Test probe for semiconductor devices and method of manufacturing of the same

Abstract: A test probe for semiconductor devices is disclosed, the test probe (1) having a tip portion which is adapted to be pressed against a test pad (2) of a semiconductor device to establish electrical contact between the tip portion and the pad (2) for testing the operation of the semiconductor device, wherein the probe (1) is formed to have a tip shape with an angle of not less than 15° formed at the surface of the pad (2) between a tangential line (4) with respect to a tip face of the probe (1) and the pad surface when the probe (1) is pressed against the pad (2), the tip shape of the probe (1) having a spherical surface meeting the relationship of:  = cos -1 (1 - t / R) ≥ 15° where the radius of curvature of the spherical surface is R, the thickness of the pad is t , and the angle formed at the pad surface between the tangential line (4) with respect to the probe tip face and the pad surface when the probe is pressed against the pad is  , the probe having a flat portion (51) at an end of the tip portion. Accordingly, a contact surface can be established between the probe (1) tip and the pad (2) with a sufficient degree of electrical continuity, and when the probe level is adjusted in the probing, a time required for positioning the probe (1) prior to the starting of measurement is cut down and variation in measurement are reduced.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a test method for testing the operation of a semiconductor device, for example semiconductor integrated circuits which are formed on semiconductor wafers, a test probe and a probe apparatus for carrying out the test method. 2. Description of the Related Art In a conventional probe, as shown in Fig. 13A, a testing (probing) is carried out by attaching a probe 202 having a fore end bent into a hook-like shape to a probe card 201 which is vertically movable, and pushing the probe 202 against a test pad of a semiconductor integrated circuit (referred to as a pad hereinafter) in such a condition that an oxide film on the pad surface is broken off to establish true contact (electrical contact) between the probe and a fresh surface of the pad. The condition of a probe tip under the probing is shown in Fig. 13B. For the sake of explanation, Fig. 13B is illustrated in the form of a simplified model with respect to dimensions and so on. A tip 200 of the conventional probe 202 is originally finished to have a flat end face, as shown in Fig. 13B. Even when the probe tip is machined to have a spherically curved surface intentionally, a sphere approximating the curved surface has a radius R of curvature as large as 20 - 30 µm. At the time of probing, therefore, the whole of flat end portion first comes into contact with a pad 203 while an oxide film 204 and contaminants on the surface of the pad 203 are interposed between the probe tip and the pad surface. Then, as the probe 202 is more closely pushed against the pad 203, the oxide film 204 on the surface of the pad 203 is partly broken off to produce an electrical continuity region 206 in which electrical true contact can be established, thereby enabling a continuity test to be performed. With repetition of the probing, however, the oxide film 204 is accumulated on a heel portion 205 of the probe 202 which is subject to maximum stresses, and an area of the true contact with the pad 203 is so reduced as to make electrical continuity unstable. To reliably establish the electrical contact, vibration is applied to the probe tip in Japanese Unexamined Patent Publication No. 6-18560, for example. Further, tungsten used as materials of the probe 202 is in the form of a powder sintered compact which has material defects (voids) therein. Accordingly, when the powder sintered compact is machined so as to provide a tip shape of the probe 202, the material defects appear on the probe surface. Pad materials such as aluminum, for example, enter the material defects appearing in the tip (end) face of the probe 202 to form deposition nuclei and grow into deposits. As a result, contact resistance is increased. For removing those material defects, heat treatment is applied to tungsten materials in Japanese Unexamined Patent Publication No. 5-140613, for example. Thus, in the conventional probe having the above-described construction, as shown in Fig. 22B, the true contact area (electrical continuity region 206) between the tip 200 of the probe 202 and the pad 203 is very small during the test of electrical characteristics. Accordingly, a sufficient degree of electrical continuity is not obtained between the probe 202 and the pad 203 in some cases. Also, voids produced in tungsten materials of the probe 202 are conceivably eliminated by heat treatment. However, if the tungsten materials are subject to heat treatment at a temperature not lower than the recrystallization temperature, there arises another problem that the probe materials become brittle. In the document "Improving Wafer Sort Yields with Radius-Tip Probe" by S. Schleifer, published in IEEE International Test Conference Proceedings, 10-14 Sept. 1990, pages 896 to 899, XP 002140401, a probe for probe cards with a radius tip is disclosed. According to that document, a