JP2000174004A - Method and apparatus for plasma etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly thin a substrate crystal by the dry etching using plasma- activated active species of a reaction gas composed of a F compd. gas or F compd. gas-contg. mixed gas mixed with at least H or ammonia gas. SOLUTION: An active species produced in a gas plasma is applied to a sample surface to etch it with the plasma. A mixed gas of SF6 with ammonia and N is injected from a gas feeder through a reaction gas feed pipe in a plasma generating chamber, a microwave generated in a microwave oscillator 1 passes through a waveguide 2 and is absorbed in the plasma generating chamber to activate the mixed gas and form a plasma activated region 6. The active species gas passing through an active species gas feed pipe 13 is restricted by an etching nozzle 4 into a high-density local beam which is fed to the surface of a semiconductor wafer 5 on a sample moving mechanism 7, thus greatly speedily etching it in a uniform thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for dry etching and, more particularly, to a crystal or SOI (Sil) of a Si semiconductor wafer for forming a semiconductor element or an integrated circuit.
The present invention relates to a method and an apparatus for uniformly thinning and flattening a crystal of an icon (icon on insulator).

[0002]

2. Description of the Related Art A plurality of semiconductor elements and integrated circuits are formed on a surface of a semiconductor wafer (hereinafter collectively referred to as a sample). At the final stage of the manufacturing process, the semiconductor wafer is cut into chips and formed into pellets. There is a dicing step for separation. Before this dicing step, the semiconductor wafer is polished or back-polished to increase the heat radiation effect of the chip or to reduce the consumption of cutting tools (such as cutters and saws) used in dicing and extend the life. There is a need for a process of reducing the thickness by cutting. Until now, when thinning the substrate crystal of a semiconductor wafer uniformly, a flat plate was pressed against the back surface of the semiconductor wafer via a polishing cloth by a polishing apparatus, and a polishing liquid was supplied to polish the wafer between the wafer and the polishing cloth. A method of polishing with a liquid interposed, a method of grinding with a grindstone in which hard material particles such as diamond particles are embedded and fixed by a grinding device, or a method of chemical mechanical polishing are generally known. Also, a technique for uniformly thinning a substrate crystal by wet etching has been used.

In order to improve the performance of semiconductor elements and integrated circuits, SOI wafers are used in large quantities in Si. In this production, the Si layer on SiO 2 is processed to be extremely thin and uniform with high precision. Technology is needed. For this, the above-mentioned conventional technology was used. Further, with the miniaturization of the dimensions of the wiring layer, irregularities on the sample surface have been required to be more strict than conventional standards. For this purpose, there is a demand to etch only the convex region existing locally on the sample. For example, US Pat. No. 5,336,355 discloses a method of performing plasma processing only on the local region.

[0004]

As semiconductor elements and integrated circuits become more sophisticated and highly integrated, the amount of heat generated increases, the temperature rises, and the characteristics of the devices decrease, resulting in a decrease in reliability. There is. The purpose of thinning the semiconductor substrate crystal is
The purpose is to effectively radiate this heat and prevent the temperature inside the semiconductor from rising. For the production of SOI wafers that have been used in large quantities for the purpose of improving the performance of semiconductor elements and integrated circuits, the Si layer on SiO2 must be extremely thin, uniformly processed with high precision and without distortion. Technology is needed.
However, in the conventional method of polishing or grinding, the substrate crystal is processed while applying a compressive stress or a shear stress, so that distortion remains in the crystal. In addition, during processing, foreign substances such as processing particles, abrasive particles, ground particles, and crystal particles are mixed, which causes a reduction in yield. Furthermore, in the machining process, a damaged layer is formed on the processed surface of the wafer to a certain depth, and a post-process of wet etching using a chemical solution is added to remove this, making the process complicated and costly There are disadvantages. Further, the above foreign matter remains on the back surface of the chip and induces a decrease in yield. In this way, the process of reducing the thickness of the wafer by machining contaminates the entire wafer with polishing liquid, adhesive, etc., so a well-established advanced cleaning technology is indispensable, and the disadvantage of increasing the cost is is there. In the method of uniformly thinning the substrate crystal by wet etching, it is particularly important to protect the wafer surface, and the etching rate is low, so that the productivity is poor. In the conventional method of plasma processing only a local region on a sample, optimization of the processing finish accuracy has not been studied, and the surface after processing with CF4 or SF6 gas is observed to be cloudy by a visual inspection using a projector. There is a problem that the surface roughness deteriorates so that it cannot be used for final finishing. This is probably because deposits due to C or S are generated. Further, a structure in which ions in plasma are mainly used for processing has a problem that strain is generated on a processed surface of a sample (crystal). Therefore, the present invention provides a method and an apparatus for uniformly thinning a substrate crystal by high-speed etching mainly by dry etching using radical atoms or radical molecules (hereinafter referred to as active species) generated by plasma. A processing method that does not leave processing distortion, simplifies the entire manufacturing process, provides extremely thin processing technology with extremely excellent processing flatness, and has excellent heat dissipation characteristics for thin chips of semiconductor elements or integrated circuits. Thinned SOI of Si
It is intended to supply a wafer and a Si surface flattening process at a high yield and at a low cost.

