JP4424701B2 - Wafer etching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer etching method for locally etching a relative thickness portion existing on the surface of a wafer.
[0002]
[Prior art]
In recent years, local etching is performed on a relative thickness portion on a surface of a silicon wafer or the like, and the wafer is thinned (thinned) or the surface is flattened to obtain TTV (Total Thickness Variation) or LTV (Local A wafer etching method has been devised to improve shape variation such as thickness variation.
[0003]
FIG. 4 is a schematic view showing a conventional wafer etching method.
In FIG. 4, reference numeral 100 denotes a plasma generator, and the plasma generator 100 generates SF 6 (sulfur hexafluoride) by plasma discharge to generate activated species gas G containing F (fluorine) ions and radicals. The activated species gas G is sprayed from the nozzle 101 onto the surface of the silicon wafer W.
The silicon wafer W is fixed on the stage 120, and the stage 120 is moved in the horizontal direction, and the nozzle 101 is scanned over the entire surface of the silicon wafer W, so that the surface of the silicon wafer W is relatively smaller than the specified thickness. A thick part (hereinafter referred to as “relative thick part”) Wa is guided directly below the nozzle 101.
Thus, the active species gas G is sprayed from the nozzle 101 onto the convex relative thickness portion Wa, and the relative thickness portion Wa is locally etched, so that the surface of the silicon wafer W is flattened.
[0004]
However, in this wafer etching method using SF6 gas, white turbidity B is generated on the surface of the silicon wafer W along the scanning line A of the nozzle 101 during the etching as shown by the oblique lines in FIG. In addition to soiling, these white turbidities may hinder uniform etching and reduce the desired TTV or LTV.
On the other hand, there is a method in which CF4 (carbon tetrafluoride) gas is plasma-discharged to perform wafer etching. When this method is used, white turbidity B does not occur on the surface of the silicon wafer W, but the etching rate is very slow compared to the method using SF6 gas.
For this reason, it has been desired to establish a wafer etching method using SF6 gas that does not cause white turbidity.
As an example of such a technique, there is a technique as shown in FIG.
In this technique, the silicon wafer W is placed in a low-pressure environment of 1 Torr. Then, with the small discharge chamber 200 that also serves as an electrode and filled with SF6 gas approaching the relative thickness portion Wa, the relative thickness portion Wa is locally etched by plasma discharge of SF6 gas at a high frequency of 13.56 Hz. To do. At this time, since the plasma in the discharge chamber 200 is close to the relative thickness portion Wa, the activated species gas G etches the relative thickness portion Wa, and at the same time, ions in the activated species gas G collide with the relative thickness portion Wa. It will be. For this reason, it is understood that the white turbidity is eliminated by the impact of these various ions, and the white turbidity does not remain on the surface of the silicon wafer W.
[0005]
[Problems to be solved by the invention]
However, in the conventional wafer etching method shown in FIG. 6, since ions in the activated species gas G collide with the surface of the silicon wafer W, the crystal structure of the silicon wafer W is disturbed or caused by the collision of the various ions. Impurities may enter the silicon wafer W and high-quality mirror processing of the silicon wafer W may not be achieved. Furthermore, in this method, white turbidity cannot be visually recognized under natural light, but white turbidity can be visually recognized under a condenser lamp, and the occurrence of white turbidity cannot be completely prevented.
[0006]
On the other hand, the apparatus shown in FIG. 4 uses SF6 gas and the plasma discharge site is far from the silicon wafer W, and only the activated species gas G is injected onto the silicon wafer W. Therefore, as long as the silicon wafer W is etched with this apparatus, the crystal of the silicon wafer W is not disturbed.