radius tip is able to exert a higher pressure as it contacts the die, in comparison to a flat tip. However, the specific shape and dimensions of the tip are not specified in a way allowing conclusions about the radius of curvature of the tip. The document EP-A-0 660 387 discloses a method and apparatus for measuring oxid charge on a semiconductor wafer where the test probe is always pressed vertically against a sample. Thus, nothing can be learned about transverse movement along the probe in order to pass an oxide film thereon. Finally, documents US 5 060 051 and US 5 090 118 disclose further teachings on semiconductor testing with pad structures of a pad thickness which may be in a range from 0.1 µm to 0.5 µm. This does not specify requirements regarding shape and size of the probe in any detail. SUMMARY OF THE INVENTION With a view of solving the problems mentioned above, the object underlying the present invention is to provide a test method for testing the operation of a semiconductor device, and a test probe and a probe apparatus for carrying out the test method in order to increase the contact area between a probe tip and a pad and hence establish a reliable electrical contact for testing purposes. This object is solved by the test method according to claim 1, a test probe according to claim 4, and a probe apparatus according to claim 7. Advantageous further developments of the invention are specified in the depending subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B are explanatory views each showing a contact condition of a probe according to Embodiment 1 of the present invention and a pad. Fig. 2 is an explanatory view showing the relationship between a probe according to Embodiment 2 of the present invention and the pad. Figs. 3A and 3B are representations each showing a probe trace left on the pad by the probe according to Embodiment 2 of the present invention. Fig. 4 is an explanatory view showing the relationship between a probe according to Embodiment 3 of the present invention and the pad. Figs. 5A and 5B are explanatory views showing a probe according to Embodiments 4 and 5 of the present invention and the relationship between the probe and the pad. Fgs. 6A, 6B and 6C are explanatory views for explaining a method of manufacturing a probe according to Embodiment 6 of the present invention and the pad. Fgs. 7A and 7B are explanatory views showing stresses applied to the pad from the probe according to Embodiment 6 of the present invention. Figs. 8A and 8B are photographs, taken with an SEM (scanning electron microscope), of respective structures of a general and a probe according to Embodiment 7 of the present invention. Fig. 9 is an explanatory view showing the relationship between the probe according to Embodiment 7 of the present invention and the pad. Fig. 10 is an explanatory view showing a probe according to Embodiment 8 of the present invention. Fig. 11 is a sectional view showing a construction of a probe apparatus according to Embodiment 9 of the present invention. Fig. 12 is a sectional view showing a construction of a probe apparatus according to Embodiment 10 of the present invention. Fig. 13A is an explanatory view for explaining a conventional probe apparatus, and Fig. 13B is an explanatory view showing a contact condition of a probe and a pad in the related art. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Embodiment 1. Figs. 1A and 1B are explanatory views each showing a contact condition of a probe according to Embodiment 1 of the present invention and a pad. In these drawings, denoted by reference numeral 1 is a probe, 2 is a pad, 3 is a crystal orientation of the pad 2, 4, 5 and 6 are slip planes, 7 is a vector in the tangential direction with respect to a tip face of the probe 1, 8 is an oxide film formed on the surface of the pad 2, 9 is an oxide-film-adhering region, 10 is an electrical continuity region, and 11 is a shearing deformation. In the probing, as shown in Fig. 1B, electrical continuity between the probe 1 and the pad 2 is established upon the probe 1 causing a shearing deformation in the pad 2 to break off the oxide film 8 on the pad surface and then coming into contact with a fresh surface of the pad 2. The angle at which a shearing deformation may occur depends on the orientation of crystals produced by sputtering. For an aluminum pad, for example, it is known that the crystal orientation 3 of the pad 2 during the sputtering is aligned with respect to the lattice place (111), i.e., exhibits the so-called C-axis orientation, as shown in Fig. 1A. An angle formed between the slip plane 4 represented by (111) and the pad surface is 0 degree. Of other slip planes, the slip plane 5 forming the pad surface at a minimum angle is given by any of (110), (101) and (011), and that angle is 35.3 degrees. If shearing may occur only at the angle of the slip plane, the pad should be subject to a shearing deformation just at discrete angles such as 0 degree, 35.3 degree, and so on. As a result of experiments, however, it was found that a shearing deformation occurs at various angles rather than discrete angles. This is attributable to that shearings along the slip plane 4 and the slip plane 5 are combined with each other, causing the shearing deformation 11 to