JP3491736B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and its manufacturing method. More specifically, the integrated circuit pattern forming the semiconductor device and the decoding of the stored information held in the integrated circuit, which are performed by irradiating infrared light from the back surface side of the substrate forming the semiconductor device, The present invention relates to a semiconductor device capable of preventing illegal acts such as falsification of information and a manufacturing method thereof. INDUSTRIAL APPLICABILITY The present invention is preferably applied to a semiconductor device having a function of storing and processing important information such as personal privacy and money used for an IC card and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Some semiconductor devices have a function of storing and processing information. Such a semiconductor device is used, for example, in an IC card or the like and handles important information such as personal privacy and money. This semiconductor device includes a CPU (Central Processing Unit), a RAM
(Random Access Memory), ROM (Read Only Me
mory), EEPROM (Electrically Erasable Prog
It has a rammable read only memory) inside, and research and development for its practical use are proceeding at a rapid pace.

In order to develop a semiconductor device having a function of storing and processing information, an IC (Integrated Circuit) constituting the semiconductor device is designed for the purpose of improving design and manufacturing techniques and investigating the cause of defective products. Function, operating method,
Techniques for analyzing circuit methods, circuit patterns, stored information, etc. are essential.

One of them is an analysis method using an optical microscope. In this analysis method, visible light, which is observation light, is applied to the surface of an IC chip on a substrate that constitutes a semiconductor device to be analyzed, and the surface of the IC chip is observed with an optical microscope to determine the circuit pattern of the IC chip. The work of reading has been done. For a fine pattern of 1 μm or less, since the wavelength of the observation light is close to the pattern width, laser light having a relatively short wavelength is used to reduce the influence of diffraction. This has improved resolution and depth of focus.

However, as the wiring layers of the semiconductor device are multi-layered, it is necessary to remove the upper layer film in order to accurately read the wiring pattern of the lower layer of the semiconductor device. For this reason, there is a drawback that the surface of the IC chip cannot be observed in a non-destructive state while the IC chip is operating.

Further, since the information of the EEPROM is stored in the gate electrode of the MOS transistor in the lowermost layer of the semiconductor device, observation of the surface of the IC chip is not always an effective means for circuit analysis of the lower layer.

As a method of supplementing the method using such an optical microscope, for example, there is a method of nondestructively observing a circuit near the front surface of the IC chip from the back surface side.
That is, by using infrared rays having a wavelength that is difficult to be absorbed by the silicon substrate which is the substrate of the IC chip as an observation light source, the transparency to the silicon substrate is increased and the wiring pattern mainly made of metal can be observed from the back surface through the silicon substrate. Is the way to do it.

According to this method, the pattern of the transistor in the lowermost layer of the semiconductor device and the wiring pattern of the first layer can be observed nondestructively. Particularly, in recent high-density mounting technology, a method is adopted in which bump electrodes for electrical connection with a mounting substrate are formed on the front surface side of the IC chip, and the IC chip is turned over and connected to the mounting substrate. ing.

Therefore, when the IC chip is mounted, the back surface of the IC chip is exposed to the outer surface, which facilitates pattern observation from the back surface side more than the front surface side of the IC chip. Also, the back surface of the IC chip is coated with epoxy resin or the like for chip protection,
It is possible to remove this coating with chemicals relatively easily. As a result, a relatively clear IC pattern can be observed from the back surface of the IC chip.

With the spread of semiconductor devices for storing and processing information, the functions, operating methods, circuit methods of integrated circuits constituting the semiconductor device are analyzed by the above-mentioned analysis method.
There is a high possibility that the circuit pattern, the stored information, etc. will be analyzed and the stored information will be tampered with. For this reason, there is a demand for the development of a technique for preventing analysis and falsification of semiconductor devices. In particular, when the semiconductor device is used for an IC card or the like to store and process important information such as personal privacy and money, a defense technique is essential.

Conventionally, as a means for protecting information stored in not only a semiconductor substrate but also a portion generally covered with a film or a plate from observation by optical means, a material that does not transmit observation light is used as the film or the film. There was a method used for the board. However, for example, when a light-shielding metal film is formed on the back surface of a semiconductor substrate, there is a problem in that the metal film is peeled off from the substrate by chemical etching relatively easily and with good selectivity. It was

Further, since the metal film is generally deposited by the vacuum evaporation method or the sputtering method, it is necessary to form the metal film on the substrate in the wafer state. On the other hand, in the step of mounting the chip in the case, since the wafer is appropriately ground and adjusted and then the wafer is diced into chips, it is difficult to deposit the metal film before cutting. Therefore, there is a problem that the light-shielding metal film cannot be easily formed on the chip.