Therefore, the inventor used this apparatus to add H2 (hydrogen) gas to SF6 gas and locally etch the silicon wafer W, and then visually observed the surface of the silicon wafer W, and no cloudiness was observed. It is assumed that the occurrence of white turbidity is suppressed by the intervention of HF (hydrogen fluoride) generated by the reaction between F (fluorine) radicals and H2. Moreover, according to this method, ions in the activated species gas G do not collide with the silicon wafer W, so that the crystal structure of the surface portion of the silicon wafer W is not disturbed. Further, it is considered that the white turbidity on the surface of the silicon wafer W can be completely prevented by heating the silicon wafer W to a predetermined temperature.
As shown in FIG. 7, there is a technique for etching the surface of the silicon wafer W by adding H2 gas to SF6 gas.
In this technique, the silicon wafer W is placed in a high-pressure environment of 1500 Torr. Then, the drum-shaped electrode 300 longer than the diameter of the silicon wafer W is brought close to the silicon wafer W, and SF6 gas added with H2 gas is interposed in a slight gap between the electrode 300 and the silicon wafer W. The surface of the silicon wafer W is etched by plasma discharge of this gas at a high frequency of 150 MHz. However, since this technique also brings the plasma discharge site close to the silicon wafer W, the same problem as the technique shown in FIG. 6 occurs. Further, since the atmospheric pressure is high, the gas temperature rises. As a result, the wafer temperature rises, causing problems such as wafer warpage. Moreover, the occurrence of white turbidity could not be suppressed.
[0007]
The present invention solves the above-described problems based on the above assumption, and by adding a mixed gas containing hydrogen gas to sulfur hexafluoride gas, the occurrence of white turbidity on the wafer surface during etching is suppressed. An object of the present invention is to provide a wafer etching method that enables high-quality wafer mirror processing.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention of claim 1 is directed to a plasma generation process in which sulfur hexafluoride gas is converted into plasma at a discharge site in an alumina discharge tube to generate activated species gas, and activated species gas generated at the discharge site. A jet that activates the relative thickness part locally by injecting the active species gas into the relative thickness part with the nozzle part of the alumina discharge tube that leads the silicon wafer side facing the relative thickness part of the silicon wafer. In a wafer etching method comprising: a mixed gas obtained by mixing sulfur hexafluoride gas and hydrogen gas for suppressing white turbidity generation on a silicon wafer surface at a predetermined ratio to a discharge site in an alumina discharge tube. The active species mixed gas containing the activated species gas is generated, the activated species mixed gas is injected from the nozzle portion, and the hydrogen gas is divided between 0.1% and 30% with respect to the mixed gas. In mixing, the relative speed of the nozzle portion relative to the silicon wafer is set to be substantially inversely proportional to the thickness of the relatively thick portion, the relative speed of the nozzle portion on a relative thick section as well as the low-speed, non-relatively thick portion It was set as the structure which makes the relative speed of the above-mentioned nozzle part high .
With this configuration, in the plasma generation process, the sulfur hexafluoride gas and the hydrogen gas are converted into plasma at the discharge site in the discharge tube, and an active species mixed gas containing the activated species gas and the hydrogen fluoride gas is generated. In the injection process, the active species gas generated at the discharge site is guided to the silicon wafer side by the nozzle portion, and the active species gas is injected from the nozzle portion facing the relative thickness portion of the silicon wafer to the relative thickness portion, The relative thickness is etched locally. At this time, since the wafer is etched by the activated species gas based on the sulfur hexafluoride gas, the etching rate is extremely high. Further, since the active species gas is jetted from the nozzle portion away from the discharge site where the plasma is generated and etching is performed, the crystal structure on the wafer surface is not disturbed. Furthermore, since a mixed gas containing hydrogen gas for generating hydrogen fluoride gas for suppressing white turbidity generation is added to the activated species gas at a predetermined ratio, the hydrogen fluoride gas generated by the hydrogen gas Generation of cloudiness on the wafer surface can be suppressed.
[0009]
According to a second aspect of the present invention, in the wafer etching method according to the first aspect, a heating process for heating the surface of the silicon wafer to a predetermined temperature is provided.
With such a configuration, the occurrence of white turbidity can be almost completely suppressed to the extent that white turbidity cannot be visually recognized even under a condenser lamp.
