JPH11163261A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device having irregular reflection surface and the manufacturing method thereof, which is capable of preventing unautorixzed acts, such as the tampering and the like for decoding and the memory information of the pattern of an integrated circuit which constitutes the semiconductor device, performed by having infrared rays irradiated from the side of the back surface of a substrate which constitutes the semiconductor device, even in the semiconductor device having a substrate with a thin plate thickness and the substrate cut into chip shapes. SOLUTION: In this semiconductor device, the irregular reflection of the light inputted from the side of a back surface 2 is promoted to the back surface 2 of a substrate 1 in the semiconductor device, in which an integrated circuit is arranged on the surface of the substrate 1. The assembly of an indentation 4 and a projection constituted of a plane, not in parallel with the surface of the substrate 1, is provided. In a manufacturing method of this semiconductor device, the indentation and the projection are formed by having the many points of the back surface 2 of the substrate 1 irradiated with the focused energy beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device and a method for manufacturing the same. More specifically, a semiconductor capable of preventing illegal acts such as decoding of an integrated circuit pattern constituting a semiconductor device and falsification of stored information, which are performed by irradiating infrared light from the back side of a substrate constituting the semiconductor device. The present invention relates to an apparatus and a method for manufacturing the same. INDUSTRIAL APPLICABILITY The present invention is suitably used for a semiconductor device having a function of storing and processing important information such as personal privacy and money used in an IC card or the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, attention has been paid to a semiconductor device having a function of storing and processing important information such as personal privacy and money used in an IC card or the like, and research and development for realizing the semiconductor device have been attracting attention. It is progressing rapidly.

In order to develop a semiconductor device having the above-mentioned functions, the functions, operating methods, and circuit functions of an integrated circuit (IC) constituting the semiconductor device have been developed for the purpose of improving design and manufacturing techniques and investigating causes of defective products. Techniques for analyzing methods, circuit patterns, stored data, and the like are essential. Conventionally, as one of the analysis methods, a method of observing an IC chip surface on a substrate constituting a semiconductor device with an optical microscope and reading a circuit pattern has been used. For fine patterns of 1 μm or less, since the wavelength of the observation light is close to the pattern width, a laser beam with a relatively short wavelength is used to reduce the effect of diffraction, and the resolution and depth of focus are improved. I have been. However, as the number of wiring layers increases, it is necessary to remove the upper film in order to accurately read the lower wiring pattern.
There is a defect that observation is not possible without destruction while C is operated. In addition, an EEPROM (Electrically Erasa
Since the data of the bleedable programmable read only memory (MEM) is stored in the gate electrode of the lowermost MOS transistor, observation from the front side of the IC chip is not always effective means for observing these circuits.

As a method for supplementing such a method using an optical microscope, for example, there is a method of observing a circuit near the chip surface in a non-destructive manner from the back side of the IC chip. In other words, a method of using infrared light having a wavelength that is hardly absorbed by a silicon wafer, which is a substrate of an IC chip, as an observation light source and increasing the transparency of the wafer so that a wiring pattern mainly made of metal can be observed through the wafer from the back side. is there. According to this method, the pattern of the lowermost transistor and the first transistor
The wiring pattern of the layer can be observed nondestructively. In particular, in recent high-density mounting technology, a bump electrode is formed on the front side of an IC chip for electrical connection with a mounting substrate, and a method of connecting the IC chip to the mounting substrate by turning over the IC chip is adopted. I have. Therefore, in the mounted state, the back surface of the IC chip is exposed to the outer surface, and pattern observation from the back surface side becomes easier than the front surface side of the IC chip. Conventionally, the back surface of an IC chip has only been coated with an epoxy film or the like for protecting the chip, and has been in a state where it can be relatively easily removed with a chemical.

On the other hand, the above-mentioned method, that is, a technique for analyzing the function, operation method, circuit method, circuit pattern, stored data, etc. of an integrated circuit (IC) constituting a semiconductor substrate, is a technique capable of protecting against misuse. Development is required.
For example, a semiconductor device having a function of storing and processing important information such as personal privacy and money used in an IC card or the like is an essential technology for widespread use.

Conventionally, as a method for protecting information stored not only on a semiconductor substrate but also on a portion generally covered with a film or a plate from observation by optical means, the following method is used to protect the surface or the back of the film or substrate. A method of forming a diffuse reflection surface has been used.

