JPH01103836A - Dry etching and apparatus therefor - Google Patents

Abstract

PURPOSE:To enable an element to be etched taking vertical shape while increasing the selection ratio by a method wherein a substrate is cooled down to the temperature not exceeding the point of inflection temperature wherein the gradient of the negative characteristics representing the relation of etching rate to the inverse number of the temperature of the first thin film increases from low to high levels. CONSTITUTION:A substrate is cooled down to the temperature not exceeding the point of inflection temperature wherein the gradient of the negative characteristics representing the relation of etching rate to the inverse number of the temperature of the first thin film increases from low to high levels. Then, an etching product low in vapor pressure such as SiCl4 can hardly be evaporated from the surface to increase the covering rate of the etching product on the surface. Thus, a material to be etched, when implanted with ion, is decomposed by excitation below the etching compound so that the primer of the material to be etched, e.g. SiO2 may produce Si due to the decomposition of SiCl4 while SiO2 may be reproduced by oxygen produced by the decomposition of SiO2. Consequently, the etching rate of SiO2 declines notably, the selection ratio is increased, undercut is minimized, and the vertical etching process can be performed easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application) The present invention is directed to selectively etching a second thin film on a first thin film with respect to the first thin film.

The present invention relates to a dry etching method and a dry etching apparatus in which the second thin film is effectively etched.

(Prior Art) The degree of integration of semiconductor integrated circuits is increasing and the pattern size is becoming finer. In the case of the gate oxide film of a type integrated circuit, 1
It is about to become below 00A.

Conventionally, a single-reactive ion etching method has been used as a V-teng method for processing electrode materials such as polycrystalline silicon. In reactive ion etching, the material to be etched is placed in a vacuum vessel equipped with a pair of parallel plate electrodes, a reactive gas is introduced, and then the gas is discharged by applying high frequency power, and the gas plasma generated by this discharge is This is a method in which the material to be etched is etched using an etching method.

In addition to this reactive ion etching, there are other methods such as plasma etching, ECR type dry etching, ion beam etching, and photoexcitation etching. Etching is performed by chemically or physically acting on ions of a reactive gas, and in this respect it can be considered similar to the reactive ion etching described above.

There are two types of reactive ion etching: a cathodic coupling method in which the material to be etched is placed on the electrode to which high-frequency power is applied, and a cathodic bonding method in which the material to be etched is placed on the electrode to which high-frequency power is applied; The electrode on which the material to be etched is placed is generally water-cooled to room temperature to prevent thermal deformation of the resist formed on the material to be etched. The material to be etched is either electrostatically or mechanically chucked and placed on this water-cooled electrode, or simply placed on the water-cooled electrode. Etching also proceeds through an ion-promoted chemical reaction in which ions in the plasma bombard the material to be etched, and a chemical reaction in which radicals proceed naturally.The former is the driving force behind directional etching.

The latter gives an isotropic etched shape. Therefore, the greater the contribution of the ion-promoted chemical reaction, the better the etching directionality (and the closer the shape becomes).

Also, when the adhesion between the material to be etched and the sample stage (an electrode is used in the case of reactive ion etching) is good due to the above-mentioned chuck or the like.

In order to prevent the resist formed on the sample from deteriorating, it was sufficient to perform water cooling to about room temperature as described above. Furthermore, since the etching rate decreases when the temperature of the material to be etched is lowered, the material to be etched is usually not cooled below a temperature at which deterioration of the resist can be suppressed even when the layer density is impaired.

Next, problems with conventionally used etching equipment will be described.

FIG. 11 is a schematic diagram of a conventional cathode-coupled parallel plate dry etching apparatus.

The vacuum vessel (1) has a pair of parallel plate electrodes (positive
fi +2) and a cathode (3)), the anode C) is grounded, and 13.56 MHz high frequency power is applied to the cathode (3) from a matching box (4).

A negative FM (31 has a passage 6 for flowing cooling water as a refrigerant) is provided to cool the cathode (3). Etching gas is introduced into the vacuum container (1) from the gas introduction pipe (6) and exhausted from the exhaust port (7).

The substrate to be etched (8) is placed on the cathode (3).

In a normal etching device with this kind of configuration.

The cathode [3] also serves as a part of the vacuum container 0). As mentioned above, a refrigerant is flowed through the cathode (3) at about room temperature.

