Method for etching wafer
Technical field
The present invention relates to a kind of semiconductor fabrication process flow process, more relate to a kind of method that in wet-etching technology, reduces the sidewall erosion degree.
Background technology
Shown in Fig. 1 a; In the manufacture craft of wafer (wafer); At first on basalis 11, form basic device layer 12 and silicon oxide layer 13 successively; On partial oxidation silicon layer 13, form second device layer 14 then, cover one deck silicon oxide layer 13 in second device layer, 14 peripheries again, thereby form the surperficial lobed device architecture shown in the figure.
Wherein, having one or more layers device that in technology before, forms in the basic device layer 12, be used in the follow-up wafer of processing, carrying out function corresponding, for example can be transistorized source-drain area.
Second device layer 14 is positioned at basic device layer 12 tops; 13 encirclements of oxidized all around silicon layer; Be used for the basic device layer 12 and second device layer 14 are kept apart on the one hand; In order to prevent the contaminated or damage in follow-up technology of second device layer 14, this second device layer 14 for example can be transistorized grid on the other hand.
For the needs of subsequent technique, the method that utilize etching is removed unnecessary silicon oxide layer 13, thereby the upper surface that reaches basic device layer 12 is exposed to the purpose of silicon oxide layer 13, but the silicon oxide layer 13 second inner device layers 14 can not incur loss.
The method of etching is just like the wet etching of the liquid state shown in Fig. 1 b, and the gaseous state shown in Fig. 1 c is main dry etching with the plasma.These two kinds of lithographic methods exist shortcoming separately:
Though dry etching has anisotropy, can control the degree of vertical and horizontal etching,, there is the problem of over etching in dry etching, and under the not etched industrial requirements of basic device layer 12, dry etching obviously can't reach requirement.
There is not the problem of over etching in wet etching; But; Wet etching is isotropic, when silicon oxide layer 13 is etched in the vertical, and the silicon oxide layer 13 that covered of second device layer, 14 sidewalls also be etched (being that sidewall corrodes) transversely; Make silicon oxide layer 13 transverse width d1 reduce greatly, become the d2 among Fig. 1 b.Under wet etching, reducing significantly of silicon oxide layer 13 transverse widths can cause the transverse width d3 of second device layer 14 also to be reduced simultaneously, and second device layer 14 can sustain damage.
Summary of the invention
The present invention proposes a kind of method that in wet-etching technology, reduces the silicon oxide side wall erosion degree, can address the above problem.
In order to achieve the above object; The present invention provides a kind of method for etching wafer; Wafer has basalis, basic device layer and second device layer successively; Adopt silicon oxide layer to separate between second device layer and the basic device layer, and the periphery of second device layer and the basic device layer surface that do not covered by second device layer also be coated with silicon oxide layer, said method comprising the steps of: ion is carried out on the silicon oxide layer surface implant; Silicon oxide layer is carried out wet etching, stop at basic device layer upper surface.
Optional, wherein in this ion implantation step, wherein in this ion implantation step, implantation be argon ion.
Optional, wherein the injection energy of this argon ion is that 2keV, concentration are 2E15/cm
2
Optional, wherein in this ion implantation step, implantation be arsenic ion.
Optional, wherein in this ion implantation step, implant along carrying out ion perpendicular to the direction on silicon oxide layer surface.
Optional, wherein in the wet etching step, the hydrofluoric acid that adopts dilution is as etching solution.
The technology that the present invention proposes; Through to the directed ion that injects of silicon oxide layer, make the silica surface structure loose, etch rate accelerates; Top layer transversely is not owing to inject ion; Keep original etch rate, thereby accelerated the time of etching procedure, reduced the sidewall erosion degree of silicon oxide layer.
Description of drawings
Fig. 1 a~1c is depicted as and adopts existing method the silicon oxide layer of wafer surface to be carried out the effect sketch map of etching;
Fig. 2 a~Fig. 2 d is depicted as in the preferred embodiment of the present invention the process sketch map that wafer is carried out etching;
Shown in Figure 3 for wafer being carried out in the preferred embodiment of the present invention the processing step of etching.
Embodiment
In order more to understand technology contents of the present invention, special act specific embodiment also cooperates appended graphic explanation following.
Fig. 2 a~Fig. 2 d is depicted as in the preferred embodiment of the present invention the process sketch map that wafer is carried out etching; Shown in Figure 3 for wafer being carried out in the preferred embodiment of the present invention the processing step of etching.