FIG. 4 shows a conventional mechanical grinding method.
It is a typical bird's-eye view of the board | substrate which provided the irregular reflection surface on the surface.
For example, in the case of forming the irregular reflection surface 12 having a 45-degree angle, the surface of the glass substrate 11 can be obtained by grinding the surface of the glass substrate 11 using a grinder having a 45-degree inclined blade containing an abrasive. The pitch of the unevenness can be set to a size of about 1 mm. In this example, the angle may be set to 45 degrees, and the thickness of the glass substrate is required to be at least 1 mm.

However, a substrate, such as an IC chip, on which a pattern with a fine line width of 1 μm or less is drawn, generally has a size of 1 m.
m or less is the mainstream. For example, in the case of a silicon substrate, a thickness of about 200 μm is generally used by further grinding from 600 μm. Therefore, to form a diffuse reflection surface on an information medium on which information such as an IC chip is drawn at a high density,
There is a problem that the above-described grinding method using a grinder cannot be applied.

FIG. 5 is a schematic cross-sectional view showing a process of forming a diffuse reflection surface on the back surface of a substrate by using a conventional chemical etching method. As a substrate, a silicon wafer 21 having a (100) plane is prepared (FIG. 5A), and a 2 μm-thick SiO ₂ film 22 is deposited on the back surface using a chemical vapor deposition method (CVD method). (FIG. 5 (b)). Next, the SiO ₂ film 22 is processed into a stripe shape by using a photolithography technique to form an SiO ₂ pattern 23 (FIG. 5C).
Thereafter, the silicon wafer 21 is chemically etched in an aqueous solution of ethylenediamine using the SiO ₂ pattern 23 as a mask, whereby an inclination is formed at an angle of about 55 degrees from the wafer surface, and the etching bottom surface 2 of (100) plane is formed.
4 sinks downward as the etching progresses (FIG. 5).
(D)). Eventually, the slopes on both sides collide with each other and the etching is automatically stopped to form a substantially V-shaped valley 25 (FIG. 5).
(E)). Then, the irregular reflection surface having the opening 26 is formed by removing the SiO ₂ pattern 23 with hydrofluoric acid (FIG. 5F).

However, this method has the following problems. (1) Since the silicon wafer 21 is chemically etched using the SiO ₂ pattern 23 as a mask, a flat portion 27 remains in a region of the back surface of the substrate where the mask is removed after the etching, and this region 27 is parallel to the substrate surface. The positional relationship is maintained. Therefore, by using this region 27, there is a possibility that an infrared light is irradiated from the back surface side of the substrate to perform an illegal act such as decoding of an integrated circuit pattern constituting the semiconductor device or falsification of stored information. Was.

(2) In this method, since a photolithography technique is used, it is necessary to put a whole circular wafer having a diameter of, for example, 6 inches into a processing step. However, since the wafer strength is reduced after the wafer thickness is reduced by grinding the back surface of the wafer, such a wafer is subjected to photographic etching technology including processes such as washing with water, immersion in an acid solution, and spin drying. Very difficult to apply. In addition, in order to process a wafer with reduced strength, there is a disadvantage that a complicated process such as attaching the wafer to another protective substrate is required. further,
Once the wafer has been cut into chips, the photolithography technique cannot be applied.

As described above, according to the conventional method of forming a diffuse reflection surface on a substrate, there are the following problems. In other words, the mechanical grinding method has a point that fine processing cannot be performed on a thin substrate, and the chemical etching method has
The region from which the mask has been removed has a point that the positional relationship parallel to the substrate surface is maintained, and there is a point that it is difficult to process the wafer substrate cut into chips.

Therefore, in the conventional method of forming a diffuse reflection surface on a substrate constituting a semiconductor device, diffuse reflection cannot be easily formed on a substrate having a small thickness or a substrate cut into chips. Therefore, once observation or analysis is performed from the back of the chip for the purpose of illegal acts such as decoding of an integrated circuit pattern constituting the semiconductor device or falsification of stored information, there is a problem that it is difficult to prevent the conventional technique.

[0014]

SUMMARY OF THE INVENTION The present invention relates to a semiconductor device comprising a thin substrate or a substrate cut into chips, which is provided by irradiating infrared light from the back side of the substrate constituting the semiconductor device. It is an object of the present invention to provide a semiconductor device having a diffuse reflection surface capable of preventing illegal actions such as decoding of an integrated circuit pattern constituting the semiconductor device and falsification of stored information, and a method of manufacturing the same.

