JP2000133639A - Plasma etching equipment and etching using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make process a thin semiconductor wafer and to enhance the heat dissipation effect of the wafer, by a method wherein activation gas produced using a radical only is locally applied to the surface of the wafer such as an Si wafer to cause a vapor phase chemical reaction and the wafer is moved to each the wafer. SOLUTION: A semiconductor wafer 5 is inserted in a sample exchange chamber 12, is fixed from the chamber 12 onto a wafer holding part in an etching chamber (p) by a transfer mechanism 7 and is set on the wafer holding part. SF6 gas s mixed with hydrogen gas by a gas feeding unit 14, the mixed gas is injected in a reaction gas feed pipe 3 through a valve 19, the mixed gas in the pipe 3 is activated in a plasma generating region 6 by making microwaves generated by a microwave oscillator 1 pass through a waveguide 2, a plasma is generated by the activation, the plasma is squeezed in a nozzle, the plasma is locally fed to the surface of the wafer 5 to cause a vapor phase chemical reaction and the wafer is etched.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching apparatus, and more particularly to a method and an apparatus for uniformly etching the back surface of a semiconductor wafer having a circuit such as an LSI formed on the front surface side to reduce the thickness of an object to be etched. Things.

[0002]

2. Description of the Related Art Generally, in the final stage of a semiconductor wafer manufacturing process, there is a process called dicing for cutting a wafer on which a plurality of circuits such as LSIs are formed into dice for each chip. Before this dicing step, the back surface of the wafer is polished or ground to increase the heat radiation effect of the chip or to reduce the consumption of the cutting tool (dicing saw) used in dicing and extend the life. There is a need for a thinning process. Until now, when uniformly reducing the thickness of a substrate such as a semiconductor wafer, a flat plate on which a polishing cloth is adhered is pressed from one side corresponding to the back surface of the substrate, a polishing liquid is supplied, and the polishing liquid is supplied between the wafer and the polishing cloth. Generally known are a method of polishing while interposing, and a method of grinding with a tool in which hard material particles such as diamond particles are embedded and fixed.

[0003]

With the high integration of Si LSIs, the amount of generated heat tends to increase and the temperature of the device tends to increase. In order to effectively cool a device that has generated heat and prevent a rise in temperature, it is necessary to increase the heat dissipation efficiency by making the Si layer on the back surface of the device as thin as possible to improve heat conduction.

However, in conventional polishing or grinding, a wafer is more likely to be damaged as the substrate becomes thinner because the substrate is processed while applying compressive stress or shear stress to the substrate. This damage rate becomes more remarkable when there is a foreign matter such as processing waste, which will be described later.

[0005] Therefore, in order not to reduce the yield, that is, to increase the breakage rate, it is important not to make the wafer too thin in order to maintain high strength, which impairs the heat radiation effect.

In addition, after machining, a deteriorated layer is always formed to a certain depth on the processing surface, and it is essential to perform chemical etching with a chemical solution in a later step in order to remove the deteriorated layer.

Further, in polishing / grinding, foreign substances such as polishing liquid, abrasive grains, scraps of abrasives, and Si debris removed by the processing are generated during the processing, and these foreign substances are formed on the processed surface according to the size. In some cases, minute irregularities are formed. This unevenness reduces the contact area with a heat radiating member such as a heat sink to which the chip is attached, and hinders effective heat radiation. In addition to the above problems, since the entire surface of the wafer is contaminated with a polishing liquid or the like, a considerably long cleaning is indispensable in the post-process.

[0008]

According to the present invention, ions and radicals are generated in a plasma chamber by a high-frequency AC electromagnetic field, particularly a microwave, and a radical active species gas is supplied through a supply pipe. A method has been proposed in which etching is performed by gas-phase chemical reaction with a wafer constituent material such as silicon. In particular, the present invention is characterized by a configuration of an apparatus in which an activation gas containing only radicals is locally applied to a wafer surface such as Si to cause a gas phase chemical reaction to move and etch a wafer. According to this method, since the semiconductor wafer is processed in a non-contact manner without applying a stress, the semiconductor wafer can be processed to a thickness which was impossible in the past, and the heat radiation effect can be greatly improved. In addition, since a work-affected layer is not formed, chemical etching using a chemical solution in a subsequent step is unnecessary.

[0009] Since only the active species gas and the wafer are present in the reaction section, impurity contamination is small. For example, SiF ₄ which is a reaction product of a reaction between a fluorine radical and a Si wafer
Since is volatile and is a gas at normal temperature and normal pressure, it does not contaminate the wafer at all and does not require cleaning or can reduce the load of the cleaning process.