Due to the temperature inside the vacuum container (1), water vapor is mixed with liquid and condenses on the surface of the cathode (3) and the passageway (5) through which the refrigerant flows. As a result, water drips into the device and the electrical seal
This may cause inconveniences such as

For example, in the above-mentioned conventional etching apparatus, a matching box (4) is connected to a cathode (3) electrode in a vacuum container (1) containing a substrate to be etched to apply an RF voltage.
), but this matching box is r
In some cases, the wires made of steel or the like connected to the electrodes are surrounded by a tube (case) made of aluminum or the like, and this tube is connected to a matching box. In some cases, it is provided so as to be connected to the circuit inside the switching box.

In either case, water droplets generated when the electrode is water-cooled can cause a sheet in the wiring circuit within the dry etching apparatus. Furthermore, conventionally, an insulating material such as Piton O-ring is generally used for the vacuum seal on the cathode side, and this material is made of a material that is strong in vertical direction. However, there is a problem in that when the temperature of the cathode decreases, the insulating material such as the O-ring hardens, causing leakage. These problems also exist to a greater or lesser extent in other etching apparatuses.

Next, problems encountered when etching, for example, polycrystalline silicon using conventional equipment will be described.

FIG. 12 shows the potential distribution within the single-reverse ion etching apparatus. (3) and 12) are used as the cathode and anode of the dry etching apparatus shown in FIG. 11, respectively.

Here, the highest potential in the discharge space in the vacuum vessel (1) is at the plasma level 1 (1) as shown in Figure 12.The movement of electrons is extremely large compared to that of ions, so the plasma Electrons accumulate on any surface in contact with the plasma potential (1), and the potential becomes lower than the plasma potential (1).The cathode (3)
), whereas the surface produces a large cathodic drop voltage to maintain the condition.

On the surface of the anode Q), a potential difference is generated only by the plasma potential (10). Therefore, in the % cathode bonding method, the contribution of the ion-promoted chemical reaction is larger and the etching directionality is better. In the cathodic bonding method, since the energy of ion bombardment is small, the directionality of etching is poorer than in the cathodic bonding method, and undercapsulation, reverse taper shapes, etc. are likely to occur. In other words, from the viewpoint of processing performance, the cathodic bonding method is superior and can be said to be suitable for forming fine patterns in the submicron region in the future.

On the other hand, in etching, not only the processed shape (1'D) but also the selectivity to the underlying material is important. For example, in etching gate materials such as polycrystalline silicon, as already mentioned, When the film thickness is as thin as 100A or less, an extremely high selectivity with respect to the silicon oxide film is required.In the cathodic method, the ion bombardment energy is large, so the surface is decomposed regardless of the properties of the material. As a result of different materials, the difference in etching rate, ie, the selectivity, is generally smaller than in the anodic bonding method.

Therefore, overall, when using the cathodic bonding method, the selectivity is good but the processed shape is poor, and when the anodic bonding method is used, the processed shape is good but the selectivity is small. There were some difficulties. Furthermore, when devices such as ordinary MOS (MOS) transistors are fabricated using both methods, in the former method, the poor shape of the 7111 process causes variations in the channel length, while in the latter method, the etching occurs on the gate oxide film. However, the problem is that the underlying silicon substrate is etched, leading to a decrease in yield (1).
There was.

Furthermore, in recent years, an etching apparatus using ECR discharge has been developed and is being applied to etching polycrystalline silicon.

In this method, the ion energy is only several tens of volts, so a selectivity of 30 or more with respect to the saponified silicon film is obtained. However, this method also has the disadvantage that, like the anodic bonding type ion etching device, the ion energy is small, so the υ loe shape requires more effort than the cathode bonding type device.

The problems of 5 reactive ion etching and ECR type etching have been described above, but even when performing the other etching mentioned above, it is necessary to have a high 1 selection ratio and an excellent υ Loe shape in order to fabricate future fine devices. An etching method and apparatus are desired.

(Problem to be solved by the invention) The object of the present invention is the above-mentioned (.

If you try to obtain a high selection ratio, the 710 machining shape will become poor.

On the other hand, an etching method and etching device that solves the problem of conventional etching in which the selectivity decreases when trying to obtain a good processed shape, and make it possible to process vertically, etc. while obtaining a high selectivity. Our goal is to provide the following.

[Structure of the invention]

(Means for Solving the Problems) In the etching apparatus conventionally used for etching, as already mentioned, the workpiece material placed in the apparatus is simply placed on the electrode, or is electrostatically or mechanically etched. It is heated and water cooled. Therefore, during etching, the temperature of the material to be etched may be reduced at most by water@
It was up to. In addition, there has been almost no attempt to consider low temperatures below the water temperature of the V-teng material to be machined at 1° C. in dryer V-teng.

