JPH011236A - Selective thin film etching method and gas mixture used therein - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

BACKGROUND OF THE INVENTION The present invention relates to the selective, preferably anisotropic etching of films formed on silicon dioxide, such as silicon nitride. More particularly, the present invention relates to a method of etching silicon nitride anisotropically with high selectivity to the underlying silicon dioxide, a controlled silicon nitride profile, and a controlled silicon dioxide reduction or increase.

Composite silicon nitride coated silicon dioxide has many applications in integrated circuits. For example, nitride-coated oxides are used to form ICs (integrated circuits) during LOGO3 formation of field isolation oxides.
It can be used as an oxidation mask for selective exposure of field areas of the wafer. In such applications the underlying oxide can be very thin. silicon nitride LOGOS
During mask patterning, a photoresist-like rough mask is accurately replicated in silicon nitride with good resolution without loss of dimension and without etching of the overlying photoresist mask and the underlying thin oxide (i.e., with suitably high selectivity). It is necessary. When the nitride is later removed from the active area, the photoresist is removed from the LO
Selectivity to photoresist is not relevant since it is stripped before GO3 oxidation. However, preventing degradation or removal of thin oxides is still very important.

Fluorocarbon etching agents such as CH, F and C
H2F2 and SF and NF were used to etch silicon nitride. The fluorocarbon etchant can deposit on the oxide and thus form a nonvolatile carbon-containing organic polymer that enhances etch selectivity.

However, carbon forms particles and thus creates an undesirable dirty process, especially for LSI (Large Scale Integration) and VLSI (Very Large Scale Integration) circuits that are sensitive to relatively few and even very small particles. moreover,
Organic polymer layers can sometimes deposit indiscriminately within the reactor, requiring relatively frequent cleaning of the reactor.

SUMMARY OF THE INVENTION A principal object of the present invention is to selectively etch thin films, such as silicon nitride, formed over a silicon dioxide underlayer.

A related objective is the selective anisotropic etching of silicon nitride coated silicon dioxide, resulting in a controlled anisotropic nitride etch profile and controlled selectivity to the underlying oxide (
increase or decrease).

Another related object is to provide a method to also achieve controlled selectivity to the photoresist mask.

These and other objects are achieved using a 5IF4 and 0□ group reactant gas stream that etches the silicon nitride and selectively deposits the oxide, thereby offsetting the inherent etching of the oxide underlayer by the fluorine layer. . As far as we know, S
iF, and 02 have been used for silicon dioxide deposition, but not for etching thin films such as nitrides and etching with controlled deposition on the underlying layer of such films. In one aspect, our method The silicon nitride layer components of an object containing a silicon nitride layer formed on a silicon oxide lower layer,
exposing the object to a plasma formed from a reactant gas stream of SiFa and oxygen adapted to selectively (and anisotropically) etch with controlled selectivity to the silicon oxide underlayer; including.

In another related aspect, our method converts the silicon nitride layer component of an object containing a layer of silicon nitride onto a silicon oxide underlayer to a silicon nitride layer formed on the silicon nitride with controlled high selectivity to the silicon oxide underlayer. This is a method of etching in a plasma etching chamber using a photoresist etch mask,
placing the masked object in an etching chamber and communicating into the chamber a selected reactive gas mixture containing NFl, SiF4, and 02 that etches silicon nitride with high selectivity to the photoresist and to the oxide underlayer; including.

DETAILED DESCRIPTION OF THE INVENTION (1) Overall Process The present invention uses an oxygen-containing etching method for etching silicon nitride with controlled anisotropy with high selectivity to organic photoresist masks and controlled selectivity to oxides. Fluorinated gas chemistry is used in a vacuum plasma reactor. This controlled silicon nitride etch is a simple 1
A stepwise method, it increases repeatability, lowers material costs, and increases operator control. Furthermore, high selectivity for oxide underlayers increases process yield and makes the process easier to adapt to other applications.

Preferred reactive gas chemistries include O,/SiF, more specifically NF, 10□/SiF4. SiF4 is a selective nitride etchant (see reaction A) NF3 can be a predominant nitride etchant (see reaction B)
. 02 combines with silicon from 5iFi to selectively form silicon oxide-containing deposits on the oxide underlayer, thus increasing the selectivity for the oxide layer (see reaction A). for example,
Typically, increasing the number of silicon nitride-containing wafers decreases the nitride etch rate, but increasing the NF3 flow rate increases the nitride etch rate by increasing the nitride etch rate, thus even when other parameters are held constant. Compensate for the number of wafers. The addition of NF3 increases the usable range of the process, ie the process window.