Shown in Fig. 2 a for carrying out the wafer sketch map before the wet-etching technology with stepped section.Wafer is bottom-up to have basalis 21, basic device layer 22, silicon oxide layer 23 and second device layer 24 successively.
Have one or more layers device that in technology before, forms in the device layer 22 of basis, be used in the follow-up wafer of processing, carrying out function corresponding.
Second device layer 24 is positioned at basic device layer 22 tops, and 23 encirclements of oxidized all around silicon layer are to prevent the contaminated or damage in follow-up technology of second device layer 24.
Can know according to background technology; Among Fig. 2 a, the silicon oxide layer sidewall 231 that covers second device layer, 24 sides is thinner, if directly carry out wet etching; Can damage second device layer 24 in the silicon oxide layer sidewall 231 because of lateral corrasion; For this reason, preferred embodiment of the present invention proposes following method, to avoid the problems referred to above.
At first, shown in Fig. 2 b,, promptly, the step that ion is implanted, i.e. step S301 are carried out in the surface of silicon oxide layer 23 perpendicular to the direction of silicon oxide layer 23 along the direction of the sidewall 231 of silicon oxide layer 23.The ion here for example is argon ion (Ar
+), arsenic ion (As
+) waiting heavier ion, preferable in the present embodiment is argon ion, the implantation of argon ion can make that the surface structure of silicon oxide layer 23 is loose, can improve the etch rate of subsequent oxidation silicon layer 23 when wet etching.
The injection energy of argon ion is that 2keV, concentration are 2E15/cm in the present embodiment
2Particularly, the energy of argon ion depends on the thickness of silicon oxide layer 23, and the injection energy span of argon ion is 0.1KeV~100KeV; The concentration of argon ion (perhaps dosage) is big more, and is many more to the raising of silicon oxide layer 23 etch rates, and the concentration span of argon ion can be 1E12/cm
2~2E16/cm
2
In addition, argon ion is implanted has directivity, and in the step that argon ion is implanted, the restriction argon ion is only along the top layer of implanting silicon oxide layer 23 perpendicular to the direction of silicon oxide layer 23.Like this, argon ion is not implanted in the sidewall 231 of silicon oxide layer 23, does not change the etch rate of sidewall 231 when wet etching yet.
Then, execution in step S302 carries out wet etching to the wafer of handling through step S301.Shown in Fig. 2 c.Wafer is inserted in the hydrofluoric acid of dilution, and the sidewall of silicon oxide layer 23 can react with different etch rates in hydrofluoric acid with the bottom.
The present invention does not have specific (special) requirements for the concentration of hydrofluoric acid, and the concentration of hydrofluoric acid can be regulated according to etching speed of wanting to reach or the thickness of desiring the silicon oxide layer of etching.
In certain density hydrofluoric acid, the ratio that carried out the etch rate of silicon oxide layer 23 vertical direction that argon ion injects and horizontal direction is about 1.5: 1~and 4: 1, these ratios depend on the implantation dosage and the concentration of argon ion in step S301.
The degree of control etching when etching into basic device layer 22 upper surfaces on vertically, stops etching, takes out wafer.
The chip architecture that etching is accomplished is shown in Fig. 2 d; Implant on the direction at argon ion, because this a part of surface structure of silicon oxide layer 23 is comparatively loose, in etching process; Can react with etching solution quickly, so the degree that this a part of top layer is etched is heavier.And the sidewall 231 of silicon oxide layer 23; Since in step S301 not by implanting ions; Therefore it has kept original etch rate, and than that part of top layer of being inserted ion, etch rate is obviously lower; Therefore the etching degree is lighter, thereby can make second device layer 24 not contaminated and damage in etching process of silicon oxide layer 23 inside.
The present invention has adjusted the sidewall of silicon oxide layer and the etch rate between other surfaces through implanting ions directionally to silicon oxide layer, reached to keep the silicon oxide layer transverse width, with the transversely not impaired purpose of assurance silicon oxide layer internal components as far as possible.
Though the present invention discloses as above with preferred embodiment, so it is not in order to limit the present invention.Have common knowledge the knowledgeable in the technical field under the present invention, do not breaking away from the spirit and scope of the present invention, when doing various changes and retouching.Therefore, protection scope of the present invention is as the criterion when looking claims person of defining.