JP5641538B2 - Heat treatment method for silicon wafer - Google Patents

Description

  The present invention relates to a heat treatment method for a silicon wafer in which heat treatment is performed on a silicon wafer (hereinafter also simply referred to as a wafer).

  Silicon wafers used as semiconductor device forming substrates reduce void defects such as COP (Crystal Originated Particles) and LSTD (Laser Scattering Tomography Defects) in the vicinity of the surface of the wafer that will be the device active region (hereinafter referred to as the surface layer portion). There is a need for efforts to make them defect-free.

  In recent years, as a method of manufacturing such a silicon wafer with high productivity, at least a surface on which a semiconductor device is formed is mirror-polished (hereinafter, the mirror-polished surface is also referred to as a polished surface). A technique for performing a thermal treatment (Rapid Thermal Process: hereinafter also simply referred to as RTP) is known.

  As such a technique, Patent Document 1 discloses that an oxygen-containing gas atmosphere (inert gas atmosphere as referred to in the present invention) that is mainly argon or helium at a temperature exceeding about 1175 ° C. under an oxygen partial pressure of less than about 5000 ppma, A heat treatment method is disclosed in which the wafer is heated for less than 60 seconds.

  However, since the method described in Patent Document 1 performs RTP in an inert gas atmosphere such as argon or helium, it is possible to greatly reduce void defects in the surface layer portion of the wafer. When RTP is performed at a high temperature exceeding 1175 ° C. in a reducing gas atmosphere such as an atmosphere or hydrogen, polishing after RTP is caused by the influence of a natural oxide film formed on the polishing surface of the wafer before RTP. There is a problem that the surface roughness of the surface deteriorates.

  In order to solve such a problem, Patent Document 2 discloses a mixed gas of argon containing 100% hydrogen or 10% or more of hydrogen using an RTP apparatus after removing a natural oxide film on the wafer surface by hydrofluoric acid treatment. Disclosed is a heat treatment method that can reduce the microroughness of the wafer surface and remove void defects existing on the wafer surface by heat treatment in an atmosphere.

JP-T-2001-509319 JP 2000-91342 A

In such a method described in Patent Document 2, since hydrogen is terminated at silicon atoms on the wafer surface by hydrofluoric acid treatment, a natural oxide film is hardly formed on the surface. Therefore, even if the RTP is performed, deterioration of the surface roughness on the wafer surface can be suppressed.
However, in order to eliminate void defects existing in the surface layer portion of the wafer by RTP, a high-temperature heat treatment of at least 1000 ° C. is required in the inert gas atmosphere or the reducing gas atmosphere. Below, the bond of the hydrogen atom terminated by the silicon atom is easily broken, and the silicon atom is easily exposed on the wafer surface. The exposed silicon atoms are unstable and are likely to react with other atoms.

  Therefore, for example, when other reactive gas (such as nitrogen) is present in the atmosphere, it reacts and bonds with the exposed silicon atoms, and the bond is repeatedly etched by the atmosphere. Therefore, there is a problem that the surface shape of the wafer changes and the surface roughness deteriorates.

Further, when the atmosphere contains a small amount of oxygen, the exposed silicon atoms and oxygen react to form an oxide film in an island shape on the wafer surface, and this oxide film is etched by the atmosphere. However, there is a problem that concave pits are formed in the etched portion.
The above problem becomes more conspicuous as the heat treatment temperature in RTP becomes higher. On the other hand, the higher the heat treatment temperature, the higher the void defect extinction power of the surface layer portion of the wafer. .

  The present invention has been made in view of the above-described circumstances, and even when RTP is performed at a high temperature at which void defect annihilation power is high, deterioration of surface roughness can be suppressed. An object of the present invention is to provide a method for heat-treating a silicon wafer that can also suppress the occurrence of the above.

