Method of Deposition

Abstract

According to the present invention there is provided a method of depositing a hydrogenated silicon carbon nitride (SiCN:H) film onto a substrate by plasma enhanced chemical vapour deposition (PECVD) comprising the steps of: providing the substrate in a chamber; introducing silane (SiH.sub.4), a hydrocarbon gas or vapour, nitrogen gas (N.sub.2), and hydrogen gas (H.sub.2) into the chamber; and sustaining a plasma in the chamber so as to deposit SiCN:H onto the substrate by PECVD at a process temperature of less than about 200° C.

Claims

1. A method of depositing a hydrogenated silicon carbon nitride (SiCN:H) film onto a substrate by plasma enhanced chemical vapour deposition (PECVD) comprising the steps of: providing the substrate in a chamber; introducing silane (SiH.sub.4), a hydrocarbon gas or vapour, nitrogen gas (N.sub.2), and hydrogen gas (H.sub.2) into the chamber; and sustaining a plasma in the chamber so as to deposit SiCN:H onto the substrate by PECVD at a process temperature of less than about 200° C.

2. The method according to claim 1, wherein the hydrocarbon gas or vapour is an alkyne, alkane or an alkene.

3. The method according to claim 2, wherein the hydrocarbon gas or vapour is a C.sub.2-C.sub.6 alkyne.

4. The method according to claim 3, wherein the C.sub.2-C.sub.6 alkyne is acetylene (C.sub.2H.sub.2).

5. The method according to claim 2, wherein the hydrocarbon gas or vapour is a C.sub.1-C.sub.6 alkane.

6. The method according to claim 1, wherein the silane (SiH.sub.4), the hydrocarbon gas or vapour, the nitrogen gas (N.sub.2), and the hydrogen gas (H.sub.2) are each introduced into the chamber at an associated flow rate in sccm, and the flow rates are in the following order, from highest to lowest: the nitrogen gas (N.sub.2), the hydrogen gas (H.sub.2), the silane (SiH.sub.4), and the hydrocarbon gas or vapour.

7. The method according to claim 1, wherein the silane (SiH.sub.4) is introduced into the chamber at a flow rate in the range of 10-800 sccm.

8. The method according to claim 1, wherein the hydrocarbon gas or vapour is introduced into the chamber at a flow rate in the range of 10-500 sccm.

9. The method according to claim 1, wherein the nitrogen gas (N.sub.2) is introduced into the chamber at a flow rate in the range of 500-5,000 sccm.

10. The method according to claim 1, wherein the hydrogen gas (H.sub.2) is introduced into the chamber at a flow rate in the range of 50-1,000 sccm.

11. The method according to claim 1, wherein the process temperature is less than 190° C.

12. The method according to claim 1, wherein whilst the plasma is being sustained in the chamber, the chamber has a pressure in the range of 1-5 Torr.

13. The method according to claim 1, wherein the steps are performed in a capacitively coupled PECVD reactor.

14. The method according to claim 1, wherein the hydrogenated silicon carbon nitride film is an amorphous hydrogenated silicon carbon nitride film (a SiCN:H).

15. The method according to claim 1, wherein the substrate is a semiconductor substrate.

16. A substrate with a SiCN:H film deposited thereon using the method according to claim 1.

17. The method according to claim 1, further comprising: providing two or more of the substrate with the SiCN:H film, wherein the two or more of the substrate includes a first substrate with the SiCN:H film and a second substrate with the SiCN:H film; and bonding the SiCN:H film of the first substrate to the SiCN:H film of the second substrate at a temperature of less than about 250° C.

18. A device comprising a stack of two or more substrates produced using the method according to claim 17.

19. The method according to claim 2, wherein the hydrocarbon gas or vapour is an unbranched alkyne, an unbranched alkane or an unbranched alkene.

20. The method according to claim 5, wherein the hydrocarbon gas or vapour is methane (CH.sub.4), propane (C.sub.3H.sub.8), butane (C.sub.4H.sub.10), pentane (C.sub.5H.sub.12) or hexane (C.sub.6H.sub.14).