[0015]

According to the present invention, there is provided a semiconductor device comprising:
In a semiconductor device in which an integrated circuit is provided on a surface of a substrate, a back surface of the substrate, which promotes irregular reflection of light incident from the back surface side, a recess formed of a surface non-parallel to the surface of the substrate, It is characterized in that a set of projections is provided.

By providing the aggregate of depressions and projections having the above-described structure on the back surface of the substrate, even if infrared light is irradiated from the back surface of the substrate, the light incident from the back surface is irregularly reflected. On the back side of the substrate, the reflected light from the integrated circuit disposed on the surface of the substrate can be obtained only in a disturbed form. Therefore, illegal acts such as decoding of the integrated circuit pattern disposed on the surface of the substrate and falsification of stored information can be prevented.

In the above feature, it is preferable that the cross-sectional shape of the depression is substantially V-shaped, since diffused reflection of light incident from the back side of the substrate occurs most effectively.

According to a method of manufacturing a semiconductor device of the present invention, an integrated circuit is provided on a front surface of a substrate, and irregular reflection of light incident from the back surface is promoted on the back surface of the substrate. In a method of manufacturing a semiconductor device provided with an aggregate of dents and projections formed of parallel surfaces, the dents and projections are formed by irradiating a focused energy beam to a plurality of points on the back surface of the substrate. And

By irradiating the focused energy beam to a plurality of points on the back surface of the substrate, a dent is formed on the back surface of the substrate, and a substance transferred from the dent is deposited on the periphery of the dent to form a projection. can do. Therefore, according to the method of the present invention, it is possible to efficiently form an aggregate of depressions and projections formed of a surface that is not parallel to the surface of the substrate on the back surface of the substrate.

In particular, it is preferable to use a condensing laser beam as the energy beam because a V-shaped recess having a high degree of irregular reflection and scattering of light can be easily formed. Since the sputtering phenomenon is not used, there is also an advantage that the adverse effect of the scattered dust is small.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a schematic sectional view showing a manufacturing process of a semiconductor device according to the present invention. FIG. 2 is a schematic cross-sectional view showing the number of laser beam irradiations and the shapes of the obtained dents and protrusions. FIG. 3 is a schematic view of the back surface of an IC chip in which depressions and protrusions are formed by using the method according to the present invention.

Hereinafter, description will be made in accordance with the procedure of the manufacturing process. (1) First, a semiconductor device having an integrated circuit having a chip size of 4 mm square was formed on the surface of a silicon wafer having a diameter of 6 inches using a thin film deposition technique and a photolithography technique. The thickness of the wafer was 625 μm, and the line width of the minimum pattern was 0.5 μm. As an integrated circuit, in addition to an 8-bit central processing unit, 1 kilobyte of RAM (Random Acces
s Memory), 8 KB ROM (Read Only Memor)
y), and 8 kilobytes of non-volatile EEPROM. A passivation film made of Si ₃ N ₄ and SiO ₂ for surface protection was formed on the surface of the wafer, and the wafer pretreatment step was completed. Then, the wafer back surface is ground to grind the wafer substrate 1
Was cut into chips having a thickness of 200 μm (FIG. 1).
(A)).

(2) Next, the back surface 2 of the substrate according to the present invention
A step of forming unevenness on the side was performed. That is, a chip was loaded into a laser marker device so that the back surface 2 of the wafer substrate was irradiated with a laser, and a converging laser beam 3 was irradiated to form irregularities on the back surface 2 of the wafer substrate (FIG. 1B). .
As a laser light source, an Nd-doped YAG laser equipped with an ultrasonic Q switch using a laser diode as an excitation light source was used. Wavelength used was 532nm second harmonic, the pulse oscillation mode single mode TEM _00, an output energy is 16MyuJ, pulse width is 1 kHz 25 nsec
It was as follows.

(3) The optical system was controlled by a galvanometer type beam positioner (not shown). The light of the laser beam was stopped down by a lens (not shown) and focused on the depth of a dent formed on the back surface 2 of the wafer substrate (FIG. 2B). A predetermined irradiation position was irradiated with three pulses (FIG. 2 (b):
(After irradiation of the first pulse → FIG. 2 (c): After irradiation of the second pulse → FIG. 2 (D): After irradiation of the third pulse).