[0005]

According to the present invention, a reaction gas is flowed, ions and radicals are generated in a plasma chamber by a high-frequency alternating-current electromagnetic field, and a semiconductor wafer is mainly produced by a gas phase chemical reaction using radical active species gas. It is based on a method of etching a crystal. The present invention is characterized in that at least one kind of hydrogen or ammonia gas is mixed with a fluorine compound gas or a mixed gas containing a fluorine compound gas and used as a reaction gas. Examples of the fluorine compound gas include sulfur hexafluoride (SF6),
Carbon tetrafluoride (CF4) and nitrogen trifluoride (NF
3), and the present invention is characterized by using at least one of these. This fluorine compound gas is N2,
It may be diluted with an inert gas such as Ar or He. It has been found through experiments that by mixing at least one kind of gas of hydrogen or ammonia gas, the surface roughness of etching is improved as compared with the surface roughness before etching. Table 1 shows the results.

[0006]

[Table 1]

[0007] Even if the addition amount of hydrogen or ammonia is as small as 0.01%, the effect of adding the improvement in the surface roughness appears. This is because the molecules of hydrogen or ammonia are activated in this reaction system, and gasification by H2S or the like, cleaning of the Si surface by generation of HF, or prevention of oxidation of the wafer surface by oxygen due to formation of H2O,
It is presumed to be mirror-finished. When the amount of added hydrogen or ammonia increases, the etching rate tends to decrease as shown in FIG. 5, and the processing time for processing becomes longer, so that there is a practical limit. Therefore, it is preferable that the mixing ratio of at least one kind of the hydrogen or ammonia gas is 20% or less with respect to the fluorine compound gas, and it is understood that ammonia is more effective. The hydrogen or ammonia gas is N2, Ar,
It may be diluted with an inert gas such as He.

In the present invention, the above-described active species generated in the gas plasma is basically applied to a sample surface to perform plasma etching. For this purpose, a method in which the active species gas is uniformly applied to the entire surface of the sample may be used, but in order to process the sample surface with high accuracy, the active species gas is etched with a smaller opening diameter than the sample area. From the tip of the nozzle to the sample surface, partially etch the sample,
A method in which desired processing was performed over the entire surface of the sample while relatively moving the nozzle and the sample, resulted in better controllability. This means that etching can be performed while measuring the local etching amount in real time and feeding back the moving speed, and that the etching rate is stable especially for active species gas generated by plasma generation by microwave excitation. And so on. The method of generating plasma is not limited to microwave excitation.

In the present invention, unlike the above-mentioned gas mixing method, a fluorine compound gas or an active species generated in a gas plasma by a mixed gas containing a fluorine compound gas is applied to a sample surface to reduce at least hydrogen or ammonia gas. There is a method in which one kind of gas is supplied as it is or diluted and supplied to the vicinity of a sample surface to perform etching. In this case, the active species gas may be applied to the entire surface of the sample, or may be applied locally to the etching nozzle. The effect of hydrogen or ammonia gas was effective in improving the surface roughness as in the case of the mixed gas. Since the processing method according to the present invention does not leave processing strain on the crystal surface, there is no need for a wet etching step using a chemical solution thereafter, and the process can be simplified.