The inventors of the present invention have intensively investigated the temperature dependence of the etching rate of materials such as polycrystalline silicon and silicon oxide films using reactive gases containing chlorine, etc., and found that materials such as polycrystalline silicon have a While the etching rate changes linearly with respect to the reciprocal, in the case of silicon oxide films, there are two types of temperature dependence: the slope of change is small on the high temperature side, and the slope is large on the low temperature side. It was found that the selectivity ratio of 5 was significantly improved. Further investigation revealed that there are other materials that exhibit high selectivity.

Based on this knowledge, the present invention provides a dry etching method for selectively etching a second thin film formed with an IC shadow on the first thin film with respect to the first thin film ζζ. Provided is a dry etching method characterized by cooling to below an inflection point temperature plate where the magnitude of the slope of the negative characteristic representing the relationship between the etching rate and the reciprocal of the temperature increases from small to large.

Further, the present invention provides a vacuum container for storing a sample in which a second thin film is formed on a first thin film, and a second thin film is selected for the @1 thin film in each vacuum container. means for introducing a reactive gas for the purpose of testing the sample; means for exhausting the reactive gas; means for activating the reactive gas; Provided is a dry etching apparatus characterized in that it is equipped with means for cooling below an inflection point temperature plate where the magnitude of the slope of the negative characteristic indicating the relationship between the etching rate and the reciprocal of the etching rate increases from small to large.

(Function) When the temperature of the substrate surface is high, reactive gases such as
SiC is an etching product produced from @ element (CZ*) and the material to be etched, such as polycrystalline silicon (St).
/4 etc. are desorbed from the surface by main evaporation.

The surface is then excited or decomposed by ion bombardment, and a new ion-promoted chemical reaction proceeds. However, when the material to be etched is cooled to a low temperature such as below freezing, the 5i
Etching products with low vapor pressure, such as Cj4, are difficult to evaporate from the surface (as a result, the etching product coverage rate on one surface is high. Therefore, when ion bombardment is applied).

Excitation or decomposition occurs at the lower surface of the etching product. As a result, the base material of the work piece becomes, for example.

If sio, St is produced from the decomposition of 5iCJ4 as described above, while oxygen comes out from the decomposition of StO, so that e S i O, is generated again. Therefore, sio
.

When the substrate temperature is low, the etching rate of St is significantly lower than that of St, and the 5 selectivity is improved.

Furthermore, in general, chemical reactions by uncharged active species (radicals) generated from the decomposition of reactive gases have greater temperature dependence than ion-promoted chemical reactions; A side effect is that the undercut is smaller and vertical etching is easier to achieve.

(Example) First, in order to explain the dry etching method according to the present invention, the relationship between the etching rate and the reciprocal of the substrate temperature when selectively etching the second thin film with respect to the first thin film is shown in FIG. This will be explained using a characteristic diagram.

That is, here, a silicon oxide film (
2), silico/nitride film 0, polycrystalline silicon y film (a) with addition/addition as the second thin film, molybdenum silicon side tb), tungsten silicide (C), and titanium silicide (tops were selected and investigated. The dry etching apparatus used in this embodiment, which is an embodiment of the present invention, is a cathode-coupled parallel plate type apparatus as shown in FIG. 11, but it differs from the dry etching apparatus shown in FIG. is that it has a means for cooling the substrate to below 0° C. Chlorine gas is used as the reactive gas introduced into the vacuum container of the dry etching apparatus, and the pressure is 0. (15 Torr, 200 W). In the figure, the vertical axis represents the etching speed.

The horizontal axis scales the reciprocal of temperature. Here, the etching rate of the second thin film decreases monotonically with decreasing temperature.

On the other hand, the etching rate of the first thin film also decreases as the temperature decreases, but around 0°C (=3.6X10-K-1
), and below that temperature the etching rate decreases rapidly. As a result, at subzero temperatures, the selectivity increases significantly. The reason for this is, as already mentioned,
Base! When the temperature decreases, etching products that do not originally have high vapor pressure (in this example, CA!, 5iCj due to the reaction between gas and polycrystalline silicon, etc.) become difficult to desorb from the surface, and the surface roughness increases. Then, when the first thin film is a silicon oxide film, the next applied ion bombardment reacts with a substance generated from the surface, that is, oxygen, to form an acid ratio film again. That is, even if silicon oxide is removed from the surface by an etching reaction, silicon oxide is deposited again by the etching product by a CVD reaction in the gas phase. As a result, the etching rate of the acid arsenic film is significantly reduced and the selectivity is improved. In the case of silicon nitride film (l), the same tendency as in silicon oxide film (2) was given, but here, when polycrystalline silicon fal is selectively etched with respect to the silicon oxide film surface, A good selectivity ratio was obtained.Other than this, when selectively etching a silicon nitride film (polycrystalline silicon Y film (a) with respect to a silicone film), or when etching a silicon acid ratio film (2), On the other hand, it can be applied to various combinations of materials using their characteristics, such as when selectively etching a silicon nitride film.Also, in the case of a silicon oxide film and a polycrystalline silicon film, the etching rate and Considering the selection ratio of 0, the most suitable temperature was -10 DEG C. to -30 DEG C. Further, the inflection point in the characteristic showing the relationship between the reciprocal of IW and the etching rate changes depending on the pressure.

