Etching method with less waste gases

[0001] 1. Field of the Invention

[0002] The present invention relates to an etching method with less waste gases. More particularly, this invnetion relates to a method for reducing the quantity of the by-product(s) of an etching process by using the C3F8 with some specific values of some etching parameters.

[0003] 2. Description of the Prior Art

[0004] Conventional semiconductor fabrication technologies usually etch the dielectric layer, such as the silicon dioxide layer and the silicon nitride layer, by some etchants such as CF₄ or C₂F₆. However, these conventional etchants have a significant disadvantage: the quantity of waste gases is irnegligible, even is huge. Hence, the production cost is increased for many inputted raw materials are wasted, and the earth environment is strongly damaged by these expelled waste gases. Herein, FIG. 1A shows some datas to briefly describe the relations between the quantity of waste gases and some practical values of some etching parameters, the unit of waste gases is MMTCE (million metric tun carbon equivalent).

[0005] To improve this disadvantage, some newly developed semiconductor fabrication technologies use some new etchant(s) to etch the dielectric layer. For example, the 3M company presented a method that uses the C₃F₈ to etch the dielectric layer with the following parameters' values: RF power is about 1200 W (Walt) to 1800 W, flow rate of C₃F₈ is larger than 150 sccm, and pressure is larger than 3 torr. Herein, according to the datas that the 3M company makes public, FIG. 1B shows the relations between the quantity of waste gases and some practical values of some etching parameters.

[0006] Clearly, according to 3M company's datas, the application of C3F8 could effectively reduce the quantity of waste gases, even the quantity of waste gases could be further reduced, and even both the consumed material and consumed power could be further reduced.

[0007] One main object of the present invention is to reduce the quantity of waste gases which are formed while the dielectric layer being treated.

[0008] Another main object of the present invention is to improve the existent etch technologies without strongly amending the details of the existent etch technologies.

[0009] To achieve these objects, the present invention amends the values of some parameters of the etching process which uses the C3F8 as the etchant. The present invention reduces the flow rate of input C3F8, reduces the pressure inside the chamber, and reduces the power of used RF power source. Thus, the present invnetion reduces the probability that the plasma incompletely react with the dielectric layer, the present invention also reduces the ratio that some raw materials are not used, and then the quantity of waste gases which induced by the incomplete reaction and non-reacted materials are effectively reduce.

[0010] A more complete appreciation and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

[0011] FIG. 1A shows the relations between some etching parameters and the quantity of waste gases in accordance with the conventional technologies;

[0012] FIG. 1B shows the relations between some etching parameters and the quantity of waste gases in accordance with the 3M company's method that uses the C3F8 as the etchant;

[0013] FIG. 2A through FIG. 2H shows the essential flow of one preferred embodiment of this invention;

[0014] FIG. 3A through FIG. 3C shows the relations between some etching parameters and the quantity of waste gases while using the present invention to etch SiN, SiON and PEOX;

[0015] FIG. 4 shows some suggested values of some parameters which could be used to etch SiN, SiON, and PEOX;

[0016] FIG. 5A through FIG. 5I show two essential flowchart of another preferred embodiment of this invention; and

[0017] FIG. 6 shows the essential flowchart of the other preferred embodiment of this invention.

[0018] One preferred embodiment of this present invention is an etching method with less waste gases, at least has following essential steps in sequence:

[0019] As FIG. 2A shows, provides substrate 10 that is covered by dielectric layer 11 and pattern mask 12 in sequence. Herein, the material of dielectric layer 11 usually is chosen from a group consisting of SiO₂, SiN and SiO_XN_y, where both X and Y being positive integers.

[0020] As FIG. 2B shows, puts substrate 10 with both dielectric layer 11 and pattern mask 12 on the wafer holder 14 inside chamber 13, Wherein, chamber 13 is coupled with reactive gases source 15 and RF power source 16. Moreover, reactive gases source 15 is used to input numerous C₃F₈ molecules through both first pipeline 17 and injector 18 into chamber 13, and RF power source 16 is used to input a RF power through second pipeline 18 into chamber 13.

[0021] As FIG. 2C shows, forms plasma 195 inside chamber 13 under the environment of a low C₃F₈ flow rate, a low RF power, and a low pressure, and let plasma 195 react with and etch partial dielectric layer 11 that is not covered by pattern mask 12. Herein, the pressure of the low pressure environment usually is smaller than about 3 torrs, the low RF power usually is about from 900 W to 1300 W, and the low C₃F₈ flow rate usually is smaller than about 150 sccm. In addition, it is possible to input the N₂O into chamber 13, but the flow rate of the N₂O gas is not the key point of the present embodiment.

[0022] Further, in the embodiment, plasma 195 could comprise one of the following components: N or Ar, plasma also could comprise one of the following components: N₂O, O, and NO₂.

[0023] As FIG. 2D shows, terminate the existence of plasma 195 and move substrate 10, residual dielectric layer 11, and pattern mask 12 out chamber 13.