(2) Process trend (trend line) The suitability and advantages of the present invention are based on the three main gas reactants NF3,
oz and 5tFa flow rates and flow ratios to match the etch selectivity to the photoresist etch mask and to control the deposition rate of silicon oxide-containing compounds and thereby reduce or (increase) the oxide during processing.
to control. is indicated by the ability of the selected process gas to be used. These results are achieved using a standard invariant actor 10 (FIG. 1). The effects of the selected process gases are summarized next.

The applicable equilibrium reactions for SiF4, NF, and 02 are: Reaction A: SiF4 + Q2 #5iOz +41' Reaction B
: 2 NF 3 #Nz + 6 dead. Reaction A dominates the selectivity mechanism since SiO□ precipitates and fluorine is the nitride etchant.

As shown, fluorine increases the nitride etch rate in reaction B.

The nitride etch rate is directly proportional to the flow rate of SiF4 used as the primary nitride etchant.

As previously discussed and shown in FIGS. 2 and 3, increasing the flow rate of NF increases both nitride etch rate and oxide reduction.

Oxide etch rate is affected by photoresist coverage on the wafer. Specifically, the oxide etch rate is inversely proportional to the area of the wafer covered by photoresist at a given process condition. Decreasing/increasing photoresist coverage increases/reduces oxide reduction during etching.

The photoresist acts as an oxygen getter to slow down or inhibit the formation and deposition of 5inX, which is a key factor in oxide reduction or increase and selectivity.

However, as discussed below, IC designs requiring large area photoresist coverage and associated nitride etch steps can be compensated for by increasing the oxygen flow rate.

As mentioned above, oxide etch/deposition rates are influenced and controlled by varying the proportion of oxygen in the total gas flow. In fact, as shown in FIGS. 4 and 5, both the nitride etch rate and the oxide etch rate are inversely proportional to the oxygen percentage of the gold nugget. However, the oxide and nitride etch rate responses differ with increasing oxygen flow, which contributes to the ability to utilize selectivity mechanisms. Additionally, the addition of NF contributes to controlling the selectivity mechanism.

Still referring to FIG. 4, decreasing/increasing the flow rate of oxygen with respect to other gases also decreases/increases the selective deposition of Sin, typically SiO□, on the oxide and thus during etching. Reduce/increase oxide loss. See reaction A. Increasing the flow rate of oxygen provides infinite selectivity to oxide (zero etch rate) and can actually increase the silicon oxide deposition rate sufficiently to provide pure oxide deposition or increase rather than decrease. In effect, changing the oxygen flow rate allows one to choose oxide etch/deposition from a continuum of speeds, ie, from high etch rates at one end of the spectrum to zero etch/deposition to deposition. Furthermore, our understanding of the different effects of photoresist coverage and oxide flow on oxide etch/deposition rates allowed us to obtain low oxide etch rates and high selectivity for different photoresist coverages by adjusting the 02 flow rate. That is, large area photoresist coverage can be compensated for by increased oxygen flow.

SiF4 is the etchant (nitride etch rate is S
i F 4 proportional to the current). Additionally, the effect of SiF4 flow on oxide etch/deposition is significant for oxides (particularly 5iOz
) Similar to the effect of oxygen flow in that the etch rate is inversely proportional to SiF4 flow. Decreasing/increasing the flow rate of SiF4 increases/decreases oxide reduction.

(3) Examples and Applications The table is a summary of optimal values and preferred and useful value ranges of parameters for etching silicon nitride on silicon dioxide using an AME8110 low pressure ion-assisted plasma reactor.

This reactor was manufactured by Applied Materials (App
Lied Materials, Inc, 5anta
C1araCalifornia). A low pressure reactive ion etching (RIE) mode plasma etching reactor of the AME8110 and more generally the 8100 series is shown schematically as system 10 in FIG.

The RIE system 10 holds a cylindrical reaction chamber 11 and illustratively twenty-four (7) wafers, four per facet, and an RF
It includes a hexagonal cathode 12 connected to a power source 13. The outlet 14 communicates between the inside of the reaction chamber 11 and the vacuum pump. The walls of the reaction chamber 11 and the base plate 16 form the grounded anode of the system. The supply of reactive gas from the gas source 17 is carried out through the conduit arrangement 1 to the population 18 and the gas distribution ring 20 in the upper part of the chamber.
9 into the interior of the chamber 11.