In other words, the lower the pressure, the lower its inflection point temperature,
At temperatures above the inflection point, the slope of the negative characteristic may become positive.

However, in either case, the slope of the negative characteristic changes from small to large at the inflection point.

Next, the cross-sectional shape of the material to be etched which was actually etched by the dry etching method according to one embodiment of the present invention will be explained using Fig. 1g2. first.

A material to be etched as shown in FIG. 2(a) is formed.

That is, a CVD-stol film (2) is formed as a first thin film on a substrate (2) such as P type 51 (100), and a doped polycrystalline silicon film (22) is further formed as a second thin film. Further, a lower resist layer (23), a middle spion glass (24), and the like are formed in this order, and patterning is carried out using a conventional exposure technique to form the material to be etched as shown in FIG. 2(a).

This material to be etched is mixed with the first thin film S i O, film (
b) As shown in Figure 2 (b), the polycrystalline silicon film (22a) is side-etched when (2)) is cooled to -20°C, which is the temperature below the inflection point of the characteristic diagram shown in Figure 1. It was etched vertically without causing any damage.

Furthermore, when etching was performed at room temperature, side etching occurred in the polycrystalline silicon film (22b) as shown in FIG. 2(c). Originally, phosphorous-doped polycrystalline silicon naturally reacts with chlorine radicals and is prone to side etching. However, in the case of 1-reactive ion/etching, the decomposition products of the resist adhere to the sidewalls of the polycrystalline silicon, preventing the sidewalls from being attacked by radicals, thereby preventing side etching and achieving vertical etching. Therefore, when a multilayer resist is used as a mask, as shown in FIG. 2(a), the resist is not directly exposed to plasma.

Since no sidewall protective film is formed and the sidewalls of polycrystalline silicon y are not protected from radical attack, side etching occurs at room temperature. However, the temperature dependence of chemical reactions that proceed naturally with radicals is greater than that of ion-promoted chemical reactions, and at low temperatures, the mobility of radicals on the etched surface decreases, resulting in negative It has been found that side etching does not occur at 20° C., which is particularly effective in such cases.

A similar effect can be obtained when etching is performed not only with a cathode-coupled type dry etching apparatus but also with an anodic-coupled dry etching apparatus. In the case of an anodic bonding type device, as already mentioned, there are difficulties in the 7JII machining shape, but the method of the present invention not only improves the selectivity but also greatly improves the machining shape. As described above, the dry etching method according to the present invention not only provides a high selectivity but also provides a good etched shape.

Next, still another best embodiment of the present invention will be described with reference to the drawings.

FIG. 9 is a schematic diagram of an apparatus according to an embodiment of the present invention used in this embodiment. This dry etching equipment is the 9th
Since the basic configuration is the same as that of the apparatus shown in the figure, the same parts as in FIG. 9 are denoted by the same reference numerals, and detailed explanation will be omitted.

This dry etching apparatus has means (5) for cooling the substrate to a temperature near the inflection point where the slope of the negative characteristic indicating the relationship between the temperature and the etching speed changes from small to large. In addition, it is characterized by having means (11) for generating a zero magnetic field within the vacuum vessel (1). The means for generating the magnetic field is a magnet provided above the anode (2), and this magnet rotates eccentrically.

Electrons move cycloidally in a region perpendicular to the leakage magnetic field supplied from the magnet toward the cathode 3) and the DC electric field (1) of the sheath on the cathode surface, generating high-density magnetron plasma. This high-density magnetron plasma moves in close proximity to the surface of the substrate (6) as the magnet rotates eccentrically, enabling highly selective etching of the substrate (8).

Figure 10 is a characteristic diagram showing the relationship between the etching rate and the reciprocal of temperature when etching is carried out by flowing CJ and gas into the vacuum chamber (1) of the apparatus using the dry etching apparatus shown in Figure @9. It is. The gas pressure and the high VT force applied to the electrode are Q, (15 Tor
r, 2'00W. Further, the substrate (8) used was one in which a phosphorous-doped polycrystalline film was formed on the entire surface as a second thin film, and a silicon oxide pattern was further patterned in a desired shape as a first thin film thereon.

