KR100281241B1 - Plasma etching by changing the lattice plane of the top of Faraday box - Google Patents

Abstract

In the processing of semiconductors, optoelectronics and micromechanical devices, it is necessary to arbitrarily adjust the angle of the etching wall surface. According to the present invention, when a Faraday box having various shapes of lattice planes is installed in a plasma etching apparatus and a substrate to be etched is placed inside the box, ions incident through the lattice plane of the Faraday box face the substrate surface in various directions. It relates to a method of arbitrarily adjusting the angle of the etch wall surface by making it.

The substrate to be etched is placed inside a conductive Faraday box consisting of one or more lattice planes. By using a Faraday box with the lattice plane parallel to the substrate surface, an etch wall that is more perpendicular to the conventional plasma etching method can be obtained.If the lattice surface is fixed at a certain angle with respect to the substrate surface, An etching cross section inclined by this angle can be obtained. In addition, using a Faraday box with two lattice planes joined together at a constant angle, it is possible to make a grating with continuous V grooves on the surface of the substrate. By using a Faraday box having a curved lattice surface, etching can be performed by varying the etching direction and the etching speed according to the position of the substrate surface. In addition, by using a Faraday box having a conductive top plate engraved with an open pattern instead of a lattice plane, an accurate pattern etching can be directly performed without using a sensitizer molecule on the substrate surface.

In the case of etching a wafer having a large diameter as a substrate in a semiconductor processing process, etching and etching depths of the etch cross section must be uniformly performed at all positions of the substrate in order to improve process yield. In the plasma etching method, non-uniform etching gas flow or non-uniform distribution of charged particles are the main causes for preventing uniform etching.

When using a Faraday box having a double curved lattice plane or a Faraday box with a lattice plane whose lattice size varies depending on the position, the etching direction is maintained at a direction perpendicular to the substrate surface, and the etching rate is arbitrarily changed according to the position. It can be adjusted to implement a uniform etching.

Description

Plasma etching by changing the lattice plane of the top of Faraday box

The present invention relates to a method of etching by controlling the direction of the ions incident on the substrate during the plasma etching process, and can be etched in various directions with respect to the surface of the substrate when using the method of the present invention, and thus various shapes that can be widely applied Etch section can be obtained. In addition, by using the method of the present invention, the etching rate can be arbitrarily adjusted according to the position of the substrate surface while etching in the direction perpendicular to the substrate surface, thereby obtaining a product having a very high uniformity of surface etching during the etching of a large diameter wafer. Can be.

In order to assist in understanding the technical field to which the present invention pertains and its prior art, the following description is made for each item.

1. Plasma

Plasma is the fourth material state connecting solid, liquid, and gas and is also referred to simply as ionized gas. Examples of plasmas range from high temperature plasmas such as the sun's surface or material state in nuclear fission and fusion to low temperature plasmas applied to fluorescent lamps and neon signs. Low temperature plasmas are widely used in semiconductor processes (B. Chapman, ″ Glow discharge processes ″, John Wiley & Sons, New York (1980)).

In general, plasmas used in semiconductor processes are high-frequency power, such as radio waves (300 KHz-30 MHz; KHz = 10 ³ Hz, MHz = 10 ⁶ Hz) or microwaves (300 MHz-30 GHz; GHz = 10 ⁹ Hz). Is produced by hooking the gas into the reactor. The gases used here vary widely, for example, from inert gases without chemical activity, such as helium (He), neon (Ne), argon (Ar), to various fluorocarbons including carbon tetrafluoride (CF ₄ ) (e.g., For example, CHF ₃ , C ₂ F ₆ , C ₄ F _8, etc.) and chlorine compounds such as sulfur hexafluoride (SF ₆ ), fluorine (F ₂ ), chlorine (Cl ₂ ) and boron trichloride (BCl ₃ ) Depending on the application, these gases may be mixed with each other and oxygen (O ₂ ), hydrogen (H ₂ ), and nitrogen (N ₂ ) may be mixed.

When high-frequency energy is delivered to the gas in the reactor, some of the gas becomes ionized and deviates from the original electric neutral state. That is, gas particles that lose electrons that are negatively charged become positive charges with positive electricity, whereas particles that have electrons become negative charges that have negative electricity. The tendency to lose and gain electrons depends on the nature of each gas. Therefore, the plasma is composed of almost the same amount of positively charged particles and negatively charged particles, and several hundred to tens of thousands of more neutral particles, and as a whole, the effect of the positive and negative charges cancels each other out of the neutral state. it means. Among the particles constituting the plasma, the electrons are very small and only about one-third of the hydrogen atom (H), which is the lightest atom, can easily absorb energy from the external electromagnetic field as kinetic energy. As a result, the fast-moving electrons collide with other gas particles, splitting the originally larger particles into two smaller mass particles (eg CF ₄ + e → CF ₃ + F + e). Particles (CF ₃ or F) that are much more reactive than the gas (CF ₄ ) originally given by. Wherein CF ₄ , CF ₃ and F are all electrically neutral particles, of which CF ₄ is a stable particle and does not react chemically, whereas CF ₃ and F are the outermost angles of carbon atom (C) and fluorine atom (F), respectively. One electron, which failed to bind to the outermost layer, remains very strong in bonding and reacting with other particles. Such particles are particularly called radicals among neutral particles. In addition, positively charged cations are generated during collisions between electrons and other particles (eg CF ₃ + e → CF ₃ ⁺ + e + e, F + e → F ⁺ + e + e), and negatively charged anions (Eg Cl + e → Cl ⁻ ).

Plasma usually emits bright light, due to the energy delivered when electrons in the plasma collide with an atom, causing electrons in the low energy state inside the atom to be excited to a higher energy level and then lower again. This is because the energy is stabilized in an energy state and the energy corresponding to the level difference is emitted in the form of light. However, a very weak area of light is formed on the surface of the object in contact with the plasma, which is called sheath. While the mass of electrons that occupy most of the negative charge is very small, the mobility is large, while the positive cations that make up most of the positive charge have low mobility, so much more electrons accumulate on the surface of the object in contact with the plasma. It is negatively charged. The pushing force acts between the negatively charged surface and the electrons to be introduced, so that the inflow of electrons is suppressed on the surface, and in the case of the cation, the attracting force is acted on, so that the induction of cations is promoted. As such, the influence of the charged surface on the charges decreases rapidly away from the surface due to the characteristics of the plasma to maintain its overall neutrality and disappears when entering the plasma bulk. The distance from the surface to the point where the influence of the surface disappears is called the thickness of the sheath. The thickness of the sheath depends on the various process conditions for generating the plasma, but in the plasma used for semiconductor processing, it is in the range of approximately 0.1-10 mm. The effect of the surface within the thickness of the sheath acts as a downhill path for cations entering the surface but as an uphill path for electrons that are negatively charged, so the concentration of electrons in the sheath is very low compared to the plasma bulk. Therefore, in the sheath, the collision frequency between electrons and other particles is also lowered, and thus, unlike light emission in an area far from the surface, that is, plasma bulk, the light rarely emits light and becomes dark.

On the other hand, since the surface is negatively charged, ions (mostly cations) entering the sheath are accelerated by the electromagnetic force attracted to the surface. In other words, the cations get energy corresponding to the potential difference between the sheath interface and the surface of the object and enter and collide with the surface. At this time, since the sheath is generated parallel to the surface of the object, an equipotential line connected between points representing the same potential in the sheath is also formed parallel to the surface of the object. On the other hand, the direction of electromagnetic force is perpendicular to the equipotential line, which is the direction perpendicular to the contour of the map where the direction of the force acting on the ball by gravity when rolling the ball on the hill is the point. It is the same principle as being. Therefore, ions entering the sheath are accelerated perpendicularly to the surface and are incident.