occur as shown in Fig. 1B. It was also found from experiments that an angle of the slip plane 6 along which shearing may occur at a minimum angle is 15 degrees, and an angle of the slip plane 6 along which shearing can stably occur is 17 degrees. Accordingly, if the probe end is shaped such that an angle formed between the vector 7 in the tangential direction with respect to the probe tip face and the pad surface is larger than 15 degrees, preferably 17 degrees, the probe tip can break off the oxide film 8 on the surface of the pad 2 to establish contact with a fresh surface of the pad, and therefore a sufficient degree of electrical continuity is established. Embodiment 2. In this embodiment, the tip of the probe 1 is formed to have an end face defined by a spherically curved surface with a radius R, as shown in Fig. 2. Assuming that the film thickness of the pad 2 is t and the angle formed at the pad surface between the tangential direction with respect to the probe tip face and the pad surface is  , the following relationship holds among R ,  and t : R - Rcos = t Hence, by designing the tip shape of the probe 1 to have a spherically curved surface which meets the relationship of;  = cos -1 (1 - t/R) ≧ 15° a shearing deformation can be smoothly developed in the pad 2 with relatively small force so that the tip of the probe 1 can establish contact with a fresh surface of the pad and a sufficient degree of electrical continuity is obtained. Note that although the shape of the tip face of the probe 1 is illustrated and described as being spherical for the sake of easier explanation about the relationship between the angle of the slip plane, at which a shearing deformation of the pad material may occur, and the shape of the probe tip, the tip face is not necessarily a perfect spherical surface in practice and a similar advantage can be obtained with the probe having a curved tip face close to a spherical surface. The above-mentioned shape of the probe tip face can be produced, as shown in Fig. 6A, by repeatedly piercing the probe 1 into an abrasive plate 63 formed by setting abrasive grains 61 with a synthetic resin 62. Starting from a flat state of a tungsten probe tip, for example, a spherically curved surface with a radius of approximately 15 µm is obtained by piercing the probe tip 3000 - 4000 times into the abrasive plate which is made up of silicone rubber and #3000-mesh diamond abrasive grains at a weight ratio of about 1 : 3. Further, by piercing the probe tip several hundred times into an abrasive plate in which grinding materials comprise diamond abrasive grains in the range of #6000 - 10000, surface roughness of the probe tip is improved to a value about 1 µm or less. Fig. 3 shows trace left on the pad 2, which is made of aluminum, by the probe 1. It is understood that because aluminum 31 has a layered (lamella) structure, the tip of the probe 1 develops shearing deformations in the pad 2 continuously. The layered structure is heaped beyond the 0.8 µm thickness of the pad 2 so as to project on the pad 2. The projected portion on the pad 2 can serve as a start point for contact or joint between the pad and a wire when wire bonding is externally carried out on the pad 2. A cutdown in bonding time and enhancement of bonding strength are therefore expected. Also, because a dimple 32, which is an evidence of ductile rupture, is observed in a contact portion between the tip face of the probe 1 and the pad 2, it is understood that the tip of the probe 1 is in contact with a fresh surface of the pad 2. As a result of conducting a continuity test with the probe of this embodiment, it was confirmed that a failure of electrical continuity did not essentially occur during the test of making contact 20000 times. While aluminum is used, by way of example, as materials of the test pad in this embodiment, a similar advantage as described above can be obtained so long as the pad is made of any of those materials which develop a slip deformation (shearing deformation) like aluminum. Examples of usable materials include gold, copper, an alloy of aluminum and copper, and an alloy of aluminum and silicon. Embodiment 3. For the test probe 1 which has the tip face formed into a spherically curved surface, assuming that the width of a probe trace marked by the probe 1 contacting the pad 2 is W as shown in Fig. 4, the relationship between W and a radius R of curvature of the probe tip face is below: (W/2) 2 = R 2 - (R - t) 2 Hence, R is given by: R = (W 2 + 4t 2 ) / 8t In other words, by monitoring the width of the probe trace, the radius R curvature of the probe tip face can be determined and the probe shape can be checked. On condition that the thickness of the pad 2 is 0.8 µm, if the width W of the probe trace marked in the test pad is 9 µm as a result of observing the probe trace with an optical microscope, the radius R of curvature of the probe tip face is calculated as about 13 µm. Thus, the tip shape of the probe 1 can be easily checked by observing the probe trace with an optical microscope and measuring the width W of the probe trace. Consequently, a conventional step of removing the probe 1 and inspecting the tip of the probe 1 off-line for each check routine can be omitted. Embodiment 4. Fig. 5A shows a probe