KR930009109B1 - Silicon nozzle structure - Google Patents

Abstract

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Description

Silicone nozzle

1 is a perspective view of a nozzle configuration according to the present invention.

2 is a cross sectional view of the nozzle configuration taken along line 2-2 of FIG.

Sequential cross-sectional view of a silicon wafer processed according to the invention of FIGS. 3-8.

* Explanation of symbols for main parts of the drawings

10: substrate 11, 13: hole

14, 15: surface 16, 17: n-type layer

In the prior art, in particular US Pat. No. 3,921,916, it is proposed that monocrystalline and crystallographically oriented silicon wafers can be selectively etched to form one or more specific shaped renewable channels in the wafer body. have. The particular type of channel referred to in this patent has a rectangular inlet cross section, an intermediate rectangular cross section that is subsequently smaller than the inlet cross section, and an outlet cross section that is not perpendicular. This particular type of channel is formed by any one of two known processes, all of which are sufficiently doped P ⁺ layers (patterned in one process and patterned in another process). Unized) is used as an etchant barrier. In both processes, the silicon wafer is sufficiently doped from one major surface to be saturated or close to forming a P ⁺ etchant barrier. Thereafter, anisotropic etching patterned from the opposite major surface proceeds until it reaches the P ⁺ barrier. Anisotropic etching forms a rectangular inlet cross section and a rectangular middle cross section defining a membrane of a size smaller than this inlet cross section.

In one processing application, the etching process continues from the inlet side until openings are made through the membrane. Another process uses patterned isotropic etching from the opposite side of the nozzle (outlet side) to complete the passage through the membrane to the intermediate cross section.

While this prior art process provides satisfactory ink jet nozzle structures, both the above described process and the resulting structure present unique problems. For example, depending on the inherent wafer thickness variation and the nonuniformity of the isotropic etching, these processes require mechanical / chemical precision polishing on both major surfaces of the wafer to improve the size control of the resulting nozzle structure. This is an expensive processing step. In addition, the nozzle structures produced by these processes have a sufficiently saturated P ⁺ region around exit openings, which are prone to brittle and are exposed to high fluid pressure or ink jet It can be destroyed when pressure transients are present in the printing system.

According to the present invention, a commercially available semiconductor wafer of crystallogr-aphically oriented single crystal P-type silicon is used to provide a single fluid nozzle without mechanical or chemical precision polishing on two major surfaces of the wafer. Or a straight array of nozzles, where a low saturated n surface layer is formed on at least one major surface of the wafer. Resistant materials for the anisotropic etchant used later are deposited on both surfaces of the waychafer. Then, aperture masks defining the inlet and outlet regions of the nozzle are formed on these major surfaces, and the outlet regions are covered with a material that provides electrical connection to the n layer with resistance to the etching solution. The cavity is anisotropically etched from the inlet region of the wafer to the n layer on the outlet side by precipitating the wafer in a caustic etching solution. The potential applied across the p / n junction at the exit side of the wafer electrochemically interrupts the etching action that causes the film to have the same thickness as the n layer. The passage is then etched granularly through the membrane from the outlet side to complete the nozzle configuration.

In multi-nozzle ink jet printing systems using nozzles made of semiconductor materials, the important characteristics required for the nozzles are the uniformity of each nozzle size, the spatial distribution of the nozzles in the arrangement, and the system. Resistance to cracking under fluid pressure occurring within, providing efficient mechanical impedance matching between fluid supply and outlet holes, and resistance to wear caused by high velocity fluid flow through the nozzle structure.

In connection with the first diagram, the first figure shows a part of a nozzle structure made in accordance with the present invention. In particular, the wafer 10 has openings 11 arranged uniformly. Each hole 11 initially starts with a tapered region and tapers and ends with a square region defining a membrane 12 that is smaller than the original square region. As shown in FIG. 2, each film 12 has an opening 13 which starts with a square area smaller than the square area and ends with a larger square area than the square area of this starting point. All of the horizontal axes of the holes 13 of the film 12 are arranged in line with the horizontal axes of the corresponding respective holes 11 in the main body of the wafer 10 by crystallography of the wafer 10.

3-8 illustrate a series of fixing steps for forming holes in the single crystal silicon wafer 10 to form one fluid nozzle or arrayed nozzles. The process steps described below may of course be used in a different order, and other film materials may be used to perform the same functions described below, and also thin film formation, size, thickness and the like. And the like can be changed. Wafer 10 is a single crystal 100 oriented P-type silicon having a thickness of about 19.5 to 20.5 mils having a front face 14 and a back face 15 and an electrical resistance of 0.5 to 10 ohm-cm. The (100) plane is parallel to the surfaces 14 and 15. As shown in FIG. 3, phosphorus diffuses to the front and rear surfaces 15 of the silicon wafer 10 to a length of about microns to form n-type layers 16 and 17. FIG. As will be evident later, only one diffusion layer (outlet side) is required to form the nozzle structure by the process. Diffusion is carried out in a known manner by flowing a gas mixture comprising 0.75% of pH ₃ , 1% of O ₂ , Ar and N ₂ , over a silicon wafer 10 held at 950 ° C. for 30 minutes. . There is then a long drive-in period (1050 ° C. for 22 hours) to form a thick layer (about 5 microns). Since the final concentration of phosphorus in the n-layers 16 and 17 is very low, this diffusion step hardly stresses the silicon wafer 10, and consequently the silicon structure maintains its strength.

