CN103531464B - Etching method of silicon nitride high depth-width ratio hole - Google Patents

Abstract

The etching method of the high aspect ratio hole of the silicon nitride film of the present invention first puts the semiconductor device of the silicon nitride film which has formed the pattern required by the semiconductor into the etching chamber, and then adopts the dry plasma process to pass through the high-carbon Chain molecular fluorocarbon-based gas, oxidizing gas, diluting gas, hydrogen-containing fluorocarbon-based gas, and radio frequency power are added to excite plasma; after plasma stabilization steps, silicon nitride film is etched until high-depth The etching morphology, pore size and depth of the aspect ratio holes meet the requirements. The invention uses a unique fluorocarbon-based gas to etch the silicon nitride film. By adjusting the gas composition and power, the deposition amount of the fluorocarbon polymer on the side wall of the deep hole can be controlled to avoid the key size of the hole from becoming larger, and the Removing the polymer that has deposited at the bottom of the deep hole allows the etch to continue, allowing the etch topography of the hole to be tuned.

Description

Etching Method of Silicon Nitride High Aspect Ratio Hole

technical field

The invention belongs to the field of semiconductor integrated circuit manufacturing, and more specifically relates to an etching method for a silicon nitride film with a high aspect ratio hole.

Background technique

Contact hole etching is a key technology of VLSI. As CMOS enters the technology era after 32nm, high aspect ratio hole etching and its filling have a considerable impact on the yield of devices. For advanced memories, the aspect ratio has reached more than 40:1, which makes the challenge even greater.

The contact hole etching medium of traditional CMOS devices is silicon dioxide film. As another widely used dielectric material, silicon nitride is hardly used as an ILD layer due to its large K value and stress. It is mainly used as a stop layer for hard mask, etch or CMP.

Similar to the etching of silicon oxide film, silicon nitride film is generally etched by fluorocarbon-based gases such as CF ₄ , CHF ₃ , CH ₂ F ₂ , CH ₃ F and the like. At present, in the mainstream CMOS integrated circuit manufacturing, the medium for contact hole etching is mainly silicon dioxide, and silicon nitride is not used. However, with the in-depth development of semiconductor integrated circuits, silicon nitride, as a dielectric material for hole etching, has come into play in Group III and Group V optoelectronic crystal devices.

For silicon nitride, in terms of materials, the growth and preparation of silicon nitride generally adopt PECVD and LPCVD methods. Compared with silicon oxide, silicon nitride has a lower bond energy and is easier to open, so etching silicon dioxide All gases can be used to etch silicon nitride, and a higher etching rate can be obtained. The difference is that when silicon nitride is etched with hydrogen-containing fluorocarbon-based gases, it is easy to produce polymers, and it is difficult to remove if it is in a deep hole, which easily affects the steepness of the deep hole and the size of CD. Therefore, when it is necessary to prepare deep holes with an aspect ratio of 5:1 (CD is about 100nm), the amount of polymer deposited on the sidewall is very important, which determines the etching morphology and reaction process. If the polymer is too little, it is difficult to obtain the ideal etching morphology, and the selectivity is low, it is difficult to control the size of the critical dimension CD of the hole; however, if too much fluorocarbon polymer film is deposited in the deep hole, it will be harmful The sidewalls and bottom act as chemical inhibitors that cause etch to stop.

Therefore, there is a need for a method for hole etching of silicon nitride thin films capable of controlling the deposition amount of fluorocarbon polymer in deep holes.

Contents of the invention

The purpose of the present invention is to overcome the defects of the prior art and provide a method for etching silicon nitride film high aspect ratio holes, which can control the deposition amount of fluorocarbon polymer on the side wall of the deep hole and remove the deposited The polymer at the bottom of the deep hole ensures that the etching can continue, which in turn can adjust the etched topography of the hole.