according to Embodiment 4 of the present invention. An apparatus called a prober is employed to perform the operation of contacting a probe with a test pad. In some models of probers, the probe is positioned by optically recognizing a probe tip. Where the radius of curvature of the tip face of the probe according to Embodiment 1 is on the order of several microns, the probe tip face cannot be confirmed by image recognition and automatic alignment cannot be effected in some cases because the probe tip has a spherically curved surface and the depth of a focus of an optical system used for observing the probe tip face is shallow. In this embodiment, therefore, the probe tip is formed to have a flat portion 51 as shown in Fig. 5A. With the provision of the flat portion 51, the probe tip face can be clearly confirmed by image recognition and a time required for automatic alignment can be cut down. Incidentally, the flat portion 51 is not necessarily perfectly flat, but may be formed to have a flat surface having such a flatness or a spherically curved surface having such a large radius of curvature that either surface can be recognized with an optical system having the depth of a focus on the order of about 3 - 6 µm. Embodiment 5. In the probe having such a tip shape as described in above Embodiment 4, assuming that the radius of curvature of a spherical surface portion 52 of the probe tip is R, the radius of the flat portion 51 of the probe tip is r, the film thickness of the test pad is t, and the angle formed at the pad surface between the tangential direction with respect to the spherical surface portion 52 of the probe tip and the pad surface is , as shown in Fig. 5B, the following relationship holds: (R 2 - r 2 ) 1/2 - Rcos = t Therefore, by forming the probe tip to have a spherically curved surface with the radius R of curvature which meets the relationship of;  = cos -1 [{(R 2 - r 2 ) 1/2 - t} / R] ≧ 15° the probe tip can develop a shearing deformation in the pad to surely break off the oxide film on the pad surface. As a result, the probe tip can be brought into contact with a fresh surface of the pad, and a sufficient degree of electrical continuity can be established. Additionally, as with Embodiment 3, on-line check of the probe tip shape can be performed based on the following relationship: (W/2) 2 = R 2 - {(R 2 - r 2 ) 1/2 - t} 2 Embodiment 6. In this embodiment, the probe having such a tip shape as described in above Embodiment 4 is modified to have a curved surface 53 smoothly joining between the flat portion 51 and the spherical surface 52, as shown in Fig. 5A. A probe having the flat portion 51 and the spherical surface 52, which are continuously joined with each other by the curved surface 53, can be manufactured as follows. First, as shown in Fig. 6A, the probe tip is rounded to have the spherical surface 52 with the radius R of curvature by repeatedly piercing the probe 1 into the abrasive plate 63 formed by setting the abrasive grains 61 with the synthetic resin 62. Then, as shown in Fig. 6B, the probe tip is rubbed against a ceramic plate 64 having higher rigidity than the probe 1, thereby forming the flat portion 51. After that, the probe tip is polished by a polisher 65 having lower rigidity than the probe 1 so that the flat portion 51 and the spherical surface 52 are joined with each other by the smooth curved surface 53. With the probe having the tip shape thus formed, stresses are less concentrated on the pad 2, whereby damages upon the pad 2 and a layer lying under the pad 2 can be abated. Figs. 7A and 7B show distribution of stresses imposed upon the pad 2 in states before and after the probe is polished by the polisher 65, respectively. When any of the probes according to Embodiments 1 to 6 is used, the material of the test pad exhibits a specific deformation as shown in Fig. 3. Specifically, the probe tip causes continuous shearing deformations in the pad material, and a trace marked upon displacement of part of the pad material has a layered structure (lamella structure) 31 heaped in multiple layers. When the material of the test pad having the lamella structure is partly displaced, deformation resistance of the test pad material is so small that a stress load applied to the layer lying under the test pad can be reduced. Further, a projection formed by the layered structure heaped on the pad surface serves to promote formation of a joint nucleus in a subsequent step of wire bonding made on the pad. As a result, it is possible to shorten a ultrasonic oscillating time necessary for the wire bonding, and to enhance the bonding strength. Embodiment 7. For comparison in structure difference between a tungsten probe according to Embodiment of the present invention and a general tungsten probe, Figs. 8A and 8B show photographs taken with an SEM (scanning electron microscope) after a section of each tungsten probe has been etched. Fig. 8A represents the structure of the general tungsten probe, and Fig. 8B represents the structure of that tungsten probe after it has been subject to heat treatment. A tungsten probe is a sintered compact and hence includes voids in the probe material after sintering. To collapse the voids, the tungsten probe has been conventionally produced by mechanically