The silicon wafer heat treatment method according to the present invention includes a silicon wafer having a mirror-polished surface on which at least a semiconductor device is formed, and a silicon atom on the surface is terminated with hydrogen using a hydrogen fluoride-based solution. The step of setting the density to 5 × 10 ¹⁴ atoms / cm ² or more and 4 × 10 ¹⁵ atoms / cm ² or less and the silicon wafer terminated with hydrogen are inert gases (referred to as rare gases excluding nitrogen gas. And the like.) A step of performing a rapid temperature raising and lowering heat treatment in which the temperature is rapidly raised and maintained in an atmosphere within a temperature range of 1300 ° C. to 1400 ° C. and then rapidly lowered.

The hydrogen termination density is preferably 1.5 × 10 ¹⁵ atoms / cm ² or more and 4.0 × 10 ¹⁵ atoms / cm ² or less.

  According to the present invention, even when RTP is performed at a high temperature with high void defect annihilation power, the deterioration of surface roughness can be suppressed, and furthermore, the generation of concave pits can be suppressed. A heat treatment method is provided.

It is a cross-sectional conceptual diagram which shows an example of the RTP apparatus applied to the heat processing method of the silicon wafer concerning this invention. It is a conceptual diagram which shows an example of the heat processing sequence in RTP applied to the heat processing method of the silicon wafer concerning this invention. It is a plot figure when each measured value in temperature T1 (degreeC) is plotted on the horizontal axis | shaft on the horizontal axis | shaft in Table 1 and surface roughness on the vertical axis | shaft.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The silicon wafer heat treatment method according to the present invention includes a silicon wafer having a mirror-polished surface on which at least a semiconductor device is formed, and a silicon atom on the surface is terminated with hydrogen using a hydrogen fluoride-based solution. A temperature range of 1300 ° C. to 1400 ° C. in an inert gas atmosphere in which the density is set to 5 × 10 ¹⁴ atoms / cm ² or more and 4 × 10 ¹⁵ atoms / cm ² or less, and the silicon wafer terminated with hydrogen And a step of performing RTP for rapidly lowering the temperature after the temperature is rapidly raised and held.
The hydrogen termination density here is a value obtained by measuring the polished surface terminated with hydrogen before RTP by X-ray photoelectron spectroscopy (XPS).

  In this way, at least 1300 ° C. or more and 1400 ° C. or less having high void defect annihilation power by terminating the silicon atoms on the polishing surface on which at least the semiconductor device of the silicon wafer is formed with hydrogen at high density with hydrogen. Even when RTP is performed at a high temperature, the deterioration of the surface roughness can be suppressed, and the generation of concave pits due to the influence of a small amount of oxygen contained in the atmosphere can also be suppressed.

That is, by terminating hydrogen with high density, the bonding force between hydrogen and silicon atoms can be increased. Therefore, even at a high temperature of 1300 ° C. or higher and 1400 ° C. or lower, the bond is hardly broken and is in a stable state.
Therefore, even if other reactive gases (such as nitrogen) are present in the atmosphere, bonding between silicon atoms and the reactive gas can be suppressed, so that deterioration of the surface roughness of the polished surface of the wafer is suppressed. can do. In addition, even when a small amount of oxygen is contained in the atmosphere, the reaction between oxygen and silicon atoms can be suppressed, so that generation of concave pits can also be suppressed.

A method of terminating hydrogen with high density by the hydrogen fluoride-based solution is a known method (a method of immersing at least a polished surface of a wafer in the solution, or spin-coating the solution on the polished surface while rotating the wafer). Method). Preferably, the method of immersing the polished surface of the wafer is suitable in terms of productivity and cost.
The hydrogen termination density in this method can be adjusted by changing the time for bringing the solution into contact with the polishing surface (immersion, spin coating, etc.) and the concentration of the hydrogen fluoride solution.
For example, when the hydrofluoric acid solution (HF) having a concentration of 5% is used as the hydrogen fluoride solution, the contact time is 10 minutes or more and 15 minutes or less. When a hydrofluoric acid solution (HF) with a concentration of 30% is used, the contact time is preferably 3 minutes or more and 7 minutes or less.

