JP5098969B2 - Etching method and apparatus - Google Patents

Description

  The present invention relates to an etching technique, particularly to a technique for removing silicon oxide on a substrate.

  In microfabrication technology represented by semiconductor device manufacturing technology, circuits are formed by etching various thin films such as metals and insulating films. For this processing, a technique using gas plasma under vacuum is frequently used.

Of these, hydrocarbon gases containing fluorine such as CF ₄ and CHF ₃ are often used for processing of silicon oxide films (see Table 1). This plasma contains radicals such as CFx * and mainly reacts with a substance to be processed.

  However, there are a large number of charged particles such as electrons and ions in the plasma, and light emission by plasma discharge includes high energy light up to soft X-rays. For this reason, it is a cause of damage due to crystal defect formation or the like on the semiconductor substrate.

  This ashing process using oxygen gas plasma enables high-speed processing of about 1 μm per minute, but the damage to the elements due to charged particles is large, and it is fatal damage to miniaturized semiconductor elements such as LSIs. May give.

  Since plasma damage is reduced when the wafer is not directly exposed to plasma, it is effective to separate the wafer and the plasma generation unit, but there is a disadvantage that the ashing rate is reduced (Non-patent Document 1).

  As a resist removing method without plasma damage, there is an ozone ashing method using ozone and ultraviolet rays. In this method, radical oxygen (O.) contributing to the ashing reaction is obtained by irradiating ozone with ultraviolet rays as shown in the following formula (1).

O ₃ + hν → O · + O ₂ (1)
h: Planck's constant, ν: Frequency Usually, a resist material composed of various hydrocarbons undergoes a decomposition reaction represented by the following formula (2) by reaction with radical oxygen and is removed. In practice, the substrate is heated from about 200 ° C. to about 300 ° C. to increase the reaction rate.

CxHy + (2x + y / 2) O.fwdarw.xCO ₂ + (y / 2) H ₂ O (2)
However, although this ozone ashing method does not cause plasma damage to the device, the resist removal rate is several hundred angstroms to several thousand angstroms per minute, compared with about 10,000 angstroms / minute (1 μm / minute) of ashing by oxygen gas plasma. There is a disadvantage of being slow. This method is often performed at atmospheric pressure, but ozone leakage must be taken into account.

  On the other hand, there is a method to improve the ashing speed by spraying high-concentration ozone on a high-temperature substrate under reduced pressure and using radical oxygen generated by thermal decomposition, but the substrate temperature is high as before, and the thermal load on the substrate is high. Is getting bigger.

  The photoresist removal completely removes the photoresist remaining on the substrate after the etching process, whereas the photoresist is exposed to light, the slight photoresist remaining at the bottom of the pattern after development, and the cause of pattern dimension error. There is also a need to remove the bottom (scum) of the bottom corner of the pattern. These cause fluctuations in wiring resistance, defective wiring, and the like, causing device performance deterioration and yield reduction.

  In addition, MEMS, sensor devices, and some semiconductor devices may use precious metals such as gold, which have extremely low reactivity, or materials that cannot be processed because the vapor pressure of substances formed after dry etching is low. Lift-off technology and plating technology are also used. In such a process, the residual film and scum of the photoresist after development become a more serious problem, which impairs the adhesion between the wiring material and the substrate.

  In order to solve such problems, conventionally, the remaining film can be removed by plasma ashing in a short time, and the resist bottoming (scum) at the bottom corner of the pattern can be removed by the same method to reduce the wiring width. (Patent Document 1 etc.).

  This method is also applied to the manufacture of photomasks used in photolithography processes that are performed multiple times in the process of manufacturing semiconductor circuit patterns that are becoming finer year by year, and corrects errors from design values in response to stricter dimensional accuracy. It is used as a method.

  In the device manufacturing process, the aspect ratio of the circuit pattern increases with the miniaturization of the size, and in the plasma process to such a shape, the microloading is likely to cause a processing residue at the bottom of the pattern groove and the corner of the bottom. The problem of effect comes out.