rolling the probe material after sintering, and then drawing the rolled material to have the probe crystal structure. Even by so producing, the tungsten probe still includes voids of 1 - 2 %. It is conceivable to carry out heat treatment for collapsing the voids. However, if the heat treatment is carried out in a temperature range where the tungsten material is recrystallized, the probe crystal structure of the tungsten material would be disintegrated and the material strength of tungsten itself would be lost. In this embodiment, therefore, voids in the tungsten material are collapsed under a combined effect of temperature and pressure by externally applying a high pressure at relatively low temperatures. For a metal material after being drawn as with tungsten of the probe, there remain considerable machining strains (residual stresses) in the material. It is thought that metal atoms arrayed in random near the grain boundary, in particular, have higher chemical potential energy due to the machining strains, and that those metal atoms are apt to move even at relatively low temperatures. With the above in mind, in this embodiment, static pressure is externally applied to the metal material including considerable machining strains when it is subject to relatively low temperatures to make metal atoms tend to move, thereby collapsing voids residing near the grain boundary in the metal material. To this end, heat treatment conditions are set to a temperature not higher than the recrystallization temperature of the metal material, a pressure under which the metal material develops cubical contraction, and a treatment time required for cubical contraction of the metal material under treatment to be almost completed or stopped. Practically, pores (voids) are remarkably reduced by carrying out the heat treatment under conditions of a treatment temperature of 300 °C - 600 °C, a treatment pressure of 200 - 2000 atm. and the treatment time of 0.5 - 5 hours. As a result of repeating experiments under those conditions for heat treatment, it was also found that voids are more remarkably reduced when setting a treatment temperature to 500 °C, a treatment pressure to be not lower than 1000 atm and the treatment time to be not shorter than 1 hour. For the pressure condition, the higher the set pressure, the shorter is the required treatment time. However, the pressure apparatus had an upper limit at 2000 atm. To collapse void defects in the material, it has been customary to carry out heat treatment (called HIP treatment) under high pressure at a temperature not lower than the recrystallization temperature of the material (usually a temperature equal to 0.4 or 0.5 of the melting point of the material). On the other hand, in this embodiment, voids can be collapsed by carrying out the heat treatment at a lower temperature that is approximately one digit, i.e., 1/10, lower than the melting point 3400 °C of tungsten, for example. Further, it was found that as a result of the heat treatment described above, the crystal orientation is markedly aligned in the direction in which the probe material has been drawn. With this effect, an etching or grinding rate in a process of forming the probe tip becomes even, and therefore the probe top can be finished to have a very smooth surface. Consequently, oxides are hard to adhere onto the probe tip, and probing can be performed with good electrical continuity. In addition, as shown in Table 1 below, mechanical properties also become uniform (e.g., a Young's modulus of the probes varies in the range of 18.8 - 25.2 × 10 3 kgf/mm 2 before the heat treatment, but in the range of 22.3 - 26.3 × 10 3 kgf/mm 2 after the heat treatment). Hence, by performing the probing with such a probe attached to a probe card, it is possible to reduce extra over-driving or load which has been necessitated in vie of variations in probe properties. Tensile Load Young's Modulus Sample gf x10 3 kgf/mm 2 Probers before heat treatment 12.800 18.8 12.960 25.2 13.060 18.8 Probers after heat treatment 13.520 22.3 13.800 23.8 13.840 26.3 Moreover, the following point was found. Since the tip face of the probe is formed to be smooth, the coefficient of friction between the probe and the test pad material with which the probe comes into contact is reduced. Even with the probe having the conventional tip shape defined by a spherically curved surface with a radius of curvature ranging from 20 to 30 microns, therefore, the pad material is slipped and moved forward of the probe upon being pushed by the probe tip. As a result, an effect of reducing and stabilizing the electrical contact resistance can be obtained. Accordingly, by forming the probe having the tip shape according to Embodiments 4 and 5 with the material which has been subject to the heat treatment described above, probing under stable electrical contact resistance and automatic recognition of the probe tip position can be achieved. This results in a remarkable reduction in time and cost for the test. Further, the above heat treatment of the probe enables contact resistance to be stabilized even in the probe having the conventional tip shape. Fig. 9 shows, in the form of a simplified model, a probing state where a probe tip is in contact with a test pad. Assuming, for