Plasma bulk, on the other hand, causes some of the highly mobile electrons to escape to the surface of the vessel surrounding the plasma, so that they are slightly neutral and generally carry electricity. Therefore, if the potential surrounding the vessel surrounding the plasma is zero, the potential of the plasma bulk is maintained at approximately 5-30 volts.

2. Plasma Etching

The etching process is a process used to manufacture semiconductor devices, optoelectronic devices, micromechanical devices, and the like, and removes only necessary portions of the substrate surface. The part that should not be removed is covered with a mask. In the early etching process of the semiconductor industry, wet etching was used, in which a substrate was immersed in an acid, an alkali, or a mixed solution thereof and selectively removed by chemical reaction to remove the surface of the substrate, which is not covered by a mask. In recent years it has been replaced by plasma dry etching in most cases (DM Manos and DL Flamm, ″ Plasma Etching ″, Academic Press, California (1989)). In the case of wet etching, the etching is entirely dependent on the chemical reaction, so the etching rate is the same in all directions of the substrate, and as a result, a round etching section is usually obtained. Since the isotropic etching cross section increases as the etching depth increases, the width of the cross section is also unsuitable for the manufacture of semiconductors requiring high integration density of devices.

On the other hand, in the case of the dry etching method using plasma, since the accelerated ions in the sheath of the substrate surface are incident perpendicularly to the surface, the etching speed is largest in the direction perpendicular to the substrate surface. By using such anisotropic etching, it is possible to etch deeply in the vertical direction without etching in the horizontal direction of the substrate surface, which is advantageous for the manufacture of highly integrated circuits.

3. Types of Plasma Etching

One of the most commonly used plasma etchers is a parallel plate plasma etcher (D. M. Manos and D. L. Flamm, Plasma Etching, Academic Press, California (1989)). In the reactor, two electrodes are fixed at regular intervals in parallel to each other. High-frequency power is transmitted to one of the two electrodes, and the other electrode is grounded. When the substrate to be etched is fixed on the ground electrode, it is called plasma etching (PE) in a narrow sense. Since the potential of the ground electrode is fixed at 0 volts, the potential difference of the sheath generated on the ground electrode is about tens of volts (about 30 volts or less), which is the potential of the plasma bulk. Therefore, the ions incident on the substrate placed on the ground electrode transfer only the minimum energy, or lower, enough to accelerate the chemical reaction, and the reactive radicals entering the surface from the plasma bulk mainly contribute to the etching. Since radicals are electrically neutral, they are not accelerated by the sheath and move with equal probability in all directions with energy corresponding to the temperature of the gas phase. When the temperature of the gas phase is 20 ℃, the kinetic energy of the neutral particles is 0.025 volts in terms of potential, which is negligibly small compared to the accelerated ions in the sheath. Therefore, when the substrate is placed on the ground electrode, chemical etching is performed mainly, similar to wet etching, and an etching section close to isotropic is generated.

On the other hand, since a sheath having a large potential difference of several hundred volts is formed on the surface of the electrode to which high frequency power is transmitted, ions having very high kinetic energy are incident in the direction perpendicular to the substrate when the substrate is placed thereon. In this case, the etching method is further subdivided depending on whether or not a reactive gas is used. In the case of using an inert gas such as argon (Ar) that does not react with the substrate, the chemical reaction with the substrate does not occur and is physically etched by ions colliding with only high energy. This etching method is called sputtering etching method. In this case, an anisotropic etching cross section can be obtained, but the surface of the substrate may be damaged because the etching is performed entirely by collision of ions. Such damage may cause defects in device manufacturing. For example, in the case of microcapacitors, a capacitor needs to be stored for a certain time, but when the surface of the substrate is damaged, the charge will leak out.

An etching method using a substrate (eg, silicon oxide film SiO ₂ ) on a power transfer electrode and using a gas (eg carbon tetrafluoride; CF ₄ ) capable of chemically reacting with the substrate is used for reactive ion etching (RIE). Ion Etching (DM Manos and DL Flamm, ″ Plasma Etching ″, Academic Press, California (1989))) offers the advantages of chemical etching (selective etching, which allows the substrate surface to be etched without masking) and physical etching. Only the advantage (anisotropic etching that can be etched in a direction perpendicular to the surface) can be used. This is because the reactive ion etching can simultaneously obtain radicals with high chemical reactivity and high energy ions. That is, ions incident at moderately high energy (hundreds of volts) transfer momentum (the amount expressed as the product of mass and velocity) to the surface to promote chemical reaction of radicals in the plasma with atoms on the substrate surface. At this time, the etching rate of the portion hit by the ions increases with the ion energy and is much larger than the etching rate of the portion not hitting the ions, so the etching proceeds in the direction perpendicular to the substrate surface in the direction of incidence of the ions. Since etching is performed by a chemical reaction, damage to the substrate can be greatly reduced compared to sputter etching. Reactive ion etching is one of the most widely used etching methods. Semiconductors such as silicon (Si), gallium arsenide (GaAs) and indium phosphorus (InP), silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), gallium nitride It is used to etch various substrates from insulators such as (GaN), and conductors such as aluminum (Al), platinum (Pt), and copper (Cu).

Recently, etching using a high density plasma generating apparatus such as TCP (Transform Coupled Plasma) has been widely used in order to minimize damage to the substrate due to ion collision energy in reactive ion etching. TPC is a plasma generated by a method similar to a transformer. In a transformer, there are two adjacent coils, and currents flow in the secondary coils by an induction magnetic field generated by applying current to the primary coils. Similarly, TPC generates a secondary current in the gas in the reactor by placing a primary coil on the dielectric window of the ceramic material forming the lid of the etch reactor and applying alternating current to the reactor. Is generated. The magnetic field lines of the induced magnetic field due to the alternating current flowing in the primary coil penetrate into the reactor through the dielectric window, and the electrons forming the plasma spirally travel along the magnetic field lines. As a result, the average propagation path of the electrons becomes longer, so that the electrons collide with more gas particles than in the case of the parallel planar plasma. In other words, a higher ionization reaction is generated, resulting in a high-density plasma in which the concentration of ions increases by about 100 times as compared with the case of the parallel plate type. In such a high-density plasma, the flux of ions, that is, the number of ions incident on a unit area per unit time increases, while the potential difference of the sheath formed on the negative electrode decreases, thereby decreasing the energy of ions incident on the substrate. The etching rate is determined not only by the energy of the ions but also by the flux of the ions, i.e. the number of incident ions, so when using a high density plasma etching apparatus such as TPC, the etching rate is not reduced compared to the reactive ion etching method. Damage to the substrate can be minimized.

In the plasma etching method, the sputtering etching method, and the reactive ion etching method in a narrow sense, external power is transferred to the plasma through a sheath formed on the electrode surface or the surface of the substrate on the electrode. The sheath is a capacitor (capacitor; Because of the nature of capacitors, the plasma used for such etching is called capacitively coupled plasma. On the other hand, in the case of TPC, electric power is transmitted through a coil having an inductor property, so it is called an inductively coupled plasma (MA Lieberman and AJ Lichtenberg, ″ Principles of plasma discharges and materials processing, John Wiley & Sons, New York (1994).

4. Control of etching direction

The etching cross-section required in the manufacturing process of semiconductors, optoelectronic devices, micromachining and the like may vary from the cross section etched in the direction perpendicular to the substrate surface to the cross section etched obliquely on the substrate surface depending on the application purpose. Grating is an example of an application in which an inclined etching section is required. Grating is an element necessary for optoelectronic devices, spectroscopy, and sound equipment, and has a surface structure in which V-shaped grooves are continuous. It is important to control the angle of the inclined plane, and the asymmetric V-groove as well as the symmetrical V-groove are often required depending on the application.

However, in the case of plasma etching, since the sheath is always formed parallel to the surface of the substrate, the ions accelerated perpendicularly to the equipotential line of the sheath are incident perpendicularly to the substrate regardless of the inclination of the substrate and thus basically the vertical etch cross section. Form.