In addition to residue removal, a method of thinning a resist pattern by ashing after exposure and development of a photoresist to obtain a fine pattern that exceeds the limit of the exposure apparatus is also practiced.
Issued electronic journal, Semiconductor Technology Taizen, 2002, pp. 320 JP 2006-294842 A

  Although etching processing using gas plasma enables high-precision processing, damage to the device due to charged particles or plasma emission is large, which may cause fatal damage to a miniaturized semiconductor device such as an LSI. There are many charged particles such as electrons and ions in this plasma, and the light emitted from the plasma discharge includes high-energy light up to soft X-rays. For this reason, it is also a cause of damage due to crystal defect formation or the like on the semiconductor substrate.

  Since plasma damage is reduced by not directly exposing the wafer to the plasma, it is effective to separate the wafer and the plasma generating portion, but there is a drawback that the ashing rate is lowered.

  However, this method cannot completely eliminate plasma damage.

  Furthermore, in recent semiconductor devices, the aspect ratio has increased with the progress of miniaturization, and in order to form a three-dimensional structure in the MEMS field, the aspect ratio is often increased, and the pattern bottom due to the microloading effect Etching failure in this is a problem. Furthermore, the plasma generation / control mechanism is complicated and expensive.

  In addition, in plasma processing, the temperature in the chamber rises during ashing, and in addition to reaching 100 ° C. or more even in processing for several minutes, the substrate surface temperature is higher due to local electric field concentration in fine and complex patterns. Since a high place is formed and the variation becomes large according to the pattern arrangement, the deformation of the resist on which the pattern is formed becomes large, and the variation in pattern dimensional accuracy becomes large. A single-wafer type apparatus is provided with a cooling mechanism for temperature rise during processing, but local variations on the photoresist processed into a circuit pattern cannot be suppressed.

  As another resist removal method, there is an ashing method using ozone. However, in order to obtain a practical ashing rate, it is necessary to heat to 200 to 300 ° C., and at 100 ° C. or less, almost no effect is obtained.

  At temperatures of 200 to 300 ° C., pattern deformation such as resist residue removal and descum process as described above occurs because the resist pattern is not deformed or softened due to thermal expansion. It cannot be used for adjustment.

  Although it can be used at 100 ° C. to 150 ° C. with relatively little deformation, in addition to its slow ashing rate, pattern deformation due to thermal expansion cannot be ignored in patterns refined beyond submicron.

  Since all of these processes are performed while heating the substrate, if there is a substance that is easily oxidized on the base, it is also oxidized and altered. Metals and other materials produce an oxide film on the surface, and many of them become insulators, which adversely affects electrical characteristics.

  In semiconductor devices, various metals such as Al, Cu, W, Ti, Au, Pt, and Cr are used as wiring materials. Among these metal groups, Cu is very easy to oxidize, oxidation proceeds even at a temperature of 100 ° C., and sometimes the film is peeled off, which may cause fatal particles to be generated as a semiconductor device having a fine structure. Become.

  As described above, conventionally, the plasma ashing method has been widely used for photoresist exposure, residual film removal after development, processing shape correction, etc., but the resist shape tends to be deformed due to the influence of plasma damage or heat generation. . In addition, the ozone ashing method that does not cause the risk of plasma damage requires heating the substrate to about 200 ° C. or more in order to obtain an effect, and cannot be applied to resist shape correction.

Therefore, the etching method of claim 1 removes silicon oxide on the substrate by supplying tetrafluoroethylene gas and ozone gas to the substrate in an atmosphere lower than atmospheric pressure where no plasma is generated .

  The etching method according to claim 2 is the etching method according to claim 1, wherein the ozone gas is an ultra-high-concentration ozone gas obtained by liquefying and separating only ozone based on a difference in vapor pressure and then vaporizing again the ozone-containing gas. .

An etching apparatus according to claim 3 is an etching apparatus for removing silicon oxide on a substrate, wherein the chamber stores a substrate in an atmosphere in which plasma is not generated, and the chamber has a pressure lower than atmospheric pressure. And means for supplying tetrafluoroethylene gas, and means for supplying ozone gas to the chamber at a pressure lower than atmospheric pressure.