[0010] The plasma etching apparatus using the method of the present invention is based on a gas supply section, a plasma generation mechanism section, an active species gas supply mechanism section, and a sample moving mechanism section, and performs efficient processing in addition to the etching section described above. for,
The apparatus includes a wafer transfer mechanism and a sample exchange chamber. An exclusion device for treating exhaust gas is also provided.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIGS. 1 and 4 show an embodiment of a plasma etching method and apparatus according to the present invention. FIG. 4 is a schematic diagram of the configuration of the entire apparatus. A mixed gas composed of SF6, ammonia gas and nitrogen is injected into the plasma generation chamber from the gas supply device 14 through the reaction gas supply pipe 3. The microwave generated by the microwave oscillator 1 passes through the waveguide 2 and is absorbed in the plasma generation chamber, and the mixed gas is activated to form the plasma active region 6. The active species gas is the active species gas supply pipe 1
In this configuration, the etching rate is greatly increased because the beam is narrowed by the etching nozzle 4 through the nozzle 3 and is supplied as a high-density local beam to the surface of the semiconductor wafer 5. The semiconductor wafer 5 is first inserted into the sample exchange chamber 11, from which the semiconductor wafer 5 is fixedly set on the movable table 8 of the etching chamber 9 by the transfer mechanism 15. The moving table 8 can be moved in the XY direction or the X-θ direction by the sample moving mechanism 7. The semiconductor wafer 5 can be etched to a uniform thickness over the entire surface by the local beam generated by the active species gas from the etching nozzle 4 and the moving mechanism of the moving table 8. Further, an exhaust head 16 having a suction action is provided around the area where the sample is etched, and the floating gas is effectively exhausted through the exhaust 19. The exhaust unit is piped to the etching chamber 9, the exhaust head 16, the sample exchange chamber 11, and the transfer chamber 10 via the gate valve 18, respectively, and each is exhausted. Exhaust gas discharged from the etching chamber 9 and the exhaust head 16 passes through a gas processing device 17 and is then harmed and exhausted. FIG. 1 is a detailed view around the etching nozzle and the sample. The etching nozzle 4 is fixed in a highly airtight manner by the active species gas supply pipe 13 and the connecting portion 22, and the etching nozzle 4 can be easily replaced. The cross-sectional shape of the opening at the tip of the etching nozzle for releasing gas may be circular, but for the purpose of high-speed etching, an elliptical, rectangular, or band-like shape is more effective for reducing the processing time. The structure is selected according to the application. The reaction gas 101 used for etching comprises an A line for hydrogen or ammonia, a B line for a fluorine compound, and a C line for an inert gas, and is mixed at the inlet of the active species gas supply pipe 13. The gas in the A line and the B line may be diluted with an inert gas. For example, the etching of Si is performed under the condition that 10% ammonia is added to SF6 gas.
At a microwave power of 500 W, about 60 μm / min
, And the finished surface had a roughness of 0.305 nm, which was a better mirror surface than the value before etching.

Embodiment 2 Another embodiment of the etching method and apparatus according to the present invention will be described with reference to FIG. Although the gas supply unit and the plasma generation unit are the same as those in the first embodiment, the difference is that the sample is collectively etched by the etching head 103 in which the active species gas spreads uniformly. In this case, a sample stage 104 may be provided instead of the sample moving mechanism. This is an effective method for a sample having a small semiconductor wafer diameter.

Embodiment 3 Another embodiment of the etching method and apparatus according to the present invention will be described with reference to FIG. Except for the gas supply unit, the plasma generation unit and the sample moving mechanism are the same as those in the first embodiment. The B line for the fluorine compound and the C line for the inert gas of the reaction gas 101 are mixed at the inlet of the active species gas supply pipe 13,
An A line for hydrogen or ammonia is supplied alone at the inlet of the bleed gas line 110. An active species gas is produced from a mixed gas containing a fluorine compound, and is supplied from the etching nozzle 4 to the sample surface. On the other hand, hydrogen or ammonia gas is supplied from the hydrogen-based gas nozzle 105 through the above path. The arrangement of the hydrogen-based gas nozzle 105 is determined so that the gas of the A line is effectively mixed with the etching atmosphere gas 106 on the sample. The effect of adding hydrogen or ammonia is the same as in the first embodiment.

As described above, the plasma generation mechanisms of the first to third embodiments are described by using the example of microwave excitation. However, it is noted that a dielectric type using a coil or a capacitive type such as a parallel plate may be used instead. I do.

[0015]

(1) By adding hydrogen or ammonia to a fluorine compound or a mixed gas containing a fluorine compound, the roughness of the finished surface in Si etching is reduced, and the finish etching step is shortened because of uniformity and high speed. Now you can. (2) The apparatus using the method of the present invention enables the semiconductor wafer precision thin layer processing to be performed by a dry process, thereby eliminating the need for a cleaning step of the semiconductor wafer or a step of attaching and removing the semiconductor wafer, thereby greatly reducing the number of steps. Was peeled off.

[Brief description of the drawings]

FIG. 1 is a detailed view of the vicinity of a sample and an etching nozzle of a plasma etching apparatus according to a first embodiment of the present invention.