[0010] Further, since the local temperature is increased by a chemical reaction in order to locally supply the active species gas, a mechanism for flowing a gas for cooling is provided to suppress the temperature increase and to affect the chip. Can be eliminated.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows an embodiment of a plasma etching apparatus according to the present invention. SF ₆ and hydrogen gas are mixed by the gas supply device 14, and the mixed gas is injected into the reaction gas supply pipe 3 having a diameter of 38 mmφ through the valve 19. Microwaves generated by the microwave oscillator 1 pass through the waveguide 2 to activate the mixed gas in the reaction gas supply pipe. The plasma generated in the plasma generation region 6 is narrowed down by a nozzle having a tip diameter of 24 mmφ to form a high-density local beam and a semiconductor wafer 5.
The structure is such that the etching rate is increased because it is supplied to the substrate. In addition, the active species gas can efficiently act on the wafer by narrowing the supply. The diameter of the nozzle does not need to be limited to 24 mmψ, and is 5 to 60 mmφ.
May be within the range. The semiconductor wafer is first inserted into the sample exchange chamber 12, and is fixedly set from the sample exchange chamber to the wafer holding unit 20 of the etching chamber 9 by the transfer mechanism 7. The sample holder is fixed on the moving table 8, and the moving table 8 is moved by X or Y or rotated by X-θ by the sample moving mechanism 15. This serves to move the wafer to treat the active species gas having a high etching rate as a local beam, and to control the time or the AC electromagnetic field at that time to make the entire wafer uniform in thickness. The sample exchange chamber 12, the transfer chamber 24, the etching chamber 9 and the like are evacuated through the gate valve 16, respectively.
In particular, the gas in the etching chamber is exhaust gas and gas processing device 1
It is exhausted through 3. FIG. 8 shows the relationship of the roughness after etching / the roughness before etching of the etched surface with respect to the amount of hydrogen added. When the amount of hydrogen added is 5% or less, the roughness of the etched surface is good. FIG. 9 shows the rate of change of the etching rate with respect to the amount of hydrogen added. As shown in FIG. 9, when the amount of hydrogen is large, the etching rate also decreases. Actually, when etching was performed, a high value of 100 μm / min could be obtained at an etching rate of about 500 W of microwave power. Further, the etched silicon surface was a mirror surface without roughening. NF ₃ instead of SF ₆ ,
CF ₄ , Cl ₂ , HCl, ClF ₃ , or BF ₃ may be used.
As a result, the backside etching of Si can be performed at a lower cost by simplifying the number of process steps than before.

Embodiment 2 FIG. 2 shows a portion around a wafer holding portion of a plasma etching apparatus according to the present invention, and shows a back surface 5 of a semiconductor wafer.
This is an embodiment of a structure in which only b is etched and the surface 5a of the semiconductor element circuit 17 is protected during the etching. In order to prevent the supplied gas from wrapping around the surface 5a of the semiconductor wafer and being etched, the wafer holding part 20 is used to partition the front and back of the wafer, the surface 5a is sealed, and an inert gas such as Ar is used. Is sprayed to prevent the active species gas from flowing around from the back side. As the inert gas, _{N 2} or He or the like may be used besides Ar. This improved the yield. This is also effective for cooling the semiconductor wafer.

Embodiment 3 Another embodiment of the plasma etching apparatus according to the present invention will be described with reference to FIGS. In the etching according to the present invention, the etching rate is not greatly affected by the temperature of the semiconductor, but the surface roughness after the etching changes. Table 1
Fig. 8 shows the results of temperature and surface observation.

[0015]

[Table 1]

From these results, the optimum temperature is between 80 ° C. and 300 ° C. The present invention is characterized in that a mechanism for maintaining the substrate temperature in this range is provided. When plasma is generated and collected locally to act, the temperature of the reaction portion tends to increase. In order to cool this effectively,
Is cooled by blowing an inert gas such as He from around the active species ejection nozzle 4, and the exhaust pipe 1 along the wafer is cooled.
It has a structure for exhausting air from the exhaust port of No. This is an effective structure in terms of removing a reactant between the wafer and the active species gas. The inert gas may be Ar, N ₂ or the like in addition to He. FIG. 4 shows a structure in which the cooling gas pipe 18 and the exhaust pipe 10 are arranged concentrically. FIG. 5 shows the cooling stage 2
A wafer holding unit 20 is provided on 1, a plurality of cooling holes 22 are opened, and an active species gas supply pipe 11 and a cooling gas pipe 18 are arranged to face each other. The semiconductor wafer is placed on the cooling stage, and the inert gas from the cooling gas pipe 18 is blown through the cooling holes 22 onto the wafer surface to cool the wafer. A heater may be provided in this cooling stage, and if the temperature does not rise, a heating mechanism may be provided.

FIG. 6 shows a structure in which a cooling gas pipe 18 is connected to the vicinity of the jet nozzle 4 of the active species gas supply pipe 11 to cool the semiconductor wafer. The slit 23 in the middle of the active species gas supply pipe prevents the inert gas from entering the gas supply direction.