  The etching apparatus according to claim 4 is the etching apparatus according to claim 3, wherein the chamber stores a mixed chamber to which the tetrafluoroethylene gas and the ozone gas are supplied, the substrate, and the tetrafluoroethylene from the mixed chamber. A treatment chamber to which a mixed gas of gas and ozone is supplied.

  The etching apparatus according to claim 5 is the etching apparatus according to claim 4, wherein the mixing chamber and the processing chamber are formed by a partition that divides the chamber into two upper and lower chambers, and the partition is configured to process the gas in the mixing chamber. A shower head to be transferred into the room is provided, and this shower head is formed by forming a plurality of holes in the partition.

  An etching apparatus according to a sixth aspect is the etching apparatus according to the fifth aspect, wherein the group of the plurality of holes is arranged to have a diameter larger than at least the diameter of the substrate.

  The etching apparatus according to claim 7 is the etching apparatus according to any one of claims 3 to 6, wherein the ozone gas is supplied by vaporizing again the ozone-containing gas after liquefying and separating only ozone based on the difference in vapor pressure. This is done with an ozone generator that generates ultra-high-concentration ozone gas.

  According to the first to seventh aspects of the present invention, ozone gas and tetrafluoroethylene gas are produced without plasma under a pressure lower than atmospheric pressure (for example, a pressure range from a medium vacuum to a low vacuum of about several Pa to several thousand Pa). The substrate is supplied to remove silicon oxide from the substrate. When tetrafluoroethylene gas and ozone react at room temperature, unstable intermediates such as ozonide are generated. The silicon oxide on the substrate is removed and processed by interposing the substrate in a gas containing CFx radicals and ozone that are further decomposed from an intermediate generated by the reaction between tetrafluoroethylene gas and ozone. Actually, an etching rate of about several tens of nm / min can be obtained.

  In particular, according to the invention of claim 2 and claim 7, the etching rate is increased by using the ultra-high concentration ozone gas.

  In the third and fourth aspects of the invention, the distance from the ozone gas outlet of the chamber to the substrate used for silicon oxide removal may be set within a range where the ozone gas flow can reach the substrate directly. In the invention of claim 5, the distance from the lower part of the shower head to the substrate with silicon oxide is preferably set within a range in which a mixed gas flow of ozone and tetrafluoroethylene reaches the substrate directly. The ozone gas and the tetrafluoroethylene gas can reach the substrate before the ozone gas and the tetrafluoroethylene gas introduced into the chamber are decomposed by mixing to produce a stable product.

  According to the fifth aspect of the present invention, since a mixed gas of ozone gas and tetrafluoroethylene gas is supplied to the substrate by the shower head, a uniform gas flow is generated over the entire surface of the substrate, so that etching can be performed uniformly.

  Furthermore, in the invention of claim 6, etching can be performed more uniformly by disposing the group of the plurality of holes so as to have a diameter larger than at least the diameter of the substrate.

  When the height of the mixing chamber according to claims 4 to 6 is, for example, 10 mm or less, the tetrafluoroethylene gas mixed with ozone gas can be led to the processing chamber without unnecessarily staying in the mixing chamber. That is, the ozone gas and tetrafluoroethylene can reach the substrate in the processing chamber before the ozone gas and the tetrafluoroethylene gas introduced into the mixing chamber are decomposed by mixing to produce a stable product.

  In the first to seventh aspects of the invention, the ratio of the partial pressure of the tetrafluoroethylene gas to the partial pressure of the ozone gas (or the partial pressure of only ozone when the ozone concentration is not 100%) is larger in the supply amount of ozone gas. It is good to set so that

  In the inventions of claims 3 to 7, the exhaust pipe of the mixed gas of tetrafluoroethylene gas and ozone gas may be provided with an ozonolysis device. It is possible to avoid a reduction in the lifetime of the vacuum pump that causes the internal pressure of the chamber to be lower than the atmospheric pressure. Examples of the ozonolysis apparatus include an unreacted or a heating element heated to at least 300 ° C. or higher in order to completely burn a product gas other than water and carbon dioxide.