The technical scheme that realizes the object of the present invention is:

A silicon nitride high aspect ratio hole etching method, first puts the silicon nitride thin film semiconductor device with the desired pattern of semiconductor into the etching chamber, and then further includes the following steps: adopting dry plasma process, Introduce high-carbon chain molecular fluorocarbon-based gas, oxidizing gas, and hydrogen-containing fluorocarbon-based gas into the etching chamber, and add radio frequency power to excite plasma; after the plasma stabilization step, perform silicon nitride Etching the thin film until the etched morphology, pore size and depth of the holes meet the requirements.

Wherein, the high-carbon chain molecular fluorocarbon-based gas also produces a fluorocarbon-containing polymer film deposited on the sidewall and bottom of the hole while etching silicon nitride, thereby forming anisotropic etching of silicon nitride. ; When the hydrogen-containing fluorocarbon-based gas chemically etches the silicon nitride film and improves the etching speed, it also produces polymer molecules containing fluorocarbon and deposits on the sidewall and bottom of the hole; the oxidizing The gas bombards and reacts the fluorocarbon polymer at the bottom of the hole so that the etching will not stop. At the same time, the oxidizing gas removes part of the fluorocarbon polymer deposited on the side wall of the hole, and the other part of the fluorocarbon polymer The material remains on the sidewall of the hole.

When increasing the high carbon chain molecule fluorocarbon-based gas to increase the amount of the polymer, the shape of the hole is slightly inclined; when increasing the oxidizing gas, the shape of the hole is steep; by When the parameters are adjusted to be between the above two, different etching shapes of holes can be obtained according to requirements.

Preferably, while the high carbon chain molecule fluorocarbon-based gas, oxidizing gas, and hydrogen-containing fluorocarbon-based gas are introduced into the etching chamber, a diluent gas for forming a stable plasma is also introduced.

Wherein the high carbon chain molecule fluorocarbon-based gas is selected from at least one of C ₄ F ₆ and C ₄ F ₈ ; the fluorocarbon-based gas is selected from at least one of CHF ₃ , CH ₂ F ₂ and CH ₃ F ; the oxidizing gas is O ₂ ; the diluting gas is He or Ar.

In one embodiment, when etching a high aspect ratio hole with a steep shape, a medium and micro semiconductor Primo-DRIE cavity is used, and a dual radio frequency system is used, with a high frequency of 60 MHz and a low frequency of 2 MHz, decoupling between the two, The high and low frequency power selection is 500W/1500W, the cavity pressure is kept at 40mt, and the gas introduced includes: 30sccm C ₄ F ₈ , 70sccm CH ₂ F ₂ , 80sccm O ₂ , 300sccm Ar.

In another embodiment, when etching a high aspect ratio hole with a slightly inclined shape, the Primo-DRIE cavity of Zhongwei Semiconductor is used, and a dual radio frequency system is adopted, with a high frequency of 60MHz and a low frequency of 2MHz, and the decoupling between the two , The high and low frequency power selection is 500W/1500W, the cavity pressure is kept at 40mt, and the gas introduced includes: 40sccm C4F8, 70sccm CH2F2, 80sccmO2, 300sccm Ar.

In yet another embodiment, it is characterized in that the high aspect ratio hole with a slightly inclined shape can also be etched by the following method: using the Sinomicro Semiconductor Primo-DRIE cavity, using a dual radio frequency system, the high frequency is 60MHz, and the low frequency is 2MHz, decoupling between the two, high and low frequency power selection 500W/1500W, chamber pressure 40mt, gas flow includes: 30sccm C4F8, 70sccm CH2F2, 70sccm O2, 300sccm Ar.

The semiconductor device of the present invention has a single-layer structure, and the etching stops on the silicon substrate; or the semiconductor device has a multi-layer structure, and the etching stops above or below the dielectric layer. The material of the dielectric layer is silicon oxide, silicon or other substrates.

The etching method of silicon nitride film with high aspect ratio hole of the present invention adopts unique fluorocarbon-based gas to etch silicon nitride film, and realizes the anisotropy of silicon nitride deep hole by adjusting gas composition and power And fast etching, which can control the deposition amount of fluorocarbon polymer on the side wall of the deep hole to avoid the critical dimension of the hole from becoming larger, and remove the polymer deposited at the bottom of the deep hole to ensure that the etching can continue, and then The etching morphology of the holes can be adjusted to obtain a satisfactory structure of holes with a high aspect ratio.

