JP2004321875A - Ultrasonic cleaning method and semiconductor device production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic cleaning method having a high removal effect on fine particles. <P>SOLUTION: An object to be cleaned is immersed in a cleaning liquid. The object is cleaned by applying thereto ultrasonic waves under conditions that the sound pressure of the ultrasonic waves propagating in the cleaning liquid is higher then 5 mV and not higher than 50 mV. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic cleaning method and a semiconductor device manufacturing method, and more particularly to an ultrasonic cleaning method suitable for a case where particles to be removed are small in size and a semiconductor device manufacturing method using the cleaning method.
[0002]
[Prior art]
In ultrasonic cleaning in which an object is cleaned by generating ultrasonic waves in the cleaning liquid, the cleaning effect can be enhanced by reducing the amount of dissolved gas in the cleaning liquid (Patent Documents 1 and 4). Further, the cleaning effect can be enhanced by increasing the sound pressure of the ultrasonic wave propagating in the cleaning liquid (Patent Document 2). It is known that sound pressure needs to be optimized in order to obtain a desired cleaning effect (Patent Document 3).
[0003]
[Patent Document 1]
JP-A-7-96258 [Patent Document 2]
JP-A-10-22246 [Patent Document 3]
JP-A-9-231561 [Patent Document 4]
Japanese Patent Application Laid-Open No. Hei 7-100445
[Problems to be solved by the invention]
As the pattern of a semiconductor integrated circuit device becomes finer, fine particles, which have not been a problem in the past, cause a decrease in reliability. In the conventional ultrasonic cleaning method, it was not sufficient to remove such fine particles.
[0005]
An object of the present invention is to provide an ultrasonic cleaning method having a high effect of removing fine particles.
Another object of the present invention is to provide a method for manufacturing a semiconductor device using the above-described ultrasonic cleaning method.
[0006]
[Means for Solving the Problems]
According to one aspect of the present invention, a step of immersing an object to be cleaned in a cleaning liquid and an ultrasonic wave applied to the cleaning liquid so that the sound pressure of the ultrasonic wave propagating in the cleaning liquid is higher than 5 mV and 50 mV or less. And a step of cleaning the object to be cleaned.
[0007]
According to another aspect of the present invention, a step of immersing the silicon substrate in the cleaning liquid, and applying an ultrasonic wave to the cleaning liquid so that the sound pressure of the ultrasonic wave propagating in the cleaning liquid is higher than 5 mV and 50 mV or less. And a step of cleaning the silicon substrate, and oxidizing a surface portion of the cleaned silicon substrate to form a silicon oxide film.
[0008]
When ultrasonic cleaning is performed under the above conditions, extremely fine particles can be efficiently removed.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
1A to 2E are cross-sectional views of a substrate in the process of manufacturing a semiconductor device according to an embodiment, and FIG. 2F is a cross-sectional view of a semiconductor device manufactured by a method according to the embodiment. .
[0010]
As shown in FIG. 1A, an element isolation insulating region 2 is formed in a surface layer portion of a semiconductor substrate 1 made of silicon by shallow trench isolation (STI) to define active regions A1 to A4. If necessary, a well is formed and ion implantation for threshold adjustment is performed.
[0011]
After the ion implantation, the surface of the semiconductor substrate 1 is cleaned. Hereinafter, this surface cleaning procedure will be described in detail. First, ultrasonic cleaning is performed using a cleaning solution obtained by diluting hydrogen peroxide solution and ammonia water with pure water. This processing is called SC-1 processing. After washing the substrate with water, the substrate surface is washed with diluted hydrofluoric acid. This processing is called DHF processing. After washing with water, the surface is washed using a washing solution obtained by diluting hydrochloric acid and aqueous hydrogen peroxide with pure water. This processing is called SC-2 processing. After the SC-2 treatment, washing and drying are performed. Note that ultrasonic cleaning is not used in the DHF processing and the SC-2 processing.
[0012]
As shown in FIG. 1B, a heat treatment is performed in a dry oxygen atmosphere to form a 5-nm-thick silicon oxide film 3 on the surface of the substrate 1.
As shown in FIG. 1C, a resist film is formed, and exposure and development are performed to form a resist pattern 4 that covers the active regions A1 and A2 and exposes the active regions A3 and A4.
[0013]
As shown in FIG. 2D, the silicon oxide film 3 is etched using hydrofluoric acid using the resist pattern 4 shown in FIG. 1C as an etching mask. After the etching, the resist pattern 4 is removed. The silicon oxide film 3 remains on the active regions A1 and A2, and the silicon surface of the semiconductor substrate 1 is exposed in the active regions A3 and A4.