Prior art that can perform inclined etching without the use of plasma etching is anisotropic wet etching (M. Kappelt and D. Bimberg, J. Electrochem. Soc. 143, 327 (1996)). When the crystalline substrate is immersed in a mixed solution of acid or alkali, the etching reaction rate of the mixed solution and the surface of the substrate may vary depending on the crystal plane. In general, the surface atomic density (number of atoms per unit area) of the crystalline material varies depending on the crystal plane, but the etching speed of the crystal surface with high surface atomic density is slow and the etching rate of the crystal surface with low surface atomic density is fast. Anisotropic wet etching takes advantage of this phenomenon. In this case, there is a restriction that the substrate must be crystalline, and the angle of the etch cross section is also limited by the crystallinity and surface atomic density of the adjacent substrate. In addition, if you want to make an asymmetrical V-groove, it is inconvenient to cut the surface of the substrate in advance obliquely from the original crystal plane and smooth the cut surface again.

Prior arts capable of performing inclined etching on the substrate surface while solving these limitations and inconveniences include ion beam etching (O. Auciello and R. Kelly, ″ Ion bombardment modification of surfaces ″, Elsevier, Amsterdam (1984))). Ion beam etching is a method of accelerating ions extracted from an ion source such as plasma through an accelerator grid and then entering a target substrate. At this time, the space in which the substrate is placed is maintained at high vacuum so as not to interfere with the incidence of ions. In general, in the ion beam etching apparatus, an ion gun for generating, extracting, accelerating, and injecting ions is disposed on the upper portion thereof, and a substrate support is installed at a predetermined distance from the bottom thereof. It is adjustable.

In ion beam etching, unlike in the case of reactive ion etching, a sheath is not formed on the substrate since the substrate is not directly exposed to the plasma. Therefore, the etching direction can be adjusted as desired by adjusting the angle of the support for fixing the substrate while the incident direction of ions is fixed. In addition, in the ion beam etching, the energy of the ions may be controlled by adjusting a DC voltage connected to the acceleration grid. Since the etching direction of the ion beam is almost independent of the crystallinity of the substrate, the ion beam etching is widely used to etch not only a crystalline substrate but also an amorphous substrate such as a silicon oxide film or a silicon nitride film that cannot be processed by anisotropic wet etching. Has been used.

However, in the case of ion beam etching, it is difficult to use radicals that are much more reactive than ions. Among the various methods of ion beam etching, ion milling (DM Manos and DL Flamm, ″ Plasma Etching ″, Academic Press, California (1989)), chemically assisted ion beam etching (CAIBE) (R. Panepucci , C. Youtset, DA Turnbull, and SQ Gu, J. Vac. Sci. Technol. B 13, 2752 (1995))), reactive ion beam etching (RIBE; AM Barklund and H.-O. Blom) , J. Vac. Sci. Technol. A 10, 1212 (1992)). Among these, ion milling is a method of physically etching by injecting an inert ion (Ar ⁺ ) beam by introducing an inert gas such as argon (Ar). Therefore, ion milling does not contain highly reactive radicals. In the case of chemical air-conditioning ion beam etching, the use of an inert ion beam is the same as that of ion milling, except that a reactive gas such as chlorine (Cl ₂ ) is introduced where the substrate is placed. The ion beam is incident on the surface of the substrate adsorbed by the reactive gas, and the etching proceeds as the chemical reaction is accelerated. However, reactive gases (eg, Cl ₂ ) are stable on their own, and their chemical reactivity is very low compared to radicals (eg, Cl) generated by decomposition in plasma. In the case of reactive ion beam etching, a reactive gas such as chlorine (Cl ₂ ) is introduced into a plasma for extracting the ion beam to extract and enter a reactive ion beam such as Cl ⁺ . At this time, radicals such as Cl are also generated, which are incident on the surface of the substrate to assist in etching. In this case, however, the flux of radicals incident on the surface of the substrate is very low, such as 0.01 to 0.1 times as compared to the case of reactive ion etching and high density plasma etching under the same process conditions. Thus, the speed of ion beam etching is very low compared to reactive ion etching or high density plasma etching. In the ion beam etching, the incident energy of the ion beam may be increased to increase the etching speed, but in this case, the substrate may be damaged.

Some radicals, such as the chlorine atom (Cl) mentioned above, may participate in chemical reactions for etching, but on the other hand, some radicals may interfere with the etching process by adhering to the surface to form a polymer film. Examples of the latter include CF ₂ in carbon fluoride plasma. They adsorb well on the surface of silicon or silicon oxide and bond well to each other to form a thin film of polymer on the surface of the substrate. Thus, the radical which becomes a material of a polymer film is called a polymer precursor. As a result, the polymer thin film is formed on all surfaces during etching, but since the ions are incident on the surface of the substrate perpendicularly, the polymer film formed on the bottom surface of the cross section is removed by the collision of ions. On the other hand, the thin film formed on the side wall of the cross section is not removed by the ions and remains as it is. The wall's thin film protects the wall from ions coming in and radicals that participate in chemical reactions, allowing for vertical etching. Therefore, in the etching process of obtaining an etch cross section with a high aspect ratio, which has a large etching depth compared to the width, a reactive ion etch that forms a polymer protective film on the etch sidewall and a high concentration of polymer precursor therefrom. Method or high density plasma etching is used a lot.

As described above, as a prior art capable of performing inclined etching while using reactive ion etching and high-density plasma etching methods having relative advantages in terms of using radicals, the invention of Boyd et al. 4309267). This installs a Faraday cage on the negative electrode to which power is delivered in the plasma etching apparatus. Faraday's box simply means a closed curved box of conductive material, all of which are kept at the same potential. Even if external charges are added to the surface of the conductor box, the surface of the box is a conductor, so the charge is always uniformly distributed on the closed surface of the conductor box. Assuming that there is a charge at a point in the inner space of the box, the force on the point's charge on the surface of the box cancels in all directions and eventually becomes zero. This principle is explained by Gauss' law in electromagnetics. The shielding effect of the Faraday box against external electromagnetic fields has been mainly used to protect electrically sensitive electronics from external electrical shocks such as electrostatic discharge or electromagnetic waves.

The method devised by Boyd et al. Applies the principle of the Faraday Cage to plasma etching. Even if the surface of the Faraday box is not composed of a complete closed surface and small holes are drilled in the surface, the electric field force remains almost near zero in most spaces inside the box except adjacent to the holes. As shown in Fig. 1, the Faraday box 1 used by Void et al. Is a rectangular parallelepiped conductor box, the upper side of which is composed of a porous lattice plane 4 of a conductor. The inside of this box is provided with the board | substrate support stand 5 in which one side was made into the inclined surface, and the board | substrate 6 can be set in the inclined angle with respect to the grid surface. At this time, a sheath is formed on the lattice plane 4 of the Faraday box placed inside the plasma. The sheath is not only formed on the conductive material forming the lattice, but also continuously formed in the open part of the lattice. In the sheath, the ions 7 accelerated in the direction perpendicular to the lattice plane enter the inside of the box through the open portion of the lattice. Inside the box, there is no electric field according to the principle of Faraday's box, so the ions move in the direction they cross the lattice plane and hit the inclined substrate. Inside the box, the substrate surface is fixed inclined with respect to the lattice plane, and ions are incident in a direction perpendicular to the lattice plane, so that etching is performed in a direction inclined with respect to the substrate surface. As a result, the inclined etching is possible while maintaining the high etching rate of reactive ion etching and high density plasma etching.