Further, as a protection technique for protecting from observation, there has been a method of forming a diffuse reflection surface on the front surface or the back surface of a film or a substrate, as shown below. That is, as shown in FIG. 16, for example, when forming the irregular reflection surface 102 with an angle of 45 degrees with respect to the glass substrate 101, a grinder with a 45-degree inclined blade containing an abrasive is used, Glass substrate 1
The surface of No. 01 is ground. As a result, the irregular reflection surface 102 is formed on the surface of the glass substrate 101. In this case, the pitch of the irregularities can be set to a size of about 1 mm. In this example, the angle of the irregular reflection surface 102 is 45 mm.
The thickness of the glass substrate 101 is 1 mm.
More was needed.

However, as a substrate on which a pattern with a fine line width of 1 μm or less such as an IC chip is drawn, generally 1
The one having a thickness of less than or equal to mm is the mainstream. For example, for a silicon substrate, generally 600 μm is further ground to obtain 200
The thickness of about μm is often used. Therefore, IC
There is a problem that the above-mentioned grinding method using a grinder cannot be applied to the formation of a diffused reflection surface on an information medium such as a chip on which information is drawn with high density.

Therefore, there is the following protection technique for a substrate on which a fine pattern such as an IC chip is drawn. That is, as shown in FIG. 17A, a silicon wafer 110 having a (100) plane is prepared as a substrate, and a chemical vapor deposition (CVD) method is provided on the back side.
(FIG. 17) by using a film forming method based on r Deposition).
As shown in (b), a SiO ₂ film 111 having a thickness of 2 μm is deposited. Then, using a photo-etching technique, FIG.
As shown in (c), the SiO ₂ film 111 is processed into a stripe shape to form a SiO ₂ pattern 112.

After that, the silicon wafer 11 is immersed in an ethylenediamine aqueous solution using the SiO ₂ pattern 112 as a mask.
0 chemical etching is performed. As a result, FIG.
As shown in (d), an inclination is formed at an angle of about 55 degrees from the wafer surface of the silicon wafer 110, and the etching bottom surface 113 composed of the (100) surface sinks downward as the etching progresses. Then, as shown in FIG. 17E, the inclined surfaces 114 on both sides finally collide with each other, and the etching is automatically stopped to form a substantially V-shaped valley 115.
After that, the SiO ₂ pattern 112 is removed by using hydrofluoric acid, so that the opening 11 is removed as shown in FIG.
An irregular reflection surface 117 having 6 is formed.

However, this defense technique has the following problems.

(1) Since the silicon wafer 110 is chemically etched using the SiO ₂ pattern 112 as a mask, a flat portion 118 remains in the region on the back surface of the substrate where the mask is removed after etching. The flat portion 118 has a positional relationship parallel to the substrate surface. Therefore, by using the flat portion 118, it is possible to irradiate infrared light from the back surface side of the substrate to perform decoding of the integrated circuit pattern and the stored information that form the semiconductor device, and illegal acts such as falsification of this stored information. The sex was left.

(2) Since this protection technique uses a photo-etching technique, it is necessary to put an entire circular wafer having a diameter of, for example, 6 inches into the processing step. However, after the wafer back surface is ground to reduce the wafer thickness, the strength of the wafer becomes smaller, so it is very difficult to apply the photo-etching technology including the steps of washing with water, dipping in an acid solution, and rotary drying. difficult. Further, there is a drawback in that a complicated process such as attaching the wafer to another protective substrate is required in order to process the wafer having the reduced strength. Further, there is a drawback that the photo-etching technique cannot be applied once the wafer is cut into chips.

As described above, the conventional method for forming the irregular reflection surface on the substrate has the following problems. In other words, mechanical grinding has a point that fine processing cannot be performed on a thin substrate, and the chemical etching method is
There are the points that the positional relationship parallel to the substrate surface is maintained in the region where the mask is removed, and that the wafer substrate cut into chips is difficult to process.

Therefore, once the observation and analysis from the back surface of the chip are carried out for the purpose of deciphering the integrated circuit pattern and the stored information constituting the semiconductor device, and the illegal acts such as falsification of the stored information, the conventional technique is used. There was a problem that it was difficult to prevent.

[0022]

SUMMARY OF THE INVENTION The present invention is also applicable to a semiconductor device including a substrate cut in a chip shape, which is performed by irradiating infrared light from the back surface side of the substrate forming the semiconductor device. It is an object of the present invention to provide a semiconductor device having a means capable of preventing illegal actions such as decoding of the integrated circuit pattern and the stored information and falsification of the stored information, and a method of manufacturing the semiconductor device.

[0023]

The semiconductor device of the present invention comprises:
In a semiconductor device in which an integrated circuit is arranged on the front surface of a substrate, an aggregate formed by forming a plurality of irregular reflection portions on the back surface of the substrate, the irregular reflection portion including concaves and projections for irregularly reflecting incident light, and the fusible particles are What is claimed is: 1. A semiconductor device , comprising: melted particles on the back surface of a substrate; and fusion particles formed by adhering to the surfaces of the depressions and protrusions of each diffuse reflection portion,
Is irradiated by the focused energy beam on the substrate
Is a trace of irradiation formed on the back surface of the fusion particle
By the energy beam, the fusible particles are
It melts on the backside of the substrate and adheres to each of the irradiation traces.
It is characterized by being made .

