RU2059321C1 - Method for producing flexible parts from single-crystalline silicon - Google Patents

Abstract

FIELD: instrumentation engineering; production of flexible parts of instruments (beams, membranes, strings, and the like) by anisotropic etching from monocrystalline silicon plates oriented in plane (100). SUBSTANCE: method involves oxidation of flat plate of single-crystalline silicon oriented in plane (100), its coating with photoresist protective layer, single-sided photolithography, opening of window near region of formation of flexible part on width greater than desired width of flexible part, silicon doping in window through depth equal to desired thickness of flexible part, removal of oxide, and repeated oxidation of silicon plate, its coating with photoresist protective layer, single-sided photolithography on side opposite to that of doped, opening of window in oxide in region of formation of flexible part on width l₂ greater than desired width of flexible part, and anisotropic etching up to doped layer of silicon. Primary anisotropic etching is made through depth equal to half the silicon plate thickness and, besides, photoresist layer is applied to plate, side opposite to that doped is subjected to photolithography, window is opened up in oxide near region of formation of flexible part over width l₄ meething relationship l₄-l₂> 2(b₂-b₁), where b₁ and b₂ is thickness of flexible part and plate, respectively, and secondary etching to doped layer of silicon. EFFECT: facilitated procedure. 7 dwg

Description

 The invention relates to instrumentation technology, and in particular to methods for manufacturing anisotropic etching of the elastic elements of devices (beams, membranes, strings, and so on) from a single-crystal silicon wafer with a (100) plane orientation.

A known method of manufacturing elastic elements of single-crystal silicon, including the operation of oxidizing the plate, coating it with a protective layer of photoresist, photolithography, opening the oxide in the places of formation of the elastic element to a width equal to the size of the elastic element, anisotropic etching to a depth less than necessary to obtain the required thickness of the elastic element, and isotropic etching to obtain the required thickness of the elastic element [1]
This analogue method has the following disadvantages:
low accuracy of manufacturing parts, since the second technological process for manufacturing an elastic element is polishing isotropic etching;
low-tech method, as it uses two technological processes (anisotropic etching and polishing isotropic etching).

The method of manufacturing monocrystalline silicon elastic elements [2] was selected as the prototype of the invention. This method involves oxidizing a flat plate of monocrystalline silicon with the surface orientation in the (100) plane, applying a photoresist protective layer on it, one-sided photolithography, opening the window in the oxide in the width of the elastic element , greater than the required width of the elastic element, doping of silicon (for example, by thermal diffusion of boron) to a depth equal to the required thickness of the elastic element. Next, silicon oxide is removed and re-oxidized silicon wafer, applying a protective layer of photoresist on it, one-sided photolithography on the side opposite to doping, opening the window in the oxide in the region of formation of the elastic element to a width l ₂ equal to
L ₂ +2 (b ₂ -b ₁ ) tg 35.3 ^about .

 After these operations, anisotropic etching to a doped silicon layer is carried out, where etching self-stops in depth.

The prototype method is illustrated in FIG. 1, where 1 wafer of a silicon single crystal with a surface orientation of (100); 2 alloyed silicon layer; l _{1 the} width of the elastic element; b _{1 the} thickness of the elastic element; l ₂ window width in oxide; b ₂ thickness of the silicon wafer; l _{3 the} width of the doped silicon layer.

 The prototype method has the following drawback: the presence of a stress concentrator along line A (see Fig. 1) in places of "terminating" an elastic element in a silicon wafer. It should be noted here that the indicated concentrator becomes the most dangerous when the silicon wafer is "milled".

The proposed method is characterized in that when conducting the first anisotropic etching from a window of width l _2, etching is performed to a depth equal to 0.5 b ₂ . The method introduces another operation of applying a photoresist protective layer to the plate, one-sided photolithography on the side opposite to doping, opening the window in the oxide in the region of formation of the elastic element to a width of l ₄ satisfying the ratio l ₄ -l ₂ > 2 (b ₂ -b ₁ )

 Next, anisotropic etching to a doped silicon layer is carried out.