However, the method of using the inclined substrate support 5 for etching in the inclined direction according to the invention devised by Boyd et al. Has various limitations. When the inclined etching is performed using a large diameter wafer as a substrate, the support of the wafer also occupies a very large volume, which acts as a large load in the plasma. For example, to obtain an etched section that is inclined at 45 degrees to the substrate surface when the diameter of the wafer is 30 cm, the maximum height of the substrate support inside the Faraday box is 22 cm. Worsens. In addition, the distance difference between the portion near the lattice plane and the portion farther than the lattice plane is significantly larger than the mean free path (0.1-10 cm) under general etching process conditions. Nonuniformity of the etching rate is increased. Here, the mean free path is the average value of the distance that ions travel between collisions when incident ions collide with neutral particles, and this decreases with increasing pressure. Therefore, the ions enter the surface of the substrate located close to the lattice surface and hardly collide with the neutral particles, thereby contributing to the etching without energy loss and the change in the direction of incidence. Because they collide a lot with radicals along the way, the kinetic energy is weakened and the direction of incidence is also changed. In addition, when the set of ions passing through one lattice hole in one of the lattice planes is called an ion beam, an ion beam dispersion effect occurs in which the ion beam diameter increases as the ion flight distance increases. Therefore, even if there is no collision with the neutral atoms, the substrate farther from the lattice plane has more ions incident in the direction away from the vertical direction than in the case of the close substrate. As described above, according to the method invented by Void or the like, the etching speed and direction of the substrate become uneven according to the angle of the substrate support, so this method is not suitable for etching of large diameter substrates.

And the invention of voids and the like is a method of passively moving the substrate in a state in which the incident flow of ions is fixed in the direction perpendicular to the negative electrode, so that the direction of incidence of ions cannot be variously controlled, and thus, there are limitations in obtaining various etching cross sections. There is.

5. Control of etching speed

When etching a large diameter wafer using a conventional plasma etching method, an uneven phenomenon of the etching speed according to the position on the wafer becomes an important problem. This is because the non-uniformity of the etching rate increases the defect rate in the fabrication of the highly integrated circuit, thereby reducing the yield. In most cases, the etching speed is high in the center of the electrode and decreases as it goes to the surroundings. It is pointed out that the phenomenon that the concentration of radicals and ions becomes uneven depending on the position and the flux that changes with the concentration also becomes uneven. As described above, radicals and ions are the most important particles that contribute to etching, so the etch rate is determined by their flux. Many researches and inventions have been conducted to solve the problem of non-uniformity of the etching rate, and the main focus is on eliminating or mitigating the two causes mentioned above. In order to uniformize the concentration of radicals according to positions, a method of controlling a gas flow is mainly used. Examples of the present invention are as follows.

The first example is a method of uniformizing the flow of gas by introducing the gas into the reactor through a sintered porous diffuser (Poor Sintered Diffuser) (US Pat. No. 5595602). In general, the diffuser directs the gas into the reactor at a lower pressure, which is much lower than atmospheric, through ten inlets and openings in a ring-shaped tube. At this time, the pressure difference is so large that the gas diffuses into the reactor very quickly. . Turbulent flows can occur in this process, resulting in non-uniform flow of gases. The method of this invention is sintered to introduce gas through a porous plate with many fine pores so that the gas flows uniformly in a laminar flow in the reactor. Secondly, there is a method of installing a gas outlet in a large-capacity annex rather than a main reactor (US Pat. No. 4,352,974), which mitigates the flow of exhaust gas in the main reactor to prevent turbulence. The former method is to increase the uniformity of the etching rate by making the flow of the introduction gas uniform, whereas the latter method is to make the flow of the exhaust gas uniform. However, these methods do not contribute significantly to improving the etching uniformity in the plasma etching process used in recent years. This is because gaseous particles move away from continuous flow by molecular flow in a recent etching process performed under tens of millitorr (mTorr), which is less than tens of thousands of atmospheric pressures. This is because the etch nonuniformity effect due to turbulence is neglected.

On the other hand, examples of the invention attempted to make the concentration of ions and the flux of ions uniform accordingly are as follows. First, there is a method of compensating for the phenomenon that the concentration of ions decreases toward the periphery by decreasing the distance between the electrodes while going from the center of the electrode to the periphery (US Patent No. 4230515). The generation of plasma is affected by the distance between the electrodes. Generally, the ion concentration increases when the distance between electrodes is close. Therefore, if the shape of the upper part of the reactor becomes lower from the center to the periphery, the distance between the electrodes decreases toward the periphery of the electrode, thereby increasing the ion concentration. However, this method is only applicable to parallel plate plasma etching apparatus that generates capacitively coupled plasma. Secondly, in the case of inductively coupled high density plasma such as TPC, a method of controlling the degree of inductive coupling according to the position by varying the thickness of the dielectric window under the induction coil (US Pat. No. 5226967, US). Patent number 5466991). In the case of inductively coupled plasma, the induced magnetic field by the primary coil penetrates into the gas in the reactor through the dielectric window, and the penetration depth and intensity are influenced by the thickness of the dielectric window. In general, the thickness of the portion located above the electrode periphery of the dielectric window is smaller than the upper portion of the electrode center to increase the ion concentration of the electrode periphery to increase the uniformity of the etching rate. However, this method can only be used in etching devices that use dielectric windows, such as TPC.

The method of the present invention focuses on the latter solution of the two causes of the non-uniformity described above, namely, the non-uniformity of the gas flow in the reactor and the nonuniformity of the ion flux, and is applicable to both capacitive and inductively coupled etching apparatuses. It is possible.

The present invention is to secure the substrate on the electrode and to change the angle of the grating plane constituting the Faraday box to adjust the etching direction according to the direction of incidence of ions to obtain the etch cross section of various shapes, the grating plane is variously modified Thus, the ion flux may be concentrated or dispersed according to the position of the substrate so that the substrate may be uniformly etched as a whole.

1: Etching apparatus used by Boyd et al. In US Pat. No. 4309267.

2 is a cross-sectional view of an etching apparatus implemented by electrically contacting a Faraday box inclined with respect to a substrate to a negative electrode of a TPC plasma etching reactor.

3 is a cross-sectional view of an etching apparatus in which the lattice plane of the Faraday box is parallel to the substrate.

4 is a cross-sectional view of the etching apparatus is a certain portion of the top of the Faraday box.

5 is a cross-sectional view of the etching apparatus with the open pattern on the top of the Faraday box.

6 is a cross-sectional view of the etching apparatus inclined so that the lattice plane of the Faraday box is at an angle with the substrate.

7A and 7B: cross-sectional views of an etching apparatus composed of two inclined lattice planes joined together so that the top surfaces of the Faraday boxes are at an angle to each other.

8: A cross-sectional view of an etching apparatus in which the top surface of a Faraday box is a single curved lattice.

9: Cross-sectional view of an etching apparatus in which a Faraday box consists of a double lattice and the substrate is placed under the Faraday box.

10: Cross-sectional view of an etching apparatus in which the lattice plane of the Faraday box is parallel to the substrate surface and the lattice size of the lattice plane changes with position.

11A: Etch sectional photographs by the conventional method in contrast with Example 1 of the present invention.

11B: Etch sectional photograph according to Example 1 of the present invention.

11C: Graph showing the degree of putting.

12A and 12B: Etch sectional photographs according to Embodiment 2 of the present invention.

13 is an etching cross-sectional photograph according to a third embodiment of the present invention.

14A and 14B: Etch sectional photographs according to Embodiment 4 of the present invention.

15A and 15B: Etch sectional photographs according to Embodiment 5 of the present invention.

16A to 16C: Etch sectional photographs according to Example 6 of the present invention.

17A to 17F: Etch sectional photographs according to Embodiment 7 of the present invention.

18A to 18C: Etch sectional photographs according to Embodiment 8 of the present invention.