The shape of the reactor cooling system 10 is asymmetrical. That is, the anode to cathode ratio is somewhat greater than 2:1, resulting in a higher energy bombardment of the cathode surface 12 compared to the anode surface 11. Such a design provides low power density and good etch uniformity, reduces contamination from chamber walls, and facilitates achieving etch anisotropy. Additionally, the cathode structure orientation vertically orients all 24 wafers during processing to minimize exposure of the wafers to particles.

In such RIE mode systems, the highly directional mechanical ion bombardment etch components dominate the more isotropic chemical components, giving a high degree of anisotropy to the etching properties of the system. Therefore, RIE mode systems are preferred for high density small feature size IC applications such as the etch manufacturing stage of LSI and VLSI circuits.

However, AME8110 etching equipment and 8100
The use of a series etching device should be considered as exemplary only. The process is also manufactured by Applied Materials, Inc.

It has been successfully used in the 8300 series etching equipment available from 5anta C1ar4, California). More generally, this method will be applied to all plasma state etching systems which are primarily chemically driven and therefore capable of handling said gases.

Table 3 shows how to process silicon nitride without damaging the underlying oxide layer.
Increasingly specific useful ranges of process parameters for antisogging are shown. In other words, Table 1 is similar to Table 2 and Table 3.
Indicates the range of parameters that are expected to yield useful results based on the data reflected therein. Furthermore, because the method is chemically driven, it has applicability to any plasma-type system, such as a wider range of pressures than shown in the table. Table 2 is narrower and therefore shows a more specific set of process parameter ranges that provide a more optimal combination of high silicon nitride etch rate, high selectivity to photoresist, and high selectivity to oxide underlayers. Table 3
is a particularly narrow set of process parameters currently preferred in that it provides a combination of high nitride etch rates, reasonable selectivity to photoresist, and very high selectivity to oxide underlayers for a full load of 24 6-inch wafers. shows.

Total gas amount, sccm 10-400 5
0-100 78NF,
0-100 0-50 13SiF
40 100 10 50 300□
0-100 10-5
0 15! Ie
0-10o 20-50 20 chamber pressure, mT 10 150 20-5
0 30 residence time (sec) 0.5-3
0 5-15 ~9 Total power setting 8100 (
W) 100-1500 100-700
600 power density (W/c+a), 0.05-0.
80 0.05 0.17 0.15Selectivity towards lower layer: Complex (11>3:1>5:1
15:1 complex (2) >5
: 1 > 10 : 1 25 : 1(
1): Thermal LPCVD Nitride/Thermal Oxide (2); Plasma Nitride/Thermal Oxide The table is generally self-explanatory. As a group, and as shown, they include a layer of about 1000-300 angstroms thick formed on a thermally grown silicon dioxide layer 80-1000 angstroms thick.
000 angstroms of thermal LPGVD silicon nitride or plasma nitride (low pressure chemical vapor deposition) layer with a thickness of 0.6
Includes etching using a ~1.5 micron AZ1470 organic photoresist mask.

Briefly, a typical etching process involves placing one or more wafers containing a photoresist mask/nitride/oxide composite on top of the Norascent in an 8110 etch system, followed by standard cleaning, seasoning, and calibration. After the step, it involves applying the gas at the indicated flow rate for a given residence time and using a given chamber pressure and power setting.

As shown, the results are quite good. The selectivity for photoresist is wide, λO: 53:1 and 1:1 for the optimum and preferred full load range. thermal LPGVD
The selectivities for the thermal oxide underlayer relative to the nitride are >3:1, >5:1 and about 15=1 for the three ranges, respectively. The selectivities for thermal oxide underlayers are >5:1, >10:1 and about 25:1 for plasma nitride, respectively.
It is 1. Our method gives excellent linewidth control and vertical nitride profiles, minimizes linewidth loss, and reduces bird's beak intrusion during LOCO3 thermal oxidation.
ncrochment) and enable good channel width definition for MOS devices.

The overall uniformity is ±4% compared to ±10% for previous experiments using 8110 in a prior art high selectivity to oxide process. Furthermore, due to the high selectivity and excellent uniformity, the uniformity of the residual thermal oxide is better than that provided by prior art methods.

As shown in Tables 2 and 3, proper flow of NF3, O2 and 5iFa is very important in achieving and controlling high selectivity towards oxides. Also, pressure range is very important for controlling and maintaining anisotropy and critical dimensions.

It is expected that a substantial increase in pressure in the AME8110 reactor will reduce critical dimension control and possibly etch rate uniformity.

As shown in the table, an inert gas such as helium can be added to the NF3/5iF410z reactant gas composition to improve uniformity. Furthermore, inert gases such as helium or argon can be added in controlled amounts for sputtering purposes.