FIG. 2 is a detailed view around an etching nozzle and a sample of a plasma etching apparatus according to a second embodiment of the present invention.

FIG. 3 is a detailed view around an etching nozzle and a sample of a plasma etching apparatus according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram of an overall configuration of a plasma etching apparatus that is Embodiment 1 of the present invention.

FIG. 5 is a graph of an etching rate with respect to an amount of added hydrogen or ammonia according to the present invention.

Table 1 shows the relationship between the processing roughness of the Si surface etched by adding hydrogen or ammonia according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Microwave oscillator 2 ... Waveguide 3 ... Reactive gas supply pipe 4 ... Etching nozzle 5 ... Semiconductor wafer 6 ... Plasma generation area 7 ... Sample moving mechanism 8 ... Moving table 9 ... Etching chamber 10 ... Transport chamber 11 ... Sample exchange Chambers 12 and 22 Connection section 13 Active gas supply pipe 14 Gas supply device 15 Transport mechanism 16 Exhaust head 17 Exhaust device and gas treatment device 18 Gate valve 19 Gas exhaust pipe 20 Control device 101 Reaction gas 102 ... Microwave matching device 103 ... Etching head 104 ... Sample table 105 ... Hydrogen-based gas nozzle 106 ... Etching atmosphere gas 110 ... Ejection gas line

Claims (11)

[Claims] In a plasma etching method for applying an active species generated in a gas plasma to a front surface and a back surface of a sample to make it flat or thin, a fluorine compound gas or a mixed gas containing a fluorine compound gas is mixed with hydrogen or hydrogen. A plasma etching method characterized by using a mixture of at least one kind of ammonia gas. 2. The method according to claim 1, wherein the fluorine compound gas is at least one of sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), and nitrogen trifluoride (NF3). The method for plasma etching according to claim 1. 3. The method according to claim 1, wherein the mixing ratio of at least one kind of the hydrogen or ammonia gas is 0.01% or more and 20% or less with respect to the fluorine compound gas. The method for plasma etching according to the above. 4. A plasma etching method in which active species generated in a gas plasma are applied to the front and back surfaces of a sample to flatten or reduce the thickness thereof. 4. The plasma etching according to claim 1, wherein the sample is partially etched by being applied from the tip to the sample surface, and desired processing is performed on the entire surface of the sample while relatively moving the nozzle and the sample. the method of. 5. An active species generated in a gas plasma by a fluorine compound gas or a mixed gas containing a fluorine compound gas is applied to a sample surface, and at least one gas of hydrogen or ammonia gas is left in the vicinity of the sample surface, or A plasma etching method characterized in that etching is performed by diluting and supplying. 6. An active species generated in a gas plasma by a fluorine compound gas or a mixed gas containing a fluorine compound gas is applied to the sample surface from the tip of an etching nozzle having an opening diameter smaller than the sample area, and is applied to the nozzle and the sample surface. At least one kind of gas of hydrogen or ammonia gas is supplied as it is or diluted and supplied, and partial etching is performed, and desired processing is performed on the entire surface of the sample while relatively moving the nozzle and the sample. Plasma etching method. 7. The fluorine compound gas is characterized in that at least one of sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), and nitrogen trifluoride (NF3) is used. The method of plasma etching according to claim 5. 8. The method according to claim 5, wherein the mixing ratio of at least one kind of gas of said hydrogen or ammonia gas is 0.01% or more and 20% or less with respect to the fluorine compound gas. 8. The method of plasma etching according to 7. 9. A plasma etching process for flattening or thinning the front and back surfaces of a sample, wherein at least one kind of hydrogen or ammonia gas is mixed with a fluorine compound gas or a mixed gas containing a fluorine compound gas. An apparatus for plasma etching, comprising: a gas system for supplying the mixed gas; a function of activating the mixed gas in plasma; and a structure in which the active species gas is applied to a sample surface. 10. The plasma etching process according to claim 9, wherein an active species generated in the gas plasma is provided to a sample surface from a tip of an etching nozzle having an opening diameter smaller than a sample area. An apparatus for plasma etching as described. 11. In the plasma etching process, a mechanism for activating a fluorine compound gas or a mixed gas containing a fluorine compound gas in a gas plasma, and at least one kind of hydrogen or ammonia gas is used as the active species. 11. The plasma etching apparatus according to claim 10, wherein the apparatus is basically provided with a mechanism for supplying a gas to a region corresponding to a sample surface.