(Explanation of symbols for the main parts of the drawing)

1: Faraday box used by Boyd, etc. 2: Top plate

3: silicon oxide film 4: lattice plane

5 substrate support 6 substrate

7: ion 8: source power

9 TPC Coil 10 Dielectric Window

11: bias power 12: blocking capacitor

13: negative electrode 14: Faraday box of the present invention

15: top plate 16: lattice plane

17 substrate 18 ion

19: Top plate engraved open pattern 20: Beveled shield plate

21: leg of the double-lattice Faraday box 22: upper lattice plane

23: bottom lattice surface 24: substrate

25: ion

26: ions passing through the upper and lower lattice planes

27: sheath formed outside the upper lattice plane

28: sheath formed outside the lower lattice plane

29: sheath formed on the substrate surface

30: lattice plane with the smallest grid size

31: lattice plane of medium grid size

32: lattice plane with the largest grid eye size

2 schematically shows an apparatus which can implement the method of the present invention. In the present invention, the incident of ions 18 is caused by electrically contacting a closed curved Faraday box 14 composed of a porous lattice plane 16 of a conductor to an electrode 13 to which electric power is transmitted in a conventional plasma etching apparatus. It relates to a technique for adjusting the direction. As a result, the etch rate distribution may be independently adjusted according to the etching direction of the substrate and the position of the substrate surface. According to the invention of Void et al. (US Pat. No. 4309267), rather than adjusting the angle of the substrate support positioned in the Faraday box, the etching angle can be obtained by controlling the angle of the grating plane 16 in contact with the plasma. In addition, it is also distinguished from the invention of Void in that it is easy to apply to the existing etching apparatus. In the case of the present invention, an electrostatic chuck or a wafer cooling device installed in an electrode of a conventional plasma etching apparatus can be used without modification. Here, the electrostatic chuck is a device for generating static electricity in order to fix the wafer on the electrode. During the etching process, the temperature of the wafer surface increases, and there is a device for flowing helium gas on the back of the wafer to cool the wafer to prevent overheating. In order to use the invention such as voids, such an electrostatic chuck or a wafer cooling device should be modified and installed in accordance with the substrate support, but in the present invention, the wafer is fixed on the electrode in a conventional manner so that they can be used as it is. In the present invention, the grid plane 16 of the Faraday box is modified in various forms and applied to etching, and the principle of the above-described Faraday box is commonly applied to the various types of boxes. That is, when the lattice surface forming part of the closed curved surface is in contact with the plasma, the ions in the plasma are incident in the direction perpendicular to the lattice surface, and the ions entering the inner space of the closed curved surface continue the inertial motion while maintaining the initial incident direction. Contribute to the etching of the substrate. In the following description, various etching sections obtained when the shape of the lattice plane 16 constituting the Faraday box is changed.

1.The lattice plane of Faraday box is parallel to the substrate surface (see Fig. 3)

Vertical etching is most demanded in high-density semiconductors, and plasma etching is widely used to realize this. However, there are various obstacles in obtaining a vertical etch wall close to 90 degrees by etching a fine pattern perpendicular to the substrate surface. One of these obstacles is the so-called facetting phenomenon in which the edges of the microstructures on the substrate are etched into the oblique plane. Deepening of the putting phenomenon adversely affects the subsequent process and causes the circuit failure even if the device manufacturing is completed.

The causes of putting are as follows. In the conventional plasma etching method, the sheath is formed directly on the surface of the substrate. As the etching progresses, as the etching depth of the microstructure on the substrate increases, the equipotential surface in the sheath is bent along the surface of the etched microstructure. Electric force lines, which represent the force of an electric field, are formed in a direction perpendicular to the equipotential surface, so the electric force lines around the microstructure are concentrated toward the convex edges of the microstructure. The flux of ions that are forced along this electric field line also concentrates on the edges of the microstructure, which is etched faster than elsewhere. Due to such a putting phenomenon, the portion to be etched vertically in the microstructure is etched into the inclined plane.

However, as shown in FIG. 3, when the lattice plane 16 is fixed in parallel with the surface of the substrate 17, the sheath is directly above the lattice plane 16 of the Faraday box 14. Since they are formed parallel to the substrate 17, the ions 18 incident thereto perpendicularly maintain the direction and etch the substrate 17. This is because, as described above, the space inside the Faraday box is kept at the same potential, so there is no electric force generated due to the potential difference, and therefore, there is no other force in the space within the box to change the direction of the incident ions. That is, using the Faraday box as shown in FIG. 3, the flux of ions 18 is incident in a direction perpendicular to the surface of the substrate 17 regardless of the microstructure on the substrate. As a result, it is possible to greatly reduce the setting phenomenon regardless of the process conditions, thereby obtaining a finer etching section that is more vertical than the conventional plasma etching method.

2. Part of the top of the Faraday box is covered (see Figure 4)

A Faraday box, as shown in FIG. 4, is used to etch a silicon oxide (SiO ₂ ) thin film under a carbon fluoride (eg CF ₄ , CHF ₃ , C ₂ F _6, etc.) plasma, directly below the lattice plane 16. The positioned substrate 17 surface is etched as described in section 1 above, but the substrate surface of the portion covered by the blocked top plate 15 is not etched. This is because when the silicon oxide thin film is etched under the carbon fluoride plasma, the surface where the ions do not enter is hardly etched. In addition, etching is performed only on the substrate surface where ions enter, such as etching silicon (Si) or silicon oxide (SiO ₂ ) thin films in an argon (Ar) plasma and etching silicon thin films in a chlorine (Cl ₂ ) plasma. In the Faraday box, the blocked top plate 15 serves as an etching mask. That is, using the Faraday box of the present invention, only the surface portion of the desired position of the substrate can be etched.

3. If there is an open pattern on the top of the Faraday box (see Fig. 5)

When applying the principles described in Sections 1 and 2 above to cover the Faraday box 14 with the top plate 19 engraved with an open pattern to allow incident ions to pass through, and greatly reduce the height of the side wall of the box. The upper plate 19 engraved with this pattern serves as a pattern mask for ions. At this time, since the ions are incident only to the open portion of the upper plate 19 having the pattern engraved thereon, the substrate surface is etched in the same shape and size as the pattern of the upper plate 19. If the distance between the patterned top plate 19 and the substrate 17 is large, the ion beam incident through the pattern is dispersed, and the pattern etched on the substrate is blurred. However, if the interval is small, the ion beam is not dispersed in the substrate. Because of the collision, a clear pattern can be transmitted to the substrate through the upper plate 19 engraved with the pattern of the Faraday box. If the pattern of the top plate 19 of the Faraday box becomes sufficiently fine, it is possible to use this principle for the photoresist coating and exposure of photoresist films currently used in semiconductor, optoelectronic and micromechanical device processing processes. By eliminating a series of photolithography processes such as removal of sensitized molecules after etching, circuit patterns can be implanted onto a substrate using only a single process, thereby eliminating various problems caused by using sensitized molecules.

4. When the grid plane of the Faraday box is inclined at an angle with the substrate (see FIGS. 2 and 6)

In the Faraday box shown in FIG. 2, a sheath is formed along the lattice plane 16 which is inclined at an angle to the substrate surface, so that the ions 18 perpendicular to the lattice plane 16 are horizontally placed on the electrode 13. An etching cross section is obtained by inclining the substrate surface in a direction inclined by the inclination angle of the lattice surface from the vertical direction of the surface of the substrate 17 placed thereon. When etching in the inclined direction with respect to the large-diameter wafer, as shown in Figure 6 it is possible to obtain an inclined etch cross-section regardless of the distance between the electrodes by using a lattice periodically repeated at a certain angle. As mentioned above, in the invention of Boyd et al. (US Pat. No. 4309267), there is a problem in that the distance between electrodes is far away when etching a large diameter wafer. By using the sloped Faraday box as shown in FIGS. 2 and 6, all of the etchings using the conventional ion beam apparatus may be realized even in the conventional reactive ion etching or the high density plasma etching apparatus. That is, in the conventional plasma etching apparatus, since the sheath is formed parallel to the surface of the substrate, the sheath can be etched only in the direction perpendicular to the substrate regardless of the placement angle of the substrate. The direction of incidence of ions can be adjusted freely.