From this figure, qualitatively similar phenomena are observed in this example and the previous example in which no magnetic field is generated. This example is thicker (.

It can be seen that a better sieve selection ratio can be obtained.

In this example, a silicon oxide film and a phosphorous-doped polycrystalline silicon film were used as the first and second thin films, and CAI gas was used as the etching gas, but other materials and reactive materials rich in halogen elements were used. Gas may also be used; in this case,
A higher selectivity can be obtained compared to etching without generating a magnetic field.

Further, other embodiments of the dry etching method according to the present invention will be described. That is, this embodiment is a method in which etching is performed in two stages. First, the material to be etched, on which the first and second thin films are formed on a substrate similar to that shown in Fig. 2, is first subjected to ordinary reactive ion etching to extremely reduce the thickness of the second thin film. The film thickness should be thin. Thereafter, the material to be etched is etched while being cooled in the same manner as explained in FIG.

Such an etching method is particularly effective when the second thin film is much thicker than the first thin film because etching proceeds quickly in the initial stage.

Next, two embodiments of the dry etching apparatus, which is applied to the dry etching method of the present invention and in which various improvements have been made to the pond of the dry etching apparatus described above, will be described in detail with reference to the drawings.

FIG. 3 is a sectional view of an improved etching apparatus manufactured to carry out the method/IL according to the present invention. This is a cathode-containing type etching apparatus, and basically has almost the same configuration as the apparatus shown in FIG.
It is installed via an insulating material (34) on the bottom plate (33) that constitutes the vacuum container (32), and constitutes the bottom plate (33) and the vacuum container (32) in order to seal the inside of the container from vacuum. Q IJ of insulating elastic material between the flange part of the wall surface
With the intervention of 7g (35).

The bottom plate (33) and the flange portion are brought into close contact. The L portion of the vacuum container is similarly vacuum-sealed by an upper plate (not shown) and an O-ring. The piping through which the refrigerant for cooling the cathode (31) connected to a power source such as an RFI source passes through the bottom plate and exits into the atmosphere is insulated from the bottom plate (33).

The part that penetrates the bottom plate (33) is a ceramic via (3
6), and this pipe is attached to the bottom plate (37) using resin (37).
33) and vacuum seal at the same time. Cathode (3
1) Inside, a stainless steel pipe (38) is placed on the cathode to effectively control the temperature of the sample.

For example, they are arranged in a spiral shape within the cathode. Then, the stainless steel pipe (38) coming out of the cathode and the ceramic via' (36) are welded on the stainless steel pipe side and connected with a connector (39) with an O-ring seal structure on the ceramic pipe side.

The refrigerant is arranged to flow to the cathode (31).

here,? 11- The medium is the material of the thin film of the sample (25) disposed on the cathode (31). Accordingly, there is an inflection point at which the negative custom slope, which indicates the relationship between the reciprocal of temperature l and the working velocity, becomes large. Sample temperature control means (
32), and flows through the ceramic pipe (36) and the stainless steel pipe (38).

Specifically, any refrigerant may be used as long as it can cool the sample as described above, but here nitrogen gas was used and was circulated in a pipe through which liquid nitrogen was passed. Alternatively, fluorocarbon gas may be supplied. Further, the cooling means may be of a water jacket type instead of a pipe.

By having such a structure, 1, for example, minus 30
It becomes possible to cool the cathode (31) to about .degree. Therefore, according to this device, as described above, good etching can be performed with a high selectivity.

In addition, since there is a means to prevent condensation such as the insulating material (34), condensation does not occur on the outside of the bottom plate (33) like in the past, and even if you use the toilet for a long time, water droplets will cause short circuits. Furthermore, because the O-ring used for vacuum sealing was made of silicone rubber in this dry etching device, the O-ring did not harden even though the cathode was cooled to temperatures as low as -30°C. No leaks were observed.

It goes without saying that other embodiments of the dew condensation prevention means provided on the cathode portion of FIG. 4 can also be applied to the apparatus shown in FIG. 3 or the pond dry etching apparatus according to the present invention, which will be described later. In this embodiment, similarly to the embodiment shown in FIG. 3, the cathode (first) has a sample@open control means that controls the slope of the negative characteristic of the etching rate with respect to the reciprocal of temperature, depending on the material of the thin film of the sample. The inflection point where it becomes big! A pipe (45) is provided for passing a refrigerant cooled to below 50°C. As a result, the sample is slowly cooled to below the desired temperature described above. Further, the back surface of the cathode (first) is covered with a thick heat insulating material (42). Vacuum seal is 0 s/g (4
5), but in this case, a heater (44) is installed in the insulating material (43) in order to prevent hardening when the temperature of the cathode drops even with the O-ring of a normal tool 7, etc.
Embedded QIJ rings are kept at room temperature.