The hydrogen termination density is preferably 5 × 10 ¹⁴ atoms / cm ² or more and 1 × 10 ¹⁶ atoms / cm ² or less.
When the hydrogen termination density is less than 5 × 10 ¹⁴ atoms / cm ² , it is difficult to increase the bonding force between hydrogen and silicon atoms. Therefore, it is difficult to suppress the deterioration of the surface roughness and the generation of concave pits. When the hydrogen termination density exceeds 1 × 10 ¹⁶ atoms / cm ² , it takes a long time to bring the polishing surface into contact with the solution.
The hydrogen termination density is more preferably 1.5 × 10 ¹⁵ atoms / cm ² or more and 4.0 × 10 ¹⁵ atoms / cm ² or less.

The hydrogen fluoride-based solution mainly includes a hydrofluoric acid solution (HF) and a buffered HF solution (NH ₄ F + HF).

The RTP is preferably performed in an inert gas atmosphere.
By performing RTP in such an atmosphere, the void defect extinction power is high, and the deterioration of the surface roughness can be efficiently suppressed.
Argon gas (Ar) is preferably used as the inert gas.

The RTP is preferably rapidly heated to a temperature range of 1300 ° C. to 1400 ° C. and held.
When the said temperature range is less than 1300 degreeC, while the annihilation power of a void defect falls, it is difficult to improve surface roughness. When the temperature range exceeds 1400 ° C., it is close to the melting point of silicon, which is not preferable because the silicon wafer may be softened or melted.
The temperature range is more preferably 1300 ° C. or higher and 1380 ° C. or lower from the viewpoint of the device life as an RTP device (described later) used for performing the RTP.

The silicon wafer before the hydrogen termination is manufactured by cutting out from a silicon single crystal ingot grown mainly by the Czochralski method (hereinafter referred to as CZ method).
The silicon single crystal ingot is grown by the CZ method by a known method.
Specifically, a silicon single crystal ingot heats a silicon raw material filled in a quartz crucible to form a silicon melt, contacts the seed crystal with the liquid surface of the silicon melt, and rotates the seed crystal and the quartz crucible. The seed crystal can be pulled up to grow the neck portion, the crown portion, and the straight body portion on the seed crystal, and then separated from the silicon melt.

Next, the grown silicon single crystal ingot is cut out by a known method and processed into a silicon wafer in which at least the surface on which the semiconductor device is formed is mirror-polished.
Specifically, a straight body portion of a silicon single crystal ingot is cut into a wafer shape with an inner peripheral blade or a wire saw, and processing such as chamfering, lapping, etching, and mirror polishing of the outer peripheral portion is performed.

FIG. 1 is a conceptual cross-sectional view showing an example of an RTP apparatus applied to a silicon wafer heat treatment method according to the present invention.
An RTP apparatus 10 shown in FIG. 1 contains a reaction chamber 20 for accommodating a wafer W and performing a heat treatment, a wafer holding unit 30 provided in the reaction chamber 20 for holding the wafer W, and heating for heating the wafer W. Unit 40. In a state where the wafer W is held by the wafer holder 30, the first space 20 a that is a space surrounded by the inner wall of the reaction chamber 20 and the surface (device formation surface) W 1 side of the wafer W, and the inner wall of the reaction chamber 20 And a second space 20b that is a space surrounded by the back surface W2 side of the wafer W facing the front surface W1 side.

The reaction chamber 20 has a supply port 22 for supplying atmospheric gas F _A (solid arrow) into the first space 20a and the second space 20b, and the supplied atmospheric gas F _A from the first space 20a and the second space 20b. And a discharge port 26 for discharging. The reaction chamber 20 is made of, for example, quartz.

  The wafer holding unit 30 includes a susceptor 32 that holds the outer peripheral portion of the back surface W2 of the wafer W in a ring shape, and a rotating body 34 that holds the susceptor 32 and rotates the susceptor 32 about the center of the wafer W. The susceptor 32 and the rotating body 34 are made of, for example, SiC.