The advantage of the method of the present invention over an ion beam etching apparatus is that many radicals present in the plasma etching apparatus are also incident on the substrate, so that a higher etching rate can be obtained than in the case of ion beam etching with a low radical content. This is because the ions together with the radicals have a synergic effect on the etching rate. In this case, even though the ions are incident at a relatively low energy, a high etching rate can be obtained and thus damage to the substrate can be reduced.

5. The top of the Faraday box consists of two slanted lattice surfaces joined together to form a certain angle to each other (see Figs. 7a and 7b).

As shown in FIGS. 7A and 7B, when the Faraday box 14 is deformed such that the two lattice planes 16 form an angle, the ion 18 fluxes in two directions can be obtained at the same time. This property cannot be obtained by the conventional ion beam etching method or the use of Faraday boxes such as voids (US Pat. No. 4309267). As such, the method of injecting ions in two directions at the same time can be variously applied to an etching process. For example, grating, which is a key component of spectrometers, optoelectronic devices, and acoustic devices, as well as semiconductor integrated circuits, can be effectively made, which increases the effect of the microstructure on the substrate by the incident ions incident from two inclined directions. This is because a cross section of a V-groove shape is generated. If the lattice surface is made asymmetrical as shown in FIG. 7B, the etched section is also formed asymmetrically, thereby obtaining a high resolution X-ray reflection grating.

6. If the top of the Faraday box is a grid of single surfaces (see Figure 8)

8 shows that the lattice surface 16 is deformed into a curved surface. In this case, the angle of incidence of the ions 18 passing therethrough is continuously changed according to the position of the lattice surface. In the case where the curved surface is convex as in the case of FIG. 8, the ions are concentrated and incident toward the center. In other words, the convex lens for the ions can be used to collect the ions at a predetermined focus. As a result, the etching speed increases under the central portion of the lattice plane, and the etching speed decreases toward the periphery. The change rate of the etching speed may be controlled by adjusting the curvature and the focal length of the grid surface. When the curved surface of the grating shown in FIG. 8 is reversed, an etching result opposite to that of a Faraday box serving as a convex lens appears. When the single lattice curved Faraday box of FIG. 8 is used, not only the etching speed but also the angle of the etching section is changed depending on the position of the substrate. That is, the etched section formed on the surface of the substrate at the position corresponding to the center of the curved surface is rounded by incident ions in various directions concentrated at the center, and the direction of incidence of the ions toward the periphery becomes far from the direction perpendicular to the substrate. The inclination angle of the etch section is also increased. Therefore, various etching characteristics can be obtained according to the position of the substrate by continuously changing the irregularities of the lattice plane and its curvature.

7. The Faraday box consists of a double curved grid and the substrate is placed underneath the Faraday box (see Figure 9).

In order to improve the uniformity of etching on a large-diameter wafer, the etching cross-section should be able to control the etching speed according to the position while maintaining the angle of the etching cross section perpendicular to the substrate surface. In this case, as shown in Fig. 9, a Faraday box composed of double curved lattice surfaces 22 and 23 can be used. In FIG. 9, the upper lattice plane 22 is curved and the lower lattice plane 23 shows a Faraday box composed of horizontal planes. Depending on the application, the lower lattice plane may also be curved, so in the present invention, the upper and lower lattice planes may be curved. Also referred to as the lattice surface of the double curved surface. In the Faraday box of FIG. 9, the etch substrate is not surrounded by the side of the box as in the other case described above, but lies between the legs 21 supporting the double curved surface, so that the substrate is in contact with the plasma in the horizontal direction of the substrate. . As described above, a sheath is always formed on the surface in contact with the plasma. In FIG. 9, three sheaths 27, 28, and 29 having a direct influence on the etching of the substrate among the sheaths formed on the outer surface of the Faraday box are shown. . The first is a sheath 27 formed on the outer surface of the upper surface of the double curved surface, the second is a sheath 28 formed on the outer surface of the lower curved surface, and the third is a sheath 29 formed on the etching substrate. In this case, since the space between the two curved surfaces 22 and 23 forms a closed curved surface, the effect of the Faraday box appears here. That is, in the sheath 27 formed on the upper lattice surface 22, the ions accelerated in a direction perpendicular to the curved surface of the upper lattice surface 22 and passed through the upper lattice surface 22 are interposed between the two curved surfaces 22 and 23. While flying in the direction of incidence to overcome the electric field of the sheath 28 generated in the lower lattice surface 23 and passes through the lower lattice surface (28). In the path of the ions, the sheath 27 formed on the upper lattice surface 22 acts downhill with respect to the ions, and the sheath 28 formed on the lower lattice surface 23 acts uphill. The ions are concentrated or dispersed depending on the lens effect of the upper curved surface 22, that is, the irregularities of the lattice surface, and the degree is adjusted according to the curvature. They are accelerated again through the sheath 29 formed on the surface of the substrate 24 overlying the electrode and the inclined ion incidence direction is adjusted vertically. Therefore, using a double lattice Faraday box as shown in FIG. 9, unlike the single lattice Faraday box, the etching section can be maintained vertically, and only the etching rate according to the position of the substrate surface can be adjusted. For example, when the center of the silicon oxide thin film used as a substrate is relatively thin and the periphery is thick, the conventional plasma etching method increases the etching speed of the center and deepens the thickness difference between the center and the periphery. By designing a double lattice Faraday box to be concentrated and placed on the electrode, the uniformity of the overall film thickness can be controlled.

8. The lattice plane of the Faraday box is parallel to the substrate surface and the lattice size of the lattice plane changes with position (see Fig. 10).

As another method of enhancing the uniformity of etching in large diameter wafers, a Faraday box as shown in FIG. 10 may be used. In this Faraday box, the lattice plane is parallel to the substrate surface, and the size of the open part of the lattice plane varies according to the position. The flux of ions passing through the lattice plane of Faraday's box is proportional to the area ratio of the open area through which ions can pass through the entire area of the lattice plane. In other words, if the area of the open portion of the lattice plane is large, ions can pass through and the etching rate is increased. At this time, since the lattice plane is parallel to the substrate surface, ions are incident in a direction perpendicular to the substrate surface, and thus a cross section etched in the vertical direction can be obtained.

Example

Embodiments introduced in the present invention are results performed in the TCP-type plasma etching apparatus shown in Figure 2, the Faraday box in electrical contact on the negative electrode 13 is the configuration of the invention according to the application of each embodiment and It was used to replace the various types of boxes introduced in the action. In the etching apparatus of FIG. 2, source power 8 is inductively transmitted to the gas under the dielectric window 10 through the TPC coil 9, and bias power 11 is the cathode. Is delivered capacitively via (13). The inner diameter of the reactor of the etching apparatus used in the example is 30 cm, the diameter of the negative electrode on which the substrate is placed is 12.5 cm, and the distance from the dielectric window to the electrode is 3.5 cm. The substrate used for etching is a silicon oxide thin film grown to 1 μm (micrometer; 10-6 m) thick on a p-type silicon wafer. For pattern etching, a wafer formed on a silicon oxide thin film in a line and space pattern with an aluminum line having a thickness of about 0.2 μm and a width of about 1 μm at about 1 μm in width was used.

Faraday boxes used in the embodiment of the present invention are schematically shown in Figs. 2 to 10, all of them using 0.1-0.4 mm thick copper plates and different types of grids with different grid sizes. Produced. Soldering was used to glue the copper plate and copper wire electrically. The selection of copper as a material is based on the convenience of fabricating Faraday boxes and experiments using the same, and is not necessary for the implementation of the present invention. In other words, any material can be used as the material of the Faraday box as long as it is a material capable of maintaining an equipotential with the electrode when it is electrically contacted with the negative electrode as a conductor. The choice of these materials is particularly important in the etching process of semiconductor devices, in which case it is better to use graphite instead of metal. This is because when a copper-based Faraday box is used in a semiconductor process, a small amount of copper is sputtered by ions and enters the substrate surface, which may cause a short circuit of the semiconductor circuit. However, graphite is a crystal of pure carbon and has no correlation with a short circuit. Even when a trace amount enters the surface of the substrate, graphite is etched and removed in a plasma environment such as carbon fluoride, and thus may be used in a semiconductor process. In fact, lattice surfaces made of graphite are widely adopted in the ion gun portion of ion beam etching.