  According to the above invention, since plasma is not generated, etching can be performed without damaging the substrate. In addition, since there is no plasma generation / control mechanism, the apparatus configuration can be simplified and the cost can be reduced.

  As shown in FIG. 3, it is generally known that ozone gas reacts with unsaturated hydrocarbons even at room temperature, and decomposes into ketones, carboxylic acids and the like via unstable intermediates such as ozonides.

  In an etching apparatus according to an embodiment of the present invention, a substrate with a thin film to be processed is interposed in the process of decomposing an unstable intermediate such as ozonide, and an etching effect is obtained without generating plasma.

  FIG. 1A is a cross-sectional view showing a schematic configuration of an etching apparatus 1 according to the first embodiment of the invention. FIG. 1B is a plan view showing a schematic configuration of the etching apparatus 1.

  The etching apparatus 1 includes a chamber 2, a tetrafluoroethylene supply device 3, an ozone generator 4, a vacuum pump 5, and an ozone decomposition device 6.

  Chamber 2 stores a substrate 10 that is subjected to removal of silicon oxide 101. Pipes 21, 22 and 23 are connected to the chamber 2. The pipe 21 is a pipe for introducing tetrafluoroethylene, and is connected to the side surface of the chamber 2. The pipe 22 is a pipe for introducing ozone gas, and is connected to the upper part (ceiling part) of the chamber 2. The pipe 23 is a pipe for discharging the gas in the chamber 2, and is connected to the side surface of the chamber 2 facing the pipe 21 so as to be substantially coaxial with the pipe 21. A vacuum pump 5 and an ozonolysis device 6 are installed in the pipe 23. The ozonolysis device 6 is disposed on the upstream side of the vacuum pump 5. Although not shown in the figure, the pipes 21, 22, and 23 are appropriately provided with mass flow controllers and valves, and the gas flow and pressure in the chamber 2 are appropriately controlled.

  The substrate 10 is held by the holder 7. The holder 7 is covered with SiC. The holder 7 is connected to a thermocouple 8 for sensing the temperature in the chamber 2. The heat detected by the thermocouple 8 is supplied as an electric signal to a control unit (not shown). The holder 7 is formed so that the ozone gas and the tetrafluoroethylene gas can reach the substrate 10 before the ozone gas and the tetrafluoroethylene gas introduced into the chamber 2 are decomposed by mixing to produce a stable product. The position of the holder 7 is set so that the distance between the ozone gas outlet and the substrate 10 is 30 mm or less.

  The tetrafluoroethylene supply device 3 supplies tetrafluoroethylene gas to the chamber 2. The tetrafluoroethylene supply device 3 includes a cylinder 31 filled with tetrafluoroethylene gas and a valve 32 for supplying and stopping the filled tetrafluoroethylene gas.

  The ozone generator 4 generates ozone gas supplied to the chamber 2. The ozone generator 4 has a function of generating ultra-high concentration ozone gas. The ultra-high-concentration ozone gas can be obtained by vaporizing again ozone-containing gas after liquefying and separating only ozone based on the difference in vapor pressure. An apparatus for obtaining the ultra-high concentration ozone gas is disclosed in, for example, Japanese Patent Laid-Open Nos. 2001-304756 and 2003-20209. The ozone generator of the above-mentioned patent document generates ozone gas with an extremely high concentration (ozone concentration≈100%) by liquefying and separating only ozone based on the difference in vapor pressure between ozone and other gas components (for example, oxygen). In particular, the ozone supply device disclosed in Japanese Patent Application Laid-Open No. 2003-20209 includes a plurality of chambers for liquefying and vaporizing only ozone, and the high purity ozone gas can be continuously supplied by individually controlling the temperature of these chambers. The ozone generator 4 is a commercially available ozone generator based on this high-purity ozone gas continuous supply system. An example of this commercially available ozone generator is a pure ozone generator (MPOGHM1A1) manufactured by Meidensha. This commercially-available ozone generator is used to oxidize and decompose tetrafluoroethylene gas more completely. However, even if the ozone gas supplied to the chamber 2 is a high-concentration ozone gas having an ozone concentration of several tens wt% or more. Good.

