a diaphragm shape. An evaluation film is deposited and patterned on the second silicon oxide film of the base test piece, and a fracture part, wiring, and wiring pads are arranged. The fracture part is arranged substantially at the center of one of the four sides at the end of the diaphragm, and the wiring is arranged so as to pass near the corners of the diaphragm. A thin film fatigue test piece characterized by this.

2. On the upper surface of a semiconductor substrate, a first silicon oxide film, a first silicon nitride film, a second silicon oxide film, a second silicon nitride film, and a third silicon oxide film are deposited in sequence. A part of the semiconductor substrate is etched into a square or rectangular shape up to the first silicon oxide film to form a base test piece having a diaphragm shape. An evaluation film is deposited and patterned on the second silicon oxide film of the base test piece, and a fracture part, wiring, and wiring pads are arranged. The fracture part is arranged substantially at the center of one of the four sides at the end of the diaphragm, and the wiring is arranged so as to pass near the corners of the diaphragm. A thin film fatigue test piece characterized by this.

3. In the thin film fatigue test piece according to Claim 1 or Claim 2, A thin film fatigue test piece characterized in that the thickness of the evaluation film is several micrometers or less.

4. Using a thin film fatigue test piece in which a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film are deposited in sequence on the upper surface of a semiconductor substrate, a part of the semiconductor substrate is etched into a square or rectangular shape up to the first silicon oxide film to form a base test piece having a diaphragm shape, an evaluation film is deposited and patterned on the second silicon oxide film of the base test piece, a fracture part, wiring, and wiring pads are arranged, the fracture part is arranged substantially at the center of one of the four sides at the end of the diaphragm, and the wiring is arranged so as to pass near the corners of the diaphragm, a repeated air pressure is applied from the upper surface of the diaphragm to perform a fatigue test of the evaluation film. A thin film fatigue test method characterized by this.

5. In the thin film fatigue test method according to Claim 4, a current is passed through the fracture part, and the voltage at both ends is monitored to evaluate the degree of fracture damage. A thin film fatigue test method characterized by this.

6. The thin film fatigue test method according to claim 4, wherein the fatigue test of the evaluation film is performed using a four-terminal method.

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