In FIG. 2 shows a plate of single-crystal silicon with a surface orientation of (100) after opening the window in the oxide in the region of formation of the elastic element to a width l ₃ greater than the required width of the elastic element; in FIG. 3 silicon plate after doping and removal of silicon oxide; in FIG. 4, the silicon wafer after opening the window in the oxide in the region of formation of the elastic element on the side opposite the doping, to a width of l ₂ and the first anisotropic etching to a depth equal to half the thickness of the silicon wafer; in FIG. 5 final configuration of the elastic element obtained according to the invention; in FIG. 6 and 7, steps for manufacturing a symmetrical elastic element using the invention.

The drawings show: 1 single-crystal silicon wafer with a surface orientation of (100); 2 silicon oxide SiO ₂ ; 3 alloyed silicon layer.

 The implementation of the method according to the invention is as follows.

A flat plate 1 of single-crystal silicon with a surface orientation in the (100) plane is oxidized to form oxide 2. Next, a protective layer of photoresist is deposited on the oxide and one-sided photolithography is performed on the side of the plate on which the elastic element is formed. A window is opened in the oxide in the region of formation of the elastic element to a width l ₃ greater than the required width of the elastic element (see Fig. 2).

The silicon wafer is alloyed through a window in the oxide to a depth of b ₁ equal to the required thickness of the elastic element, and the oxide is removed (see Fig. 3).

The silicon wafer is re-oxidized, a photoresist protective layer is deposited on it, one-sided photolithography on the side opposite to doping, opening the window in the oxide in the region of formation of the elastic element to a width of l ₂ and anisotropic etching to a depth of 0.5 b ₂ (see Fig. 4 )

Next, the protective layer of the photoresist is again applied to the plate, one-sided photolithography is performed on the side opposite to doping, the window in the oxide is opened in the region of formation of the elastic element to a width of l ₄ satisfying the ratio l ₄ -l ₂ > 2 (b ₂ -b ₁ ).

 Then anisotropic etching is carried out to a doped silicon layer. The obtained profile of the elastic element is shown in FIG. 4.

 The proposed method of manufacturing elastic elements can be implemented with any known technological process of silicon doping (ion doping, plasma doping, and so on). Naturally, the use of these other alloying processes requires the correction of the general technical process presented in the invention.

 Using the invention, symmetrical elastic elements can also be manufactured (FIGS. 6 and 7).

 For this, at the first stage of manufacture, a profile is formed on the upper surface of the silicon wafer 1 using the method [1] and its surface is alloyed (Fig. 6).

 Next, on the lower surface of the plate, the operations according to the invention are carried out and (if necessary) doping of the places of "sealing" of the elastic element into the plate is carried out (Fig. 7).

 The claimed method is described in relation to the manufacture of elastic elements such as a membrane. To produce elastic elements such as beams and strings in this way, silicon doping should not be carried out over the entire length of the membrane, but only at the locations of the beams (or strings) for a length equal to the width of the beam (or string).

Claims (1)

METHOD FOR PRODUCING ELASTIC ELEMENTS FROM SINGLE CRYSTAL SILICON, including oxidation of a flat wafer of single-crystal silicon with a surface orientation in the (100) plane, applying a photoresist protective layer on it, single-sided photolithography, opening a window in the oxide in the width of the elastic element of the required width element, alloying silicon in the window to a depth equal to the required thickness of the elastic element, removing oxide and re-oxidizing the silicon wafer, protecting it Nogo photoresist layer, single-sided photolithography on the side opposite doping, opening windows in the oxide in the formation of the elastic member to the width l _2, most of the desired width of the elastic member, and anisotropic etching of silicon to the doped silicon layer, characterized in that the anisotropic etching to the doped layer carried out in two stages, the first stage of anisotropic etching is carried out to a depth equal to half the thickness of the silicon wafer, after the first stage, additionally applied to the wafer protective layer of photoresist, one-sided photolithography from the side opposite to doping, and opening the window in the oxide in the region of formation of the elastic element to a width of l ₄ satisfying the ratio
l ₄ l ₂ > 2 (b ₂ b ₁ ),
where b ₁ and b _2, respectively, the thickness of the elastic element and the silicon plate,
and then carry out the second stage of anisotropic etching to the doped layer.

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