In addition, even if a thin plate made of a material such as silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ) or alumina (Al ₂ O ₃ ) is applied to the outer surface of the Faraday box exposed to the plasma, the effect on the etching of the Faraday box Does not change. Even in this case, it is possible to prevent contamination of the etching substrate due to the sputtering of the conductive material.

Example 1 Faraday Box Using a Grid Surface Horizontal to the Substrate Surface (See FIGS. 3, 11A-11C)

As described in the configuration and operation 1 of the invention, a Faraday box with a lattice plane parallel to the surface of the substrate was used, and as the process conditions, carbon tetrafluoride (CF ₄ ) was flowed at a flow rate of 10 cm ³ / min, and the pressure was 10 millimeters. Torr (1 millitorr = 1 / 760,000 atm). At this time, the source power delivered to the TPC coil was fixed at 200 watts, and the bias power delivered to the negative electrode was adjusted so that the sheath bias voltage of the negative electrode became -300 volts. The value of the bias power is determined by the bias voltage. Etching was performed for 10 minutes.

As a result of etching as described above, as shown in FIG. 11B, a rectangular cross section having an etch wall perpendicular to the substrate surface was obtained. On the contrary, the etching result of placing the substrate on the electrode according to the conventional etching method without the Faraday box in the etching apparatus of FIG. 2 under the above process conditions is as shown in the electron micrograph of FIG. 11A. For the same reason as described in the action, faceting occurred and became trapezoidal. The angle formed by the trapezoid and the plane was 73.8 degrees.

When using a Faraday box with the lattice plane parallel to the surface of the substrate, the effect of etching in a direction more perpendicular to that of the conventional etching method is independent of the type of gas introduced for plasma generation. As the index indicating the degree of facetting, the width of the top surface of the microstructure, which is etched in the horizontal direction, divided by the depth of etching, was used as a percentage (%) in FIG. 11C. The closer to 0%, the nearer the wall of the etched microstructure with respect to the surface of the substrate. As shown in FIG. 11C, when oxygen (O ₂ ) is mixed with carbon tetrafluoride (CF ₄ ) as well as 25% of the total inlet gas volume (CF ₄ / O ₂ ), CHF ₃ and argon (Ar) Even in each case, the use of a Faraday box whose lattice plane is parallel to the substrate surface is significantly reduced compared to the conventional etching method, which shows that the present invention has a significant improvement in the vertical etching. .

Example 2 Etching When a Part of the Top of the Faraday Box is Covered (Refer to FIG. 4, FIG. 12A, and FIG. 12B)

In this embodiment, as shown in FIG. 4, a Faraday box is used, in which part of the upper surface parallel to the substrate is a flat plate 15 of a conductor and a lattice surface 16, and the etching process condition is a bias voltage of a negative electrode. Same as the process conditions of Example 1 except that -180 volts and the etching time is 7 minutes. 12A and 12B show etching results obtained therefrom. 12A shows an etching cross section obtained under the lattice surface 16 and shows that the etching has proceeded by the ion 18 entering through the lattice surface. On the other hand, FIG. 12B is a surface photograph of the substrate located under the shielded portion 15 of the upper surface, and the silicon oxide thin film is not etched at all, and only the aluminum mask originally formed on the substrate is shown. This result shows that only certain parts of the surface of the substrate can be etched by blocking certain portions of the Faraday box.

Example 3: Etching when there is an Open Pattern on the Top of Faraday Box (See FIGS. 5 and 13)

The conductive top plate 19 engraved with the pattern of the Faraday box used in this embodiment has a pattern through which ions can pass, as shown in FIG. 5. The upper plate (19) engraved with a pattern was used as a stylus (Stylus) copper plate engraved with the word ″ SNU ″. The copper plate is 0.3 mm thick and 1.6 cm wide and 1.2 cm long. The size of one letter engraved here is 2 mm wide by 3 mm long and the line width is 0.1 mm. The height of the side wall of the Faraday box 14 shown in FIG. 5 was etched by bringing the top plate close to the substrate at 2 mm. The etching process conditions are the same as in Example 1. As a result, as shown in FIG. 13, the surface of the silicon oxide thin film was clearly etched along the letter shape of the upper plate 19 in which the pattern was engraved accurately. At this time, the size of the letters etched on the substrate surface was consistent with the size of the top plate. From this, as shown in FIG. 5, it can be seen that the pattern can be directly transferred to the surface of the substrate without having to go through a photo-drawing process using a sensitized molecular film on the surface of the conductive upper plate.

Example 4 Etching in the Inclination of the Faraday Box to be Slanted to Form a Constant Angle with the Substrate (See FIGS. 2, 6, 14A, and 14B)

14A and 14B are cross-sectional photographs of substrates having the inclination angles of the Faraday box lattice planes shown in FIG. 2 fixed to 30 degrees and 50 degrees with respect to the substrate surface, respectively. The process conditions used here are the same as in Example 1 except that the bias voltage is -250 volts and the etching time is 12 minutes. The angle of the etched section was determined by the angle formed by the straight line connecting the center point of the top and bottom sides of the cross section. The inclination angles of the cross sections shown in FIGS. 14A and 14B are 30.3 degrees and 50.3 degrees, respectively, and coincide with the inclination angle of the Faraday box lattice plane within the measurement error range. This means that the inclined plane of the etching section can be adjusted by the angle of the Faraday box lattice plane.

Example 5 Etching When the Tops of a Faraday Box Consist of Two Inclined Lattice Surfaces Bonded to Form a Constant Angle to Each Other (See FIGS. 7A, 7B, 15A, and 15B)

15A is a cross section etched using a Faraday box of a symmetrical lattice plane shown in FIG. 7A. The etching process used here is similar to that of Example 1 except that the bias voltage is -350 volts and the etching time is 20 minutes. same. The aluminum mask, which was originally formed on the silicon oxide film, was almost eliminated by the progress of the settling by the ion flux simultaneously incident on both sides during etching, and the V-groove-shaped grating was formed on the surface of the silicon oxide film.

FIG. 15B is a cross-sectional view of the asymmetric lattice plane shown in FIG. 7B under the same process conditions as in Example 1, using the Faraday box. At this time, the direction of incidence of the ion flux passing through the lattice planes on both sides is determined by the angle of inclination of each lattice plane. Asymmetric V-shaped gratings were formed.

Faraday box was used to suppress the setting and vertical etching in the case of Example 1, but in the same manner as in this embodiment, if the shape of the lattice surface is deformed, it may rather be used to promote the settling to form V-shaped oblique surface etching.

Example 6 Etching When the Top of the Faraday Box is a Single Curved Grid (See FIGS. 8, 16A-16C)

16A to 16C show the result of etching using the Faraday box of the single curved lattice shown in FIG. 8, in which FIG. 16A is an etched section obtained at its central portion, and FIGS. 16B and 16C are obtained at positions away from the periphery in that order. Etch section. The process conditions are the same as in Example 1 except that the etching time is 3 minutes. Comparing the etching depths of FIGS. 16A to 16C, the etching speed of the center portion of the substrate is the largest and decreases toward the periphery. In the center of the lattice curved surface, the flux of each ion incident on the curved surface at each position of the curved surface is concentrated, so the etching speed is the greatest. In FIG. 16A, the aluminum mask and the silicon oxide under the mask are also etched and removed. In addition, when the shape of the etching cross section is compared, in the center of the substrate where ions in all directions are concentrated, the bottom of the etching cross section is etched in a substantially vertical direction, and the etching wall of the etching cross section is formed on the substrate surface toward the periphery of the substrate. It is inclined at a large angle with respect to

As such, when a single curved lattice plane is used in a Faraday box, the flux of incident ions can be concentrated or dispersed and the etch rate and the inclination angle of the etch section can be changed according to the position of the substrate surface.