As a preferred example of the wafer heating temperature, the invention according to claim 3 is the wafer etching method according to claim 2, wherein the heating temperature of the silicon wafer in the heating process is set to a temperature between 60 ° C and 170 ° C. The configuration is as follows.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a structural view of a wafer etching apparatus for realizing a wafer etching method according to a first embodiment of the present invention.
The wafer etching apparatus includes a plasma generator 1 and a chamber 6 for storing a silicon wafer W.
[0011]
The plasma generator 1 includes a discharge tube 2 made of alumina, a gas supply system 3, a microwave oscillator 4, and a waveguide 5.
[0012]
The discharge tube 2 is a cylindrical body that also serves as the nozzle unit 20 at the lower end, and the supply pipe 30 of the gas supply system 3 is connected to the upper end.
The gas supply system 3 is a system for supplying gas into the discharge tube 2, and includes an SF 6 gas cylinder 31 and an H 2 gas cylinder 32, and the cylinders 31 and 32 pass through flow rate controllers 33 and 34. Connected to the supply pipe 30.
Reference numeral 35 denotes a valve.
The microwave oscillator 4 is a magnetron and can oscillate a microwave M having a predetermined frequency.
The waveguide 5 is for propagating the microwave M oscillated from the microwave oscillator 4 and is extrapolated to the discharge tube 2 through the hole 50.
A reflection plate (short plunger) 51 that reflects the microwave M to form a standing wave is attached inside the left end of the waveguide 5. Further, in the middle of the waveguide 5, a three stub tuner 52 that performs phase matching of the microwave M, and an isolator 53 that bends the reflected microwave M toward the microwave oscillator 4 in a 90 ° direction (surface direction in FIG. 1). Is attached.
[0013]
When the plasma generator 1 adopts such a configuration, when gas is supplied from the gas supply system 3 to the discharge tube 2 and the microwave M is oscillated from the microwave oscillator 4, at the portion of the discharge tube 2 corresponding to the hole 50. Plasma discharge is performed, and gas generated by the plasma discharge is ejected from the nozzle unit 20.
By the way, in this wafer etching apparatus, the extrapolation position of the waveguide 5 with respect to the microwave oscillator 4, that is, the discharge site is set far above the nozzle portion 20. Therefore, the plasma itself generated at the discharge site does not contribute to the etching of the silicon wafer W, and only the activated species gas G generated by the plasma discharge contributes to the etching of the silicon wafer W.
[0014]
On the other hand, the chamber 6 is a box for storing the silicon wafer W, and the inside of the chamber 6 is evacuated by the vacuum pump 60.
A hole 61 is formed in the center of the upper surface of the chamber 6, and the nozzle portion 20 of the discharge tube 2 is inserted into the chamber 6 through the hole 61. An O-ring 62 is mounted between the hole 61 and the discharge tube 2 so that the space between the hole 61 and the discharge tube 2 is kept airtight, and the entire chamber 6 moves up and down with respect to the discharge tube 2. Can be done.
A duct 63 is provided around the nozzle portion 20 inserted into the hole 61, and the reaction product gas at the time of etching is discharged to the outside of the chamber 6 by driving the vacuum pump 64. .
[0015]
A chuck 7 is disposed in the chamber 6, and the silicon wafer W is held by the chuck 7.
The chuck 7 is an electrostatic chuck and has a mechanism for adsorbing the silicon wafer W by electrostatic force. In addition, a heater 70 is incorporated in the chuck 7 as indicated by a broken line, and the silicon wafer W can be heated to a predetermined temperature by turning on the power supply 71. .
[0016]
The chuck 7 is supported by an XY drive mechanism 8, and the entire chamber 6 is supported by a Z drive mechanism 9.
Specifically, the chuck 7 is moved left and right in FIG. 1 by the X drive motor 80 of the XY drive mechanism 8, and the chuck 7 and the X drive motor 80 are integrated with each other on the front and back of FIG. 1 by the Y drive motor 81. It has been moved. Further, the entire chamber 6 is moved up and down by the Z drive motor 90 of the Z drive mechanism 9.