By providing the aggregate of diffuse reflection portions having the above structure on the back surface of the substrate, even if the back surface of the substrate is irradiated with infrared light for observation, the incident infrared light forms a fusion product. It is absorbed or diffusely reflected by the aggregate of diffused reflections. Further, from the back surface side of the substrate, the reflected light from the integrated circuit arranged on the front surface of the substrate can be obtained only in the absorbed or disturbed form. Therefore, it is possible to prevent the decoding of the integrated circuit pattern arranged on the surface of the substrate, the stored information of the integrated circuit, and the falsification of the stored information.

Further, even if the aggregate is to be removed by chemical etching, the aggregate is composed of a fusion product of the fusible particles to the substrate, and therefore the aggregate is removed from the substrate with good selectivity. I can't. As a result, it is not possible to obtain a smooth surface excluding the aggregate. Therefore, it is possible to reliably prevent decoding of the integrated circuit pattern arranged on the surface of the substrate, stored information of the integrated circuit, falsification of the stored information, and the like.

A method of manufacturing a semiconductor device according to the present invention is the method of manufacturing a semiconductor device in which an integrated circuit is arranged on the surface of a substrate, wherein a coating film containing fusible particles that is melted by a focused energy beam is formed on the substrate. Formed on the back surface, a large number of the energy beam is applied to the coating film to form an aggregate of irradiation traces, and the fusible particles are melted on the back surface of the substrate by the energy beam, and each irradiation is performed as a fusion product. It is characterized in that it adheres to traces.

By irradiating the coating film formed on the back surface of the substrate by the above-mentioned method with a large number of the energy beams, a part of the surface of the substrate is melted to form depressions and projections as irradiation traces, and at the same time, the coating film is formed. The fusible particles therein are fused to the back surface of the substrate, forming a fused material on the irradiation trace. That is, in the above method, since the coating is formed and the energy beam is irradiated, the shape of the semiconductor substrate such as a wafer is not limited, and the irradiation trace and the fusion substance can be applied to a chip-shaped substrate. It is possible to efficiently form the following aggregate on the back surface.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION [Embodiment 1] Hereinafter, Embodiment 1 of the present invention will be described in detail with reference to FIGS.

FIG. 1 is a schematic sectional view showing a manufacturing process of a semiconductor device according to the first embodiment. FIG. 2 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment. FIG. 5 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment. Figure 6
FIG. 5 is a schematic cross-sectional view showing a manufacturing process of the semiconductor device according to the first embodiment. FIG. 7 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment. Figure 8
FIG. 6 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment. FIG. 9 is an explanatory diagram for explaining the setting of the irradiation area according to the first embodiment. FIG. 10 is a schematic cross-sectional view showing the shape of the irradiation trace obtained by the irradiation of the laser beam according to the first embodiment. FIG. 11 is a perspective view of an IC chip having a recess and a protrusion formed by the manufacturing process of the semiconductor device according to the first embodiment.

The semiconductor device of the first embodiment will be described below in accordance with the procedure of the manufacturing process. First, as shown in FIG. 1, an integrated circuit 2 for a semiconductor device is formed on the surface of a silicon wafer 1 having a diameter of 6 inches and a thickness of 625 μm by using a thin film deposition technique and a photo-etching technique. Were formed respectively. The size of the IC chip on which the integrated circuit 2 is formed is 4 mm square, and the minimum pattern line width is 0.5 μm.
m. Then, on the wafer surface of the silicon wafer 1,
A passivation film made of Si ₃ N ₄ and SiO ₂ for surface protection was formed, and the pretreatment process of the silicon wafer 1 was completed.

When the pretreatment process is completed, as shown in FIG. 2, the bumps 3 for electrically connecting to the IC card substrate, which will be described later, are formed on the surface of the silicon wafer 1.
Two chips were formed on each of the four corners of the chip, for a total of eight chips. Bump 3
After the formation of the above, the back surface of the wafer was ground, and the thickness d of the silicon wafer 1 was set to 200 μm as shown in FIG. Thereafter, as shown in FIG. 4, the cut portion 1A of the silicon wafer 1 was diced and separated into chips 4. As a result, the chip 4 has a structure in which one integrated circuit 4B is provided on the silicon substrate 4A. As the integrated circuit 4B, in addition to an 8-bit CPU, a 1-kilobyte RA
M, 8 kilobytes ROM and 8 kilobytes non-volatile EEPROM.

After this, as shown in FIG. 5, the surface of the chip 4, that is, the surface on which the bumps 3 are formed, is arranged so as to face the IC card substrate 5 made of a metal and a glass epoxy substrate. As a result, the back surface 4C of the chip 4 was exposed to the outside. When the placement of the chip 4 is completed, the bumps 3 of the chip 4 are connected to the electrodes 6 of the IC card substrate 5.
Bump 3 was electrically connected to electrode 6.
When the connection was completed, a gap was generated between the chip 4 and the IC card substrate 5. Therefore, as shown in FIG.
Underfill agent 7 made of highly fluid epoxy resin
Was filled in the gap formed by the chip 4 and the IC card substrate 5, and cured and cured.