  The heating unit 40 is disposed outside the reaction chamber 20 above the front surface W1 and below the back surface W2 of the wafer W held by the wafer holding unit 30, and heats the wafer W from both sides. The heating unit 40 is composed of, for example, a plurality of halogen lamps 50.

When RTP is performed using the RTP apparatus 10 shown in FIG. 1, the wafer W is introduced into the reaction chamber 20 from a wafer introduction port (not shown) provided in the reaction chamber 20, and the outer periphery of the back surface W <b> 2 of the wafer W is introduced. part was held on the susceptor 32 of the wafer holder 30 in a ring shape, it supplies the atmospheric gas F _a, while rotating the wafer W, carried out by heating the wafer W by the heating unit 40.

The RTP is charged at a temperature of 1300 ° C. or higher and 1400 ° C. or lower by introducing the hydrogen-terminated silicon wafer into the reaction chamber 20 of the RTP apparatus 10 as shown in FIG. It is preferable that the temperature is rapidly raised to the range and maintained.
By introducing in such a temperature range, in the RTP, it is possible to suppress the occurrence of slip due to a rapid temperature change at the time of introduction while suppressing the productivity from decreasing.

FIG. 2 is a conceptual diagram showing an example of a heat treatment sequence in RTP applied to the silicon wafer heat treatment method according to the present invention.
In the heat treatment sequence used for the RTP, as shown in FIG. 2, at least a semiconductor device is formed in the reaction chamber 20 of the RTP apparatus 10 as shown in FIG. 1 held at a temperature T0 (for example, 500 ° C.). The surface W1 side is mirror-polished, and a wafer W in which silicon atoms on the surface W1 are terminated with high-density hydrogen is installed, and an inert gas is supplied into the first space 20a and the second space 20b.

Next, the temperature is rapidly increased from the temperature T0 (° C.) to a temperature range of 1300 ° C. to 1400 ° C. (temperature T1 (° C.)) at a temperature increase rate ΔTu (° C./second), and then the temperature T1 (° C.) is reached. Then, the temperature is kept constant for a predetermined time t1 (second), and then, for example, the temperature is rapidly decreased to a temperature T0 (° C.) at a temperature decrease rate ΔTd (° C./second).
The temperatures T0 and T1 were measured by a radiation thermometer (not shown) installed below the wafer holder 30 when the wafer W was installed in the reaction chamber 20 of the RTP apparatus 10 as shown in FIG. It is the surface temperature of the wafer W (the average temperature when a plurality of radiation thermometers are arranged in the radial direction of the wafer W).

The temperature increase rate ΔTu in the RTP is preferably 10 ° C./second or more and 150 ° C./second or less.
By setting such a temperature increase rate ΔTu, it is possible to suppress the occurrence of contact marks and slips due to a rapid temperature change at the time of rapid temperature increase, while suppressing the decrease in productivity in the RTP.

The temperature drop rate ΔTd in the RTP is preferably 10 ° C./second or more and 150 ° C./second or less.
By setting such a temperature decrease rate ΔTd, it is possible to suppress the occurrence of contact traces and slips due to a rapid temperature change at the time of rapid temperature decrease, while suppressing a decrease in productivity in the RTP.

The holding time t1 in the temperature range of 1300 ° C. to 1400 ° C. (temperature T1 (° C.)) in the RTP is preferably 1 second to 30 seconds.
By setting the holding time t1 as described above, it is possible to efficiently eliminate void defects without reducing productivity.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limitedly interpreted by the following Example.
(Test 1)
Controlling v / G (v: pulling speed, G: temperature gradient in the pulling axis direction in the single crystal) by the CZ method to produce a silicon single crystal ingot having a region in which vacant point defects exist, A silicon wafer (diameter 300 mm, surface orientation {100}, thickness 775 μm, oxygen concentration 1.2 to 1.3 × 10 ¹⁸ atoms / cm ³ ) obtained by cutting out from the region and having both surfaces mirror-polished The entire wafer was immersed in a 5% hydrofluoric acid solution, and then washed with pure water and dried (hydrogen termination treatment). At that time, a plurality of samples (silicon wafers) in which the immersion time with the hydrofluoric acid solution was changed were produced.
Next, the hydrogen termination density of each polished surface of the plurality of samples was measured by X-ray photoelectron spectroscopy (XPS).