Description

[0037] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0038] FIG. 1 is a schematic side view of two substrates ready to undergo a surface activated substrate-substrate bonding process;

[0039] FIG. 2 shows prior art FTIR spectra for PECVD SiCN films from Nagano et al, using NH.sub.3/SiH.sub.x(CH.sub.3).sub.y precursors deposited at process temperatures of 370 and 200° C.;

[0040] FIG. 3 shows FTIR spectra of a SiCN:H film deposited using a method of the present invention, the spectra obtained on the film as deposited and after seven days exposed to atmosphere;

[0041] FIG. 4 shows refractive index (RI) for two types of SiCN:H films deposited using methods of the present invention at 175° C. with/without H.sub.2 when exposed to air over a seven day period;

[0042] FIG. 5 shows stress for the two types of SiCN:H films deposited using methods of the present invention at 175° C. with/without H.sub.2 when exposed to air over a seven day period; and

[0043] FIG. 6 shows FTIR spectra for the two types of SiCN:H films deposited using methods of the present invention at 175° C. with/without H.sub.2;

[0044] FIG. 1 shows a schematic of a surface activated bonding process used to bond two substrates together. The substrates 10a, 10b may comprise temperature sensitive features, such as device layers 12a, 12b. An adhesion layer 14a, 14b, such as a silicon carbon nitride (SiCN) layer, such as a hydrogenated silicon carbon nitride (SiCN:H) layer, is deposited on a surface of each substrate 10a, 10b. The two adhesion layers 14a, 14b can be smoothed, for example by chemical mechanical planarization (CMP), precisely aligned, pressed together at an elevated temperature, and annealed so as to bond the two substrates together via the adhesion layers 14a, 14b.

[0045] Apparatus suitable for depositing silicon carbon nitride (SiCN) films, such as SiCN:H films, according to exemplary methods of the present invention (and comparative examples) include an SPTS Delta™ parallel plate PECVD apparatus, which is commercially available from SPTS Technologies Limited, located in Newport, South Wales, UK. All exemplary embodiments and comparative examples described below were performed using this apparatus.

EXEMPLARY EMBODIMENTS

[0046] The present invention provides a method of depositing hydrogenated silicon carbon nitride (SiCN:H) films that are acceptable for use as adhesion layers in a surface activated bonding process. In particular, acceptable SiCN:H films can be deposited onto substrates at temperatures of less than about 200° C., optionally less than 190° C., or optionally about 175° C. The substrate can be a semiconductor substrate, such as a silicon substrate or silicon wafer. The substrate can comprise a plurality of die. The substrate can comprise temperature sensitive features, such as device layers and interconnects, which may include copper layers embedded in a dielectric.

[0047] Exemplary embodiments of the invention comprise introducing silane (SiH.sub.4), a hydrocarbon gas or vapour, nitrogen gas (N.sub.2), and hydrogen gas (H.sub.2) into a PECVD chamber. Optionally, one or more non-reactive carrier gases may also be introduced into the chamber. A plasma is sustained within the chamber so that a PECVD process can occur, which causes SiCN:H to deposit onto the substrate. The hydrocarbon gas or vapour can be an alkyne, alkane or an alkene.

[0048] To control the H content in the film and to promote the growth of Si—N bonds, the conventional approach of using ammonia as the main nitrogen-donating precursor was replaced by using N.sub.2 as the source of N in the film. A reduction in the CH.sub.x incorporation in the film was achieved by using silane with a hydrocarbon carbon-donating precursor such as C.sub.2H.sub.2. By using C.sub.2H.sub.2 as a dopant as opposed to an organosilane as is standard practice in the art, it was possible to achieve fine tuning of the film properties at low temperatures. Surprisingly it was found that the post deposition stability of the film was improved by the addition of H.sub.2.

[0049] Table 1 shows exemplary PECVD process parameters suitable for achieving stable SiCN:H films at a deposition temperature in a range of 100-250° C. These parameters are for 300 mm diameter wafers, and HF power levels would be expected to be reduced for wafers having a diameter of 200 mm or less in order to maintain similar power densities. As a general trend the optimal gas flows were found to be in the order N.sub.2>H.sub.2>SiH.sub.4>hydrocarbon.

TABLE-US-00001 TABLE 1 Representative process parameters. Preferred Process Parameters Unit Range Range Chamber pressure mTorr 1000-5000  1400-2000 N.sub.2 flow rate Sccm 500-5000 1000-3000 Hydrocarbon gas or Sccm 10-500  20-300 vapour flow rate SiH.sub.4 flow rate Sccm 10-800  20-500 H.sub.2 Sccm  50-1000 100-750 HF RF power W 300-2000  800-1200 LF RF power W  0-200  0-50 Temperature ° C. 100-200  150-200

[0050] In exemplary embodiments, SiCN:H films were deposited onto a 300 mm silicon wafer at 175° C. by PECVD. The reactive precursors were silane (SiH.sub.4), acetylene, nitrogen gas (N.sub.2), and hydrogen gas (H.sub.2).