When the filling of the gap is completed, the process of providing the chip 4 with the aggregate of the irradiation traces is started. In this process,
The coating film 10 was formed using the mixed solution prepared as follows. That is, the binder 11 made of a high molecular material epoxy resin was diluted with the solvent xylene. After that, the tungsten particles 12 having an average diameter of 5 μm, which were made of tungsten, were used as the fusible particles. Tungsten is a light blocking material that blocks light such as infrared light. Then, 10% by weight of the tungsten particles 12 used as the fusible particles were blended with the binder 11 to disperse the tungsten particles 12.

The mixture thus prepared was loaded into a syringe, and the syringe was equipped with an injection needle. Then, the mixed solution was dropped on the back surface 4C of the chip 4 from an injection needle. As a result, as shown in FIG.
The coating film 10 containing the binder 11 and the tungsten particles 12 was formed so as to cover the chip 4 and the periphery of the chip 4 on the IC card substrate 5. After forming the coating film 10, the chip 4 on the IC card substrate 5 was cured at about 150 ° C. As a result, the coating film 10 is cured, and the film thickness of the coating film 10 is reduced to 20.
μm.

The chip 4 on which the coating 10 had been formed was loaded into the laser marker device. At the time of this loading, the chip 4 was placed in an atmosphere of nitrogen gas. In this state, as shown in FIG. 8, the laser beam A was irradiated from the upper side of the coating film 10 toward the back surface 4C of the chip 4 to form an irradiation trace 4D. A YAG laser is used as the laser light source, the wavelength is 532 nm of the second harmonic, and the pulse oscillation mode is TEM _00.
The single mode, the output energy was 16 μJ, and the pulse width was 25 nsec or less at 1 kHz. Further, the optical system of the laser marker device is controlled by a galvanometer type beam positioner, the light is focused by a lens, and the rear surface 4C of the chip 4 is controlled.
Focused the light on top.

In the laser marker device, the irradiation position of the laser beam A was set as follows. That is, as shown in FIG. 9, an irradiation trace forming region 20 is set as an irradiation region on the back surface 4C of the chip 4, and the irradiation trace forming region 20 is further set.
Was divided vertically and horizontally to form a mesh-shaped irradiation area portion 21. The size of the irradiation area portion 21 is set to the laser beam A
It was determined by the diameter of. The irradiation region portion 21 was irradiated with three pulses of the laser beam A. This allows
A part of the binder 11 in the coating film 10 was sublimated or evaporated, and a part was baked on the back surface 4C of the chip 4. As a result, a circular irradiation trace 4D was formed as an irregular reflection portion on the back surface 4C of the chip 4.

A cross-sectional view of one irradiation trace 4D is shown in FIG. When the coating film 10 is irradiated with the laser beam A, a part of the silicon substrate 4A is melted by the heat due to the absorption of the laser beam and reacts with a part of the tungsten particles 12 to form the tungsten particles 12 and the silicon substrate 4A. Tungsten silicide was generated at the contacting area. Due to this tungsten silicide, the tungsten particles 12 became a fusion material to the silicon substrate 4A.

At the same time, the central portion of the irradiation region 22 irradiated with the laser beam A was dented, and a concave portion 4E was formed as a depression. As the number of pulses of the laser beam A increases, the recess 4E becomes deeper, and in the first embodiment, three pulses were optimal as described above. Further, by the irradiation of the laser beam A, the melted material of the silicon substrate 4A was pushed to the peripheral portion, and the peripheral portion was raised above the back surface 4C of the chip 4, and an annular convex portion 4F was formed as a protrusion. That is, a crater-shaped irradiation trace 4D was formed by the concave portion 4E and the convex portion 4F.

Thus, the concave portion 4E and the convex portion 4F of the irradiation trace 4D formed a surface non-parallel to the back surface 4C, and the tungsten particles 12 were formed on the non-parallel surface of the irradiation trace 4D. The average shape of the irradiation trace 4D was as follows. That is, the diameter of the irradiation trace 4D was 60 μm, the depth of the irradiation trace 4D from the back surface 4C was 4 μm, and the height of the raised portion in the peripheral portion which was the convex portion 4F was 7 μm.

On the back surface 4C of the chip 4, a large number of crater-shaped irradiation traces 4D are formed adjacently on the entire surface by the above-mentioned method.
An assembly of irradiation traces 4D was provided. Then, as shown in FIG. 11, an irradiation trace forming region 20 is set on the back surface corresponding to the chip front surface position where the EEPROM is formed, and 2 × 3 m
The area of m ² was set as one surface of the irradiation trace forming region 20. The crater central portion of the irradiation traces 4D formed in each irradiation region 22 was arranged at an interval of 60 μm, and the irradiation traces 4D were circumscribed to each other so as to form a close-packed structure.