Furthermore, past experience indicates that SF can be used in place of NF, i.e. to function similarly to NF3 (except that non-volatile sulfur can form on the surface). Freon-containing gases designated by the series Cn) I, P, X can also be added to increase selectivity to photoresist.

CO or Cog can be used instead of oxygen (
However, judicious selection is necessary to prevent adverse side effects such as the formation of organic deposits). Finally, but not exhaustively, nitrogen-containing gases such as N2 itself, NO□ or N
20 substitutions can result in the deposition of silicon nitride and/or silicon oxynitride on silicon, silicon nitride, silicon dioxide, polysilicon or metal conductors such as aluminum or tungsten during etching or deposition.

In general, the method is readily applicable to etching films that form volatile products with fluorine chemistry when high selectivity to the underlying or masking silicon oxide is required. Therefore, 5iF410□, N F :l /St
F a /O□ and N F :l /Si F
In addition to etching silicon nitride using a/O□/lie, the method can be used for selective etching of both doped and undoped polysilicon formed on a silicon dioxide underlayer using N F /SiF a /O. □
/C, H, F, X, using reactive gas; NF for selective etching of tungsten on silicon dioxide underlayer.

NF for selective etching of both doped and undoped crystalline silicon using /5iFa10z/CnH,FxXz reactive gas; and with high selectivity to the underlying silicon dioxide and/or silicon dioxide mask.
3/SiF4/O□. One such application is trench etching of single crystal silicon. The method could also be extended to planar deposition of plasma silicon dioxide on polysilicon or aluminum lines using a deposition and etch bank. Planar deposition of silicon dioxide can be used for device passivation. AME8100 and A
The capabilities of the batch in-situ multi-step process of the ME8300 reactive ion etch system may be well applied to the present invention for the fabrication of 1 megabit and large buried capacitor designs. Other applications include isotropic removal of organic materials (eg photoresists and polyimides) for profile control using multi-step control methods.

[Brief explanation of drawings]

FIG. 1 is a schematic representation of a suitable plasma etch system for carrying out the method, and FIGS. 2-5 show trend lines showing the effect of various gases on oxide and nitride etch rates. , FIG. 2 is nitride etch rate vs. N F z flow, FIG. 3 is oxide etch rate vs. NF3 flow, FIG. 4 is nitride etch rate vs. 02 flow,
FIG. 5 is a graph of oxide etch rate versus 02 flow. 10... Plasma etching reactor, 11...
Reaction chamber, 12... cathode, 13... RF power supply, 1
7... Gas source, 20... Distribution ring. 71r Machining speed (man/min) = 1 Procedural amendment (method) Yoshi, Commissioner of the Japan Patent Office 1) Tsuyoshi Moon 1, Indication of case Patent Application No. 67977 of 1988 2, Title of invention Selective thin film etching method 3. Relationship with the case of the person making the amendment Applicant 4. Agent address: 3-3-1 Marunouchi, Chiyoda-ku, Tokyo Telephone: 211-8741 Name: (5995) Patent attorney Minoru Nakamura!
', -+1-・Engraving of the specification and drawings originally attached to the application (no changes to the contents)

Claims (30)