[0051] The chamber pressure was in the range of 1.75 Torr. The plasma was sustained using RF power at 13.56 Hz and 1000 W. The flow rates of the reactive precursors were 200 sccm silane, 150 sccm acetylene, 1450 sccm nitrogen, and 550 sccm hydrogen.

[0052] In FIG. 3 we can see a seven consecutive daily FTIR spectra, absorbance (a.u.) vs wavenumber cm.sup.−1, for a SiCN:H film (LDR A) deposited using SiH/N.sub.2/C.sub.2H.sub.2/H.sub.2 as the source gases. Note the absence of a distinct Si—CH.sub.3 peak and no clear Si—O peak at 1260 cm−1 and 1025 cm−1 respectively indicating that the levels of methyl groups incorporated into the film are low and that oxygen is absent. Also present are Si—H at 2100 cm−1, C—H at ˜2900 cm−1 and Si—NH.sub.2 at ˜3380 cm−1. Over a seven day period at atmosphere and at room temperature the spectra so not show any significant changes suggesting that the films are stable. We attribute the ˜3380 cm−1 peak to be Si—NH.sub.2 as opposed to O—H as ERD measurements indicate that there is <1 at % O in the films and the FTIR spectra does not change with time.

[0053] FIGS. 4 and 5 respectively show the RI (refractive index) and stress stability of two types of SiCN:H films with and in the absence of H.sub.2. The process parameters for these two films used conditions from Table 1 with the exception of the H.sub.2 content for the films where no H.sub.2 was present in the depositions. We can see that H.sub.2 significantly improves the stability of the film. FTIR spectra for these films can be seen in FIG. 6.

[0054] Unexpectedly, the addition of H.sub.2 to the plasma results in a reduction in the H content in the as deposited film as indicated in FIG. 6. Table 2 indicates that the H content of the film associated with Si—H bonding, determined from the ratio of the area of the Si—H and SiN peaks, is reduced to approximately half of the value when H.sub.2 dilution was not used. This is consistent with the RI values in FIG. 4 where the SiCN:H films deposited without H.sub.2 as a precursor are lower than those deposited in with H.sub.2. The lower RI values of the as-deposited film are indicative of a lower density film which would be expected when the H content of the film is increased. We speculate that the use of H.sub.2 in the deposition step creates a more energetic plasma which reduces the amount of H to Si bonds formed. We speculate further that this also increases the in-situ densification of the film.

TABLE-US-00002 TABLE 2 FTIR SiH:SiN peak area ratio for films in FIGS. 4-6. Film SiH:SiN LDR A 0.0487 LDR A no H.sub.2 0.112 LDR B 0.0549 LDR B no H.sub.2 0.101

[0055] We can see that the FTIR spectra for the two films that use H.sub.2 as a precursor have very similar spectra. However, films deposited without H.sub.2 present show an increase of absorbance of all major peaks coupled with a movement of the Si—N peak to higher wave numbers. The presence of a stable peak at ˜3380 cm−1 which is attributed to Si—NH.sub.2 seems to be a characteristic of this novel type of low temperature SiCN:H films.

[0056] The surface roughness of the as deposited films with H.sub.2 as measured by Atomic Force Microscopy was 1.67 & 1.89 nm for the two films LDR A & LDR B. Deposition rates of 90-520 nm/min can be achieved for stable films over a wide range of deposition parameters.

[0057] By varying the C.sub.2H.sub.2 flow for a fixed N.sub.2/H.sub.2/SiH.sub.4 flow it was possible to tune the C content of the film. In this way, a stoichiometric composition could be achieved at 175° C. which was similar to that achieved by the high temperature process at 370° C. using NH.sub.3/SiH.sub.x(CH.sub.3).sub.y precursors as determined from ERD, EDAX and FTIR.

[0058] The use of acetylene as a source of carbon reduces CH.sub.3 incorporation into the film. This is advantageous, since the presence of CH.sub.3 is believed to result in an unstable film. Acetylene is also a relatively low cost source of carbon. It is cheaper than an organosilane and offers more control over carbon content. However, other hydrocarbon precursors might be used instead as a source of carbon, for example methane, propane, butane, pentane and hexane.