After this, an assembly of irradiation traces 4D is formed and the IC card substrate 5 which is a glass epoxy substrate.
Epoxy resin is further applied to the chip 4 mounted on the exposed back surface 4C of the chip 4 to protect the chip 4, and the entire chip 4 is covered with a card substrate made of vinyl chloride resin. Completed as an IC card.

The information of the IC card manufactured by the above process is protected from unauthorized analysis and the like as follows.

In the analysis, first, the back surface 4C of the chip 4 is exposed by dissolving a part of vinyl chloride on the surface of the IC card and a base material made of epoxy resin with heated fuming nitric acid. After that, an optical microscope is used to observe the transistor circuit and the first layer wiring near the surface of the chip 4. As the observation light of the optical microscope, H of wavelength 1.15 μm
The infrared light of an e-Ne laser is used.

However, since the back surface 4C of the chip 4 inside the IC card is provided with an assembly of the irradiation traces 4D, most of the infrared light incident on the chip 4 has a concave portion 4E and a convex portion of the irradiation trace 4D. It is diffusely reflected by the back surface 4C by 4F and is further absorbed by the tungsten particles 12. Further, the light reaching the vicinity of the surface of the chip 4 and reflected from the circuit pattern is absorbed by the tungsten particles 12 or is significantly distorted by the concave portions 4E and the convex portions 4F.

That is, the absorption of the observation light and the reflected light, and the reflection of the light which disturbs the normal observation due to the irregular reflection,
Refraction, scattering, etc. occur. Observation light that has entered the medium, such as a film or a plate, that covers the portion of the integrated circuit 4B in which information is stored, from the observer's air or vacuum,
When the boundary surface is smooth compared to the wavelength of the observation light, it is specularly reflected and cannot enter the coating material, or it is refracted and enters the coating material. In the case of specular reflection, light does not reach the integrated circuit 4B, which is the object to be observed, so normal observation is hindered. When refracted, it reaches the object to be observed,
With that image information, it travels backward through the coating material and escapes into the medium where the observer is. At this time, the object to be observed can be seen, but if the size of one reflecting surface is sufficiently smaller than the size required to grasp the shape of the object to be observed or its outline, normal observation is possible. Disturbed. When the unevenness of the boundary surface is equal to or larger than the wavelength, the reflected light travels in various directions, and diffuse reflection in a narrow sense occurs,
Normal observation is disturbed. That is, if the irradiation trace 4D and the diameter of the tungsten particles 12 are matched with the wavelength of the observation light, diffuse reflection of the observation light effectively occurs.

Thus, the irradiation traces 4 arranged in a grid pattern
Since an accurate observation image of the integrated circuit 2 in the vicinity of the surface of the chip 4 cannot be obtained by the aggregate of D, in the IC card having the aggregate of the irradiation traces 4D, the integrated circuit pattern forming the IC card is formed. Also, it is possible to easily prevent illegal acts such as deciphering the memory division method and falsification of the stored information.

Further, since the diameter of the converging laser beam A used for processing the coating film 10 can be narrowed down from several tens of nm to several tens of μm, it is possible to process the size which is likely to cause scattering and irregular reflection of infrared light. There are suitable advantages. Further, since the energy can be injected into a minute position with high density by the converging laser beam A, there is an advantage that the tungsten particles 12 as the light shielding material are easily fused and a trace of melting generated by irradiation is easily formed.

Further, since the condensing laser beam A is used as the energy beam, the spattering phenomenon is not accompanied, so that the adverse effect of scattered dust can be prevented,
Further, since the laser beam A can be irradiated in a normal pressure atmosphere without being limited to the vacuum atmosphere, the aggregate of the tungsten particles 12, the concave portions 4E and the convex portions 4F can be formed by a simple process.

Further, since the tungsten particles 12 are dispersed in the binder 11 and dropped together with the binder 11 and a liquid phase carrier such as a solvent to form a film, the laser beam A is cut even after cutting into chips. It has the advantage that it can be processed by. Therefore, it is possible to form an aggregate in a chip state even on a semiconductor substrate that is ground and polished to a thickness of 100 μm or less, which makes handling in a wafer form extremely difficult. Further, this processing has a property that no special external force is applied to the silicon wafer 1,
An aggregate can be formed even on a thin wafer that has been ground and has low strength. Moreover, since it is possible to form a film in the atmosphere and control the material supply amount in an extremely wide range, there is an advantage that the light-shielding material can be easily supplied even after cutting into chips.

Further, since the silicon substrate 4A has a high absorptivity for infrared light and visible light, when the laser beam A is used as the energy beam, melting due to the light absorption of silicon is likely to occur and the tungsten particles 12 are melted. There is an advantage that the formed concave portions 4E and convex portions 4F can be easily formed.

If the particle size of the light-shielding material is smaller than the diameter of the irradiation trace, a light-shielding material having an arbitrary diameter can be used. When using a beam with a fine diameter of 1 μm or less, there are various variations such as reducing the particle size of the light-shielding material according to the beam diameter and thinning the coating film containing the light-shielding material. To do.