That is, the nozzle unit 20 can be moved in the XY direction relative to the silicon wafer W by the XY drive mechanism 8 and can be moved in the vertical direction by the Z drive mechanism 9.
The drive control of the X drive motor 80, the Y drive motor 81 of the XY drive mechanism 8 and the Z drive motor 90 of the Z drive mechanism 9 is performed by the control computer 89 based on a predetermined program.
[0017]
Next, a method for executing the wafer etching method of this embodiment using the wafer etching apparatus having the above-described configuration will be described.
First, with the silicon wafer W adsorbed to the chuck 7, the vacuum pump 60 is driven to bring the inside of the chamber 6 into a low pressure state of 0.1 Torr to 5.0 Torr, and the Z driving mechanism 9 is driven to drive the chamber. By raising the whole 6, the silicon wafer W is brought close to about 5 mm below the nozzle portion 20.
[0018]
In this state, the valve 35 of the gas supply system 3 is opened, and the SF6 gas G1 in the cylinder 31 and the H2 gas G2 in the cylinder 32 are supplied into the discharge tube 2 through the flow rate controllers 34 and 35 and the supply pipe 30. .
At this time, the opening degree of the valve 35 is adjusted to maintain the pressures of the SF6 gas G1 and the H2 gas G2 at predetermined pressures, and the flow rates of the SF6 gas G1 and the H2 gas G2 are adjusted by the flow rate controllers 33 and 35. Then, the ratio of the H2 gas G2 to the mixed gas of the SF6 gas G1 and the H2 gas G2 supplied into the discharge tube 2 is set to a value between 0.1% and 30%.
[0019]
When the microwave oscillator 4 is driven in parallel with the supply operation of the mixed gas, the mixed gas existing at the discharge site is plasma-discharged by the microwave M, and the activated species gas G and the HF gas G3 are generated. (Plasma generation process).
Then, the activated species mixed gas G ′ having the activated species gas G and the HF gas is guided to the nozzle portion 20 and sprayed from the opening of the nozzle portion 20 to the silicon wafer W side.
[0020]
In this state, the control computer 89 drives the XY drive mechanism 8 to move the chuck 7 on which the silicon wafer W is sucked in a zigzag manner in the XY direction.
That is, as shown in FIG. 2, the nozzle portion 20 is scanned relative to the silicon wafer W in a zigzag manner. At this time, the relative speed of the nozzle portion 20 with respect to the silicon wafer W is set so as to be approximately inversely proportional to the thickness of the relative thickness portion.
As a result, as shown in FIG. 3, the nozzle portion 20 moves at a high speed directly above the non-relative thickness portion Wb, and when the nozzle portion 20 comes above the relative thickness portion Wa, the speed is increased according to the thickness of the relative thickness portion Wa. Lower. As a result, the etching time with respect to the relative thick part Wa becomes long, and the relative thick part Wa is cut flat (injection process).
The gaseous reaction product generated during such etching is discharged from the duct 63 to the outside of the chamber 6 by driving the vacuum pump 64 shown in FIG.
[0021]
By the way, since the mixed gas of the SF6 gas G1 and the H2 gas G2 is plasma-discharged during the etching, the activated species gas G containing F radicals and the HF gas generated by the reaction of the F radicals and the H2 gas G2 are produced. The active species mixed gas G ′ is sprayed onto the silicon wafer W. For this reason, it is considered that the HF gas in the active species mixed gas G ′ acts chemically or physically on the surface of the silicon wafer W to suppress the occurrence of white turbidity on the surface of the silicon wafer W.
Further, since the silicon wafer W is etched with the activated species gas G obtained by the plasma discharge of the SF6 gas G1, the etching rate is fast.
