JP2008108953A - Semiconductor substrate backside foreign matter removal method - Google Patents

Abstract

When a semiconductor substrate is held on a sample stage having pyrolytic boron nitride (PBN) as the outermost surface layer and the semiconductor substrate is processed, BN flakes adhering to the back surface of the semiconductor substrate are effectively removed. To remove.
A method of removing PBN flakes adhering to the back surface of a semiconductor substrate when a semiconductor substrate is held on a sample stage having PBN as the outermost surface layer and the semiconductor substrate is processed. Then, the semiconductor substrate after the process treatment is held in a state in which the back surface thereof is substantially opened by lift pins 11 or the like, and the PBN flakes adhering to the back surface of the semiconductor substrate are removed in the fluorine-based gas plasma 12. Since PBN has extremely low corrosion resistance against fluorine-based gas, it is effectively and selectively removed in a short time by being exposed to fluorine-based gas.
[Selection] Figure 2

Description

  The present invention relates to a method for removing foreign substances adhering to the back surface of a semiconductor substrate such as a wafer. More specifically, the semiconductor substrate is held on a sample stage having pyrolytic boron nitride as the outermost surface layer, and the semiconductor substrate is processed. The present invention relates to a method for effectively removing pyrolytic boron nitride flakes adhering to the back surface of the semiconductor substrate.

As a sample stage used for holding a semiconductor substrate, a ceramic base such as Al ₂ O ₃ formed on a metal surface or a sintered ceramic such as Al ₂ O ₃ or AlN is widely used. The sample stage is embedded with a heater electrode for heating and / or an electrode for electrostatic adsorption, and when both electrodes are used together, it is used as a sample stage having a function as an electrostatic adsorption heater.

  When holding a semiconductor substrate on such a sample stage and performing a predetermined process such as a film forming process such as CVD or sputtering, an etching process, or a heating process, the outermost surface layer of the material stage is scraped by contact with the substrate. There is a problem that particles are generated and the particles adhere to the back surface of the substrate.

In order to solve this problem, in Patent Document 1 below, “in the plasma apparatus, the wafer is supported on the opposite surface side so that both the device forming surface and the opposite surface can come into contact with the plasma. A foreign substance on a wafer, wherein a foreign substance adhering to the opposite surface is removed by radicals in the plasma while protecting a device formation surface with a deposit layer formed by depositing a depositing substance generated in the plasma. "Removal method" (cited from claim 1) is proposed.
JP-A-6-120175

In process processing, the substrate temperature during processing affects the processing result as an important condition, and therefore the substrate is required to be held in close contact with the surface of the sample stage. However, ceramic materials such as Al ₂ O ₃ and AlN used for the sample stage described above are highly brittle and hold the semiconductor substrate in point contact. Since the process is performed under reduced pressure, the semiconductor substrate held in point contact on these ceramic sample stands has almost no heat transfer from the sample stand, and a gas such as He is filled between them. It has been common to heat a semiconductor substrate by heat transfer with a gas.

  On the other hand, the sample stage having the non-brittle pyrolytic boron nitride (PBN) as the outermost surface layer has excellent adhesion to the substrate, and therefore heat transfer from the sample stage to the substrate is large, and the gas filling that has been required in the past can be achieved. This is unnecessary and has a great advantage in terms of temperature control. For this reason, instead of the conventional Al-based ceramic material, it has become promising to perform a process while supporting a semiconductor substrate in surface contact using a sample stage having a PBN outermost surface layer. Has also been successful.

  However, the fact that the PBN outermost surface layer has excellent adhesiveness to the substrate, on the other hand, causes a problem that PBN flakes are likely to adhere to the back surface of the substrate. The PBN flakes are thin and are deposited so as to cover a relatively large area on the backside of the substrate, unlike the conventional foreign particles that are scraped off when the Al-based ceramic material comes into contact with the substrate. It is difficult to completely remove the particles of the ceramic material by the conventional foreign matter removing method aiming at removing particles from the back surface of the substrate.

  When considering the technical demands associated with the miniaturization of semiconductor devices, which are becoming stricter year by year, the effect of PBN flakes attached to the backside of the substrate on the process cannot be ignored, and this PBN flakes are effectively removed from the backside of the substrate It is an essential task.