Description of drawings

Fig. 1 is the wafer that has the silicon nitride film structure that photolithography develops desired pattern of the present invention;

Fig. 2 is a cross-sectional view of a steep etched topography of a high aspect ratio hole in a single-layer silicon nitride film in one embodiment of the present invention;

Fig. 3 is another embodiment of the present invention, the cross-sectional view of the slightly inclined etching morphology of the high aspect ratio hole of the single-layer silicon nitride film;

Fig. 4 is a cross-sectional view of etching topography of a high aspect ratio hole in a multilayer silicon nitride film in another embodiment of the present invention.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and by taking specific implementations as examples. However, those skilled in the art should know that the present invention is not limited to the specific embodiments listed, as long as it conforms to the spirit of the present invention, it should be included in the protection scope of the present invention.

The etching method of the silicon nitride high aspect ratio hole of the present invention comprises the following steps:

First, put the silicon nitride film structure wafer with the required pattern developed by photolithography into the etching chamber; Inert gas, hydrogen-containing fluorocarbon-based gas, and radio frequency power are added to excite the plasma; after the plasma stabilization step, the silicon nitride film is etched until the etching morphology and aperture size of the high aspect ratio hole and Depth meets requirements.

The high carbon chain molecular fluorocarbon-based gas of the present invention can be selected from at least one of C ₄ F ₆ and C ₄ F ₈ ; the hydrogen-containing fluorocarbon-based gas can be selected from CHF ₃ , CH ₂ F ₂ and CH ₃ F at least One: the oxidizing gas is O ₂ ; the diluting gas is He or Ar.

Among them, the high-carbon chain molecular fluorocarbon-based gas C ₄ F ₆ or C ₄ F ₈ is not only used for etching silicon nitride, but more importantly, it can produce more fluorocarbon-containing polymer films, which are deposited on the side of the hole. The wall and the bottom, thereby forming anisotropic etching on silicon nitride. Similarly, the hydrogen-containing fluorocarbon-based gas CHF ₃ , CH ₂ F ₂ or CH ₃ F is mainly used to chemically etch silicon nitride films to increase the etching speed, and fluorine-containing fluorocarbons will also be produced during the reaction process. Polymer molecules are also deposited on the sidewall and bottom of the hole; the oxidizing gas _O2 is used to assist in removing the polymer that has been produced and produced during the etching process, bombarding and reacting the fluorocarbon polymer at the bottom of the hole So that the etching will not stop, and at the same time, the oxidizing gas has a slightly weaker removal effect on the fluorocarbon polymer deposited on the side wall, and a part of the fluorocarbon polymer deposited on the side wall will remain. The diluent gas He or Ar is used to excite the plasma, form a stable plasma and control the etching speed.

The etching method of the silicon nitride thin film high aspect ratio hole of the present invention can etch different shapes of the deep hole as required without changing the shape characteristics of the etched hole in other aspects. When the high carbon chain molecule fluorocarbon-based gas is added to increase the amount of polymer, slightly inclined deep pores can be produced; when the oxidizing gas is added, relatively steep deep pores can be formed. Therefore, by adjusting the content of each gas, especially the content of high carbon chain molecule fluorocarbon-based gas and oxidizing gas, the amount of polymer can be adjusted, and a sufficient amount of polymer can be deposited on the side wall of the deep hole to The ideal etching morphology can be obtained, and it can also ensure that the fluorocarbon polymer film deposited at the bottom of the deep hole is not too much, which will cause the etching to stop.