As described above, the provision of such a cooling mechanism markedly improved the processing yield.

Embodiment 4 FIG. 7 shows that a plurality of active species gas nozzles generated by the respective microwave oscillators are arranged so as to achieve uniform etching, and the semiconductor wafer on the moving table 8 is sent in one direction. Thus, the processing time is shortened. The arrangement of the plurality of active species gas supply pipes may be arranged in a line or in a grid pattern.

[0020]

(1) The etching rate can be increased by using a mixed gas containing a halogen compound in the plasma etching apparatus of the present invention and having a function of locally collecting active species gas generated in the plasma chamber. , At low cost. (2) By using a mixture of a halogen compound gas and a hydrogen gas in the plasma etching apparatus of the present invention, a mirror surface can be obtained without roughening the silicon surface, and a high quality processed surface can be provided. (3) An inert gas is blown onto the non-etched surface of the wafer to prevent the active species gas from flowing around, thereby improving the yield. (4) A cooling mechanism is provided at the nozzle portion of the supply pipe for the active species gas to improve the processing yield.

[Brief description of the drawings]

FIG. 1 is a main sectional view of a plasma etching apparatus of the present invention.

FIG. 2 is a sectional view of a main processing unit of a plasma etching apparatus according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a main processing unit of a plasma etching apparatus according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a main processing unit of a plasma etching apparatus according to a third embodiment of the present invention.

FIG. 5 is a sectional view of a main processing unit of a plasma etching apparatus according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a main processing unit of a plasma etching apparatus according to a third embodiment of the present invention.

FIG. 7 is a sectional view of a main processing unit of a plasma etching apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a graph showing the ratio of the surface roughness before and after etching to the amount of hydrogen added in Example 1 of the present invention.

FIG. 9 is a graph showing the etching rate versus the amount of hydrogen added in Example 1 of the present invention.

Table 1 shows the relationship between the temperature and the surface roughness during the etching process of the wafer of Example 3 of the present invention.

[Explanation of symbols]

 1. 1. Microwave oscillator Waveguide 3. 3. Reaction gas supply pipe Nozzle 5. Semiconductor wafer 5a. Semiconductor wafer surface 5b. 5. Backside of semiconductor wafer Plasma generation area 7. Transport mechanism 8. Mobile platform 9. Etching chamber 10. Exhaust pipe 11. Active species gas supply pipe 12. Sample exchange chamber 13. 13. Exhaust device and gas treatment device Gas supply device 15. Sample moving mechanism 16. Gate valve 17. Semiconductor element circuit 18. Cooling gas pipe 19. Valve 20. Wafer holder 21. Cooling stage 22. Cooling hole 23. Slit 24. Transfer machine room

Claims (9)

[Claims] In an etching apparatus, a plasma chamber for generating a plasma by applying an AC electromagnetic field to a halogen compound gas or a mixed gas containing a halogen compound gas and an active species gas generated in the plasma chamber are guided through an active species gas supply pipe. The apparatus has an etching chamber for etching the back surface of the wafer thereby, a transport mechanism for transporting the wafer to the etching chamber, and an exhaust device for exhausting the plasma chamber and the etching chamber, and has a detoxification facility for treating the exhausted gas. Plasma etching equipment. 2. The plasma etching apparatus according to claim 1, wherein said plasma etching apparatus has a function of locally collecting active species gas generated in said plasma chamber. 3. The plasma etching apparatus according to claim 1, further comprising a mechanism for preventing an active species gas from flowing around the surface of the wafer. 4. The plasma etching apparatus according to claim 1, further comprising a mechanism for etching a back surface of the wafer while moving the wafer in the etching chamber. 5. The plasma etching apparatus according to claim 1, further comprising a function of cooling the wafer with an inert gas such as He, Ar, and N ₂ . 6. A plurality of active species gas supply pipes generated in each of the plasma chambers, each of which is independently introduced into an etching chamber to have a mechanism for etching the back surface of a wafer. The plasma etching apparatus according to claim 1, 2, 3, 4, or 5. 7. The method according to claim 1, wherein the halogen compound gas is sulfur hexafluoride gas, nitrogen trifluoride gas, carbon tetrafluoride gas, chlorine gas, hydrogen chloride gas, chlorine trifluoride gas, or boron trichloride gas. A plasma etching method using the apparatus according to claim 1, 2, 3, 4, 5, or 6. 8. The plasma etching method according to claim 7, wherein said mixed gas contains 5% or less of hydrogen gas. 9. The semiconductor device according to claim 7, wherein said wafer is maintained at a temperature in a range from 80 ° C. to 300 ° C.
The plasma etching method as described above.