  The vacuum pump 5 is a pump for adjusting the pressure inside the chamber 2 and discharging the gas in the chamber 2. A dry pump that is resistant to ozone may be used as the pump. This is in order to avoid a decrease in performance due to ozone gas that may be included in the exhaust gas and a decrease in life due to deterioration.

  The ozone decomposition device 6 decomposes ozone in the gas by completely burning the gas discharged from the chamber 2. As an example of the ozonolysis apparatus, there is an apparatus in which a heating element heated to 300 ° C. or more is provided in a container to which exhaust gas is supplied, and the exhaust gas is burned by this heating element.

  An example of the operation of the etching apparatus 1 will be described with reference to FIG.

  Tetrafluoroethylene gas is introduced from the tetrafluoroethylene supply device 3 through the pipe 21 while the inside of the chamber 2 is maintained at room temperature, and ozone gas is sprayed from the ozone generator 4 to the substrate 10 through the pipe 22. Thereby, the silicon oxide 101 on the substrate 10 is decomposed and removed. At this time, tetrafluoroethylene gas is used to prevent the reaction between tetrafluoroethylene and ozone and unstable intermediates (FIG. 3) such as ozonide generated in the process from abruptly decomposing and losing control of the reaction. The total pressure of ozone is controlled in the range of medium vacuum to low vacuum of about several Pa to several thousand Pa. This control is executed by a mass flow controller or a valve.

  FIG. 2A is a sectional view showing a schematic configuration of an etching apparatus 11 according to the second embodiment of the invention. FIG. 2B is a plan view showing a schematic configuration of the etching apparatus 11.

  The etching apparatus 11 has basically the same configuration as the etching apparatus 1 except that the chamber 2 has a mixed chamber 9 of tetrafluoroethylene gas and ozone gas. The mixing chamber 9 is formed in the chamber 2 by a partition 24. The processing chamber 12 for storing the substrate 10 used for removing the silicon oxide 101 is disposed in the lower stage of the mixing chamber 9 with a partition 24 interposed therebetween.

  A shower head 25 for supplying the gas in the mixing chamber 9 to the substrate 10 in the processing chamber 11 is formed at a substantially central portion of the partition 24. The shower head 25 is formed by forming a plurality of holes 26 for discharging the gas in the mixing chamber 9 in the partition 24 as shown in FIGS. 2 (a) and 2 (b). The group 26 a of the holes 26 is arranged so as to have a diameter that is at least larger than the diameter of the substrate 10 on the holder 7.

  A pipe 27 for introducing tetrafluoroethylene gas and a pipe 28 for introducing ozone gas are connected to the upper part of the chamber 2, that is, the ceiling part of the mixing chamber 9. The pipes 27 and 28 are connected in a branched form into a plurality of pipes as illustrated in FIG.

  The distance between the shower head 25 and the silicon oxide-attached substrate 10 minimizes the distance from mixing in the mixing chamber 9 to reaching the surface of the substrate 10, and further uniformizing the gas flow by the shower head 25. For example, the distance between the shower head 25 and the silicon oxide-attached substrate 10 is set to 5 mm so as not to impair the etching uniformity as an effect of the above. In this case, the height of the mixing chamber 9 (distance from the shower head 25 surface to the ceiling surface of the mixing chamber 9) is set to avoid unnecessary retention of the tetrafluoroethylene gas and ozone gas mixed in the mixing chamber 9. Set within 10 mm.

  An example of the operation of the etching apparatus 11 will be described with reference to FIG.