Example 7 Etching When a Faraday Box is Composed of a Double Curved Grid and Substrate Laid Under a Faraday Box (See FIGS. 9, 17A-17F)

17A through 17F are etching results obtained using the Faraday box of the double curved lattice shown in FIG. 9 under the same process conditions as those of Example 1. FIG. 17C is an etching result obtained below the central portion of the curved surface, and the remaining photographs are results obtained at positions away from the center to both sides in the arrangement order. These etching cross sections show that the etching depths are etched in the vertical direction without shifting from side to side while decreasing the etching depth as they move away from the center part. This is because the flux of the ions is maintained in the vertical direction while the incidence direction of the ions is varied depending on the position of the substrate. As a result, it can be seen that using a Faraday box having a double curved surface as shown in FIG. 9, the flux of ions can be concentrated on a desired portion of the substrate surface while maintaining the etching cross section in a direction perpendicular to the substrate surface.

Example 8 Etching in the case where the lattice plane of the Faraday box is parallel to the substrate surface and the lattice size of the lattice plane varies with position (see FIGS. 10, 18A to 18C)

18A to 18C are etching results obtained by using a Faraday box in which the size of the open portion of the lattice plane which is generally parallel to the substrate surface is changed depending on the position as shown in FIG. 10 under the same process conditions as in Example 1. FIGS. . Here, three types of lattice planes 30, 31, and 32 having different sizes of open portions were connected horizontally. FIG. 18A shows an etching result obtained under the grating plane 30 having the smallest area ratio of the open area to the grating plane total area among these grating planes with 60%, and FIGS. 18B and 18C show that the area ratios are 65% and 70%, respectively. It is an etching result obtained under the lattice surfaces 31 and 32. Their etching cross-section is perpendicular to the substrate and the etching depth increases according to the area ratio of the open portion of the lattice plane. As such, by changing the area of the open part of the horizontal grid plane of the Faraday box, the etching direction can be maintained vertically, and the etching speed can be adjusted according to the position.

The most commonly required etch cross section is an etch section in which the etch wall surface is perpendicular to the substrate surface. In the case of etching by the conventional plasma etching method, as shown in FIG. 11A, the inclined plane due to the setting is easily formed, and thus it is difficult to obtain a vertical etching wall. On the other hand, by using a Faraday box in which the lattice plane shown in FIG. 3 is parallel to the substrate surface, as shown in FIG. 11B, an etch wall that is more vertical than the conventional plasma etching method can be obtained. This improvement is shown regardless of the gas used for etching as shown in FIG. 11C.

Conventional plasma etching method could not obtain an etched section that is inclined at a certain angle. As shown in FIG. 1, the substrate is placed in a Faraday box having a horizontal lattice plane and the angle of the pedestal is adjusted to obtain an inclined etched section in the plasma etching apparatus. However, this method is not suitable for etching large diameter wafers in an inclined direction. As shown in FIG. 6 of the present invention, when the shape of the lattice plane of the Faraday box is properly modified, an inclined etch section can be obtained even in a wafer having a large diameter. In the present invention, as shown in Figure 14a and 14b it is possible to accurately adjust the inclination angle of the etch wall by the angle of the grid plane of the Faraday box.

In the conventional plasma etching method, in order to etch the surface of a substrate in a predetermined pattern, first, the sensitized molecular film is coated on the surface of the substrate and irradiated with light through a photomask having a pattern thereon. An etch mask had to be formed on the substrate via a removed or left photographic process. This conventional method is not only costly, but also influences the etching mask chemically and electrically in the subsequent plasma etching process, thereby preventing the implementation of the target etching cross-section. Using the Faraday box shown in FIG. 4 of the present invention, as shown in FIGS. 12A and 12B, ions can be selectively irradiated to a certain portion of the surface of the substrate. As shown in FIG. 2, the micro pattern may be etched in a single process without using the sensitized molecular film, thereby solving this problem. However, Void et al.'S invention is not suitable for solving this problem.

Grating with continuous V-grooves is a key component that is widely used in spectroscopy as well as semiconductors, optoelectronics and micromechanical devices. In the invention of voids and the like, since the direction of the ion beam is fixed in one direction, it is difficult to obtain gratings having inclined surfaces on the left and right sides. However, by using the Faraday boxes shown in FIGS. 7A and 7B of the present invention, the angle of incidence of ions can be adjusted at the same time in two or more directions, so that the X-ray high-resolution spectroscopy shown in FIG. 15B as well as the symmetrical grating shown in FIG. Asymmetrical gratings can also be made. The left and right oblique angles of these gratings can be adjusted by the angle of the Faraday box lattice plane.

Using a Faraday box having a single curved lattice surface shown in FIG. 8 of the present invention, as shown in FIGS. 16A to 16C, an etch section having different inclination angles and etching depths may be obtained according to the position of the substrate surface. . The inclination angle and the etching depth can be adjusted by the curvature of the lattice plane. By using this, various etching cross sections can be obtained from one wafer. This characteristic of the present invention is also not obtainable by the invention of voids.

In etching a large diameter wafer in a semiconductor processing process, in most cases, the shape and the etching depth of the etch cross section need to be uniform at all positions of the substrate in order to improve the process yield. However, as the diameter of the wafer increases, the variation of the ion and radical concentrations according to the position in the reactor increases, thereby increasing the unevenness of the etching rate. By using a Faraday box having a double curved lattice plane shown in FIG. 9 or a Faraday box having a lattice plane in which the lattice size varies depending on the position, the flux of ions incident on the substrate is controlled. As shown in FIGS. 17A to 17F and 18A to 18C, the etching direction may be arbitrarily adjusted according to the position while maintaining the etching direction in a direction perpendicular to the surface of the substrate, thereby achieving uniform etching even on a large diameter wafer. However, such characteristics cannot be obtained by the invention of voids and the like.

Claims (9)

In placing a Faraday box in a plasma etching apparatus and etching a substrate placed inside the box, the etching portion, the etching direction, or the etching rate is controlled by using a part or all of the upper surface of the Faraday box as a porous porous grid of various shapes. Plasma etching method characterized in that. The plasma etching method of claim 1, wherein the surface of the substrate is etched vertically by paralleling the surface of the substrate as shown in FIG. 3. The method of claim 1, wherein the substrate surface is partially etched by covering a portion of the upper surface as shown in FIG. The plasma etching method of claim 1, wherein the porous lattice surface has an open pattern as shown in FIG. 5, thereby etching the same pattern as the open pattern on the substrate surface. The plasma etching method of claim 1, wherein the etching direction is controlled by forming the porous lattice surface at a predetermined angle with the substrate as shown in FIG. 6. 2. The plasma etching method of claim 1, wherein the substrates are simultaneously etched in two directions by allowing the porous lattice surfaces to stick together as shown in FIGS. 7A and 7B. The plasma etching method of claim 1, wherein the porous lattice surface is a single curved surface as shown in FIG. 8, thereby controlling the etching direction and the etching speed according to the position of the substrate surface. The plasma etching method of claim 1, wherein the etching rate according to the position of the substrate surface is adjusted while maintaining the etching direction vertically by setting the porous lattice surface as a double curved surface. The method according to claim 1, wherein the etching speed is adjusted according to the position of the substrate surface while keeping the etching direction vertical by changing the size of the open portion of the porous lattice surface parallel to the substrate surface as shown in FIG. Plasma etching method.