FIG. 5C (roll) is a schematic cross-sectional view of a cylindrical plasma etching apparatus. A cylindrical vacuum container (51) made of quartz, a gas introduction system (52), an exhaust system (53), and a coil or electrode (not shown) for applying high frequency power are installed in the container (51).
). Etching gas is introduced from (52), the pressure is maintained at 0.1 to ITorr, and high frequency power is applied capacitively or conductively through the coil or electrode to generate plasma, and the material ( 54). The etching sample (54) is usually placed on a quartz bowl (55) and is in an electrically floating state, and since the only potential difference is the difference between the plasma potential and the floating potential, the ion-promoted chemical reaction is The contribution is small, and etching progresses mainly due to radicals. Therefore, the processed shape of the sample is monoisotropic. Usually, a mixed gas of CF and oxygen (approximately 10%) is introduced to remove polycrystalline silicon or silicon nitride.
Used for etching membranes. After all, a large selection ratio with respect to the silicon oxide film is required. As shown in FIG. 5 1al, in a normal device, a selectivity of about 20 is obtained between a phosphorus-doped 710 polycrystalline silicon film and a silicon oxide film, but a selectivity ratio of about 20 is obtained between a silicon nitride film and a silicon oxide film. teeth,
It is about 5 to 6 at most, and an improvement in the selectivity has been desired for purposes such as peeling off the silicon nitride film of LOGO8. FIG. 5(b) is a sectional view showing another embodiment of the dry etching apparatus according to the present invention, which is improved so as to be able to cool the sample (54). Components that are the same as those in FIG. 5 Ta) are indicated with the same reference numerals. The difference from Fig. 5(a) is that
A printed plate (57) is placed on a quartz sample stand (56), and the sample (54) is electrostatically chucked. This is the point where it is cooled by flowing water. In this example, as in the example shown in FIG. 3, the silicon oxide film was cooled to, for example, -20° C. below the temperature of the inflection point where the characteristics of the silicon oxide film change. This is the result of adding about 30 grams of chlorine to the mixed gas of CF and oxygen.

The selectivity ratio between polycrystalline silicon and silicon oxide is 30
In addition, the silicon nitride film and the silicon oxide film have 12~
15, and the effect of this example was confirmed.

FIG. 6 (al is a schematic diagram of an ECR type dora dry etching device. This device can be roughly divided into a discharge chamber made of quartz (
61) and a separate engineering room (62). Around the discharge chamber (61) is an a of 875 Gauss.
A magnet (63) that generates ducks is provided. The microwave is supplied from a microwave power supply (not shown) to a microwave introduction pipe (64
] is supplied to the discharge chamber (61). Pipes (65) and (66) are provided so that the etching gas can be introduced into both the discharge chamber (61) and the etching chamber (62). The sample (67) is placed on a sample stage (68) installed in the etching chamber (62). On the sample stand,
A cooling means (69) is provided for cooling the sample to an inflection point of 1 degree or less at which the slope of the negative characteristic of etching rate with respect to the reciprocal of temperature changes from small to large depending on the material of the thin film of the sample. or,
This cooling means is connected to a means for controlling the cooling temperature, so that it can be cooled to an arbitrary cooling temperature. ECR discharge occurs in the discharge chamber, and the generated ions y are pushed out along the gradient of the magnetic field and irradiated almost perpendicularly onto the etching sample. Since the operating pressure is low, on the order of 10-' torr, the amount of radicals is small, and etching occurs mainly.

This is a kind of ion shower-like etching device that uses ions. In this device, the plasma potential is low and the sample (67) is normally electrically (floating), so
It is characterized by low ion energy. Since chlorine gas alone would leave a residue as the reactive gas introduced, a mixed gas of SFs and chlorine, for example, is used to etch the phosphorous-doped polycrystalline silicon. With this equipment, etching conditions that do not produce residue even without cooling (chlorine 80 *, SF, 10%, total gas flow rate 15
sec, pressure 0.0003 Torr, microwave 200W), a selectivity ratio of about 40 to silicon oxide/membrane can be obtained.

However, silicon oxide (71) is formed as a #11 thin film on the substrate (70), and further on top of it.