example, that a probe 1 has a tip shape formed into a spherically curved surface, the radius of curvature of the tip shape is R, the diameter of a beam or stem portion of the probe 1 joining with the spherically curved surface is D, and when the probe 1 contacts at an inclination angle (with a test pad 2 having a thickness t, the greatest distance between a line, at which the beam portion of the probe 1 intersects the spherically curved surface, and a bottom surface of the test pad 2 is H, it is essential to meet not only the following contact condition; H = R - Rsin(β-α) ≧ t ( where β = cos -1 (D/2R)) but also the condition explained above in connection with Embodiment 1 for developing a shearing deformation in the pad material. However, material defects in the probe 1 can be eliminated and the tip face of the probe can be finished to be very smooth by heat-treating the probe 1 in a non-oxidizing atmosphere at a temperature not higher than the recrystallizaiton temperature of the metal material while raising the pressure of a non-oxidizing gas to a level enough to make the volume of the metal material contracted over time. As a result, the coefficient of friction between the pad material and the tip face of the probe 1 is so reduced that the pad material is pushed to move forward and the tip face of the probe 1 is brought into contact with a fresh surface of the pad material so long as the probe is in the contact state shown in Fig. 9 regardless of the probe tip shape. It was thus confirmed that stable contact can be obtained due to the effect of the heat treatment even with the probe 1 having the conventional tip shape. Embodiment 8. Fig. 10 shows a probe according to Embodiment 8 of the present invention. During the probing, the contact surface between a tip of a probe 90 and a pad 2 may produce high temperatures not lower than 1000 °C due to a shearing deformation. Tungsten is very apt to oxidize under high temperatures. To avoid oxidation of tungsten, in this embodiment, the heat treatment described above in connection with Embodiment 7 is carried on the probe 90, and a surface coating layer 91 of 0.01-0.1 µm made from Pt, Ir, Rh, Au, Cd or an alloy of these elements formed is formed over the tip of the probe 90 by plating or vacuum deposition. By performing the probing with a probe apparatus which includes the probe 90 attached thereto, oxides are more hard to adhere onto the tip of the probe 90 and the probing can be achieved with good electrical continuity. Embodiment 9. Fig. 11 is a sectional view showing a construction of a probe apparatus according to Embodiment 9 of the present invention. The probe apparatus includes cantilever probes 100 attached to one side of a probe board (card) 101. The probe board 101 has an opening formed in such a position that tips of the probes 100 can be seen through the opening from the opposite side of the probe board including no probes. A plate 104 provided with nozzles 105 formed therethrough is fitted to the opening of the probe board 101 from the opposite side including no probes in facing relation to the tips of the probes 100 so that gas can be sprayed to the tips of the probes 100. Further, a cover 103 is attached to the opposite side of the probe board 101 in covering relation to the plate 104 so as to define a space between itself and the plate 104. A tube 102 for injecting gas is attached to the cover 103, and a non-oxidizing gas such as argon or nitrogen is injected to the space between the cover 103 and the plate 104 through the tube 102 at a rate of 5 - 10 liters/minute. The injected non-oxidizing gas is directly sprayed to the tips of the probes 100 from the nozzles 105. Accordingly, the density of the non-oxidizing gas in the vicinity of the probe tips is so increased as to prevent oxidization of the probes 100. Further, since the gas is ejected in violent flows, dust on the wafer can be removed at the same time. In addition, by attaching cantilever probes, which have been subject to the heat treatment described above in connection with Embodiment 7, to the probe apparatus thus constructed, electrical continuity during the probing is improved and oxidization of the probes can be avoided. Embodiment 10. Fig. 12 is a sectional view showing a construction of a probe apparatus according to Embodiment 10 of the present invention. The probe apparatus has a multi-layered structure comprising a plurality of vertical or like probes 110, a probe fixed plate 111, and a plate 113 provided with guide holes 115 for guiding the probes 110. A space is defined between the probe fixed plate 111 and the plate 113 provided with the guide holes 115, and is sealed off by an air-tight seal 114, thereby providing an air-tightly sealed structure. The guide holes 115 each have a diameter 1.2 - 1.5 times larger than the diameter of the guide holes 115. With that structure, by supplying a non-oxidizing gas to the enclosed space between the probe fixed plate 111 and the plate 113 and ejecting the non-oxidizing gas through the guide holes 115 at a rate of 2 - 5 liters/minute, a non-oxidizing atmosphere can be produced near the tip of each of the probes 110 and oxidization of the probes 110 is avoided. Further, since the gas is ejected in violent flows, dust on the wafer can be