[0014]
After removing the resist pattern 4, the same cleaning as the surface cleaning performed before the oxidation step shown in FIG. 1B is performed.
As shown in FIG. 2E, heat treatment is performed in a dry oxygen atmosphere, and the surface of the semiconductor substrate 1 is oxidized under the same conditions as in the oxidation step shown in FIG. Thus, a silicon oxide film 5 is formed. In the active regions A1 and A2, the silicon surface is oxidized through the remaining silicon oxide film 3, and thicker silicon oxide films 3 and 5 are formed. In the figure, the silicon oxide films 3 and 5 are clearly shown for easy understanding. However, in practice, the two cannot be distinguished from each other, and the silicon oxide films are formed as a single-layer silicon oxide film.
[0015]
A silicon oxide film 5 having a thickness of 5 nm is formed on the surfaces of the active regions A3 and A4. The total thickness of the silicon oxide films 3 and 5 formed on the active regions A1 and A2 is 7.5 nm.
[0016]
As shown in FIG. 2F, PMOS transistors QP1 and QP2 are formed in the active regions A1 and A3, respectively, and NMOS transistors QN1 and QN2 are formed in the active regions A2 and A4, respectively. These transistors can be formed using well-known techniques such as film formation, photolithography, etching, and ion implantation.
[0017]
The gate insulating films of the PMOS transistor QP1 and the NMOS transistor QN1 formed in the active regions A1 and A2 have a thickness of 7.5 nm. The thicknesses of the gate insulating films of the PMOS transistor QP2 and the NMOS transistor QN2 formed in the active regions A3 and A4 are 5 nm. Thus, a plurality of MOS transistors having different gate insulating film thicknesses can be formed.
[0018]
Hereinafter, of the above manufacturing steps, the ultrasonic cleaning process performed before the oxidation step in the state of FIG. 1A and the state of FIG. 2D will be described in detail.
FIG. 3 shows a schematic sectional view of the ultrasonic cleaning apparatus. A processing tank 11 is arranged in the outer tank 10. The propagation water 12 is filled between the outer tank 10 and the processing tank 11. A plurality of high-frequency vibrators 13 are attached to the bottom of the outer tub 10. The processing bath 11 is filled with a cleaning liquid 15 and a plurality of semiconductor wafers 16 to be cleaned are immersed therein. For example, 50 semiconductor wafers 16 are held by a holder so as to be arranged at regular intervals, and are immersed in the cleaning liquid 15.
[0019]
Cleaning was performed by changing the amount of dissolved gas in the cleaning liquid used in the SC-1 treatment to 2 ppm and changing the sound pressure of ultrasonic waves generated in the cleaning liquid.
FIG. 4A shows a detection result of 0.09 μm or more particles of the wafer cleaned under the condition that the sound pressure is 5 to 50 mV. FIG. 4B shows a detection result of 0.09 μm or more particles of the wafer cleaned under the condition that the sound pressure is 100 to 150 mV. The sound pressure was measured at a position 7 cm deeper than the upper end of the wafer 16 immersed in the cleaning solution 15 of the ultrasonic cleaning apparatus of FIG. 3 using an ultrasonic sound pressure meter HUS-5 or HUS-7 manufactured by Honda Electronics Co., Ltd. Was measured. The depth from the level of the cleaning liquid 15 to the upper end of the wafer 16 is about 3 cm. That is, the depth to the sound pressure measurement point is about 10 cm. The measured value of the sound pressure in the state where the wafer was not immersed was almost the same as the result of measuring the sound pressure of the portion where the wafer was removed by removing the central 10 wafers out of the 50 wafers. .
[0020]
Generally, it is considered that the higher the sound pressure, the higher the particle removal ability. However, in consideration of extremely fine particles having a size of about 0.09 μm, it can be understood that if the sound pressure is increased, the particle removing ability cannot be said to be increased. It is considered that there is a suitable range of sound pressure in order to enhance the particle removing effect. Furthermore, if the range of the sound pressure is 5 to 50 mV, the particle removing effect does not depend on the wafer size.
[0021]
FIG. 5 shows the relationship between the megasonic power of the ultrasonic cleaner shown in FIG. 3 and the particle removal rate when performing the SC-1 process. The horizontal axis represents megasonic power in units of “W”, and the vertical axis represents particle removal rates in units of “%”. The particles to be detected have a size of 0.16 μm or more. When the megasonic power is increased, the particle removal rate shows a maximum value at about 100 W, and shows a minimum value at about 430 W. It can be seen that increasing the megasonic power is not the only way to increase the particle removal rate.