The above method will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

The etching equipment of the specific embodiment of the present invention adopts Sinomicro Semiconductor Primo-DRIE cavity, and adopts a dual radio frequency system. The high frequency is 60MHz, which is mainly used to generate plasma and adjust the plasma density; the low frequency is 2MHz, which is used to enhance ion energy. And the bombardment intensity, improve the etching directionality. The two are decoupled so as not to affect each other. This makes it possible to perform different optimizations according to the specific characteristics of the etched deep hole without changing the morphology of the etched hole in other aspects.

As shown in Figure 1, a layer of silicon nitride film 11 is deposited by PECVD on the substrate forming the basic semiconductor structure, and photoresist is used as the mask layer 10 (depending on the requirements of different process nodes, sometimes it may be necessary to add a hard mask ), and the desired pattern is etched out by photolithography.

FIG. 2 is a cross-sectional view of a steep etching topography of a high aspect ratio hole in a single-layer silicon nitride film in one embodiment of the present invention. The etching gas is introduced into the etching chamber, excited by radio frequency power, and the silicon nitride is etched after the plasma is stabilized. As an example, C ₄ F ₈ , CH ₂ F ₂ , O ₂ etc. are preferred for etching. Due to the large number of etching equipment manufacturers, the parameter setting here takes the etching equipment of AMEC Primo-DRIE as an example. The chamber pressure is kept at 40mt, the gases introduced include: 30sccm C ₄ F ₈ , 70sccm CH ₂ F ₂ , 80sccm O ₂ , 300sccm Ar, and the high and low frequency power is selected as 500W/1500W, so as to etch out a steep shape.

For etching holes with a high aspect ratio, the above-mentioned steep topography will bring considerable challenges to the subsequent filling. Sometimes for the subsequent process, the size of the bottom will be made smaller to make a slightly inclined shape. Fig. 3 is a cross-sectional view of the slightly inclined etching morphology of the high aspect ratio hole of a single-layer silicon nitride film in another embodiment of the present invention. In this embodiment, the polymerization is enhanced by increasing the flow rate of the fluorocarbon-based gas C ₄ F ₈ Deposition of substances on the sidewalls reduces lateral etching. The polymer deposited on the bottom can be bombarded by oxidizing gas at low frequency and high power without affecting the anisotropic etching. Finally, a slightly inclined etching profile is formed, as shown in Figure 3. The process parameters can be set as follows, the high and low frequency power is 500W/1500W, the chamber pressure is 40mt, and the gas introduced includes: 40sccm C ₄ F ₈ , 70sccm CH ₂ F ₂ , 80sccm O ₂ , 300sccm Ar.

In another embodiment, the slightly inclined etching morphology can also be obtained by adjusting the flow rate of O2: high and low frequency power 500W/1500W, chamber pressure 40mt, the gas introduced includes: 30sccm C ₄ F ₈ , 70sccm CH ₂ F ₂ , 70 sccm O ₂ , 300 sccm Ar.

FIG. 4 is another embodiment of deep hole etching of a multilayer silicon nitride film. The process parameters can parameterize the above examples. The multi-layer semiconductor structure device also includes a stop layer 12 under the silicon nitride film 11 in addition to the silicon nitride film 11 and the mask layer 10 thereon. The method of the present invention is equally applicable to deep hole etching of multilayer silicon nitride films, and its etching profile can be steep as shown in Figure 2, or slightly inclined as shown in Figure 3, or between the two. The etch morphology between them. The difference between this embodiment and the previous two embodiments is that the previous two embodiments have a single-layer structure, and the etching stops on the silicon substrate, while the present embodiment has a multi-layer structure, and the etching stops on the stop layer 12 Alternatively, the material of the stop layer 12 can be silicon oxide, silicon or other materials.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

Claims (9)

1. a kind of lithographic method of silicon nitride high depth-to-width ratio hole, will form the silicon nitride film of quasiconductor required figure first Semiconductor device be put in etching cavity, it is characterised in that methods described then also comprises the steps：

Using dry plasma process, be passed through into the etching cavity high carbon chain molecular carbon fluorine base gas, oxidizing gas, Hydrogen-containing carbon fluorine base gas, adds radio-frequency power, inspires plasma；After plasma stability step, silicon nitride is carried out The etching of thin film, until the etch topography in the hole, pore size and depth reach requirement；