[0024] Indisputably, because that the byproducts, such as waste gases, are formed by the reaction between plasma 195 and dielectric layer 11, the application of the embodiment is not limited by FIGS. 2A-2D that etches partial dielectric layer 11 to form an opening inside dielectric layer 11, the application of the embodiment should be limited by applying plasma 195, which formed by the present conditions, to treat dielectric layer 11.

[0025] For example, the embodiment could be used to completely thin dielectric layer 11, as shown in FIG. 2E to FIG. 2H. In the mean time, pattern mask is omitted, dielectric layer 11 being completely etch by plasma 195 after dielectric layer 11 is formed, and then the thickness of dielectric layer 11 is overall thinned.

[0026] In order to describe the relation between the adjusted parameters' values and the quantity of waste gases in the present embodiment, FIG. 3A through FIG. 3C separately shows three practical applications of this embodiment. Herein, these figures show the flow rate of C₃F₈, the flow rate of N₃O, the pressure inside the chamber, the power of the RF power source, the quantity of waste gases (in the unit of MMTCE), and the MMTEC reduction percentage while comparing with the FIG. 1A. FIG. 3A shows the case of etching SiN, FIG. 3B shows the case of etching SiON, and FIG. 3C shows the case of etching PEOX, the oxide formed by the plasma enhanced chemical vapor deposition.

[0027] By comparing FIG. 3A through FIG. 3B with FIG. 1A through FIG. 1B, indisputably, the quantity of waste gases of this present embodiment not only is strongly lesser than the conventional technologies which never use the C₃F₈ as the etchant, but also is lesser significantly than the 3M method which also uses the C₃F₈ as the etchant. Moreover, by comparing the required parameters' values of this embodiment and the required parameters' values of the 3M company's method, indisputably, the present embodiment required lesser C₃F₈ gas, lesser RF power, and lower pressure. Hence, the present embodiment not only reduces the quantity of waste gases, but also reduces the consumption of raw materials. Further, even the present embodiment required lesser pressure than the 3M company's method, owing to the order of pressure used by the method also is torr, the required pressure could be easily provided by the conventional technology, and then no specific difficulty or extra cost would be appeared.

[0028] Finally, to balance some requirements such as reducing waste gases and reducing cost, the present embodiment provides some suggested parameters' values, separately corresponds to SiN, SiON, and PEOX. However, it should be emphasized that these suggested parameters' values only are a specific suggestion, the main characteristics and available parameters' values are not limited by FIG. 4. In short, the present embodiment uses C₃F₈ to etch the dielectric layer by the application of RF power is about 900 W to 1300 W, pressure is lesser than 3 torrs, and flow rate of C₃F₈ is lesser than about 150 sccm.

[0029] Another preferred embodiment of this invention also is an etching method with less waste gases. Details of the embodiment are basically similar with the previous embodiment, both embodiments being focused on how to form the required plasma for treating dielectric layer but not being focused on the dielectric layer is treated by the formed plasma. The main differences between this current embodiment and the least embodiment is that the current embodiment only requires low RF power and low pressure but does not limit the flow rate of C3F8.

[0030] The current embodiment is based on the following experimental results: the flow rate of C3F8 essentially only affect how many particles, such as ions, could be used to etch. In fact, whether a reaction is complete, how fast the reacting rate is, and how many raw materials are wasted are essentially decided by the pressure inside the chamber and the RF power inputted into the chamber.

[0031] Clearly, to compare with the 3M company's method, the present invention also uses the C₃F₈ as the etchant, but the present invention uses both lower pressure and lower RF power, even uses lower C₃F₈ flow rate, than the 3M company's method. However, the differences are significant and non-obvious.

[0032] For most of the conventional etch technologies, include the 3M company's method, the key issues are increasing both the etch rate and the etch selectivity, and the adjustment of all related parameters is focused on how to achieve previous issues. In this way, the routine test of all related parameters' values would not try to reduce the waste gases.

[0033] Next, most of the conventional etch technologies, include the 3M company's method, only disclose and/or hint something about how to increase the etch rate and/or the etch selectivity. For example, the 3M company's method only disclosed a preferred range of these parameters, but never discloses/teaches what is the benefit to reduce the values of these parameters, even never clearly discloses/teaches anything about reducing the values of these parameters.

[0034] Accordingly, it is not reasonable to consider that 3M company's method had disclosed/taught the etching process by using C₃F₈ could be preformed with the parameter's value that presented by these previous present embodiments.

[0035] Accordingly, the invention forms a plasma under an environment with low pressure and low RF power, even with low C₃F₈ flow rate, and uses the plasma to treat a dielectric layer to reduce the quantity of waste gas. Significantly, the invention not only could treat any dielectric layer located on the substrate, or called as wafer, but also could treat any dielectric layer which could react with the plasma.