(4) Due to the processing in the above step (3), a circular crater-shaped depression (recess) is formed on the back surface 2 of the wafer substrate.
4 was formed. The silicon was melted by the heat due to the absorption of the laser beam, the central portion was dented and the melt was pushed to the peripheral portion, and the peripheral portion was formed with a portion (convex portion) 5 protruding from the back surface of the wafer 1 ( FIG. 2 (d), FIG. 1 (c)
(Enlarged view shown in a circle). Hereinafter, the concavo-convex portion formed of the combination of the concave portion 4 and the convex portion 5 is referred to as an irradiation trace. The average uneven shape was as follows: the diameter: L was 60 μm, the depth of the concave portion from the wafer surface: D was 5 μm, and the height of the peripheral convex portion: H was 3 μm. The cross-sectional shape of the concave portion is substantially V
A letter-shaped shape was obtained (the enlarged view shown in the circles of FIGS. 2D and 1C).

FIG. 3 is a schematic view of the back surface of an IC chip on which concavities and convexities have been formed using the method described above. In FIG. 3, 1
Is an IC chip made of a Si substrate, and a large number of crater-shaped irregularities are formed adjacently on the back surface 2 of the chip 1. The concavo-convex formation region 6 is a back surface corresponding to the chip surface position on which the EEPROM is formed, and has a surface area of about 2 × 3 mm ² . The concave portions (V-shaped concave portions) 4 were arranged adjacent to each other at intervals of about 60 μm so as to have a close-packed structure.

In the manufacture of an IC card, which is an example of a semiconductor device, the IC chip obtained by the above process is mounted on a glass epoxy substrate by flip chip technology with the chip surface facing down. Further, the exposed chip back surface was coated with an epoxy resin to protect the chip, and the entire chip was covered with a card base material made of vinyl chloride resin to complete an IC card.

The information of the IC card manufactured by such a process is illegally analyzed by the following procedure. First, a part of the vinyl chloride on the surface of the IC card and the base material made of epoxy resin are dissolved with heated fuming nitric acid,
Expose the back of the chip. In the prior art, at this stage, infrared light of a He-Ne laser having a wavelength of
The back surface of the chip is scanned by condensing light to a size of not more than μm, and the back surface of the chip is observed with a microscope that detects reflected light with a photodiode. Thereby, the transistor circuit and the first layer wiring near the chip surface can be observed. However, in the case of the IC card having the uneven shape according to the present invention, the back surface of the chip is irradiated with an energy beam, and is formed of a surface that is non-parallel to the surface of the substrate, which promotes irregular reflection of light incident from the back surface side. Due to the formation of the concavo-convex shape formed by the aggregate of the depressions and projections, the reflected light from the circuit pattern near the chip surface is significantly distorted, and an accurate observation image cannot be obtained. Therefore, in the semiconductor device having an uneven shape (for example, an IC card) according to the present invention, illegal acts such as decoding of an integrated circuit pattern constituting the semiconductor device and falsification of stored information can be easily prevented.

In the above embodiment, a condensing laser beam is used as an energy beam. However, any other energy beam may be used as long as a crater-like depression can be formed. Specific examples include an electron beam and an ion beam. As an example, a case where unevenness for irregularly reflecting light is formed using an electron beam will be described. Using a tungsten hairpin type thermoelectron emission source, an electron beam was extracted with an electrostatic field while being heated, accelerated at 30 kV, and set to a beam current of 100 μA and a beam diameter of 1 μm. By scanning this beam on the back surface of the IC chip under computer control, a part of the surface of the silicon substrate was melted based on the heating effect of the electron beam to form a groove. By adjusting the drawing data on the computer, a groove having a depth of 2 μm and a width of 4 μm was obtained. By arranging the grooves at a periodic interval of 4 μm, a substantially striped uneven structure could be formed on one surface of the back surface of the wafer.

The method using a condensing laser beam has an advantage that a V-shaped recess having high irregular reflection and scattering of light can be easily formed. Further, since the melt by the laser beam is pushed to the periphery to form a projection, the efficiency of irregular reflection of light is further improved. In general, since a silicon substrate has high absorption of infrared light and visible light, there is an advantage that melting due to light absorption of silicon is easily caused by using a condensing laser beam as an energy beam. further,
Since the sputtering phenomenon is not used, the adverse effect of the scattered dust is small.