Furthermore, since the plasma discharge site is set at a position far above the silicon wafer W (for example, 15 cm above the surface of the silicon wafer W), the plasma generated at the discharge site affects the etching of the silicon wafer W. Not give. That is, the plasma only functions as a source of the activated species gas G, and the etching of the silicon wafer W is performed only by the activated species gas G. Therefore, unlike the prior art shown in FIG. 6, ions in the activated species gas G do not collide with the silicon wafer W and disturb the crystal structure on the surface of the silicon wafer W.
[0022]
The inventor conducted the following comparative experiments in order to demonstrate the above-described effects.
First, in the first experiment, an 8-inch silicon wafer W is adsorbed to the chuck 7 in the chamber 6 held at 1 Torr, the valve 35 of the gas supply system 3 is opened and the flow rate controller 33 is adjusted to adjust the cylinder. From 31 to 200 SCCM, that is, 200 liters of SF6 gas G1 per minute was supplied to the discharge tube 2, and a microwave M with an output of 300 W was transmitted from the microwave oscillator 4 to plasma discharge the SF6 gas G1. Then, as shown in FIG. 2, the nozzle portion 20 was scanned in a zigzag pattern at a pitch of 8 mm, and the entire surface of the silicon wafer W was etched by the activated species gas G injected from the nozzle portion 20. Then, it was visually observed that white turbidity B as shown in FIG. 5 was generated along the scanning line A on the surface of the etched silicon wafer W under natural light.
Next, a second experiment was performed, the valve 35 was opened and the flow rate controllers 33 and 34 were adjusted to output 200 SCCM SF6 gas G1 from the cylinder 31 and 10 SCCM H2 gas G2 from the cylinder 32. These mixed gases were supplied to the discharge tube 2. Other conditions were set in the same manner as in the first experiment. Then, the generation of white turbidity could not be visually observed on the surface of the etched silicon wafer W under natural light. In addition, it was possible to obtain a good quality mirror surface with no disorder of the crystal structure.
[0023]
(Second Embodiment)
In the said 1st Embodiment, generation | occurrence | production of white turbidity can be suppressed to such an extent that it cannot visually observe under natural light. However, when the surface of the etched silicon wafer W is visually observed under a condenser lamp, a thin white turbidity remains. This also applies to the wafer etching method using the CF4 gas described above.
The silicon wafer W having such a degree of white turbidity is established as a product, but in order to obtain a higher quality mirror surface, it is necessary to perform a mirror polishing process on the surface of the silicon wafer W with a CMP apparatus. Therefore, in such a case, since a mirror polishing process is required, the equipment cost is high and the work processing time becomes long.
[0024]
In consideration of this point, in this embodiment, a heating process is provided that can almost completely prevent the occurrence of white turbidity on the surface of the silicon wafer W without causing an increase in equipment cost.
Specifically, the same method as the wafer etching method of the first embodiment is executed, and the power supply 71 is turned on during the etching of the silicon wafer W, the heater 70 is operated, and the silicon wafer W is moved to 60 ° C. Heat to a temperature between ~ 170 ° C.
Thereby, the white turbidity on the surface of the silicon wafer W is reduced to such an extent that it cannot be visually observed even under a condenser lamp.
[0025]
In order to verify this effect, the inventor etched the silicon wafer W under the same conditions as in the second experiment and further heated the silicon wafer W to 80 ° C. using the heater 70. Went.
Then, the occurrence of white turbidity on the surface of the silicon wafer W was almost completely suppressed, and the white turbidity could not be visually observed even under a condenser lamp.
[0026]
As described above, according to the wafer etching method of this embodiment, it is possible to perform the same processing as the above mirror polishing with simple equipment, and it is possible to reduce the equipment cost and shorten the work processing time. .
[0027]
In addition, this invention is not limited to the said embodiment, A various deformation | transformation and change are possible within the range of the summary of invention.
For example, in the first and second embodiments, the plasma generator 1 that generates plasma by oscillating microwaves is used as means for executing the plasma generation process. However, the means that can generate activated species gas is used. For example, various plasma generators such as a plasma generator that generates plasma by high frequency to generate active species gas can be used.
