JPH0817172B2 - How to control the gate structure profile - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reactive ion etching (Reactiv) for etching metal silicide.
e Ion Etch (RIE) method, and more specifically,
The present invention relates to a reactive ion etching method for etching a polysilicon sandwich structure containing titanium silicide.

[0002]

2. Description of the Related Art Refractory metal silicides such as TiSi2 and WSi are used for dynamic random access
Memory (DRAM) is rapidly becoming the material of choice for interconnects in high performance devices. Metal silicide is a particularly attractive material because of its low resistivity, which is important for gate structures.

Recently, a DRA that requires a thinner line width
In the current trend of M, an etching process that gives a vertical etching profile is needed. Roth et al., “J. Vac. Sci. Technol., B7.
(3) ", May 1989, by reducing the amount of undercut, the speed of the device is increased and overall performance can be improved.
In the most extreme case, the metal silicide undercut in the sandwich structure allows lift-off or isolation of the mask line (silicon dioxide or silicon nitride) from the polysilicon layer.

Carbon fluorocarbons, such as CF4 --O2 gas mixtures, have been used in the RIE of silicon. When the gas mixture is separated by electric discharge, fluorine atoms are released and silicon is evaporated as SiF4. This type of processing works isotropically. Undercutting of the metal silicide and the gate structure occurs when a sandwich structure with an insulating mask is used.

US Pat. No. 4,450,042 discloses BCl which provides an etch similar to anisotropic etching.
The etching process based on 3 is disclosed. H-BC
High etch rates were obtained with the l3 -Br2 gas mixture. It is stated in this U.S. patent that bromine molecules were found to be able to etch only polysilicon when combined with chlorine or fluorine containing compounds.

US Pat. No. 4,490,209 discloses anisotropic RIE of monolayer silicon with a mixed gas of HBr, HCl and He. In this U.S. patent, during etching, bromine is absorbed on the sidewalls as silicon tetrabromide, which acts as a passivating material to prevent lateral etching, and vertical ion bombardment causes passivation on the etched areas. The hypothesis is that it prohibits the formation of baking substances. Silicon is etched as a Si-Cl-Br compound.
This U.S. patent proposes that other silicon-containing materials, including silicon nitride and metal suicides, can be effectively etched using the gas mixture.
Also, in this U.S. Patent, a pressure of 1.5 torr is used in a single substrate reactor when polysilicon is etched, the pressure varying between 0.25 and 5.00 torr. I suggest that you can.

US Pat. No. 4,744,861 discloses a treatment when bromine gas is used alone or mixed with an inert gas such as helium, neon or krypton. This is contrary to the idea disclosed in the above-mentioned US Pat. No. 4,450,042. The process of U.S. Pat. No. 4,744,861 is used to etch titanium or tungsten silicide because it is not used to etch multilayer structures and is not reactively etched by bromine gas alone. I can't.

US Pat. No. 5,007,982 discloses RIE of polysilicon using HBr alone or a mixed gas of HBr and an inert gas. This R
IE is for a structure using only a resist mask with a single layer structure selective for thin oxides. In addition, this process, in a batch reactor,
It is also proposed in this U.S. patent to be used to etch only tantalum or titanium silicide layers. In single-wafer reactors, the power densities are extremely different, and within the limits of the system, HBr
The use of HBr alone or in combination with an inert gas does not provide a viable reactive etching process for the silicide structures discussed in US Pat. No. 5,007,982.

[0009]

Accordingly, it is an object of the present invention to provide a thin gate oxide for a stop layer and a multi-layer metal silicide selective for silicon dioxide or silicon nitride for a mask or any combination thereof. /
It is to provide a sub-micron (line width less than 0.3 μm) RIE process that allows precise control of the etching profile of polysilicon structures. The polysilicon layer is uniformly n + or p + doped or undoped.