Next, for each sample for which the hydrogen termination density was measured, an RTP having a temperature T1 (° C.) changed by a heat treatment sequence as shown in FIG. 2 using an RTP apparatus 10 as shown in FIG. An annealed wafer was produced.
Specifically, the measured wafer is put into a reaction chamber maintained at 200 ° C., argon gas (Ar) is supplied as an atmosphere, and the temperature T1 (° C.) is set to 1100 at a heating rate of 75 ° C./second. The temperature was changed rapidly to 1200 ° C., 1200 ° C., 1300 ° C., and 1350 ° C., and each temperature was maintained at T1 (° C.) for 15 seconds, and then rapidly decreased to 500 ° C. at a temperature decrease rate of 90 ° C./second. The argon gas (Ar) is known to contain a very small amount of oxygen of 0.1 ppm or less as measured by an oxygen concentration meter installed in the reaction chamber.

RMS (measurement range: 3 μm × 3 μm) of the surface roughness of the obtained annealed wafer on the semiconductor device formation surface was evaluated using an AFM (Atomic Force Microscope).
Further, the generation density of concave pits on the semiconductor device forming surface was calculated from the AFM image.
Furthermore, regarding the defect density in the surface layer part from the wafer surface to a depth of 5 μm, an LSTD scanner (Laser Scattering Topology Defect)
(Scanner) at a wavelength of 680 nm.
Further, as a reference example, the surface roughness on the semiconductor device forming surface of the wafer before hydrogen termination treatment was similarly evaluated by RMS (measurement range: 3 μm × 3 μm) using AFM.
Table 1 shows the test conditions and evaluation results in this test, and FIG. 3 is a plot when the measured values at temperature T1 (° C.) are plotted with the hydrogen termination density in Table 1 as the horizontal axis and the surface roughness as the vertical axis. Respectively.

As shown in Table 1 and FIG. 3, the hydrogen termination density is set to 5.0 × 10 ¹⁴ atoms / cm ² or higher, and the temperature T1 (° C.) is set to 1300 ° C. or higher to reduce the surface roughness (RMS). Further, it can be seen that the surface roughness (RMS) is better than before the hydrogen termination treatment, no concave pits are generated, and the defect density is low. In addition, when the hydrogen termination density is 1.5 × 10 ¹⁵ atoms / cm ² or more and 4.0 × 10 ¹⁵ atoms / cm ² or less, the surface roughness (RMS) is particularly improved to be less than 0.10 nm. Is recognized.

10 RTP apparatus 20 Reaction chamber 30 Wafer holding part 40 Heating part

Claims (2)

A silicon wafer on which at least a surface on which a semiconductor device is to be formed is mirror-polished is terminated with hydrogen in a hydrogen fluoride-based solution, and the hydrogen termination density of the surface is 5 × 10 ¹⁴ atoms / cm ² or more. A step of 4 × 10 ¹⁵ atoms / cm ² or less;
And a step of performing a rapid heating / cooling heat treatment in which the silicon wafer terminated with hydrogen is rapidly heated and held in a temperature range of 1300 ° C. to 1400 ° C. in a rare gas atmosphere and then rapidly cooled. A heat treatment method for silicon wafers. ^2. The heat treatment method for a silicon wafer according to claim 1, wherein the hydrogen termination density is 1.5 × 10 ¹⁵ atoms / cm ² or more and 4.0 × 10 ¹⁵ atoms / cm ² or less.

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