Furthermore, tungsten, that is, metal, was used as the light-shielding material. Since the metal has a high light absorption property, the effect of hindering the observation of the integrated circuit 4B can be significantly enhanced.

[Second Embodiment] Next, a second embodiment of the present invention will be described.

FIG. 12 is a schematic sectional view showing the shape of the irradiation trace obtained by the laser beam irradiation according to the second embodiment. In the second embodiment, as the material of the fusible particles, the transparent material particles 13 made of a transparent material having a refractive index different from that of the silicon substrate 41 are used. As this transparent material, for example, there is Si ₃ N ₄ having a larger refractive index than Si which is the material of the silicon substrate 41.

By using such transparent material particles 13, incident observation light B and reflected light C from the integrated circuit 2 are incident.
Is largely diffused by the transparent material particles 13 to prevent the analysis of the integrated circuit 2.

[Third Embodiment] Next, a third embodiment of the present invention will be described.

FIG. 13 is an explanatory diagram for explaining the setting of the irradiation area according to the third embodiment. In the third embodiment, after setting the irradiation trace forming region 30, the irradiation trace forming region 30 is further subdivided in the vertical or horizontal direction to form a large number of stripe-shaped irradiation region portions 31. The width of the irradiation region portion 31 was determined by the diameter of the laser beam A. After this,
The laser beams A were continuously irradiated so as to overlap each other to form an aggregate on the back surface side of the silicon substrate 4A. That is, the striped concave-convex portion 4J having the striped mountain ranges 4H on both sides is formed in the irradiation trace forming region 30 with the striped groove portion 4G formed by continuous irradiation of the laser beam A interposed therebetween.

In this way, an assembly was formed by a large number of stripe-shaped uneven portions 4J. Diffuse reflection of the observation light is generated by the groove portion 4G and the mountain range portion 4H of the aggregate, and further the observation light is generated by the fusion of the tungsten particles 12 formed in the stripe-shaped groove portion 4G and the mountain range portion 4H of the aggregate. Is absorbed, the analysis of the integrated circuit 2 can be prevented.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described.

FIG. 14 is an explanatory diagram for explaining the setting of the irradiation area according to the fourth embodiment. In the fourth embodiment, after the irradiation trace forming area 40 is set, the frame-shaped irradiation area portions 411, 412, ..., 41n are sequentially set inward. The width of the irradiation area portions 411, ..., 41n was determined by the diameter of the laser beam A. After that, the irradiation region portion 41 is continuously irradiated with the laser beam A so that they overlap each other.
The inside of 1 was irradiated to form an aggregate on the back surface side of the silicon substrate 4A. As a result, a frame-shaped concave-convex portion 4M having frame-shaped mountain ranges 4L on both sides was formed in the irradiation trace region 40 with the frame-shaped groove portion 4K formed by the irradiation of the laser beam A interposed therebetween. In the same manner, quadrangular uneven portions were formed in the frame-shaped irradiation area portions 412, ..., 41n.

In this way, an assembly was formed by n square irregularities. Diffuse reflection of observation light occurs due to the frame-shaped groove portion and mountain range portion of this aggregate, and further,
Since the observation light is absorbed by the fusion product of the tungsten particles 12 formed in the frame-shaped groove portion and the mountain range portion of the aggregate, analysis of the integrated circuit 2 can be prevented.

[Fifth Embodiment] Next, a fifth embodiment of the present invention will be described.

FIG. 15 is an explanatory diagram for explaining the setting of the irradiation area according to the fifth embodiment. In the fifth embodiment, after setting the irradiation trace forming area 50, the spiral irradiation area portion 51 is set. The width of the spiral irradiation area portion 51 is
It was determined by the diameter of the laser beam A. Then, the laser beam A was continuously irradiated so as to overlap. That is, sandwiching the spiral groove portion 4N, both sides of the spiral mountain range portion 4
A spiral stripe-shaped uneven portion Q of P was formed in the irradiation trace forming region 50.

In this way, an assembly was formed by the spiral stripe-shaped uneven portions Q. Diffuse reflection of observation light occurs due to the spiral groove portion 4N and the mountain range portion 4P of the aggregate, and further, due to the fusion of the tungsten particles 12 formed in the spiral groove portion 4N and the mountain range portion 4P of the aggregate. Since the observation light is absorbed, the analysis of the integrated circuit 2 can be prevented.

Although the first to fifth embodiments have been described above, the present invention is not limited to these embodiments. For example, the first to fifth embodiments
Then, the silicon substrate 4A is used, but the substrate is not limited to silicon. In other words, if the transparency of the substrate with respect to the observation light beam of a specific wavelength becomes high, and the collection of the irradiation traces 4D on the back surface side of the substrate can enhance the absorption, diffuse reflection and scattering of these light beams, The invention can be applied. Therefore, it goes without saying that the present invention can be applied to various compound semiconductors.