When the high carbon chain molecular carbon fluorine base gas is increased so as to increase the amount of polymer, the pattern in the hole is slightly to incline； When the oxidizing gas are increased, the pattern in the hole is steep；By adjust the high carbon chain molecular carbon fluorine base gas and The content of the oxidizing gas, you can obtain the etch topography in different holes according to demand；

It is 5 that said method is applied to depth-to-width ratio:1 and the above nitridation silicon hole etching；

The etching cavity adopts dijection display system, and high frequency is 60MHz, for producing plasma, for adjusting plasma Density；Low frequency is 2MHz, for strengthening ion energy and bombardment intensity, lifts etching directivity；Go between the high frequency, low frequency Coupling.

2. method as claimed in claim 1, it is characterised in that

While etch silicon nitride, the thin polymer film for also producing carbon containing fluorine is deposited on the high carbon chain molecular carbon fluorine base gas The side wall in hole and bottom, so that form anisotropic etching to silicon nitride；

The hydrogen-containing carbon fluorine base gas is produced while the chemical to silicon nitride film is etched and lifts etching speed, also and is contained The polymer molecule for having carbon fluorine also is deposited upon the side wall in hole and bottom；

The oxidizing gas by the fluorocarbon polymer of the bottom in the hole bombard and react away so that etching be unlikely to stop, together The fluorocarbon polymer of the deposited on sidewalls in the hole is removed a part, another part fluorocarbon polymer by Shi Suoshu oxidizing gas It is retained on the side wall in the hole.

3. method as claimed in claim 1 or 2, it is characterised in that be passed through high carbon chain molecular carbon fluorine into the etching cavity While base gas, oxidizing gas, hydrogen-containing carbon fluorine base gas, the dilution gas for forming stable plasma is also passed through Body.

4. method as claimed in claim 3, it is characterised in that the high carbon chain molecular carbon fluorine base gas is selected from C₄F₆、C₄F₈In extremely Few one；The carbon fluorine base gas is selected from CHF₃、CH₂F₂And CH₃At least one in F；The oxidizing gas are O₂；The dilution Property gas be He or Ar.

5. method as claimed in claim 4, it is characterised in that during the high-aspect-ratio hole of the steep pattern of etching, micro- using in partly to lead Body Primo-DRIE cavitys, using dijection display system, high frequency is 60MHz, and low frequency is 2MHz, uncoupling between the two, low-and high-frequency Power selection 500W/1500W, chamber pressure are maintained at 40mt, and being passed through gas includes：30sccm C₄F₈, 70sccm CH₂F₂, 80sccm O₂, 300sccm Ar.

6. method as claimed in claim 4, it is characterised in that when etching slightly inclines the high-aspect-ratio hole of pattern, micro- half using in Conductor Primo-DRIE cavitys, using dijection display system, high frequency is 60MHz, and low frequency is 2MHz, uncoupling between the two, height Frequency power selection 500W/1500W, chamber pressure are maintained at 40mt, and being passed through gas includes：40sccm C₄F₈, 70sccm CH₂F₂, 80sccm O₂, 300sccm Ar.

7. method as claimed in claim 4, it is characterised in that can also etch in the following manner slightly incline pattern profundity it is wide Compare hole：The micro semiconductor Primo-DRIE cavitys using in, using dijection display system, high frequency is 60MHz, and low frequency is 2MHz, both Between uncoupling, low-and high-frequency power selection 500W/1500W, chamber pressure 40mt, being passed through gas includes：30sccm C₄F₈, 70sccm CH₂F₂, 70sccm O₂, 300sccm Ar.

8. method as claimed in claim 1, it is characterised in that the semiconductor device is single layer structure, etching stopping is served as a contrast in silicon On bottom；Or

The semiconductor device is multiple structure, and etching stopping is on or below dielectric layer.

9. method as claimed in claim 8, it is characterised in that the material of the dielectric layer is silicon oxide or silicon.