Another object of the present invention is to etch HBr and other metal suicides by a control method that does not use a photoresist mask, so as to etch HBr.
And the use of chlorine-containing gas. The insulating mask used during the etching process of the present invention is contoured in a previous step in which a photoresist mask is used as a contouring layer, the insulating mask is etched with fluorocarbon and then: This structure is the gate structure RI of the present invention.
The resist for E treatment is removed.

Still another object of the present invention is to optimize the pressure of the magnetic field enhanced reaction chamber and optimize the mixing ratio of the mixed gas when etching the sandwich structure so that chlorine atoms and H 2 are mixed.
When a mixed gas of Br is used, it produces the desired vertical profile or etch bias.

[0012]

According to the present invention, HBr is used.
An etching gas mixture composed of a gas containing chlorine and chlorine is used to etch a sandwich structure composed of an insulating mask, a thin metal silicide layer, and a polysilicon layer. The profile of the silicide / polysilicon layer varies from vertical to graded (if necessary) by adjusting the magnitude of the magnetic field in the reactor, the magnitude of the pressure in the reactor, and the mixing ratio of HBr and chlorine. , It was investigated that controllable changes could be made. A combination of these factors (magnetic field, pressure, mix ratio) can be used to controllably change the profile of the silicide / polysilicon layer. The reason is that these factors can be determined without interfering with each other.

Due to the insulating mask used in this process (eg, silicon dioxide or silicon nitride), low pressure conditions (less than 30 mTorr) cause mixing ratios to impart anisotropy to the etching for profile control. It is necessary to use it regardless of. Depending on the low pressure condition,
Simultaneous Si-Br sidewall passivation to the layer is possible, preventing undercutting of the structure.

The HBr: Cl2 mixing ratio and pressure should be optimized for profile control and selectivity to the gate oxide. H based on gate oxide thickness
The Br: Cl2 mixing ratio can be easily adjusted within the established process conditions to maintain selectivity and profile.

The optimization process uses a mask of silicon nitride or silicon dioxide, and the mixing ratio is different.
This is because each film provides a different amount of sidewall passivation. As long as the deposition method results in a vertical mask profile, the insulating mask deposition method (LPCVD,
PECVD, etc.).

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a schematic diagram of a magnetic field enhanced single wafer reactor. This reaction apparatus includes a reaction chamber 10, a platform 12 disposed in the reaction chamber 10, and a platform 1.
Radio frequency power source 1 electrically connected to electrodes 16 in 2
4, a gas source 18 having an inflow port 20 in the reaction chamber 10,
It is composed of a magnetic coil 22 surrounding the reaction chamber 10 and a vacuum pump 24 connected to the reaction chamber 10. In the RIE process, the substrate (not shown) is mounted on the platform 1
2 and is etched by the plasma generated from the gas in the reaction chamber 10 by applying a radio frequency power supply 14. The inlet 20 preferably has a diffusion screen 26 that evenly distributes the gas over the substrate so that the etching plasma is uniform. Valve 28
Adjusts the vacuum pressure in the reaction chamber 10, and the vacuum pump 24
Removes etching products that occur as the substrate is etched.

The present invention is particularly directed to metal suicides (eg, most preferably titanium suicides) on silicon substrates.
The present invention relates to an etching gas used when etching a sandwich gate structure. Especially low pressure (30
under m torr) and high power (over 200 watts),
HBr can be mixed with a chlorine-containing gas to produce a structure having vertical or controlled graded sidewalls on a gate stack containing metal silicide, while the use of a fluorine or chlorine based etchant can reduce the pressure used or It has been discovered that regardless of the magnetic field, it often causes a significant undercut in the structure.

In FIG. 2a, when HBr is mixed with chlorine gas (Cl2, HCl, BCl3, etc.) in a ratio of 1: 1 to 1: 9, an insulating mask placed on a thin layer of gate oxide. There is no undercut of the silicide layers in the stack consisting of (Si3 N4 or SiO2), metal silicide layers (such as TiSi2, etc.) and polysilicon layers (doped or undoped with N + or P +). Changes in pressure and magnetic field in the reactor do not adversely affect anisotropic etching by the mixed gas. The polysilicon profile, regardless of dopant, slopes positively with increasing HBr when all other conditions are constant. The increase in magnetic field affects the increase in etch rate and polymerization on the etched sidewalls. The amount of free atom halogen species increases with magnetic field (0-75 gauss). This is determined by the light emission spectrum and the resulting profile on the SEM concurrence.