removed at the same time. In addition, by attaching vertical or like probes, which have been subject to the heat treatment described above in connection with Embodiment 7, to the probe apparatus thus constructed, electrical continuity during the probing is improved and oxidization of the probes can be avoided. While the above embodiments have been described in connection with the probes and the probe apparatus for testing primarily wafers on which semiconductor integrated circuits are formed, the present invention is also applicable to, by way of example, probes used for testing semiconductor products fabricated by other manufacturing processes such as a film forming process, and enables the probing to be carried out with good electrical continuity. Further, the probe of the present invention can be applied to the case where it is required to establish contact with a lead frame of a semiconductor device which is formed by plating a soft solder on a material such as a 42-alloy, whereby a final test can be performed with good electrical continuity. Additionally, the probe of the present invention can be applied to an operation test for an electronic circuit board on which semiconductors are mounted, enabling the probing to be carried out with good electrical continuity. As described hereinabove, with the test probe for semiconductor devices according to the present invention, the probe tip can efficiently develop a shearing deformation in the pad during the probing, whereby a contact surface can be established between the probe tip and the pad with a sufficient degree of electrical continuity. Also, with the test probe for semiconductor devices according to the present invention, the probe tip can be always brought into contact with a fresh surface of the pad to provide a sufficient degree of electrical continuity. With the test probe for semiconductor devices according to the present invention, when a probe level is adjusted in the probing, a time required for positioning the probe prior to the start of measurement is cut down and variations in measurement are reduced. Further, with the test probe for semiconductor devices according to the present invention, there is obtained such a probe end shape that a flat portion is formed at the probe tip and the flat portion is joined with a spherical surface by a smooth curved surface. As a result, a probe capable of providing good electrical continuity and being easily positioned in place can be manufactured. In addition, stresses are less concentrated on the pad, whereby damages upon the pad and the layer lying under the pad can be abated. With the test probe for semiconductor devices according to the present invention, voids in the vicinity of the grain boundary can be collapsed under action of pressure while crystals in the metal material are suppressed from becoming coarse. Accordingly, the voids are remarkably reduced and mechanical properties are made uniform. By employing the probe which has been subject to the heat treatment of the present invention, therefore, a probe having good and uniform electrical characteristics can be provided. As a result, a margin that must be taken into consideration in relation to an amount of pressing of the probe into the pad can be reduced, and electrical continuity can be established for all probes under a smaller probe load. With the test probe for semiconductor devices according to the present invention, since the voids are remarkably reduced and mechanical properties are made uniform by properly carrying out the heat treatment of the present invention, it is possible to overcome such a conventional problem that, in a probe made of, e.g., tungsten and containing voids therein, substances having large electrical resistance, such as oxides peeled off from the pad, may enter the voids to impede establishment of electrical continuity during the probing. As a result, a probe having good and uniform electrical characteristics can be provided. With the test probe for semiconductor devices according to the present invention, there appear no material defects in the probe tip face after being finished, and hence stable contact can be achieved with even with a probe having a conventional probe tip shape. With the test probe for semiconductor devices according to the present invention, even when the pad is subject to high temperatures due to a shearing deformation during the probing, oxidation of the metal material constituting the probe can be avoided, and therefore a probe having good electrical continuity can be provided. With the probe apparatus according to the present invention, a probe apparatus having good electrical continuity between the probe tip and the pad can be provided. With one testing method according to the present invention, the probe tip face can be stably brought into contact with a fresh surface of the test pad material, and the probing can be performed with good electrical continuity. With another testing method according to the present invention, the probe tip shape can be easily checked. With the semiconductor device according to the present invention, a projection is formed on the test pad. When wire boding, for example, is performed on the test pad, a bonding time can be shortened by utilizing the projection.