In the second embodiment, the heater 70 is used as a means for achieving the heating process. However, the present invention is not limited to this. For example, an infrared lamp or the like can be used as the heating process execution means.
[0028]
【The invention's effect】
As described above in detail, according to the wafer etching method of the present invention, the wafer is etched with the activated species gas based on the sulfur hexafluoride gas, so that the etching rate of the wafer can be increased. Further, since the active species gas is jetted from the nozzle portion away from the discharge site where the plasma is generated and etching is performed, the crystal structure on the wafer surface is not disturbed, and a high quality wafer can be provided. Furthermore, since the generation of white turbidity on the wafer surface can be suppressed by adding a mixed gas containing hydrogen gas for generating hydrogen fluoride gas for suppressing white turbidity generation , a high-quality wafer can be provided. .
Furthermore, according to the wafer etching method of the present invention, the occurrence of white turbidity on the wafer surface can be almost completely suppressed to the extent that white turbidity cannot be visually recognized even under a condenser lamp. A wafer can be provided.
[Brief description of the drawings]
FIG. 1 is a structural diagram of a wafer etching apparatus for realizing a wafer etching method according to a first embodiment of the present invention.
FIG. 2 is a plan view showing a scanning pattern of a wafer.
FIG. 3 is a cross-sectional view showing a local etching state of a relative thickness portion.
FIG. 4 is a schematic view showing a conventional wafer etching method.
FIG. 5 is a plan view showing a state of occurrence of white turbidity on the surface of a silicon wafer etched by a conventional wafer etching method.
FIG. 6 is a cross-sectional view showing a wafer etching method according to another conventional example.
FIG. 7 is a cross-sectional view showing a conventional wafer etching method for etching the surface of a silicon wafer W by adding H 2 gas to SF 6 gas.
[Explanation of symbols]
[0029]
DESCRIPTION OF SYMBOLS 1 ... Plasma generator, 2 ... Discharge tube, 3 ... Gas supply system, 4 ... Microwave oscillator, 5 ... Waveguide, 6 ... Chamber, 7 ... Chuck, 8 ... XY drive mechanism, 9 ... Z drive mechanism 20 ... Nozzle part 31, 32 ... Cylinder, G ... Active species gas, G '... Active species mixed gas, G1 ... SF6 gas, G2 ... H2 gas, W ... Silicon wafer, Wa ... Relative thickness part.

Claims (3)

A plasma generation process in which sulfur hexafluoride gas is converted into plasma at a discharge site in an alumina discharge tube to generate activated species gas;
By injecting the active species gas into the relative thickness portion with the nozzle portion of the alumina discharge tube that guides the active species gas generated at the discharge site to the silicon wafer side facing the relative thickness portion of the silicon wafer. In the wafer etching method comprising a spraying process for locally etching the relative thickness portion,
An active gas containing the active species gas by supplying a mixed gas, in which hydrogen gas for suppressing white turbidity generation on the surface of the silicon wafer is mixed with the sulfur hexafluoride gas to a discharge site in the alumina discharge tube. A seed mixed gas is generated, and this active seed mixed gas is injected from the nozzle part,
The hydrogen gas is mixed at a ratio between 0.1% and 30% with respect to the mixed gas,
The relative speed of the nozzle part with respect to the silicon wafer is set so as to be approximately inversely proportional to the thickness of the relative thickness part, and the relative speed of the nozzle part on the relative thickness part is decreased and the relative speed on the non-relative thickness part is set. Increase the relative speed of the nozzle part at
A wafer etching method. The wafer etching method according to claim 1,
A heating process for heating the surface of the silicon wafer to a predetermined temperature is provided.
A wafer etching method. The wafer etching method according to claim 2,
The heating temperature of the silicon wafer in the heating process was set to a temperature between 60 ° C and 170 ° C.
A wafer etching method.

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