In the first embodiment, tungsten is used as the light shielding material, and in the second embodiment, Si ₃ N ₄ is used as the transparent material. However, fusible particles made of the light shielding material or the transparent material are used. Due to its action, if the material has a strong absorption and opacity for wavelengths ranging from visible light to infrared light, or has a function of giving scattering or irregular reflection due to the refractive index or the uneven shape of the material surface, etc. Good. Further, even a material such as SiO ₂ which is transparent to visible light diffusely reflects the observation light depending on its shape, so that a material such as SiO ₂ can also be used.

As the light-shielding material, a metal having a high reactivity with silicon, such as titanium, molybdenum, or nickel, may be used instead of tungsten. In this case, at the time of fusion at a high temperature by energy beam irradiation, a reaction occurs between these metals and the fusion product of the silicon substrate 4A, and the recesses and protrusions of the aggregate contain silicides of these metals. Since metal silicide has a property that it is more difficult to remove metal silicide from a silicon substrate by chemical etching with good selectivity as compared with a metal alone, these pits and protrusions that obstruct circuit observation are removed, It has the advantage of making it difficult to obtain a smooth silicon surface.

Further, the film containing the light-shielding material was formed on the back surface of the chip after being mounted on the IC card substrate. However, there is a change such that the film forming step is performed in a wafer state before cutting into the chip. It's extremely easy.

Further, although the processing by the laser beam A is shown, an ion beam, an electron beam or the like may be used as the beam capable of fusion bonding, in addition to the laser beam A.

[0070]

As described above, according to the invention according to claim 1, a fused substance is formed even when infrared light for observation is irradiated from the back side of the substrate. The infrared light is absorbed or diffusely reflected by the aggregate of the irregular reflection parts, and the reflected light from the integrated circuit arranged on the front surface of the substrate is absorbed or disturbed from the back surface of the substrate. I can't get it. As a result, it becomes possible to prevent illegal acts such as decoding of the integrated circuit pattern arranged on the surface of the substrate, stored information of the integrated circuit, and falsification of the stored information.

According to the inventions according to claims 2 and 3, when the material of the fusible particles is a light-shielding material, and particularly when the light-shielding material is a metal material, high light due to the fusion product of the metal material is obtained. The absorptivity and the high diffuse reflectance due to the depressions and projections of the irradiation trace overlap each other, so that the light blocking function can be more effectively generated.

According to the invention of claim 4 , when the substrate material is silicon and the light-shielding material contains a metal, the fusion product of the irradiation trace can be composed of a metal silicide. Obstruct circuit observation,
It becomes most difficult to selectively remove the aggregate of the irradiation traces on which the fused material is formed from the silicon substrate by the chemical etching technique. Furthermore, since the high light absorption due to the metal material and the high diffuse reflection due to the depressions and projections of the irradiation trace can be obtained, the light shielding function can be most effectively generated.

According to the fifth aspect of the present invention, the fusible particles are supplied to the back surface of the substrate in the form of a coating film, and the energy beam is irradiated onto the coating film to form the depressions formed on the back surface of the substrate. And, the protrusion and the fusion product in which the fusible particles are fused with the back surface of the substrate can be formed as an irradiation trace. Therefore, since the coating film forming step is not affected by the area of the substrate, the assembly is not limited to the shape of a semiconductor substrate such as a wafer, and even in the case of a chip-shaped substrate, the aggregate can be efficiently applied to the back surface of the substrate. It is possible to form it.

According to the inventions of claims 6 and 7, when a light-shielding material is used as the material of the fusible particles, and particularly when a metal is used as the light-shielding material, a high light-absorbing property due to the light-shielding material, The high diffuse reflection due to the formation of the dents and projections of the irradiation traces overlap, and the light blocking function can be more effectively generated.

According to the invention of claim 8 , the coating film can be formed in a step of supplying the material of the coating film containing the light-shielding material onto the substrate, for example, a step of dropping a carrier agent, and divided into chips. The aggregate can also be formed on the substrate after the above by a simple process.

According to the invention of claim 9 , since a converging laser beam is used as the energy beam, it is possible to avoid an adverse effect of scattered dust without accompanying a sputtering phenomenon. Also, without being limited to the vacuum atmosphere,
Since the irradiation can be performed in a normal pressure atmosphere, there is an advantage that the aggregate can be formed by a simple process.

[0077] According to the invention according to claim 1 0, 1 1, an energy beam separated in a mesh shape or a stripe shape, so that irradiates the irradiation region portion of the irradiated region, and in close array of radiation traces, It is possible to reliably generate light absorption and diffuse reflection.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a manufacturing process of a semiconductor device according to a first embodiment.

FIG. 2 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 3 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 4 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 5 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 6 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 7 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 8 is a schematic cross-sectional view showing the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 9 is an explanatory diagram illustrating setting of an irradiation area according to the first embodiment.

FIG. 10 is a schematic cross-sectional view showing the shape of an irradiation trace obtained by laser beam irradiation according to the first embodiment.