  In order to solve the above-mentioned problems, the present invention provides a BN flake adhering to the back surface of a semiconductor substrate when a semiconductor substrate is held on a sample stage having PBN as the outermost surface layer and the semiconductor substrate is processed. Provide a method for effective removal.

  More specifically, the PBN flakes adhering to the back surface of the substrate are removed by the fluorine-based gas by utilizing the characteristic of PBN that is extremely corrosive to the fluorine-based gas.

  That is, the present invention according to claim 1 removes PBN flakes adhering to the back surface of the semiconductor substrate when the semiconductor substrate is held on the sample stage having PBN as the outermost surface layer and the semiconductor substrate is processed. The semiconductor substrate after the process is held in a state where the back surface thereof is substantially open, and the PBN flakes adhering to the back surface of the semiconductor substrate are removed with a fluorine-based gas. This is a method for removing foreign matter on the back surface of a semiconductor substrate.

  According to a second aspect of the present invention, in the foreign matter removing method according to the first aspect, the PBN flakes adhering to the back surface of the semiconductor substrate are removed in a plasma atmosphere of a fluorine-based gas.

The present invention according to claim ₃ is characterized in that in the foreign matter removing method according to claim 1 or 2, NF ₃ gas is used as the fluorine-based gas.

According to a fourth aspect of the present invention, in the foreign matter removing method according to the _{third aspect} , the NF ₃ gas is generated by high-frequency discharge.

  According to a fifth aspect of the present invention, in the foreign matter removing method according to any one of the first to fourth aspects, the treatment is performed with a fluorine-based gas without applying a potential to the semiconductor substrate.

  According to a sixth aspect of the present invention, in the foreign matter removing method according to any one of the first to fifth aspects, the foreign matter removing process is performed in a reaction chamber different from the reaction chamber for the process treatment.

  According to a seventh aspect of the present invention, in the foreign matter removing method according to the sixth aspect, the foreign matter removing process is performed in a reaction chamber adjacent to the reaction chamber for the process treatment.

  According to an eighth aspect of the present invention, in the foreign matter removing method according to any one of the first to seventh aspects, the semiconductor substrate after the process is supported by lift pins at several places on the back surface thereof.

  According to a ninth aspect of the present invention, in the foreign matter removing method according to any one of the first to seventh aspects, the semiconductor substrate after the process treatment is held at an outer peripheral portion thereof, and the entire back surface can be treated with a fluorine-based gas. It is characterized by that.

  According to the present invention, when a semiconductor substrate is held on a sample stage having PBN as the outermost surface layer and the semiconductor substrate is processed, even if PBN flakes adhere to the back surface of the semiconductor substrate, Can be effectively removed by treating with a fluorine-based gas. Since PBN has a characteristic that it is extremely corrosive to fluorine-based gas, it is possible to selectively remove PBN flakes that are foreign substances by using this characteristic.

  In order to demonstrate that PBN has a characteristic that it is extremely susceptible to corrosion by fluorine gas, an etching test was conducted under the following conditions.

In a parallel plate type dry etching apparatus, sample pieces made of various materials (Si, quartz, PBN, AlN) having a size of approximately 50 mm square are placed on a water-cooled quartz sample stage, and NF ₃ gas and Ar gas are respectively supplied. Mixing at a flow rate of 16 cc per minute and 34 cc per minute was introduced into the reaction chamber. The pressure in the reaction chamber was kept at 100 mTorr, and 400 W of high frequency power of 13.56 MHz was applied to the sample stage. The sample piece is etched with F ions or F radicals by the plasma generated by the application of the high frequency power. Etching rate was determined by etching in plasma continuously for 1 hour or longer and normalizing the amount of change in the sample weight before and after etching with the surface area excluding the back surface of the sample. FIG. 1 is a graph showing the results.

As shown in FIG. 1, PBN was etched at 1 micron or more per minute, and showed an etching rate 20 times or more higher than Si, 40 times higher than quartz (SiO ₂ ), and 300 times higher than that of AlN. This indicates that even if the base of the semiconductor substrate is Si or SiO ₂ , only PBN can be selectively removed while substantially suppressing the influence of etching on the base.