When etching a material to be etched on which a $2 thin film of IJ y-doped polycrystalline silicon (72λ) (73) is formed as a mask on the second thin film (72) which is not further etched, the second thin film is etched. As shown in Figure 7+a), slight side etching may occur.

It was easy to form an overhang shape.

On the other hand, when the cooling means (69) was operated to cool the sample to -20°C and etching was performed under the same conditions, the 1 selectivity was improved to more than 50, and the processed shape was also improved as shown in Figure 7. (As shown in BL, there were no side edges, overhangs, etc., and the product was in extremely good condition.

This device is very similar to the ECR-type V-etching device described above, but the discharge section and etching section are separated, and a negative potential is applied to the grid from the plasma formed in the discharge section to extract positive ions, and the sample is sampled at a speed of 7111. In both ion beam etching equipment that irradiates the substrate with chlorine and electron beam etching equipment that applies a positive potential to the grid to draw out negative ions and screws and irradiates the substrate, if a reactive gas containing chlorine is used as the etching gas, the substrate can be etched. Cooling was found to have a similar effect.

FIG. 8 is a schematic diagram of a photoexcited etching apparatus, which is still another dry etching apparatus according to the present invention. A vacuum container (81) having a quartz window (80) for introducing ultraviolet light is equipped with a sample stage (82) which can be cooled in the same manner as in the above embodiment. (
83), and the light emitted from 84) is converted into ultraviolet light.
85) is irradiated onto the sample (86). Gas is extracted from the exhaust system (8
7) Exhaust from f. In this device, chlorine gas is introduced into the device, maintained at a pressure of several tens of Torr, irradiated with ultraviolet light to dissociate the chlorine, and the generated chlorine radicals are used to etch polycrystalline silicon. Unlike etching using plasma, photo-excited etching does not damage the device and chlorine radicals do not naturally react with the silicon oxide film. It has the advantage of providing a large selection ratio. However, as already mentioned, in conventional etching, phosphorous-doped polycrystalline silicon reacts spontaneously with chlorine radicals, resulting in side etching, making it extremely difficult to perform straight processing. Therefore.

When the sample (86) was cooled to -20°C by a cooling means and etched using sc1M gas at 50'porr and irradiated with an excimer laser (Xecl) as an ultraviolet light source, side etching was prevented and vertical etching was prevented. It is clear that this can be achieved. This is because the etching rate due to radicals is extremely reduced by cooling.
This is thought to be due to the fact that only the area irradiated with light increases in size and the reaction is promoted by light.

In this example, an excimer laser (Xe
Cj light, 303 nm)% was used, but any light with a wavelength that can dissociate chlorine gas may be used; for example, low-pressure H
A g lamp, a Hg-Xe lamp, etc. may be used. Furthermore, substrate cooling provides a similar effect in optically excited etching using vacuum ultraviolet light or SOR light, which has a shorter wavelength.

The first embodiment of the present invention has been described above, but the fifth embodiment of the present invention is as follows.

This is basically based on the knowledge that the etching rate of a first thin film such as silico/film is abnormally reduced due to substrate cooling. Moreover, as the first thin film,
In addition to silicon oxide/films (silicon nitride films are also effective in the present invention. In the present invention, as the second thin film, not only polycrystalline silicon/films but also acid-ratio silicon/films such as tungsten, molybdenum, titanium, and their silicides) can be used. It is effective in etching materials that require a high selectivity to the film.

〔Effect of the invention〕

As mentioned above, the effect of the present invention is that the etching rate of the first thin film such as the first silicon oxide film is significantly reduced, so that the etching selectivity with respect to the second thin film is significantly increased. Also,
By cooling the substrate, side etching is suppressed and vertical etching is more easily achieved.

[Brief explanation of the drawing]

1 is a characteristic diagram for explaining the dry etching method according to the present invention, FIG. 2 is a diagram for explaining the dry etching method according to the present invention, and FIGS. 3 to 6 and 9.
Figure 1 is a schematic diagram for explaining the dry etching apparatus according to the present invention, Figure 7 is a diagram for explaining the effect of the dry etching apparatus according to the present invention, and Figure 8 is a schematic diagram for explaining the dry etching apparatus according to the present invention. Diagram for explanation, No. 10
FIG. 9 is a characteristic diagram for explaining the effect of one embodiment of the present invention, and FIGS. 11 and 12 are explanatory diagrams for explaining the problems of the conventional technology. 11...Means for generating a magnetic field, 2)...Silicon oxide film%22...Polycrystalline silicon 7Kh 3L No. 157
t69.82--cooling means, 34.42--dew condensation prevention means. Agent: Patent Attorney Noriyuki Chika Attorney: Hikaru Matsuyama 3-1)
:? , 2 3, 4 3. ζ 3.8, θ
η (X yo-J' to 10 Figure 1 Figure 2 Figure 4 - "-/S2 " = Korokoko (a) SiB6 7-/S3 Figure 8 Figure 9