FIG. 11 is a perspective view of an IC chip having a recess and a protrusion formed by the manufacturing process of the semiconductor device according to the first embodiment.

FIG. 12 is a schematic cross-sectional view showing the shape of an irradiation trace obtained by laser beam irradiation according to the second embodiment.

FIG. 13 is an explanatory diagram illustrating setting of an irradiation area according to the third embodiment.

FIG. 14 is an explanatory diagram illustrating setting of an irradiation area according to the fourth embodiment.

FIG. 15 is an explanatory diagram illustrating setting of an irradiation area according to the fifth embodiment.

FIG. 16 is a perspective view for explaining a defense technique using a conventional mechanical grinding method.

FIG. 17 is a schematic cross-sectional view showing a process of forming a diffused reflection surface on the back surface of a substrate by using a conventional chemical etching method.

[Explanation of symbols]

1 Silicon Wafer 1A Cut Part 2 Integrated Circuit 3 Bump 4 Chip 4A Silicon Substrate 4B Integrated Circuit 4C Backside 4D Irradiation Trace 4E Recess 4F Convex 4G Striped Groove 4H Striped Mountain Range 4J Striped Uneven 4K Frame Shape Groove part 4L Frame-shaped mountain range part 4M Frame-shaped irregular part 4N Spiral groove part 4P Spiral mountain range part 5 IC card substrate 6 Electrode 7 Underfill agent 10 Coating 11 Binder 12 Tungsten particle 13 Transparent material particle 20, 30, 40, 50 Irradiation trace forming area 21 Mesh-shaped irradiation area portion 22 Irradiation area 31 Stripe-shaped irradiation area portions 411 to 41n Frame-shaped irradiation area portion 51 Spiral irradiation area portion 101 Glass substrate 102 Diffuse reflection surface 110 silicon wafer 111 SiO ₂ film 112 SiO ₂ pattern 113 d Quenching bottom 114 inclined surface 115 valleys 116 opening 117 diffuse surface 118 flat part

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Ogawa 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Masahiko Maeda 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo No. Nippon Telegraph and Telephone Corporation (56) Reference JP 62-183151 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/822 H01L 27/04 H01L 21 / 58

Claims (11)

(57) [Claims] 1. A semiconductor device in which an integrated circuit is arranged on a front surface of a substrate, and an aggregate formed by forming a plurality of irregular reflection portions on a back surface of the substrate, the irregular reflection portions including recesses and protrusions for irregularly reflecting incident light. fusible particles melt in the rear surface of the substrate, wherein the irregular reflection portion of the recess and is formed by adhering to the surface of the protrusion fusion-bonded particle
A semiconductor device provided with a child , wherein the irregular reflection portion is formed by irradiating a focused energy beam.
Is the irradiation trace formed on the back surface of the substrate,
The fusion particle is melted by the energy beam.
The fusible particles melt on the backside of the substrate, leaving a trace of each irradiation.
A semiconductor device characterized by being formed by adhesion . 2. The semiconductor device according to claim 1, wherein the material of the fusible particles is a light-shielding material. 3. The semiconductor device according to claim 2 , wherein the light shielding material is a metal. Wherein said substrate is made of silicon, according to claim 3, wherein the fused matter characterized in that it comprises a silicide of the metal
The semiconductor device according to. 5. A method of manufacturing a semiconductor device in which an integrated circuit is arranged on a front surface of a substrate, wherein a coating film containing fusible particles that are melted by a focused energy beam is formed on the back surface of the substrate, Is irradiated to the coating film in large numbers to form an aggregate of irradiation traces, and the fusible particles are melted on the back surface of the substrate by the energy beam,
A method for manufacturing a semiconductor device, characterized in that it is adhered to each of the irradiation traces as a fusion material. 6. The method of manufacturing a semiconductor device according to claim 5 , wherein a light-shielding material is used as the material of the fusible particles. 7. The method of manufacturing a semiconductor device according to claim 6 , wherein a metal is used as the light shielding material. 8. The material of the coating film containing the light-shielding material, a method of manufacturing a semiconductor device according to claim 6 or 7, characterized in that deposited onto the back surface of the substrate using the transfer agent in the liquid phase . Wherein said energy beam is a method of manufacturing a semiconductor device according to any one of claims 5 to 8, characterized in that a light collecting laser beam. 10. An irradiation area set on the back surface of the substrate is divided into a mesh shape, and each energy-irradiated area portion is sequentially irradiated with the energy beam to arrange crater-like irradiation traces. 6. The method according to claim 5, wherein
The method of manufacturing a semiconductor device according to any one of 9. 11. An irradiation region set on the back surface of the substrate is divided into stripes, and the irradiation region portions divided into stripes are continuously irradiated with the energy beam to form stripe-shaped depressions and protrusions. any of claims 5 to 9, characterized in arranging the irradiation traces consisting of
Item 1. A method of manufacturing a semiconductor device according to item 1 .