Based on this test result, the electrostatic adsorption heater having the PBN film as the outermost surface layer is heated and held at 400 ° C., the wafer is electrostatically adsorbed to the electrostatic adsorption heater at a DC voltage of 1 kV, and held for 2 minutes. The wafer was removed from the electrostatic adsorption heater with a lift pin and carried out of the reaction chamber. This wafer, after foreign matters adhered to the back surface of the (PBN flakes) measured by a particle counter, NF ₃ by plasma processing, the NF ₃ plasma treatment after Incidentally measured again particle counter the foreign matter adhering to the wafer back surface Thus, the effect of removing foreign matters was evaluated. NF ₃ plasma is generated by introducing 50 sccm of NF ₃ gas into a vacuum chamber in which a wafer is mounted on a water-cooled sample stage, maintaining the pressure at 0.5 Pa, and supplying 500 W of power from a 13.56 MHz high frequency power source. did. The plasma treatment time was 5 minutes. Table 1 shows the results.

As shown in Table 1, it was confirmed that, by performing the NF ₃ plasma treatment, foreign matters attached to the back surface of the wafer were effectively removed, and particularly large foreign matters were effectively removed.

In the above embodiment, although using NF ₃ plasma treatment for removing foreign substances wafer backside, not limited _{thereto, CF 4, SF 6, ClF} 3 (3 chlorine fluoride) such as fluorine atom in the plasma Any fluorine-based gas that ionizes can be used in the present invention. The plasma generation is not limited to 13.56 MHz in the above-described embodiment as long as it can generate a fluorine-based gas plasma with any high-frequency power source of kHz to GHz.

  FIG. 2 shows an example of an apparatus configuration for this foreign substance removal plasma processing and its usage. The apparatus 10 is provided adjacent to a process processing apparatus 20 that holds a wafer W on a sample table (electrostatic adsorption heater) 21 having PBN as the outermost surface layer 22 and performs a predetermined process process on the wafer W. A reaction chamber separate from the processing apparatus 20 is provided.

In the process processing apparatus 20, a plurality of lift pins 23 are provided so as to be able to move up and down through the sample stage 1, and when the wafer W is processed, the lift pins 23 are retracted to the lowered position, W is electrostatically held on the sample stage 21. After completion of the predetermined time of process processing, the lift pins 23 are raised to separate the wafer W from the sample stage 21 and are unloaded from the process processing apparatus 20 by the wafer transfer means 24 such as a transfer arm, and from the gate valve 25 to the adjacent foreign substance removal plasma. It is transferred into the processing apparatus 10 and placed on the plurality of lift pins 11. In this state, fluorine-based plasma 12 is generated to remove foreign matters (PBN flakes) adhering to the back surface of the wafer W. After the foreign substance removal processing is completed, the wafer W is unloaded from the apparatus 10 by the wafer unloading means 13 which is substantially the same as the transfer arm 24 or an arbitrary configuration. For generation of the fluorine-based plasma 12, so-called remote plasma in which NF ₃ gas is excited by microwaves to introduce fluorine radicals can be employed.

  The foreign substance removal plasma processing apparatus 10 may be installed at a location distant from the process processing apparatus 10, but it is preferable to install adjacently as shown in FIG. 2 in order to improve the transfer efficiency of the wafer W. Since the transfer chamber is adjacent to the process processing apparatus 10 via the gate valve 24, it is practically advantageous to modify the transfer chamber to form the foreign substance removal plasma processing apparatus 10.

  In the embodiment shown in FIG. 2, the wafer W is supported by the lift pins 11 in the foreign substance removal plasma processing apparatus 10. However, the present invention is not limited to this. For example, the wafer support means is configured to support the wafer W at its outer periphery. May be provided. Further, the wafer transfer means 24 may be used also as a wafer support means in the foreign matter removal plasma processing apparatus 10. As the wafer transfer means 23, a structure that supports the wafer W at several points from the back surface, a structure that supports the wafer W at its outer peripheral portion, or a structure that combines these structures is known. A structure having a structure can also be employed, and can also be used as a wafer support means in the foreign matter removal plasma processing apparatus 10.