[0036] For example, wafer holder 14 shown in FIGS. 2A-2H only is a simplified example. To effectively fixed the wafer (substrate 10), the real wafer holder 145 usually is not completely covered by the wafer, and the edge of the wafer is partially surrounded, even hold, by the wafer holder 145. Herein, FIG. 5A shows a possible real wafer holderl4. On the other wafer, the practical formation of a dielectric layer usually is not perfectly precise to let the dielectric layer only be formed on a wafer, and then the dielectric layer usually is diffused to other places. Therefore, as FIG. 5B shows, except the fabrication parameters are perfect to let all dielectric layer 11 is thoroughly removed by plasma 195, after the semiconductor fabrication is finished and the wafer is moved, partial dielectric layer 11 is left on the wafer holder 14, especial on the part not covered by the wafer during the fabrication, and on the sidewall of chamber 13. Clearly, the non-removed dielectric layer 11 would be a pollution source in the sequential fabrication inside chamberl3.

[0037] Therefore, another preferred embodiment of this invention is a method of cleaning the chamber with less waste gases. The embodiment at least has following essential steps:

[0038] As shown in FIG. 5B, provide chamber 13 to be cleaned. Chamber 13 is coupled with power source 15 and C₃F₈ reactive gases source 16. Dielectric layer 11 is located on the sidewall of chamber 13 and wafer holder 145.

[0039] As shown in Fig, 5C, form plasma 195 inside chamber 13 under an environment having a low RF power and a low pressure, and treat dielectric layer 11 by plasma 195. Moreover, it is allowable to lower the flow rate of C₃F₈ during the formation of plasma 195, an also is possible to low the C₃F₈ flow rate of during the existence of plasma 195.

[0040] As shown in FIG. 5D, terminate the existence of plasma 195. Surely, it is better to terminate after no dielectric layer 11 is left inside chamber 13.

[0041] Certainly, because the semiconductor fabrication is changeable, the embodiment has other variations. For example, as shown in FIG. 5E, it is possible that the surface of wafer holder 14ahs been covered by dielectric layer 115 before wafer 10 is putted.

[0042] Obviously, as shown in FIG. 5F and FIG. 5G, wafer 10 is located on dielectric layer 115 during a fabricating process that forms dielectric layer 11 on dielectric layer. Herein, dielectric layer 115 is independent of dielectric layer 11, material of dielectric layer 115 could be different from the material of dielectric layer 11.

[0043] Again, after wafer 10 being removed, as shown in FIG. 5H, plasma 195 is formed under a environment with the low PR frequency and the low pressure and is used to remove both dielectric layer 11 and dielectric layer 115. Surely, it is possible to reduce the C₃F₈ flow rate of during the existence of plasma 195.

[0044] Clearly, as shown in FIG. 5I, while the reaction with plasma 195 being enough, all dielectric layer 11 and dielectric layer 11 on wafer holder 105 would be cleaned and removed by plasma 195.

[0045] Furthermore, because that the experimental results how that the quantity of waste gases is strongly dependent on the density of the CF2* radials, another preferred embodiment of this invention still being an etching method with less waste gases. As FIG. 6 shows, at least has following essential steps:

[0046] As preparation block 21 shows, form a dielectric layer on a substrate. Surely, the dielectric layer usually is covered by a patterned mask to define which part of the dielectric layer should be etched.

[0047] As etch block 22 shows, applies a plasma to the dielectric layer so let at least partial the dielectric layer be etched by the plasma under a low RF power and low pressure environment. Herein, the main material of the plasma is the fluorocarbon which could produce numerous CF2* radials under the low RF power and low pressure environment. Herein, the standard of numerous CF2* radials means that the fluorocarbon could produce more CF2* radials than CF4, and also could produce more CF2* radials than C2F6.

[0048] Indisputably, the main characteristic of this preferred embodiment is that the usage of fluorocarbon (molecules) which could produce numerous CF2* radials.

[0049] Consider that each the carbon atom has four outer shell electrons and each fluorine atom has one outer electron, consider that the strain chain usually only use the single bond to connect neighboring atoms, and consider that the lighter molecules are easier to product/control/react than the heavier molecules. It is reasonable that straight chain fluorocarbon molecules could provide the most fluorine ions than other fluorocarbon molecules, and then the etch result of straight chain fluorocarbon molecules would be better than other fluorocarbon molecules.

[0050] Therefore, by the usage of straight chain fluorocarbon molecules, the preferred embodiment could effectively improve the efficiency of the dielectric layer etching process.

[0051] Besides, because the main difference between this preferred embodiment and last preferred embodiments is that C₃F₈ is replaced by the fluorocarbon which produce more CF2* radials, many details of the preferred embodiment are similar with that of the previous preferred embodiments. For example, by the usage of both lower pressure and lower RF power, even lower fluorocarbon flow rate, during the existence of the plasma, the quantity of the waste gases could be further effective reduced.

[0052] Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.