  The inside of the chamber 2 is maintained at room temperature. Tetrafluoroethylene gas is introduced from the tetrafluoroethylene supply device 3 into the mixing chamber 9 through the pipe 27, and ozone gas is introduced from the ozone generator 4 through the pipe 28. A mixed gas of tetrafluoroethylene and ozone in the mixing chamber 9 is sprayed from the shower head 25 to the substrate 10 in the processing chamber 12. Thereby, the silicon oxide 101 on the substrate 10 is decomposed and removed. In the etching apparatus 2 as well, the total pressure of the tetrafluoroethylene gas and ozone is controlled in a range from a medium vacuum to a low vacuum of about several Pa to several thousand Pa. As a result, the reaction between tetrafluoroethylene and ozone and an unstable intermediate such as ozonide (FIG. 3) generated in the process, like the etching apparatus 1, are prevented from abruptly decomposing and making it impossible to control the reaction. Is done. This control is executed by a mass flow controller or a valve. The gas in the processing chamber 12 is sucked by the vacuum pump 5 and discharged through the ozonolysis device 6. In the ozonolysis device 6, the exhaust gas in which ozone or the like is left is burned by a heating element heated to 300 ° C. or higher. Thereby, deterioration of the vacuum pump 5 is prevented.

  Examples of the above etching apparatuses 1 and 11 will be described. A silicon wafer about 2 cm square chip with a thermal oxide film of about 1 μm was etched. As a result, an etching rate of about 50 nm / min was obtained when the temperature in the chamber 2 of the etching apparatuses 1 and 11 was room temperature (20 to 30 ° C.). At this time, a temperature rise of 1 to 2 ° C. per minute is recognized due to reaction heat, but this is not a problem in practice.

(A) Sectional drawing which showed schematic structure of etching apparatus which concerns on 1st embodiment of invention, (b) The top view which showed schematic structure of the said etching apparatus. (A) Sectional drawing which showed schematic structure of etching apparatus which concerns on 2nd embodiment of invention, (b) The top view which showed schematic structure of the said etching apparatus. Explanatory drawing which showed reaction of unsaturated hydrocarbon and ozone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 ... Etching apparatus 2 ... Chamber, 21-23, 27, 28 ... Piping 3 ... Tetrafluoroethylene supply apparatus (means to supply tetrafluoroethylene gas), 31 ... Cylinder, 32 ... Valve 4 ... Ozone generator ( Means for supplying ozone gas)
5 ... Vacuum pump 6 ... Ozonizer 7 ... Holder 8 ... Thermocouple 9 ... Mixing chamber 10 ... Substrate, 101 ... Silicon oxide 12 ... Processing chamber 24 ... Partition 25 ... Shower head, 26 ... Hole, 26a ... Group

Claims (7)

An etching method, wherein tetrafluoroethylene gas and ozone gas are supplied to a substrate in an atmosphere lower than atmospheric pressure where no plasma is generated to remove silicon oxide on the substrate.   2. The etching method according to claim 1, wherein the ozone gas is an ultra-high concentration ozone gas obtained by vaporizing and re-vaporizing only ozone based on a difference in vapor pressure from an ozone-containing gas. An etching apparatus for removing silicon oxide on a substrate,
A chamber for storing the substrate under an atmosphere in which plasma is not generated ;
Means for supplying tetrafluoroethylene gas to the chamber at a pressure lower than atmospheric pressure;
An etching apparatus comprising: means for supplying ozone gas to the chamber under a pressure lower than atmospheric pressure. The chamber is
A mixing chamber to which the tetrafluoroethylene gas and the ozone gas are supplied;
The etching apparatus according to claim 3, further comprising a processing chamber that stores the substrate and is supplied with a mixed gas of tetrafluoroethylene gas and ozone from the mixing chamber. The mixing chamber and the processing chamber are formed by partitions that divide the chamber into two upper and lower chambers,
The partition includes a shower head for transferring the gas in the mixing chamber to the processing chamber,
The etching apparatus according to claim 4, wherein the shower head has a plurality of holes formed in the partition. The etching apparatus according to claim 5, wherein the group of the plurality of holes is arranged to have a diameter that is at least larger than a diameter of the substrate.   The ozone gas supply is performed by an ozone generator that generates an ultra-high-concentration ozone gas by liquefying and separating only ozone from the ozone-containing gas based on a difference in vapor pressure and then vaporizing it again. The etching apparatus according to any one of 6.

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