  In any case, considering that the object of the present invention is to remove foreign matter attached to the back surface of the wafer W, the wafer support means in the foreign matter removal plasma processing apparatus 10 is excluded from coming into contact with the back surface of the wafer W. It is preferable that the entire back surface of the wafer W supported by the wafer support means is exposed to the plasma 12. Therefore, it is preferable to employ a wafer support means having a structure in which the wafer W is supported only by its outer peripheral portion.

Further, since the lift pins 11 and other wafer support means are exposed to the plasma 12 together with the wafer W in the foreign matter removal plasma processing apparatus 10, a material that is resistant to fluorine radicals, such as Al ₂ O ₃ , AlN, etc. It is preferable to form with metal materials, such as ceramic, aluminum, and stainless steel.

  Furthermore, when performing foreign matter removal processing on the backside of a substrate such as a wafer in plasma, if any potential, such as a bias potential, is applied to the substrate, damage to the elements in the substrate may be caused by ion bombardment or the like. The substrate is preferably held or placed in an insulating state in the plasma. For this reason, it is preferable that the lift pins 11 in contact with the back surface of the wafer W as the wafer support means in the foreign matter removal plasma processing apparatus 10 of FIG.

When the wafer W is processed with the plasma 12 in the foreign matter removal plasma processing apparatus 10, not only the back surface but also the surface of the wafer W is affected by fluorine radicals, but the surface of the semiconductor substrate such as the wafer W is affected by fluorine radicals. On the other hand, since it is usually covered with a corrosion-resistant material having a sufficiently high selection ratio with PBN, such as Si crystal, SiO ₂ crystal, or resist, generally no particular problem arises. However, in the case where a high-density device is formed on the surface of the wafer W, as shown in FIG. 3, by providing a protective lid 14 that covers the surface of the wafer W, the influence of fluorine radicals on the surface of the wafer W is achieved. Is preferably excluded. In this case, the gap between the wafer W surface and the protective lid 14 is preferably 1 mm or less.

NF ₃ is a graph showing the etching rate of the PBN according to the plasma compared with other materials. It is the schematic which shows an example of the apparatus structure for a foreign material removal plasma processing, and its usage. It is the schematic which shows the apparatus structural example which provided the protective cover which covers a wafer surface.

Explanation of symbols

10 Foreign matter removal plasma processing apparatus 11 Lift pin (wafer support means)
12 Plasma 13 Wafer carrying means 14 Protective cover 20 Process processing device 21 Sample stage (electrostatic adsorption heater)
22 PBN outermost surface layer 23 Lift pin 24 Wafer transfer means 25 Gate valve W Wafer

Claims (9)

A method of removing PBN flakes adhering to the back surface of a semiconductor substrate when the semiconductor substrate is held on a sample stage having PBN as the outermost surface layer and the semiconductor substrate is processed. A method of removing foreign matter from a semiconductor substrate back surface, wherein the back surface of the semiconductor substrate is held substantially open, and PBN flakes adhering to the back surface of the semiconductor substrate are removed with a fluorine-based gas. 2. The foreign matter removing method according to claim 1, wherein the PBN flakes adhering to the back surface of the semiconductor substrate are removed in a plasma atmosphere of a fluorine-based gas. The foreign matter removing method according to claim 1 or 2, wherein NF ₃ gas is used as the fluorine-based gas. 4. The foreign matter removing method according to claim 3, wherein the NF ₃ gas is generated by high frequency discharge. 5. The foreign matter removing method according to claim 1, wherein the treatment is performed with a fluorine-based gas in a state where no potential is applied to the semiconductor substrate. 6. The foreign matter removing method according to claim 1, wherein the foreign matter removing process is performed in a reaction chamber different from the reaction chamber for the process treatment. The foreign matter removing method according to claim 6, wherein the foreign matter removing process is performed in a reaction chamber adjacent to the reaction chamber for the process treatment. 8. The foreign matter removing method according to claim 1, wherein the processed semiconductor substrate is supported by lift pins at several places on the back surface thereof. 8. The foreign matter removing method according to claim 1, wherein the semiconductor substrate after the process treatment is held at an outer peripheral portion thereof, and the entire back surface can be treated with a fluorine-based gas.

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