Claims: A test method for testing the operation of a semiconductor device, using a test probe (1) having a tip portion which is pressed against a test pad (2) of the semiconductor device and is penetrated into the test pad (2) to a predetermined depth equal to the thickness (t) of the test pad (2) in order to establish an electric contact between the tip portion and the test pad (2), wherein the test probe (1) is formed to have a tip with a spherical surface meeting the following relationship:  = cos -1 (1 - t/R) ≥ 15° , wherein R is the radius of curvature of the spherical surface, t is the thickness of the test pad (2), and  is an angle formed at the test pad (2) surface between a tangential line (7) with respect to the test probe (1) tip face and the test pad (2) surface when the test probe (1) is pressed against the test pad (2), wherein a test probe (1) is used which has a radius of curvature R of the spherical surface below 20 µm, so that the contact between the test probe (1) and the test pad (2) is adapted to cause a shearing deformation in the test pad surface. The test method according to claim 1, wherein a test probe (1) with a flat portion (51) at an end of the tip portion is used. The test method according to claim 1 to 2, wherein a test probe (1) is used which is made of a metal rod material prepared by sintering powdered raw materials, which has been subjected to a heat treatment in an atmosphere of non-oxidizing gas under such conditions that the treatment temperature is not higher than the recrystallization temperature of the metal material and the pressure of the non-oxidizing gas has been raised to a level at which the volume of the metal material is contracted over time. A test probe for carrying out a test method according to any of claims 1 to 3, wherein the test probe (1) is formed to have a tip with a spherical surface which is adapted to the thickness ( t ) of the test pad (2) to meet the following relationship:  = cos -1 (1 - t/R) ≥ 15° , wherein R is the radius of curvature of the spherical surface, t is the thickness of the test pad (2), and  is an angle formed at the test pad (2) surface between a tangential line (7) with respect to the test probe (1) tip face and the test pad (2) surface when the test probe (1) is pressed against the test pad (2), wherein the radius of curvature R of the spherical surface is below 20 µm, so that the contact between the test probe (1) and the test pad (2) is adapted to cause a shearing deformation on the test pad surface. The test probe according to claim 4, wherein the test probe (1) has a flat portion (51) at an end of the tip portion. The test probe according to claim 4 to 5, wherein the test probe is made of a metal rod material prepared by sintering powdered raw materials, which has been subjected to a heat treatment in an atmosphere of non-oxidizing gas under such conditions that the treatment temperature is not higher than the recrystallization temperature of the metal material and the pressure of the non-oxidizing gas has been raised to a level at which the volume of the metal material is contracted over time. A probe apparatus for carrying out the test method according to any of claims 1 to 3, which is adapted to press the test probe (1) against the test pad (2) of the semiconductor device, and to relatively slide the test probe (1) on the test pad (2) to partly displace material (8) on the surface of the test pad (2) with the material (8) heaped in multiple layers (11), thereby testing the operation of the semiconductor device.

Inventors: KANO MUTSUMI, KASHIBA YOSHIHIRO, MAEKAWA SHIGEKI, MIKI KAZUNOBU, NAGATA TAKAHIRO, TAKEMOTO MOGUMI, KANO, MUTSUMI, KASHIBA, YOSHIHIRO, MAEKAWA, SHIGEKI, MIKI, KAZUNOBU, NAGATA, TAKAHIRO, TAKEMOTO, MOGUMI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1998
Main classification: G01R1
IPC codes: G01R1, G01R3