[Claims] (1) selectively etching the silicon nitride layer of an object comprising a silicon nitride layer on a silicon oxide underlayer with a photoresist mask formed thereon with controlled selectivity to the silicon oxide underlayer; A method of
A method comprising exposing an object to a plasma formed from a gas stream of SiF_4, oxygen and NF_3. (2) The reactant gas stream further includes a freon-containing gas to enhance selectivity to the photoresist.
) method described. (3) The reactant gas stream further comprises an inert gas selected from gases such as argon and helium.
) method described. (4) Photoresist, a gas mixture that selectively etches silicon nitride with high selectivity to silicon oxide, the gas mixture comprising SiF_4, oxygen and NF_3. 5. The gas mixture of claim 4, further comprising a Freon-containing gas to increase selectivity to photoresist. (6) A method for etching a film with high selectivity compared to an underlying oxide layer or a masking oxide layer, the method comprising etching the film and simultaneously etching the underlying layer or mask by the etchant component of the plasma. A method comprising exposing the film to a plasma formed from a silicon-containing and fluorine-containing etchant-forming gas and an oxygen-containing gas that deposits a silicon oxide compound at a rate selected to offset the inherent etching of the mask. (7) The thin film is silicon nitride and the reactant gas stream is SiF
The method of claim (6), comprising _4 and oxygen. (8) a silicon nitride layer has a photoresist mask formed thereon, and the reactant gas stream further includes NF_3;
The method according to claim (7). (9) The reactant gas stream further comprises an inert gas selected from argon and helium.
) method described. (10) Remove the silicon nitride layer components of an object containing a layer of silicon nitride over a silicon oxide underlayer with controlled selectivity to the silicon oxide underlayer in a plasma etch chamber using a photoresist etch mask formed on the silicon nitride. A method of selectively etching a photoresist comprising: placing a masked object in an etching chamber; communicating a reactive gas mixture comprising NF_3, SiF_4, and O_2 into the chamber; and energizing the reactive gas mixture to remove photoresist. and forming a plasma that etches silicon nitride with high selectivity to the oxide underlayer. (11) The method according to claim (10), further comprising an inert gas selected from argon and helium. (12) Reactant gas flow is NF_3/SiF_4/O_2
/He at a flow rate ratio of ≦100/≦100/≦100/≦100. (13) Reactant gas flow is NF_3/SiF_4/O_2
/He≦/50/10~15/10~50/20~5
The method according to claim 10 or 11, comprising at a flow rate ratio of 0. (14) Reactant gas flow is NF_3/SiF_4/O_2
/He in a flow ratio of about 13/30/15/20. (15) A plasma method for selectively etching a film selected from silicon and silicon nitride with high selectivity for a silicon dioxide film, in which the film is etched and at the same time the plasma etching agent component is etched on the oxide layer. depositing silicon oxide at a rate selected to offset the etching of the oxide layer by (i) SiF_4; (ii) a fluorinated gas selected from NF_3, and SF_6; and (iii)
) A plasma method comprising exposing the membrane to a plasma formed from a gas mixture comprising an oxygenating gas selected from oxygen, CO and CO_2. (16) The plasma method of claim (15), wherein the reactant gas mixture further comprises a gas selected from argon and helium. (17) The reactant gas mixture further contains NF_4, SiF_
4. The method of claim 16, comprising oxygen and helium. 18. The plasma method of claim 15 or 17, wherein the reactant gas mixture further includes a freon-containing gas to increase selectivity to photoresist. (19) A gas mixture that etches silicon or silicon nitride with high selectivity to silicon dioxide, the gas mixture comprising:
A gas mixture comprising: i) SiF_4; (ii) a fluorinated gas selected from NF_3 and SF_6; and (iii) an oxygenated gas selected from oxygen, CO and CO_2. (20) The gas mixture according to claim (19), further comprising (iv) a gas selected from argon and helium. (21) The gas mixture according to claim (19), wherein the mixture comprises NF_3, SiF_4, oxygen and helium. (22) The gas mixture according to claim (19) or (20), further comprising (v) a Freon-containing gas to increase selectivity to photoresist. (23) A plasma that selectively etches a film selected from a tungsten-containing film and a polysilicon film with high selectivity to silicon oxide, the plasma comprising: (1) SiF_4;
(ii) a fluorinated gas selected from NF_3 and SF_6; (iii) an oxygenated gas selected from oxygen, CO and CO_2; and (iv) exposing the membrane to a plasma formed from a gas stream comprising a Freon-containing gas. Contains plasma. (24) A gas mixture that selectively etches tungsten-containing layers and polysilicon-containing layers with high selectivity to silicon oxide, comprising: (i) SiF_4; (ii)
Fluorinated gas selected from NF_3 and SF_6; (
iii) an oxygenated gas selected from oxygen, CO and CO_2; and (iv) a gas mixture comprising a Freon-containing gas. (25) The gas mixture according to claim (24), comprising NF_3, SiF_4, oxygen and Freon-containing gas. (26) A method for selectively etching silicon nitride layer components of an object including a layer of silicon nitride and a layer of silicon oxide in a reactor chamber, the method comprising: etching the silicon nitride;
At the same time, in order to deposit silicon oxide on the silicon oxide layer and suppress the etching of the silicon oxide layer, the oxygen flow rate is
Oxygen and SiF_ that are at least 15% of the F_4 flow rate
4. A method comprising generating a plasma in a reactor formed from a stream of gases. (27) O_2/SiF_4 flow rate ratio is about 50%,
The method according to claim (26). 28. The method of claim 26 or 27, wherein the O_2/SiF_4 flow ratio is greater than about 1/1 to provide pure oxide deposition. (29) Claim (25) wherein the gas further comprises NF_3 to enhance etch selectivity of nitride to oxide.
) or the method described in (26). 30. The method of claim 25 or 26, wherein the nitride layer is masked with photoresist and the gas stream further includes NF_3 to increase etch selectivity of silicon nitride with respect to photoresist and oxide.