The effects of power and pressure (and hence DC bias voltage) are well documented in the literature. As the DC bias increases, the etch anisotropy increases. As the pressure decreases and the power increases, the vertical profile of the metal silicide is achieved by the vertical component of the etch (when other variables are constant). Furthermore, the amount of passivation film on the sidewalls also increases under these conditions.

In a series of etching experiments, 2500
~ 4000 Angstrom SiN4 or SiO2
, 1000 Angstrom TiSi2, 2000
The angstrom polysilicon stack is HB
It is etched at a high rate (4000 angstroms / minute or more) by r and chlorine, and is 0.00 to irrespective of the dopant concentration of polysilicon under the above-mentioned changing conditions.
An etching bias of 0.05 was proven. Mixing a small amount of inert gas (0 to 10% of the total flow rate) has almost no effect on the profile. Moreover, this process results in an etch rate non-uniformity of less than 10%, ie 6
mm Edge Exclusion (edgeexclu
3 sigma on a 200 mm substrate with a sion) can easily be provided. In particular, within 6 mm from the edge of a 200 mm silicon substrate, the etching is uniform on 90% of the 99.73% of the wafer surface. The advantage is profile control and accurate endpoint detection. Depending on the selectivity required for the gate oxide thickness, highly selective overetching can be achieved by lowering the HBr: Cl2 mixing ratio or at low or high pressures (20 mTorr to 200 mTorr).
It can be used by adding oxygen (mTorr). Given the etch uniformity, a 100% overetch, if desired, will not affect the overall profile of the structure.

US Pat. No. 5,007,982 and US Pat. No. 5,013,398 disclose etching and refractory metal silicides such as titanium silicide and tungsten silicide.
It has been proposed to use only HBr as the gas,
In the experiments according to the invention, HBr alone or a mixture of HBr and an inert gas gives a very low etching rate, even in combination with a high DC bias.
Further, etching with HBr alone or a mixed gas of HBr and an inert gas produces a profile with high non-uniformity. Therefore, etching with HBr alone or a mixed gas of HBr and an inert gas is not suitable for manufacturing. When HBr is mixed with chlorine, the etching rate increases dramatically due to the increased reaction rate of chlorine with silicon. Mixing the gases increases overall manufacturing throughput.

An important feature of the gate stack shown in FIG. 2 (a) is that the etch process uses a hard mask (silicon nitride or silicon dioxide) rather than photoresist. Vertical sidewalls during resist-less etching are of particular interest. Because, due to the selectivity of the plasma over the hard mask, the hard mask does not provide a large amount of sidewall passivation film. Chlorine and bromine have a low selectivity to the resist compared to insulators, and this mask layer can be essentially sputtered down to provide a sidewall passivation film. After this treatment, it is necessary to remove this sidewall with a subsequent hydrofluoric acid etch.
This adds processing time to get the right product.

US Pat. No. 4,490,209 discloses the etching of metal suicides with HBr and HCl. However, this process uses a photoresist mask that provides a sidewall passivation film for the etch layer. The use of insulating masks designed according to the invention, especially for gate structures, is
Gives higher selectivity to the gate oxide. This is because there is no carbon chloride in the plasma from the resist film that reacts with silicon dioxide, and because of the lower selectivity to silicon dioxide.