[0022]
FIG. 6 shows the relationship between megasonic power and sound pressure. The horizontal axis represents megasonic power in units of “W”, and the vertical axis represents sound pressure in units of “mV”. This sound pressure is a result measured by an ultrasonic sound pressure meter HUB-5 or HUB-7 manufactured by Honda Electronics Co., Ltd. As can be seen from FIG. 5, the megasonic power may be set to about 100 W in order to increase the particle removal rate. Also, when the megasonic power is increased to 300 W, the particle removal rate decreases.
[0023]
From this result and the relationship shown in FIG. 6, it is considered that the sound pressure is preferably set to 50 mV or less in order to secure a high particle removal rate. On the other hand, if the sound pressure is too low, particles cannot be removed. For this reason, it is preferable that the sound pressure be higher than 5 mV.
[0024]
FIG. 7 shows the results of a Qbd life test of the silicon oxide films 3 and 4 having a thickness of about 7.5 nm formed in the active regions A1 and A2 in FIG. The horizontal axis represents the accumulated charge amount moved in the silicon oxide film on a logarithmic scale, and the left vertical axis represents the Weibull value. The right vertical axis indicates the cumulative failure rate corresponding to the Weibull value on the left vertical axis in units of “%”. The asterisk symbol and the plus symbol in the figure indicate the Weibull value of the sample subjected to ultrasonic cleaning with the sound pressure set to 20 mV and 100 mV, respectively, during the SC-1 treatment.
[0025]
It can be seen that the silicon oxide film formed by cleaning under the condition of a sound pressure of 20 mV has higher reliability.
The area where many particles remained after the cleaning did not always coincide with the measurement point where the dielectric breakdown occurred early in the Qbd life test. From this, it is considered that the decrease in the breakdown voltage of the silicon oxide film is caused not only by the particles remaining after the cleaning, but also by other factors. For example, if the sound pressure at the time of ultrasonic cleaning is increased, it is considered that cavities are concentrated on a non-uniform portion of the silicon oxide film, causing damage. By setting the sound pressure at the time of ultrasonic cleaning to be higher than 5 mV and equal to or lower than 50 mV, a highly reliable silicon oxide film can be formed.
[0026]
In the above example, the dissolved gas amount in the cleaning liquid was 2 ppm. When the amount of dissolved gas increases, the sound pressure of the ultrasonic wave cannot be increased. Therefore, the dissolved gas amount is preferably set to 5 ppm or less. Further, in the above embodiment, a mixed solution of hydrogen peroxide solution, aqueous ammonia and water is used as the cleaning liquid, but the preferred range of the sound pressure will not change even when another cleaning liquid is used.
[0027]
Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.
[0028]
【The invention's effect】
As described above, according to the present invention, the effect of removing particles can be enhanced by setting the sound pressure during ultrasonic cleaning to be higher than 5 mV and equal to or lower than 50 mV.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a device in the process of manufacturing, for explaining a method of manufacturing a semiconductor device according to an embodiment.
FIGS. 2D and 2E are cross-sectional views of a device in the course of manufacture for explaining a method of manufacturing a semiconductor device according to an example; FIG. FIG.
FIG. 3 is a schematic sectional view of an ultrasonic cleaning device.
FIG. 4 is a diagram showing a state of particle attachment to a wafer after cleaning.
FIG. 5 is a graph showing a relationship between megasonic power and a particle removal rate.
FIG. 6 is a graph showing the relationship between megasonic power and sound pressure.
FIG. 7 is a graph showing Qbd life test results of silicon oxide films manufactured by methods according to the examples and the comparative examples.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 semiconductor substrate 2 element isolation insulating region 3, 5 silicon oxide film 4 resist pattern 10 outer tank 11 processing tank 12 propagation water 13 high frequency oscillator 15 cleaning liquid 16 wafer

Claims (5)

A step of immersing the object to be cleaned in a cleaning liquid,
Applying an ultrasonic wave to the cleaning liquid so that the sound pressure of the ultrasonic wave propagating in the cleaning liquid is higher than 5 mV and equal to or lower than 50 mV, and cleaning the object to be cleaned. The ultrasonic cleaning method according to claim 1, wherein a total dissolved gas amount in the cleaning liquid is 5 ppm or less. A step of immersing the silicon substrate in a cleaning solution,
Cleaning the silicon substrate by applying ultrasonic waves to the cleaning liquid so that the sound pressure of the ultrasonic wave propagating in the cleaning liquid is higher than 5 mV and equal to or lower than 50 mV; and the surface layer portion of the cleaned silicon substrate. Oxidizing to form a silicon oxide film. 4. The method according to claim 3, wherein a total dissolved gas amount in the cleaning liquid is 5 ppm or less. The method of manufacturing a semiconductor device according to claim 3, wherein the cleaning liquid includes a hydrogen peroxide solution and an aqueous ammonia.

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