As shown in FIG. 4, both the front side 14 and the rear side 15 of the wafer 10 form LPCVD silicon that forms layers 18 and 19 that can withstand long etching periods in a corrosive (KDH) solution. Coated with a resistive material such as nitride. One way to accomplish this is to use low pressure chemical vapor deposition of silicon nitride deposited at about 800 ° C. An oxide layer (not shown) smaller than 0.5 microns thick is grown on both sides of layers 18 and 19 to reduce the stress effect between nitride and silicon and improve the adhesion of photoresist to nitride. To facilitate photoshaping it is selected to have a backside 15 etched in a solution that is more acidic than the corrosive solution when the wafer 10 is provided.

After that, a mask corresponding to the predetermined inlet region 20 and outlet 21 region of the nozzle is prepared. Since the holes in the silicon wafer 10 defined by the circular mask are etched from a square parallel to the plane of 100, the shape of the mask for the inlet region 20 and the outlet region 21 is circular and each square Circumscribe each of its circles. The use of circular masks eliminates the errors caused by theta misalinments that occur when visual masks are used. Silicon nitride layers 18 and 19 are simultaneously photoshaped on both sides using photopinners (not shown) on both sides and aligners (not shown) on both sides. The resulting configuration after etching the portions of the layers 18, 19 defining the inlet area 20 and the outlet area 21 is shown in FIG. 5.

The outlet region 21 is protected from etching solution by coating the metal layer 22 thereon as shown in FIG. 6 or by using a sealed mechanical fixture (not shown). The wafer is then precipitated in a hot (80-85 ° C.) KOH solution (not shown), and the backside ( There is a potential across the p / n junction in 15). Other alkali etching solutions such as NaOH, NH ₄ OH and the like may be used, for example metal hydroxides of group IA of the periodic table. The use of electrochemically controlled thin film processing in semiconductors is a known technique, and is also described in detail in US Patent Application No. 3,689,389 to one of the applicants of the present application.

The holes 11 in the single crystal silicon wafer 10 are anisotropically etched until they reach the back diffusion layer 17 and, when reached, an oxide layer formed at the p / n junction by the potential applied across the junction (not shown). Is stopped), the etching operation is stopped. It is known in the art that when the KOH etching solution is used (111) the plane is the slow etch plane of the single crystal silicon material. Therefore, the etching step forms a pyramidal hole in the wafer 10, which ends with the film 12 when encountering an electrochemical etching barrier formed at the silicon and diffusion layer 17 interface (p / n junction).

Thereafter, the wafer 10 is removed from the etching solution, the resistive metal layer 22 and associated electrical connections on the outlet side are removed, and the inlet side 20 is protected from the etching solution by the layer 24 formed by air oxidation. do. The wafer 10 is then reprecipitated into the etching solution and the pyramidal passages are anisotropically etched from the backside 15 to form the holes 13 at the exit. The resulting structure is shown in FIG.

If desired, the resistive coating layers 18, 19, and 24 may be removed, leaving the complete pure silicon nozzle structure as shown in FIG. Typically the initial hole of the inlet 20 has a width of about 35 mils, and the smallest portion of the outlet hole 13 has a width of about 1.5 to 4 mils.

Since the etch rate perpendicular to the (111) plane is very low compared to the etch rate perpendicular to the (100) plane, overetch also does not degrade the high accuracy defined by the exit mask. In order to prevent the ink from wetting the wafer surface on the exit side, the backside 15 of the wafer 10 may be coated with a material having a low surface energy such as Teflon.

Claims (2)

A single nozzle body formed of P-type single crystal silicon having a first cross-sectional area that is a square inlet hole and tapered therefrom and a second square cross-sectional area that is less than the first cross-sectional area of the inlet hole, and 10 formed in the second cross-sectional area. A membrane of n-type single crystal silicon having a thickness of less than a micron, the film having a single square outlet hole, the outlet hole having a first cross-sectional area smaller than the second cross-sectional area of the inlet hole; The first cross-sectional area is tapered from the second cross-sectional area of the inlet hole to the second cross-sectional area of the outlet hole, and the first cross-sectional area of the outlet hole is smaller than the second cross-sectional area, and the cross section is Are parallel to the (100) plane of single crystal silicon, and wherein the inlet and outlet holes are concentric. A nozzle body formed of crystallographically oriented P-type single crystal silicon sections having first and second major surfaces, and an n-type layer formed on the first major surface of the section, the section being the second major part of this section. Having an anisotropically etched pyramidal cavity from the surface to the n layer, the cavity having a rectangular inlet of the first cross-sectional area tapered to a second rectangular cross-sectional area smaller than the first cross-sectional area. Wherein the n-layer has an exit hole anisotropically etched from the first major surface of the section, the exit hole has a first cross-sectional area that is smaller than the second cross-sectional area of the pyramidal cavity, and the first cross-section of the outlet hole The area is taped to a second cross-sectional area larger than the first cross-sectional area of this outlet hole.

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