FIGS. 3 (a)-(c) show that magnetic field containment and / or reduced pressure can be used with the HBr: chlorine gas mixture of the present invention to control the sidewall profile of the gate structure. Shows. In most applications, a vertical profile (shown in Figure 3 (a)) is required. However, some other applications require a tilt profile (shown in FIGS. 3 (b) and 3 (c)) to achieve the desired device speed. The general effect of using a magnetic field during etching is
Increasing the amount of ionic species in the plasma. This was confirmed by atomic emission spectroscopy of the plasma. Therefore, the use of a magnetic field increases the etching rate,
In order to prevent lateral etching, the sidewall passivation film is increased by increasing the free liberated bromine absorbed and / or reacted on the sidewalls. As a result, the positive slope profile for the silicide undercut and overall structure is reduced, assuming all other variables (mixing ratio, power, etc.) are constant. The optimum conditions of the magnetic field are as follows:
It is 0 to 30 gauss. However, good results were obtained in etching experiments when the magnetic field was varied from 0 to 75 Gauss.

The insulating mask used in this process (eg, silicon dioxide or silicon nitride) allows low pressure conditions (less than 30 mTorr) to provide a sufficient mixing anisotropy to provide sufficient anisotropy for etching for profile control. It is necessary to use it regardless of. Depending on the low pressure condition,
The undercut of the Si-Br sidewall passivation film gate structure can be prevented. Lower HBr:
By using a low pressure in combination with the Cl2 mixing ratio, a more positive slope profile could be obtained as shown in Figure 3 (c).

Although the present invention has been described in terms of a particularly preferred embodiment, those skilled in the art will appreciate that various modifications can be made without departing from the spirit and scope of the invention.

[0027]

In accordance with the present invention, a thin gate oxide film for a stop layer and an etch of a multi-layer metal silicide / polysilicon structure selective to silicon dioxide or silicon nitride for a mask or any combination of these.
Submicron RIE capable of precise profile control
Processing is obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of one embodiment of a magnetically enhanced single wafer reactor.

FIG. 2 is a cross-sectional view showing an example of a gate stack, (a)
Shows a gate stack etched with a chlorine-containing gas mixed with HBr, and (b) shows a gate stack etched with a chlorine mixed gas not mixed with HBr.
Further, (a) and (b) also show the influence of the pressure control and the magnetic field when removing the etching undercut.

FIG. 3 is a cross-sectional view of a gate stack structure formed by changing a magnetic flux and / or a HBr: Cl 2 mixing ratio and / or a pressure in an etching reactor.

[Explanation of symbols]

 10 Reaction Chamber 12 Platform 14 Radio Frequency Source 16 Electrode 18 Gas Source 20 Inlet 22 Magnetic Coil 24 Vacuum Pump 26 Diffusion Screen 28 Valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01L 29/78 301 F (72) Inventor Dana Christine Northcut PAKI PUSH Jackman Drive, New York, USA 97B (56) Reference JP-A-3-127826 (JP, A) JP-A-1-103836 (JP, A) JP-A-2-125425 (JP, A)

Claims (4)

[Claims] 1. A method of controlling the profile of the gate structure, composed of a polysilicon layer, a metal silicide layer, the patterned insulating mask to expose portions of the metal silicide layer for etching The complex structure
A step of preparing the provided substrate in an etching chamber; and a plasma generated from a mixed gas of hydrogen bromide and chlorine gas in a ratio of 1: 1 to 1: 9, the metal silicide layer and the polysilicon layer. And a step of etching the etching chamber during the etching step.
Magnetic field and pressure in the etching chamber
And adjusting the mixing ratio of hydrogen bromide and chlorine gas.
To change the profile from vertical to tilted
Flop, characterized in that it is possible to controllably vary
Profile control method. 2. The magnetic field is reduced to 0 during the etching process.
Given in the range of ~ 75 gauss, the pressure is less than 30 mTorr
Hold at low pressure and apply high power over 200 watts
The control method according to claim 1, wherein: 3. The metal silicide is titanium-silica
The control method according to claim 1, wherein the control method is a mode. 4. The insulating mask is made of silicon dioxide and nitrogen.
Characterized in that it is selected from the group consisting of silicon oxide,
The control method according to claim 1.