Claims (17)

[Claims] (1) A first thin film and a substrate on which a second thin film is formed are placed in a vacuum container, and an activated reactive gas is introduced into the vacuum container to In a dry etching method in which a thin film of No. 2 is selectively etched with respect to a first thin film, the slope of a negative characteristic indicating the relationship between the etching rate and the reciprocal of the temperature of the first thin film is small. A dry etching method characterized by cooling to a temperature below a temperature near a large inflection point. (2) A first thin film and a substrate on which a second thin film is formed on the first thin film are placed in a vacuum container, and an activated reactive gas is introduced into the vacuum container, and the vacuum In a dry etching method in which the second thin film is selectively etched with respect to the first thin film by generating a magnetic field in a container, the relationship between the etching rate of the substrate and the reciprocal of the temperature of the first thin film is shown. 2. The dry etching method according to claim 1, wherein the dry etching method is cooled to a temperature below a temperature near an inflection point at which the magnitude of the slope of the negative characteristic changes from small to large. (3) The dry etching method according to claim 1 or 2, wherein the reactive gas is a gas containing at least one halogen element. (4) The second thin film is polycrystalline silicon, phosphorous-doped polycrystalline silicon, silicon nitride film, tungsten, molybdenum, titanium, or any of these silicides, and the first thin film is silicon oxide Claims 1 and 2 characterized in that it is a film or a silicon nitride film.
Dry etching method described. (5) The first thin film is a silicon oxide film, the second thin film is a polycrystalline silicon film added with impurities, chlorine is used as the reactive gas, and the temperature range is below zero degrees Celsius. The dry etching method according to claim 1 or 2. (6) The activation of the reactive gas is performed at 10^-^4 Torr.
3. The dry etching method according to claim 1, wherein the dry etching method is carried out at a temperature of r or more. (7) The dry etching method according to claim 1 or 2, wherein the substrate is separated from a means for activating a reactive gas. (8) Activation of the reactive gas is performed by applying high frequency power to a pair of parallel plate electrodes provided in each vacuum chamber;
3. The dry etching method according to claim 1, characterized in that the dry etching method is carried out by one of a method of applying high frequency power to a cylindrical vacuum container by capacitive coupling or inductive coupling, or a method of applying microwaves. (9) Activation of the reactive gas is performed using ultraviolet light or SOR.
2. The dry etching method according to claim 1, wherein the dry etching method is carried out by irradiating a reactive gas with light. (10) A vacuum container for storing a sample in which a second thin film is formed on the first thin film, and a vacuum container for selectively etching the second thin film with respect to the first thin film in the vacuum container. means for introducing a reactive gas; means for exhausting the reactive gas; means for activating the reactive gas; A dry etching apparatus characterized in that it is equipped with means for cooling below an inflection point temperature at which the magnitude of the slope of a characteristic changes from small to large. (11) A vacuum container for storing a sample in which a second thin film is formed on the first thin film, and a vacuum container for selectively etching the second thin film with respect to the first thin film in the vacuum container. means for introducing a reactive gas, means for exhausting the reactive gas, means for activating the reactive gas, means for generating a magnetic field in the vacuum container, and Claim 1 characterized by comprising means for cooling to below an inflection point temperature at which the magnitude of the slope of the negative characteristic indicating the relationship between the etching rate and the reciprocal of the temperature increases from small to large.
The dry etching apparatus described in 0. (12) Claim 1 characterized in that the sample stage on which the sample is placed is provided with piping for passing a refrigerant for cooling the sample.
The dry etching apparatus described in 0 and 11. (13) The dry etching apparatus according to Claims 10 and 11, wherein the sample is placed on an electrode that discharges a reactive gas. (14) The dry etching apparatus according to claim 13, wherein means for applying a voltage to the electrode is provided adjacent to the outside of the vacuum container. (15) The dry etching apparatus according to Claims 10 and 11, wherein the means for cooling the sample is provided with a dew condensation prevention means to prevent dew condensation from forming on the outside of the vacuum container. (16) The dry etching apparatus according to claim 15, wherein the dew condensation prevention means covers a portion to be cooled with a heat insulating material. (17) Claim 1, wherein the cooling means includes means for controlling the cooling temperature of the sample to 0° C. or less.
The dry etching apparatus described in 0 and 11.