In addition, the above-mentioned irradiation traces may be arranged not only in the form of a circular crater but also in a continuous groove-like manner, and may be arranged in the form of stripes in close proximity. Furthermore, when a beam with a fine diameter of 1 μm or less is used, various variations or combinations thereof, such as forming a substantially V-shaped groove having a width of several μm by connecting a number of traces from a shallow to a deep one, etc. No problem.

Further, in the above two embodiments, beam processing is performed on the back surface after cutting into chips, but it is needless to say that beam processing may be performed with the wafer shape before cutting.

According to the present invention, on the back surface of the substrate, there is provided a concave-convex shape formed of an aggregate of depressions and projections formed of a surface non-parallel to the front surface of the substrate, which promotes irregular reflection of light incident from the rear surface side. However, it is the most preferable form that the recess is formed in a substantially V shape because light can be efficiently diffused and reflected efficiently.

In the above embodiment, an example using a silicon substrate has been described, but the substrate is not limited to silicon. That is, the present invention can be applied as long as the transparency of the substrate is increased with respect to the observation light beam having a specific wavelength, and irregular reflection and scattering of these light beams can be enhanced by unevenness on the back surface of the substrate. Therefore, it is needless to say that the present invention can be applied to various compound semiconductors.

[0035]

As described above, according to the first aspect of the present invention, even if infrared light is irradiated from the back side of the substrate, the light incident from the back side is irregularly reflected. On the back side of the substrate, a semiconductor device is obtained in which the reflected light from the integrated circuit disposed on the front surface of the substrate can be obtained only in a disturbed form. As a result, the integrated device disposed on the front surface of the substrate is obtained. It is possible to prevent illegal acts such as decoding of circuit patterns and falsification of stored information.

According to the second aspect of the present invention, by making the cross-sectional shape of the dent substantially V-shaped, diffuse reflection of light incident from the back side of the substrate can be generated most effectively.

According to the third aspect of the present invention, a dent can be formed on the back surface of the substrate, and a substance transferred from the dent can be deposited around the dent to form a projection. Therefore, according to the present invention, it is possible to efficiently form an aggregate of depressions and projections formed of a surface that is not parallel to the surface of the substrate on the back surface of the substrate.

According to the fourth aspect of the present invention, it is possible to easily form a V-shaped recess having a high degree of irregular reflection and scattering of light. Further, since the sputtering phenomenon is not used, the adverse effect of the scattered dust hardly occurs.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a manufacturing process of a semiconductor device according to the present invention.

FIG. 2 is a schematic cross-sectional view showing the number of laser beam irradiations and the shapes of the obtained dents and protrusions.

FIG. 3 is a schematic view of the back surface of an IC chip in which a depression and a projection are formed by using the method according to the present invention.

FIG. 4 is a schematic bird's-eye view of a substrate provided with a diffuse reflection surface on the surface using a conventional mechanical grinding method.

FIG. 5 is a schematic cross-sectional view showing a step of forming a diffuse reflection surface on the back surface of a substrate by using a conventional chemical etching method.

[Explanation of symbols]

Reference Signs List 1 substrate, 2 back surface of substrate, 3 laser beam, 4 dent (concave portion), 5 raised portion (convex portion), 6 irregularity forming region, 11 glass substrate, 12 diffuse reflection surface, 21 silicon wafer, 22 SiO ₂ film, 23 SiO ₂ pattern, 24 etched bottom, 25 substantially V-shaped valley, 26 opening, 27 flat portion remaining after removing SiO ₂ pattern 23.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeo Ogawa 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Masahiko Maeda 3-19, Nishishinjuku, Shinjuku-ku, Tokyo 2 Nippon Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. A semiconductor device having an integrated circuit disposed on a surface of a substrate, the surface of the substrate having a surface non-parallel to the surface of the substrate for promoting irregular reflection of light incident from the rear surface. A semiconductor device provided with an aggregate of the formed depressions and projections. 2. The semiconductor device according to claim 1, wherein the recess has a substantially V-shaped cross section. 3. An integrated circuit is provided on a front surface of the substrate, and diffused reflection of light incident from the rear surface side is promoted on the back surface of the substrate.
In a method for manufacturing a semiconductor device provided with an aggregate of dents and projections formed of a plane not parallel to the surface of the substrate, the dents and projections irradiate a focused energy beam to a plurality of points on the back surface of the substrate. A method for manufacturing a semiconductor device, comprising: 4. The method according to claim 3, wherein the energy beam is a converging laser beam.